Additionally, WDR62 (WD repeat domain 62) has been implicated in noncanonical activation of JNK via association with JNK and MKK7. In response to stress resulting from X-rays and genotoxic drugs, RACK1 (Receptor for Activated C Kinase 1) has been shown to bind and activate JNK1 and MTK1. Following cleavage by caspase-3, the C-terminal domain of GRASP1 is released to promote activation of JNK. In neurons, GRASP-1 (GRIP1-associated protein 1) binds both JNK1 and MEKK1. In 2016, another MKP, DUSP22, was reported to interact with ASK1, MKK7, and JNK1 to promote JNK activation independent of its phosphatase activity. DUSP19 physically interacts with MKK7 and indirectly regulates JNK. ĭUSP19 (dual-specificity phosphatase 19) is the first MAPK phosphatase (MKP) identified as a scaffold protein. Crk II activates HPK1 (hematopoietic progenitor kinase 1) and SEK1-dependent activation of the JNK pathway, by recruiting JNK1 to a p130Cas multiprotein complex. β-Arrestin-2 contains a MAP kinase docking site and mainly functions as a scaffold protein in activation of JNK3, by tethering ASK1, SEK1, and JNK3. JIP1 recruits DLK, MKK7, and JNK as a complex, whereas JIP3 binds SEK1 and MEKK1 to stimulate SEK1, leading to JNK3 activation. Scaffolds JIP1 (JNK-interacting protein 1) and JIP3 recruit several different activators and JNKs. POSH complexes with and sequentially stimulates RAC1, MLKs, SEK1, MKK7, and JNKs. The scaffold proteins POSH (plenty of SH3s) promote JNK pathway activation by directly interacting with GTP-bound RAC1. In melanoma cells, filamin was found to interact with SEK1 as a scaffold protein, in response to TNF-α stimulation. Several scaffold proteins have been identified that bind to JNKs and upstream activators. Scaffold proteins play key roles in providing a platform for signaling molecules to assemble, promoting the localization of signaling molecules at specific sites and coordinating positive and negative feedback signals for pathway regulation. Johnson, in Targeting Cell Survival Pathways to Enhance Response to Chemotherapy, 2019 4.2.3 The Role of Scaffold Proteins
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