Constitutively phosphorylated Smad3 interacts with Sp1 and p300 in scleroderma fibroblasts.
OBJECTIVE
To elucidate the role of transforming growth factor-beta (TGF-beta)/Smad signalling in the increased expression of the collagen gene in systemic sclerosis (SSc) fibroblasts.


METHODS
Dermal fibroblasts from seven patients with diffuse SSc of recent onset and from seven healthy individuals were studied. The expression levels of Smad2, Smad3 and Smad4 proteins were determined by immunoblotting. Smad3 phosphorylation and the interaction of Smad3 with Sp1 or p300 were analysed using immunoprecipitation. The effects of overexpression of Smad proteins or Sp1 on the human alpha2(I) collagen gene transcription were investigated with chloramphenicol acetyltransferase (CAT) assays using the -772 COL1A2/CAT construct.


RESULTS
Constitutive increased Smad3 phosphorylation was detected in SSc fibroblasts compared with normal fibroblasts. Increased interaction of Smad3 with Sp1 as well as p300 was also detected in SSc fibroblasts. The overexpression of Smad3 caused an increase of up to 5-fold in COL1A2 promoter activity in normal fibroblasts, while Smad3 caused a small increase in COL1A2 promoter activity in SSc fibroblasts. However, neither Smad2 nor Smad4 caused significant effects in COL1A2 promoter activity in normal fibroblasts or SSc fibroblasts. The overexpression of Sp1 caused further increase in COL1A2 promoter activity stimulated by TGF-beta in normal fibroblasts, but did not change COL1A2 promoter activity in the presence of TGF-beta in SSc fibroblasts. The combined overexpression of Smad3 and Sp1 significantly enhanced TGF-beta response in normal fibroblasts, but less markedly in SSc fibroblasts.


CONCLUSIONS
These results suggested that SSc fibroblasts are less sensitive to exogenous TGF-beta stimulation because they are already activated by the autocrine TGF-beta loop.
Ihn
H
H
Department of Dermatology, Faculty of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan. IN-DER@h.u-tokyo.ac.jp
Yamane
K
K
Asano
Y
Y
Jinnin
M
M
Tamaki
K
K
D002478:Cells, Cultured; D003094:Collagen / Q000235:genetics / Q000378:metabolism; D024042:Collagen Type I; D050881:E1A-Associated p300 Protein / Q000378:metabolism*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism*; D005786:Gene Expression Regulation; D006801:Humans; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000494:pharmacology; D012595:Scleroderma, Systemic / Q000378:metabolism*; D012867:Skin / Q000378:metabolism; D051899:Smad2 Protein / Q000378:metabolism; D051900:Smad3 Protein / Q000378:metabolism*; D051901:Smad4 Protein / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D015533:Transcriptional Activation; D016212:Transforming Growth Factor beta / Q000494:pharmacology
D024042:Collagen Type I; D011994:Recombinant Proteins; C497782:SMAD2 protein, human; C497790:SMAD3 protein, human; C497796:SMAD4 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D051901:Smad4 Protein; D016329:Sp1 Transcription Factor; D016212:Transforming Growth Factor beta; D003094:Collagen; D050881:E1A-Associated p300 Protein; C494360:EP300 protein, human