ERK3/MAPK6

null ERK3 (MAPK6) is an atypical MAP kinase that departs from the family in several respects. Its activation segment contains a single SEG phospho-acceptor motif instead of the canonical TEY, it is not activated by MEK1/2 or by stress stimuli, and it is constitutively phosphorylated in cells. A long C-terminal extension mediates binding to MAPK-activated protein kinase 5, the principal known substrate, which ERK3 activates and stabilizes. Protein levels are controlled by ubiquitin-dependent degradation. ERK3 supports endothelial cell migration and angiogenesis, and knockout mice show growth retardation with poor neonatal survival. Recombinant ERK3 is used for atypical-MAPK biochemistry and inhibitor screening.