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Analysis of R-Ras signalling pathways
A J Self1, E Caron, H F Paterson
1MRC Laboratory for Molecular Cell Biology, CRC Oncogene and Signal Transduction Group, University College London, Gower Street, London WC1E 6BT, UK.
Abstract:
R-Ras has a high degree of sequence homology to Ras and to other members of the Ras subfamily including Rap, TC21 and M-Ras. Activated versions of Ras 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 with many of the same proteins as Ras and TC21, including c-Raf1, and can induce transformed foci, although this activity is weak compared to Ras and appears to be cell-type specific. Here, we have investigated R-Ras signalling pathways in a variety of cell types. We find that microinjection of activated R-Ras into quiescent fibroblasts stimulates cell cycle progression through G(1) phase and subsequent DNA synthesis. However, unlike Ras, R-Ras does 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 spreading, consistent with R-Ras having a role in integrin activation. Finally, in a macrophage cell line, R-Ras activates the alpha(M)beta(2) integrin via the small GTPase Rap1, leading to phagocytosis of opsonized red blood cells, whereas Ras does not. These results indicate that R-Ras has an important role in the regulation of cell growth and adhesion, but that this is mediated through downstream signals distinct from those used by Ras.
Insights
Ras-related protein R-Ras regulates cell growth and adhesion through distinct pathways. Unlike Ras, R-Ras does not activate ERK MAP kinase but influences cell cycle and integrin activation, impacting cellular functions.
Area of Science:
- Cell Biology
- Molecular Biology
- Signal Transduction
Background:
- Ras-related protein R-Ras shares homology with Ras and other Ras subfamily members.
- Activated Ras and TC21 proteins are transforming, and mutated forms are found in human tumors.
- R-Ras interacts with proteins like c-Raf1 and can induce transformed foci, though weakly and cell-type specifically.
Purpose of the Study:
- To investigate R-Ras signaling pathways in various cell types.
- To elucidate the downstream signaling mechanisms of R-Ras in cellular processes.
- To differentiate R-Ras signaling from that of Ras.
Main Methods:
- Microinjection of activated R-Ras into quiescent fibroblasts and PC12 cells.
- Analysis of MAP kinase pathway activation (ERK, JNK, p38/Mpk2).
- Investigation of integrin activation and phagocytosis in a macrophage cell line.
Main Results:
- Microinjected R-Ras stimulated cell cycle progression and DNA synthesis in fibroblasts.
- R-Ras did not activate ERK, JNK, or p38/Mpk2 MAP kinase pathways.
- R-Ras induced cell spreading in PC12 cells and activated alpha(M)beta(2) integrin via Rap1 in macrophages, leading to phagocytosis.
Conclusions:
- R-Ras plays a significant role in regulating cell growth and adhesion.
- R-Ras mediates its effects through downstream signaling pathways distinct from those of Ras.
- These findings highlight R-Ras as a regulator of integrin-mediated processes like phagocytosis.