The activation of the MAPK/ERK pathway typically begins with the reception of specific external signals by growth factor receptors on the cell surface. This signal first activates the guanyl nucleotide exchange factor (Ras), and the activation of Ras leads to a series of kinase cascade reactions, including Raf, MEK, and ERK (MAPK). During this cascade, Raf kinase phosphorylates and activates MEK, which in turn phosphorylates and activates ERK. The activated ERK migrates to the cell nucleus, phosphorylates, and regulates the activity of multiple transcription factors, such as ELK1, c-Fos, and c-Jun, thereby regulating a variety of biological activities including cell proliferation, differentiation, survival, and death.