Cellular Importin-α3 Expression Dynamics in the Lung Regulate Antiviral Response Pathways against Influenza A Virus Infection.

Importin-α adaptor proteins orchestrate dynamic nuclear transport processes involved in cellular homeostasis. Here, we show that importin-α3, one of the main NF-κB transporters, is the most abundantly expressed classical nuclear transport factor in the mammalian respiratory tract. Importin-α3 promoter activity is regulated by TNF-α-induced NF-κB in a concentration-dependent manner. High-level TNF-α-inducing highly pathogenic avian influenza A viruses (HPAIVs) isolated from fatal human cases harboring human-type polymerase signatures (PB2 627K, 701N) significantly downregulate importin-α3 mRNA expression in primary lung cells. Importin-α3 depletion is restored upon back-mutating the HPAIV polymerase into an avian-type signature (PB2 627E, 701D) that can no longer induce high TNF-α levels. Importin-α3-deficient mice show reduced NF-κB-activated antiviral gene expression and increased influenza lethality. Thus, importin-α3 plays a key role in antiviral immunity against influenza. Lifting the bottleneck in importin-α3 availability in the lung might provide a new strategy to combat respiratory virus infections.

Regulation of the Ebola Virus VP24 Protein by SUMO.

Some viruses take advantage of conjugation of ubiquitin or ubiquitin-like proteins to enhance their own replication. One example is Ebola virus, which has evolved strategies to utilize these modification pathways to regulate the viral proteins VP40 and VP35 and to counteract the host defenses. Here, we show a novel mechanism by which Ebola virus exploits the ubiquitin and SUMO pathways. Our data reveal that minor matrix protein VP24 of Ebola virus is a bona fide SUMO target. Analysis of a SUMOylation-defective VP24 mutant revealed a reduced ability to block the type I interferon (IFN) pathway and to inhibit IFN-mediated STAT1 nuclear translocation, exhibiting a weaker interaction with karyopherin 5 and significantly diminished stability. Using glutathione S-transferase (GST) pulldown assay, we found that VP24 also interacts with SUMO in a noncovalent manner through a SIM domain. Mutation of the SIM domain in VP24 resulted in a complete inability of the protein to downmodulate the IFN pathway and in the monoubiquitination of the protein. We identified SUMO deubiquitinating enzyme ubiquitin-specific-processing protease 7 (USP7) as an interactor and a negative modulator of VP24 ubiquitination. Finally, we show that mutation of one ubiquitination site in VP24 potentiates the IFN modulatory activity of the viral protein and its ability to block IFN-mediated STAT1 nuclear translocation, pointing to the ubiquitination of VP24 as a negative modulator of the VP24 activity. Altogether, these results indicate that SUMO interacts with VP24 and promotes its USP7-mediated deubiquitination, playing a key role in the interference with the innate immune response mediated by the viral protein.IMPORTANCE The Ebola virus VP24 protein plays a critical role in escape of the virus from the host innate immune response. Therefore, deciphering the molecular mechanisms modulating VP24 activity may be useful to identify potential targets amenable to therapeutics. Here, we identify the cellular proteins USP7, SUMO, and ubiquitin as novel interactors and regulators of VP24. These interactions may represent novel potential targets to design new antivirals with the ability to modulate Ebola virus replication.

Genome-wide meta-analysis reveals shared new loci in systemic seropositive rheumatic diseases.

OBJECTIVE: Immune-mediated inflammatory diseases (IMIDs) are heterogeneous and complex conditions with overlapping clinical symptoms and elevated familial aggregation, which suggests the existence of a shared genetic component. In order to identify this genetic background in a systematic fashion, we performed the first cross-disease genome-wide meta-analysis in systemic seropositive rheumatic diseases, namely, systemic sclerosis, systemic lupus erythematosus, rheumatoid arthritis and idiopathic inflammatory myopathies. METHODS: We meta-analysed ~6.5 million single nucleotide polymorphisms in 11 678 cases and 19 704 non-affected controls of European descent populations. The functional roles of the associated variants were interrogated using publicly available databases. RESULTS: Our analysis revealed five shared genome-wide significant independent loci that had not been previously associated with these diseases: NAB1, KPNA4-ARL14, DGQK, LIMK1 and PRR12. All of these loci are related with immune processes such as interferon and epidermal growth factor signalling, response to methotrexate, cytoskeleton dynamics and coagulation cascade. Remarkably, several of the associated loci are known key players in autoimmunity, which supports the validity of our results. All the associated variants showed significant functional enrichment in DNase hypersensitivity sites, chromatin states and histone marks in relevant immune cells, including shared expression quantitative trait loci. Additionally, our results were significantly enriched in drugs that are being tested for the treatment of the diseases under study. CONCLUSIONS: We have identified shared new risk loci with functional value across diseases and pinpoint new potential candidate loci that could be further investigated. Our results highlight the potential of drug repositioning among related systemic seropositive rheumatic IMIDs.

Induction of immunogenic cell death by radiation-upregulated karyopherin alpha 2 in vitro.

Accumulating evidence suggests the potential for radiation therapy to generate antitumor immune responses against tumor cells by inducing immunogenic cell death and phenotypic changes. We recently found that ionizing radiation upregulated karyopherin α2 (KPNA2) in HT-29 colorectal tumor cells using quantitative proteomic analysis. To determine whether this increased KPNA2 could function as a damage-associated molecular pattern to induce antitumor immune responses, mouse bone-marrow-derived dendritic cells (BMDCs) were treated with KPNA2. KPNA2 enhanced the surface expression of CD40, CD54, CD80, CD86, and MHC class I/II on BMDCs. DCs treated with KPNA2 exhibited increased secretion of pro-inflammatory cytokines such as IL-1ß, IL-6, IL-12, IL-23, and TNF-α. Co-culture of CD4(+) T cells and KPNA2-treated DCs resulted in induction of Th1/17 cytokines (IFN-γ and IL-17) and reduction of TGF-ß production. Moreover, KPNA2-treated DCs were capable of increasing granzyme B and perforin expression in cytotoxic T lymphocytes. These results demonstrated that radiation-induced dying colorectal cancer cells released considerable amounts of KPNA2 that induce the maturation and activation of DCs for synergistic antitumor effect of radiation.

Lloviu virus VP24 and VP35 proteins function as innate immune antagonists in human and bat cells.

Lloviu virus (LLOV) is a new member of the filovirus family that also includes Ebola virus (EBOV) and Marburg virus (MARV). LLOV has not been cultured; however, its genomic RNA sequence indicates the coding capacity to produce homologs of the EBOV and MARV VP24, VP35, and VP40 proteins. EBOV and MARV VP35 proteins inhibit interferon (IFN)-alpha/beta production and EBOV VP35 blocks activation of the antiviral kinase PKR. The EBOV VP24 and MARV VP40 proteins inhibit IFN signaling, albeit by different mechanisms. Here we demonstrate that LLOV VP35 suppresses Sendai virus induced IFN regulatory factor 3 (IRF3) phosphorylation, IFN-α/ß production, and PKR phosphorylation. Additionally, LLOV VP24 blocks tyrosine phosphorylated STAT1 binding to karyopherin alpha 5 (KPNA5), STAT1 nuclear accumulation, and IFN-induced gene expression. LLOV VP40 lacks detectable IFN antagonist function. These activities parallel EBOV IFN inhibitory functions. EBOV and LLOV VP35 and VP24 proteins also inhibit IFN responses in bat cells. These data suggest that LLOV infection will block innate immune responses in a manner similar to EBOV.

KPNA2 Contributes to the Inflammatory Processes in Synovial Tissue of Patients with Rheumatoid Arthritis and SW982 Cells.

Karyopherin-α2 (KPNA2) functions as an adaptor that transports several proteins to the nucleus. We investigated the function and possible mechanisms of KPNA2 involved in rheumatoid arthritis (RA). Western blotting and immunohistochemistry showed the protein expression of KPNA2 increased in synovial tissue of RA patients compared with the healthy controls. Double immunofluorescent staining indicated that KPNA2 co-localized with T cells, macrophage-like synoviocytes, fibroblast-like synoviocytes, and neutrophils in synovial tissue of RA patients. Moreover, the expression of KPNA2 in SW982 cells was increased in a time-dependent manner in response to TNFα stimulation. Both Western blotting and immunofluorescent staining assay revealed the co-localization of KPNA2 and P65 and their translocation from cytoplasma in TNFα-treated SW982 cells. Furthermore, knocking down the expression of KPNA2 by siRNA inhibited TNFα-induced expression of IL-6, MMP-1, and MMP-13 and, more importantly, decreased the P65 phosphorylation in SW982 cells. We therefore suggested that KPNA2 may play a key role in the inflammation process of RA via NF-κB P65 signal transduction pathway.

MicroRNA-181b regulates NF-κB-mediated vascular inflammation.

EC activation and dysfunction have been linked to a variety of vascular inflammatory disease states. The function of microRNAs (miRNAs) in vascular EC activation and inflammation remains poorly understood. Herein, we report that microRNA-181b (miR-181b) serves as a potent regulator of downstream NF-κB signaling in the vascular endothelium by targeting importin-α3, a protein that is required for nuclear translocation of NF-κB. Overexpression of miR-181b inhibited importin-α3 expression and an enriched set of NF-κB-responsive genes such as adhesion molecules VCAM-1 and E-selectin in ECs in vitro and in vivo. In addition, treatment of mice with proinflammatory stimuli reduced miR-181b expression. Rescue of miR-181b levels by systemic administration of miR-181b "mimics" reduced downstream NF-κB signaling and leukocyte influx in the vascular endothelium and decreased lung injury and mortality in endotoxemic mice. In contrast, miR-181b inhibition exacerbated endotoxin-induced NF-κB activity, leukocyte influx, and lung injury. Finally, we observed that critically ill patients with sepsis had reduced levels of miR-181b compared with control intensive care unit (ICU) subjects. Collectively, these findings demonstrate that miR-181b regulates NF-κB-mediated EC activation and vascular inflammation in response to proinflammatory stimuli and that rescue of miR-181b expression could provide a new target for antiinflammatory therapy and critical illness.

Generation of rat monoclonal antibody specific for mouse importin α8.

The transport of proteins in and out of the nucleus plays important roles in major cellular processes, such as signal transduction and regulation of cell cycle. Proteins that contain a nuclear localization signal (NLS) are recognized by an importin α/ß heterodimer and targeted to the nucleus. Here, we report the generation of a rat monoclonal antibody (MAb) that recognizes a novel importin α family member, importin α8, which is expressed during oocyte maturation and early embryonic development. Immunoblot and immunolocalization analyses showed that this MAb was specific for mouse importin α8 and not other importin α family members. These data suggest that this MAb is useful for analyzing molecular functions of importin α8.

Generation and characterization of a monoclonal antibody against importin α7/NPI-2.

Many nuclear proteins are transported into the nucleus via the importin α/ß-mediated pathway. Importin α comprises a multigene family. In this study, we generated and characterized a rat monoclonal antibody (MAb) 3F8 to importin α7. The antibody was generated by the hybridization of mouse myeloma cells with lymph node cells from an immunized rat. The MAb 3F8 specifically recognized importin α7 among importin α isoforms as evidenced by immunoblotting analysis. Furthermore, MAb 3F8 detected exogenous importin α7 in COS-7 cells by immunofluorescence. This MAb will be useful in the analysis of the isoform-specific function of importin α7.

Karyopherin alpha 2 (KPNA2) is associated with the natural resistance to Schistosoma japanicum infection in Microtus fortis.

Microtus fortis is a naturally vertebrate host resistant to Schistosoma japonicum infection. In order to understand the molecular mechanism and identify the molecules related to the natural resistance to S. japanicum infection of M. fortis, we screened a gene pool named gE76 by expression cloning and proved it to have high anti-schistosomula effects in our previous work. In this study we identified a clone named gE76.44. We found that the conditioned medium of pcDNA1.1-gE76.44 caused 14.0% schistosomula death rate in 96 h, which was significantly higher than that of negative control (P<0.05). The gE76.44 was sequenced and the full-length cDNA was 2008 bp with ORF of 1590bp encoding a polypeptide of 529 amino acid residues. Bioinformatics analysis indicated it was the homologue of karyopherin alpha 2 (KPNA2). To further confirm its anti-schistosome activity, we inserted full length of Mf-KPNA2 (KPNA2 of M. fortis) gene into a retroviral expression vector pLXSN and packaged the recombinant virus with PA317 cells. Mice infected with S. japanicum cercariae were administrated by intravenous injection through tail vein and treated with pLXSN-KPNA2. Adult worms and egg reduction were counted after heart perfusion of mice 42 d after infection. We found that compared with the control, mice injected with Mf-KPNA2 had 39.42% worm burden reduction and 76.50% reduction in LEPG (liver eggs per gram) (P<0.01), indicating its anti-schistosome effect of Mf-KPNA2 in vivo. Taken together, the results suggested Mf-KPNA2 as a novel anti-schistosome molecule in vitro and in vivo.

Suppression of GATA-3 nuclear import and phosphorylation: a novel mechanism of corticosteroid action in allergic disease.

BACKGROUND: GATA-3 plays a critical role in regulating the expression of the cytokines interleukin (IL)-4, IL-5, and IL-13 from T helper-2 (Th2) cells and therefore is a key mediator of allergic diseases. Corticosteroids are highly effective in suppressing allergic inflammation, but their effects on GATA-3 are unknown. We investigated the effect of the corticosteroid fluticasone propionate on GATA-3 regulation in human T-lymphocytes in vitro and in vivo. METHODS AND FINDINGS: In a T lymphocyte cell line (HuT-78) and peripheral blood mononuclear cells stimulated by anti-CD3 and anti-CD28 in vitro we demonstrated that fluticasone inhibits nuclear translocation of GATA-3 and expression of Th2 cytokines via a mechanism independent of nuclear factor-kappaB and is due, in part, to competition between GATA-3 and the ligand-activated glucocorticoid receptor for nuclear transport through the nuclear importer importin-alpha. In addition, fluticasone induces the expression of mitogen-activated protein kinase (MAPK) phosphatase-1 (MKP-1), the endogenous inhibitor of p38 MAPK, which is necessary for GATA-3 nuclear translocation. These inhibitory effects of fluticasone are rapid, potent, and prolonged. We also demonstrated that inhaled fluticasone inhibits GATA-3 nuclear translocation in peripheral blood lymphocytes of patients with asthma in vivo. CONCLUSIONS: Corticosteroids have a potent inhibitory effect on GATA-3 via two interacting mechanisms that potently suppress Th2 cytokine expression. This novel mechanism of action of corticosteroids may account for the striking clinical efficacy of corticosteroids in the treatment of allergic diseases.

The roles of the RAG1 and RAG2 "non-core" regions in V(D)J recombination and lymphocyte development.

The enormous repertoire of the vertebrate specific immune system relies on the rearrangement of discrete gene segments into intact antigen receptor genes during the early stages of B-and T-cell development. This V(D)J recombination is initiated by a lymphoid-specific recombinase comprising the RAG1 and RAG2 proteins, which introduces double-strand breaks in the DNA adjacent to the coding segments. Much of the biochemical research into V(D)J recombination has focused on truncated or "core" fragments of RAG1 and RAG2, which lack approximately one third of the amino acids from each. However, genetic analyses of SCID and Omenn syndrome patients indicate that residues outside the cores are essential to normal immune development. This is in agreement with the striking degree of conservation across all vertebrate classes in certain non-core domains. Work from multiple laboratories has shed light on activities resident within these domains, including ubiquitin ligase activity and KPNA1 binding by the RING finger domain of RAG1 and the recognition of specific chromatin modifications as well as phosphoinositide binding by the PHD module of RAG2. In addition, elements outside of the cores are necessary for regulated protein expression and turnover. Here the current state of knowledge is reviewed regarding the non-core regions of RAG1 and RAG2 and how these findings contribute to our broader understanding of recombination.

Microinjected antibodies interfere with protein nucleocytoplasmic shuttling by distinct molecular mechanisms.

The observation that some antibodies can enter the nucleus after their microinjection into the cytoplasm established the principle of protein nucleocytoplasmic shuttling. Here, we introduce the concept of stationary antibodies for studying nuclear transport, particularly of native proteins. Contrary to the aforementioned translocating immunoglobulins, stationary antibodies do not cross the nuclear envelope. They are distinguished by their ability to trigger the nucleocytoplasmic redistribution of their antigen. What determines these apparently contradictory outcomes has not been explored. We studied a stationary STAT1 antibody and a translocating importin-beta antibody. The stationary phenotype resulted from the inhibition of carrier-independent transport. This was not due to crosslinking or precipitation of antigen, because the antigen-antibody complex remained highly mobile. Rather, decoration with stationary antibody precluded actual nuclear pore passage of antigen. In addition, both antibodies inhibited the carrier-dependent translocation via importin-alpha, but by diverse mechanisms. The translocating antibody blocked the association with importin-alpha, whereas the stationary antibody prevented the phosphorylation of its antigen, and thus functioned upstream of the importin-alpha binding step. We identified a stationary antibody to green-fluorescent protein (GFP) and probed the translocation of GFP fusions of STAT1, thyroid hormone receptor and histones, demonstrating general application of this approach. Our results provide an experimental rationale for the use of antibodies as unique tools for dissecting protein nuclear translocation. As the microinjection of stationary antibodies extends to analyses of native proteins, this method can complement and validate results obtained with fluorescent-labeled derivatives.

Generation and characterization of a monoclonal antibody against NPI-1 subfamily of importin alpha.

Most karyophilic proteins are transported into the nucleus through the importin-mediated pathway. Importin alpha acts as a receptor for classical nuclear localization signal (NLS)-containing proteins. At present, the existence of several isoforms of importin alpha in mammals is known. In this study we report on the generation of a rat monoclonal antibody (MAb) 2D9 to importin alpha NPI-1 subfamily members (importin alpha5/NPI-1 and importin alpha7/S2) using the rat lymph node method and the characterization of this antibody. In several different cultured cell extracts, MAb 2D9 reacted to endogenous NPI-1 subfamily in Western blotting experiments. Epitope mapping using recombinant deletion mutants indicated that MAb 2D9 recognized arm motif in importin alpha5/NPI-1. Using immunofluorescence, MAb 2D9 detected NPI-1 subfamily in the cytoplasm of HeLa cells. Moreover, endogenous NPI-1 subfamily was dominantly localized in the nuclei of H(2)O(2)-treated HeLa cells, suggesting that NPI-1 subfamily accumulates in the nucleus in response to oxidative stress, like importin alpha1/Rch1.

Severe acute respiratory syndrome coronavirus ORF6 antagonizes STAT1 function by sequestering nuclear import factors on the rough endoplasmic reticulum/Golgi membrane.

The host innate immune response is an important deterrent of severe viral infection in humans and animals. Nuclear import factors function as key gatekeepers that regulate the transport of innate immune regulatory cargo to the nucleus of cells to activate the antiviral response. Using severe acute respiratory syndrome coronavirus (SARS-CoV) as a model, we demonstrate that SARS-COV ORF6 protein is localized to the endoplasmic reticulum (ER)/Golgi membrane in infected cells, where it binds to and disrupts nuclear import complex formation by tethering karyopherin alpha 2 and karyopherin beta 1 to the membrane. Retention of import factors at the ER/Golgi membrane leads to a loss of STAT1 transport into the nucleus in response to interferon signaling, thus blocking the expression of STAT1-activated genes that establish an antiviral state. We mapped the region of ORF6, which binds karyopherin alpha 2, to the C terminus of ORF6 and show that mutations in the C terminus no longer bind karyopherin alpha 2 or block the nuclear import of STAT1. We also show that N-terminal deletions of karyopherin alpha 2 that no longer bind to karyopherin beta 1 still retain ORF6 binding activity but no longer block STAT1 nuclear import. Recombinant SARS-CoV lacking ORF6 did not tether karyopherin alpha 2 to the ER/Golgi membrane and allowed the import of the STAT1 complex into the nucleus. We discuss the likely implications of these data on SARS-CoV replication and pathogenesis.

Regulation of Th2 cytokine genes by p38 MAPK-mediated phosphorylation of GATA-3.

GATA-3 plays a critical role in allergic diseases by regulating the release of cytokines from Th2 lymphocytes. However, the molecular mechanisms involved in the regulation of GATA-3 in human T lymphocytes are not yet understood. Using small interfering RNA to knock down GATA-3, we have demonstrated its critical role in regulating IL-4, IL-5, and IL-13 release from a human T cell line. Specific stimulation of T lymphocytes by costimulation of CD3 and CD28 to mimic activation by APCs induces translocation of GATA-3 from the cytoplasm to the nucleus, with binding to the promoter region of Th2 cytokine genes, as determined by chromatin immunoprecipitation. GATA-3 nuclear translocation is dependent on its phosphorylation on serine residues by p38 MAPK, which facilitates interaction with the nuclear transporter protein importin-alpha. This provides a means whereby allergen exposure leads to the expression of Th2 cytokines, and this novel mechanism may provide new approaches to treating allergic diseases.

Specific monoclonal antibody against nuclear import factor, importin alpha1/Rch1.

Importin alpha1/Rch1, an importin alpha family member, mediates the nuclear import of karyophilic proteins. The present study reports on a monoclonal antibody (MAb) directed against mammalian importin alpha1/Rch1, which was produced by the hybridization of mouse myeloma cells with lymph node cells of an immunized rat. The MAb 1A6 specifically recognized importin alpha1/Rch1 among the importin alpha isoforms, as evidenced by Western blotting. Furthermore, 1A6 detected importin alpha1/Rch1 in HeLa cells by immunofluorescence. This MAb will be useful in immunolocalization and immunoblotting experiments, conducted on different tissue types, to determine the levels of expression of importin alpha1/Rch1 throughout development, as well as further analyses of the biological function and cellular dynamics of this protein.