The control of ccn2 (ctgf) gene expression in normal and scleroderma fibroblasts

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Abstract
Although the role of transforming growth factor β (TGFβ) in initiating fibrosis is well established, the role that TGFβ plays in maintaining fibrosis is unclear. The gene encoding connective tissue growth factor (ccn2; ctgf), which promotes fibrosis, is not normally expressed in dermal fibroblasts unless TGFβ is present. However, in dermal fibroblasts cultured from lesional areas of scleroderma, ccn2 (ctgf) is expressed constitutively. The contribution of several elements in the ccn2 (ctgf) promoter to basal and TGFβ induced ccn2 (ctgf) expression in normal and scleroderma fibroblasts has been investigated. A functional SMAD binding site in the ccn2 (ctgf) promoter that is necessary for the TGFβ mediated induction of this gene has been identified. The previously termed TGFβ responsive enhancer (TGFβRE) in the ccn2 (ctgf) promoter has been found to be necessary for basal promoter activity in normal fibroblasts. The SMAD element is not necessary for the high ccn2 (ctgf) promoter activity seen in scleroderma fibroblasts. However, mutation of the previously termed TGFβRE reduces ccn2 (ctgf) promoter activity in scleroderma fibroblasts to that seen in normal fibroblasts. Thus, the maintenance of the scleroderma phenotype, as assessed by a high degree of ccn2 (ctgf) promoter activity, appears to be relatively independent of SMAD action and seems to reflect increased basal promoter activity.