Figure 2.

Mitogen-activated protein kinase (MAPK) signaling cascades. MAPK signaling cascades are organized hierarchically into three-tiered modules. MAPKs are phosphorylated and activated by MAPK kinases (MAP2K), which in turn are phosphorylated and activated by MAP2K kinases (MAP3K). MAP3Ks are activated by several modes, including interaction with the family of small GTPases and/or other protein kinases, connecting the MAPK module to cell surface receptors or external stimuli. MAPK cascades activation results in a diverse set of biological responses depending on stimulus and cellular context.