JNK (c-Jun N-terminal kinase), a kinase subfamily belonging to the MAPK, is activated in response to various stress stimuli and possesses a wide variety of regulatory functions. The JNK family of serine/threonine protein kinases comprises three isoforms (JNK1, JNK2 and JNK3). JNKs are involved in the emergence and progression of diverse pathologies such as neurodegenerative, cardiovascular and metabolic disorders as well as inflammation and cancer.
Similar to the other MAP kinases, JNKs are activated by a phosphorylation cascade generally involving two types of upstream kinases, the so-called MAP kinase kinase kinases (MAP3K, MKKK) and the MAP kinase kinases (MAP2K; MKK). At the MAP2K level, JNKs are activated by MKK4 and MKK7, the former is a common activator of the JNK and the p38 MAP kinase signaling pathway. The JNK cascade shares various intersection points with other pathways making it a part of a complex signaling network.