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Activating point mutations in the K-Ras oncogene are among the most common genetic alterations in pancreatic cancer, occurring early in the progression of the disease. However, the function of mutant K-Ras activity in tumor angiogenesis remains poorly understood. Using human pancreatic duct epithelial (HPDE) and K-Ras4BG12V–transformed HPDE (HPDE-KRas) cells, we show that activated K-Ras significantly enhanced the production of angiogenic factors including CXC chemokines and vascular endothelial growth factor (VEGF). Western blot analysis revealed that K-Ras activation promoted the phosphorylation of Raf/mitogen-activated protein kinase kinase-1/2 (MEK1/2) and expression of c-Jun. MEK1/2 inhibitors, U0126 and PD98059, significantly inhibited the secretion of both CXC chemokines and VEGF, whereas the c-Jun NH2-terminal kinase inhibitor SP600125 abrogated only CXC chemokine production. To further elucidate the biological functions of oncogenic K-Ras in promoting angiogenesis, we did in vitro invasion and tube formation assays using human umbilical vein endothelial cells (HUVEC). HUVEC cocultured with HPDE-KRas showed significantly enhanced invasiveness and tube formation as compared with either control (without coculture) or coculture with HPDE. Moreover, SB225002 (a CXCR2 inhibitor) and 2C3 (an anti-VEGF monoclonal antibody) either alone or in a cooperative manner significantly reduced the degree of both Ras-dependent HUVEC invasiveness and tube formation. Similar results were obtained using another pair of immortalized human pancreatic duct–derived cells, E6/E7/st and its oncogenic K-Ras variant, E6/E7/Ras/st. Taken together, our results suggest that angiogenesis is initiated by paracrine epithelial secretion of CXC chemokines and VEGF downstream of activated oncogenic K-Ras, and that this vascular maturation is in part dependent on MEK1/2 and c-Jun signaling. (Mol Cancer Res 2009;7(6):799–808)

Supplementary Data from K-Ras Promotes Angiogenesis Mediated by Immortalized Human Pancreatic Epithelial Cells through Mitogen-Activated Protein Kinase Signaling Pathways

Purpose: We investigated the contribution of Sonic hedgehog (SHH) to pancreatic cancer progression.Experimental Design: We expressed SHH in a transformed primary ductal-derived epithelial cell line from the human pancreas, transformed hTert-HPNE (T-HPNE), and evaluated the effects on tumor growth. We also directly inhibited the activity of SHH in vivo by administering a blocking antibody to mice challenged orthotopically with the Capan-2 pancreatic cancer cell line, which is known to express SHH and form moderately differentiated tumors in nude mice.Results: Our data provide evidence that expression of SHH influences tumor growth by contributing to the formation of desmoplasia in pancreatic cancer. We further show that SHH affects the differentiation and motility of human pancreatic stellate cells and fibroblasts.Conclusions: These data suggest that SHH contributes to the formation of desmoplasia in pancreatic cancer, an important component of the tumor microenvironment.

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Effect of PR55α expression on clonogenicity of pancreatic cancer cells

Legends for Supplementary Figures S1-S4

The protein phosphatase 2 (PP2A) holoenzyme consists of a catalytic subunit, a scaffold subunit, and a regulatory subunit. Based on loss-of-function analysis using PP2A catalytic inhibitors or inhibition via tumor viral antigens, limited studies suggest that PP2A is a putative tumor suppressor. However, PP2A has also been shown to facilitate the activation of oncogenic signaling pathways when associated with specific regulatory subunits. In this study, we investigated the possible oncogenic role of PP2A in pancreatic cancer. We found a striking increase in the expression of PR55α (PPP2R2A), a PP2A regulatory subunit, in pancreatic cancer cells compared with normal pancreatic epithelial cells. Consistently, PR55α expression was markedly elevated in pancreatic ductal adenocarcinoma tissues compared with adjacent normal pancreatic tissues (P < 0.0001) and correlated with poor survival of pancreatic cancer patients (P < 0.0003). RNAi-mediated depletion of PR55α in pancreatic cancer cell lines resulted in diminished phosphorylation of both AKT and ERK1/2 (MAPK3/1) and decreased protein levels of β-catenin (CTNNB1). Accordingly, pancreatic cancer cells with reduced PR55α expression exhibited significantly impaired properties of transformation, including attenuated cell growth, clonogenicity, mobility, and anchorage-independent growth. Moreover, orthotopic implantation of PR55α-depleted pancreatic cancer cells into nude mice resulted in markedly reduced tumorigenicity (P < 0.001) and distant metastases. Together, these results suggest that PR55α promotes pancreatic cancer development by sustaining hyperactivity of multiple oncogenic signaling pathways, including AKT, ERK, and Wnt. These studies also provide a basis for exploring PR55α as a diagnostic or therapeutic target in pancreatic cancer. Cancer Res; 76(8); 2243–53. ©2016 AACR.

Clinical characteristics of the PDAC specimens used for the study of PR55α expression by IHC

Description of additional details of materials and methodologies used in this study

We have previously reported an important role of PR55α, a regulatory subunit of PP2A Ser/Thr phosphatase, in the support of critical oncogenic pathways required for oncogenesis and the malignant phenotype of pancreatic cancer. The studies in this report reveal a novel mechanism by which the p53 tumor suppressor inhibits the protein-stability of PR55α via FBXL20, a p53-target gene that serves as a substrate recognition component of the SCF (Skp1_Cullin1_F-box) E3 ubiquitin ligase complex that promotes proteasomal degradation of its targeted proteins. Our studies show that inactivation of p53 by siRNA-knockdown, gene-deletion, HPV-E6-mediated degradation, or expression of the loss-of-function mutant p53R175H results in increased PR55α protein stability, which is accompanied by reduced protein expression of FBXL20 and decreased ubiquitination of PR55α. Subsequent studies demonstrate that knockdown of FBXL20 by siRNA mimics p53 deficiency, reducing PR55α ubiquitination and increasing PR55α protein stability. Functional tests indicate that ectopic p53R175H or PR55α expression results in an increase of c-Myc protein stability with concomitant dephosphorylation of c-Myc-T58, which is a PR55α substrate, whose phosphorylation otherwise promotes c-Myc degradation. A significant increase in anchorage-independent proliferation is also observed in normal human pancreatic cells expressing p53R175H or, to a greater extent, overexpressing PR55α. Consistent with the common loss of p53 function in pancreatic cancer, FBXL20 mRNA expression is significantly lower in pancreatic cancer tissues compared to pancreatic normal tissues and low FBXL20 levels correlate with poor patient survival. Collectively, these studies delineate a novel mechanism by which the p53/FBXL20 axis negatively regulates PR55α protein stability.

High-risk human papillomaviruses (HPV), exemplified by HPV16/18, are causally linked to human cancers of the anogenital tract, skin, and upper aerodigestive tract. Previously, we identified Ecdysoneless (ECD) protein, the human homolog of the Drosophila ecdysoneless gene, as a novel HPV16 E6–interacting protein. Here, we show that ECD, through its C-terminal region, selectively binds to high-risk but not to low-risk HPV E6 proteins. We demonstrate that ECD is overexpressed in cervical and head and neck squamous cell carcinoma (HNSCC) cell lines as well as in tumor tissues. Using The Cancer Genome Atlas dataset, we show that ECD mRNA overexpression predicts shorter survival in patients with cervical and HNSCC. We demonstrate that ECD knockdown in cervical cancer cell lines led to impaired oncogenic behavior, and ECD co-overexpression with E7 immortalized primary human keratinocytes. RNA-sequencing analyses of SiHa cells upon ECD knockdown showed to aberrations in E6/E7 RNA splicing, as well as RNA splicing of several HPV oncogenesis–linked cellular genes, including splicing of components of mRNA splicing machinery itself. Taken together, our results support a novel role of ECD in viral and cellular mRNA splicing to support HPV-driven oncogenesis. Implications: This study links ECD overexpression to poor prognosis and shorter survival in HNSCC and cervical cancers and identifies a critical role of ECD in cervical oncogenesis through regulation of viral and cellular mRNA splicing.

Inhibitor of nuclear factor kappa-B kinase subunit beta (IKKβ) is a key regulator of the cannonical NF-κB pathway. IKKβ has been validated as a drug target for pathological conditions, which include chronic inflammatory diseases and cancer. Pharmacological studies revealed that chronic administration of ATP-competitive IKKβ inhibitors resulted in unexpected toxicity. We previously reported the discovery of 13-197 as a non-toxic IKKβ inhibitor that reduced tumor growth. Here, we show that 13-197 inhibits IKKβ in a ATP non-competitive manner and an allosteric pocket at the interface of the kinase and ubiquitin like domains was identified as the potential binding site.

The G-quadruplex (GQ) is a well-studied non-canonical DNA structure formed by G-rich sequences found at telomeres and gene promoters. Biological studies suggest that GQs may play roles in regulating gene expression, DNA replication, and DNA repair. Small molecule ligands were shown to alter GQ structure and stability and thereby serve as novel therapies, particularly against cancer. In this work, we investigate the interaction of a G-rich sequence, 5’-GGGTTGGGTTGGGTTGGG-3’ (T1), with a water-soluble porphyrin, N-methyl mesoporphyrin IX (NMM) via biophysical and X-ray crystallographic studies. UV-vis and fluorescence titrations, as well as a Job plot, revealed a 1:1 binding stoichiometry with an impressively tight binding constant of 30–50 μM-1 and ΔG298 of -10.3 kcal/mol. Eight extended variants of T1 (named T2 –T9) were fully characterized and T7 was identified as a suitable candidate for crystallographic studies. We solved the crystal structures of the T1- and T7-NMM complexes at 2.39 and 2.34 Å resolution, respectively. Both complexes form a 5’-5’ dimer of parallel GQs capped by NMM at the 3’ G-quartet, supporting the 1:1 binding stoichiometry. Our work provides invaluable details about GQ-ligand binding interactions and informs the design of novel anticancer drugs that selectively recognize specific GQs and modulate their stability for therapeutic purposes.

PP2A holoenzymes are the majority of Ser/Thr phosphatases in human cells and each PP2A complex contains one scaffold subunit, one catalytic subunit, and one regulatory subunit. PP2A regulatory subunits, existing in four sub-families encoded by 15 genes, determine the substrate specificities and intracellular localizations of PP2A. We previously reported an essential role for PR55α, a PP2A regulatory subunit, in the support of malignant potential of pancreatic cancer cells, which includes promoting YAP-activation that supports anchorage-independent growth and metastasis. Furthermore, our data showed that PR55α level is elevated in pancreatic cancer relative to normal tissues and high PR55α levels correlate with poor patient survival. The studies in this report reveal a novel mechanism by which the p53 tumor suppressor negatively regulates PR55α protein stability. The results show that p53 inactivation by siRNA-knockdown, gene-deletion, HPV-E6 promoted degradation, or p53R175H mutant expression all results in the increase of PR55α expression. Subsequent studies demonstrate that this p53 function is mediated through its target gene FBXL20, a substrate recognition component of the SCF (Skp_Cullin_F-box) ubiquitin ligase complex that facilitates proteasomal degradation. As a result, the expression of mutant p53R175H in human pancreatic ductal cells mimics the PR55α effect, increasing c-Myc protein stability, and promoting anchorage-independent proliferation. Additionally, FBXL20 mRNA levels are significantly reduced in pancreatic cancers relative to normal control, and low FBXL20 levels correlate with poor patient survival, both of which inversely resemble the pathological effects of PR55α in pancreatic cancer. Collectively, these results define a novel p53 function in the suppression of PR55α expression. Citation Format: Ying Yan, Lepakshe Madduri, Nichole Brandquist, Chitra Palanivel, Sumin Zhou, Charles Enke, Michel Ouellette. p53/FBXL20 axis negatively regulates the protein stability of PR55α, a PP2A regulatory subunit [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1986.

Imetelstat (GRN163L) is a potent and selective inhibitor of telomerase. We have previously reported that GRN163L could shorten telomeres and limit the lifespan of CD18/HPAF and CAPAN1 pancreatic cancer cells. Here, we examined the effects of GRN163L on two other pancreatic cancer cell lines: AsPC1 and L3.6pl. In both lines, chronic exposure to GRN163L led to an initial shortening of telomeres followed by a stabilization of extremely short telomeres. In AsPC1 cells, telomere attrition eventually led to the induction of crisis and the loss of the treated population. In L3.6pl cells, crisis was transient and followed by the emergence of GRN163L-resistant cells, which could grow at increasing concentrations of GRN163L. The Shelterin complex is a telomere-associated complex that limits the access of telomerase to telomeres. The telomerase inhibitory function of this complex can be enhanced by drugs that block the poly(ADP-ribosyl)ation of its TRF1 and/or TRF2 subunits. Combined treatment of the GRN163L-resistant L3.6pl cells with GRN163L and 3-aminobenzamide (3AB), a general inhibitor of poly(ADP-ribose) polymerases, led to additional telomere shortening and limited the lifespan of the resistant cells. Results from this work suggest that inhibitors of telomerase and poly(ADP-ribose) polymerases can cooperate to limit the lifespan of pancreatic cancer cells.

Aberrant activation of Rho GTPase Rac1 has been observed in various tumor types, including pancreatic cancer. Rac1 activates multiple signaling pathways that lead to uncontrolled proliferation, invasion and metastasis. Thus, inhibition of Rac1 activity is a viable therapeutic strategy for proliferative disorders such as cancer. Here we identified small molecule inhibitors that target the nucleotide-binding site of Rac1 through in silico screening. Follow up in vitro studies demonstrated that two compounds blocked active Rac1 from binding to its effector PAK1. Fluorescence polarization studies indicate that these compounds target the nucleotide-binding site of Rac1. In cells, both compounds blocked Rac1 binding to its effector PAK1 following EGF-induced Rac1 activation in a dose-dependent manner, while showing no inhibition of the closely related Cdc42 and RhoA activity. Furthermore, functional studies indicate that both compounds reduced cell proliferation and migration in a dose-dependent manner in multiple pancreatic cancer cell lines. Additionally, the two compounds suppressed the clonogenic survival of pancreatic cancer cells, while they had no effect on the survival of normal pancreatic ductal cells. These compounds do not share the core structure of the known Rac1 inhibitors and could serve as additional lead compounds to target pancreatic cancers with high Rac1 activity.

PP2A holoenzyme complexes are responsible for the majority of Ser/Thr phosphatase activities in human cells. Each PP2A consists of a catalytic subunit (C), a scaffold subunit (A), and a regulatory subunit (B). While the A and C subunits each exists only in two highly conserved isoforms, a large number of B subunits share no homology, which determines PP2A substrate specificity and cellular localization. It is anticipated that different PP2A holoenzymes play distinct roles in cellular signaling networks, whereas PP2A has only generally been defined as a putative tumor suppressor, which is mostly based on the loss-of-function studies using pharmacological or biological inhibitors for the highly conserved A or C subunit of PP2A. Recent studies of specific pathways indicate that some PP2A complexes also possess tumor-promoting functions. We have previously reported an essential role of PR55α, a PP2A regulatory subunit, in the support of oncogenic phenotypes, including in vivo tumorigenicity/metastasis of pancreatic cancer cells. In this report, we have elucidated a novel role of PR55α-regulated PP2A in the activation of YAP oncoprotein, whose function is required for anchorage-independent growth during oncogenesis of solid tumors. Our data show two lines of YAP regulation by PR55α: (1) PR55α inhibits the MOB1-triggered autoactivation of LATS1/2 kinases, the core member of the Hippo pathway that inhibits YAP by inducing its proteasomal degradation and cytoplasmic retention and (2) PR55α directly interacts with and regulates YAP itself. Accordingly, PR55α is essential for YAP-promoted gene transcriptions, as well as for anchorage-independent growth, in which YAP plays a key role. In summary, current findings demonstrate a novel YAP activation mechanism based on the PR55α-regulated PP2A phosphatase.

Pancreatic cancer remains a highly lethal malignancy. We have recently shown that simultaneous expression of Kras and mutant Tp53(R175H) promotes invasive ductal adenocarcinoma from pancreatic ductal cells. We hypothesized specific mutations in TP53 have divergent mechanisms of transforming ductal cells. In order to understand the role of mutant TP53 in transforming pancreatic ductal cells, we used a lentiviral system to express mutant TP53(R175H) and TP53(R273H), two of the most frequently mutated TP53 alleles in pancreatic cancer patients, in immortalized, but not transformed, pancreatic ductal epithelial cells carrying a KRAS mutation (HPNE:KRAS(G12D)). Mutant TP53 expression enhanced colony formation and an RPPA assay results revealed TP53(R175H) uniquely induced HSP70 expression in HPNE:KRAS(G12D) cells. In the context of TP53(R175H) expression; we observed nuclear localization of HSP70. We performed immunoprecipitation experiments to show mutant p53(R175H) binds to HSP70. We also provide evidence mutant p53(R175H) is important for HSP70 stability and, more importantly, HSP70 is required for mutant p53 stability. These data are critical in the context of events leading to cellular transformation in the pancreas.

// Abhilasha Purohit 1 , Michelle Varney 1 , Satyanarayana Rachagani 2 , Michel M. Ouellette 3 , Surinder K. Batra 1, 2, 3 , Rakesh K. Singh 1 1 Department of Pathology and Microbiology, 985900 Nebraska Medical Center, Omaha, NE, USA 2 Department of Biochemistry and Molecular Biology, 985870 Nebraska Medical Center, Omaha, NE, USA 3 Eppley Institute, 985950 Nebraska Medical Center, Omaha, NE, USA Correspondence to: Rakesh K. Singh, e-mail: rsingh@unmc.edu Keywords: KRAS (G12D) , PDAC, CXCR2, autocrine growth, ERK Received: August 05, 2015 Accepted: November 25, 2015 Published: January 13, 2016 ABSTRACT Pharmacological inhibition of RAS , the master regulator of pancreatic ductal adenocarcinoma (PDAC), continues to be a challenge. Mutations in various isoforms of RAS gene, including KRAS are known to upregulate CXC chemokines; however, their precise role in KRAS-driven pancreatic cancer remains unclear. In this report, we reveal a previously unidentified tumor cell-autonomous role of KRAS (G12D) -induced CXCR2 signaling in mediating growth of neoplastic PDAC cells. Progressively increasing expression of mCXCR2 and its ligands was detected in the malignant ductal cells of Pdx1-cre;LSL- Kras (G12D) mice. Knocking-down CXCR2 in KRAS (G12D) -bearing human pancreatic duct-derived cells demonstrated a significant decrease in the in vitro and in vivo tumor cell proliferation. Furthermore, CXCR2 antagonists showed selective growth inhibition of KRAS (G12D) -bearing cells in vitro. Intriguingly, both genetic and pharmacological inhibition of CXCR2 signaling in KRAS (G12D) -bearing pancreatic ductal cells reduced the levels of KRAS protein, strongly implying the presence of a KRAS-CXCR2 feed-forward loop. Together, these data demonstrate the role of CXCR2 signaling in KRAS (G12D) -induced growth transformation and progression in PDAC.

// Arokia Priyanka Vaz 1 , Shonali Deb 1 , Satyanarayana Rachagani 1 , Parama Dey 1 , Sakthivel Muniyan 1 , Imayavaramban Lakshmanan 1 , Saswati Karmakar 1 , Lynette Smith 2 , Sonny Johansson 3 , Subodh Lele 3 , Michel Ouellette 1, 4 , Moorthy P. Ponnusamy 1, 5 , Surinder K. Batra 1, 3, 5 1 Department of Biochemistry and Molecular Biology, University of Nebraska Medical Center, Omaha, NE, USA 2 Department of Biostatistics, University of Nebraska Medical Center, Omaha, NE, USA 3 Department of Pathology and Microbiology, University of Nebraska Medical Center, Omaha, NE, USA 4 Department of Internal Medicine, Division of Gastroenterology and Hepatology, University of Nebraska Medical Center, Omaha, NE, USA 5 Eppley Institute for Research in Cancer and Allied Disease, University of Nebraska Medical Center, Omaha, NE, USA Correspondence to: Surinder K. Batra, e-mail: sbatra@unmc.edu Moorthy P. Ponnusamy, e-mail: mpalanim@unmc.edu Keywords: PD2, CSC, c-Myc, PDAC Received: August 12, 2015 Accepted: November 16, 2015 Published: December 12, 2015 ABSTRACT Pancreatic differentiation 2 (PD2), an important subunit of the human PAF complex, was identified after differential screening analysis of 19q13 amplicon, and its overexpression induces oncogenic transformation of NIH3T3 cells, hence raising the possibility of a role for PD2 in tumorigenesis and metastasis. To test this hypothesis, we analyzed here the functional role and clinical significance of PD2 in pancreatic ductal adenocarcinoma (PDAC) and its pathogenesis. Using immunohistochemical analysis, we found that PD2 is detected in the acini but not in the ducts in the normal pancreas. In human PDAC specimens, PD2 was instead primarily detected in the ducts (12/48 patients 25%; p -value < 0.0001), thereby showing that PDAC correlates with increased ductal expression of PD2. Consistently, PD2 expression was increased in telomerase-immortalized human pancreatic ductal cells (HPNE cells) modified to express the HPV16 E6 and E7 proteins, whose respective functions are to block p53 and RB. In addition, ectopic expression of PD2 in PDAC cells (Capan-1 and SW1990) led to increased clonogenicity and migration in vitro , and tumor growth and metastasis in vivo . Interestingly, PD2 overexpression also resulted in enrichment of cancer stem cells (CSCs) and upregulation of oncogenes such as c-Myc and cell cycle progression marker, cyclin D1. Taken together, our results support that PD2 is overexpressed in the ducts of PDAC tissues, and results in tumorigenesis and metastasis via upregulation of oncogenes such as c-Myc and cyclin hence D1 implicating PD2 upregulation in pancreatic oncogenesis with targeted therapeutic potential.

PP2A holoenzyme complexes constitute the majority of Ser/Thr phosphatase activities in human cells. Each PP2A consists of a catalytic subunit (C), a scaffold subunit (A), and a regulatory subunit (B). While the A and C subunits are highly conserved, a large number of B subunits share no homology, which determines PP2A substrate specificity and/or cellular localization. Although different PP2A complexes play distinct roles in cell signaling networks, PP2A has been defined only as a putative tumor suppressor, mostly based on loss-of-function studies using inhibitors (pharmacologic or biologic) for the highly conserved A or C subunit of PP2A. Many studies of specific pathways indicate that PP2A also possesses tumor-promoting function. We have reported an essential role of PR55α, a PP2A regulatory subunit, in supporting oncogenic phenotypes and in vivo tumorigenicity and metastasis of pancreatic cancer cells. In this study, we investigated a novel mechanism by which PR55α activates the YAP oncoprotein that plays an essential role in oncogenesis and metastasis of solid tumors including pancreatic cancer, resulting in its stabilization and nuclear retention. This mechanism involves PR55α’s inhibition of the MOB1-mediated LATS1/2 autoactivation, which otherwise would suppress YAP activation, and its direct activation of YAP itself. However, this mechanism does not involve the inhibition of upstream MST1/2 kinases and their subsequent T1079/T1041-phosphorylation of the LATS1/2 kinases. Furthermore, PR55α has the predominant effect on YAP activation, and the effect cannot be substituted by the depletion of either LATS1/2 or MOB1. Accordingly, PR55α is essential for YAP-promoted gene transcription, as well as for the anchorage-independent growth of cancer cells. In summary, current studies demonstrate a novel pancreatic cancer promoting mechanism through the PR55α-regulated PP2A. Citation Format: Ashley L. Hein, Nichole D. Brandquist, Caroline Y. Ouellette, Parthasarathy Seshacharyulu, Charles A. Enke, Michel M. Ouellette, Surinder K. Batra, Ying Yan. PR55α regulatory subunit of PP2A inhibits the MOB1/LATS cascade and activates YAP in pancreatic cancer cells [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr A44.

Radiation therapy is a staple treatment for pancreatic cancer. However, owing to the intrinsic radioresistance of pancreatic cancer cells, radiation therapy often fails to increase survival of pancreatic cancer patients. Radiation impedes cancer cells by inducing DNA damage, which can activate cell cycle checkpoints. Normal cells possess both a G1 and G2 checkpoint. However, cancer cells are often defective in G1 checkpoint due to mutations/alterations in key regulators of this checkpoint. Accordingly, our results show that normal pancreatic ductal cells respond to ionizing radiation (IR) with activation of both checkpoints whereas pancreatic cancer cells respond to IR with G2/M arrest only. Overexpression/hyperactivation of Rac1 GTPase is detected in the majority of pancreatic cancers. Rac1 plays important roles in survival and Ras-mediated transformation. Here, we show that Rac1 also plays a critical role in the response of pancreatic cancer cells to IR. Inhibition of Rac1 using specific inhibitor and dominant negative Rac1 mutant not only abrogates IR-induced G2 checkpoint activation, but also increases radiosensitivity of pancreatic cancer cells through induction of apoptosis. These results implicate Rac1 signaling in the survival of pancreatic cancer cells following IR, raising the possibility that this pathway contributes to the intrinsic radioresistance of pancreatic cancer.

Pancreatic cancer remains a daunting foe despite a vast number of accumulating molecular analyses regarding the mutation and expression status of a variety of genes. Indeed, most pancreatic cancer cases uniformly present with a mutation in the KRAS allele leading to enhanced RAS activation. Yet our understanding of the many epigenetic/environmental factors contributing to disease incidence and progression is waning. Epidemiologic data suggest that diet may be a key factor in pancreatic cancer development and potentially a means of chemoprevention at earlier stages. While diets high in &omega, 3 fatty acids are typically associated with tumor suppression, diets high in &omega, 6 fatty acids have been linked to increased tumor development. Thus, to better understand the contribution of these polyunsaturated fatty acids to pancreatic carcinogenesis, we modeled early stage disease by targeting mutant KRAS to the exocrine pancreas and administered diets rich in these fatty acids to assess tumor formation and altered cell-signaling pathways. We discovered that, consistent with previous reports, the &omega, 3-enriched diet led to reduced lesion penetrance via repression of proliferation associated with reduced phosphorylated AKT (pAKT), whereas the &omega, 6-enriched diet accelerated tumor formation. These data provide a plausible mechanism underlying previously observed effects of fatty acids and suggest that administration of &omega, 3 fatty acids can reduce the pro-survival, pro-growth functions of pAKT. Indeed, counseling subjects at risk to increase their intake of foods containing higher amounts of &omega, 3 fatty acids could aid in the prevention of pancreatic cancer.

The POT1 protein plays a critical role in telomere protection and telomerase regulation. POT1 binds single-stranded 5'-TTAGGGTTAG-3' and forms a dimer with the TPP1 protein. The dimer is recruited to telomeres, either directly or as part of the Shelterin complex. Human POT1 contains two Oligonucleotide/Oligosaccharide Binding (OB) fold domains, OB1 and OB2, which make physical contact with the DNA. OB1 recognizes 5'-TTAGGG whereas OB2 binds to the downstream TTAG-3'. Studies of POT1 proteins from other species have shown that some of these proteins are able to recognize a broader variety of DNA ligands than expected. To explore this possibility in humans, we have used SELEX to reexamine the sequence-specificity of the protein. Using human POT1 as a selection matrix, high-affinity DNA ligands were selected from a pool of randomized single-stranded oligonucleotides. After six successive rounds of selection, two classes of high-affinity targets were obtained. The first class was composed of oligonucleotides containing a cognate POT1 binding sites (5'-TTAGGGTTAG-3'). The second and more abundant class was made of molecules that carried a novel non-telomeric consensus: 5'-TNCANNAGKKKTTAGG-3' (where K = G/T and N = any base). Binding studies showed that these non-telomeric sites were made of an OB1-binding motif (TTAGG) and a non-telomeric motif (NT motif), with the two motifs recognized by distinct regions of the OB1 domain. POT1 interacted with these non-telomeric binding sites with high affinity and specificity, even when bound to its dimerization partner TPP1. This intrinsic ability of POT1 to recognize NT motifs raises the possibility that the protein may fulfill additional functions at certain non-telomeric locations of the genome, in perhaps gene transcription, replication, or repair.

Radiation therapy is a staple cancer treatment approach that has significantly improved local disease control and the overall survival of cancer patients. However, its efficacy is still limited by the development of radiation resistance and the presence of residual disease after therapy that leads to cancer recurrence. Radiation impedes cancer cell growth by inducing cytotoxicity, mainly caused by DNA damage. However, radiation can also simultaneously induce multiple pro-survival signaling pathways, such as those mediated by AKT, ERK and ATM/ATR, which can lead to suppression of apoptosis, induction of cell cycle arrest and/or initiation of DNA repair. These signaling pathways act conjointly to reduce the magnitude of radiation-induced cytotoxicity and promote the development of radioresistance in cancer cells. Thus, targeting these pro-survival pathways has great potential for the radiosensitization of cancer cells. In the present review, we summarize the current literature on how these radiation‑activated signaling pathways promote cancer cell survival.

Despite recent advances in radiotherapy, a majority of patients diagnosed with pancreatic cancer (PC) do not achieve objective responses due to the existence of intrinsic and acquired radioresistance. Identification of molecular mechanisms that compromise the efficacy of radiation therapy and targeting these pathways is paramount for improving radiation response in PC patients. In this review, we have summarized molecular mechanisms associated with the radio-resistant phenotype of PC. Briefly, we discuss the reversible and irreversible biological consequences of radiotherapy, such as DNA damage and DNA repair, mechanisms of cancer cell survival and radiation-induced apoptosis following radiotherapy. We further describe various small molecule inhibitors and molecular targeting agents currently being tested in preclinical and clinical studies as potential radiosensitizers for PC. Notably, we draw attention towards the confounding effects of cancer stem cells, immune system, and the tumor microenvironment in the context of PC radioresistance and radiosensitization. Finally, we discuss the need for examining selective radioprotectors in light of the emerging evidence on radiation toxicity to non-target tissue associated with PC radiotherapy.

The protein phosphatase 2 (PP2A) holoenzyme consists of a catalytic subunit, a scaffold subunit, and a regulatory subunit. Based on loss-of-function analysis using PP2A catalytic inhibitors or inhibition via tumor viral antigens, limited studies suggest that PP2A is a putative tumor suppressor. However, PP2A has also been shown to facilitate the activation of oncogenic signaling pathways when associated with specific regulatory subunits. In this study, we investigated the possible oncogenic role of PP2A in pancreatic cancer. We found a striking increase in the expression of PR55α (PPP2R2A), a PP2A regulatory subunit, in pancreatic cancer cells compared with normal pancreatic epithelial cells. Consistently, PR55α expression was markedly elevated in pancreatic ductal adenocarcinoma tissues compared with adjacent normal pancreatic tissues (P < 0.0001) and correlated with poor survival of pancreatic cancer patients (P < 0.0003). RNAi-mediated depletion of PR55α in pancreatic cancer cell lines resulted in diminished phosphorylation of both AKT and ERK1/2 (MAPK3/1) and decreased protein levels of β-catenin (CTNNB1). Accordingly, pancreatic cancer cells with reduced PR55α expression exhibited significantly impaired properties of transformation, including attenuated cell growth, clonogenicity, mobility, and anchorage-independent growth. Moreover, orthotopic implantation of PR55α-depleted pancreatic cancer cells into nude mice resulted in markedly reduced tumorigenicity (P < 0.001) and distant metastases. Together, these results suggest that PR55α promotes pancreatic cancer development by sustaining hyperactivity of multiple oncogenic signaling pathways, including AKT, ERK, and Wnt. These studies also provide a basis for exploring PR55α as a diagnostic or therapeutic target in pancreatic cancer. Cancer Res; 76(8); 2243–53. ©2016 AACR.

In some cellular systems, particularly neurons, amyloid precursor-like protein 2 (APLP2), and its highly homologous family member amyloid precursor protein (APP), have been linked to cellular growth. APLP2 and APP undergo regulated intramembrane proteolysis to produce C-terminal fragments. In this study, we found comprehensive expression of APLP2 C-terminal fragments in a panel of pancreatic cancer cell lines; however, APP C-terminal fragments were notably limited to the BxPC3 cell line. Extensive glycosaminoglycan modification on APLP2 was also found in the majority of pancreatic cancer cell lines. Glycosaminoglycan-modified and -unmodified APLP2, and particularly APLP2 C-terminal fragments, also demonstrated increased expression in oncogene-transformed pancreatic ductal cells. Additionally, elevated APLP2 levels were confirmed in human pancreatic cancer tissue. Downregulation of APLP2 and APP expression, alone or in combination, caused a decrease in the growth of a pancreatic cancer cell line with representatively low APP C-terminal fragment expression, the S2-013 cell line. Furthermore, we found that treatment with β-secretase inhibitors to block formation of APLP2 C-terminal fragments decreased the growth and viability of S2-013 cells, without affecting the survival of a non-transformed pancreatic ductal cell line. In conclusion, our studies demonstrate that abundant APLP2, but not APP, C-terminal fragment expression is conserved in pancreatic cancer cell lines; however, APP and APLP2 equally regulated the growth of S2-013 pancreatic cancer cells. Chiefly, our discoveries establish a role for APLP2 in the growth of pancreatic cancer cells and show that inhibitors preventing APLP2 cleavage reduce the viability of pancreatic cancer cells.

Despite evidence that long-term smoking is the leading risk factor for pancreatic malignancies, the underlying mechanism(s) for cigarette-smoke (CS)-induced pancreatic cancer (PC) pathogenesis has not been well established. Our previous studies revealed an aberrant expression of the MUC4 mucin in PC as compared with the normal pancreas, and its association with cancer progression and metastasis. Interestingly, here we explore a potential link between MUC4 expression and smoking-mediated PC pathogenesis and report that both cigarette smoke extract and nicotine, which is the major component of CS, significantly upregulates MUC4 in PC cells. This nicotine-mediated MUC4 overexpression was via the α7 subunit of nicotinic acetylcholine receptor (nAChR) stimulation and subsequent activation of the JAK2/STAT3 downstream signaling cascade in cooperation with the MEK/ERK1/2 pathway; this effect was blocked by the α7nAChR antagonists, α-bungarotoxin and mecamylamine, and by specific siRNA-mediated STAT3 inhibition. In addition, we demonstrated that nicotine-mediated MUC4 upregulation promotes the PC cell migration through the activation of the downstream effectors, such as HER2, c-Src and FAK; this effect was attenuated by shRNA-mediated MUC4 abrogation, further implying that these nicotine-mediated pathological effects on PC cells are MUC4 dependent. Furthermore, the in vivo studies showed a marked increase in the mean pancreatic tumor weight (low dose (100 mg/m(3) total suspended particulate (TSP)), P=0.014; high dose (247 mg/m(3) TSP), P=0.02) and significant tumor metastasis to various distant organs in the CS-exposed mice, orthotopically implanted with luciferase-transfected PC cells, as compared with the sham controls. Moreover, the CS-exposed mice had elevated levels of serum cotinine (low dose, 155.88±35.96 ng/ml; high dose, 216.25±29.95 ng/ml) and increased MUC4, α7nAChR and pSTAT3 expression in the pancreatic tumor tissues. Altogether, our findings revealed for the first time that CS upregulates the MUC4 mucin in PC via the α7nAChR/JAK2/STAT3 downstream signaling cascade, thereby promoting metastasis of PC.

Radiation therapy is a staple approach for cancer treatment, whereas radioresistance of cancer cells remains a substantial clinical problem. In response to ionizing radiation (IR) induced DNA damage, cancer cells can sustain/activate pro-survival signaling pathways, leading to apoptotic resistance and induction of cell cycle checkpoint/DNA repair. Previous studies show that Rac1 GTPase is overexpressed/hyperactivated in breast cancer cells and is associated with poor prognosis. Studies from our laboratory reveal that Rac1 activity is necessary for G2/M checkpoint activation and cell survival in response to IR exposure of breast and pancreatic cancer cells. In this study, we investigated the effect of Rac1 on the survival of breast cancer cells treated with hyper-fractionated radiation (HFR), which is used clinically for cancer treatment. Results in this report indicate that Rac1 protein expression is increased in the breast cancer cells that survived HFR compared with parental cells. Furthermore, this increase of Rac1 is associated with enhanced activities of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and nuclear factor-κB (NF-κB) signaling pathways and increased levels of anti-apoptotic protein Bcl-xL and Mcl-1, which are downstream targets of ERK1/2 and NF-κB signaling pathways. Using Rac1-specific inhibitor and dominant-negative mutant N17Rac1, here we demonstrate that Rac1 inhibition decreases the phosphorylation of ERK1/2 and inhibitory κBα (IκBα), as well as the levels of Bcl-xL and Mcl-1 protein in the HFR-selected breast cancer cells. Moreover, inhibition of Rac1 using either small molecule inhibitor or dominant-negative N17Rac1 abrogates clonogenic survival of HFR-selected breast cancer cells and decreases the level of intact poly(ADP-ribose) polymerase, which is indicative of apoptosis induction. Collectively, results in this report suggest that Rac1 signaling is essential for the survival of breast cancer cells subjected to HFR and implicate Rac1 in radioresistance of breast cancer cells. These studies also provide the basis to explore Rac1 as a therapeutic target for radioresistant breast cancer cells.

Purpose: To evaluate the nature of cyclin-dependent kinase 5 (CDK5) hyperactivity in pancreatic cancer progression. Experimental Design: We used genetic, biochemical, and molecular biology methods to investigate the nature and function of overexpression of CDK5 and its activators p35 and p39 during the progression of pancreatic cancer. Results: Amplification of the CDK5 gene or either of its main activators, p35 and p39, was observed in 67% of human pancreatic ductal adenocarcinoma (PDAC). CDK5, p35, and p39 were rarely expressed in pancreatic ducts whereas more than 90% of PDACs had increased levels of CDK5 and p35. Increased levels of CDK5, p35, and p39 protein were observed in several pancreatic cancer cell lines. Inhibition of CDK5 kinase activity using a CDK5 dominant-negative mutant or the drug roscovitine significantly decreased the migration and invasion of pancreatic cancer cells in vitro. Increased CDK5 kinase activity was also observed in immortalized human pancreatic nestin-expressing (HPNE) cells expressing a mutant form of K-Ras (G12D) compared with HPNE cells expressing native K-Ras. G12D K-Ras increased cleavage of p35 to p25, a stable and greater activator of CDK5, thus implicating a role for CDK5 in early progression of PDAC. Inhibition of the signaling cascade downstream of mutant K-Ras (G12D) that involves mitogen-activated protein/extracellular signal–regulated kinase, phosphoinositide 3-kinase, or CDK5 decreased p25 protein levels. Conclusion: These results suggest that mutant K-Ras acts in concert with CDK5 and its activators to increase malignant progression, migration, and invasion of pancreatic cancer cells. Clin Cancer Res; 17(19); 6140–50. ©2011 AACR.

The Shelterin complex associates with telomeres and plays an essential role in telomere protection and telomerase regulation. In its most abundant form, the complex is composed of six core components: TRF1, TRF2, POT1, TIN2, TPP1 and RAP1. Of these subunits, three can interact directly with either single-stranded (POT1) or double-stranded (TRF1, TRF2) telomeric DNA. In this report, we have developed assays to measure the DNA binding activity of Shelterin complexes in human cell extracts. With these assays, we have characterized the composition and DNA binding specificity of two Shelterin complexes: a 6-member complex that contains all six core components and a second complex that lacks TRF1. Our results show that both of these complexes bind with high affinity (KD = 1.3–1.5 � 10 � 9 M) and selectively to ds/ss-DNA junctions that carry both a binding site for POT1 (ss-TTAGGGTTAG) and a binding site for the SANT/Myb domain of TRF1 or TRF2 (ds-TTAGGG TTA). This DNA binding specificity suggests the preferential recruitment of these complexes to areas of the telomere where ss- and ds-DNA are in close proximity, such as the 3 0 -telomeric overhang, telomeric DNA bubbles and the D-loop at the base of T-loops.

Replication protein A (RPA), a key player in DNA metabolism, has 6 single-stranded DNA-(ssDNA-) binding domains (DBDs) A-F. SELEX experiments with the DBDs-C, -D, and -E retrieve a 20-nt G-quadruplex forming sequence. Binding studies show that RPA-DE binds preferentially to the G-quadruplex DNA, a unique preference not observed with other RPA constructs. Circular dichroism experiments show that RPA-CDE-core can unfold the G-quadruplex while RPA-DE stabilizes it. Binding studies show that RPA-C binds pyrimidine- and purine-rich sequences similarly. This difference between RPA-C and RPA-DE binding was also indicated by the inability of RPA-CDE-core to unfold an oligonucleotide containing a TC-region 5′ to the G-quadruplex. Molecular modeling studies of RPA-DE and telomere-binding proteins Pot1 and Stn1 reveal structural similarities between the proteins and illuminate potential DNA-binding sites for RPA-DE and Stn1. These data indicate that DBDs of RPA have different ssDNA recognition properties.

Background & Aims Cigarette smoking is a major risk factor for pancreatic cancer. Aggressive pancreatic tumors contain cancer cells with stem cell features. We investigated whether cigarette smoke induces stem cell features in pancreatic cancer cells. Methods KrasG12D; Pdx1-Cre mice were exposed to cigarette smoke or clean air (controls) for up to 20 weeks; pancreata were collected and analyzed by histology, quantitative reverse transcription polymerase chain reaction, and confocal immunofluorescence microscopy. HPNE and Capan1 cells were exposed to cigarette smoke extract (CSE), nicotine and nicotine-derived carcinogens (NNN or NNK), or clean air (controls) for 80 days and evaluated for stem cell markers and features using flow cytometry–based autofluorescence, sphere formation, and immunoblot assays. Proteins were knocked down in cells with small interfering RNAs. We performed RNA sequencing analyses of CSE-exposed cells. We used chromatin immunoprecipitation assays to confirm the binding of FOS-like 1, AP-1 transcription factor subunit (FOSL1) to RNA polymerase II-associated factor (PAF1) promoter. We obtained pancreatic ductal adenocarcinoma (PDAC) and matched nontumor tissues (n = 15) and performed immunohistochemical analyses. Results Chronic exposure of HPNE and Capan1 cells to CSE caused them to increase markers of stem cells, including autofluorescence and sphere formation, compared with control cells. These cells increased expression of ABCG2, SOX9, and PAF1, via cholinergic receptor nicotinic alpha 7 subunit (CHRNA7) signaling to mitogen-activated protein kinase 1 and FOSL1. CSE-exposed pancreatic cells with knockdown of PAF1 did not show stem cell features. Exposure of cells to NNN and NNK led to increased expression of CHRNA7, FOSL1, and PAF1 along with stem cell features. Pancreata from KrasG12D; Pdx1-Cre mice exposed to cigarette smoke had increased levels of PAF1 mRNA and protein, compared with control mice, as well as increased expression of SOX9. Levels of PAF1 and FOSL1 were increased in PDAC tissues, especially those from smokers, compared with nontumor pancreatic tissue. CSE exposure increased expression of PHD-finger protein 5A, a pluripotent transcription factor and its interaction with PAF1. Conclusions Exposure to cigarette smoke activates stem cell features of pancreatic cells, via CHRNA7 signaling and FOSL1 activation of PAF1 expression. Levels of PAF1 are increased in pancreatic tumors of humans and mice with chronic cigarette smoke exposure.

Activating mutations in the K-Ras gene are the earliest and most common genetic alterations detected in human pancreatic cancer (PC) specimens. In genetically engineered mouse models of PC, oncogenic K-Ras drives the formation of PanIN precursor lesions and their progression to invasive PC. Oncogenic K-Ras has at least four effector pathways that play distinct roles in malignant transformation: MAPK pathway, PI3K pathway, Ral-GDS, and the Rac1 GTPase (Ras-related C3 botulinum toxin substrate 1). Among these effectors, the least well understood is the Rac1 pathway. Yet, this pathway has now been shown to be critical for Ras-driven PC development and malignant transformation. However, the specific mechanisms by which Rac1 promotes anchorage-independent growth and tumorigenicity are still unclear. In recent studies, we have discovered that the Rac1 pathway regulates the stability of the Yes-associated protein 1 (YAP1). YAP1 is a transcriptional co-activator that controls the transcription of genes involved in proliferation and survival. The stability, location, and activity of YAP are controlled by signaling pathways involved in sensing cell-cell and cell-matrix interactions, such as the Hippo and Wnt pathways. In mouse models of Ras-driven PC, YAP1 is required for the formation of PanIN precursor lesions and their progression to invasive PC. In our telomerase-immortalized human pancreatic ductal cells, overexpressed YAP alone is sufficient to allow anchorage-independent growth. Our results show that in PC treated with Rac1 inhibitors (NSC23766, EHT-1864, AZA1, and Rac1T17N), YAP1 is rapidly and almost completely degraded within 24 hours. Importantly, this degradation of YAP1 is blocked by the preincubation of the cells with proteasome inhibitor MG-132, thereby suggesting the involvement of an ubiquitin ligase complex. A phosphodegron activated by the LATS1/2 kinases is present in YAP1 that promotes the degradation of the protein by the SCF-βTRCP ubiquitin ligase complex. Yet, the knockdown of neither the LATS1/2 kinases nor βTRCP affected the degradation of YAP1 after Rac1 inhibition. The knockdown of Elongin B and C, which are part of a different ubiquitin ligase complex controlling YAP1, also yielded similar results. A mutant of YAP1 lacking its LATS1/2 phosphorylation sites was also tested (YAP1-5SA). After Rac1 inhibition, this mutant was degraded with similar kinetics as the wild-type YAP1 protein. These findings reveal the existence of a novel ubiquitin ligase complex regulating YAP1 stability, this time in response to the inhibition of the Rac1 pathway. The screening of a siRNA library has now been undertaken to identify components of the ubiquitin ligase involved. The proposed work is expected to shed light on novel mechanisms underlying the development of PC and of other Ras-driven malignancies. Citation Format: Chitra Palanivel, Bailey Gabler, Ying Yan, Surinder K. Batra, Michel M. Ouellette. The small GTPase Rac1 controls the stability of the Yes-associated protein 1 (YAP1) independently of the LATS1/2 kinases and SCF-βTRCP ubiquitin ligase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4366.

Activating mutation of K-ras and inactivation of DPC4 are two common genetic alterations that occur in the development and progression of pancreatic ductal adenocarcinomas (PDAC). A separate common event in PDAC progression is increased expression of phosphotyrosine kinase receptors (PTKRs). In this study, we examined whether activating mutations of K-ras and loss of Smad4 play a role in causing the aberrant expression of PTKRs. Immortalized human pancreas ductal cells (HPNE) were genetically modified by expressing oncogenic K-ras and /or by shRNA knock down of Smad4. EGFR and erbB2 protein levels but not Ron or IGF-1R were substantially up regulated in HPNE cells that express K-ras (GD12). The increased expression of EGFR in HPNE cells that expressed K-ras (GD12) was mediated by both stabilizing EGFR protein and by increasing EGFR transcription. TGF-β signaling partially suppressed K-ras (GD12) induced EGFR transcription in Smad4 intact HPNE cells; whereas, knockdown of Smad4 in cells expressing K-ras (GD12) further enhanced expression of EGFR and erbB2. The up regulation of EGFR and erbB2 was associated with an increase of invasion, which was blocked by a kinase inhibitor of EGFR. This study indicates for the first time, that oncogenic ras and loss of Smad signaling cooperate to up regulate EGFR and erbB2, which plays a role in promoting invasion.

Background and aims: Pancreatic cancer is among the most dismal of human malignancies. Current therapeutic strategies are virtually ineffective in controlling advanced, metastatic disease. Recent evidence suggests that the Hedgehog signalling pathway is aberrantly reactivated in the majority of pancreatic cancers, and that Hedgehog blockade has the potential to prevent disease progression and metastatic spread. Methods: Here it is shown that the Hedgehog pathway is activated in the Pdx1-Cre;LsL-Kras G12D ;Ink4a/Arf lox/lox transgenic mouse model of pancreatic cancer. The effect of Hedgehog pathway inhibition on survival was determined by continuous application of the small molecule cyclopamine, a smoothened antagonist. Microarray analysis was performed on non-malignant human pancreatic ductal cells overexpressing Gli1 in order to screen for downstream Hedgehog target genes likely to be involved in pancreatic cancer progression. Results: Hedgehog inhibition with cyclopamine significantly prolonged median survival in the transgenic mouse model used here (67 vs 61 days; p = 0.026). In vitro data indicated that Hedgehog activation might at least in part be ascribed to oncogenic Kras signalling. Microarray analysis identified 26 potential Hedgehog target genes that had previously been found to be overexpressed in pancreatic cancer. Five of them, BIRC3, COL11A1, NNMT, PLAU and TGM2, had been described as upregulated in more than one global gene expression analysis before. Conclusion: This study provides another line of evidence that Hedgehog signalling is a valid target for the development of novel therapeutics for pancreatic cancer that might be worth evaluating soon in a clinical setting.

Pancreatic adenocarcinomas display foci of duct-like structures that are positive for markers of pancreatic ductal cells. The development of these tumors is promoted by conditions leading to acinar-to-ductal metaplasia, a process by which acinar cells are replaced by ductal cells. Acinar-to-ductal metaplasia has recently been shown to proceed through intermediary cells expressing Nestin. To create an in vitro system to study pancreatic adenocarcinomas, we had used an hTERT cDNA to immortalize primary cells of the human pancreas. In this report, we show that the immortalized cells, termed hTERT-HPNE cells, have the ability to differentiate to pancreatic ductal cells. Exposing hTERT-HPNE cells to sodium butyrate and 5-aza-2'-deoxycytidine lead to the formation of pancreatic ductal cells marked by the expression of MDR-1, carbonic anhydrase II, and the cytokeratins 7, 8, and 19. hTERT-HPNE cells were found to have properties of the intermediary cells formed during acinar-to-ductal metaplasia, which included their undifferentiated phenotype, expression of Nestin, evidence of active Notch signaling, and ability to differentiate to pancreatic ductal cells. These results provide further evidence for the presence in the adult pancreas of a precursor of ductal cells. hTERT-HPNE cells should provide a useful model to study acinar-to-ductal metaplasia and the role played by this process in pancreatic cancer development.

A major obstacle to the immortalization of primary human cells and the establishment of human cell lines is telomere-controlled senescence. Telomere-controlled senescence is caused by the shortening of telomeres that occurs each time somatic human cells divide. The enzyme telomerase can prevent the erosion of telomeres and block the onset of telomere-controlled senescence, but its expression is restricted to the early stages of embryonic development, and in the adult, to rare cells of the blood, skin and digestive track. However, we and others have shown that the transfer of an exogenous hTERT cDNA, encoding the catalytic subunit of human telomerase, can be used to prevent telomere shortening, overcome telomere-controlled senescence, and immortalize primary human cells. Most importantly, hTERT alone can immortalize cells without causing cancer-associated changes or altering phenotypic properties. Primary human cells that have so far been established by the forced expression of hTERT alone include fibroblasts, retinal pigmented epithelial cells, endothelial cells, oesophageal squamous cells, mammary epithelial cells, keratinocytes, osteoblasts, and Nestin-positive cells of the pancreas. In this article, we discuss the use of hTERT to immortalize of human cells, the properties of hTERT-immortalized cells, and their applications to cancer research and tissue engineering.

Background: Aberrant expression of mucins underlie pancreatic cancer (PC) progression and metastasis. Mucin-type O-glycosylation is the principal post-translational modification on mucins and is regulated by myriad of glycosyltransferases. Not much has been investigated about the specific glycosyltransferases involved in increased PC aggressiveness. We found that core 1 β1,3-galactosyltransferase (C1GALT1), which is essential for O-glycosylation, is not expressed in some of the PC patients. C1GALT1 adds galactose in O-glycosylation pathway that forms core 1 structure, which is usually elongated to several carbohydrate structures. Loss of C1GALT1 is accompanied by incomplete O-glycosylation that results in increased expression of truncated carbohydrate antigens (Tn and sTn). Increased expression of these truncated carbohydrate antigens on mucins has been associated with augmented aggressiveness in several malignancies. Based on these results, we hypothesized that loss of C1GALT1 in PC patients is associated with altered mucin O-glycosylation and increased aggressiveness. Methods: Expression of C1GALT1 was examined in HPNE (human pancreatic nestin expressing cells) and oncogenic transformed HPNE cells. To understand the role of C1GALT1 in PC, CRISPR/Cas9 mediated knockout of CIGALT1 was performed in PC cells. Impact of C1GALT1 knockout on glycosylation profile and mucin glycosylation was evaluated using lectin blotting and lectin-pull down assay. Wound-healing assay was performed to examine the effect of C1GALT1 knockout on migration. To gain mechanistic insight, protein expression of signaling molecules involved in growth and motility was evaluated using western blotting. Orthotopic implantation of C1GALT1 knockout cells was carried in pancreas of nude mice to study its role in tumor growth and metastasis. KPC mouse model (KrasG12D; Trp53R172H/+; Pdx-1- Cre) of PC progression was crossed with C1galt1 floxed mice (resulted in KPCC mice) to study the involvement of C1galt1 in disease progression and metastasis in vivo. Results: Oncogenic transformed HPNE cells showed decreased expression of C1GALT1 as compared to untransformed HPNE cells. Knockout of C1GALT1 in PC cells resulted in increased expression of truncated carbohydrate antigens (Tn and sTn). Further, knockout cells displayed increased cellular protrusions, which was associated with significantly increased migration. Western blotting demonstrated increased expression of proteins involved in growth and motility. Lectin-pull down assay revealed altered MUC16 glycosylation in C1GALT1 knockout cells. In vivo studies using orthotopic implantation and KPCC mouse model demonstrated increased tumor weight and metastasis with knockout of C1GALT1. Conclusion: Overall, our results indicate that loss of C1GALT1 in PC is associated with altered MUC16 glycosylation and increased PC aggressiveness. Citation Format: Seema Chugh, Satyanarayana Rachagani, Xinheng Yu, Sriram Neelamegham, Lijun Xia, Michel M. Ouellette, Moorthy P. Ponnusamy, Surinder K. Batra. Loss of core 1 β1,3-galactosyltransferase (C1GALT1) in pancreatic cancer leads to altered mucin glycosylation and increased tumor aggressiveness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5801. doi:10.1158/1538-7445.AM2017-5801