Smad3 mediates immediate early induction of Id1 by TGF-β

摘要

Id1 is a member of the inhibitor of diflferentiation(Id) protein family that regulates a wide range of cell functions.Previous studies have shown that expression of the ID1 gene is down-regulated by TGF-β in epithelial cells,whereas it is up-regulated by BMP in a variety of cell types.During our study of the biological function of TGF-β1,we found that ldl can be strongly up-regulated by TGF-β1 in the human mammary gland epithelial cell line MCF10A.Quanti-taftve real-time RT-PCR has revealed as high as 7.5-fold induction of ID1 mRNA by TGF-β1 in MCFlOA cells after 1 h of TGF-β1 stimulation,and this induction does not require de novo protein synthesis.Using Smad knockdown and knockout approaches.we have identiffed Smad3 as the responsible R-Smad for mediating transcriptional activation of the Id1 gene.Chromatin immunoprecipitation assay confirms that Smad3 and Smad4 bind to the upstream region of the Id1 gene.Our resuIts demonstrate that Smad3,but not Smad2,mediates TGF-β1-dependent early transcrip-tional induction of Id1.