Up-regulation of Transforming Growth Factor (TGF)-β Receptors by TGF-β1 in COLO-357 Cells

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In the present study we investigated the actions of transforming growth factor (TGF)-beta1 on gene induction and cyclin-dependent kinase inhibitors in relation to TGF-beta receptor modulation in COLO-357 pancreatic cancer cells. TGF-beta1 inhibited the growth of COLO-357 cells in a time- and dose-dependent manner and caused a rapid but transient increase in plasminogen activator inhibitor-I and insulin-like growth factor binding protein-3 mRNA levels. TGF-beta1 caused a delayed but sustained increase in the protein levels of the cyclin-dependent kinase inhibitors p15(Ink4B), p21(Cip1), and p27(Kip1) and a sustained increase in type I and II TGF-beta receptors (TbetaRI and TbetaRII) mRNA and protein levels. The protein synthesis inhibitor cycloheximide (10 microg/ml) completely blocked the TGF-beta1-mediated increase in TbetaRI and TbetaRII expression. Furthermore, a nuclear runoff transcription assay revealed that the increase in receptor mRNA levels was due to newly transcribed RNA. There was a significant increase in TbetaRI and TbetaRII mRNA levels in confluent cells in comparison to subconfluent (</=80% confluent) controls, as well as in serum- starved cells when compared with cells incubated in medium containing 10% fetal bovine serum. COLO-357 cells expressed a normal SMAD4 gene as determined by Northern blot analysis and sequencing. These results indicate that TGF-beta1 modulates a variety of functions in COLO-357 cells and up-regulates TGF-beta receptor expression via a transcriptional mechanism, which has the potential to maximize TGF-beta1-dependent antiproliferative responses.