To stimulate cells to proliferate, differentiate or undergo apoptosis, extracellular signals need to be relayed to the nucleus where they alter the pattern of gene expression. One of the main mechanisms for relaying such signals involves a group of proteins called the mitogen-activated protein kinases (MAPK). These enzymes are proline-directed serine/threonine kinases that are activated by dual phosphorylation of threonine and tyrosine residues in response to diverse extracellular stimuli. Small molecules that inhibit MAPKs, such as U0126, are important for understanding cell signaling.
Cell Notes 22, 15–17.