Platelet-derived growth factor (PDGF) binding promotes physical association of PDGF receptor with phospholipase C

Phospholipase C (PLC)-mediated production of inositol trisphosphate and diacylglycerol is stimulated by binding of platelet-derived growth factor (PDGF) to cell-surface receptors. Antibodies recognizing native PDGF receptors through peptide-domain epitopes coprecipitated 4-fold more PLC activity with receptors from PDGF-stimulated than from unstimulated BALB/c 3T3 cells, despite equivalent PDGF receptor recovery. Activity coprecipitated from unstimulated cells was comparable to nonspecific activity recovered with preimmune sera or in the presence of competing peptide immunogen. PLC activity coprecipitating with PDGF receptors represented 60% of anti-phosphotyrosine antibody-recovered activity from PDGF-stimulated cells. Coprecipitation was rapidly induced in cells treated with PDGF at 4 degrees C, reversibly lost with acid dissociation of PDGF from receptors, and recovered with PDGF readdition. PDGF concentrations effecting coprecipitation correlated with stimulation of intact-cell inositol phosphate production. Monoclonal antibodies to PLC gamma (145 kDa) coprecipitated from PDGF-stimulated cell lysates (but not from unstimulated cell lysates) tyrosine kinase activity that phosphorylated PDGF receptor and PLC gamma. Stable physical association of PDGF receptors with PLC may participate in coupling ligand binding to increased PLC activity.