Background & Aims Oncogenic Kras mutation is a defining genetic alteration in pancreatic ductal adenocarcinoma (PDAC), but is not sufficient to promote cancer formation on ist own. Secondary events, such as inflammation-induced signaling via the epidermal growth factor receptor (EGFR) and expression of the SOX9 gene, are required for tumor formation. In this study we sought to identify the underlying mechanisms which link EGFR signaling to Sox9 gene induction during acinar–ductal metaplasia (ADM), a transdifferentiation process that precedes pancreatic carcinogenesis. Methods We analyzed pancreatic tissues from KrasG12D;pdx1-Cre and KrasG12D;NFATc1Δ/Δ;pdx1-Cre mice after intraperitoneal administration of caerulein or dimethyl suloxide (controls). Pharmacological inhibition of NFATc1 activation was achieved by application of cyclosporin A. Induction of EGFR signaling and its effects on expression of NFATc1 or SOX9 were investigated by quantitative reverse transcription PCR, immunoblot, and immunohistochemical analyses of mouse and human tissues and acinar cell explants. Interactions between NFATc1 and partner proteins and effects on DNA binding or chromatin modifications were studied using co-immunoprecipitation and chromatin immunoprecipitation assays in acinar cell explants and mouse tissue. Results EGFR activation induced NFATc1 expression in metaplastic tissues from patients with chronic pancreatitis and in pancreatic tissues from KrasG12D mice and promoted complex-formation with c-Jun in dedifferentiating acinar cells, thereby stimulating the transcription of ductal gene signatures to provoke ADM. This process involved NFATc1:c-Jun-mediated activation of Sox9 transcription in converting acinar cells. Pharmacological inhibition of NFATc1 or disruption of the Nfatc1 gene inhibited EGFR-mediated induction of Sox9 transcription and blocked acinar–ductal transdifferentiation and pancreatic cancer initiation. Conclusion Our findings identify an EGFR-NFATc1-Sox9 signaling cascade as a critical mediator of inflammation-induced PDAC initiation and suggest that disruption of this pathway may offer a novel chemopreventive target for high-risk pancreatitis patients.
BACKGROUND & AIMS Transcriptional silencing of the p15INK4b tumor suppressor pathway overcomes cellular protection against unrestrained proliferation in cancer. Here we show a novel pathway involving the oncogenic transcription factor nuclear factor of activated T cells (NFAT) c2 targeting a p15INK4b-mediated failsafe mechanism to promote pancreatic cancer tumor growth. METHODS Immunohistochemistry, real-time polymerase chain reaction, immunoblotting, and immunofluorescence microscopy were used for expression studies. Cancer growth was assessed in vitro by [3H]thymidine incorporation, colony formation assays, and in vivo using xenograft tumor models. Protein-protein interactions, promoter regulation, and local histone modifications were analyzed by immunoprecipitation, DNA pull-down, reporter, and chromatin immunoprecipitation assays. RESULTS Our study uncovered induction of NFATc2 in late-stage pancreatic intraepithelial neoplasia lesions with increased expression in tumor cell nuclei of advanced cancers. In the nucleus, NFATc2 targets the p15INK4b promoter for inducible heterochromatin formation and silencing. NFATc2 binding to its cognate promoter site induces stepwise recruitment of the histone methyltransferase Suv39H1, causes local H3K9 trimethylation, and allows docking of heterochromatin protein HP1γ to the repressor complex. Conversely, inactivation of NFATc2 disrupts this repressor complex assembly and local heterochromatin formation, resulting in restoration of p15INK4b expression and inhibition of pancreatic cancer growth in vitro and in vivo. CONCLUSIONS Here we describe a novel mechanism for NFATc2-mediated gene regulation and identify a functional link among its repressor activity, the silencing of the suppressor pathway p15INK4b, and its pancreatic cancer growth regulatory functions. Thus, we provide evidence that inactivation of oncogenic NFATc2 might be an attractive strategy in treatment of pancreatic cancer.
In adaptation to oncogenic signals, pancreatic ductal adenocarcinoma (PDAC) cells undergo epithelial-mesenchymal transition (EMT), a process combining tumor cell dedifferentiation with acquisition of stemness features. However, the mechanisms linking oncogene-induced signaling pathways with EMT and stemness remain largely elusive. Here, we uncover the inflammation-induced transcription factor NFATc1 as a central regulator of pancreatic cancer cell plasticity. In particular, we show that NFATc1 drives EMT reprogramming and maintains pancreatic cancer cells in a stem cell-like state through Sox2-dependent transcription of EMT and stemness factors. Intriguingly, NFATc1-Sox2 complexmediated PDAC dedifferentiation and progression is opposed by antithetical p53-miR200c signaling, and inactivation of the tumor suppressor pathway is essential for tumor dedifferentiation and dissemination both in genetically engineered mouse models (GEMM) and human PDAC. Based on these findings, we propose the existence of a hierarchical signaling network regulating PDAC cell plasticity and suggest that the molecular decision between epithelial cell preservation and conversion into a dedifferentiated cancer stem cell-like phenotype depends on opposing levels of p53 and NFATc1 signaling activities.
In studies of human and mouse pancreatic cells and tissue, we identified context-specific epigenetic regulation of NFATc1 activity as an important mechanism of pancreatic cell plasticity. Inhibitors of EZH2 might therefore interfere with oncogenic activity of NFATC1 and be used in treatment of pancreatic ductal adenocarcinoma.
<p>PDF file 2546K, Supplementary Figure 1 refers to Figure 1 and shows additional morphological and expression changes in KrasG12D mice upon caerulein challenge</p>
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