Role Of EIF3 In ETC Protein Synthesis And Cancer Cell Proliferation

The multi-subunit eukaryotic translation initiation factor 3(eIF3)complex is the largest factor that mediate translation initiation in eukaryotes.eIF3 promots the binding of methionyl-tRNA and mRNA to the 40S ribosomal subunit,facilitates scanning of the mRNA for the AUG initiation codon and plays additional important roles in translation termination and ribosome recycling.Altered expression levels in specific subunits of eIF3 are frequently observed in various types of cancer and developmental disorders.As such,eIF3 appears to play an important role in the control of cell growth and proliferation and represents a potential target for the development of novel therapeutics.Using global transcriptomics,proteomics and metabolomics analysis,in the previous research results of our lab,it was found that Schizosaccharomyces pombe yeast cells lacking eIF3e and eIEF3d were impaired in synthesizing components of the mitochondrial electron transport chain,resulting in respiratory defects,endogenous oxidative stress and shortened lifespan.However,the defect is balanced by increased glucose uptake and a switch to glycolysis.This metabolic regulation function appears to be conserved in human cells,where the eIF3d-eIF3e module mediates mRNA-specific translational control of energy metabolism that may be disrupted in cancer.In this study,employing in vivo and in vitro translation reporter assays,we found that eIF3e is required for efficient translation of luciferase constructs driven by the 5’-UTRs of mRNA encoding components of the mitochondrial electron transport chain.The active human eIF3 protein complex(800KDa)was extracted and purified from mammalian cells and used for translation rescue experiments in vitro.The translation of mitochondrial reporters was restored by purified eIF3.To study the effect of acute depeletion of eIF3 on cells,cells were constructing by CRISPR/Cas9 technology that enabled auxin-inducible rapid degradation of endogenous eIF3e through SCFOsTIR1 E3 ligase.eIF3e depletion arrested the cell cycle and inhibited the proliferation of cancer cells in vitro and in mouse xenografts.This is a powerful tool for studying proteins of interest and dissecting cellular processes,laying the foundation for the subsequent knockout of other translation initiation subunits in long-term studies of eIF3s.In conclusion,our studies demonstrate that eIF3,presumably by promoting the synthesis of the mitochondrial electron transport chain and energy production is an important regulator of the proliferation of cancer cells thus nominating it as a promising novel target for therapeutic intervention.