Regulation of alpha-smooth muscle actin and CRBP-1 expression by retinoic acid and TGF-beta in cultured fibroblasts

We have reported that Cellular Retinol Binding Protein-1 (CRBP-1) is expres sed de novo during skin wound healing by a proportion of fibroblastic cells which then differentiate into myofibroblasts and express alpha -smooth mus cle actin. In fibroblasts cultured from different tissues we have shown tha t alpha -smooth muscle actin expression, mainly controlled by Transforming Growth Factor-beta (TGF-beta), is also regulated by retinoic acid and that CRBP-1, known to be a retinoic acid-responsive gene, is modulated by TCF-be ta. The aim of the present study has been to investigate the relationships between retinoic acid and TGF-beta in regulating the expression of CRBP-1 a nd alpha -smooth muscle actin in cultured rat subcutaneous tissue fibroblas ts. We have observed that the TGF-beta -induced, but not the retinoic acid- induced, alpha -smooth muscle actin expression is associated with a modulat ion of endogenous TGF-beta and TGF-beta receptors, suggesting that the acti on of retinoic acid on alpha -smooth muscle actin expression is not mediate d by TCF-beta. The expression of CRBP-1 is regulated at the transcriptional level by TCF-beta and retinoic acid but not synergistically, suggesting a possible common pathway. However, retinoic acid, but not TCF-beta, increase s the transcription of a transiently transfected chimeric construct contain ing the retinoic acid response element of the CRBP-1 promoter, indicating t hat TGF-beta does not influence CRBP-1 through the retinoic acid pathway. O ur results indicate that distinct pathways regulate the genes involved in t he appearance and evolution of the myofibroblastic cells. The characterizat ion of these pathways will be helpful for the design of drugs influencing w ound healing. I. Cell. Physiol. 187: 315-325, 2001. (C) 2001 Wiley-Liss, In c.