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Autophagy and interferon (IFN)-mediated innate immunity are critical antiviral defense mechanisms, and recent evidence indicated that tripartite motif (TRIM) proteins are important regulators of both processes. While the role of TRIM proteins in modulating antiviral cytokine responses has been well established, much less is known about their involvement in autophagy in response to different viral pathogens. Through a targeted RNAi screen examining the relevance of selected TRIM proteins in autophagy induced by herpes simplex virus 1 (HSV-1), encephalomyocarditis virus (EMCV), and influenza A virus (IAV), we identified several TRIM proteins that regulated autophagy in a virus-species specific manner, as well as a few TRIM proteins that were essential for autophagy triggered by all three viruses and rapamycin, among them TRIM23. TRIM23 was critical for autophagy-mediated restriction of multiple viruses, and this activity was dependent on both its RING E3 ligase and ADP-ribosylation factor (ARF) GTPase activity. Mechanistic studies revealed that unconventional K27-linked auto-ubiquitination of the ARF domain is essential for the GTP hydrolysis activity of TRIM23 and activation of TANK-binding kinase 1 (TBK1) by facilitating its dimerization and ability to phosphorylate the selective autophagy receptor p62. Our work identifies the TRIM23-TBK1-p62 axis as a key component of selective autophagy and further reveals a role for K27-linked ubiquitination in GTPase-dependent TBK1 activation.

Vibrio cholerae, the causative agent of the devastating diarrheal disease cholera, can form biofilms on diverse biotic and abiotic surfaces. Biofilm formation is important for the survival of this organism both in its natural environment and in the human host. Development of V. cholerae biofilms are regulated by complex regulatory networks that respond to environmental signals. One of these signals, norspermidine, is a polyamine that enhances biofilm formation via the NspS/MbaA signaling system. In this work, we have investigated the role of the polyamine spermidine in regulating biofilm formation in V. cholerae. We show that spermidine import requires PotD1, an ortholog of the periplasmic substrate-binding protein of the spermidine transport system in Escherichia coli. We also show that deletion of the potD1 gene results in a significant increase in biofilm formation. We hypothesize that spermidine imported into the cell hinders biofilm formation. Exogenous spermidine further reduces biofilm formation in a PotD1-independent, but NspS/MbaA-dependent, manner. Our results suggest that polyamines affect biofilm formation in V. cholerae via multiple pathways involving both transport and signaling networks.

STING is a protein in the cytosolic DNA and cyclic dinucleotide sensor pathway that is critical for the initiation of innate responses to infection by various pathogens. Consistent with this, herpes simplex virus 1 (HSV-1) causes invariable and rapid lethality in STING-deficient (STING ؊/؊ ) mice following intravenous (i.v.) infection. In this study, using real-time bioluminescence imaging and virological assays, as expected, we demonstrated that STING ؊/؊ mice support greater replication and spread in ocular tissues and the nervous system. In contrast, they did not succumb to challenge via the corneal route even with high titers of a virus that was routinely lethal to STING ؊/؊ mice by the i.v. route. Corneally infected STING ؊/؊ mice also showed increased periocular disease and increased corneal and trigeminal ganglia titers, although there was no difference in brain titers. They also showed elevated expression of tumor necrosis factor alpha (TNF-␣) and CXCL9 relative to control mice but surprisingly modest changes in type I interferon expression. Finally, we also showed that HSV strains lacking the ability to counter autophagy and the PKR-driven antiviral state had near-wild-type virulence following intracerebral infection of STING ؊/؊ mice. Together, these data show that while STING is an important component of host resistance to HSV in the cornea, its previously shown immutable role in mediating host survival by the i.v. route was not recapitulated following a mucosal infection route. Furthermore, our data are consistent with the idea that HSV counters STING-mediated induction of the antiviral state and autophagy response, both of which are critical factors for survival following direct infection of the nervous system. Herpes simplex virus 1 (HSV-1) is a member of the Alphaherpesvirus subfamily with high seroprevalence in the human population (1). Infection at mucosal surfaces such as the mouth, eyes, and genitalia leads initially to lytic replication in mucosal epithelial cells, followed by infection of the innervating sensory neurons. HSV-1 then travels in a retrograde direction to the neuronal cell body, where it establishes latency. It is this ability to establish latency that renders HSV-1 refractory to clearance by the immune system, allowing persistence for the lifetime of the host. During periods of reactivation from latency, HSV-1 can travel in the anterograde direction to mucosal tissues, causing diseases ranging in severity from the common cold sore to herpetic stromal keratitis (HSK), the most common cause of infectious blindness in the developed world (2). HSV-1 can also gain entry into the central nervous system (CNS) to cause herpes simplex encephalitis (HSE) (3). HSE is a leading cause of viral encephalitis, further underscoring the significant morbidity and mortality associated with HSV-1.In order to effectively respond to infection, host cells have evolved a broad spectrum of sensors of evolutionarily conserved pathogen-associated molecular patterns (PAMPS) (for reviews, see refer...

Interferon regulatory factors IRF-3 and IRF-7 are central to the establishment of the innate antiviral response. This study examines HSV-1 pathogenesis in IRF-3−/−, IRF-7−/− and double-deleted IRF3/7−/− (DKO) mice. Bioluminescence imaging of infection revealed that DKO mice developed visceral infection following corneal inoculation, along with increased viral burdens in all tissues relative to single knockout mice. While all DKO mice synchronously reached endpoint criteria 5 days post infection, the IRF-7−/− mice survived longer, indicating that although IRF-7 is dominant, IRF-3 also plays a role in controlling disease. Higher levels of systemic proinflammatory cytokines were found in IRF7−/− and DKO mice relative to wild-type and IRF-3−/− mice, and IL-6 and G-CSF, indicative of sepsis, were increased in the DKO mice relative to wild-type or single-knockout mice. In addition to controlling viral replication, IRF-3 and −7 therefore play coordinating roles in modulation of inflammation during HSV infection.