Figure 1.

The mammalian MAP kinase cascade. ASK1 and ASK2 belong to the MAPKKK family, whose members respond to various external stimuli and initiate the MAPK cascade. There are at least 20 MAPKKKs in vertebrates that selectively phosphorylate and activate MAPKKs leading to a specific activation profile of MAPK family members. The ASK family can activate the JNK and p38 pathways but not the ERK pathway.