A proteomics view of SIRT6 functions and the anti-viral roles of sirtuin proteins

Abstract

Viruses have evolved effective means for hijacking host molecular mechanisms for their replication and spread. Recent work from our laboratory and other groups has established that protein deacetylases are targeted by viral proteins and play critical roles during infection. Importantly, we have discovered that human sirtuins are a new family of anti-viral proteins with broad-range properties against both DNA and RNA viruses. One of the sirtuins with prominent anti-viral functions is SIRT6, a nuclear enzyme just recently established as a critical factor in human disease. Multiple biological processes, including DNA repair, gene expression, telomere maintenance, and metabolism, have been linked to SIRT6. Still, the mechanisms involved in regulating its functions and protein interactions have remained largely undefined. Here, we utilize a multidisciplinary approach integrating proteomics, virology, genetics, microscopy, and bioinformatics to characterize SIRT6 protein interaction networks, and assess their dynamic regulation during human cytomegalovirus (HCMV) infection. First, we provide an overview of advancements in proteomic approaches for studying protein interactions, several of which have been pioneered by our laboratory. These methods can provide direct insight into associations required for host defense against infections or virus spread. Second, we present the first network of SIRT6 interactions and identify prominent phosphorylations within a C-terminus naturally disordered region. Importantly, we report a previously unrecognized interplay between SIRT6 enzymatic activity and its associations. Next, we identify infection-triggered changes in SIRT6 interactions and sub-cellular localization. We demonstrate SIRT6 redistribution from the nucleus to the cytoplasm during late stages of HCMV infection, suggesting a repurposing of its functions and associations with different substrates and protein complexes. Notably, we report that SIRT6 is specifically targeted by viral proteins, including the viral kinase pUL97, at different time points during infection. Further strengthening the SIRT6 contribution to immune responses following infection, we identify and validate its interactions with the viral tegument protein pUL83--involved in viral immune evasion, and the host DNA sensor IFI16--necessary for inducing antiviral cytokines after infection. Finally, we demonstrate that the antiviral properties of sirtuins are evolutionarily conserved, showing that the bacterial homolog CobB in <italic>Escherichia coli</italic> has protective functions during bacteriophage infection.