Jin, J.; Ma, S.; Shi, J.; Lou, H.; Li, Y.; Yao, Y.; Fang, N.; Liu, Y.; Yang, L.

Glucose starvation leads to the degradation of intracellular proteins to generate amino acids for energy production. However, it remains unclear which proteins undergo rapid degradation to supply amino acids as energy sources during glucose starvation. To investigate the molecular mechanism underlying the transition of carbon source from glucose to proteins under glucose starvation, we first employed quantitative proteomics to examine the impact of glucose deprivation on protein levels. We discovered that histone degradation produces the highest amount of glutamine during glucose starvation. Further investigation revealed that histone H2A undergo degradation in the nucleolus in the form of mono-ubiquitination (H2Aub). The nucleolus contains lysosome-like structures that degrade monoubiquitinated histones, potentially participating in the carbon source shift from glucose to amino acids for energy production. Through preliminary screening, we identified Midnolin as the receptor for H2Aub, mediating its degradation in nucleolar lysosome-like structures. Dysregulation of carbon source transition from glucose to proteins, through knockdown of Midnolin results in cell cycle arrest, affecting cellular growth and proliferation. In conclusion, our findings demonstrate that nucleolar lysosome-like structures degrading monoubiquitinated histones exist during glucose starvation, which may play crucial roles in the carbon source transition from glucose to proteins, providing new potential therapeutic targets for metabolic disorders.