| Modification Notes |
Mitogen-activated protein (MAP) kinase cascades are activated by various extracellular stimuli including growth factors. The MEK kinases (also designated MAP kinase kinase kinases, MKKKs, MAP3Ks or MEKKs) phosphorylate and thereby activate the MEKs (also called MAP kinase kinases or MKKs), including ERK, JNK and p38. These activated MEKs in turn phosphorylate and activate the MAP kinases. The MEK kinases include Raf-1, Raf-B, Mos, MEK kinase-1, MEK kinase-2, MEK kinase-3, MEK kinase-4, ASK 1 (MEK kinase-5) and MAP3K6 (MEK kinase-6). MAP3K6, also called ASK 2, activates the JNK kinase pathway but not the ERK or p38 kinase pathways. It is activated by phosphorylation on Thr-806 and is only stable and catalytically active when coupled with ASK 1. Three isoforms exist for MAP3K6 due to alternative splicing. Isoform 1 represents the full length protein. Isoform 2 lacks the amino acid sequences 1-277 and 1075-1288 and contains a unique sequence between amino acid residues 1065-1074. Isoform 3 lacks the amino acid sequence 161-168. |