THE DUAL-SPECIFICITY MITOGEN-ACTIVATED PROTEIN-KINASE PHOSPHATASE-1 AND PHOSPHATASE-2 ARE INDUCED BY THE P42 P44(MAPK) CASCADE/

Mitogen-activated protein (MAP) kinase phosphatase-1 (MKP-1) and MKP-2 are two members of a recently described family of dual specificity ph osphatases that are capable of dephosphorylating p42/p44(MAPK). Overex pression of MKP-1 or MKP-2 inhibits MAP kinase-dependent intracellular signaling events and fibroblast proliferation. By using specific anti bodies that recognize endogenous MKP-1 and MKP-2 in CCL39 cells, we sh ow that MKP-1 and MKP-2 are not expressed in quiescent cells, but are rapidly induced following serum addition, with protein detectable as e arly as 30 min (MKP-1) or 60 min (MKP-2). Serum induction of MKP-1 and MKP-2 is sustained, with protein detectable up to 14 h after serum ad dition. Induction of MKP-1 and, to a lesser extent, MKP-2 temporally c orrelates with p42/p44(MAPK) inactivation. To analyze the contribution of the MAP kinase cascade to MKP-1 and MKP-2 induction, we examined C CL39 cells transformed with either v-ras or a constitutively active di rect upstream activator of MAP kinase, mitogen-activated protein kinas e kinase-l (MKK-1; MKK-1(SD/SD) mutant). In both cell models, MKP-1 an d MKP-2 are constitutively expressed, with MKP-2 being prevalent. In a ddition, in CCL39 cells expressing an estradiol-inducible Delta Raf-1: :ER chimera, activation of Raf alone is sufficient to induce MKP-1 and MKP-2. The role of the MAP kinase cascade in MKP induction was highli ghted by the MKK-1 inhibitor PD 098059, which blunted both the activat ion of p42/p44(MAPK); and the induction of MKP-1 and MKP-2. However, t he MAP kinase cascade is not absolutely required for the induction of MKP-1, as this phosphatase, but not MKP-2, was induced to detectable l evels by agents that stimulate protein-kinases A and C. Thus, activati on of the p42/p44(MAPK) cascade promotes the induction of MKP-1 and MK P-2, which may then attenuate p42/p44(MAPK)-dependent events in an inh ibitory feedback loop.