Epstein-Barr virus (EBV) SM protein induces and recruits cellular Sp110b to stabilize mRNAs and enhance EBV lytic gene expression

Promyelocytic leukemia protein (PML) nuclear bodies or nuclear domain 10s (ND10s) are multiprotein nuclear structures implicated in transcriptional and posttranscriptional gene regulation that are disrupted during replication of many DNA viruses. Interferon increases the size and number of PML nuclear bodies and stimulates transcription of several genes encoding PML nuclear body proteins. Moreover, some PML nuclear body proteins colocalize at sites of viral DNA synthesis and transcription. In this study, the relationship between lytic Epstein-Barr virus (EBV) replication and Sp110b, a PML nuclear body protein, was investigated. Sp110b is shown to physically and functionally interact with the EBV protein SM. SM is expressed early in the EBV replicative cycle and posttranscriptionally increases the level of target EBV lytic transcripts. SM bound to Sp110b via two distinct sites in Sp110b in an RNA-independent manner. SM also specifically induced expression of Sp110b during lytic EBV replication and in several cell types. Exogenous expression of Sp110b synergistically enhanced SM-mediated accumulation of intronless and lytic viral transcripts. This synergistic effect was shown to be promoter independent, posttranscriptional, and the result of increased stabilization of target transcripts. Finally, inhibiting Sp110b expression decreased accumulation of an SM-responsive lytic EBV transcript in EBV-infected cells. These findings imply that SM induces Sp110b expression, binds to Sp110b, and utilizes the recruited Sp110b protein to increase the stability of lytic EBV transcripts, indicating that Sp110b is a component of the cellular machinery that EBV utilizes to enhance lytic EBV replication.