Both Sp1 and Smad participate in mediating TGF-beta1-induced HGF receptor expression in renal epithelial cells.
Hepatocyte growth factor (HGF) receptor is a transmembrane receptor tyrosine kinase encoded by the c-met protooncogene. In this study, we demonstrated that c-met expression was upregulated in the kidney after obstructive injury in mice. Because the pattern of c-met induction was closely correlated with transforming growth factor-beta1 (TGF-beta1) expression in vivo, we further investigated the regulation of c-met expression in renal tubular epithelial (HKC) cells by TGF-beta1 in vitro. Real-time RT-PCR and Northern and Western blot analyses revealed that TGF-beta1 significantly induced c-met expression in HKC cells, which primarily took place at the gene transcriptional level. Overexpression of inhibitory Smad7 completely abolished c-met induction, indicating its dependence on Smad signaling. Interestingly, TGF-beta1-induced c-met expression was also contingent on a functional Sp1, as ablation of Sp1 binding with mithramycin A abrogated c-met induction in HKC cells. Transfection and sequence analysis identified a cis-acting TGF-beta1-responsive region in the c-met promoter, in which resided a putative Smad-binding element (SBE) and an adjacent Sp1 site. TGF-beta1 not only induced Smad binding to the SBE/Sp1 sites in the c-met promoter, but also enhanced the binding of Sp proteins. Furthermore, Sp1 could form a complex with Smads in a TGF-beta1-dependent fashion. These results suggest a novel regulatory mechanism controlling c-met expression by TGF-beta1 in renal epithelial cells, in which both Smad and Sp proteins participate and cooperate in activating c-met gene transcription.
Zhang
Xianghong
X
Department of Pathology, University of Pittsburgh School of Medicine, S-405 Biomedical Science Tower, 200 Lothrop St., Pittsburgh, PA 15261, USA.
Yang
Junwei
J
Li
Yingjian
Y
Liu
Youhua
Y
D000818:Animals; D001483:Base Sequence; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology*; D006801:Humans; D007668:Kidney / Q000378:metabolism*; D008297:Male; D051379:Mice; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D019859:Proto-Oncogene Proteins c-met / Q000096:biosynthesis*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D051785:Smad Proteins; D016329:Sp1 Transcription Factor / Q000502:physiology*; D015534:Trans-Activators / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000502:physiology*; D053773:Transforming Growth Factor beta1; D015854:Up-Regulation; D014517:Ureteral Obstruction / Q000378:metabolism
D004268:DNA-Binding Proteins; D012333:RNA, Messenger; D051785:Smad Proteins; D016329:Sp1 Transcription Factor; C508960:TGFB1 protein, human; C508961:Tgfb1 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; D019859:Proto-Oncogene Proteins c-met