[Evidence for retinoic acid modulating expression of cyclin-dependent kinase inhibitors in rat hepatic stellate cells].

OBJECTIVE: To study the effects of retinoic acid on regulation of expressions of cyclin-dependent kinase inhibitors, i.e. p16, p21 and p27 in cultured rat hepatic stellate cells. METHODS: Stellate cells were isolated from healthy rat livers and cultured. After stimulated with 1 ng/ml transforming growth factor beta 1, subcultured hepatic stellate cells were treated with or without 1 nmol/ml retinoic acid. MTT assay, immunocytochemistry for p16, p21, p27 and alpha-smooth muscle actin protein, in situ hybridization for retinoic acid receptor beta 2 and p16, p21 and p27 mRNA and quantitative image analysis (partially) were performed. RESULTS: Retinoic acid markedly inhibited hepatic stellate cells proliferation (41.50%, P<0.05), decreased the protein level of alpha-smooth muscle actin (55.09%, P<0.05), and induced hepatic stellate cells to express retinoic acid receptor beta 2 mRNA. In addition, retinoic acid increased the protein level of p16 (218.75%, P <0.05) and induced p21 protein expression; meanwhile, p27 was undetectable by immunocytochemistry in both control and retinoic acid-treated hepatic stellate cells. However, retinoic acid had no influence on the mRNA level of p16, p21 or p27 as determined by in situ hybridization. CONCLUSIONS: Up-regulation of p16 and p21 on post-transcriptional level may contribute, in part, to retinoic acid inhibition of transforming growth factor beta 1-initiated rat hepatic stellate cells activation in vitro.