Perturbation of pancreatic acinar cell state can lead to acinar-to-ductal metaplasia (ADM), a precursor lesion to the development of pancreatic ductal adenocarcinoma (PDAC). In the pancreas, Notch signaling is active both during development and in adult cellular differentiation processes. Hes1, a key downstream target of the Notch signaling pathway, is expressed in the centroacinar compartment of the adult pancreas as well as in both preneoplastic and malignant lesions. In this study, we used a murine genetic in vivo approach to ablate Hes1 in pancreatic progenitor cells (Ptf1a; Hes1). Using this model, we studied the role of Hes1 in both acinar cell plasticity and pancreatic regeneration after caerulein-induced pancreatitis and in Kras-driven PDAC development. We show that, although pancreatic development is not perturbed on the deletion of Hes1, terminal acinar differentiation in the adult pancreas is compromised. Moreover, the loss of Hes1 leads to the impaired regeneration of the exocrine compartment, accelerated fatty metaplasia, and persistent ADM after acute caerulein-induced pancreatitis. In Kras-driven carcinogenesis, Hes1 ablation resulted in increased ADM, decreased formation of high-grade pancreatic intraepithelial neoplasias, and accelerated development of PDAC with shortened survival time. In conclusion, Hes1 plays a key role in acinar cell integrity and plasticity on cellular insults. Furthermore, Hes1 is an essential component of the pancreatic intraepithelial neoplasias-to-PDAC route in Kras-driven mouse pancreatic carcinogenesis.

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Introduction: Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cause of cancer-related death in the United States and, to date, without effective treatment. PDAC develops through defined preneoplastic lesions of which pancreatic intraepithelial neoplasia (PanIN) are the most common precursors. Acinar-to-ductal metaplasia (ADM) appears to be an important prerequisite for PanIN development, especially under inflammatory conditions. The Notch signaling pathway plays a key role in cell fate and differentiation and is activated during ADM and PanIN development, suggesting a role in initiation of transformation processes. We have recently shown that Notch2 but not Notch1 regulates PanIN progression in a Kras-driven model of endogenous PDAC. Methods: To determine the role of Notch2 in acinar plasticity as well as in PanIN development, R0SA26R-LSL-N2-IC mice were crossed to Ela-CreERT mice to produce mice with an inducible pancreas-specific constitutively active Notch2 intracellular domain (ElaCreERT; N2-IC). Additionally, ElaCreERT; N2-IC mice were crossed to floxed Hes1 mice to assess the role of Hes1. Morphological and molecular analyses were performed using immunohistochemistry, immunofluorecence, Western Blot, real time quantitative PCR (qRT-PCR) and microarray based gene profiling. Results: Starting 3 days post tamoxifen induction in adult acinar cells, ADM developed in ElaCreERT;N2-IC mice. Acinar cells down-regulated typical acinar genes such as amylase, increasingly expressed the ductal marker CK19 and showed a high proliferative rate. The ADM cells showed high expression of the Notch target gene HES1 and the progenitor marker SOX9 but stained negative for MUC5AC, a marker found in PanIN lesions. In order to investigate the role of the downstream target Hes1 in ADM, ElaCreERT;N2-IC mice were crossed with Hes1lox/Iox mice to produce mice with additional deletion of Hes1. ElaCreERT;N2IC; Hes1lox/iox mice showed a significant attenuation, but no complete rescue of ADM development. Using qRT-PCR, we assayed for Notch downstream target genes and found a strong up-regulation of the Hes family member Hes5. In accordance with other studies of ADM, protein-expression levels of pSTAT3 were up-regulated in ductal cells in ElaCreERT;N2-IC mice. Interestingly, pSTAT3 was expressed in the acinar cells in ElaCreERT; N2IC; Hes1lox/lox mice, which had not undergone N2-IC mediated ADM, suggesting the expression of HES1 to be a decisive part in ADM induction and progression. Conclusion: We have thus shown that Notch2-IC is sufficient for ADM induction in adult acinar cells. The mechanism of phenotype rescue in mice with additional deletion of Hes1 needs to be further investigated but may involve regulation of Stat3. Hes5 was increasingly up-regulated in Hes1-deficient cells, pointing to a potential role in ADM development. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the Second AACR International Conference on Frontiers in Basic Cancer Research; 2011 Sep 14-18; San Francisco, CA. Philadelphia (PA): AACR; Cancer Res 2011;71(18 Suppl):Abstract nr A32.