RAF kinases have restricted substrate specificity and have a...

created [InstanceEdit:5672604] Rothfels, Karen, 2015-02-05
dbId 5672603
displayName RAF kinases have restricted substrate specificity and have a...
modified [InstanceEdit:5678728] Rothfels, Karen, 2015-02-26
schemaClass Summation
text RAF kinases have restricted substrate specificity and have as their primary substrates the two MAP2K proteins MAP2K1 and MAP2K2 (also known as MEK1 and 2). MAP2K1 knockout is embryonic lethal in mice, while MAP2K2 knockouts have no apparent abnormalities, suggesting that MAP2K1 can compensate for MAP2K2 in vivo (Giroux et al, 1999; Belanger et al, 2003). MAP2K proteins exist as stable homo- and heterodimers independent of growth factor stimulation and are generally recruited to activated RAF proteins in conjunction with a scaffolding protein and the MAP2K substrates, MAPK1 and 3 (also known as ERK1 and 2) (Ohren et al, 2004; Catalanotti et al, 2009; Catling et al, 1995; reviewed in Matallanas et al, 2011; Roskoski et al, 2012a; Roskoski et al, 2012b).

Scaffolding proteins promote signaling by providing a docking platform that colocalizes components of the signaling cascade, and provide specificity by controlling the spatial and temporal regulation of the pathway (reviewed in Brown and Sacks, 2009; Matallanas et al, 2011). KSR1 and 2, CNKSR1 and 2, IQGAP1 and the beta arrestins are among the known MAPK scaffold proteins that act at the plasma membrane upon MAPK pathway activation; in addition, paxillin localizes MAPK pathway components to focal adhesion sites in the plasma membrane (Roy et al, 2005; Ren et al, 2007; DeFea et al, 2000; Togho et al, 2003; Ishibe et al, 2003; reviewed in Claperon and Therrien, 2007; Brown and Sacks, 2009; Matallanas et al, 2011). Although this reaction depicts these scaffolding proteins acting equivalently, the details of how they promote pathway activation vary. For instance, KSR1 and 2 are constitutively bound to MAP2K dimers but recruit MAPKs only upon pathway stimulation, while IQGAP1 associates constitutively with both MAP2K and MAPK proteins in unstimulated cells and shows increased interaction with MAP2K1 upon pathway activation by EGF (Stewart et al, 1999; Cacace et al, 2000; Muller et al, 2000; Roy et al, 2004; Roy et al, 2005; reviewed in Brown and Sacks, 2009). Scaffolding complexes may be particularly important for the phosphorylation of cytosolic MAPK targets (reviewed in Casar et al, 2009).
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