Ligand induced upregulation of the type II transforming growth factor (TGF-β) receptor enhances TGF-β responsiveness in COLO-357 cells

The effects of transforming growth factor (TGF)β1 on type I and type II TGF-β receptor (TβRI and TβRII) expression were examined in five pancreatic cancer cell lines. In contrast to its actions in COLO-357, a TGF- β-sensitive pancreatic cancer cell line, TGF-β1 did not significantly alter TGF-β receptor expression in either the TGF-β-sensitive BXPC-3 and PANC-1 cells or in the TGF-β-resistant CAPAN-1 and T3M4 cells. Neutralizing anti- TβRII antibodies blocked TGF-β1-dependent signaling in COLO-357 cells but exhibited an attenuated effect in COLO-357 cells preincubated with TGF-β1 for 48 h. Basal TβRII expression levels were comparable in all five cell lines examined. In contrast, COLO-357 cells and BX-PC-3 cells expressed relatively high basal levels of TβRI. However, COLO-357 cells harbored a normal Smad4 gene, whereas BX-PC-3 cells exhibited a complete deletion of this gene. We conclude that the TGF-β1-induced TβRII upregulation serves to enhance TGF-β1 responsiveness in COLO-357 cells, and that this upregulation requires the presence of adequate levels of TβRI and TβRII, and a functional Smad4 gene product. Our findings also indicate that TGF-β1 may inhibit pancreatic cancer cell growth via a Smad4-independent pathway.