SUMOylation is a dynamically regulated post-translational modification involving covalent attachment of small ubiquitin-like modifiers (SUMOs) to lysine residues of target proteins. SUMOylation modulates multiple fundamental host cellular pathways, including pathways hijacked by HIV-1 to enable replication, but has not been explored by large-scale proteomics in the context of HIV-1 infection. Here, we performed a proteome-wide, mass spectrometry-based screen to identify proteins that are SUMOylated in response to HIV-1 infection. We show that infection with HIV-1 leads to the widespread increased SUMOylation of the heterogeneous nuclear ribonucleoprotein (HNRNP) A/B family. This phenotype was driven by expression of HIV-1 Viral Infectivity Factor (Vif), suggesting an unexplored function for this protein. Depletion of HNRNP A/B proteins led to altered splicing of HIV-1 viral RNAs and dramatically reduced HIV-1 infectivity. Our data suggest a mechanism involving HIV-1-induced, Vif-mediated SUMOylation of host RNA splicing factors as a means to regulate HIV-1 alternative splicing.

Since its emergence in 2019, circulating SARS-CoV-2 has been dominated by waves of genetically distinct variants with varying pathogenicity. Understanding the multidimensional responses to SARS-CoV-2 infection and their associations with pathogenesis is critical for developing therapies to prevent severe illness and death. Here, we applied quantitative proteome and phosphoproteome analyses to compare host responses to infections with an ancestral variant (WA-1/2020), a Delta variant (B.1.617.2), and an Omicron variant (BA.1) of SARS-CoV-2 in Syrian golden hamster tissues at 5 days postinfection, when peak inflammatory responses were observed. As has been observed by others, animals infected with the Delta variant lost more weight than those infected with other variants, and this effect was associated with decreased cilia proteins in the trachea tissue and increased signatures of fibrosis in lung tissue. Phosphoproteome analysis revealed a downregulation of Raf-MEK-ERK signaling across all variants, suggesting a suppressed proliferative response in tissues following SARS-CoV-2 infection. These data provide critical in vivo confirmation of observations from in vitro studies and provide a quantitative tissue- and SARS-CoV-2 variant-specific resource of proteome and phosphoproteome responses.

ABSTRACT Studies of herpes simplex virus (HSV) entry revealed a previously unrecognized “outside-in” signaling pathway involving phosphatidylserine (PS) scrambling and associated translocation and subsequent extracellular activation of canonical intracellular proteins, including Akt. We hypothesized that HIV-1, which activates a different scramblase, TMEM16F, to induce PS externalization, may similarly trigger an “outside-in” signaling response to promote viral entry. To study this process, we utilized a cell-impermeable staurosporine analog, alkyl-CIMSS, which is a broadly active kinase inhibitor that blocks HSV-induced exofacial Akt phosphorylation, and HSV entry. We show that TMEM16F-mediated PS externalization in response to HIV is not associated with Akt translocation; however, surprisingly, pretreatment of cells with alkyl-CIMSS enhanced HIV-1 infection post-entry. To identify potential biological processes that mediated this enhancement, we performed whole-cell total and phosphoproteomics, and bulk RNA sequencing. Cells treated with alkyl-CIMSS exhibited increased cyclin-dependent kinase (CDK) activity, resulting in higher levels of phosphorylated SAMHD1. Further, alkyl-CIMSS treatment robustly upregulated the cell surface density of the proteoglycan glypican-1 (GPC1). Lentivirus-driven GPC1 overexpression or shRNA knockdown demonstrated that, independent of alkyl-CIMSS treatment, GPC1 expression promotes HIV infection. Collectively, these findings demonstrate that alkyl-CIMSS modulates the exofacial plasma membrane to promote susceptibility to HIV infection by increasing CDK activity and upregulating GPC1.IMPORTANCEThe cell-impermeable pan-kinase inhibitor alkyl-CIMSS inhibits HSV infection by blocking phosphorylation of exofacial Akt. In contrast, alkyl-CIMSS enhances HIV infection. This increase was associated with enhanced cyclin-dependent kinase activity and upregulation of surface-presented glypican-1. These results illustrate that distinct processes associated with the exofacial proteome can either promote viral infection, as observed for HIV, or impede infection, as in the case of HSV, and may facilitate the identification of pathways that can be targeted for future antiviral drug development.

Orthoflaviviruses are RNA viruses responsible for significant diseases in humans, domesticated animals and wildlife. Their NS5 protein is central in viral replication, functioning both as an RNA-dependent RNA polymerase and a methyltransferase, while also modulating cellular processes, including the interferon response. Although viral replication is cytoplasmic, the NS5 protein of several mosquito-borne orthoflaviviruses cycles between the cytoplasm and the nucleus of infected human cells. However, the nuclear localization and function of NS5 of tick-borne orthoflaviviruses, such as tick-borne encephalitis virus (TBEV), remained poorly understood. Microscopy analysis and cell fractionation revealed that the NS5 protein of TBEV localized to both the cytoplasm and nucleoplasm of infected cells. Mutagenesis studies identified critical residues required for its nuclear targeting. Mutating these residues in a TBEV replicon abolished viral replication. Immunoprecipitation-mass spectrometry analyses performed in two human cell lines infected with TBEV recovered 352 NS5 partners. Among them, 187 were nuclear or partially nuclear. By integrating our interactome data with that of Powassan virus (POWV), another tick-borne orthoflavivirus, we refined a list of 20 high-confidence NS5 partners, including splicing factors and chromatin modulators. Functional analysis revealed that seven of these nuclear partners significantly modulated viral replication, further underscoring the importance of nuclear NS5 in the viral life cycle. Our work advances our understanding of the nuclear function of the NS5 proteins of tick-borne orthoflaviviruses.

Coronaviruses, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), can cause severe disease in humans, whereas reservoir hosts such as horseshoe bats remain asymptomatic. To investigate how host-specific protein-protein interactions (PPIs) influence infection, we generated comparative PPI maps for SARS-CoV-2 and its bat progenitor RaTG13, using affinity purification mass spectrometry (AP-MS) in human and greater horseshoe bat cells. We identify both conserved and virus- and host-specific interactions that regulate infection dynamics. Notably, SARS-CoV-2 requires a nonsynonymous mutation in the nucleocapsid to replicate in bat cells expressing human ACE2 and TMPRSS2. Strikingly, a single amino acid difference in Orf9b between viruses acts as a molecular switch that reprograms mitochondrial targeting: in human cells, enhanced translocase of outer mitochondrial membrane 70 (Tom70) binding promotes immune evasion, whereas in bat cells, strengthened interaction with the bat-enriched restriction factor mitochondrial amidoxime reducing component 2 (MTARC2) limits infection. These findings establish a general principle by which minimal sequence variation can reshape virus-host interactions and contribute to immune antagonism, host adaptation, and species barriers.

Powassan virus (POWV) is an emerging neurotropic tick-borne flavivirus, yet the mechanisms by which POWV evades host antiviral immunity remain poorly defined. Here, we identify multiple mechanisms of POWV innate immune antagonism with the viral polymerase NS5 protein as a central inhibitor of cytokine signaling. Both POWV lineages potently inhibited type I interferon (IFN) signaling, and NS5 expression suppressed signaling and downstream interferon-stimulated gene expression. Affinity purification-mass spectrometry identified the host kinase TYK2 as a conserved NS5 interactor. POWV NS5 binds the TYK2 kinase domain through a discrete interface within the RNA-dependent RNA polymerase (RdRp) region between catalytic motifs B and C and inhibits TYK2 phosphorylation. Disruption of this interface abrogated TYK2 binding and reduced NS5-mediated IFN antagonism, while revealing additional TYK2-independent mechanisms of immune suppression. POWV NS5 also inhibited TYK2-dependent IFN-λ and IL-12 signaling, demonstrating that its immune antagonism extends beyond type I IFN. Together, these findings identify TYK2 as a central target of POWV immune evasion and implicate the variable RdRp B-C region as an interface for flavivirus-host interactions. More broadly, our results reveal how POWV can coordinately suppress multiple antiviral cytokine pathways and provide insight into mechanisms that may shape tick-borne flavivirus host adaptation and pathogenesis.

Tuberculosis remains a globally significant infection, and new insights into the biology of Mycobacterium tuberculosis are badly needed. Discovery of protein localization and protein complex composition are powerful approaches to determine protein function but have not been widely applied in mycobacteria, in part due to technical barriers. Here we develop a multifunctional system that utilizes the ALFA tag and functional protein fusions to an anti-ALFA nanobody (NBALFA) to target proteins in fast- and slow-growing mycobacteria. Insertion of the ALFA epitope tag on the target protein, coupled with conditional expression of the NBALFA fused to a fluorescent protein, faithfully recapitulates cytosolic and membrane protein localization by fluorescent microscopy in living cells. Targeted NBALFA can relocalize an ALFA-tagged protein to inclusion bodies or the cytoplasmic membrane, demonstrating enforced protein localization. Finally, the conditional expression of the NBALFA fused to TurboID for proximity proteomics allowed the identification of known partner proteins of the RNA polymerase complex and the PKS13 mycolic acid biosynthesis protein. We conclude that the split ALFA tag-nanobody system is a flexible platform for discovering protein biology in mycobacteria.IMPORTANCEThis study establishes a new platform for discovery proteomics in mycobacteria using a new nanobody-based approach. The findings will be of interest for all bacteriologists as the approach will be applicable to a variety of microbial systems.

Type I interferons (IFN-Is) are cytokines with potent antiviral and inflammatory capacities. IFN-I signaling drives the expression of thousands of IFN-I-stimulated genes (ISGs), whose aggregate function results in the control of viral infections. A few of these ISGs are tasked with negatively regulating the IFN-I response to prevent overt inflammation. ISG15 is a negative regulator whose absence leads to persistent, low-grade elevation of ISG expression and concurrent, often self-resolving, mild autoinflammation. The limited breadth and low-grade persistence of ISGs expressed in ISG15 deficiency are sufficient to confer broad-spectrum antiviral resistance. Inspired by the antiviral state of humans with ISG15 deficiency, we identified a nominal collection of 10 ISGs that recapitulated the broad antiviral potential of the IFN-I system, which typically induces the expression of thousands of ISGs. The expression of this 10-ISG collection in an IFN-I-nonresponsive cell line increased cellular resistance to Zika virus, vesicular stomatitis virus, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A lipid nanoparticle-encapsulated messenger RNA (mRNA) formulation of this 10-ISG collection reduced influenza A virus plaque size in samples collected from infected mice when given prophylactically. Moreover, when used collectively and delivered prophylactically, the 10-ISG collection was able to protect hamsters against a lethal SARS-CoV-2 challenge, in contrast with the lack of efficacy when mRNAs were delivered individually. These findings suggest that these 10 ISGs have potential as a broad-spectrum antiviral prophylactic.

Despite the success of antiretroviral therapy (ART), HIV-1 persists in latently infected cells, posing a central barrier to a cure. "Shock-and-kill" strategies using latency-reversing agents (LRAs) have shown some promise in reactivating viral gene expression ex vivo, but have yielded little clinical efficacy, underscoring the need for deeper insight into the molecular mechanisms that govern reactivation. Here, we performed deep quantitative phosphoproteomics of J-Lat 10.6 cells treated with diverse LRAs: SAHA, PMA, or prostratin. We identified 48,476 confidently localized phosphorylation sites mapping to 6,672 proteins, with SAHA inducing the most extensive changes. Regulated phosphoproteins were enriched in chromatin organization, transcription, RNA processing, nuclear transport, and cytoskeletal remodeling. Although LRAs regulated overlapping pathways, they elicited divergent kinase activities and site-specific phosphorylation patterns. A reproducible core of 3,502 phosphorylation sites on 1,432 proteins mapped to 39 nuclear protein complexes, including the spliceosome, Mediator, NF-κB, and RNA polymerase II. Remarkably, 20 protein complexes were phosphoregulated by all three LRAs, but at distinct sites, revealing convergence on shared nuclear machinery through distinct mechanisms. This study provides a comprehensive map of protein complex phosphorylation remodeling during HIV-1 reactivation and highlights signaling mechanisms that could guide the rational design of next-generation LRAs with improved efficacy and reduced toxicity.

To usurp host defenses and establish a replicative niche, obligate intracellular pathogens are tasked with remodeling the host cell using a comparatively small repertoire of effector proteins. For Chlamydia trachomatis (C.t), discovery of secreted proteins and their host targets has been particularly challenging due to the bacterium's historical genetic intractability. Using affinity purification-mass spectrometry, we defined host interaction partners for 21 secreted effector proteins, providing the first comprehensive type III secretion system (T3SS) effector-host interactome generated during infection. Among these, we show that the C-terminus of CebN (CT584) binds multiple nucleoporins and Rae1, host factors previously associated only with viral immune evasion. Remarkably, we shown that CebN localizes to the nuclear envelope not only in infected cells but also in uninfected bystander cells. Functionally, CebN is both necessary and sufficient to perturb STAT1 nuclear import following IFN-γ stimulation and its expression is critical for C.t. survival, as evidenced by reduced bacterial replication and smaller inclusions in cells infected with a CebN mutant. Together, these finds expand our understanding of chlamydia effector biology and highlight novel bacterial strategies for manipulating host defenses at the nuclear pore.

The obligate intracellular pathogen Chlamydia trachomatis replicates in a specialized membrane-bound compartment where it repositions host organelles during infection to acquire nutrients and evade host surveillance. We describe a bacterial effector, Dre1, that binds specifically to dynactin associated with host microtubule organizing centers without globally impeding dynactin function. Dre1 is required to reposition the centrosome, mitotic spindle, Golgi apparatus, and primary cilia around the inclusion and contributes to pathogen fitness in cell-based and mouse models of infection. We utilized Dre1 to affinity purify the megadalton dynactin protein complex and determined the first cryoelectron microscopy (cryo-EM) structure of human dynactin. Our results suggest that Dre1 binds to the pointed end of dynactin and uncovers the first bacterial effector that modulates dynactin function. Our work highlights how a pathogen employs a single effector to evoke targeted, large-scale changes in host cell organization that facilitate pathogen growth without inhibiting host viability.

Influenza A virus (IAV) infection remodels cellular processes to support viral replication. The modulation of host factors by the virus drives pathogenesis during infection, and these factors may serve as therapeutic targets. Here, we infect mice with two IAV strains, H1N1 and H5N1, and analyze lung tissue with multi-omics. Using network propagation analysis, we identify twenty-four distinct host modules altered by infection, encompassing 2920 genes/proteins. Independently, we develop a computational pipeline, MidTOD, which integrates metabolomic data with other OMICs data-types, linking metabolites to gene/protein alterations. Combining datasets from both approaches reveals alterations in mitochondrial and peroxisomal metabolism in IAV-infected cells and identifies arginine:glycine amidinotransferase (GATM) as a host dependency factor in both human cells and mice. Knockdown of this enzyme reduces IAV-mediated pathology and host inflammatory responses after infection. Collectively, this work provides an integrated systems-level view of host changes during infection and identifies an abundance of IAV-host factors.

HIV-1 exploits host cell post-translation modifications (PTMs) to facilitate production of infectious particles. These modifications include SUMOylation, a dynamically regulated PTM involving covalent attachment of small ubiquitin-like modifiers (SUMOs) to lysine (K) residues of target proteins. SUMOylation modulates the activity of thousands of proteins and multiple fundamental host cellular processes, including pathways hijacked by HIV-1 to promote infection and spread. The SUMOylation of several proteins during HIV-1 infection has been characterized. However, the broad effects of HIV-1 infection on the SUMOylation of the host cell proteome is largely unknown. To date, SUMOylation has not been explored by large-scale proteomics in the context of HIV infection, where many SUMO-regulated host dependency factors remain to be identified. In this study, we performed a proteome-wide, mass spectrometry (MS)-based screen to identify proteins that are SUMOylated during HIV-1 infection. Here, and in immunoprecipitation assays, infection with HIV-1 led to the widespread increased SUMOylation of heterogeneous nuclear ribonucleoprotein (HNRNP) A/B family members. We selected HNRNPA2B1 (A2/B1) and HNRNPA3 for further study. We find that infection with HIV-1 specifically induced the SUMOylation of both proteins by SUMO1 and SUMO2 paralogs in multiple biochemical assays and in multiple human cell lines. Current efforts include generating non-SUMOylatable HNRNPA2B1 and HNRNPA3 mutants to test the functional consequences of their SUMOylation on the splicing of HIV-1 mRNAs. Together, our data point to a novel mechanism involving HIV-1-induced SUMOylation of these host RNA splicing factors as a means to regulate HIV-1 splice variant production. Broadly, our findings suggest that infection with HIV-1 alters the SUMOylation of many unexplored host cellular proteins, and provides a proteomic resource for their future mechanistic study. ### Competing Interest Statement The authors have declared no competing interest.

Upon infection, viruses alter the proteome, creating a hospitable environment for infection. Cells respond to limit viral replication, including through protein regulation by post-translational modifications. We use mass spectrometry to define proteome alterations during West Nile virus (WNV) infection. Our studies identify upregulation of HERPUD1, which restricts WNV replication through a mechanism independent of its role in endoplasmic reticulum (ER)-associated degradation (ERAD). We also identify modifications on viral proteins, including a WNV NS3 phosphorylation site that impacts viral replication. Finally, we reveal activation of two host kinases with antiviral activity. We identify phosphorylation at S108 of AMPKβ1, a non-catalytic subunit that regulates activity of the AMPK complex. We also show activation of PAK2 by phosphorylation at S141, which restricts translation of the viral genome. This work contributes to our understanding of the interplay between host and virus while providing a resource to define the changes to the proteome that regulate viral infection.

Human endogenous retroviruses (HERVs) occupy a large portion of the human genome. Most HERVs are transcriptionally silent, but they can be reactivated during pathological states such as viral infection and certain cancers. The HERV-K HML-2 clade includes elements that recently integrated have in the human germ line and often contain intact open reading frames that possibly support peptide and protein expression. Understanding HERV-K-host interactions and their potential as biomarkers is problematic due to the high similarity among different elements. Previously, we described a long-read single molecule real-time sequencing (PacBio) strategy to analyze HERV-K RNA expression profiles in different cell types. However, identifying HERV-K HML-2 proteins accurately is difficult without robust and reliable methods and reagents. Here we present a new approach to characterize the HML-2 elements that (a) are being translated and (b) produce enough protein to be detected and identified by mass spectrometry. Our data reveal that RNA expression profiling alone cannot accurately predict which HML-2 elements are responsible for protein production, as we observe several differences between the highest expressed RNAs and the elements that are the predominant source of HERV-K HML-2 protein synthesis. These studies represent an important advance toward untangling the complexity of HERV-K-host interactions.

Persistent HIV reservoirs in CD4+ T-cells pose a barrier to curing HIV infection. We identified overexpression of enhancer of zeste homolog 2 (EZH2) in HIV-infected CD4+ T-cells that survive cytotoxic T lymphocyte (CTL) exposure, suggesting a mechanism of CTL resistance. Inhibition of EZH2 with the FDA-approved drug tazemetostat increased surface expression of major histocompatibility complex class I (MHC-I) on CD4+ T-cells, counterbalancing HIV Nef-mediated MHC-I downregulation. This improved CTL-mediated elimination of HIV-infected cells and suppressed viral replication in vitro. In a participant-derived xenograft mouse model, tazemetostat elevated MHC-I and the pro-apoptotic protein BIM in CD4+ T-cells, facilitating CD8+ T-cell-mediated reductions of HIV reservoir seeding. Additionally, tazemetostat promoted sustained skewing of CD8+ T-cells toward less differentiated and exhausted phenotypes. Our findings reveal EZH2 overexpression as a novel mechanism of CTL resistance and support the clinical evaluation of tazemetostat to enhance clearance of HIV reservoirs and improve CD8+ T-cell function. ### Competing Interest Statement R.B.J has served as an advisor to ViiV Healthcare and received payment for this role.

The cellular DNA damage response pathway can have vastly different outcomes depending on the source of its activation. Justice and colleagues apply phosphoproteomics to uncover a divergence in DNA-PK and ATM kinase activities in the contexts of DNA damage and DNA virus infection.

Sensory signaling pathways use adaptation to dynamically respond to changes in their environment. Here, we report the mechanism of sensory adaptation in the Pil-Chp mechanosensory system, which the important human pathogen Pseudomonas aeruginosa uses to sense mechanical stimuli during surface exploration. Using biochemistry, genetics, and cell biology, we discovered that the enzymes responsible for adaptation, a methyltransferase and a methylesterase, are segregated to opposing cell poles as P. aeruginosa explore surfaces. By coordinating the localization of both enzymes, we found that the Pil-Chp response regulators influence local receptor methylation, the molecular basis of bacterial sensory adaptation. We propose a model in which adaptation during mechanosensing spatially resets local receptor methylation, and thus Pil-Chp signaling, to modulate the pathway outputs, which are involved in P. aeruginosa virulence. Despite decades of bacterial sensory adaptation studies, our work has uncovered an unrecognized mechanism that bacteria use to achieve adaptation to sensory stimuli.