PLATELET-DERIVED GROWTH FACTOR-INDUCED P21RAS-MEDIATED SIGNALING IS INDEPENDENT OF PLATELET-DERIVED GROWTH-FACTOR RECEPTOR INTERACTION WITHGTPASE-ACTIVATING PROTEIN OR PHOSPHATIDYLINOSITOL-3-KINASE

Stimulation with platelet-derived growth factor (PDGF) results in the association of several SH2 domain-containing proteins with the activat ed PDGF receptor, including GAP, a GTPase-activating protein of p21ras , and phosphatidylinositol-3-kinase (PI-3K). To investigate the role o f GAP-PI-3K receptor interaction in p21ras signaling, we have used cel l lines expressing mutant PDCF receptors that either are impaired in C AP binding or fail to bind both CAP and PI-3K. In these cell lines, PD CF treatment resulted in activation of extracellular signal-regulated kinase 2 (ERK2), which could be blocked by the expression of a dominan t-negative mutant of p21ras (p21ras(asn17)), indicating that these mut ations in the PDCF receptor do not abolish p21ras-mediated activation of ERK2. In addition, the PDGF-induced increase in levels of p21rasGTP , as measured either in intact cells or in permeabilized cells, appear s to be normal in the cell lines expressing the mutant PDGF receptors. These results indicate that binding of CAP and/or PI-3K to the PDGF r eceptor is not necessary for PDGF-induced p21ras activation and p21ras -mediated signaling to ERK2. We also show that, in contrast to the act ivation of ERK2, PDGF-induced CAP and PI-3K interaction with the PDGF receptor are not inhibited by p21ras(asn17) expression, indicating tha t these interactions do not require p21ras activation.