MAPK9

MAPK9 Background

Mitogen-activated protein kinase 9 is a protein in humans that is encoded by the MAPK9 gene ^[1]. MAPK9 is also called JNK2 ^[1]. JNK2 is ubiquitously expressed ^[2]. JNK2 exhibits 83% identity and similar regulation to JNK1 ^[3]. Despite the close similarity, the two JNKs differ greatly in their ability to interact with c-Jun. JNK2 binds c-Jun approximately 25 times more efficiently than JNK1 ^[3]. And JNK1 and JNK2 have different, non-redundant roles during toxic liver injury. JNK2 is essential for TNF-mediated apoptosis, whereas JNK1 is not involved in this pathway at all ^[4]. As a serine/threonine-protein kinase, MAPK9/JNK2 is involved in various processes such as cell proliferation, differentiation, migration, transformation, and apoptosis. Extracellular stimuli such as proinflammatory cytokines or physical stress stimulate the stress-activated protein kinase/c-Jun N-terminal kinase (SAP/JNK) signaling pathway. In this cascade, two dual specificity kinases MAP2K4/MKK4 and MAP2K7/MKK7 phosphorylate and activate MAPK9/JNK2. In turn, MAPK9/JNK2 phosphorylates many transcription factors, primarily components of AP-1 such as JUN and ATF2 and thus regulates AP-1 transcriptional activity, eventually inducing cell proliferation, differentiation, and stress responses ^[5-8].

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