Extracellular signal-regulated kinases Erk1 (p44 MAPK) and Erk2 (p42 MAPK) Serine/Threonine protein kinase are part of a subfamily of mitogen-activated protein kinases. The p44/42 MAPK (Erk1/2) signaling pathway can be activated in response to a diverse range of extracellular stimuli including mitogens, growth factors and cytokines. Upon stimulation, a sequential three-part protein kinase cascade is initiated consisting of a MAP kinase kinase kinase (MAPKKK or MAP3K), a MAP kinase kinase (MAPKK or MAP2K) and a MAP kinase (MAPK). Phospho-ERK1/2 is negatively regulated by a family of dual-specificity (Thr/Tyr) MAPK phosphatases, known as DUSPs or MKPs (10), along with MEK inhibitors such as U0126 and PD98059.
