Mitogen-activated Protein Kinase (MAPK) Phosphatase 3-mediated Cross-talk between MAPKs ERK2 and p38α

MAPK phosphatase 3 (MKP3) is highly specific for ERK1/2 inactivation via dephosphorylation of both phosphotyrosine and phosphothreonine critical for enzymatic activation. Here, we show that MKP3 is able to effectively dephosphorylate the phosphotyrosine, but not phosphothreonine, in the activation loop of p38 alpha in vitro and in intact cells. The catalytic constant of the MKP3 reaction for p38 alpha is comparable with that for ERK2. Remarkably, MKP3, ERK2, and phosphorylated p38 alpha can form a stable ternary complex in solution, and the phosphatase activity of MKP3 toward p38 alpha substrate is allosterically regulated by ERK2-MKP3 interaction. This suggests that MKP3 not only controls the activities of ERK2 and p38 alpha but also mediates cross-talk between these two MAPK pathways. The crystal structure of bisphosphorylated p38 alpha has been determined at 2.1 angstrom resolution. Comparisons between the phosphorylated MAPK structures reveal the molecular basis of MKP3 substrate specificity.