Palmitoylation regulates vesicular trafficking of R-Ras to membrane ruffles and effects on ruffling and cell spreading

Abstract

In this study we investigated the dynamics of R-Ras intracellular trafficking and its contributions to the unique roles of R-Ras in membrane ruffling and cell spreading. Wild type and constitutively active R-Ras localized to membranes of both Rab11- and transferrin-positive and -negative vesicles, which trafficked anterograde to the leading edge in migrating cells. H-Ras also co-localized with R-Ras in many of these vesicles in the vicinity of the Golgi, but R-Ras and H-Ras vesicles segregated proximal to the leading edge, in a manner dictated by the C-terminal membrane-targeting sequences. These segregated vesicle trafficking patterns corresponded to distinct modes of targeting to membrane ruffles at the leading edge. Geranylgeranylation was required for membrane anchorage of R-Ras, whereas palmitoylation was required for exit from the Golgi in post-Golgi vesicle membranes and trafficking to the plasma membrane. R-Ras vesicle membranes did not contain phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P(3)), whereas R-Ras co-localized with PtdIns(3,4,5)P(3) in membrane ruffles. Finally, palmitoylation-deficient R-Ras blocked membrane ruffling, R-Ras/PI3-kinase interaction, enrichment of PtdIns(3,4,5)P(3) at the plasma membrane, and R-Ras-dependent cell spreading. Thus, lipid modification of R-Ras dictates its vesicle trafficking, targeting to membrane ruffles, and its unique roles in localizing PtdIns(3,4,5)P(3) to ruffles and promoting cell spreading.