WDR62 is a novel JNK-binding protein. WDR62 potentiates JNK kinase activity but inhibits AP-1 transcription. Cells transfected with WDR62 display cytoplasmic granular localization. WDR62 is localized to stress granule and activated JNK to processing bodies following arsenite treatment. WDR62 may mediate mRNA fate following stress.

JNK (c-Jun N-terminal kinase) is part of a MAPK (mitogen-activated protein kinase) signalling cascade. Scaffold proteins simultaneously associate with various components of the MAPK signalling pathway and play a crucial role in signal transmission and MAPK regulation. WDR62 (WD repeat domain 62) is a JNK scaffold protein. Recessive mutations within WDR62 result in severe cerebral cortical malformation. In the present study we demonstrate the association of WDR62 with endogenous and overexpressed proteins of both JNK2 and the JNK2-activating kinase MKK7 (MAPK kinase 7). Association of WDR62 with JNK2 and MKK7 occurs via direct protein–protein interactions. We mapped the docking domain of WDR62 responsible for the association with JNK. WDR62 interacts with all JNK isoforms through a D domain motif located at the C-terminus. A WDR62 mutant lacking the putative JNK-binding domain fails to activate and recruit JNK to cellular granules. Furthermore, a synthetic peptide composed of the WDR62 docking domain inhibits JNK2 activity in vitro. WDR62 association with JNK2 requires both the JNK CD and ED domains, and the binding requisite is distinct from that of the previously described JNK2 association with JIP1 (JNK-interacting protein 1). Next, we characterized the association between WDR62 and MKK7. WDR62 associates directly with the MKK7β1 isoform independently of JNK binding, but fails to interact with MKK7α1. Furthermore, MKK7β1 recruits a protein phosphatase that dephosphorylates WDR62. Interestingly, a premature termination mutation in WDR62 that results in severe brain developmental defects does not abrogate WDR62 association with either JNK or MKK7. Therefore such mutations represent a loss of WDR62 function independent of JNK signalling.

Background: WDR62 is a JNK scaffold protein. Results:We identified at the WDR62 C terminus a loop-helix domain that is responsible for its homodimerization and association with another JNK scaffold protein, MAPKBP1. WDR62 dimerization is required for JNK and MKK7␤1 recruitment. Conclusion: WDR62 dimerization is required for its scaffolding function. Significance: Scaffold protein association offers another layer of complexity for the fine tuning of signaling pathways.

High grade serous carcinoma (HGSC) is the most common subtype of ovarian cancer and it is now widely accepted that this disease often originates from the fallopian tube epithelium. PAX8 is a fallopian tube lineage marker with an essential role in embryonal female genital tract development. In the adult fallopian tube, PAX8 is expressed in the fallopian tube secretory epithelial cell (FTSEC) and its expression is maintained through the process of FTSEC transformation to HGSC. We now report that PAX8 has a pro-proliferative and anti-apoptotic role in HGSC. The tumor suppressor gene TP53 is mutated in close to 100% of HGSC; in the majority of cases, these are missense mutations that endow the mutant p53 protein with potential gain of function (GOF) oncogenic activities. We show that PAX8 positively regulates the expression of TP53 in HGSC and the pro-proliferative role of PAX8 is mediated by the GOF activity of mutant p53. Surprisingly, mutant p53 transcriptionally activates the expression of p21, which localizes to the cytoplasm of HGSC cells where it plays a non-canonical, pro-proliferative role. Together, our findings illustrate how TP53 mutations in HGSC subvert a normal regulatory pathway into a driver of tumor progression.