Figure 1.

Mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) pathway. The MAPK/ERK signaling pathway is activated by many different extracellular signals such as binding of growth factors (e.g., EGF) to its receptors (e.g., EGFR). Activated receptor tyrosine kinase phosphorylates and activates RAS family proteins through GRB2-SOS adaptor protein complex. Activated RAS protein, in turn, activates the serine/threonine kinase function of RAF proteins. RAF phosphorylates MEK, which phosphorylates and activates ERK, initiating the signal transduction of many genes involved in various cellular processes.