Transforming growth factor-beta up-regulates the beta 5 integrin subunit expression via Sp1 and Smad signaling.

Academic Article

Abstract

  • Integrin-mediated cell-matrix interactions play important roles in regulating cell function. Since transforming growth factor-beta (TGF-beta) modulates many osteoblast activities, we hypothesized that the growth factor acts in part by modulating integrin expression. TGF-beta increased cell adhesion to vitronectin and up-regulated the surface level of alpha(v)beta(5) via increasing beta(5) protein synthesis by a transcriptional mechanism. Promoter activity analysis demonstrated that a TGF-beta-responsive element resides between nucleotides -63 and -44. Electrophoretic mobility shift assay and immunoprecipitation/Western studies indicated that the nuclear complex formed using the -66/-42 oligonucleotide contained both Sp1/Sp3 and Smad proteins. Since nuclear Sp1/Sp3 levels were not altered, whereas Smad levels were increased by TGF-beta, we investigated the roles of Smad proteins in the up-regulation of beta(5) gene activation. Co-transfection of cells with beta(5) promoter reporter construct and expression vectors for Smad3, Smad4, and Sp1 increased the stimulatory effect of TGF-beta. Furthermore, expression of dominant negative Smad3 or Smad4 in cells decreased or abolished the stimulation of beta(5) promoter activity by TGF-beta. Smad4 mutant also inhibited the up-regulation of surface beta(5) level by TGF-beta. Thus, TGF-beta increases expression of the integrin beta(5) gene by mechanisms involving Sp1/Sp3 and Smad transcription factors.
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    Keywords

  • Animals, Base Sequence, Cell Adhesion, Cell Line, DNA, DNA-Binding Proteins, Integrins, Mice, Molecular Sequence Data, Mutation, Nuclear Proteins, Osteoblasts, Promoter Regions, Genetic, Protein Binding, RNA, Messenger, Receptors, Vitronectin, Response Elements, Signal Transduction, Smad3 Protein, Smad4 Protein, Sp1 Transcription Factor, Sp3 Transcription Factor, Trans-Activators, Transcription Factors, Transcription, Genetic, Transforming Growth Factor beta, Transforming Growth Factor beta2, Up-Regulation, Vitronectin
  • Digital Object Identifier (doi)

    Author List

  • Lai CF; Feng X; Nishimura R; Teitelbaum SL; Avioli LV; Ross FP; Cheng SL
  • Start Page

  • 36400
  • End Page

  • 36406
  • Volume

  • 275
  • Issue

  • 46