Significance: DNA replication is error-prone. Mechanisms to recognize errors in DNA lead to arrest of cell proliferation at various checkpoints to allow for repair. Suppression of these mechanisms is necessary for recovery from these checkpoints and continuation of cell division. We show that signal transducer and activator of transcription 3 (STAT3), a protein overactive in many human cancers, can abnormally evade recognition of DNA errors and damage leading to bypass of a critical cell-cycle checkpoint and uncontrolled cell proliferation. While relevant to understanding cancer development and prevention, this will also bring fresh insights into the role of STAT3 in the central biology of cell proliferation, particularly since STAT3 is necessary for critical processes including embryonic development and immunity.

Trials to reintroduce chloroquine into regions of Africa where P. falciparum has regained susceptibility to chloroquine are underway. However, there are long-standing concerns about whether chloroquine increases lytic-replication of Epstein-Barr virus (EBV), thereby contributing to the development of endemic Burkitt lymphoma. We report that chloroquine indeed drives EBV replication by linking the DNA repair machinery to chromatin remodeling-mediated transcriptional repression. Specifically, chloroquine utilizes ataxia telangiectasia mutated (ATM) to phosphorylate the universal transcriptional corepressor Krüppel-associated Box-associated protein 1/tripartite motif-containing protein 28 (KAP1/TRIM28) at serine 824 –a mechanism that typically facilitates repair of double-strand breaks in heterochromatin, to instead activate EBV. Notably, activation of ATM occurs in the absence of detectable DNA damage. These findings i) clarify chloroquine’s effect on EBV replication, ii) should energize field investigations into the connection between chloroquine and endemic Burkitt lymphoma and iii) provide a unique context in which ATM modifies KAP1 to regulate persistence of a herpesvirus in humans. Viruses that persist for the life of the host, like the herpesvirus Epstein-Barr virus (EBV), tightly regulate lytic replication to reduce killing of host cells and ensure virus survival. We show that repression of EBV replication is disrupted by the antimalarial drug chloroquine which modifies an otherwise normal cellular mechanism that repairs DNA, to influence gene expression through a process known as chromatin remodeling. This finding a) reveals a new connection between the DNA repair machinery and gene regulation and b) resolves a long-standing dispute over whether chloroquine increases EBV replication, thereby contributing to endemic Burkitt lymphoma, a cancer almost uniformly associated with EBV. There are ongoing efforts to re-introduce chloroquine into parts of Africa where falciparum malaria has regained susceptibility to chloroquine.

Viruses activate inflammasomes but then subvert resulting inflammatory responses to avoid elimination. We asked whether viruses could instead use such activated or primed inflammasomes to directly aid their propagation and spread. Since herpesviruses are experts at coopting cellular functions, we investigated whether Epstein−Barr virus (EBV), an oncoherpesvirus, exploits inflammasomes to activate its replicative or lytic phase. Indeed, our experiments reveal that EBV exploits several inflammasome sensors to actually activate its replicative phase from quiescence/latency. In particular, TXNIP, a key inflammasome intermediary, causes assembly of the NLRP3 inflammasome, resulting in caspase-1−mediated depletion of the heterochromatin-inducing epigenetic repressor KAP1/TRIM28 in a subpopulation of cells. As a result, only TXNIP^hiKAP1^lo cells, that is, in a primed/prolytic state, turn expression of the replication/lytic/reactivation switch protein on to enter the replicative phase. Our findings 1) demonstrate that EBV dovetails its escape strategy to a key cellular danger-sensing mechanism, 2) indicate that transcription may be regulated by KAP1 abundance aside from canonical regulation through its posttranslational modification, 3) mechanistically link diabetes, which frequently activates the NLRP3 inflammasome, to deregulation of a tumor virus, and 4) demonstrate that B lymphocytes from NOMID (neonatal onset multisystem inflammatory disease) patients who have NLRP3 mutations and suffer from hyperactive innate responses are defective in controlling a herpesvirus. Significance Infectious agents, including viruses, activate cellular inflammasomes. Viruses have evolved strategies to parry such host defense mechanisms, and cancer-causing gammaherpesviruses such as Epstein−Barr virus (EBV) are no exception. In distinct contrast, we show that this ubiquitous virus exploits assembly of the NLRP3 inflammasome to kick-start its lytic cascade; this allows EBV to reactivate from quiescence, propagate, and leave the cell when the cell perceives intrinsic or extrinsic threats. This discovery also provides a predictive signature that marks cells in which EBV is poised to enter the lytic phase. Importantly also, with hyperglycemia known to activate the NLRP3 inflammasome, our findings provide a mechanistic basis for recent clinical observations of diabetes as a significant risk factor for EBV-lymphomas in transplant recipients.

Cancer-causing herpesviruses infect nearly every human and persist indefinitely in B lymphocytes in a quiescent state known as latency. A hallmark of this quiescence or latency is the presence of extrachromosomal viral genomes with highly restricted expression of viral genes. Silencing of viral genes ensures both immune evasion by the virus and limited pathology to the host, yet how multiple genes on multiple copies of viral genomes are simultaneously silenced is a mystery. In a unifying theme, we report that both cancer-causing human herpesviruses, despite having evolved independently, are silenced through the activities of two members of the Krüppel-associated box (KRAB) domain–zinc finger protein (ZFP) (KRAB-ZFP) epigenetic silencing family, revealing a novel STAT3-KRAB-ZFP axis of virus latency. This dual-edged antiviral strategy restricts the destructive ability of the lytic phase while promoting the cancer-causing latent phase. These findings also unveil roles for KRAB-ZFPs in silencing of multicopy foreign genomes with the promise of evicting herpesviruses to kill viral cancers bearing clonal viral episomes. IMPORTANCE Despite robust immune responses, cancer-causing viruses Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) persist for life. This persistence is accomplished partly through a stealth mechanism that keeps extrachromosomal viral genomes quiescent. Quiescence, or latency, ensures that not every cell harboring viral genomes is killed directly through lytic activation or indirectly via the immune response, thereby evicting virus from host. For the host, quiescence limits pathology. Thus, both virus and host benefit from quiescence, yet how quiescence is maintained through silencing of a large set of viral genes on multiple viral genomes is not well understood. Our studies reveal that members of a gene-silencing family, the KRAB-ZFPs, promote quiescence of both cancer-causing human viruses through simultaneous silencing of multiple genes on multicopy extrachromosomal viral genomes.

Recent studies have strengthened the evidence for Epstein–Barr Virus (EBV) as an important contributing factor in the development of multiple sclerosis (MS). Chronic inflammation is a key feature of MS. EBV⁺ B cells can express cytokines and exosomes that promote inflammation, and EBV is known to be reactivated through the upregulation of cellular inflammasomes. Inflammation is a possible cause of the breakdown of the blood–brain barrier (BBB), which allows the infiltration of lymphocytes into the central nervous system. Once resident, EBV⁺ or EBV-specific B cells could both plausibly exacerbate MS plaques through continued inflammatory processes, EBV reactivation, T cell exhaustion, and/or molecular mimicry. Another virus, SARS-CoV-2, the cause of COVID-19, is known to elicit a strong inflammatory response in infected and immune cells. COVID-19 is also associated with EBV reactivation, particularly in severely ill patients. Following viral clearance, continued inflammation may be a contributor to post-acute sequelae of COVID-19 infection (PASC). Evidence of aberrant cytokine activation in patients with PASC supports this hypothesis. If unaddressed, long-term inflammation could put patients at risk for reactivation of EBV. Determining mechanisms by which viruses can cause inflammation and finding treatments for reducing that inflammation may help reduce the disease burden for patients suffering from PASC, MS, and EBV diseases.