MORC3, a Component of PML Nuclear Bodies, Has a Role in Restricting Herpes Simplex Virus 1 and Human Cytomegalovirus

Abstract

We previously reported that MORC3, a protein associated with promyelocytic leukemia nuclear bodies (PML NBs), is a target of herpes simplex virus 1 (HSV-1) ICP0-mediated degradation (E. Sloan, et al., PLoS Pathog 11:e1005059, 2015, http: //dx.doi.org/10.1371/journal.ppat.1005059). Since it is well known that certain other components of the PML NB complex play an important role during an intrinsic immune response to HSV-1 and are also degraded or inactivated by ICP0, here we further investigate the role of MORC3 during HSV-1 infection. We demonstrate that MORC3 has antiviral activity during HSV-1 infection and that this antiviral role is counteracted by ICP0. In addition, MORC3's antiviral role extends to wild-type (wt) human cytomegalovirus (HCMV) infection, as its plaque-forming efficiency increased in MORC3-depleted cells. We found that MORC3 is recruited to sites associated with HSV-1 genomes after their entry into the nucleus of an infected cell, and in wt infections this is followed by its association with ICP0 foci prior to its degradation. The RING finger domain of ICP0 was required for degradation of MORC3, and we confirmed that no other HSV-1 protein is required for the loss of MORC3. We also found that MORC3 is required for fully efficient recruitment of PML, Sp100, hDaxx, and ␥H2AX to sites associated with HSV-1 genomes entering the host cell nucleus. This study further unravels the intricate ways in which HSV-1 has evolved to counteract the host immune response and reveals a novel function for MORC3 during the host intrinsic immune response. IMPORTANCEHerpesviruses have devised ways to manipulate the host intrinsic immune response to promote their own survival and persistence within the human population. One way in which this is achieved is through degradation or functional inactivation of PML NB proteins, which are recruited to viral genomes in order to repress viral transcription. Because MORC3 associates with PML NBs in uninfected cells and is a target for HSV-1-mediated degradation, we investigated the role of MORC3 during HSV-1 infection. We found that MORC3 is also recruited to viral HSV-1 genomes, and importantly it contributes to the fully efficient recruitment of PML, hDaxx, Sp100, and ␥H2AX to these sites. Depletion of MORC3 resulted in an increase in ICP0-null HSV-1 and wt HCMV replication and plaque formation; therefore, this study reveals that MORC3 is an antiviral factor which plays an important role during HSV-1 and HCMV infection. Herpes simplex virus 1 (HSV-1) is prevalent in populations throughout the world and is responsible for a number of clinically important diseases that range from facial and genital lesions to encephalitis (1, 2). This alphaherpesvirus establishes lifelong persistence within the host, remaining latent within sensory ganglia after the primary infection is resolved. Periodically the virus is reactivated from its latent state, resulting in recurrent lesions. HSV-1 has the capacity to remain persistent within the host and allow transmission within the popu...

High-Definition Analysis of Host Protein Stability during Human Cytomegalovirus Infection Reveals Antiviral Factors and Viral Evasion Mechanisms

“…Overall, 131 proteins were rescued by application of MG132 within 24 hr of infection, with 46 proteins rescued at 12 hr post infection, the earliest time point studied ( Figure 1 C). Of the 46 proteins, 7 have already been reported to be degraded by HCMV, including HCMV restriction factors Sp100 and MORC3 ( Kim et al., 2011 , Sloan et al., 2016 , Tavalai et al., 2011 ), E3 ubiquitin ligases ANAPC1, 4, and 5 (anaphase promoting complex subunits 1, 4, and 5) and ITCH (itchy E3 ubiquitin protein ligase) ( Figures 1 B and S2 A) (reviewed in Weekes et al., 2014 ). The remaining 39 proteins have not previously been reported to be targeted for proteasomal degradation by HCMV, including HLTF ( Figures 1 D and 1E).…”

“…The ten members of the US12 gene family act in concert to suppress the expression of cell-surface immune ligands, with many targeted for lysosomal degradation ( Fielding et al., 2017 ). The degradation of intrinsic cellular restriction factors (e.g., Sp100, DAXX, and MORC3) is induced by virion components or viral proteins expressed early in infection and dramatically enhances the efficiency of infection ( Schreiner and Wodrich, 2013 , Sloan et al., 2016 , Tavalai et al., 2011 ).…”

“…A common final pathway for many host protein targets is proteasomal or lysosomal degradation (reviewed in Halenius et al., 2015 ). HCMV also modulates intrinsic immunity to facilitate viral replication, degrading components of cellular promyelocytic leukemia nuclear bodies (PML-NB) Sp100, MORC3, and DAXX that act as restriction factors ( Kim et al., 2011 , Schreiner and Wodrich, 2013 , Sloan et al., 2016 , Tavalai et al., 2011 ). We previously published a systematic temporal analysis that detailed how HCMV orchestrates the expression of >8,000 cellular proteins over the whole course of infection ( Weekes et al., 2014 ).…”

Tuning the Orchestra: HCMV vs. Innate Immunity

“…One of the best characterized HCMV RFs is certainly the ND10 complex, formed by the proteins PML, hDaxx, and Sp100 (Zhang and van Drunen Littel-van den Hurk, 2017). In addition to these components, other molecules, such as the nuclear matrix protein microrchidia family CW-type zinc-finger 3 (MORC3/NXP-2), have been shown to associate with the ND10 complex and exert antiviral activity through an unknown mechanism (Sloan et al, 2016).…”

Swine Promyelocytic Leukemia Isoform II Inhibits Pseudorabies Virus Infection by Suppressing Viral Gene Transcription in PML-NBs

“…Promyelocytic leukaemia nuclear bodies (PML-NBs) is a PML protein-based sub-nuclear structure with an intrinsic anti-viral activity against a wide range of RNA and DNA viruses. More than 150 proteins have been identified either transiently or residentially associated with PML-NBs, many of which possesses an anti-viral activity including Sp100, Daxx, ATRX, HIRA and MORC3 (1-7). As a countermeasure, numerous viruses have evolved strategies to disrupt or degrade PML-NBs underscoring the importance of this structure in cellular anti-viral defense.…”