The mechanism of hydralazine-induced collagen biosynthesis in cultured fibroblasts

The finding that hydralazine (HYD) affects collagen metabolism led us to investigate the mechanism of its action on collagen biosynthesis, prolidase expression and activity, expression of alpha(2)beta(1) integrin, insulin-like growth factor-I receptor (IGF-IR), focal adhesion kinase (FAK), mitogen-activated protein (MAP) kinases (ERK1, ERK2), and transcription factors hypoxia-inducible factor-1 alpha (HIF-1 alpha) and nuclear factor-kappa B p65 (NF-kappa B p65) in human dermal fibroblasts. Confluent fibroblasts were treated with micromolar concentrations (50-500 mu M) of HYD for 24 h. HYD had no influence on cell viability. It was found that HYD-dependent increase in collagen biosynthesis was accompanied by a parallel increase in prolidase activity and expression, HIF-1 alpha expression, and decrease in DNA biosynthesis, compared to untreated cells. Since collagen biosynthesis and prolidase activity are regulated by a signal induced by activated alpha(2)beta(1) integrin receptor as well as IGF-IR, the expression of these receptors was measured by Western immunoblot analysis. The exposure of the cells to HYD contributed to the increase in IGF-IR expression without any effect on alpha(2)beta(1) integrin receptor and FAK expressions. It was accompanied by a decrease in expression of MAP kinases and NF-kappa B p65, the known inhibitor of collagen gene expression. The data suggest that the HYD-dependent increase of collagen biosynthesis in cultured human skin fibroblasts results from activation of IGF-IR expression and prolidase activity and downregulation of NF-kappa B p65.