Both Sp1 and Smad participate in mediating TGF-beta1-induced HGF receptor expression in renal epithelial cells

Am J Physiol Renal Physiol. 2005 Jan;288(1):F16-26. doi: 10.1152/ajprenal.00318.2003. Epub 2004 Aug 31.

Abstract

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.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Base Sequence
  • Cells, Cultured
  • DNA-Binding Proteins / physiology*
  • Humans
  • Kidney / metabolism*
  • Male
  • Mice
  • Promoter Regions, Genetic
  • Protein Binding
  • Proto-Oncogene Proteins c-met / biosynthesis*
  • RNA, Messenger / metabolism
  • Signal Transduction
  • Smad Proteins
  • Sp1 Transcription Factor / physiology*
  • Trans-Activators / physiology*
  • Transcription, Genetic / physiology
  • Transcriptional Activation
  • Transforming Growth Factor beta / physiology*
  • Transforming Growth Factor beta1
  • Up-Regulation
  • Ureteral Obstruction / metabolism

Substances

  • DNA-Binding Proteins
  • RNA, Messenger
  • Smad Proteins
  • Sp1 Transcription Factor
  • TGFB1 protein, human
  • Tgfb1 protein, mouse
  • Trans-Activators
  • Transforming Growth Factor beta
  • Transforming Growth Factor beta1
  • Proto-Oncogene Proteins c-met