Name
ORF57 enables SOX-dependent host shutoff to support accumulation of the KSHV lytic proteome
Presenter
Eric Pringle, Dalhousie
Co-Author(s)
Eric S. Pringle, Craig McCormick. Dalhousie University
Abstract Category
Expressing & Multiplying
Abstract
Kaposi's sarcoma–associated herpesvirus (KSHV) ORF57 is an essential mRNA-binding protein that promotes nuclear export of unspliced viral mRNAs and enhances translation of select viral transcripts. Here, we show that ORF57 does not alter viral mRNA dependence on canonical host eIF4F cap-binding complexes for efficient translation. We also identify a previously unrecognized role for ORF57 in supporting efficient translation of the viral host-shutoff endoribonuclease SOX. Although SOX is known to promote degradation of both cellular and viral mRNAs, its contribution to viral protein accumulation has not been comprehensively defined. Using quantitative proteomics, we demonstrate that SOX endoribonuclease activity is critical for efficient accumulation of the KSHV lytic proteome. Loss of either ORF57 or SOX results in a global reduction in viral protein abundance and severely impairs production of infectious virions. Structural proteins are disproportionately sensitive to SOX inactivation, consistent with late viral mRNAs being unable to compete effectively for translational resources in the absence of host shutoff. Infection with an ORF57-deficient virus yields a proteome that closely parallels SOX inactivation, though with less severe depletion of viral proteins. Aside from SOX itself, the viral DNA polymerase processivity factor ORF59 was the only viral protein showing strong ORF57-specific sensitivity, suggesting that many ORF57-dependent defects arise indirectly through impaired host shutoff. Loss of ORF57 or SOX also alters production of alternative proteoforms of the repetitive, proline-rich viral proteins LANA and Kaposin, favoring higher molecular weight species.