Ubiquitination Status Does Not Affect VPS34 Protein Level

VPS34(vacuolar protein-sorting 34)plays important role in autophagy and endosomal trafficking.VPS34 kinase activity was decreased in brain tissue of AD patients and its pathological model mouse APP/PS1 mice,and VPS34 affected APP endocytic transport.It is suggested that VPS34 is involved in the pathogenesis of AD.We have hypothesized that VPS34 ubiquitination status should control its protein levels.Here,we report that our results did not support this assumption.In cells transiently transfected with ubiquitin(UB)constructs contained different lysine residues(Ks),Vps34 ubiquitination could occur regardless of the presence of any Ks in UB.However,VPS34 protein levels were not significantly altered among these UB mutants.On the other hand,Vps34 did subject to proteasomal or lysosomal degradation,as in the presence of proteasomal inhibitor MG132 or lysosomal inhibitor chloroquine,Vps34 protein levels were not elevated at 12 and 18 h,but were increased at 24 h,suggesting that VPS34 is relatively stable within 18 h.In vivo experiments revealed that in APP/PS1 mice,an animal model of Alzheimer's disease(AD),although VPS34 protein levels remained unchanged,ubiquitination of VPS34 wassignificantly reduced,suggesting that alterations of ubiquitination and protein level of VPS34 did not coincide in APP/PS1 mice.These results indicated that ubiquitination status did not affect VPS34 protein levels.