Mitogen-Activated Protein Kinase Cascades: Terminology and Properties The best-characterized subfamilies of the mitogen-activated protein kinase (MAPK) superfamily are the extracellularly responsive kinases (ERKs) and the two “stress-responsive” MAPK subfamilies, namely, the c-Jun N-terminal kinases (JNKs) and the p38-MAPKs. As yet, no single nomenclature has been determined, and the synonyms c...