The extracellular-signal-regulated kinase (ERK) pathway is one of the major signaling cassettes of the mitogen activated protein kinase (MAPK) signaling pathway. The ERK cascade is activated by a variety of extracellular agents, including growth factors, hormones and also cellular stresses to induce cellular processes that include mainly proliferation and differentiation, but under some conditions also stress response and others. The main MAPK/ERK kinase kinase (MEKK) components are the Raf family members Raf-1, A-Raf and B-Raf that phosphorylate two serine residues on the MAPK/ERK kinase (MEK) components MEK1/2. ERK1/2 are responsible for stimulating the downstream effectors, many of which are transcription factors. One of the major transcription factors is cyclic AMP response element-binding protein (CREB).
