Site-specific SUMOylation of viral polymerase processivity factor: a way of localizingtoND10 subnuclear domains for restricted and self-controlled reproduction of herpesvirus.

Lytic replication of human cytomegalovirus (HCMV), a member of β-herpesvirus, is a highly complicated and organized process that requires its DNA polymerase processivity factor, UL44, the first reported HCMV replication protein subjected to SUMO post-translational modification (PTM). SUMOylation plays a pleiotropic role in protein functions of host cells and infecting viruses. Particularly, formation of herpesviral replication compartments (RCs) upon infection is induced in proximity to ND10 subnuclear domains, the host cell's intrinsic antiviral immune devices and hot SUMOylation spots, relying just on SUMOylation of their protein components to become mature and functional in restriction of the viral replication. In this study, to unveil the exact role of SUMO PTM on UL44 involved in HCMV replication, we screened and identified PIAS3, an annotated E3 SUMO ligase, as a novel UL44-interacting protein engaged in cellular SUMOylation pathway. Co-existence of PIAS3 could enhance the UBC9-based SUMO modification of UL44 specifically at its conserved 410lysine residue lying within the single canonical ψKxE SUMO Conjugation Motif (SCM). Intriguingly, we found this SCM-specific SUMOylation contributes to UL44 co-localization and interaction with subnuclear ND10 domains during infection, which in turn exerts an inhibitory effect on HCMV replication and growth. Together, these results highlight the importance of SUMOylation in regulating viral protein subnuclear localization, representing a novel way of utilizing ND10-based restriction to achieve the self-controlled replication and reproduction of herpesviruses.ImportanceIn this study, we found PIAS3 serves as an additional E3 SUMO ligase towards UL44 possessing modification site specificity at canonical SCM, which renders the UL44 SUMOylation system more integral. We reveal how the site-specific SUMOylation mediates the recruitment of viral replication protein onto the host antiviral subnuclear structures, shedding light on virus-host interplay during infection and meanwhile providing insight into antiviral mechanism of ND10 domains. In addition, from the view of viral evolution, the site-specific SUMOylation motif, genetically retained in HCMV replicating protein to exert an ND10-based antiviral effect, might in turn guarantee the virus a self-controlled slower replication progression upon infection, which is beneficial for viral long-term reproduction.