Modulation of prostaglandin G/H synthase expression in mesangial cells transfected by pp60c-src proto-oncogene

The role of the protein tyrosine kinase pp60c-src in the expression of prostaglandin G/H synthase (PGHS), the key enzyme of prostaglandin synthesis, was investigated in rat renal mesangial cells. Transfection of mesangial cells with the proto-oncogene c-src resulted in nontransformed cells with constitutively enhanced pp60c-src kinase activity. As a control, mesangial cells were transfected with inactive pp60c-src, mutated in position 295 (lysine replaced by methionine). Expression of the constitutive isoform PGHS-1 was enhanced in cells overexpressing wild-type c-src compared to cells transfected with the kinase negative c-src mutant. Levels of other constitutively expressed proteins such as GAPDH and beta-actin were also enhanced. PGHS-2 was barely detectable in resting cells but was inducible by PDGF-AB, PDGF-BB, serotonin, FCS, and calcium ionophore A23187. Induction was diminished in pp60c-src kinase-overexpressing cells, independent of the stimulus used, suggesting interference at a late step in the signaling cascade. No induction of PGHS-2 mRNA was observed in mesangial cells transformed by the oncogene v-src. An increase in intracellular calcium levels is an early step in signal transduction by PDGF and serotonin in mesangial cells. c-src kinase overexpression reduced PDGF- and serotonin-mediated changes in Ca2+ signaling, indicating multiple targets of pp60c-src action. Overexpression of pp60c-src in mesangial cells thus affected basal protein expression, reflected by the enhanced PGHS-1 mRNA and protein expression. With regard to induction of PGHS-2, overexpression of pp60c-src reduced induction by stimuli coupled to different types of signaling pathways.