Mitogen-activated protein kinases (MAPK) are a family of protein kinases involved in cell proliferation, cell differentiation, cell movement, and cell death.

MAPK signaling cascades are organized hierarchically where:

-MAPKs are phosphorylated and activated by MAPK-kinases (MAPKKs),
-MAPKKs are phosphorylated and activated by MAPKK-kinases (MAPKKKs).
-MAPKKKs are in turn activated by interaction with the family of small GTPases and/or other protein kinases, connecting the MAPK module to cell surface receptors or external stimuli.