Induction of p21waf1 expression and growth inhibition by transforming growth factor beta involve the tumor suppressor gene DPC4 in human pancreatic adenocarcinoma cells.

The tumor suppressor gene deleted in pancreatic cancer locus 4 (DPC4) is inactivated in about 50% of pancreatic adenocarcinomas. DPC4 was found to be homologous to Smad4 and may function as a transcription factor in the transforming growth factor beta (TGF-beta) receptor-mediated signal transduction pathway. We have investigated the role of DPC4 in the TGF-beta receptor-mediated signal transduction cascade in five human pancreatic cancer cell lines (Panc-1, MDAPanc-28, HS766T, Capan-1, and MiaPaCa-2). Our results demonstrate that the loss of responsiveness to TGF-beta-induced growth inhibition correlates with the loss of expression of DPC4. We have shown that TGF-beta induces p21waf1 expression in Panc-1 cells, whereas no induction of p21waf1 expression by TGF-beta was detected in the other four cell lines lacking either DPC4 expression or the TGF-beta type II receptor. No increase in p21waf1 mRNA stability was observed after treatment with TGF-beta, which suggests that the induction of p21waf1 in Panc-1 cells is transcriptionally regulated by TGF-beta. Our data also demonstrate that the expression of DPC4 is directly involved in TGF-beta-mediated induction of the 3TP-lux reporter gene, which contains a known TGF-beta-inducible plasminogen activator inhibitor promoter. These data suggest that: (a) TGF-beta-mediated induction of p21waf1 and subsequent growth inhibition require the expression of DPC4; (b) p21waf1 is a downstream target gene of DPC4; and (c) transfection of the DPC4 gene restores the TGF-beta-inducible gene expression. Inactivation of the tumor suppressor gene DPC4 and other components of the TGF-beta signal cascades may abolish one of the key negative controls of cell proliferation in pancreatic adenocarcinomas.