c-Jun N-terminal kinases (JNKs) phosphorylate and augment transcriptional activity of c-Jun. JNKs originate from three genes that yield 10 isoforms through alternative mRNA splicing, including JNK1a1,JNK1b1, JNK2a1, JNK2b1, and JNK3a1, which represent the p46 isoforms, and JNK1a2, JNK1b2, JNK2a2, JNK2b2, and JNK3b2, which represent the p54 isoforms. JNKs coordinate cell responses to stress and influence regulation of cell growth and transformation. Members of the MAP kinase family are activated by dual phosphorylation at a Thr-Pro-Tyr motif, specifically at Thr-183 and Tyr-185 residues, in response to ultraviolet (UV) light. This motif is divergent from the Thr-Glu-Tyr motif characteristic of the MAP kinase family. JNK is phosphorylated by JNK-activating kinase (JNKK1 and JNKK2), which are members of the MEK family.
