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PDF file - 3639K, Representative images of pancreatic lesions in wild type mice implanted with DMBA, or in Pdx1-Cre; LSL-Kras G12D mice.

PDF file - 56K, Proliferation rate analysis.

PDF file - 39K, Pathologic score of PanIN lesions in Pdx1-Cre; LSL-KRAS G12D mice, wild type (n=4 mice) or heterozygous (n=7) for the phospho-rpS6 mutant.

PDF file - 66K

PDF file - 44K, Staining for γH2AX (brown) in sections of the intestine from a CK1α-deficient mouse

PDF file - 47K, Mosaic phosphorylation of rpS6 in wild type islets.

The signaling pathways that mediate the development of pancreatic ductal adenocarcinoma (PDAC) downstream of mutant Kras remain incompletely understood. Here, we focus on ribosomal protein S6 (rpS6), an mTOR effector not implicated previously in cancer. Phosphorylation of rpS6 was increased in pancreatic acinar cells upon implantation of the chemical carcinogen 7,12-dimethylbenz(a)anthracene (DMBA) or transgenic expression of mutant Kras. To examine the functional significance of rpS6 phosphorylation, we used knockin mice lacking all five phosphorylatable sites in rpS6 (termed rpS6P−/− mice). Strikingly, the development of pancreatic cancer precursor lesions induced by either DMBA or mutant Kras was greatly reduced in rpS6P−/− mice. The rpS6 mutants expressing oncogenic Kras showed increased p53 along with increased staining of γ-H2AX and 53bp1 (Trp53bp1) in areas of acinar ductal metaplasia, suggesting that rpS6 phosphorylation attenuates Kras-induced DNA damage and p53-mediated tumor suppression. These results reveal that rpS6 phosphorylation is important for the initiation of pancreatic cancer. Cancer Res; 73(6); 1811–20. ©2012 AACR.