Constitutive connective tissue growth factor expression in scleroderma fibroblasts is dependent on Sp1.
Fibrotic diseases such as scleroderma (systemic sclerosis, SSc) are characterized by an excessive production of extracellular matrix and profibrotic proteins such as connective tissue growth factor (CTGF). In normal dermal fibroblasts, CTGF is not expressed unless induced by proteins such as tumor growth factor-beta (TGFbeta). Conversely, in fibroblasts cultured from fibrotic lesions CTGF mRNA and protein are constitutively expressed, even in the absence of exogenously added TGFbeta. Thus, studying the mechanism underlying CTGF overexpression in SSc fibroblasts is likely to yield valuable insights into the basis of the fibrotic phenotype of SSc and possibly other scarring disease. CTGF overexpression is mediated primarily by sequences in the CTGF promoter. In this report, we identify the minimal promoter element involved with the overexpression of CTGF in SSc fibroblasts. This element is distinct from the element necessary and sufficient for the induction of CTGF expression by TGFbeta in normal fibroblasts. Within this region is a functional Sp1 binding site. Blocking Sp1 activity reduces the elevated, constitutive levels of CTGF promoter activity and protein expression observed in SSc fibroblasts. Relative to those prepared from normal dermal fibroblasts, nuclear extracts prepared from SSc fibroblasts possess increased Sp1 binding activity. Removal of phosphate groups from nuclear extracts enhanced Sp1 binding activity, suggesting that phosphorylation of Sp1 normally reduces Sp1 binding to DNA. Thus, the constitutive overexpression of CTGF in SSc fibroblasts seems to be independent of TGFbeta signaling but dependent at least in part on Sp1.
Holmes
Alan
A
Royal Free and University College Medical School, Center for Rheumatology, Department of Medicine, Rowland Hill St., London, United Kingdom NW3 2PF.
Abraham
David J
DJ
Chen
Youjun
Y
Denton
Christopher
C
Shi-wen
Xu
X
Black
Carol M
CM
Leask
Andrew
A
D001483:Base Sequence; D001665:Binding Sites; D055513:Connective Tissue Growth Factor; D005347:Fibroblasts / Q000378:metabolism*; D006801:Humans; D017874:Immediate-Early Proteins / Q000096:biosynthesis / Q000235:genetics*; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000235:genetics*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic / Q000235:genetics; D012595:Scleroderma, Systemic / Q000473:pathology*; D017384:Sequence Deletion; D016329:Sp1 Transcription Factor / Q000378:metabolism / Q000502:physiology*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000502:physiology
C526317:CCN2 protein, human; D017874:Immediate-Early Proteins; D036341:Intercellular Signaling Peptides and Proteins; D016329:Sp1 Transcription Factor; D016212:Transforming Growth Factor beta; D055513:Connective Tissue Growth Factor