Chronic exposure of transforming growth factor beta 1 confers a more aggressive tumor phenotype through downregulation of p21WAF1/CIP1 in conditionally immortalized pancreatic epithelial cells

Abstract

BackgroundRecent studies have demonstrated that transforming growth factor beta 1 (TGF-β1) expression is markedly enhanced in invasive ductal pancreatic adenocarcinomas, 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 (IMPE) cells. MethodsSixty-one PanIN lesions were immunohistochemically stained with a polyclonal rabbit antibody against human TGF-β1. Growth-inhibitory effects of short-term exposure to TGF-β1 were examined in IMPE cells. IMPE cells resistant to TGF-β1 (IMPE-Tr cells) were generated by continuous exposure to 1 ng/mL of TGF-β1 for more than 50 days. Phenotypic alterations of IMPE-Tr cells were examined by soft agar and Matrigel assay and Western blot analysis. IMPE and IMPE-Tr cells were injected subcutaneously into nude mice for an in vivo tumorigenicity assay. ResultsForty-six percent of PanINs (28/61) were positive for TGF-β1 expression, whereas all the epithelia of normal pancreatic ducts were negative. TGF-β1 treatment showed the marked growth-inhibitory effects (>75%) in IMPE cells, whereas its effects were not observed in IMPE-Tr cells. IMPE-Tr cells were more spindle shaped compared with IMPE cells. In soft agar and Matrigel, formations of many colonies were observed in IMPE-Tr cells, but not in IMPE cells. Interestingly, the expression of p21WAF1/CIP1 was induced by short-term exposure to TGF-β1 in IMPE cells, whereas the induction was decreased in IMPE-Tr cells. All of the IMPE-Tr cell-injected mice (5/5) had subcutaneous tumors, although no tumor was found in the IMPE cell-injected mice. ConclusionsTGF-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.