O-GlcNAcylation Of Core Components Of The Translation Initiation Machinery Regulates Protein Synthesis

Protein synthesis is essential for cell growth,proliferation and survival.Protein synthesis is a tightly regulated process.Dysregulation of protein synthesis is considered as one of the characteristics of tumors.Protein translation initiation is the rate-limiting step of the protein synthesis,and the assembly of 43 S complex involved in eIF4 F complex is the rate-limiting step of protein translation initiation,so the regulation of eIF4 F complex plays an important role in the regulation of the efficiency of the whole protein translation.Therefore,the regulation of eIF4 F complex is often used as a drug target for tumor therapy.eIF4 F comprises eIF4 E,eIF4A and eIF4 G,and the mechanism of eIF4 E regulation and drug targets have been well studied,while the principles of eIF4 A and eIF4 G regulation remain to be elucidated.O-linked ?-N-acetylglucosamine(O-GlcNAc)is a cellular prevalent posttranslational modification by transferring N-acetylglucosamine to the hydroxyl group on Serine or threonine.Researches have identified thousands of intracellular proteins containing the modification.Increasing evidence has shown that OGlcNAcylation regulates various important biological processes,including transcription,stem cell differentiation,signal transduction,cell cycle progression,and metabolic reprogramming.O-GlcNAcylation disorders can lead to type 2 diabetes,neurodegenerative diseases,alzheimer's disease,tumors and other major diseases.Studies in the past sevelar years have implicated O-GlcNAcylation as regulators of many cancer including multiple “Hallmarks of Cancer”.Therefore,O-GlcNAcylation can be used as a target for tumor treatment.Here we show that the dynamic modification of proteins by O-linked ?-N-acetylglucosamine(O-GlcNAcylation)regulates translation initiation by modifying core initiation factors eIF4 AI and eIF4 GI,respectively.Mechanistically,site-specific OGlcNAcylation of eIF4 AI on Ser322/323 disrupts the formation of the translation initiation complex by perturbing its interaction with eIF4 GI.In addition,OGlcNAcylation uncouples the ATPase activity from the duplex unwinding activity of eIF4 AI,leading to impaired protein synthesis,decreased cell proliferation and tumor growth in xenograft models.In contrast,site-specific O-GlcNAcylation of eIF4 GI on Ser61 promotes its interaction with poly(A)-binding protein(PABP)and poly(A)mRNA.Depletion of eIF4 GI O-GlcNAcylation results in inhibition of protein synthesis,cell proliferation,soft agar colony formation and and tumor growth in xenograft models.In addition,we also reveal that tumor specifically upregulates the glycosylation level of eIF4 GI and down-regulates the glycosylation level of eIF4 AI in clinical tumor tissues,which also endows our results with clinical significance.Finally,we find that this differential glycosylation regulation is reflected in cell cycle progression.The differential glycosylation of eIF4 AI and eIF4 GI appears to be regulated in the initiation complex to fine tune protein synthesis and promotes the smooth progress of the cell cycle,which also gives our results important biological significance.Our study thus expands the previous understanding of protein synthesis,and adds another dimension of complexity to translational control of cellular proteins,which is particularly reflected in translation of cancer cells.So we expect to provide new drug targets for targeted therapy of tumors.