MEK5 is a dual specificity protein kinase belonging to thr Ser/Thr protein kinase family, (MAP kinase kinase family). It is activated by phosphorylation on Ser/Thr by MAP kinase kinases and interacts specifically with ERK5, and not with another MAP kinase like P38. This kinase specifically interacts with and activates MAPK7/ERK5. This kinase itself can be phosphorylated and activated by MAP3K3/MEKK3, as well as by atypical protein kinase C isoforms (aPKCs). It is not phosphorylated by RAFA,