The exchange factor Ras-GRF2 activates Ras-dependent and Rac-dependent mitogen-activated protein kinase pathways.
Ras and Rac are membrane-associated GTPases that function as molecular switches activating intracellular mitogen-activated protein kinase ( MAPK) cascades and other effector pathways in response to extracellular signals [1]. Activation of Ras and Rac into their GTP-bound conformations is directly controlled by specific guanine-nucleotide exchange factors (GEFs), which catalyze GDP release. Several Ras-specific GEFs that are related to the budding yeast protein Cdc25p have been described, whereas GEFs for Rac-related GTPases contain a region that is homologous to the oncoprotein DbI [2-3]. The Ras-GRF1 and Ras-GRF2 proteins, which couple Ras activation to serpentine receptors and calcium signals, contain both Cdc25 and DbI homology (DH) regions [3-4]. Here, we demonstrate that Ras-GRF2 is a bifunctional signaling protein that is able to bind and activate Ras and Rac, and thereby coordinate the activation of the extracellular-signal-regulated kinase ( ERK) and stress- activated protein kinase (SAPK) pathways.[1]References
- The exchange factor Ras-GRF2 activates Ras-dependent and Rac-dependent mitogen-activated protein kinase pathways. Fan, W.T., Koch, C.A., de Hoog, C.L., Fam, N.P., Moran, M.F. Curr. Biol. (1998) [Pubmed]
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