Negative regulation of MAPKK by phosphorylation of a conserved serine residue equivalent to Ser212 of MEK1

Abstract

The MAPKKs MEK1 and MEK2 are activated by phosphorylation, but little is known about how these enzymes are inactivated. Here, we show that MEK1 is phosphorylated in vivo at Set212, a residue conserved among all MAPKK family members. Mutation of Ser212 to alanine enhanced the basal activity of MEK1, whereas the phosphomimetic aspartate mutation completely suppressed the activation of both wild-type MEK1 and the constitutively activated MEK1(S218D/S222D) mutant. Phosphorylation of Set212 did not interfere with activating phosphorylation of MEK1 at Ser218/Ser222 or with binding to ERK2 substrate. Importantly, mimicking phosphorylation of the equivalent Ser212 residue of the yeast MAPKKs Pbs2p and Ste7p similarly abrogated their biological function. Our findings suggest that Ser212 phosphorylation represents an evolutionarily conserved mechanism involved in the negative regulation of MAPKKs.