E3 ubiquitin ligase targets nucleolin and modulates its phase separation to suppress ribosome biogenesis in myocardial infarction hearts

Background Myocardial infarction (MI) continues to pose a major global health challenge, largely because coronary interventions exhibit limited long-term efficacy due to insufficient cardiomyocyte (CM) regeneration. Ribosome biogenesis, a central driver of cellular regeneration, and Nucleolin (NCL), a known cardioprotective protein, have both been recognized as critical factors in post-MI recovery. While liquid–liquid phase separation (LLPS) plays an active regulatory role in cellular processes, its influence on NCL-mediated ribosome biogenesis after MI remains poorly understood. Aims To elucidate the molecular mechanisms by which NCL regulates ribosome biogenesis in the setting of myocardial infarction. Methods We employed Ribo-Halo, Ribo-disome, and AgNOR staining to profile ribosome biogenesis, together with co-immunoprecipitation, molecular docking, FRAP, and confocal imaging to investigate NCL ubiquitination and LLPS dynamics. Results In MI mouse models and hypoxic cells, we observed an inverse correlation between the E3 ubiquitin ligase β-TrCP and NCL protein levels. β-TrCP directly targeted NCL for proteasomal degradation in the cytoplasm, while hypoxia promoted the transition of nuclear NCL into a liquid-droplet state via LLPS. Depletion of NCL impaired ribosome biogenesis and hindered CM renewal. Conclusion Our findings demonstrate that MI activates the E3 ligase β-TrCP, which promotes NCL degradation and consequently inhibits downstream ribosome biogenesis. This process attenuates the regenerative capacity of cardiomyocytes and exacerbates MI progression. Moreover, following MI, NCL transitions into a droplet-like state, which is associated with its function in ribosome collision. Together, these results reveal key molecular mechanisms in MI pathology and highlight NCL modulation as a promising therapeutic strategy.