p38, JNK, and ERK5 are regulated by different protein kinase cascades. Various MAPKK kinases, including MLK3, and TAK, can regulate p38. MEK3 and MEK6 are MAPK kinases that phosphorylate and activate p38 (a MAP kinase). MEKK1 and MEKK4 are among the MAPKK kinases that regulate JNK. MEK4 and MEK7 are MAPK kinases that phosphorylate and activate JNK (a MAP kinase). MEKK2 and MEKK3 are MAPKK kinases that can regulate ERK5. MEK5 is a MAPK kinase that phosphorylates and activates ERK5 (a MAP kinase).