Interaction of smad3 with a proximal smad-binding element of the human alpha2(I) procollagen gene promoter required for transcriptional activation by TGF-beta.
Transcription of the alpha2(I) collagen gene (COL1A2) in fibroblasts is potently induced by transforming growth factor-beta (TGF-beta). Smad family proteins function as intracellular signal transducers for TGF-beta that convey information from the cell membrane to the nucleus. In the present study, we establish the functional requirement for endogenous Smad3 and Smad4 in TGF-beta-stimulated COL1A2 transcription in human skin fibroblasts in vitro. Furthermore, using transfections with a series of 5' deletions of the human COL1A2 promoter, we identify a proximal region between -353 and -148 bp, which is required for full stimulation of transcription by a constitutively active TGF-beta type I receptor. This region of the COL1A2 promoter contains a CAGA motif also found in the promoter of the plasminogen activator inhibitor-1. Substitutions disrupting this sequence decreased the binding of nuclear extracts or recombinant Smad3 to the CAGACA oligonucleotide, and markedly reduced the transcriptional response to TGF-beta or overexpressed Smad3 in transient transfection assays. The insertion of tandem repeats of CAGACA conferred TGF-beta stimulation to a heterologous minimal promoter-reporter construct. Inhibition of endogenous Smad expression in fibroblasts by antisense oligonucleotides or cDNA against Smad3 or Smad4, and transfection of COL1A2 promoter constructs into Smad4-deficient breast adenocarcinoma cells, indicated the critical role of Smads for the full TGF-beta response. The importance of Smad binding to the CAGACA box of COL1A2 was further established by transcriptional decoy oligonucleotide competition. Taken together, the results identify a functional Smad-binding element of the COL1A2 promoter harboring a CAGACA consensus sequence that is both necessary and sufficient for stimulation by TGF-beta, and demonstrate that interaction of this Smad-binding element with endogenous Smads is required for the full TGF-beta response in fibroblasts.
Chen
S J
SJ
Section of Rheumatology, University of Illinois College of Medicine at Chicago, Chicago, Illinois 60607-7171, USA.
Yuan
W
W
Lo
S
S
Trojanowska
M
M
Varga
J
J
D000230:Adenocarcinoma; D001665:Binding Sites; D001943:Breast Neoplasms; D006528:Carcinoma, Hepatocellular; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D017353:Gene Deletion; D006801:Humans; D008113:Liver Neoplasms; D011347:Procollagen / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012867:Skin / Q000166:cytology / Q000378:metabolism*; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation / Q000187:drug effects / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D004268:DNA-Binding Proteins; D011347:Procollagen; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051900:Smad3 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta