I. Nassour1,2, X. Sun1, S. Zhang1, X. Luo1, L. H. Nguyen1, L. Li1, L. Peng3, J. Shen4, H. Zhu1, S. Wang1,2 1University Of Texas Southwestern Medical Center,Children’s Research Institute,Dallas, TX, USA 2University Of Texas Southwestern Medical Center,Division Of Surgical Oncology,Dallas, TX, USA 3University Of Texas Southwestern Medical Center,Department Of Pathology,Dallas, TX, USA 4Stanford University,Department Of Pathology,Palo Alto, CA, USA
Introduction: Intraductal papillary mucinous neoplasms (IPMN) are precursors to pancreatic ductal adenocarcinoma (PDAC). While activating KRAS mutations are the most common alterations found in PDAC and IPMN, ARID1A, which is a component of the SWI/SNF chromatin remodeling complex, is also commonly mutated. However, the functional effects of ARID1A mutations in pancreas tumorigenesis are not known. Understanding molecular mechanisms that drive IPMN progression may lead to the development of novel therapies that prevent IPMN transformation into PDAC.
Methods: We generated transgenic mice that had pancreas-specific activating Kras mutations and Arid1a deletion (KrasG12D; Ptf1a-Cre; Arid1af/f, or “KCA” mice). We identified 35 human IPMN resection samples, performed immunohistochemistry staining for ARID1A, and graded the expression intensity. We knocked down ARID1A and MYC in human pancreatic ductal epithelial (HPDE) cells with siRNA. siScramble was used as the negative control. To measure protein synthesis, we used an assay based on the incorporation of modified puromycin molecules (O-propargyl-puromycin (OPP)) into nascent peptides. OPP was then fluorescently labelled and quantified by fluorescence-activated cell sorting. Fluorescence level was proportional to the extent of cellular protein synthesis.
Results: Mice with only pancreas-specific activating Kras mutations (KrasG12D; Ptf1a-Cre) had significant pancreatitis and pancreatic intraepithelial neoplasia, which is another type of PDAC precursor, consistent with previous reports. In contrast, KCA mice developed macroscopic mucinous pancreatic cysts at 100% penetrance. Histologic and biochemical assessment showed that these cysts most resembled gastric subtype IPMN. Evaluation of human IPMN samples revealed that gastric subtype IPMN frequently had little to no ARID1A expression while other subtypes had high expression, confirming the fidelity of our model (Fig. A). RNA-seq from Arid1a null pancreas showed significant upregulation of gene networks involved with MYC activity and protein translation. Knocking down ARID1A (siARID1A) in HPDE cells induced increased MYC expression (Fig. B) and protein synthesis (Fig. C). Concurrent knockdown of MYC (siMYC) and ARID1A abrogated the increase in protein synthesis (Fig. D).
Conclusions: Pancreas-specific ARID1A deletion resulted in the formation of gastric subtype IPMN and increased protein synthesis that was mediated through elevated MYC activity (Fig. E). These data suggest that translation is a potential therapeutic target to block the formation and progression of gastric subtype IPMN.
