CTGF and SMADs, maintenance of scleroderma phenotype is independent of SMAD signaling

In normal adult fibroblasts, transforming growth factor-beta (TGF beta) ind uces the expression of connective tissue growth:factor (CTGF). CTGF indepen dently promotes fibroblast proliferation and matrix deposition, and in acut e models of fibrosis promotes cell proliferation and collagen deposition ac ting synergistically with TGF-beta, In contrast to normal fibroblasts, fibr oblasts cultured from fibrotic tissues express high basal levels of CTGF, e ven in the absence of added TGF beta, Induction of transcription by TGF bet a requires the action of SMAD proteins. In this report we have investigated the role of SMADs in the TGF beta -induction of CTGF in normal fibroblasts and in the elevated levels of CTGF expression found in dermal fibroblasts cultured from lesional areas of patients with scleroderma, a progressive fi brotic disorder that can affect all organs of the body. We have identified a functional SMAD binding site in the CTGF promoter. TGF beta -induction of CTGF is dependent on SMAD3 and SMAD4:but not SMAD2 and is p300-independent , However, mutation of the SMAD binding site does not reduce the high level of CTGF promoter activity observed in dermal fibroblasts cultured from les ional areas of scleroderma patients, Conversely, the previously termed TGF beta RE in the CTGF promoter is required for basal CTGF promoter activity i n normal fibroblasts and for the:elevated level of CTGF promoter activity i n scleroderma fibroblasts, Thus, the maintenance of the fibrotic phenotype in scleroderma fibroblasts, as visualized by: excess CTGF expression, appea rs to be independent of SMAD-dependent TGF beta signaling. Furthermore, giv en CTGF's activities, the high level of CTGF expression observed in sclerod erma lesions may contribute to the excessive scarring observed in this diso rder.