Differential regulation of transforming growth factor-β receptors type I and II by platelet-derived growth factor in human dermal fibroblasts

Background Elevated expression of platelet-derived growth factor (PDGF) and transforming growth factor (TGF)-beta have been observed in a number of fibrotic diseases, including systemic sclerosis (SSc). This suggests a possible interaction between these factors in establishing a profibrotic programme in dermal fibroblasts. Objectives To examine the effects of PDGF isoforms on the expression of TGF-beta receptors in human dermal fibroblasts. Methods Steady-state mRNA levels of TGF-beta receptor I and II (T betaR-I and T betaR-II) were analysed by northern blot. T betaR-I protein levels were analysed by immunoprecipitation of S-35 metabolically labelled cells. T betaR-II protein levels were analysed by western blot. Results Steady-state mRNA levels of T betaR-I and T betaR-II were induced in response to PDGF isoforms. PDGF-AA and PDGF-AB stimulated both receptors with similar potency, whereas PDGF-BB was less potent. The MEK1 (mitogen-activated protein kinase [MAPK] or extracellular signal regulated kinase) inhibitor, PD98059, abrogated the stimulatory effect of PDGF-AB. In contrast to mRNA levels, only TPR-II protein levels were elevated in response to PDGF. Conclusions These data suggest that PDGF receptor alpha and MAPK mediate stimulation of TGF-beta receptors by PDGF. Furthermore, TGF-beta receptor protein levels are discordantly regulated by PDGF.