c-Jun N-terminal kinases (JNKs), were originally identified as
kinases that bind and
phosphorylate c-Jun on
Ser-63 and Ser-73 within its transcriptional activation domain. They belong to the
mitogen-activated protein kinase family, and are responsive to stress stimuli, such as
cytokines,
ultraviolet irradiation, heat shock, and
osmotic shock. They also play a role in
T cell differentiation and the cellular
apoptosis pathway. Activation occurs through a dual phosphorylation of
threonine (Thr) and
tyrosine (Tyr) residues within a Thr-
Pro-Tyr motif located in kinase subdomain VIII. Activation is carried out by two MAP kinases,
MKK4 and
MKK7 and JNK can be inactivated by Ser/Thr and Tyr
protein phosphatases. It has been suggested that this signaling pathway contributes to inflammatory responses in mammals and insects.