The Cellular Factor NXP2/MORC3 Is a Positive Regulator of Influenza Virus Multiplication

Abstract

Transcription and replication of influenza A virus are carried out in the nuclei of infected cells in the context of viral ribonucleoproteins (RNPs). The viral polymerase responsible for these processes is a protein complex composed of the PB1, PB2, and PA proteins. We previously identified a set of polymerase-associated cellular proteins by proteomic analysis of polymerase-containing intracellular complexes expressed and purified from human cells. Here we characterize the role of NXP2/MORC3 in the infection cycle. NXP2/MORC3 is a member of the Microrchidia (MORC) family that is associated with the nuclear matrix and has RNA-binding activity. Influenza virus infection led to a slight increase in NXP2/MORC3 expression and its partial relocalization to the cytoplasm. Coimmunoprecipitation and immunofluorescence experiments indicated an association of NXP2/MORC3 with the viral polymerase and RNPs during infection. Downregulation of NXP2/MORC3 by use of two independent short hairpin RNAs (shRNAs) reduced virus titers in low-multiplicity infections. Consistent with these findings, analysis of virus-specific RNA in high-multiplicity infections indicated a reduction of viral RNA (vRNA) and mRNA after NXP2/MORC3 downregulation. Silencing of NXP2/MORC3 in a recombinant minireplicon system in which virus transcription and replication are uncoupled showed reductions in cat mRNA and chloramphenicol acetyltransferase (CAT) protein accumulation but no alterations in cat vRNA levels, suggesting that NXP2/MORC3 is important for influenza virus transcription. IMPORTANCE Influenza virus infections appear as yearly epidemics Influenza viruses cause an acute respiratory disease that annually affects millions of people worldwide (Global Influenza Surveillance and Response System [GISRS] [http://www.who .int/influenza/gisrs_laboratory/en/]). The genome of influenza A viruses is about 13 kb long and consists of eight single-stranded negative-sense RNA segments. The viral proteome includes 10 viral proteins that have been studied extensively (1) and another 8 proteins, probably accessory proteins, that were identified more recently (reviewed in reference 2). The transcription and replication of influenza viruses occur in the nuclei of infected cells and are mediated by the viral polymerase, a heterotrimer composed of the PB1, PB2, and PA subunits, in the context of viral ribonucleoprotein complexes (RNPs) (3; reviewed in references 4 to 7). The virus recruits host cell factors to help carry out these processes, and in some specific cases, their roles in virus replication have been determined (reviewed in references 4 and 8 to 10). In one such study, we identified the nuclear matrix NXP2 protein as a factor associated with influenza virus polymerase in vivo by proteomic analysis of recombinant purified polymerase complexes (11). Since influenza virus RNA synthesis is connected to the nuclear matrix (12, 13), we decided to further characterize the role of NXP2 in the virus infection cycle.The NXP2 protein (also called MORC3, ZCW...

Perimysial microarteriopathy in dermatomyositis with anti‐nuclear matrix protein‐2 antibodies

“…Clinically, subcutaneous edema was common in our patients and others reported with DM with anti‐NXP‐2 antibodies . Subcutaneous edema was strongly associated with vascular lesions, especially capillary damage, which led to a marked decrease in serum albumin levels . Prevalence of microinfarcts in muscle was higher in DM with subcutaneous edema , suggesting underlying vasculopathy.…”

Influenza Virus and Chromatin: Role of the CHD1 Chromatin Remodeler in the Virus Life Cycle

“…The H3N2 subtype NS1 protein has a histone H3K4-like sequence (histone mimic) at its carboxyl terminus that is used by the virus to target the human PAF1 transcription elongation complex, leading to suppression of hPAF1C-mediated transcriptional control of inducible antiviral gene expression (74). The NXP2/MORC3 protein, a histone reader that recognizes H3K4me3 (75), interacts with the influenza virus polymerase complex and positively modulates viral transcription (76); this protein relocalizes partially to the cytoplasm late in influenza virus infection (76). Although NXP2/MORC3, unlike the CHD1 H3K4me3 reader, is not degraded during infection, its relocalization could inhibit its still-uncharacterized nuclear function.…”

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

“…In our analysis of HFT cells, we found that MORC3 was detectable in only a subset of PML NBs, whereas others reported that in HeLa and Saos-2 cells MORC3 was colocalized to the majority of PML nuclear foci. This difference in detail may be due to cell type or efficiency of antibody detection, and indeed Ver et al found no significant colocalization of MORC3 with PML in A549 cells (50). One reported role of MORC3 in PML NBs is to recruit Sp100 and p53 into these complexes (12), although in the HF-derived cells used here the former function was not evident.…”

“…Our previous study identified sumoylated MORC3 as a degradation target of the HSV-1 E3 ubiquitin ligase protein ICP0 (9), which led us to further investigate the function of MORC3 during HSV-1 infection. Until now, the role of MORC3 during virus infections was relatively unknown, although one other report suggested that MORC3 was required for efficient influenza A virus (IAV) infection (50). MORC3 is a sumoylated nuclear matrix protein with RNA and DNA binding activities (13,17) that associates with PML NBs.…”

“…Members of the MORC family of proteins have been associated with a number of types of cancers (45)(46)(47)(48)(49). However, to date there is little known about the role that MORC3 may play during a virus infection, although one recent study reported that MORC3 is required for efficient influenza replication (50). Until now, MORC3 has not been previously reported to have an antiviral role.…”