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Engagement of community participation is an innovative driver of modern research. However, to benefit the communities being studied, it is imperative to continuously evaluate ethical considerations, the relationship dynamic between researchers and community members, and the responsiveness of research teams to the needs and preferences of communities. Northwestern University's Center for Health Equity Transformation founded a community scientist program in 2018 that implemented a study using the Community-Based Participatory Research (CBPR) model. This project is an ongoing study of heavy metal exposure by geographic location in Chicago. Community scientists from various backgrounds, communities, and organizations formed an advisory panel, partnering with the cancer research team. This commentary describes lessons learned in structuring meaningful community involvement and benefit in CBPR, with a focus on three lessons learned that relate to ethics, relationships, and responsiveness. Our findings lay new groundwork for iteratively shaping best practices in CBPR., (© 2023. The Author(s), under exclusive licence to Springer Nature Switzerland AG.)

In the U.S., disparities in the healthcare workforce have led to inadequate health outcomes in communities of historically underserved groups. To address the lack of resources and opportunities in health career education for historically underserved group students, Project MED was established. The mission is to expose high school students to the breadth of opportunities in the healthcare field and to prepare students for successful careers in healthcare. Through 3 main pillars-Learn, Lead, and Launch-Project MED has developed a robust repository of 20 workshops, recruited and trained eight mentors, and curated a database of ≥100 opportunities for over 50 students., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

The Dobbs decision overturned the right to abortion in the United States and allowed states to enact total abortion bans. In addition to restricting access to abortion, laws criminalizing pregnancy outcomes deter providers from offering timely, appropriate care for pregnancy complications. To avoid litigation or prosecution, providers are under pressure to strictly guard the privacy of patient health information related to pregnancy. Perinatal care is at risk of repeating the experience of similar enhanced privacy rules for substance use disorders, which have impeded information sharing and care coordination that improves outcomes., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Racial health disparities within gynecologic cancers persist. We aim to explore the impact of epigenetics on these disparities and how social determinants of health fuel this effect. We queried PubMed with terms associated with social determinants of health and epigenetics in the scope of 3 gynecologic cancers: ovarian, endometrial, and cervical. Using the publications found, we highlight various socioeconomic and environmental factors that may influence epigenetic mechanisms and further disparities in cancer incidence, mortality, and treatment. This narrative review exposes existing gaps in evidence and provides recommendations of future preventive efforts that can target the mitigation of gynecologic cancer disparities., Competing Interests: The authors declare no conflicts of interest ., (Copyright © 2022 Wolters Kluwer Health, Inc. All rights reserved.)

Background: There are persistent disparities in maternal and infant perinatal outcomes experienced by Black birthing persons compared with non-Hispanic white (NHW) individuals in the US. The differences in outcomes arise from not only socioeconomic factors and individual health behaviors but also structural racism. Recent research is beginning to elucidate the benefits of patient navigation to support underserved minoritized individuals who experience this constellation of barriers to equitable care. Qualitative research that utilizes both the experiences of Black birthing individuals and the expert opinion of healthcare providers working with them can serve to guide a patient navigation intervention to further decrease disparities in perinatal outcomes., Methods: We conducted 30 interviews between August and December 2020 with Black birthing individuals in the Chicago metropolitan area and healthcare providers who care for this population both in Chicago and across the nation to explore their experiences, perceptions of barriers to care and ways to decrease inequities., Results: Clinical care team members acknowledged the presence of health disparities experienced by Black pregnant individuals compared with their NHW counterparts stemming from racism, discrimination, and lack of resources. Patients similarly reported personal experiences with these disparities and barriers to care. The successful methods used by clinical care teams to help decrease these differences in the past included patient education on important topics such as breastfeeding and the use of patient advocates. Effectively screening for social determinants of health by someone the patient trusts was also cited as important. Regarding perinatal care practices, clinical care team members described the importance of patient education needs and care team cultural competency. Patients' reported positive and negative experiences corroborated these findings, emphasizing the importance of trust, listening, education, access to care, support, and patient advocacy. Finally, the care team members and patients agreed that active trust-building can help the provider/patient relationship and ultimately improve outcomes., Conclusions: These qualitative research findings improve the understanding of barriers to care and will help guide development of an intervention to reduce the health disparities experienced by Black pregnant persons., (© 2022. The Author(s).)

Underrepresentation of individuals with limited English proficiency (LEP) who speak Spanish is ongoing in phase 3 biomedical clinical trials and exacerbates health inequity. This article suggests strategies for increasing representation of Spanish speakers in clinical rials by emphasizing the importance of early engagement with Spanish language communities, inclusive participant recruitment, and collaborative trial design and implementation. Although investigators and institutions administering government-funded research must meet federal requirements for language assistance, journal editors, peer reviewers, institutional review board members, academic health centers, and all beneficiaries of the biomedical and behavioral research enterprise in the United States must motivate linguistic inclusion., (Copyright 2022 American Medical Association. All Rights Reserved.)

Background: Female genital cutting (FGC) is a form of gender-based violence with obstetrical and gynecological complications that require recognition and care. Data suggest that United States' physicians are not prepared to care for those who have been affected by this practice. This study evaluated the knowledge and practices of United States' obstetricians and gynecologists to care for patients who have undergone FGC. Materials and Methods: This was a cross-sectional confidential survey distributed electronically to a sample of clinically active members of the American College of Obstetricians and Gynecologists. The survey consisted of questions characterizing care of patients who had undergone FGC and barriers to optimal support. Results: Five hundred forty-eight participants representing a wide range of years in practice, geographical locations, subspecializations, and patient demographics participated. Sixty-six percent of participants had cared for patients who had undergone FGC. Participants' description of their patient population racial/ethnic composition did not correlate with likelihood of treating this patient population. Forty percent of participants reported some form of education about FGC, more often among women, younger physicians, and those in practice for fewer years. Thirty-one percent of participants were comfortable counseling about and 20% were comfortable performing deinfibulation; these percentages were higher among those who had received education or had recently cared for an affected patient. Participants reported insufficient training as the largest barrier to providing care to women. Conclusions: While most physicians in this national cohort had cared for women who had undergone cutting, a minority had any form of education. However, prior education correlated with indicators of improved care. Physicians require additional guidance in treating this important and growing patient population.

Purpose: The maternal mortality ratio for the United States (US) has consistently risen over recent decades. This mortality is especially pronounced within minority populations who experience a maternal mortality and morbidity rate that are much higher than their non-Hispanic white counterparts. Qualitative data are critical in gaining true insight from minority pregnant and postpartum persons. Such data should serve as the basis for building interventions and programs that seek to eradicate perinatal inequities. This review examines the qualitative literature on racial and ethnic minority pregnant patients with low income and their experiences during perinatal care (PNC) to identify recurrent themes that can be addressed through targeted interventions. Methods: PubMed, CINAHL, and Web of Science databases were searched for qualitative studies on racial and ethnic minority pregnant patients with low income and their experiences during PNC. Twenty-two articles were included for analysis. Thematic synthesis was performed to identify categories and recurring themes in each article. Results: Five major categories were identified as consistent experiences of pregnant patients with PNC clinicians: support, education, connection, communication, and trust. Of these, clinician support was the most consistently coded category. Eighteen of the 23 articles discussed tangible support patients had received from their clinicians, such as care coordination and referrals to support services. The second most coded category was education, which was represented in 16 articles. Education was mostly represented negatively as lack of adequate perinatal care education given during the perinatal period. Finally, the categories of connection, communication, and trust were represented by 18, 17, and 17 articles, respectively. Conclusions: These qualitative studies provided specific examples of what racial and ethnic minority pregnant patients with low income deemed positive and negative during the perinatal period and outline ways that these experiences can be improved. Future studies can take the experiences reported in this review to help inform interventions to improve patient experiences and health outcomes that minority persons face in the perinatal period., Competing Interests: No other authors have financial, commercial, or other funding disclosures., (© Danielle Wishart et al., 2021; Published by Mary Ann Liebert, Inc.)

Objective: Inadequate diversity in clinical trials is widely recognized as a significant contributing factor to health disparities experienced by racial/ethnic minorities and other diverse populations in the US. To address this in a scalable way, we sought to develop a web tool that could help enhance underserved minority participation in clinical research., Methods: We used our research literacy support flashcard tool as the initial prototype for human-centered design and usability testing of the web tool Health for All in public library settings. After forming partnerships with leadership from Chicago Public Libraries (CPL), local medical libraries, and the Chicago Department of Public Health, we conducted seven iterative design sessions with focus groups of library patrons and library staff from six CPL branches serving underserved communities followed by two rounds of usability testing and website modification., Results: Based on the qualitative research findings from Design Sessions 1-7, we enacted the design decision of a website that was a hybrid of fact-filled and vignette (personal stories) paper prototypes divided into 4 modules (trust, diversity, healthy volunteers, pros/cons), each with their own outcome metrics. The website was thus constructed, and navigation issues identified in two rounds of usability testing by library patrons were addressed through further website modification, followed by the launch of a beta version of a hybridized single-scrolling and guided module prototype to allow further development with website analytics., Conclusions: We report the development of Health for All, a website designed to enhance racial/ethnic minority participation in clinical trials by imparting research literacy, mitigating distrust engendered by longstanding racism and discrimination, and providing connections to clinical trials recruiting participants., Competing Interests: The authors have declared that no competing interests exist. Melissa Simon is a member of the United States Preventive Services Task Force (USPSTF). This article does not necessarily represent the views and policies of the USPSTF.

Purpose: Patient navigation uses trained personnel to eliminate barriers to timely care across all phases of the health care continuum, thereby reducing health disparities. However, patient navigation has yet to be systematized in implementation models to improve processes of care at scale rather than remain a band-aid approach focused solely on improving care for the individual patient. The 4R systems engineering approach (right information and right treatment to the right patient at the right time) uses project management discipline principles to develop care sequence templates that serve as patient-centered project plans guiding patients and their care team., Methods: A case-study approach focused on the underserved patient shows how facilitators to timely breast cancer screening and care pragmatically identified as emergent data by patient navigators can be actionized by iteratively revising 4R care sequence templates to incorporate new insights as they emerge., Results: Using a case study of breast cancer screening of a low-income patient, we illustrate how 4R care sequence templates can be revised to incorporate emergent facilitators to care identified through patient navigation., Conclusion: Use of care sequence templates can inform the care team to optimize a particular patient's care, while functioning as a learning health care system for process improvement of patient care and patient navigation scaling. A learning health care system approach that systematically integrates data patterns emerging from multiple patient navigation experiences through in-person navigators and 4R care sequence templates may improve processes of care and allow patient navigation scaling to reduce cancer disparities.

Helping Her Live (HHL) is a community health worker-led outreach model that navigates women from vulnerable communities to mammography screening and diagnostic follow-up. The objective of this study was to evaluate HHL implementation on the southwest side of Chicago. HHL has been implemented on the west side of Chicago since 2008, where it has increased mammogram completion and diagnostic follow-up rates among Black and Hispanic women from resource poor communities. In 2014, HHL was translated to the southwest side of Chicago; implementation success was evaluated by comparing outreach, navigation request, and mammogram completion metrics with the west side. During January 2014-December 2015, outreach was less extensive in the southwest setting (SW) compared to the benchmark west setting (W); however, the proportion of women who completed mammograms in SW was 50%, which compared favorably to the proportion observed in the benchmark setting W (42%). The distribution of insurance status and the racial and ethnic makeup of individuals met on outreach in the W and SW were significantly different (p < 0.0005). This successful expansion of HHL in terms of both geographic and demographic reach justifies further studies leveraging these results and tailoring HHL to additional underserved communities.

Introduction: Because lifetime trauma exposure has been linked to multiple adverse pregnancy outcomes, there is a need for all perinatal care providers to be versed in trauma-informed care practices. However, there are few data to guide trauma-informed practice during the perinatal period. The objective of this study was to refine ongoing development of a trauma-informed care framework for perinatal care by conducting a qualitative study of all trauma experiences and preferred screening practices of pregnant patients at an urban prenatal clinic., Methods: In this qualitative study, we conducted semistructured interviews with 30 women receiving prenatal care at an urban clinic. Participants also completed a trauma history questionnaire. Inductive coding was used to generate themes and subthemes., Results: Participants described multiple lifetime traumatic exposures as well as background exposure to community violence. Not all participants desired routine trauma screening; factors limiting disclosure included fear of retraumatization and belief that prior trauma is unrelated to the current pregnancy. Strong therapeutic relationships were identified as critical to any trauma history discussion., Discussion: This study supports a trauma-informed care approach to caring for pregnant women with prior traumatic exposures, including trauma screening without retraumatization and trusting patient-provider relationships., (© 2020 by the American College of Nurse-Midwives.)

Racial/ethnic minorities are underrepresented in clinical research in the USA for multifarious reasons, including barriers to effective communication between researchers and potential research participants. To address the communication barriers between researchers and potential participants, we developed a Research Literacy Support (RLS) tool. The focus of this report is to present findings from the second and third phases of development that refined and assessed usability of the RLS tool. We utilized a mixed-methods approach that entailed iterative cognitive testing with participants (N = 52) from diverse racial/ethnic backgrounds and interviews with clinical research recruiters (N = 20) to modify and refine the design and content of the RLS tool (phase 2). This was followed by assessment of the usability of the RLS tool by 100 participants (phase 3). During phase 2, participants provided feedback about layout, word choice, and comprehension of the tool. In phase 3, participants recognized that they had gained knowledge about clinical research from the RLS tool, although they still had a substantial learning gap after using the tool, indicating an opportunity for further refinement. The RLS tool may help advance health equity by addressing communication barriers that may impede minority participation in clinical research.

Language is powerful and can have a strong impact on perceptions as well as behavior. A task force, consisting of representatives from the American Association of Diabetes Educators (AADE) and the American Diabetes Association (ADA), convened to discuss language in diabetes care and education. This document represents the expert opinion of the task force. The literature supports the need for a language movement in diabetes care and education. There are effective ways of communicating about diabetes. This article provides recommendations for language used by health care professionals and others when discussing diabetes through spoken or written words-whether directed to people with diabetes, colleagues, or the general public, as well as research questions related to language and diabetes., (© 2017 by the American Diabetes Association and the American Association of Diabetes Educators.)

Purpose: The purpose of this report is (1) to describe the use of the American Association of Diabetes Educators' (AADE's) model of implementation of the National Diabetes Prevention Program through nationally certified diabetes self-management education (DSME) programs and (2) to report the aggregated program outcomes as defined by the Diabetes Prevention and Recognition Program standards of the Centers for Disease Control and Prevention (CDC)., Methods: In 2012, the AADE worked with the CDC to select 30 certified DSME programs for National Diabetes Prevention Program delivery. For the following 3 years, the AADE continued to work with 25 of the 30 original programs. Results for all CDC recognition standards have been collected from these 25 programs and analyzed as aggregated data over the course of 36 months., Results: At the end of the full-year program, average percentage body weight loss for participants across all 25 programs exceeded the CDC's minimum requirement of 5% weight loss. All programs on average met the CDC requirements for program attendance., Conclusion: Increasing access to the National Diabetes Prevention Program, through an array of networks, including certified DSME programs, will better ensure that people are able to engage in an effective approach to reducing their risk of diabetes., (© 2016 The Author(s).)

Purpose: The purpose of the study was to examine the field of diabetes education along with identifying facilitators and barriers for future health care professionals entering the specialty field of diabetes education., Method: Faculty members who were currently teaching in a health-related discipline, the students of those faculty members, and nursing students who were members of the National Student Nursing Association were surveyed to gather descriptive data., Results: While faculty members reported they are promoting diabetes education to their health professions students, many nursing students are not aware of this career path. Nursing students understand that diabetes is a significant problem and will be something they encounter in all areas of their careers, but many were not sure they wanted to specialize in it., Conclusions: There is a gap between what faculty members and students report as far as awareness of the diabetes education specialty. In addition, misinformation about diabetes and people living with diabetes may be a deterrent for potential future diabetes educators. American Association of Diabetes Educators, health professions faculty members, and practicing diabetes educators can do more to clear up misconceptions and promote diabetes education as a career path for students in the health professions., (© 2015 The Author(s).)

Purpose: The purpose of this comprehensive role delineation study of the Board Certification for Advanced Diabetes Management (BC-ADM) examination was to ensure its content validity., Method: The comprehensive role delineation study was conducted in 3 phases. In the first phase, a panel of 12 currently credentialed BC-ADM subject matter experts produced a list of practice domains, a unique set of content subdomains for each, and a series of knowledge statements for every subdomain. In the second phase, a validation study survey consisting of 3 sections was created. The first section was to rate each subdomain on three factors: criticality, frequency, and point in career at which knowledge is first used. The second section asked respondents to estimate the percentage of the examination to dedicate to the four domains. The third section captured demographic information of the respondents. A total of 667 BC-ADMs and 18 physicians were invited to take the survey. In the third phase, the subject matter expert panel analyzed the survey results and determined the weight that the domains and subdomains should have on the 150-item BC-ADM examination., Results: Final domain weights and the corresponding number of items for the BC-ADM examination are provided in this report; these constitute the BC-ADM examination blueprint., Conclusions: The national role delineation study reported here for the BC-ADM examination ensures that it is reflective of the current practice and required knowledge of the advanced diabetes manager., (© 2015 The Author(s).)

Purpose: The purpose of this study is to gain insight about patient experience of diabetes self-management education in a patient-centered medical home., Methods: Six focus groups consisting of 37 people with diabetes, diverse in race and ethnicity, were conducted at 3 sites. Participants described their experience in the program and their challenges in diabetes self-management; they also suggested services to meet their diabetes care needs., Results: The most common theme was ongoing concerns about care and support. There was much discussion about the value of the support provided by health navigators integrated in the diabetes health care team. Frequent concerns expressed by participants centered on personal challenges in engaging in healthy lifestyle behaviors. Ongoing programmatic support of self-management goals was widely valued., Conclusions: Individuals who received health care in a patient-centered medical home and could participate in diabetes self-management education with integrated support valued both activities. The qualitative results from this study suggest need for more formalized exploration of effective means to meet the ongoing support needs of people with diabetes., (© 2015 The Author(s).)

Protein kinase (PK)Calpha and epsilon are rational targets for cancer therapy. However, targeted experimental therapeutics that inhibit PKCalpha or epsilon are unavailable. The authors established recently that covalent modification of an active-site cysteine in human PKCepsilon, Cys452, by small molecules, for example 2-mercaptoethanolamine, is necessary and sufficient to render PKCepsilon kinase-dead. Cys452 is conserved in only eleven human protein kinase genes, including PKCalpha. Therefore, the design of small molecules that bind PKC active sites with an electrophile substituent positioned proximal to the Cys452 side chain may lead to targeted therapeutics that selectively inhibit PKCepsilon, PKCalpha or other PKC isozymes.

Critical roles played by some protein kinases in neoplastic transformation and progression provide a rationale for developing selective, small-molecule kinase inhibitors as antineoplastic drugs. Protein kinase Cepsilon (PKCepsilon) is a rational target for cancer therapy, because it is oncogenic and prometastatic in transgenic mouse models. PKCepsilon is activated by sn-1,2-diacylglycerol (DAG). Attempts to develop selective PKCepsilon inhibitors that block activation by DAG or compete with ATP have not yet met with success, suggesting a need for new strategies. We previously reported that cystamine and a metabolic cystine precursor inactivate PKCepsilon in cells in a thiol-reversible manner. In this report, we first determined that PKCepsilon became resistant to inactivation by disulfides when Cys452 was replaced with alanine by site-specific mutagenesis of human PKCepsilon or a constitutively active PKCepsilon mutant. These results showed that the disulfides inactivated PKCepsilon by thiol-disulfide exchange, either upon Cys452 S-thiolation or by rearrangement to an intra-protein disulfide. Mass spectrometric analysis of peptide digests of cystamine-inactivated, carbamidomethylated PKCepsilon detected a peptide S-cysteaminylated at Cys452, indicating that Cys452 S-cysteaminylation is a stable modification. Furthermore, PKCepsilon inactivation by N-ethylmaleimide was Cys452 dependent, providing corroborative evidence that PKCepsilon inhibitors can be designed by targeting Cys452 with small molecules that stably modify the residue. Cys452 is an active site residue that is conserved in only 11 human protein kinase genes. Therefore, the PKCepsilon-inactivating Cys452 switch is a rational target for the design of antineoplastic drugs that selectively inhibit PKCepsilon.

The protein kinase C (PKC) isozyme family plays key roles in cell growth regulation and influences neoplastic disease development and progression. For example, PKCepsilon is oncogenic, and PKCdelta tumor-suppressive. PKC isozymes are characterized by distinct activation mechanisms entailing phosphatidylserine-dependent cofactor binding to the regulatory domain. Evidence is now emerging that redox signaling offers another platform of PKC regulation. We have established that PKC isozymes are regulated by S-thiolation, a posttranslational modification entailing disulfide linkage of low-molecular-weight species to select protein sulfhydryls. Our recent studies demonstrate that physiologically occurring disulfides with cysteinyl constituents, e.g., cystine, regulate cellular PKC isozymes by S-thiolation-triggered mechanisms. This report shows that PKC isozymes are also molecular targets of a chemically distinct class of disulfides. Disulfiram is a thiuram disulfide with potent cancer preventive activity in in vivo models of chemical carcinogenesis. Our results indicate that PKC Sthiolation by disulfiram induces differential regulatory effects on PKC isozymes that correlate with the cancer preventive activity of the drug. The implication of these findings is that PKC-regulatory effects of thiuram disulfides may offer a useful pharmacological guide for development of disulfiram analogues with superior cancer preventive activity.

Cell signaling entails a host of post-translational modifications of effector-proteins. These modifications control signal transmission by regulating the activity, localization or half-life of the effector-protein. Prominent oxidative modifications induced by cell-signaling reactive oxygen species (ROS) are cysteinyl modifications such as S-nitrosylation, sulfenic acid and disulfide formation. Disulfides protect protein sulfhydryls against oxidative destruction and simultaneously influence cell signaling by engaging redox-regulatory sulfhydryls in effector-proteins. The types of disulfides implicated in signaling span (1) protein S-glutathionylation, e.g. as a novel mode of Ras activation through S-glutathionylation at Cys-118 in response to a hydrogen-peroxide burst, (2) intra-protein disulfides, e.g. in the regulation of the stability of the protein phosphatase Cdc25C by hydrogen-peroxide, (3) inter-protein disulfides, e.g. in the hydrogen peroxide-mediated inactivation of receptor protein-tyrosine phosphatase alpha (RPTPalpha) by dimerization and (4) protein S-cysteaminylation by cystamine. Cystamine is a byproduct of pantetheinase-catalyzed pantothenic acid recycling from pantetheine for biosynthesis of Coenzyme A (CoA), a ubiquitous and metabolically indispensable cofactor. Cystamine inactivates protein kinase C-epsilon (PKCepsilon), gamma-glutamylcysteine synthetase and tissue transglutaminase by S-cysteaminylation-triggered mechanisms. The importance of protein S-cysteaminylation in signal transmission in vivo is evident from the ability of cystamine administration to rescue the intestinal inflammatory-response deficit of pantetheinase knockout mice. These mice lack the predominant epithelial pantetheinase isoform and have sharply reduced levels of cystamine/cysteamine in epithelial tissues. In addition, intraperitoneal administration of cystamine significantly delays neurodegenerative pathogenesis in a Huntington's disease mouse model. Thus, cystamine may serve as a prototype for the development of novel therapeutics that target effector-proteins regulated by S-cysteaminylation.

Progression of human prostate cancer to a malignancy that is refractory to androgen-ablation therapy renders the disease resistant to available treatment options and accounts for the high prostate cancer mortality rate. Epidermal growth factor receptor (EGFR) expression in human prostate cancer specimens increases with disease progression to androgen-refractory prostate cancer, and experimental models implicate EGFR-dependent signaling to Erk1/2 activation in the androgen-refractory prostate cancer phenotype. 12-O-Tetradecanoylphorbol-13-acetate (TPA)-induced Erk1/2 activation in human prostate cancer PC-3 cells is a paradigm of diacylglycerol-induced EGFR transactivation in androgen-independent prostate cancer. In this report, we establish an obligatory role for TPA-induced protein kinase C (PKC)-alpha activation in EGFR transactivation and signaling to Erk1/2 activation in PC-3 cells. TPA-regulated molecules include PKCs, PKDs, and Ras guanyl nucleotide-releasing proteins. The PKC-selective inhibitors GF109203X and Go6983 each blocked TPA-induced EGFR transactivation, indicating a requirement for PKC. PC-3 cells express four PKC isozymes. Prolonged bryostatin 1 treatment abrogated PKCalpha expression without altering expression levels of the other PKC isozymes. Pharmacologic PKCalpha "knockdown" abrogated TPA-induced Erk1/2 activation without affecting the EGF/EGFR-induced response, indicating that PKCalpha was required for EGFR transactivation but dispensable for signaling of ligand-activated EGFR to Erk1/2 activation. We corroborated this by showing that Go6976, which is a PKCalpha-selective inhibitor in PC-3 cells, likewise abolished TPA-induced Erk1/2 activation and did not inhibit EGF/EGFR-induced Erk1/2 activation. Go6976 had similar effects in DU145 cells, providing evidence for a common PKCalpha-dependent Erk1/2 activation mechanism in androgen-independent human prostate cancer cells of distinct genetic origin. These results constitute a rational basis for selective PKCalpha inhibition as a modality of prostate cancer therapy.

We reported previously that cystine produces regulatory responses in purified, recombinant human protein kinase C-delta (PKCdelta) and PKCepsilon via S-thiolation-triggered mechanisms that are consistent with a cancer preventive effect, i.e. stimulation of the pro-apoptotic, tumor-suppressive isozyme PKCdelta and inactivation of the growth-stimulatory, oncogenic isozyme PKCepsilon, at S-cysteinylation stoichiometries that correspond to modification of a single redox-regulatory cysteine (Cys) switch in each isozyme. In this report, we show that the oxidative regulatory responses of purified PKCdelta and PKCepsilon to cystine are recapitulated in disulfide-treated cells. We report that treatment of COS7-PKCepsilon transfectants with the cystine precursor cystine dimethyl ester (CDME) produced concentration- and time-dependent PKCepsilon inactivation that was associated with oxidative PKCepsilon modification manifested as attenuated band intensity in PKCepsilon immunoblot analyses, and that both PKCepsilon inactivation and modification were reversed by dithiothreitol (DTT) as well as by thioredoxin. We also show that CDME induced biphasic PKCdelta regulation in COS7-PKCdelta transfectants, with DTT-irreversible PKCdelta stimulation at low and DTT-reversible PKCdelta inactivation at high CDME concentrations. The degrees of PKCdelta versus PKCepsilon inactivation by CDME treatment of COS7-PKC transfectants indicate substantial resistance of PKCdelta to inactivation. The PKCdelta stimulatory response in COS7-PKCdelta cells was triggered only by the disulfide agent and not by its reduced thiol counterpart, providing evidence for an oxidative mechanism. Also paralleling the oxidative stimulation of purified PKCdelta by cystine, the stimulation of PKCdelta elicited by CDME treatment of cells involved a stable structural change, which was evident from the stability of the stimulated form of PKCdelta to immunoprecipitation. Demonstration of oxidative regulation of cellular PKCdelta and PKCepsilon by disulfides in this report provides evidence that redox-regulatory sites in PKCdelta and PKCepsilon may offer novel targets for development of cancer preventive or therapeutic agents that selectively inactivate PKCepsilon or stimulate PKCdelta.

The development of androgen-independent prostate cancer (AI PrCa) involves constitutive Erk1/2 activation sustained by the epidermal growth factor/transforming growth factor-alpha/EGF receptor (EGF/TGFalpha/EGFR) axis and other trophic signaling mechanisms in neoplastic human prostate epithelial cells in vivo. In this report, we show that growth-inhibitory concentrations of the dietary phytochemical resveratrol suppress EGFR-dependent Erk1/2 activation pathways stimulated by EGF and phorbol ester (12- O -tetradecanoyl phorbol 13-acetate, TPA) in human AI PrCa PC-3 cells in vitro. Because protein kinase C (PKC) is the major cellular receptor for phorbol esters and taking into consideration that resveratrol is PKC-inhibitory, we investigated resveratrol effects on cellular PKC isozymes associated with the suppression of TPA-induced Erk1/2 activation. The PKC isozyme composition of PC-3 cells was defined by Western analysis of the cell lysate with a comprehensive set of isozyme-selective PKC Ab's. PC-3 cells expressed PKCalpha, epsilon, zeta, iota, and PKD (PKCmicro), as did another human AI PrCa cell line of distinct genetic origin, DU145. The effects of resveratrol on TPA-induced PKC isozyme activation were defined by monitoring PKC isozyme translocation and autophosphorylation. Under conditions where resveratrol suppressed TPA-induced Erk1/2 activation, the phytochemical produced isozyme-selective interference with TPA-induced translocation of cytosolic PKCalpha to the membrane/cytoskeleton and selectively diminished the amount of autophosphorylated PKCalpha in the membrane/cytoskeleton of the TPA-treated cells. These results demonstrate that resveratrol abrogation of a PKC-mediated Erk1/2 activation response in PC-3 cells correlates with isozyme-selective PKCalpha inhibition. The results provide evidence that resveratrol may have value as an adjuvant cancer therapeutic in advanced prostate cancer.

The dietary stilbene resveratrol is a major constituent of a variety of edible plant products, including grapes and peanuts. Resveratrol has been identified as an excellent candidate cancer chemopreventive, based on its safety and efficacy in animal models of carcinogenesis. Resveratrol is a prototype of a plethora of bioactive polyphenols in the food supply that has just begun to be mined for cancer preventive agents. For example, polyphenolic grapeseed fractions were shown recently to potently antagonize chemical carcinogenesis. Taking into consideration that the identification of resveratrol as a cancer preventive agent is largely owed to its high abundance in nature (e.g., it accounts for 5-10% of the grapeskin biomass), it is logical to expect that naturally occurring stilbenes that are superior to resveratrol in their cancer preventive properties await identification. Thus, resveratrol may represent the tip of the iceberg of a broad class of stilbene and related polyphenolic natural products that include safe and highly effective agents for cancer prevention. We hypothesize that resveratrol may be especially suitable as a lead agent for prostate cancer prevention given its ability to: 1) inhibit each stage of multistage carcinogenesis, 2) scavenge incipient populations of androgen-dependent prostate cancer cells through androgen receptor antagonism, and 3) scavenge incipient populations of androgen-independent prostate cancer cells by short-circuiting the epidermal growth factor-receptor (EGFR)-dependent autocrine loops in the cancer cells.

Protein kinase C (PKC) is a family of ten isozymes that play distinct and in some cases opposing roles in cell growth and survival. We recently reported that diamide, a diazene carbonyl derivative which oxidizes thiols to disulfides through addition/displacement reactions at the diazene bond, induces potent GSH-dependent inactivation of several PKC isozymes, including the oncogenic isozyme PKC epsilon, via S-glutathiolation. PKC delta, a pro-apoptotic isozyme, was distinguished by its resistance to inactivation. In this report, we show that PKC-regulatory S-thiolation modifications produced by physiological disulfides elicit opposing effects on PKC delta and PKC epsilon activity. We report that PKC delta is stimulated 2.0-2.5 fold by GSSG, (Cys-Gly)(2) and cystine, under conditions where PKC gamma and PKC epsilon are fully inactivated by cystine, and PKC alpha activity is affected marginally or not at all by the disulfides. Focusing on cystine, we show that DTT quenches cystine-induced PKC delta stimulation and PKC gamma and PKC epsilon inactivation, indicative of oxidative regulation. By analyzing DTT-reversible isozyme radiolabeling by [(35)S]cystine, we demonstrate that PKC gamma, PKC delta and PKC epsilon are each [(35)S] S-cysteinylated in association with the concentration-dependent regulation of isozyme activity by cystine. The restricted reactivity of cystine, together with the effects of DTT and thioredoxin on cystine-induced PKC isozyme regulation reported here, indicate that the cystine-induced PKC-regulatory effects entail isozyme S-cysteinylation. We recently hypothesized that antagonism of tumor promotion/progression by small cellular thiols may involve PKC regulation via oxidant-induced S-thiolation reactions with PKC isozymes. The findings of cystine-induced PKC isozyme regulation by S-cysteinylation reported here offer correlative support to the hypothetical model. Thus, PKC delta, a potent antagonist of DMBA-TPA-induced tumor promotion/progression in mouse skin, is stimulated by S-cysteinylation, PKC epsilon, an important mediator of the tumor promotion/progression response, is inactivated by S-cysteinylation, and PKC alpha, which is not influential in DMBA-TPA-induced tumor promotion/progression, is not regulated by cystine. Furthermore, PKC gamma has oncogenic activity, and S-cysteinylation inactivated PKC gamma and PKC epsilon similarly. These findings provide evidence that S-cysteinyl acceptor-sites in PKC isozymes may offer attractive targets for development of novel cancer preventive agents.

To design side chain variants for modulation of immunogenicity, we modeled the complex of the HLA-A2 molecule with an immunodominant peptide, E75, from the HER-2/neu protooncogene protein recognized by CTL. We identified the side chain orientation of E75. We modified E75 at the central Ser(5) (E75 wild-type), which points upward, by removing successively the HO (variant S5A) and the CH2-OH (variant S5G). Replacement of the OH with an aminopropyl (CH2)3-NH3 (variant S5K) maintained a similar upward orientation of the side chain. S5A and S5G were stronger stimulators while S5K was a weaker stimulator than E75 for induction of lytic function, indicating that the OH group and its extension hindered TCR activation. S5K-CTL survived longer than did CTL induced by E75 and the variants S5A and S5G, which became apoptotic after restimulation with the inducer. S5K-CTL also recognized E75 endogenously presented by the tumor by IFN-gamma production and specific cytolysis. S5K-CTL expanded at stimulation with E75 or with E75 plus agonistic anti-Fas mAb. Compared with S5K-CTL that had been restimulated with the inducer S5K, S5K-CTL stimulated with wild-type E75 expressed higher levels of E75(+) TCR and BCL-2. Activation of human tumor-reactive CTL by weaker agonists than the nominal Ag, followed by expansion with the nominal Ag, is a novel approach to antitumor CTL development. Fine tuning of activation of tumor-reactive CTL by weak agonists, designed by molecular modeling, may circumvent cell death or tolerization induced by tumor Ag, and thus, may provide a novel approach to the rational design of human cancer vaccines.

The transmembrane (TM) receptor encoded by the HER-2 proto-oncogene (HER-2) is amplified in several types of human carcinomas and premalignant states and provides an important target for cancer therapy. While overexpression of HER-2 should lead to increased CTL epitope formation due to the attendant increase in higher protein turnover, breast tumors are poor stimulators of CTL. In this report, we show that treatment of SKBR3.A2 tumor cells with HER-2 receptor agonists (EGF and NDF) enhanced tumor ability to activate CTL from tumor associated lymphocytes (TAL) and from T cells from peripheral blood in vitro. The enhanced ability of tumor cells to stimulate CTL was paralleled by tyrosine phosphorylation of HER-2, and its oligo-ubiquitination compared with control untreated, or TPA-treated tumor cells. Our results demonstrate that HER-2 ligands used at concentrations which induce tyrosine phosphorylation but not downregulation of the receptor can be used to enhance the ability of tumor cells to activate CTL. This may have implications for overcoming Ag ignorance and tolerance in human cancers.

Heregulins are a group of growth factors that play diverse and critical roles in the signaling network of the human epidermal growth factor receptor (HER or EGFR) superfamily. Our earlier studies have shown that recombinant heregulinbeta1 (HRG) induces apoptosis in SKBr3 breast cancer cells that overexpress HER2. Here we report molecular mechanisms of HRG-induced apoptosis. HRG treatment of SKBr3 cells for 72 h decreased the level of Bcl-2 protein. HRG treatment led to degradation of poly (ADP-ribose) polymerase (PARP) and activated both caspase-9 and caspase-7. No significant activation of caspase-3, -6, or -8 was detected. Expression of exogenous caspase-7 by adenovirus-caspase-7 (Ad-casp-7) in SKBr3 cells resulted in apoptosis, which mimicked the effect of HRG treatment. Expression of exogenous caspase-7 had no impact on Bcl-2 expression, but promoted PARP degradation. Two highly selective inhibitors of protein kinase C (PKC), GF109203X (GF) and Ro318425 (Ro), significantly enhanced HRG-induced apoptosis as determined by flow cytometric analysis and DNA fragmentation assay. Accordingly, the PKC inhibitor GF further decreased the level of Bcl-2 protein and further degraded PARP in HRG-treated cells. Assay of PKC activity indicated that HRG activated PKC in SKBr3 cells, predominantly affecting the PKCalpha isoform. To confirm which PKC isoform(s) mediated potentiation of HRG-induced apoptosis, the profile of PKC isoforms was measured in SKBr3 cells. Five PKC isoforms, PKCalpha, PKCiota, PKCzeta, PKClambda, and PKCdelta as well as their receptors (RACK1) were expressed in this cell line. Treatment with PKC inhibitors GF and Ro decreased protein levels of both PKCalpha and PKCdelta at 24 h. PKCalpha levels were still depressed at 72 h. GF and Ro had little effect on the expression of other PKC isoforms. An inhibitor of classical PKC isoforms (Go6976) enhanced HRG-induced apoptosis, whereas the PKCdelta selective inhibitor rottlerin did not. As PKCalpha was the only classical isoform expressed in SKBr3 cells, the effect of Go6976 on HRG-induced apoptosis largely related to inhibition of PKCalpha. Constitutive expression of wild-type PKCalpha attenuated the apoptosis produced by HRG and GF. Consequently, HRG-induced apoptosis in SKBr3 cells appeared to involve down-regulation of Bcl-2 protein, activation of caspase-9 and caspase-7, and degradation of PARP. Inhibition of PKC function enhanced HRG-induced apoptosis, leading to synergistic down-regulation of Bcl-2 expression. Impairment of the PKCalpha isoform alone was sufficient to potentiate HRG-induced apoptosis.

We recently established that S-glutathiolation of cPKCalpha fully inactivates the isozyme, at a stoichiometry of approximately 1 mol GSH/mol cPKCalpha. In this report we demonstrate that, in addition to cPKCalpha, six other PKC isozymes that are representative of the three subfamilies within the PKC family (cPKCbeta1, cPKCbeta2 and cPKCgamma, nPKCdelta and nPKCepsilon and aPKC-zeta) are subject to inactivation by S-glutathiolation induced by the thiol-specific oxidant diamide, which induces disulfide bridge formation. Among PKD and the seven PKC isozymes examined in this report only nPKCdelta has been directly implicated as an antagonist of tumor promotion/progression, while several of the kinases have been implicated in the mediation of tumor promotion/progression. We report that of the kinases examined nPKCdelta was the most resistant to inactivation by diamide-induced S-glutathiolation. In the absence of GSH only nPKCdelta activity exhibited a biphasic response to diamide, with low diamide concentrations oxidatively enhancing nPKCdelta activity and higher concentrations inactivating the isozyme; the other seven kinases were subject to monophasic, concentration-dependent, oxidative inactivation by diamide to various extents. The results provide evidence that at least some pro-oxidant environments may support the potent inactivation of nPKCepsilon and other PKC isozymes implicated in tumor promotion/progression by the mechanisms of S-glutathiolation and, in some cases, disulfide bridge formation among the isozyme thiols, without inducing substantial nPKCdelta inactivation. The results also show that neither the seven PKC isozymes examined nor PKD are inactivated by S-cysteinylation under conditions that support potent inactivation by S-glutathiolation. This indicates that the protection that the tumor promotion/progression antagonist GSH may afford against oxidative tumor promotion/progression mechanisms by S-thiolating and inactivating PKC isozymes and PKD cannot be afforded by the metabolic GSH precursor cysteine. These observations support a role for PKC inactivation via S-glutathiolation in the mechanism of tumor promotion/progression antagonism by GSH in pro-oxidant environments.

In this phase II study we assessed the efficacy of bryostatin-1 (NSC 339555) in metastatic melanoma patients when given intravenously either once a week at a dose of 25 microg/m2 per day over 24 h for 3 weeks or at 40 microg/m2 per day over 72 h every 2 weeks. Treatment courses were repeated every 4 weeks. Patients who had received one prior chemotherapy regimen for advanced melanoma, with or without biotherapy, were randomized to one or the other bryostatin-1 dose schedules until 12 patients were registered to each arm. Because there was one confirmed response among the 12 patients who received the 72 h dose schedule, 25 more patients were added to that arm. No prophylactic medications were given. Objective tumour measurements were used to assess the efficacy of the regimen. The National Cancer Institutes common toxicity criteria were used to grade reactions. In total, 49 patients with metastatic melanoma, none having symptomatic brain metastasis, were studied. Of these, 12 patients received the 24 h bryostatin-1 regimen, while the remaining 37 received the 72 h regimen. One patient receiving the 72 h regimen had a partial response lasting over 7 months. Muscle pain occurred in over 90% of the patients and was the dose-limiting side effect of the 72 h regimen. Grade 3/4 nausea and vomiting were more common on the 24 h regimen than on the 72 h one (35% versus 5% of patients). There was no therapy-related thrombocytopenia. Neutropenia was mild and mainly limited to patients receiving the 72 h regimen. Bryostatin-1 has limited activity against melanoma when given by 72 h intravenous infusion.

The seminal discovery in 1988 that selective protein kinase C (PKC) activators induce multidrug resistance (MDR) in human cancer cells spawned several years of intensive investigations; these studies were primarily directed at the question of whether isozyme-selective PKC antagonism could reverse MDR phenotypes produced in cancer cells by P-glycoprotein and other ATP-binding cassette (ABC) transporters. The first section of this commentary provides a succinct overview of those studies. In the second section, we evaluate why the enthusiasm for studies of the involvement of PKC in transport-related drug resistance is currently diminished, and we offer an assessment of whether the PKC/MDR field should be revisited. The final section of the commentary highlights recent developments in studies of PKC targeting in experimental cancer therapeutics, which continues to be a vibrant field. Highlights include the sensitization of cancer cells to radiation- and drug-induced apoptosis by PKC inhibition.

We investigated the ubiquitination and degradation of a tumor antigen, the HER-2/neu (HER-2) protooncogene product which is overexpressed in epithelial cancers. HER-2 degradation was investigated in the ovarian tumor line, SKOV3.A2, that constitutively overexpressed long-life HER-2. We used as agonist geldanamycin (GA), which initiated downmodulation of HER-2 from the cell surface. HER-2 was polyubiquitinated and degraded faster in the presence than in the absence of GA. GA did not decrease HLA-A2 expression. Presentation of the immunodominant cytotoxic T lymphocyte (CTL) epitope, E75 (369-377) from SKOV.A2 was inhibited by proteasome inhibitors, such as LLnL but was enhanced by cysteine protease inhibitors such as E64, indicating that both the proteasome and cysteine proteases are involved in epitope formation but have different effects. Enhanced tumor recognition was not an immediate or early effect of GA treatment, but was evident after 20 h of GA treatment. In contrast, 20 h GA treatment did not increase tumor sensitivity to LAK cell lysis. Twenty hour GA-treated SKOV3.A2 cells expressed an unstable HER-2 protein synthesized in the presence of GA, of faster electrophoretic mobility than control HER-2. This suggested that the newly synthesized HER-2 in the presence of GA was the main source of epitopes recognized by CTL. Twenty hour GA-treated SKOV3.A2 cells were better inducers of CTL activity directed to a number of HER-2 CTL epitopes, in peripheral blood mononuclear cells compared with control untreated SKOV3.A2 cells. Thus, induction of HER-2 protein instability enhanced the sensitivity of tumor for CTL lysis. Increased HER-2 CTL epitopes presentation may have implications for overcoming the poor immuno-genicity of human tumors, and design of epitope precursors for cancer vaccination.

The natural product resveratrol is a potent antagonist of phorbol ester-mediated tumor promotion and in vitro cellular responses to phorbol-ester tumor promoters, but it is only weakly inhibitory against the phosphorylation of conventional exogenous substrates by phorbol ester-responsive protein kinase C (PKC) isozymes. In this report, we compare the effects of resveratrol against the autophosphorylation reactions of PKC isozymes versus the novel phorbol ester-responsive kinase, protein kinase D (PKD). We found that resveratrol inhibits PKD autophosphorylation in a concentration-dependent manner, but has only negligible effects against the autophosphorylation reactions of representative members of each PKC isozyme subfamily (cPKC-alpha, -beta(1), and -gamma, nPKC-delta and -epsilon, and aPKC-zeta). Resveratrol was comparably effective against PKD autophosphorylation (IC(50) = 52 microM) and PKD phosphorylation of the exogenous substrate syntide-2 (IC(50) = 36 microM). The inhibitory potency of resveratrol against PKD is in line with the potency of resveratrol observed in cellular systems and with its potency against other purified enzymes and binding proteins that are implicated in the cancer chemopreventive activity of the polyphenol. Thus, PKD inhibition may contribute to the cancer chemopreventive action of resveratrol.

Protein kinase C (PKC) isozymes are subject to inactivation by reactive oxygen species (ROS) through as yet undefined oxidative modifications of the isozyme structure. We previously reported that Cys-containing, Arg-rich peptide-substrate analogues spontaneously form disulfide-linked complexes with PKC isozymes, resulting in isozyme inactivation. This suggested that PKC might be inactivated by oxidant-induced S-glutathiolation, i.e., disulfide linkage of the endogenous molecule glutathione (GSH) to PKC. Protein S-glutathiolation is a reversible oxidative modification that has profound effects on the activity of certain enzymes and binding proteins. To directly examine whether PKC could be inactivated by S-glutathiolation, we used the thiol-specific oxidant diamide because its oxidant activity is restricted to induction of disulfide bridge formation. Diamide weakly inactivated purified recombinant cPKC-alpha, and this was markedly potentiated to nearly full inactivation by 100 microM GSH, which by itself was without effect on cPKC-alpha activity. Diamide inactivation of cPKC-alpha and its potentiation by GSH were both fully reversed by DTT. Likewise, GSH markedly potentiated diamide inactivation of a PKC isozyme mixture purified from rat brain (alpha, beta, gamma, epsilon, zeta) in a DTT-reversible manner. GSH potentiation of diamide-induced cPKC-alpha inactivation was associated with S-glutathiolation of the isozyme. cPKC-alpha S-glutathiolation was demonstrated by the DTT-reversible incorporation of [(35)S]GSH into the isozyme structure and by an associated change in the migration position of cPKC-alpha in nonreducing SDS-PAGE. Diamide treatment of NIH3T3 cells likewise induced potent, DTT-reversible inactivation of cPKC-alpha in association with [(35)S] S-thiolation of the isozyme. Taken together, the results indicate that PKC isozymes can be oxidatively inactivated by S-thiolation reactions involving endogenous thiols such as GSH.

Resveratrol, a polyphenolic natural product abundantly present in grape skins, is a candidate cancer chemopreventive agent that antagonizes each stage of carcinogenesis and inhibits protein kinase C (PKC), a key mediator of tumor promotion. While resveratrol has been shown to antagonize both isolated and cellular forms of PKC, the weak inhibitory potency observed against isolated PKC cannot account for the reported efficacy of the polyphenol against PKC in cells. In this report, we analyze the mechanism of PKC inhibition by resveratrol. Our results indicate that resveratrol has a broad range of inhibitory potencies against purified PKC that depend on the nature of the substrate and the cofactor dependence of the phosphotransferase reaction. Resveratrol weakly inhibited the Ca2+/phosphatidylserine-stimulated activity of a purified rat brain PKC isozyme mixture (IC(50) = 90 microM) by competition with ATP (K(i) = 55 microM). Consistent with the kinetic evidence for a catalytic domain-directed mechanism, resveratrol inhibited the lipid-dependent activity of PKC isozymes with divergent regulatory domains similarly, and it was even more effective in inhibiting a cofactor-independent catalytic domain fragment (CDF) of PKC generated by limited proteolysis. This suggested that regulatory features of PKC might impede resveratrol inhibition of the enzyme. To explore this, we examined the effects of resveratrol on PKC-catalyzed phosphorylation of the cofactor-independent substrate protamine sulfate, which is a polybasic protein that activates PKC by a novel mechanism. Resveratrol potently inhibited protamine sulfate phosphorylation (IC(50) = 10 microM) by a mechanism that entailed antagonism of the activation of PKC by protamine sulfate and did not involve competition with either substrate. On the basis of the presence of PKC isozymes at subcellular sites rich in polybasic proteins, it has been proposed that certain endogenous polybasic PKC substrates may activate PKC in cells by the same mechanism as protamine sulfate. Our results suggest that antagonism by resveratrol of the phosphorylation of cellular PKC substrates that resemble protamine sulfate in their interactions with PKC may contribute to the efficacy of resveratrol against PKC in cells.

Studies focused on the cAMP-dependent protein kinase (PKA) have led to the identification of conserved active-site residues involved in Ser/Thr protein kinase catalysis and have ruled out a role for Cys residues in the catalytic mechanism. Protein kinase C (PKC) is a Ser/Thr protein kinase isozyme family. We recently reported that the peptide-substrate analog N-biotinyl-Arg-Arg-Arg-Cys-Leu-Arg-Arg-Leu (N-biotinyl-RRRCLRRL) spontaneously forms intermolecular disulfide bridges with the active-site region of PKC isozymes concomitant with inactivation of histone kinase catalysis. Because Cys does not participate in PKC catalysis, one can analyze the active-site topology of PKC by examining which catalytic reactions are sterically hindered when the inactivator peptide is tethered to Cys in the active-site region of the enzyme. In this report, we show that N-biotinyl-RRRCLRRL inactivates the bulky PKC-catalyzed histone phosphorylation reaction, the comparatively less bulky PKC-catalyzed phosphorylation of a series of octapeptide, hexapeptide, and pentapeptide substrates, the intramolecular autophosphorylation reaction of PKC, and the least bulky PKC-catalyzed reaction, ATP hydrolysis, in a dithiothreitol-sensitive manner with comparable efficacy. Our results provide evidence that the covalent linkage of N-biotinyl-RRRCLRRL to the active-site region of PKC sterically hinders PKC catalysis, even in the absence of peptide and protein substrates., (Copyright 1999 Academic Press.)

Glutathione (GSH) and the GSH metabolic precursor N-acetylcysteine (NAC) are potent antioxidants that have clear potential either as cancer chemopreventive agents or as lead compounds for new cancer chemopreventive agents. The potential efficacy of GSH and NAC in clinical cancer chemoprevention is suggested by their antagonism of tumor promotion in animal models. Protein kinase C (PKC) is an isozyme family that plays a critical role in phorbol ester-mediated tumor promotion. We recently found that GSH and NAC exert direct inhibitory effects against a purified PKC isozyme mixture by a mechanism that did not involve their antioxidant properties. In this report, we characterize non-redox inhibitory effects of glutathiones on PKC isozymes that have been shown to produce partially or fully transformed phenotypes in mammalian cells. We show that GSH, NAC, and oxidized GSH analogs exert potent inhibition of the isozyme cPKC-ç and are somewhat less effective against cPKC- 1. In contrast, the oncogenic isozyme nPKC-â was unaffected by NAC, and it was inhibited by GSH and oxidized GSH analogs very modestly. Our results suggest that the potential impact of non-redox GSH/NAC-mediated PKC inhibition on cellular responses to tumor promoters and indeed, on cell growth regulation in general, may depend upon the pattern of PKC isozyme expression in the cells.

The peptides N-biotinyl-RRRCLRRL and N-biotinyl-RKRCLRRL covalently modify protein kinase C (PKC) through reaction of the Cys sulfhydryl group with the active site of the enzyme. The labeling of PKC occurs only in the presence of the cofactors phosphatidylserine, diacylglycerol, and Ca2+ but not in their absence. Low concentrations of the Arg-rich substrate, R4YGSR6Y greatly increase the extent of the reaction of these biotinylated peptides with PKC in the presence of lipid cofactors but in the absence of calcium. This effect can be observed at 50 nM R4YGSR6Y and suggests the presence of a high-affinity binding site for Arg-rich peptides which is separate from the active site but which enhances accessibility of the active site. The study also demonstrates the utility of the biotinylated peptides as active site labels which can detect the conformational change accompanying the activation of PKC., (Copyright 1998 Academic Press.)

The tripeptide glutathione (GSH) is the predominant low molecular weight thiol reductant in mammalian cells. In this report, we show that at concentrations at which GSH is typically present in the intracellular milieu, GSH and the oxidized GSH derivatives GSH disulfide (GSSG) and glutathione sulfonate each irreversibly inactivate up to 100% of the activity of purified Ca2+- and phosphatidylserine (PS)-dependent protein kinase C (PKC) isozymes in a concentration-dependent manner by a novel nonredox mechanism that requires neither glutathiolation of PKC nor the reduction, formation, or isomerization of disulfide bridges within PKC. Our evidence for a nonredox mechanism of PKC inactivation can be summarized as follows. GSSG antagonized the Ca2+- and PS-dependent activity of purified rat brain PKC with the same efficacy (IC50 = 3 mM) whether or not the reductant dithiothreitol was present. Glutathione sulfonate, which is distinguished from GSSG and GSH by its inability to undergo disulfide/thiol exchange reactions, was as effective as GSSG in antagonizing Ca2+- and PS-dependent PKC catalysis. The irreversibility of the inactivation mechanism was indicated by the stability of the inactivated form of PKC to dilution and extensive dialysis. The inactivation mechanism did not involve the nonspecific phenomena of denaturation and aggregation of PKC because it obeyed pseudo-first order kinetics and because the hinge region of PKC-alpha remained a preferential target of tryptic attack following GSH inactivation. The selectivity of GSH in the inactivation of PKC was also indicated by the lack of effect of the tripeptides Tyr-Gly-Gly and Gly-Ala-Gly on the activity of PKC. Furthermore, GSH antagonism of the Ser/Thr kinase casein kinase 2 was by comparison weak (<25%). Inactivation of PKC-alpha was not accompanied by covalent modification of the isozyme by GSH or other irreversible binding interactions between PKC-alpha and the tripeptide, but it was associated with an increase in the susceptibility of PKC-alpha to trypsinolysis. Treatment of cultured rat fibroblast and human breast cancer cell lines with N-acetylcysteine resulted in a substantial loss of Ca2+- and PS- dependent PKC activity in the cells within 30 min. These results suggest that GSH exerts negative regulation over cellular PKC isozymes that may be lost when oxidative stress depletes the cellular GSH pool.

Prostate cancer is a leading cause of cancer death among men in Western countries. A major reason for this is that the malignancy often progresses to an androgen-independent phenotype that is highly aggressive and unresponsive to available therapies. Protein kinase C (PKC) is an isozyme family with at least eleven mammalian members that play important roles in cell growth regulation and differentiation. Based on the emerging understanding of the role played by PKC isozymes in the regulation of prostate cancer cell growth and programmed death, in this report we develop the hypothesis that a defective PKC-a-mediated apoptotic pathway in androgen-independent human prostate cancer cells has allowed the cells to acquire a selective growth advantage by overexpression of PKC-a and that this adaptive response renders the cells dependent on constitutively active PKC-a for their survival. Studies reviewed in this report provide strong evidence that expression of constitutive PKC-a activity is required for the survival and growth of androgen-independent human prostate cancer cells, but direct evidence for this is still lacking. We outline experimental approaches that will be required to definitively test the importance of PKC-a to androgen-independent human prostate cancer cell growth and survival. If constitutive PKC-a activity is in fact found to be required for the growth and survival of androgen-independent human prostate cancer, then the development of PKC-a-targeted therapeutics for use in the clinical treatment of prostate cancer will be justified.

The multidrug resistance (MDR) phenotype of cancer cells often correlates with the level and activity of protein kinase C (PKC). We studied the ability of the staurosporine derivative PKC inhibitor CGP 41251 to reverse the MDR phenotype in MCF-7 human breast carcinoma and CT-26 murine colon adenocarcinoma cells and their doxorubicin (DXR)-selected MDR variants. Nontoxic concentrations of CGP 41251 significantly enhanced the cytotoxic properties of DXR, actinomycin D, vinblastine, and vincristine but not those of 5-fluorouracil. CGP 41251 increased intracellular concentrations of [14C]DXR but did not cause significant differences in P-glycoprotein (P-gp) expression. Pretreatment of MCF-7adr cells with phorbol 12-myristate 13-acetate reduced the CGP 41251 mediated intracellular accumulation of [14C]DXR. At concentrations that induced drug uptake, CGP 41251 significantly decreased the level of P-gp phosphorylation in the cells but did not compete with [3H]azidopine for photoaffinity labeling of P-gp. These data provide evidence that CGP 41251 reverses the MDR phenotype by modulating the phosphorylation of P-gp and/or other PKC substrates critical to the maintenance of the MDR phenotype.