DIFFERENTIAL REGULATION OF NEUROFIBROMIN AND P120 GTPASE-ACTIVATING PROTEIN BY NUTRITIONALLY RELEVANT FATTY-ACIDS

Arachidonic acid, phosphatidic acid and other lipids inhibit the catal ytic fragment of neurofibromin more potently than that of p120 guanosi ne triphosphatase-activating protein (GAP). The effects of fatty acids other than arachidonic acid on full-length neurofibromin and p120 GAP , to our knowledge, have not been studied In this study, we analyzed t he effects of eight nutritionally relevant fatty acids on guanosine tr iphosphatase (GTPase) stimulatory activity of full-length neurofibromi n and p120 GAP. The fatty acids tested were saturated stearic acid, mo nounsaturated oleic acid, and three n-6 and three n-3 polyunsaturated fatty acids. Analysis was performed by Pas immunoprecipitation GTPase assay. The full-length p120 GAP expressed in insect Sf9 cells and immu noaffinity-purified full-length neurofibromin were used. In contrast t o neurofibromin, which was readily inhibited by stearic and oleic acid , p120 GAP was only weakly inhibited even at high concentrations (>80 mu M). Neurofibromin was also two-to threefold more sensitive to inhib ition by other fatty acids tested. A chimeric protein in which the neu rofibromin catalytic domain was fused to the NH2-terminal sequences of p120 GAP was used to determine that differential sensitivity to fatty acid inhibition maps to the catalytic domain of the proteins. These r esults indicate that nutritionally relevant fatty acids can modulate t he GTPase function of c-Ha-Ras protein by inhibiting GTPase stimulator y activity of two Pas regulators, full-length neurofibromin and p120 G AP, at physiologically relevant concentrations in vitro.