IndraLab

"PP2 might inhibit Raf-mediated activation of MEK1 by reducing MEK1 S298 phosphorylation, or alternatively might reduce Raf activity directly, because Src phosphorylation of Raf has been shown to increase its activity (Fabian et al., 1993; Marais et al., 1995)."

"Because Src-dependent MEK1 S298 phosphorylation is required for adhesion-mediated activation of MEK ( xref ) and subsequent MAPK activation ( xref ), we examined the effect of Src inhibition on phospho-MAPK localization in REF52 cells."

"Inhibition of Src family kinases with PP2 not only inhibited MEK1 S298 phosphorylation, but also decreased phosphorylation of both MEK and MAPK on their respective activating sites in response to adhesion."

"FAK and Src positively regulate phosphorylation of MEK1 on S298 by PAK1."

"We propose that FAK and Src dependent PAK phosphorylation of MEK1 on S298 is central to the organization and localization of active Raf-MEK1-MAPK signaling complexes and that formation of such complexes underlies the observed adhesion dependence of growth factor signaling to MAPK."

"In addition to regulating MEK1 S298 phosphorylation, PP2 treatment virtually eliminated MEK activation measured by S218/S222 phosphorylation and significantly decreased MAPK phosphorylation in response to FN stimulation (Fig. 7 A). At least two mechanisms exist by which MEK1 activation could be blocked by the Src inhibitor. Because S298 phosphorylation is necessary for MEK1 activation upon adhesion and is blocked by PP2, Src might regulate activation through its effects on S298 phosphorylation. Alternatively, because Src is reported to phosphorylate and activate Raf (Fabian et al., 1993; Marais et al., 1995), PP2 might function to decrease Raf activation upon adhesion in addition to regulating S298 phosphorylation."

"We propose that FAK and Src dependent, PAK1 mediated phosphorylation of MEK1 on S298 is central to the organization and localization of active Raf-MEK1-MAPK signaling complexes, and that formation of such complexes contributes to the adhesion dependence of growth factor signaling to MAPK."

"In addition to regulating MEK1 S298 phosphorylation, PP2 treatment virtually eliminated MEK activation measured by S218/S222 phosphorylation and significantly decreased MAPK phosphorylation in response to FN stimulation (Fig. 7 A). At least two mechanisms exist by which MEK1 activation could be blocked by the Src inhibitor. Because S298 phosphorylation is necessary for MEK1 activation upon adhesion and is blocked by PP2, Src might regulate activation through its effects on S298 phosphorylation."