FIG. 1.
Canonical mitogen-activated protein kinase (MAPK) signaling. MAPK are prototypically activated by canonical three-tiered sequential phosphorylation events. The most well-known MAPKKK and MAPKK are listed for each MAPK; however, this is only a small representation of all identified upstream kinases. Furthermore, multiple steps may exist between the cell stimulus and activation of the MAPKKK and between activation of the MAPK and the biological response.