Ras Signaling Pathway
Ras activates many signaling cascades. Here we illustrate some of the well-characterized cascades in a generic compilation of effector molecules. The effectors mediate Ras stimulation to a diverse set of cellular signals. Many of these signals are interpreted differently depending on the cell type or microenvironment receiving the stimulus. Not all of these effectors are activated in any given cell type. The primary method of activation is to promote the translocation of the molecule to the plasma membrane where additional interactions lead to the activation of the molecule.RalGDS is a Guanine Exchange Factor (GEF) for Ral but also has other independent functions. RalGDS activates RalA/B-related small GTPases. RalBP1 is a GTPase activating protein that leads to the inhibition of the Rac and CDC42 GTPases. Ral can also interact with phospholipase D1 (PLD1) that can also be activated by RhoA. Ras stimulation of the lipid kinase activity of PI3K occurs through an interaction with the p110 catalytic subunit. PI3K phosphorylates the D3 position of phosphatidylinositides. In this example Pip2 is converted to PIP3. PIP3 stimulates the AKT/PKB kinase and several of the Rac-GEF’s such as Sos1 AND Vav. AKT activation inhibits apoptosis by inhibiting the actions of Bad, Caspase9 and AFX. AKT further hinders apoptosis by phosphorylating the IkB repressor of NFkB. Stimulus of Rac causes among other things (see RacPathway) the activation of NFkB. Ras also stimulates the mitogen-activated kinases ERK1/2 via the Raf1 cascade. The Erk kinases translocate to the nucleus where they phosphorylate various transcription factors such as ELK1
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