Analysis of R-Ras signalling pathways

R-Ras has a high degree of sequence homology to Ras and to other members of the Ras subfamily including Rap, TC21 and ill-Ras. Activated versions of R as and TC21 are highly transforming in a variety of cell lines and mutated forms of both proteins have been found in human tumours, R-Ras interacts wi th many of the same proteins as Res and TC21, including c-Raf1, and call in duce transformed foci, although this activity is weak compared to Ras and a ppears to be cell-type specific, Here, we have investigated R-Ras signallin g pathways in a variety of cell types, We find that microinjection of activ ated R-Ras into quiescent fibroblasts stimulates cell cycle progression thr ough G(1) phase and subsequent DNA synthesis. However, unlike Bas, R-Ras do es not activate the ERK MAP kinase pathway nor does it activate the JNK or p38/Mpk2 MAP kinase pathways. microinjection of R-Ras into PC12 cells does not induce terminal differentiation, but instead causes extensive cell spre ading, consistent with R-Ras having a role in integrin activation. Finally, in a macrophage cell line, R-Ras activates the alphaM beta (2) integrin ri a the small GTPase Rapt, leading to phagocytosis of opsonized red blood cel ls, whereas Ras does not, These results indicate that R-Ras has an importan t role in the regulation of cell growth and adhesion, but that this is medi ated through downstream signals distinct from those used by Ras.