Abstract Thu033: SUMO2/3 excludes YAP5SA from the nucleus and inhibits cardiomyocyte proliferation

Background: Adult mammals, including humans, have limited cardiomyocyte (CM) regeneration, so cardiac injuries, such as myocardial infarction (MI), cause permanent damage and impaired heart function, leading to heart failure. In adult hearts, Hippo signaling is active and prevents CM proliferation by repressing the YAP1 transcription co-factor. However, a constitutively active form of YAP1, known as YAP5SA, bypasses this regulation and promotes adult CM proliferation in mice. We aimed to understand how YAP5SA nuclear and cytoplasmic localization contribute to CM proliferation and find interactors that regulate this process. Methods: We used co-immunoprecipitation (Co-IP) and mass spectrometry (MS), immunofluorescence (IF) staining and western blotting (WB) to determine YAP5SA subcellular localization and its interactors. We then used pharmacologic reagents, adeno-associated viruses, and genetic mouse models to determine if inhibition of SUMO2/3, a YAP5SA interactor, affects subcellular YAP5SA localization and CM proliferation. Results: Using Co-IP and MS, we found SUMO2/3 to be a YAP5SA interactor and upregulated in YAP5SA-expressing hearts. We confirmed the interactions using IF and WB. IF showed colocalization of YAP5SA and SUMO2/3, which moved from the nucleus into the cytoplasm over six days after tamoxifen-induced activation of YAP5SA. To assess the role of SUMO 2/3 in CM proliferation, we inhibited SUMOylation and found increased nuclear YAP5SA, sarcomere disassembly, and cell cycle activity in CMs. Conclusions: These findings suggest that SUMOylation plays a crucial role in regulating the nuclear localization of YAP, and its inhibition may improve the efficacy of YAP-based therapeutics for cardiac renewal.