The Effect of GTPase Activating Protein Upon Ras Is Inhibited by Mitogenically Responsive Lipids

Abstract

Bacterially synthesized c-Ha-ras protein (Ras) was incubated with guanosine triphosphatase (GTPase) activating (GA) protein in the presence of various phospholipids. The stimulation of Ras GTPase activity by GA protein was inhibited in some cases. Among the lipids most active in blocking GA protein activity were lipids that show altered metabolism during mitogenic stimulation. These included phosphatidic acid (containing arachidonic acid), phosphatidylinositol phosphates, and arachidonic acid. Other lipids, including phosphatidic acid with long, saturated side chains, diacylglycerols, and many other common phospholipids, were unable to alter GA protein activity. The interaction of lipids with GA protein might be important in the regulation of Ras activity during mitogenic stimulation.

Arachidonic acid mediates angiotensin II effects on p21ras in renal proximal tubular cells via the tyrosine kinase-Shc-Grb2-Sos pathway

“…It has been reported that arachidonic acid and other fatty acids can activate ras by inhibition of GTPase-activating proteins; however, this paradigm has not been show to be a functional signaling model in intact cells (9). Furthermore, the concentrations of arachidonic acid and other fatty acids used were significantly higher than those used in the present study (9,10).…”

“…The ratio of GTP͞GDP bound to p21ras is regulated by both guanine nucleotide exchange factors, which catalyze GDP release and GTP binding (11)(12)(13), and the GTPase-activating protein, which stimulates the intrinsic p21ras GTPase activity (9,10). It has been reported that arachidonic acid and other fatty acids can activate ras by inhibition of GTPase-activating proteins; however, this paradigm has not been show to be a functional signaling model in intact cells (9). Furthermore, the concentrations of arachidonic acid and other fatty acids used were significantly higher than those used in the present study (9,10).…”

“…We reasoned that p21ras activation by Ang II in kidney epithelial cells and other cell types may involve arachidonic acid as a critical mediator because arachidonic acid release is common to many signaling pathways (PLA 2 , PLD, and PLC). Earlier studies indicated that arachidonic acid, its metabolites, and other fatty acids inhibited GTPase-activating proteins (GAPs) thereby allowing p21ras to remain in its active GTP bound form (9,10). …”

Endothelin-1 activates phospholipase D and thymidine incorporation in fibroblasts overexpressing protein kinase C beta 1.

“…The direct product of PLD activity, PA, and its lyso derivative have also been suggested to play possible second messenger roles in the regulation of cell growth (Jalink et aL., 1990;Tsai et al, 1990). These observations along with our results emphasize the potential importance of PLD activation in the mitogenic response.…”

Cancer cachexia

“…It is most likely that the mitogenic effect results from the release of polyunsaturated fatty acids such as linoleic or arachidonic acids. Phospholipids containing such polyunsaturated fatty acids, esterfied to the sn-2 position of the glycerol moiety, have been shown to stimulate cell growth (Imagawa et al, 1989), possibly by inhibiting a guanosine triphosphatase activating protein, which in turn inactivates the ras protein (Tsai et al, 1989). This suggests that these lipids can potentiate ras functions.…”