Platelet-derived growth factor-induced p21ras-mediated signaling is independent of platelet-derived growth factor receptor interaction with GTPase-activating protein or phosphatidylinositol-3-kinase

Abstrad Stimulation with platelet-derived growth fador (PDGF) results in the association of several 5H2 domain-containing proteins with the activated PDGF receptor, including GAP, a GTPase-adivating protein of p21 ras, and phosphatidylinositol-3-kinase (P1-3K). To investigate the role of GAP-PI-3K receptor interadion in p21 ras signaling, we have used cell lines expressing mutant PDGF receptors that either are impaired in GAP binding or fail to bind both GAP and P1-3K. In these cell lines, PDGF treatment resulted in adivation of extracellular signal-regulated kinase 2 (ERK2), which could be blocked by the expression of a dominant-negative mutant of p21 ras (p21 rasa 7), indicating that these mutations in the PDGF receptor do not abolish p21 ras-mediated adivation of ERK2. In addition, the PDGF-induced increase in levels of p21 rasGTP, as measured either in intad cells or in permeabilized cells, appears to be normal in the cell lines expressing the mutant PDGF receptors. These results indicate that binding of GAP and/or P1-3K to the PDGF receptor is not necessary for PDGF-induced p21 ras adivation and p21 ras-mediated signaling to ERK2. We also show that, in contrast to the adivation of ERK2, PDGF-induced GAP and P1-3K interadion with the PDGF receptor are not inhibited by p21 ras ’ 7 expression, indicating that these interadions do not require p2lras adivation.