Abstract 264: The E3 ubiquitin ligase WWP2 regulates stability of the chromatin remodeler ARID1B

Abstract The Switch/sucrose-non-fermentable (SWI/SNF; also known as BRG1 associated factors (BAF)) chromatin remodeling complex functions to slide/evict nucleosomes thus making DNA available for multiple DNA-protein interactions to facilitate cardinal nuclear processes. Work during past two decades has revealed the cardinal role of the BAF complex in modulating tumorigenesis. ARID1B, a well-known tumor suppressor and a key subunit of the cBAF complex, is frequently mutated across various cancer types. Although the downregulation of ARID1B transcript levels has been observed in many cancers, our knowledge about the regulation of ARID1B at the protein level remains meagre. Here, using BioGRID (Biological General Repository for Interaction Datasets) and PDC (Proteomic Data Commons) datasets, multiple ubiquitination sites were predicted to be localized at the C-terminal end of ARID1B. We performed affinity purification followed by mass spectrometry for ARID1B and further mined previously published ARID1B interactome to identify a comprehensive list of potential ARID1B interactors that included several hitherto unidentified proteins. More importantly, this analysis identified WWP1 and WWP2, well characterized E3 ubiquitin ligases, as interacting partners of ARID1B. Interestingly, WWP2 is known to modulate levels of BAF155, another SWI/SNF subunit, via poly-ubiquitination mediated proteasomal degradation. We confirmed the interaction of ARID1B with both WWP1 and WWP2 through bi-directional pull down-immunoblotting assays. Domain mapping of the interaction is currently underway. Ectopic expression of WWP2 resulted in significant downregulation of ARID1B levels. Further, cycloheximide chase assay revealed that wild-type (but not catalytically inactive) WWP2 modulates ARID1B protein stability. Specifically, WWP2 facilitates the K48-linked ubiquitination of ARID1B, leading to the latter's subsequent proteasomal degradation. Interestingly, silencing WWP2 expression results in a decrease in ubiquitination and a subsequent increase in endogenous ARID1B protein levels. Our preliminary observations suggest that ARID1B protein level varies during cell cycle progression. Work is currently underway to determine a possible oncogenic function of WWP2 via downregulation of ARID1B mediated tumor suppression. Our results therefore highlight a novel mechanism of post-translational regulation of ARID1B, which may have implications in the regulation of ARID1B-mediated tumor suppression and cell cycle progression. Given the recent interest to target BAF complex as a therapeutic option in many cancers, our results on regulation of ARID1B protein stability form a foundation for development of possible targeted therapy in cancer. Citation Format: Pradipta Hore, Sandipkumar Bambhaniya, Murali Dharan Bashyam. The E3 ubiquitin ligase WWP2 regulates stability of the chromatin remodeler ARID1B [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 264.