XPO1 (Exportin-1/CRM1) is a nuclear export protein that is frequently overexpressed in cancer and functions as a driver of oncogenesis. Currently small molecules that target XPO1 are being used in the clinic as anticancer agents. We identify XPO1 as a target for natural killer (NK) cells. Using immunopeptidomics, we have identified a peptide derived from XPO1 that can be recognized by the activating NK cell receptor KIR2DS2 in the context of human leukocyte antigen-C. The peptide can be endogenously processed and presented to activate NK cells specifically through this receptor. Although high XPO1 expression in cancer is commonly associated with a poor prognosis, we show that the outcome of specific cancers, such as hepatocellular carcinoma, can be substantially improved if there is concomitant evidence of NK cell infiltration. We thus identify XPO1 as a bona fide tumor antigen recognized by NK cells that offers an opportunity for a personalized approach to NK cell therapy for solid tumors.

BACKGROUND: Exportin 1 (XPO1) is a nuclear export protein that facilitates the transportation of various substances. XPO1 promotes tumor development as a poor prognostic factor in a variety of tumors and is a therapeutic target for screening inhibitors. However, the role of XPO1 in oral squamous cell carcinoma (OSCC) has yet to be determined.
METHODS: The expression patterns of XPO1 mRNA in OSCC were investigated using bioinformatics tools, and the expression levels of XPO1 protein in OSCC specimens were confirmed by immunohistochemical assays. Survival analysis was conducted to evaluate the impact of XPO1 on prognosis. GO and KEGG enrichment analyses were utilized to uncover the signaling pathways mediated by XPO1. Additionally, we examined the association between XPO1 and AKT/MAPK/TGFBR1 and immune infiltration.
RESULTS: XPO1 mRNA and protein expression levels were significantly enhanced in OSCC and associated with OSCC severity. Enhanced XPO1 expression was indicative of poor survival. Functional analysis showed that XPO1 mediated pathways associated with cell cycle and DNA replication and reduced immune infiltration in OSCC. Additionally, XPO1 mRNA and protein expression levels had significant positive relationships with AKT/MAPK/TGFBR1.
CONCLUSIONS: XPO1, as a marker of poor prognosis in OSCC, can promote OSCC through AKT/MAPK/TGFBR1.

Flaviviridae is a family of positive-stranded RNA viruses, including human pathogens, such as Japanese encephalitis virus (JEV), dengue virus (DENV), Zika virus (ZIKV), and West Nile virus (WNV). Nuclear localization of the viral core protein is conserved among Flaviviridae, and this feature may be targeted for developing broad-ranging anti-flavivirus drugs. However, the mechanism of core protein translocation to the nucleus and the importance of nuclear translocation in the viral life cycle remain unknown. We aimed to identify the molecular mechanism underlying core protein nuclear translocation. We identified importin-7 (IPO7), an importin-β family protein, as a nuclear carrier for Flaviviridae core proteins. Nuclear import assays revealed that core protein was transported into the nucleus via IPO7, whereas IPO7 deletion by CRISPR/Cas9 impaired their nuclear translocation. To understand the importance of core protein nuclear translocation, we evaluated the production of infectious virus or single-round-infectious-particles in wild-type or IPO7-deficient cells; both processes were significantly impaired in IPO7-deficient cells, whereas intracellular infectious virus levels were equivalent in wild-type and IPO7-deficient cells. These results suggest that IPO7-mediated nuclear translocation of core proteins is involved in the release of infectious virus particles of flaviviruses.

Though RNAi and RNA-splicing machineries are involved in regulating severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication, their precise roles in coronavirus disease 2019 (COVID-19) pathogenesis remain unclear. Herein, we show that decreased RNAi component (Dicer and XPO5) and splicing factor (SRSF3 and hnRNPA3) expression correlate with increased COVID-19 severity. SARS-CoV-2 N protein induces the autophagic degradation of Dicer, XPO5, SRSF3, and hnRNPA3, inhibiting miRNA biogenesis and RNA splicing and triggering DNA damage, proteotoxic stress, and pneumonia. Dicer, XPO5, SRSF3, and hnRNPA3 knockdown increases, while their overexpression decreases, N protein-induced pneumonia\'s severity. Older mice show lower expression of Dicer, XPO5, SRSF3, and hnRNPA3 in their lung tissues and exhibit more severe N protein-induced pneumonia than younger mice. PJ34, a poly(ADP-ribose) polymerase inhibitor, or anastrozole, an aromatase inhibitor, ameliorates N protein- or SARS-CoV-2-induced pneumonia by restoring Dicer, XPO5, SRSF3, and hnRNPA3 expression. These findings will aid in developing improved treatments for SARS-CoV-2-associated pneumonia.

Nuclear export of the viral ribonucleoprotein (vRNP) is a critical step in the influenza A virus (IAV) life cycle and may be an effective target for the development of anti-IAV drugs. The host factor ras-related nuclear protein (RAN) is known to participate in the life cycle of several viruses, but its role in influenza virus replication remains unknown. In the present study, we aimed to determine the function of RAN in influenza virus replication using different cell lines and subtype strains. We found that RAN is essential for the nuclear export of vRNP, as it enhances the binding affinity of XPO1 toward the viral nuclear export protein NS2. Depletion of RAN constrained the vRNP complex in the nucleus and attenuated the replication of various subtypes of influenza virus. Using in silico compound screening, we identified that bepotastine could dissociate the RAN-XPO1-vRNP trimeric complex and exhibit potent antiviral activity against influenza virus both in vitro and in vivo. This study demonstrates the important role of RAN in IAV replication and suggests its potential use as an antiviral target.

SF3B1 mutations frequently occur in cancer yet lack targeted therapies. Clinical trials of XPO1 inhibitors, selinexor and eltanexor, in high-risk myelodysplastic neoplasms (MDS) revealed responders were enriched with SF3B1 mutations. Given that XPO1 (Exportin-1) is a nuclear exporter responsible for the export of proteins and multiple RNA species, this led to the hypothesis that SF3B1-mutant cells are sensitive to XPO1 inhibition, potentially due to altered splicing. Subsequent RNA sequencing after XPO1 inhibition in SF3B1 wildtype and mutant cells showed increased nuclear retention of RNA transcripts and increased alternative splicing in the SF3B1 mutant cells particularly of genes that impact apoptotic pathways. To identify novel drug combinations that synergize with XPO1 inhibition, a forward genetic screen was performed with eltanexor treatment implicating anti-apoptotic targets BCL2 and BCLXL, which were validated by functional testing in vitro and in vivo. These targets were tested in vivo using Sf3b1K700E conditional knock-in mice, which showed that the combination of eltanexor and venetoclax (BCL2 inhibitor) had a preferential sensitivity for SF3B1 mutant cells without excessive toxicity. In this study, we unveil the mechanisms underlying sensitization to XPO1 inhibition in SF3B1-mutant MDS and preclinically rationalize the combination of eltanexor and venetoclax for high-risk MDS.

Intron-containing RNA expressed from the HIV-1 provirus activates type 1 interferon in primary human blood cells, including CD4+ T cells, macrophages, and dendritic cells. To identify the innate immune receptor required for detection of intron-containing RNA expressed from the HIV-1 provirus, a loss-of-function screen was performed with short hairpin RNA-expressing lentivectors targeting twenty-one candidate genes in human monocyte-derived dendritic cells. Among the candidate genes tested, only knockdown of XPO1 (CRM1), IFIH1 (MDA5), or MAVS prevented activation of the interferon-stimulated gene ISG15. The importance of IFIH1 protein was demonstrated by rescue of the knockdown with nontargetable IFIH1 coding sequence. Inhibition of HIV-1-induced ISG15 by the IFIH1-specific Nipah virus V protein, and by IFIH1-transdominant 2-CARD domain-deletion or phosphomimetic point mutations, indicates that IFIH1 (MDA5) filament formation, dephosphorylation, and association with MAVS are all required for innate immune activation in response to HIV-1 transduction. Since both IFIH1 (MDA5) and DDX58 (RIG-I) signal via MAVS, the specificity of HIV-1 RNA detection by IFIH1 was demonstrated by the fact that DDX58 knockdown had no effect on activation. RNA-Seq showed that IFIH1 knockdown in dendritic cells globally disrupted the induction of IFN-stimulated genes by HIV-1. Finally, specific enrichment of unspliced HIV-1 RNA by IFIH1 (MDA5), over two orders of magnitude, was revealed by formaldehyde cross-linking immunoprecipitation (f-CLIP). These results demonstrate that IFIH1 is the innate immune receptor for intron-containing RNA from the HIV-1 provirus and that IFIH1 potentially contributes to chronic inflammation in people living with HIV-1, even in the presence of effective antiretroviral therapy.

Molecular glues can induce proximity between a target protein and ubiquitin ligases to induce target degradation, but strategies for their discovery remain limited. We screened 3,200 bioactive small molecules and identified that C646 requires neddylation-dependent protein degradation to induce cytotoxicity. Although the histone acetyltransferase p300 is the canonical target of C646, we provide extensive evidence that C646 directly targets and degrades Exportin-1 (XPO1). Multiple cellular phenotypes induced by C646 were abrogated in cells expressing the known XPO1C528S drug-resistance allele. While XPO1 catalyzes nuclear-to-cytoplasmic transport of many cargo proteins, it also directly binds chromatin. We demonstrate that p300 and XPO1 co-occupy hundreds of chromatin loci. Degrading XPO1 using C646 or the known XPO1 modulator S109 diminishes the chromatin occupancy of both XPO1 and p300, enabling direct targeting of XPO1 to phenocopy p300 inhibition. This work highlights the utility of drug-resistant alleles and further validates XPO1 as a targetable regulator of chromatin state.

Myeloid-derived suppressor cells (MDSCs) are a main driver of immunosuppression in tumors. Understanding the mechanisms that determine the development and immunosuppressive function of these cells could provide new therapeutic targets to improve antitumor immunity. Here, using preclinical murine models, we discovered that exportin 1 (XPO1) expression is upregulated in tumor MDSCs and that this upregulation is induced by IL-6-induced STAT3 activation during MDSC differentiation. XPO1 blockade transforms MDSCs into T-cell-activating neutrophil-like cells, enhancing the antitumor immune response and restraining tumor growth. Mechanistically, XPO1 inhibition leads to the nuclear entrapment of ERK1/2, resulting in the prevention of ERK1/2 phosphorylation following the IL-6-mediated activation of the MAPK signaling pathway. Similarly, XPO1 blockade in human MDSCs induces the formation of neutrophil-like cells with immunostimulatory functions. Therefore, our findings revealed a critical role for XPO1 in MDSC differentiation and suppressive functions; exploiting these new discoveries revealed new targets for reprogramming immunosuppressive MDSCs to improve cancer therapeutic responses.

As the world\'s first oral nuclear export inhibitor, selinexor is increasingly being used in clinical applications for malignant tumors. However, there is no extensive exploration on selinexor\'s adverse events (ADEs), necessitating a real-word assessment of its clinical medication safety. FAERS data (July 2019-June 2023) were searched for selinexor ADE reports across all indications. Use the system organ class (SOC) and preferred terms (PT) from the medical dictionary for regulatory activities (MedDRA) to describe, categorize, and statistic ADEs. Disproportionality analysis was employed through calculation of reporting odds ratio (ROR) and proportional reporting ratio (PRR). Based on total of 4392 selinexor related ADE reports as the primary suspect (PS), of which 2595 instances were severe outcomes. The predominant ADEs included gastrointestinal disorders, myelosuppression symptoms, and various nonspecific manifestations. 124 signals associated with selinexor ADE were detected, and 10 of these top 15 signals were not included into the instructions. Our study provides real-world evidence regarding the drug safety of selinexor, which is crucial for clinicians to safeguard patients\' health.