Elucidation of mechanisms of tumorigenesis and invasiveness of pancreatic cancer by gene rearrangement using immortalized pancreatic epithelial cells.

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Pancreatic ductal adenocarcinomas arise through the accumulation of certain genetic alterations including ras, p16, p53, and DPC4. We found that activation of ras and inactivation of p53 could cooperatively induce in vitro tumorigenicity in conditionally immortalized pancreatic epithelial (IMPE) cells. IMPS cells were established from transgenic mice bearing a, temperature-sensitive mutant SV40 Large T (LT) antigen. IMPS cells-grew continuously under permissive conditions (33℃ with interferon-γ), but rapidly suffered growth arrest under non-permissive conditions (39℃ without interferon-γ). The cells showed strong expression of E-cadherin and β-catenin as epithelial markers, and cytokeratin 19, a specific ductal cell marker. Cell proliferation under permissive conditions was associated with down-regulation of p21 expression through inactivation of p53 after over-expression of LT antigen. Intriguingly, the shift from the permissive to non-permissive culture conditions caused G2/M arrest of IMPE cells. Although the cells did not form colonies when cultured in soft agar without activation of ras, cells with ras activation via, an adenovirus vector formed colonies under permissive conditions. These findings suggest that activation of ras and inactivation of p53 can cooperatively induce anchorage-independent growth of IMPE cells.Recent studies have demonstrated that TGF-β1 expression is markedly enhanced in invasive ductal pancreatic adenocarcinomas (DPA), although the precise role of TGF-β1 in pancreatic carcinogenesis remains unclear. We analyzed TGF-β1 expression in pancreatic intraepithelial neoplasias (PanINs) and the effects of chronic TGF-β1 exposure on conditionally immortalized pancreatic epithelial (IMPS) cells. We have clarified that TGF-β1 expression in PanINs and neoplastic transformation of IMPE cells by long-term exposure to TGF-β1 suggest that TGF-β1 may act as a tumor promoter in the early stage of pancreatic carcinogenesis.