Translation Regulation during Human Cytomegalovirus Infection

About This Grant

ABSTRACT Like all viruses, Human Cytomegalovirus (HCMV) does not encode a ribosome, instead requiring host ribosomes and translation machinery to translate viral mRNAs. While many viruses inhibit host translation to blunt host antiviral responses and ensure viral mRNAs access to ribosomes, HCMV is somewhat unique in that infection actually increases overall levels of protein synthesis in infected cells. The general increase in protein synthesis has been interpreted as a global increase in the translation of all mRNAs, both viral and cellular, as infection activates key cellular translation factors and complexes. However recent studies have challenged this dogma by revealing a more complex relationship between infection and mRNA translation. Our preliminary data show that rather than causing a non-specific increase in translation efficiency, infection leads to surprisingly diverse outcomes for different mRNAs; the translation efficiency of some cellular mRNAs is increased, while others are unaffected or show temporal changes in translation efficiency during different stages of infection, suggesting different factors regulate distinct groups of RNAs during different stages of infection. Consistent with this idea, while infection activates key translation initiation complexes like the eIF4F complex, which bridges the interaction between mRNAs and ribosomes, eIF4F is only required for the translation of cellular mRNAs encoding host factors that HCMV needs to replicate, with multiple studies showing that eIF4F activity and integrity are largely dispensable for the translation of HCMV mRNAs. We hypothesize that infection activates alternative host, and potentially viral, factors to temporally regulate the translation of viral mRNAs. Using a variety of proteomics approaches we identified changes in the composition of the translation machinery caused by infection and found novel roles for several alternative host and viral proteins in HCMV mRNA translation and replication. These include the cellular DHX29 RNA helicase and the YBX1 RNA binding protein, which both regulate the translation of specific subsets of cellular RNAs under different conditions. In this proposal we determine the molecular mechanisms these factors use to regulate viral protein synthesis by defining how they recognize viral and cellular RNAs, recruit translation initiation complexes, and ultimately control mRNA translation. In the process we uncover new aspects of cell biology and the host:pathogen interface critical for remodeling cell signaling and survival in infection and other disease states.