Smad-dependent stimulation of type I collagen gene expression in human skin fibroblasts by TGF-beta involves functional cooperation with p300/CBP transcriptional coactivators

Transforming growth factor-beta (TGF-beta) stimulation of Type I collagen g ene (COL1A2) transcription involves the Smad signal transduction pathway, b ut the mechanisms of Smad-mediated transcriptional activation are not fully understood. We now demonstrate that the ubiquitous transcriptional coactiv ators p300 and CREB-binding protein (CBP) enhanced basal as well as TGF-bet a- or Smad3-induced COL1A2 promoter activity, and stimulated the expression of endogenous Type I collagen. The adenoviral E1A oncoprotein abrogated st imulation of COL1A2 activity in transfected fibroblasts, and reduced the ba sal level of collagen gene expression. This effect was due to specific inte raction of E1A with cellular p300/CBP because (a) a mutant form of EIA defe ctive in p300 binding failed to abrogate stimulation, and (b) forced expres sion of D300/CBP restored the ability of TGF-beta to stimulate COL1A2 promo ter activity in the presence of EIA, The effect of p300 on COL1A2, transcri ption appeared to be due, in part, to its intrinsic acetyltransferase activ ity, as stimulation induced by a histone acetyltransferase-deficient mutant p300 was substantially reduced. Transactivation of COL1A2 by p300 involved the Smad signaling pathway, as Smad4-deficient cells failed to respond to p300, and stimulation nas rescued by overexpression of Smad4, Furthermore, minimal constructs containing only the Smad-binding CAGACA element of COL1A 2 were transactivated by p300 in the presence of TGF-beta, These results in dicate, for the first time, that the multifunctional p300/CBP coactivators play a major role in Smad-dependent TGF-beta stimulation of collagen gene e xpression in fibroblasts.