MAPK Family

Six groups of MAPK have so far been identified:

1. Extracellular signal-regulated kinases (ERK1, ERK2).
2. c-Jun N-terminal kinases (JNKs)
3. p38 isoforms (MAPK11, MAPK12, MAPK13, MAPK14)
4. ERK5 (MAPK7)
5. ERK3 (MAPK6) and ERK4 (MAPK4)
6. ERK7/8 (MAPK15)

ERK 1 and ERK 2 transduce signals from growth factors and are key in regulating differentiation and proliferation in many cell types. Upon activation by MEK, ERK1 and 2 translocate to the nucleus where they phosphorylate transcription factors such as Elk1 and downstream kinases such as p90 RSK. JNK 1,2 and 3 (sometimes known as SAPKs or stress-activated kinases) and the p38 MAPKs (α-, β-, δ and γ- isoforms) are activated by UV irradiation, inflammatory cytokines and hyperosmolarity. The p38 MAPKs are also activated by lipopolysaccharide. Dysregulation of MAPK kinase pathways has been associated with various diseases including cancer (ERK), neurodegeneration (JNK) and inflammation (p38).