Constitutive phosphorylation of MEK in v-fes–overexpressing macrophages.

VFB or KB cells were incubated for 16 to 18 hours in DMEM supplemented with 10% FBS and lysed. Equal amounts of proteins were separated by SDS-PAGE in a 12.5% gel and immunoblotted with α-pMEK1/2 antibody (A) or, after stripping, with α-MEK antibody (B). The graph in C represents the -fold increase of MEK phosphorylation/activity in VFB with respect to KB cells, as determined by band densitometry (arbitrary units, MEK phosphorylation of KB cells being assumed = 1); values referring to MEK phosphorylation (A) were normalized on the basis of those of MEK expression (B).