MAPK cascade An intracellular protein kinase cascade containing at least a MAPK, a MAPKK and a MAP3K. The cascade can also contain an additional tiers: the upstream MAP4K. The kinases in each tier phosphorylate and activate the kinase in the downstream tier to transmit a signal within a cell. MAPK signalling MAPK signaling Wikipedia:MAPK_cascade MAPK signal transduction ERK/MAPK cascade MAP kinase cascade MAPKKK cascade during sporulation GO:0007255 biological_process MAP kinase kinase kinase cascade MAPK cascades lie downstream of many cell surface receptors and cooperate in transmitting various extracellular signals to the nucleus. One way by which the specificity of each cascade is regulated is through the existence of several distinct components in each tier of the different cascades. The cascades are typically named according to the component in the MAPK tier. MAPKKK cascade GO:0000165 mitogen-activated protein kinase cascade Wikipedia:Mitogen-activated_protein_kinase signal transduction