Chronic exposure of transforming growth factor beta 1 confers a more aggressive tumor phenotype through downregulation of p21(WAF1/CIP1) in conditionally immortalized pancreatic epithelial cells.
BACKGROUND
Recent studies have demonstrated that transforming growth factor beta 1 (TGF-beta1) expression is markedly enhanced in invasive ductal pancreatic adenocarcinomas, although the precise role of TGF-beta1 in pancreatic carcinogenesis remains unclear. We analyzed TGF-beta1 expression in pancreatic intraepithelial neoplasias (PanINs) and the effects of chronic TGF-beta1 exposure on conditionally immortalized pancreatic epithelial (IMPE) cells.


METHODS
Sixty-one PanIN lesions were immunohistochemically stained with a polyclonal rabbit antibody against human TGF-beta1. Growth-inhibitory effects of short-term exposure to TGF-beta1 were examined in IMPE cells. IMPE cells resistant to TGF-beta1 (IMPE-Tr cells) were generated by continuous exposure to 1 ng/mL of TGF-beta1 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.


RESULTS
Forty-six percent of PanINs (28/61) were positive for TGF-beta1 expression, whereas all the epithelia of normal pancreatic ducts were negative. TGF-beta1 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 p21(WAF1/CIP1) was induced by short-term exposure to TGF-beta1 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.


CONCLUSIONS
TGF-beta1 expression in PanINs and neoplastic transformation of IMPE cells by long-term exposure to TGF-beta1 suggest that TGF-beta1 may act as a tumor promoter in the early stage of pancreatic carcinogenesis.
Department of Surgery and Surgical Basic Science, Kyoto University, Kyoto, Japan.
Daisuke
D
Ito
Koji
K
Fujimoto
Ryuichiro
R
Doi
Masayuki
M
Koizumi
Eiji
E
Toyoda
Tomohiko
T
Mori
Kazuhiro
K
Kami
Yoshiya
Y
Kawaguchi
Robert
R
Whitehead
Masayuki
M
Imamura
D000818:Animals; D002455:Cell Division / Q000187:drug effects; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D003094:Collagen; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000502:physiology*; D015536:Down-Regulation; D004338:Drug Combinations; D004847:Epithelial Cells / Q000473:pathology; D006801:Humans; D007797:Laminin; D051379:Mice; D008819:Mice, Nude; D010179:Pancreas / Q000378:metabolism / Q000473:pathology*; D010190:Pancreatic Neoplasms / Q000209:etiology*; D011509:Proteoglycans; D016212:Transforming Growth Factor beta / Q000633:toxicity*; D053773:Transforming Growth Factor beta1
C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004338:Drug Combinations; D007797:Laminin; D011509:Proteoglycans; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C059485:matrigel; D003094:Collagen