ERK, or extracellular signal-regulated kinase, is a protein kinase that plays a crucial role in the mitogen-activated protein kinase (MAPK) signaling pathway. It is involved in various cellular processes, including cell growth, differentiation, and survival. ERK is activated by various growth factors and hormones, which trigger a cascade of signaling events within the cell. Once activated, ERK translocates to the nucleus, where it can influence gene expression by phosphorylating specific transcription factors. This process helps regulate important biological functions, such as cell division and response to stress. Dysregulation of ERK signaling is associated with several diseases, including cancer.