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The kinome is a dynamic system of kinases regulating signaling networks in cells and dysfunction of protein kinases contributes to many diseases. Regulation of the protein expression of kinases alters cellular responses to environmental changes and perturbations. We configured a library of 672 proteotypic peptides to quantify >300 kinases in a single LC-MS experiment using ten micrograms protein from human tissues including biopsies. This enables absolute quantitation of kinase protein abundance at attomole-femtomole expression levels, requiring no kinase enrichment and less than ten micrograms of starting protein from flash-frozen and formalin fixed paraffin embedded tissues. Breast cancer biopsies, organoids, and cell lines were analyzed using the SureQuant method, demonstrating the heterogeneity of kinase protein expression across and within breast cancer clinical subtypes. Kinome quantitation was coupled with nanoscale phosphoproteomics, providing a feasible method for novel clinical diagnosis and understanding of patient kinome responses to treatment.

TAM-family tyrosine kinases (TYRO3, AXL and MERTK) are potential cancer therapeutic targets. In previous studies MERTK inhibition in the immune microenvironment was therapeutically effective in a B-cell acute leukemia (B-ALL) model. Here, we probed anti-leukemia immune mechanisms and evaluated roles for TYRO3 and AXL in the leukemia microenvironment. Host Mertk knock-out or MERTK inhibitor MRX-2843 increased CD8α + dendritic cells (DCs) with enhanced antigen-presentation capacity in the leukemia microenvironment and inhibited leukemogenesis. High MERTK or low DC gene expression were associated with poor prognosis in pediatric ALL patients, indicating the clinical relevance of these findings. MRX-2843 increased CD8 + T-cell numbers and prevented induction of exhaustion markers, implicating a DC - T-cell axis. Indeed, combined depletion of CD8α + DCs and CD8 + T-cells was required to abrogate anti-leukemia immunity in Mertk -/- mice. Tyro3 -/- mice were also protected against B-ALL, implicating TYRO3 as an immunotherapeutic target. In contrast to Mertk -/- mice, Tyro3 -/- did not increase CD8α + DCs with enhanced antigen-presentation capacity and therapeutic activity was less dependent on DCs, indicating a different immune mechanism. Axl -/- did not impact leukemogenesis. These data demonstrate differential TAM kinase roles in the leukemia microenvironment and provide rationale for development of MERTK and/or TYRO3-targeted immunotherapies., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

Background: Rapid growth in the number of U.S. cancer survivors drives the need for ongoing research efforts to improve outcomes and experiences after cancer. Here we describe the University of North Carolina (UNC) Cancer Survivorship Cohort, a medical center-based cohort of adults with cancer that integrates medical record-abstracted cancer information, patient-reported outcomes, and biologic specimens., Methods: Participants ages 18+ were recruited from UNC oncology clinics between April 2010 and August 2016. After enrollment, participants completed questionnaires on a range of topics including demographics, health history, health care access and utilization, quality of life, and symptoms. Blood samples and tumor tissue specimens were collected and processed by study staff, and cancer characteristics and other clinical data were abstracted from electronic medical records. Participants consented to recontact for future studies and linkage of their data with other data resources., Results: In total, 3,999 participants with a cancer diagnosis were enrolled in the cohort. The most common cancer types among those enrolled included breast (N=866), uterine (N=458), colorectal (N=300), prostate (N=296), and head and neck (N=248). Blood specimens were collected for 3,027 (76%). Additional participants without cancer (N=1,299) were also enrolled, and the majority (62%) provided biospecimen samples., Conclusions: We encourage wide collaboration with investigators across institutions seeking to advance research in cancer survivorship. Procedures are in place to support proposals for use of existing or linked data and for proposals that require participant recontact or analysis of biospecimens., Impact: The UNC Cancer Survivorship Cohort is a unique resource for cancer survivorship research.

Checkpoint inhibitors, specifically anti-programmed cell death protein 1 (PD1), have shown success in treating metastatic melanoma; however, some patients develop resistance. Dendritic cells (DC) play a key role in initiating an immune response, but in certain circumstances they become ineffective. We investigated the role of MerTK, a receptor tyrosine kinase responsible for myeloid cell clearance of dead cells, in the regulation of DC function and metabolism in the tumor microenvironment. Tumors resistant to anti-PD1 exhibited increased levels of MerTK+ DCs. Treating wild-type DCs with apoptotic melanoma cells in vitro resulted in increased MerTK expression, elevated mitochondrial respiration and fatty acid oxidation, and reduced T-cell stimulatory capacity, all characteristics of dysfunctional DCs. In contrast, dead cells had only limited effect on the metabolism of MerTK-deficient DCs, which instead maintained an antigen-presenting, stimulatory phenotype. The efficacy of anti-PD1 to slow tumor progression and induce antigen specific T-cell infiltration was markedly increased in mice with selective ablation of MerTK in the DC compartment, suggesting the possibility of therapeutically targeting MerTK to modulate DC metabolism and function and enhance anti-PD1 therapy., (©2024 American Association for Cancer Research.)

Kelp species function as important foundation organisms in coastal marine ecosystems where they provide biogenic habitat and ameliorate environmental conditions, often facilitating the development of diverse understorey assemblages. The structure of kelp forests is influenced by a variety of environmental factors, changes in which can result in profound shifts in ecological structure and functioning. Intense storm-induced wave action in particular, can severely impact kelp forest ecosystems. Given that storms are anticipated to increase in frequency and intensity in response to anthropogenic climate change, it is critical to understand their potential impacts on kelp forest ecosystems. During the 2021/22 northeast Atlantic storm season, the United Kingdom (UK) was subject to several intense storms, of which the first and most severe was Storm Arwen. Due to the unusual northerly wind direction, the greatest impacts of Storm Arwen were felt along the northeast coast of the UK where wind gusts exceeded 90 km/h, and inshore significant wave heights of 7.2 m and wave periods of 9.3 s were recorded. Here, we investigated temporal and spatial variation in the structure of L. hyperborea forests and associated understorey assemblages along the northeast coast of the UK over the 2021/22 storm season. We found significant changes in the cover, density, length, biomass, and age structure of L. hyperborea populations and the composition of understorey assemblages following the storm season, particularly at our most north facing site. We suggest continuous monitoring of these systems to further our understanding of temporal variation and potential recovery trajectories, alongside enhanced management to promote resilience to future perturbations., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Hannah Earp reports financial support was provided by Natural Environment Research Council. Dan Smale reports financial support was provided by Natural Environment Research Council. Adam Gouraguine reports financial support was provided by Natural Environment Research Council. Pippa Moore reports financial support was provided by Natural Environment Research Council. Dan Smale reports financial support was provided by UK Research and Innovation. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Outcomes are poor in patients with advanced or relapsed Ewing sarcoma (EWS) and current treatments have significant short- and long-term side effects. New, less toxic and more effective treatments are urgently needed. MER proto-oncogene tyrosine kinase (MERTK) promotes tumor cell survival, metastasis, and resistance to cytotoxic and targeted therapies in a variety of cancers. MERTK was ubiquitously expressed in five EWS cell lines and five patient samples. Moreover, data from CRISPR-based library screens indicated that EWS cell lines are particularly dependent on MERTK. Treatment with MRX-2843, a first-in-class, MERTK-selective tyrosine kinase inhibitor currently in clinical trials, decreased the phosphorylation of MERTK and downstream signaling in a dose-dependent manner in A673 and TC106 cells and provided potent anti-tumor activity against all five EWS cell lines, with IC 50 values ranging from 178 to 297 nM. Inhibition of MERTK correlated with anti-tumor activity, suggesting MERTK inhibition as a therapeutic mechanism of MRX-2843. Combined treatment with MRX-2843 and BCL-2 inhibitors venetoclax or navitoclax provided enhanced therapeutic activity compared to single agents. These data highlight MERTK as a promising therapeutic target in EWS and provide rationale for the development of MRX-2843 for the treatment of EWS, especially in combination with BCL-2 inhibitors.

In this issue honoring the contributions of Greg Lemke, the Earp and Graham lab teams discuss several threads in the discovery, action, signaling, and translational/clinical potential of MERTK, originally called c-mer, a member of the TYRO3, AXL, and MERTK (TAM) family of receptor tyrosine kinases. The 30-year history of the TAM RTK family began slowly as all three members were orphan RTKs without known ligands and/or functions when discovered by three distinct alternate molecular cloning strategies in the pre-genome sequencing era. The pace of understanding their physiologic and pathophysiologic roles has accelerated over the last decade. The activation of ligands bridging externalized phosphatidylserine (PtdSer) has placed these RTKs in a myriad of processes including neurodevelopment, cancer, and autoimmunity. The field is ripe for further advancement and this article hopefully sets the stage for further understanding and therapeutic intervention. Our review will focus on progress made through the collaborations of the Earp and Graham labs over the past 30 years.

Purpose: Genomic tests, such as the Oncotype Dx 21-gene and Prosigna risk of recurrence (ROR-P) assay, are commonly used for breast cancer prognostication. Emerging data suggest variability between assays, but this has not been compared in diverse populations., Materials and Methods: RNA sequencing was performed on 647 previously untreated stage I-III estrogen receptor-positive/human epidermal growth factor receptor 2-negative tumors in the Carolina Breast Cancer Study, which oversampled Black and younger women (age <50 years at diagnosis), using research versions of two common RNA-based prognostic assays: ROR-P R and the 21-gene recurrence score (RS R ). Relative frequency differences and 95% CIs were estimated for associations with race and age, and hazards of 5-year local or distant recurrence were modeled with Cox regression. Proliferation and estrogen module scores from each assay, representing broad activity of genes in those pathways, were examined to guide interpretation of differences between tests., Results: Among both younger and older individuals, Black women had higher frequency of intermediate and high ROR-P R scores than non-Black women. Race was not significantly associated with RS R in either age group. High (hazard ratio [HR], 4.67 [95% CI, 1.73 to 12.70]) and intermediate (HR, 2.12 [95% CI, 0.98 to 4.62]) ROR-P R scores were associated with greater risk of recurrence, but RS R did not predict recurrence. RS R emphasized estrogen over proliferation modules, whereas ROR-P R emphasized proliferation. Higher proliferation scores were associated with younger age and Black race in both assays. Modifications to the RS R algorithm that increased emphasis on proliferation improved prognostication in this diverse population., Conclusion: ROR-P R and the 21-gene RS R differentially emphasize estrogen-related and proliferative biology. The emphasis of 21-gene RS on estrogen-related biology and lower endocrine therapy initiation among Black women may contribute to poorer prognostic ability in heterogeneously treated populations.

Ewing sarcoma is a pediatric bone and soft tissue tumor treated with chemotherapy, radiation, and surgery. Despite intensive multimodality therapy, ~50% patients eventually relapse and die of the disease due to chemoresistance. Here, using phospho-profiling, we find Ewing sarcoma cells treated with chemotherapeutic agents activate TAM (TYRO3, AXL, MERTK) kinases to augment Akt and ERK signaling facilitating chemoresistance. Mechanistically, chemotherapy-induced JAK1-SQ phosphorylation releases JAK1 pseudokinase domain inhibition allowing for JAK1 activation. This alternative JAK1 activation mechanism leads to STAT6 nuclear translocation triggering transcription and secretion of the TAM kinase ligand GAS6 with autocrine/paracrine consequences. Importantly, pharmacological inhibition of either JAK1 by filgotinib or TAM kinases by UNC2025 sensitizes Ewing sarcoma to chemotherapy in vitro and in vivo. Excitingly, the TAM kinase inhibitor MRX-2843 currently in human clinical trials to treat AML and advanced solid tumors, enhances chemotherapy efficacy to further suppress Ewing sarcoma tumor growth in vivo. Our findings reveal an Ewing sarcoma chemoresistance mechanism with an immediate translational value., (© 2024. The Author(s).)

Kelp forests occur on more than a quarter of the world's coastlines, serving as foundation species supporting high levels of biodiversity. They are also a major source of organic matter in coastal ecosystems, with the majority of primary production released and exported as detritus. Kelp detritus also provides food and shelter for macroinvertebrates, which comprise important components of inshore food-webs. Hitherto, research on kelp detritus-associated macroinvertebrate assemblages remains relatively limited. We quantified spatiotemporal variability in the structure of detritus-associated macroinvertebrate assemblages within Laminaria hyperborea forests and evaluated the influence of putative drivers of the observed variability in assemblages across eight study sites within four regions of the United Kingdom in May and September 2015. We documented 5167 individuals from 106 taxa with Malacostraca, Gastropoda, Isopoda and Bivalvia the most abundant groups sampled. Assemblage structure varied across months, sites, and regions, with highest richness in September compared to May. Many taxa were unique to individual regions, with few documented in all regions. Finally, key drivers of assemblage structure included detritus tissue nitrogen content, depth, sea surface temperature, light intensity, as well as L. hyperborea canopy density and canopy biomass. Despite their dynamic composition and transient existence, accumulations of L. hyperborea detritus represent valuable repositories of biodiversity and represent an additional kelp forest component which influences secondary productivity, and potentially kelp forest food-web dynamics., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Crown Copyright © 2024. Published by Elsevier Ltd. All rights reserved.)

MERTK and AXL are members of the TAM (TYRO3, AXL, MERTK) family of receptor tyrosine kinases that are aberrantly expressed and have been implicated as therapeutic targets in a wide variety of human tumors. Dual MERTK and AXL inhibition could provide antitumor action mediated by both direct tumor cell killing and modulation of the innate immune response in some tumors such as nonsmall cell lung cancer. We utilized our knowledge of MERTK inhibitors and a structure-based drug design approach to discover a novel class of macrocyclic dual MERTK/AXL inhibitors. The lead compound 43 had low-nanomolar activity against both MERTK and AXL and good selectivity over TYRO3 and FLT3. Its target engagement and selectivity were also confirmed by NanoBRET and cell-based MERTK and AXL phosphorylation assays. Compound 43 had excellent pharmacokinetic properties (large AUC and long half-life) and mediated antitumor activity against lung cancer cell lines, indicating its potential as a therapeutic agent.

Novel treatment approaches are needed to overcome innate and acquired mechanisms of resistance to current anticancer therapies in cancer cells and the tumour immune microenvironment. The TAM (TYRO3, AXL and MERTK) family receptor tyrosine kinases (RTKs) are potential therapeutic targets in a wide range of cancers. In cancer cells, TAM RTKs activate signalling pathways that promote cell survival, metastasis and resistance to a variety of chemotherapeutic agents and targeted therapies. TAM RTKs also function in innate immune cells, contributing to various mechanisms that suppress antitumour immunity and promote resistance to immune-checkpoint inhibitors. Therefore, TAM antagonists provide an unprecedented opportunity for both direct and immune-mediated therapeutic activity provided by inhibition of a single target, and are likely to be particularly effective when used in combination with other cancer therapies. To exploit this potential, a variety of agents have been designed to selectively target TAM RTKs, many of which have now entered clinical testing. This Review provides an essential guide to the TAM RTKs for clinicians, including an overview of the rationale for therapeutic targeting of TAM RTKs in cancer cells and the tumour immune microenvironment, a description of the current preclinical and clinical experience with TAM inhibitors, and a perspective on strategies for continued development of TAM-targeted agents for oncology applications., (© 2023. Springer Nature Limited.)

Ecological communities are structured by a range of processes that operate over a range of spatial scales. While our understanding of such biodiversity patterns in macro-communities is well studied, our understanding at the microbial level is still lacking. Bacteria can be free living or associated with host eukaryotes, forming part of a wider "microbiome," which is fundamental for host performance and health. For habitat forming foundation-species, host-bacteria relationships likely play disproportionate roles in mediating processes for the wider ecosystem. Here, we describe host-bacteria communities across multiple spatial scales (i.e., from 10s of m to 100s of km) in the understudied kelp, Eisenia cokeri, in Peru. We found that E. cokeri supports a distinct bacterial community compared to the surrounding seawater, but the structure of these communities varied markedly at the regional (~480 km), site (1-10 km), and individual (10s of m) scale. The marked regional-scale differences we observed may be driven by a range of processes, including temperature, upwelling intensity, or regional connectivity patterns. However, despite this variability, we observed consistency in the form of a persistent core community at the genus level. Here, the genera Arenicella, Blastopirellula, Granulosicoccus, and Litorimonas were found in >80% of samples and comprised ~53% of total sample abundance. These genera have been documented within bacterial communities associated with kelps and other seaweed species from around the world and may be important for host function and wider ecosystem health in general., (© 2023. The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.)

Artificial structures are an increasingly common feature of coastal marine environments. These structures are poor surrogates of natural rocky shores, and generally support less diverse communities and reduced population sizes. Little is known about sub-lethal effects of such structures in terms of demographic properties and reproductive potential, both of which may influence the dynamics and long-term viability of populations. This study examines the population structure, reproductive states and embryo production of Nucella lapillus populations on artificial structures and natural shores in Ireland and Wales. Population density was measured twice at six natural shores and six artificial structures: once in winter and once in spring. At each sampling, the shell height of 100 individuals from each site was measured. Monthly collections of adult specimens and egg capsules were made at each site from November-January and from March-May, in order to determine sex ratios, reproductive states, and embryo abundances. Artificial structures supported larger individuals and very few juveniles compared to natural shores. Between December and January, natural shores experienced a distinctive pulse in spawning activity followed by a decline in the proportion of females in a reproductive state, whereas on artificial structures the proportion of reproductive females remained relatively stable. Differences observed may be due to a lack of microhabitats on artificial structures, along with subtle variations in structure slope. Eco-engineering interventions, including the addition of refugia such as cracks and crevices, may allow N. lapillus populations on artificial structures to approximate those on natural shores., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Published by Elsevier Ltd.)

Background: Previous studies show that the spleen and bone marrow can serve as leukemia microenvironments in which macrophages play a significant role in immune evasion and chemoresistance. We hypothesized that the macrophage driven tolerogenic process of efferocytosis is a major contributor to the immunosuppressive leukemia microenvironment and that this was driven by aberrant phosphatidylserine expression from cell turnover and cell membrane dysregulation., Methods: Since MerTK is the prototypic efferocytosis receptor, we assessed whether the MerTK inhibitor MRX2843, which is currently in clinical trials, would reverse immune evasion and enhance immune-mediated clearance of leukemia cells., Results: We found that inhibition of MerTK decreased leukemia-associated macrophage expression of M2 markers PD-L1, PD-L2, Tim-3, CD163 and Arginase-1 compared to vehicle-treated controls. Additionally, MerTK inhibition led to M1 macrophage repolarization including elevated CD86 and HLA-DR expression, and increased production of T cell activating cytokines, including IFN-β, IL-18, and IL-1β through activation of NF-κB. Collectively, this macrophage repolarization had downstream effects on T cells within the leukemia microenvironment, including decreased PD-1 + Tim-3 + and LAG3 + checkpoint expression, and increased CD69 + CD107a + expression., Discussion: These results demonstrate that MerTK inhibition using MRX2843 altered the leukemia microenvironment from tumor-permissive toward immune responsiveness to leukemia and culminated in improved immune-mediated clearance of AML., Competing Interests: SF and XW have filed a patent application describing MRX2843. HE, DG, XW, and SF are stockholders in Meryx, Inc. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest, (Copyright © 2023 Cruz Cruz, Allison, Page, Jenkins, Wang, Earp, Frye, Graham, Verneris and Lee-Sherick.)

The challenge of rapid macromolecular synthesis enforces the energy-hungry cancer cell mitochondria to switch their metabolic phenotypes, accomplished by activation of oncogenic tyrosine kinases. Precisely how kinase activity is directly exploited by cancer cell mitochondria to meet high-energy demand, remains to be deciphered. Here we show that a non-receptor tyrosine kinase, TNK2/ACK1 (tyrosine kinase non receptor 2), phosphorylated ATP5F1A (ATP synthase F1 subunit alpha) at Tyr243 and Tyr246 (Tyr200 and 203 in the mature protein, respectively) that not only increased the stability of complex V, but also increased mitochondrial energy output in cancer cells. Further, phospho-ATP5F1A (p-Y-ATP5F1A) prevented its binding to its physiological inhibitor, ATP5IF1 (ATP synthase inhibitory factor subunit 1), causing sustained mitochondrial activity to promote cancer cell growth. TNK2 inhibitor, ( R )- 9b reversed this process and induced mitophagy-based autophagy to mitigate prostate tumor growth while sparing normal prostate cells. Further, depletion of p-Y-ATP5F1A was needed for ( R )- 9b -mediated mitophagic response and tumor growth. Moreover, Tnk2 transgenic mice displayed increased p-Y-ATP5F1A and loss of mitophagy and exhibited formation of prostatic intraepithelial neoplasia (PINs). Consistent with these data, a marked increase in p-Y-ATP5F1A was seen as prostate cancer progressed to the malignant stage. Overall, this study uncovered the molecular intricacy of tyrosine kinase-mediated mitochondrial energy regulation as a distinct cancer cell mitochondrial vulnerability and provided evidence that TNK2 inhibitors can act as "mitocans" to induce cancer-specific mitophagy. Abbreviations : ATP5F1A: ATP synthase F1 subunit alpha; ATP5IF1: ATP synthase inhibitory factor subunit 1; CRPC: castration-resistant prostate cancer; DNM1L: dynamin 1 like; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; Mdivi-1: mitochondrial division inhibitor 1; Mut-ATP5F1A: Y243,246A mutant of ATP5F1A; OXPHOS: oxidative phosphorylation; PC: prostate cancer; PINK1: PTEN induced kinase 1; p-Y-ATP5F1A: phosphorylated tyrosine 243 and 246 on ATP5F1A; TNK2/ACK1: tyrosine kinase non receptor 2; Ub: ubiquitin; WT: wild type.

The chemokine receptor CCR2 plays a key role in cellular migration and inflammatory processes. While tremendous progress has been made in elucidating CCR2 function and inhibition, the majority of approaches target its N-terminal domain and less is known about the function of the remaining extracellular loops and their potential as targets. Here, we used phage display to identify an antibody-derived scFv (single chain variable fragment) clone that specifically targets the second extracellular epitope of CCR2 (ECL2) for inhibition. Using in silico molecular docking, we identified six potential primary binding conformations of the novel scFv to the specified CCR2 epitope. In silico molecular dynamic analysis was used to determine conformational stability and identify protein-protein interactions. Umbrella sampling of a range of configurations with incrementally increasing separation of scFv and target generated by force pulling simulations was used to calculate binding energies. Downstream characterization by ELISA showed high binding affinity of the ECL2-scFv to CCR2. Furthermore, we showed that blocking the second extracellular loop inhibits macrophage migration and polarized macrophages towards M1 inflammatory cytokine production as potently as lipopolysaccharide (LPS). These studies highlight the applicability of epitope-specific targeting, emphasize the importance of in silico predictive modeling, and warrant further investigation into the role of the remaining epitopes of CCR2., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Natalie Jasiewicz reports financial support was provided by Pharmaceutical Research and Manufacturers of America Foundation. Adam D. Brown reports financial support was provided by National Institutes of Health. Michael Deci and Juliane Nguyen have a patent: Compositions and methods to block and bind CCR2 to modulate cellular function pending with the Research Foundation of the State University of New York., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Artificial structures often support depauperate communities compared to natural rocky shores. Understanding variation in ecological success across shore types, particularly regarding habitat-forming species or those with structuring roles, is important to determine how artificial structure proliferation may influence ecosystem functioning and services. We investigated the population structure, sex ratio and reproductive potential of limpets on natural shores and artificial structures on Irish Sea coasts. Limpets were generally less abundant and Patella vulgata populations were often male dominated on artificial structures compared to natural shores, suggesting that shore type may influence these factors. P. vulgata length varied across sites within the Irish Sea (nested in coast and shore type) in autumn/winter, as well as temporally across sites along the Welsh coast. There was no difference in the proportion of P. vulgata in advanced stages of gonad development across shore types. The results suggest that rip-rap artificial structures may provide a habitat comparable to natural shores, however, the addition of ecological engineering interventions on artificial structures may allow limpet populations to better approximate those on natural shores., Competing Interests: Declaration of competing interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: All authors reports financial support was provided by European Regional Development Fund., (Copyright © 2022 The Authors. Published by Elsevier Ltd.. All rights reserved.)

T-cell acute lymphoblastic leukemia (T-ALL) accounts for 15% of childhood ALL. The early T-precursor (ETP-ALL) subset is characterized by an immature T-cell phenotype, chemoresistance, and high rates of induction failure. MERTK receptor tyrosine kinase is ectopically expressed in half of T-ALLs, particularly those with an immature T-cell phenotype, suggesting a role in ETP-ALL. The anti-apoptotic protein B-cell lymphoma-2 (BCL-2) is essential for ETP-ALL cell survival. Here, we show that MERTK and BCL-2 mRNA and protein are preferentially expressed in ETP-ALL patient samples. The dual MERTK/FLT3 inhibitor MRX-2843 decreased MERTK activation and downstream signaling, inhibited cell expansion, and induced cell death in ETP-ALL cell lines. Further, 54% (21/39) of primary T-ALL patient samples were sensitive to MERTK inhibition. Treatment with MRX-2843 significantly reduced leukemia burden and prolonged survival in cell-line-derived T-ALL and ETP-ALL xenograft models. In a patient-derived ETP-ALL xenograft model, treatment with MRX-2843 markedly reduced peripheral blood leukemia and spleen weight compared to vehicle-treated mice and prolonged survival. MRX-2843 also synergized with venetoclax to provide enhanced anti-leukemia activity in ETP-ALL cell cultures, with a dose ratio of 1:20 MRX-2843:venetoclax providing optimal synergy. These data demonstrate the therapeutic potential of MRX-2843 in patients with T-ALL and provide rationale for clinical development. MRX-2843 monotherapy is currently being tested in patients with relapsed leukemia (NCT04872478). Further, our data indicate that combined MERTK and BCL-2 inhibition may be particularly effective for treatment of ETP-ALL.

Enhancer of Zeste Homolog 2 (EZH2) and androgen receptor (AR) are crucial chromatin/gene regulators involved in the development and/or progression of prostate cancer, including advanced castration-resistant prostate cancer (CRPC). To sustain prostate tumorigenicity, EZH2 establishes non-canonical biochemical interaction with AR for mediating oncogene activation, in addition to its canonical role as a transcriptional repressor and enzymatic subunit of Polycomb Repressive Complex 2 (PRC2). However, the molecular basis underlying non-canonical activities of EZH2 in prostate cancer remains elusive, and a therapeutic strategy for targeting EZH2:AR-mediated oncogene activation is also lacking. Here, we report that a cryptic transactivation domain of EZH2 (EZH2TAD) binds both AR and AR spliced variant 7 (AR-V7), a constitutively active AR variant enriched in CRPC, mediating assembly and/or recruitment of transactivation-related machineries at genomic sites that lack PRC2 binding. Such non-canonical targets of EZH2:AR/AR-V7:(co-)activators are enriched for the clinically relevant oncogenes. We also show that EZH2TAD is required for the chromatin recruitment of EZH2 to oncogenes, for EZH2-mediated oncogene activation and for CRPC growth in vitro and in vivo. To completely block EZH2's multifaceted oncogenic activities in prostate cancer, we employed MS177, a recently developed proteolysis-targeting chimera (PROTAC) of EZH2. Strikingly, MS177 achieved on-target depletion of both EZH2's canonical (EZH2:PRC2) and non-canonical (EZH2TAD:AR/AR-V7:co-activators) complexes in prostate cancer cells, eliciting far more potent antitumor effects than the catalytic inhibitors of EZH2. Overall, this study reports a previously unappreciated requirement for EZH2TAD for mediating EZH2's non-canonical (co-)activator recruitment and gene activation functions in prostate cancer and suggests EZH2-targeting PROTACs as a potentially attractive therapeutic for the treatment of aggressive prostate cancer that rely on the circuits wired by EZH2 and AR., (© The Author(s) 2022. Published by Oxford University Press on behalf of Nucleic Acids Research.)

Acquired resistance is inevitable in non-small cell lung cancers (NSCLCs) treated with osimertinib (OSI), and the mechanisms are not well defined. The MERTK ligand GAS6 promoted downstream oncogenic signaling in EGFR-mutated (EGFRMT) NSCLC cells treated with OSI, suggesting a role for MERTK activation in OSI resistance. Indeed, treatment with MRX-2843, a first-in-class MERTK kinase inhibitor, resensitized GAS6-treated NSCLC cells to OSI. Both GAS6 and EGF stimulated downstream PI3K/AKT and MAPK/ERK signaling in parental cells, but only GAS6 activated these pathways in OSI-resistant (OSIR) derivative cell lines. Functionally, OSIR cells were more sensitive to MRX-2843 than parental cells, suggesting acquired dependence on MERTK signaling. Furthermore, MERTK and/or its ligands were dramatically upregulated in EGFRMT tumors after treatment with OSI in both xenograft models and patient samples, consistent with induction of autocrine/paracrine MERTK activation. Moreover, treatment with MRX-2843 in combination with OSI, but not OSI alone, provided durable suppression of tumor growth in vivo, even after treatment was stopped. These data identify MERTK as a driver of bypass signaling in treatment-naive and EGFRMT-OSIR NSCLC cells and predict that MRX-2843 and OSI combination therapy will provide clinical benefit in patients with EGFRMT NSCLC.

MERTK and AXL are members of the TAM family of receptor tyrosine kinases and are abnormally expressed in 69% and 93% of non-small cell lung cancers (NSCLCs), respectively. Expression of MERTK and/or AXL provides a survival advantage for NSCLC cells and correlates with lymph node metastasis, drug resistance, and disease progression in patients with NSCLC. The TAM receptors on host tumor infiltrating cells also play important roles in the immunosuppressive tumor microenvironment. Thus, MERTK and AXL are attractive biologic targets for NSCLC treatment. Here, we will review physiologic and oncologic roles for MERTK and AXL with an emphasis on the potential to target these kinases in NSCLCs with activating EGFR mutations.

Inhibition of MER receptor tyrosine kinase (MERTK) causes direct tumor cell killing and stimulation of the innate immune response. Therefore, MERTK has been identified as a therapeutic target in a wide variety of human tumors. Clinical trials targeting MERTK have recently been initiated, however, none of these drugs are MERTK-specific. Herein, we present the discovery of a highly MERTK-selective inhibitor UNC5293 (24). UNC5293 has subnanomolar activity against MERTK with an excellent Ambit selectivity score (S 50 (100 nM) = 0.041). It mediated potent and selective inhibition of MERTK in cell-based assays. Furthermore, it has excellent mouse PK properties (7.8 h half-life and 58% oral bioavailability) and was active in bone marrow leukemia cells in a murine model., Competing Interests: Declaration of competing interest The authors declared the following financial interests/personal relationships which may be considered as potential competing interests: HSE, DKG & SVF report equity ownership and membership on the Meryx Board of Directors. DK, DD & XW report equity ownership in Meryx. HZ, JZ, WZ, SVF & XW report patents from the University of North Carolina., (Copyright © 2021 Elsevier Masson SAS. All rights reserved.)

Artificial structures are widespread features of coastal marine environments. These structures, however, are poor surrogates of natural rocky shores, meaning they generally support depauperate assemblages with reduced population sizes. Little is known about sub-lethal effects of such structures, for example, in terms of demographic properties and reproductive potential that may affect the dynamics and long-term viability of populations. Such understanding is particularly important for ecosystem engineer species, such as the intertidal seaweed Fucus vesiculosus. In this study, F. vesiculosus was sampled on eight artificial structures and eight natural shores along the east coast of Ireland and the west coast of Wales. Algal percentage cover, biomass, density of individuals, and growth rate did not differ between artificial and natural shores. Growth and reproductive cycles were consistent with previous studies for this species. While there was considerable variation from site to site, on average, populations on natural shores produced a higher number of mature receptacles during the peak reproductive period in April, and lower rates of dislodgement than on artificial structures. As F. vesiculosus reach peak reproductive output after 24 months, this suggests that individuals may be removed from populations on artificial structures before reaching their full reproductive potential. In this case, this did not influence density, percentage cover, or biomass, which suggests that F. vesiculosus populations on artificial structures may function similarly to those on natural shores if supported by suitable source populations, but potentially may not persist otherwise., (Copyright © 2021 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Castration-resistant prostate cancer (CRPC) is a terminal disease and the molecular underpinnings of CRPC development need to be better understood in order to improve its treatment. Here, we report that a transcription factor Yin Yang 1 (YY1) is significantly overexpressed during prostate cancer progression. Functional and cistrome studies of YY1 uncover its roles in promoting prostate oncogenesis in vitro and in vivo, as well as sustaining tumor metabolism including the Warburg effect and mitochondria respiration. Additionally, our integrated genomics and interactome profiling in prostate tumor show that YY1 and bromodomain-containing proteins (BRD2/4) co-occupy a majority of gene-regulatory elements, coactivating downstream targets. Via gene loss-of-function and rescue studies and mutagenesis of YY1-bound cis-elements, we unveil an oncogenic pathway in which YY1 directly binds and activates PFKP, a gene encoding the rate-limiting enzyme for glycolysis, significantly contributing to the YY1-enforced Warburg effect and malignant growth. Altogether, this study supports a master regulator role for YY1 in prostate tumorigenesis and reveals a YY1:BRD2/4-PFKP axis operating in advanced prostate cancer with implications for therapy., (© The Author(s) 2021. Published by Oxford University Press on behalf of Nucleic Acids Research.)

Inhibition of the HER2/ERBB2 receptor is a keystone to treating HER2-positive malignancies, particularly breast cancer, but a significant fraction of HER2-positive (HER2+) breast cancers recur or fail to respond. Anti-HER2 monoclonal antibodies, like trastuzumab or pertuzumab, and ATP active site inhibitors like lapatinib, commonly lack durability because of adaptive changes in the tumor leading to resistance. HER2+ cell line responses to inhibition with lapatinib were analyzed by RNAseq and ChIPseq to characterize transcriptional and epigenetic changes. Motif analysis of lapatinib-responsive genomic regions implicated the pioneer transcription factor FOXA1 as a mediator of adaptive responses. Lapatinib in combination with FOXA1 depletion led to dysregulation of enhancers, impaired adaptive upregulation of HER3, and decreased proliferation. HER2-directed therapy using clinically relevant drugs (trastuzumab with or without lapatinib or pertuzumab) in a 7-day clinical trial designed to examine early pharmacodynamic response to antibody-based anti-HER2 therapy showed reduced FOXA1 expression was coincident with decreased HER2 and HER3 levels, decreased proliferation gene signatures, and increased immune gene signatures. This highlights the importance of the immune response to anti-HER2 antibodies and suggests that inhibiting FOXA1-mediated adaptive responses in combination with HER2 targeting is a potential therapeutic strategy.

We evaluated the joint associations between a new 313-variant PRS (PRS313) and questionnaire-based breast cancer risk factors for women of European ancestry, using 72 284 cases and 80 354 controls from the Breast Cancer Association Consortium. Interactions were evaluated using standard logistic regression and a newly developed case-only method for breast cancer risk overall and by estrogen receptor status. After accounting for multiple testing, we did not find evidence that per-standard deviation PRS313 odds ratio differed across strata defined by individual risk factors. Goodness-of-fit tests did not reject the assumption of a multiplicative model between PRS313 and each risk factor. Variation in projected absolute lifetime risk of breast cancer associated with classical risk factors was greater for women with higher genetic risk (PRS313 and family history) and, on average, 17.5% higher in the highest vs lowest deciles of genetic risk. These findings have implications for risk prevention for women at increased risk of breast cancer., (© The Author(s) 2020. Published by Oxford University Press.)

The Carolina Breast Cancer Study (CBCS) phases I-II was a case-control study of biological and social risk factors for invasive breast cancer that enrolled cases and controls between 1993 and 1999. Case selection was population-based and stratified by ancestry and age at diagnosis. Controls were matched to cases by age, self-identified race, and neighborhood of residence. Sequencing genomic DNA from 1370 cases and 1635 controls yielded odds ratios (with 95% confidence limits) for breast cancer of all subtypes of 26.7 (3.59, 189.1) for BRCA1, 8.8 (3.44, 22.48) for BRCA2, and 9.0 (2.06, 39.60) for PALB2; and for triple-negative breast cancer (TNBC) of 55.0 (7.01, 431.4) for BRCA1, 12.1 (4.18, 35.12) for BRCA2, and 10.8 (1.97, 59.11) for PALB2. Overall, 5.6% of patients carried a pathogenic variant in BRCA1, BRCA2, PALB2, or TP53, the four most highly penetrant breast cancer genes. Analysis of cases by tumor subtype revealed the expected association of TNBC versus other tumor subtypes with BRCA1, and suggested a significant association between TNBC versus other tumor subtypes with BRCA2 or PALB2 among African-American (AA) patients [2.95 (1.18, 7.37)], but not among European-American (EA) patients [0.62 (0.18, 2.09)]. AA patients with pathogenic variants in BRCA2 or PALB2 were 11 times more likely to be diagnosed with TNBC versus another tumor subtype than were EA patients with pathogenic variants in either of these genes (P = 0.001). If this pattern is confirmed in other comparisons of similarly ascertained AA and EA breast cancer patients, it could in part explain the higher prevalence of TNBC among AA breast cancer patients.

Background: Black women have higher hormone receptor positive (HR+) breast cancer mortality than White women. Early recurrence rates differ by race, but little is known about genomic predictors of early recurrence among HR+ women., Methods: Using data from the Carolina Breast Cancer Study (phase III, 2008-2013), we estimated associations between race and recurrence among nonmetastatic HR+/HER2-negative tumors, overall and by PAM50 Risk of Recurrence score, PAM50 intrinsic subtype, and tumor grade using survival curves and Cox models standardized for age and stage. Relative frequency differences (RFD) were estimated using multivariable linear regression. To assess intervention opportunities, we evaluated treatment patterns by race among patients with high-risk disease., Results: Black women had higher recurrence risk relative to White women (crude hazard ratio = 1.81, 95% confidence interval [CI] = 1.34 to 2.46), which remained elevated after standardizing for clinical covariates (hazard ratio = 1.42, 95% CI = 1.05 to 1.93). Racial disparities were most pronounced among those with high PAM50 Risk of Recurrence score (5-year standardized recurrence risk = 18.9%, 95% CI = 8.6% to 29.1% in Black women vs 12.5%, 95% CI = 2.0% to 23.0% in White women) and high grade (5-year standardized recurrence risk = 16.6%, 95% CI = 11.7% to 21.5% in Black women vs 12.0%, 95% CI = 7.3% to 16.7% in White women). However, Black women with high-grade tumors were statistically significantly less likely to initiate endocrine therapy (RFD = -8.3%, 95% CI = -15.9% to -0.6%) and experienced treatment delay more often than White women (RFD = +9.0%, 95% CI = 0.3% to 17.8%)., Conclusions: Differences in recurrence by race appear greatest among women with aggressive tumors and may be influenced by treatment differences. Efforts to identify causes of variation in cancer treatment are critical to reducing outcome disparities., (© The Author(s) 2020. Published by Oxford University Press.)

Purpose of Review: To review research on breast cancer mortality disparities, emphasizing research conducted in the Carolina Breast Cancer Study, with a focus on challenges and opportunities for integration of tumor biology and access characteristics across the cancer care continuum., Recent Findings: Black women experience higher mortality following breast cancer diagnosis, despite lower incidence compared to white women. Biological factors, such as stage at diagnosis and breast cancer subtypes, play a role in these disparities. Simultaneously, social, behavioral, environmental, and access to care factors are important. However, integrated studies of biology and access are challenging and it is uncommon to have both data types available in the same study population. The central emphasis of Phase 3 of the Carolina Breast Cancer Study, initiated in 2008, was to collect rich data on biology (including germline and tumor genomics and pathology) and health care access in a diverse study population, with the long term goal of defining intervention opportunities to reduce disparities across the cancer care continuum., Summary: Early and ongoing research from CBCS has identified important interactions between biology and access, leading to opportunities to build greater equity. However, sample size, population-specific relationships among variables, and complexities of treatment paths along the care continuum pose important research challenges. Interdisciplinary teams, including experts in novel data integration and causal inference, are needed to address gaps in our understanding of breast cancer disparities., Competing Interests: Conflict of Interest Marc A. Emerson, Katherine E. Reeder-Hayes, Heather J. Tipaldos, Mary E. Bell, Marina R. Sweeney, Lisa A. Carey, H. Shelton Earp, Andrew F. Olshan and Melissa A. Troester declare no conflicts of interest relevant to this manuscript.

Purpose: Understanding breast cancer mortality disparities by race and age is complex due to disease heterogeneity, comorbid disease, and the range of factors influencing access to care. It is important to understand how these factors group together within patients., Methods: We compared socioeconomic status (SES) and comorbidity factors in the Carolina Breast Cancer Study Phase 3 (CBCS3, 2008-2013) to those for North Carolina using the 2010 Behavioral Risk Factor Surveillance Study. In addition, we used latent class analysis of CBCS3 data to identify covariate patterns by SES/comorbidities, barriers to care, and tumor characteristics and examined their associations with race and age using multinomial logistic regression., Results: Major SES and comorbidity patterns in CBCS3 participants were generally similar to patterns in the state. Latent classes were identified for SES/comorbidities, barriers to care, and tumor characteristics that varied by race and age. Compared to white women, black women had lower SES (odds ratio (OR)  6.3, 95% confidence interval (CI) 5.2, 7.8), more barriers to care (OR 5.6, 95% CI 3.9, 8.1) and several aggregated tumor aggressiveness features. Compared to older women, younger women had higher SES (OR 0.5, 95% CI 0.4, 0.6), more barriers to care (OR 2.1, 95% CI 1.6, 2.9) and aggregated tumor aggressiveness features., Conclusions: CBCS3 is representative of North Carolina on comparable factors. Patterns of access to care and tumor characteristics are intertwined with race and age, suggesting that interventions to address disparities will need to target both access and biology.

Purpose: Female breast cancer demonstrates bimodal age frequency distribution patterns at diagnosis, interpretable as two main etiologic subtypes or groupings of tumors with shared risk factors. While RNA-based methods including PAM50 have identified well-established clinical subtypes, age distribution patterns at diagnosis as a proxy for etiologic subtype are not established for molecular and genomic tumor classifications., Methods: We evaluated smoothed age frequency distributions at diagnosis for Carolina Breast Cancer Study cases within immunohistochemistry-based and RNA-based expression categories. Akaike information criterion (AIC) values compared the fit of single density versus two-component mixture models. Two-component mixture models estimated the proportion of early-onset and late-onset categories by immunohistochemistry-based ER (n = 2860), and by RNA-based ESR1 and PAM50 subtype (n = 1965). PAM50 findings were validated using pooled publicly available data (n = 8103)., Results: Breast cancers were best characterized by bimodal age distribution at diagnosis with incidence peaks near 45 and 65 years, regardless of molecular characteristics. However, proportional composition of early-onset and late-onset age distributions varied by molecular and genomic characteristics. Higher ER-protein and ESR1-RNA categories showed a greater proportion of late age-at-onset. Similarly, PAM50 subtypes showed a shifting age-at-onset distribution, with most pronounced early-onset and late-onset peaks found in Basal-like and Luminal A, respectively., Conclusions: Bimodal age distribution at diagnosis was detected in the Carolina Breast Cancer Study, similar to national cancer registry data. Our data support two fundamental age-defined etiologic breast cancer subtypes that persist across molecular and genomic characteristics. Better criteria to distinguish etiologic subtypes could improve understanding of breast cancer etiology and contribute to prevention efforts.

Aberrant activation of the androgen receptor (AR) may play a critical role in castration resistant prostate cancer. After ligand binding, AR is recruited to the androgen responsive element (ARE) sequences on the DNA where AR interaction with coactivators and corepressors modulates transcription. We demonstrated that phosphorylation of AR at Tyr-267 by Ack1/TNK2 tyrosine kinase results in nuclear translocation, DNA binding, and androgen-dependent gene transcription in a low androgen environment. In order to dissect downstream mechanisms, we searched for proteins whose interaction with AR was regulated by Ack1. SLIRP (SRA stem-loop interacting RNA binding protein) was identified as a candidate protein. Interaction between AR and SLIRP was disrupted by Ack1 kinase activity as well as androgen or heregulin treatment. The noncoding RNA, SRA, was required for AR-SLIRP interaction. SLIRP was bound to ARE's of AR target genes in the absence of androgen. Treatment with androgen or heregulin led to dissociation of SLIRP from the ARE. Whole transcriptome analysis of SLIRP knockdown in androgen responsive LNCaP cells showed that SLIRP affects a significant subset of androgen-regulated genes. Our data suggest that Ack1 kinase and androgen regulate interaction between AR and SLIRP and that SLIRP functions as a coregulator of AR with properties of a corepressor in a context-dependent manner.

As a key homeostasis regulator in mammals, the MERTK receptor tyrosine kinase is crucial for efferocytosis, a process that requires remodeling of the cell membrane and adjacent actin cytoskeleton. Membrane and cytoskeletal reorganization also occur in endothelial cells during inflammation, particularly during neutrophil transendothelial migration (TEM) and during changes in permeability. However, MERTK's function in endothelial cells remains unclear. This study evaluated the contribution of endothelial MERTK to neutrophil TEM and endothelial barrier function. In vitro experiments using primary human pulmonary microvascular endothelial cells found that neutrophil TEM across the endothelial monolayers was enhanced when MERTK expression in endothelial cells was reduced by siRNA knockdown. Examination of endothelial barrier function revealed increased passage of dextran across the MERTK-depleted monolayers, suggesting that MERTK helps maintain endothelial barrier function. MERTK knockdown also altered adherens junction structure, decreased junction protein levels, and reduced basal Rac1 activity in endothelial cells, providing potential mechanisms of how MERTK regulates endothelial barrier function. To study MERTK's function in vivo, inflammation in the lungs of global Mertk-/- mice was examined during acute pneumonia. In response to P. aeruginosa, more neutrophils were recruited to the lungs of Mertk-/- than wildtype mice. Vascular leakage of Evans blue dye into the lung tissue was also greater in Mertk-/- mice. To analyze endothelial MERTK's involvement in these processes, we generated inducible endothelial cell-specific (iEC) Mertk-/- mice. When similarly challenged with P. aeruginosa, iEC Mertk-/- mice demonstrated no difference in neutrophil TEM into the inflamed lungs or in vascular permeability compared to control mice. These results suggest that deletion of MERTK in human pulmonary microvascular endothelial cells in vitro and in all cells in vivo aggravates the inflammatory response. However, selective MERTK deletion in endothelial cells in vivo failed to replicate this response., Competing Interests: H. Shelton Earp is a co-founder of Meryx, a UNC startup that is developing MERTK small molecule kinase inhibitors for cancer. None of these agents were used in the present research. This does not alter our adherence to PLOS ONE policies on sharing data and materials.

Controlling which particular members of a large protein family are targeted by a drug is key to achieving a desired therapeutic response. In this study, we report a rational data-driven strategy for achieving restricted polypharmacology in the design of antitumor agents selectively targeting the TYRO3, AXL, and MERTK (TAM) family tyrosine kinases. Our computational approach, based on the concept of fragments in structural environments (FRASE), distills relevant chemical information from structural and chemogenomic databases to assemble a three-dimensional inhibitor structure directly in the protein pocket. Target engagement by the inhibitors designed led to disruption of oncogenic phenotypes as demonstrated in enzymatic assays and in a panel of cancer cell lines, including acute lymphoblastic and myeloid leukemia (ALL/AML) and nonsmall cell lung cancer (NSCLC). Structural rationale underlying the approach was corroborated by X-ray crystallography. The lead compound demonstrated potent target inhibition in a pharmacodynamic study in leukemic mice.

Myeloid cell receptor tyrosine kinases TYRO3, AXL, and MERTK and their ligands, GAS6 and PROTEIN S, physiologically suppress innate immune responses, including in the tumor microenvironment. Here, we showed that myeloid-derived suppressor cells (MDSC) dramatically upregulated TYRO3, AXL, and MERTK and their ligands [monocytic MDSCs (M-MDSC)>20-fold, polymorphonuclear MDSCs (PMN-MDSC)>15-fold] in tumor-bearing mice. MDSCs from tumor-bearing Mertk -/- , Axl -/- , and Tyro3 -/- mice exhibited diminished suppressive enzymatic capabilities, displayed deficits in T-cell suppression, and migrated poorly to tumor-draining lymph nodes. In coimplantation experiments using TYRO3 -/- , AXL -/- , and MERTK -/- MDSCs, we showed the absence of these RTKs reversed the protumorigenic properties of MDSCs in vivo Consistent with these findings, in vivo pharmacologic TYRO3, AXL, and MERTK inhibition diminished MDSC suppressive capability, slowed tumor growth, increased CD8 + T-cell infiltration, and augmented anti-PD-1 checkpoint inhibitor immunotherapy. Mechanistically, MERTK regulated MDSC suppression and differentiation in part through regulation of STAT3 serine phosphorylation and nuclear localization. Analysis of metastatic melanoma patients demonstrated an enrichment of circulating MERTK + and TYRO3 + M-MDSCs, PMN-MDSCs, and early-stage MDSCs (e-MDSC) relative to these MDSC populations in healthy controls. These studies demonstrated that TYRO3, AXL, and MERTK control MDSC functionality and serve as promising pharmacologic targets for regulating MDSC-mediated immune suppression in cancer patients., (©2019 American Association for Cancer Research.)