Murine Gammaherpesvirus 68 LANA and SOX Homologs Counteract ATM-Driven p53 Activity during Lytic Viral Replication

Abstract

Tumor suppressor p53 is activated in response to numerous cellular stresses, including viral infection. However, whether murine gammaherpesvirus 68 (MHV68) provokes p53 during the lytic replication cycle has not been extensively evaluated. Here, we demonstrate that MHV68 lytic infection induces p53 phosphorylation and stabilization in a manner that is dependent on the DNA damage response (DDR) kinase ataxia telangiectasia mutated (ATM). The induction of p53 during MHV68 infection occurred in multiple cell types, including splenocytes of infected mice. ATM and p53 activation required early viral gene expression but occurred independently of viral DNA replication. At early time points during infection, p53-responsive cellular genes were induced, coinciding with p53 stabilization and phosphorylation. However, p53-related gene expression subsided as infection progressed, even though p53 remained stable and phosphorylated. Infected cells also failed to initiate p53-dependent gene expression and undergo apoptosis in response to treatment with exogenous p53 agonists. The inhibition of p53 responses during infection required the expression of the MHV68 homologs of the shutoff and exonuclease protein (muSOX) and latency-associated nuclear antigen (mLANA). Interestingly, mLANA, but not muSOX, was necessary to prevent p53-mediated death in MHV68-infected cells under the conditions tested. This suggests that muSOX and mLANA are differentially required for inhibiting p53 in specific settings. These data reveal that DDR responses triggered by MHV68 infection promote p53 activation. However, MHV68 encodes at least two proteins capable of limiting the potential consequences of p53 function. IMPORTANCEGammaherpesviruses are oncogenic herpesviruses that establish lifelong chronic infections. Defining how gammaherpesviruses overcome host responses to infection is important for understanding how these viruses infect and cause disease. Here, we establish that murine gammaherpesvirus 68 induces the activation of tumor suppressor p53. p53 activation was dependent on the DNA damage response kinase ataxia telangiectasia mutated. Although active early after infection, p53 became dominantly inhibited as the infection cycle progressed. Viral inhibition of p53 was mediated by the murine gammaherpesvirus 68 homologs of muSOX and mLANA. The inhibition of the p53 pathway enabled infected cells to evade p53-mediated cell death responses. These data demonstrate that a gammaherpesvirus encodes multiple proteins to limit p53-mediated responses to productive viral infection, which likely benefits acute viral replication and the establishment of chronic infection. G ammaherpesviruses (GHVs) are DNA tumor viruses that include Epstein-Barr virus (EBV), Kaposi's sarcoma-associated herpesvirus (KSHV), and murine gammaherpesvirus 68 (MHV68), among others (1). Like all herpesviruses, GHVs exhibit two distinct infectious cycle phases, lytic replication and latency (2). The lytic cycle is the productive phase of infection and is characterized by tem...

p53 Controls Murine Gammaherpesvirus Latency and Prevents Infection-AssociatedIgH/c-MycTranslocations

“…S2). This indicates that p53 is not critical to control MHV68 during the acute phase of infection and is consistent with viral shut-down of p53 function during lytic replication (39,40).…”

“…Infection of PBMCs with EBV likewise triggers an ATMmediated DDR that must be overcome for LCL formation(10,68). It is reasonable to suggest that MHV68 likewise triggers p53 through an ATM-mediated DDR, and we previously demonstrated that this is the case during lytic viral replication(39). Whether MHV68 causes ATM activation during latency establishment specifically in infected B cells has not been directly evaluated.However, the observation that B-cell-specific deletion of ATM correlates with a global defect in MHV68 latency(19), rather than the early enhancement in infection we observed in the absence of p53 during initial colonization of the host, suggests that ATM and p53 function independently in latently infected cells in vivo.…”

“…In contrast, KSHV-infected cells are resistant to p53-mediated death during lytic replication(73). This is also true for MHV68, in that LANA does not in-and-of-itself inhibit p53, but is required for p53 inhibition as the lytic cycle progresses(39,40). In retrospect, since p53 inhibition is potently transforming, the assertion that p53 is not directly inhibited during long-term chronic infection agrees with the truth that GHV infection does not cause cancer in the majority of infected individuals.GHVs co-evolved with their hosts, resulting in a virus-host relationship in which severe disease is not a common outcome.…”

Herpesviruses and Their Host Cells: A Successful Liaison

“…HCMV codes for a gH/gL/gO complex which drives infection of cells expressing platelet-derived growth factor receptor alpha (PDGFR-/) [16], and for a gH/gL/pUL(128,130,131A) complex which drives infection of most PDGFR-/-negative cells through a still unknown receptor. In cell culture, fibroblasts infected with HCMV release virions with high or low amounts of gH/gL/pUL Noncoding RNAs (including miRNAs) [44,45,47] Origins of lytic replication (oriLyts) [51] Antiapoptotic genes [70] Genes counteracting host cell defense mechanisms (immune evasion genes) [71][72][73][74][75][76][77][78] Genes influencing cell cycle or proliferation [79,80] Genes interfering with epigenetic silencing [63,81] Cellular (host) factors Refs…”

Murine Gammaherpesvirus 68 Expressing Kaposi Sarcoma-Associated Herpesvirus Latency-Associated Nuclear Antigen (LANA) Reveals both Functional Conservation and Divergence in LANA Homologs

“…Encoded by the conserved gene ORF73, LANA homologs are expressed with immediate-early (IE) kinetics during lytic replication, and LANA is one of the few viral proteins expressed during latency. LANA homologs function as transcriptional regulators of viral and host genes and as inhibitors of host tumor suppressors, especially p53 (13)(14)(15)(16). LANA is abundantly expressed in all known KSHV-related cancers, suggesting a role in cellular transformation (13).…”