Repression of transforming growth factor-beta receptor type I promoter expression by Sp1 deficiency

In this report, we describe the mechanism of TGF-beta receptor type I (RI) repression in the CEO human colon carcinoma cells. Treatment of GEO cells w ith the DNA methyltransferase inhibitor, 5 azacytidine induced RI expressio n and restored TGF-beta response. A stably transfected RI promoter-reporter construct (RI-Luc) expressed higher activity in the 5 aza C treated GEO ce lls, suggesting the activation of a transactivator for RI transcription. Ge l shift analysis indicated enhanced binding of proteins from the 5 aza C tr eated nuclear extracts to radiolabeled Sp1 oligonucleotides specifically co ntained in the RT promoter, Protein stability studies after cyclohexamide t reatment suggested an increase in the Spl protein stability from the 5 aza C treated GEO cells. Further, transfection of Sp1 cDNA into untreated GEO c ontrol cells increased RI promoter activity and thus induced RI expression. 5 aza C mediated Spl expression in Sp1 deficient CEO colon and MCF-7 breas t cancer cells also enhanced the activity of several other Sp1 dependent pr omoters such as TGF-beta receptor type II (RII), Cyclin A and p21/waf1/cip1 . These results indicate that restoration of Sp1 in several different types of Sp1 deficient cells leads to enhanced activation of a wide range of Sp1 dependent promoters.