Search

The cyclic GMP-AMP synthase and stimulator of interferon (IFN) genes (cGAS-STING) pathway serves as a crucial component of innate immune defense and exerts immense antiviral activity by inducing the expression of type I IFNs. Currently, STING-activated production of type I IFNs has been thought to be mediated only by TANK-binding kinase 1 (TBK1). Here, we identified that porcine IKKe (pIKKe) is also directly involved in STING-induced type I IFN expression and antiviral response by using IKKe -/- porcine macrophages. Similar to pTBK1, pIKKe interacts directly with pSTING on the C-terminal tail. Furthermore, the TBK1-binding motif of pSTING C-terminal tail is essential for its interaction with pIKKe, and within the TBK1-binding motif, the leucine (L) 373 is also critical for the interaction. On the other hand, both kinase domain and scaffold dimerization domain of pIKKe participate in the interactions with pSTING. Consistently, the reconstitution of pIKKe and its mutants in IKKe -/- porcine macrophages corroborated that IKKe and its kinase domain and scaffold dimerization domain are all involved in the STING signaling and antiviral function. Thus, our findings deepen the understanding of porcine cGAS-STING pathway, which lays a foundation for effective antiviral therapeutics against porcine viral diseases. [ABSTRACT FROM AUTHOR]

Cytoplasmic stress granules (SGs) are generally triggered by stress-induced translation arrest for storing mRNAs. Recently, it has been shown that SGs are regulated by different stimulators including viral infection, which is involved in the antiviral activity of host cells to limit viral propagation. To survive, several viruses have been reported to execute various strategies, such as modulating SG formation, to create optimal surroundings for viral replication. African swine fever virus (ASFV) is one of the most notorious pathogens in the global pig industry. However, the interplay between ASFV infection and SG formation remains largely unknown. In this study, we found that ASFV infection inhibited SG formation. Through SG inhibitory screening, we found that several ASFV-encoded proteins are involved in inhibition of SG formation. Among them, an ASFV S273R protein (pS273R), the only cysteine protease encoded by the ASFV genome, significantly affected SG formation. ASFV pS273R interacted with G3BP1 (Ras-GTPase-activating protein [SH3 domain] binding protein 1), a vital nucleating protein of SG formation. Furthermore, we found that ASFV pS273R cleaved G3BP1 at the G140-F141 to produce two fragments (G3BP1-N1-140 and G3BP1-C141-456). Interestingly, both the pS273R-cleaved fragments of G3BP1 lost the ability to induce SG formation and antiviral activity. Taken together, our finding reveals that the proteolytic cleavage of G3BP1 by ASFV pS273R is a novel mechanism by which ASFV counteracts host stress and innate antiviral responses. [ABSTRACT FROM AUTHOR]

The innate immune DNA-sensing cyclic GMP-AMP synthase (cGAS)-stimulator of interferon (IFN) gene (STING) pathway exerts strong antiviral activity through downstream IFN production; however, it has been recently recognized that an IFN-independent activity of STING also plays an important role in antiviral functions. Nevertheless, the IFN-independent antiviral activity of STING is not fully understood. Here, we showed that porcine STING (pSTING) played a critical role against herpes simplex virus 1 (HSV-1) and vesicular stomatitis virus (VSV) infections, and IFN-defective mutants, including pSTING pLxIS sub, S365A, and ΔCTT, all exhibited similar antiviral functions, compared to wild-type (WT) pSTING. Furthermore, all of these IFN-defective pSTING mutants possessed comparable autophagy activity, relative to WT pSTING, as expected. From pSTING WT, S365A, and ΔCTT, the residues responsible for autophagy, including L333A/R334A, Y167A/L170A, and Y245A/L248A, were mutated. Surprisingly, all of these autophagydefective pSTING mutants still resisted the two viral infections, demonstrating that the pSTING antiviral function is independent of IFN as well as autophagy. On the other hand, all of the autophagy-defective pSTING mutants triggered cell apoptosis, which was associated with and participated in the antiviral functions. Additionally, pSTING lost its antiviral activity in TANK-binding kinase 1 (TBK1)-/- and IFN regulatory factor 3 (IRF3)-/- porcine macrophages, indicating the involvement of TBK1 and IRF3 in other STING activities such as apoptosis. Collectively, our results revealed that STING exerts both IFN- and autophagy-independent antiviral activity, and they also suggested that STING-triggered cell apoptosis resists viral infections. IMPORTANCE The IFN-independent antiviral function of the cGAS-STING pathway has attracted great attention in recent years; however, the nature of this IFN-independent antiviral function is unknown, although STING-induced autophagy has been shown to mediate the STING antiviral activity. First, we analyzed the antiviral activity through the porcine cGAS-pSTING pathway and established that pSTING signaling exerts an IFN-independent antiviral function. Second, we found that pSTING-induced IFN-independent autophagy and the antiviral activity of pSTING are independent of both IFN and autophagy. Finally, pSTING signaling activates cell apoptosis independently of IFN and autophagy, and the apoptosis is associated with antiviral activity. Our results suggest that pSTING-activated apoptosis at least partially mediates the antiviral activity or multiple pSTING-activated signals, including IFN production, nuclear factor k light chain enhancer of activated B cells (NF-kB) expression, autophagy, and apoptosis, exert a redundant antiviral role. Thus, the work reveals a new layer of complexity in STING antiviral activity. [ABSTRACT FROM AUTHOR]

The glycosylphosphatidylinositol (GPI) anchors of Plasmodium falciparum have been proposed to be the major factors that contribute to malaria pathogenesis through their ability to induce proinflammatory responses. In this study we identified the receptors for P. falciparum GPI-induced cell signaling that leads to proinflammatory responses and studied the GPI structure-activity relationship. The data show that GPI signaling is mediated mainly through recognition by TLR2 and to a lesser extent by TLR4. The activity of sn-2-lyso-GPIs is comparable with that of the intact GPIs, whereas the activity of Man3-GPIs is about 80% that of the intact GPIs. The GPIs with three (intact GPIs and Man3-GPIs) and two fatty acids (sn-2-lyso- GPIs) appear to differ considerably in the requirement of the auxiliary receptor, TLR1 or TLR6, for recognition by TLR2. The former are preferentially recognized by TLR2/TLR1, whereas the latter are favored by TLR2/TLR6. However, the signaling pathways initiated by all three GPI types are similar, involving the MyD88-dependent activation of extracellular signal-regulated kinase, c-Jun N-terminal kinase, and p38 and NF-κB-signaling pathways. The signaling molecules of these pathways differentially con- tribute to the production of various cytokines and nitric oxide (Zhu, J., Krishnegowda, G., and Gowda, D. C. (2004) J. Biol. Chem. 280, 8617–8627). Our data also show that GPIs are degraded by the macrophage surface phospholipases predominantly into inactive species, indicating that the host can regulate GPI activity at least in part by this mechanism. These results imply that macrophage surface phospholipases play important roles in the GPI-induced innate immune responses and malaria pathogenesis. [ABSTRACT FROM AUTHOR]

Kaposi's sarcoma-associated herpesvirus (KSHV) infection is required for the development of several AIDS-related malignancies, including Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). The high incidence of AIDS-KS has been ascribed to the interaction of KSHV and HIV-1. We have previously shown that HIV-1-secreted proteins Tat and Nef regulate the KSHV life cycle and synergize with KSHV oncogenes to promote angiogenesis and tumorigenesis. Here, we examined the regulation of KSHV latency by HIV-1 viral protein R (Vpr). We found that soluble Vpr inhibits the expression of KSHV lytic transcripts and proteins, as well as viral particle production by activating NF-κB signaling following internalization into PEL cells. By analyzing the expression profiles of microRNAs combined with target search by bioinformatics and luciferase reporter analyses, we identified a Vpr-upregulated cellular microRNA (miRNA), miR-942-5p, that directly targeted IκαC. Suppression of miR-942-5p relieved the expression of IκαC and reduced Vpr inhibition of KSHV lytic replication, while overexpression of miR-942-5p enhanced Vpr inhibition of KSHV lytic replication. Our findings collectively illustrate that, by activating NF-κB signaling through upregulating a cellular miRNA to target IκαC, internalized HIV-1 Vpr inhibits KSHV lytic replication. These results have demonstrated an essential role of Vpr in the life cycle of KSHV. [ABSTRACT FROM AUTHOR]

2'-5'-Oligoadenylate synthetase-like protein (OASL) is an interferon-inducible antiviral protein. Here we describe differential inhibitory activities of human OASL and the two mouse OASL homologs against respiratory syncytial virus (RSV) replication. Interestingly, nonstructural protein 1 (NS1) of RSV promoted proteasome-dependent degradation of specific OASL isoforms. We conclude that OASL acts as a cellular antiviral protein and that RSV NS1 suppresses this function to evade cellular innate immunity and allow virus growth. [ABSTRACT FROM AUTHOR]

Histological observation of dual-stained colon sections is usually performed by visual observation under a light microscope, or by viewing on a computer screen with the assistance of image processing software in both research and clinical settings. These traditional methods are usually not sufficient to reliably differentiate spatially overlapping chromogens generated by different dyes. Hyperspectral microscopic imaging technology offers a solution for these constraints as the hyperspectral microscopic images contain information that allows differentiation between spatially co-located chromogens with similar but different spectra. In this paper, a hyperspectral microscopic imaging (HMI) system is used to identify methyl green and nitrotetrazolium blue chloride in dual-stained colon sections. Hyperspectral microscopic images are captured and the normalized score algorithm is proposed to identify the stains and generate the co-expression results. Experimental results show that the proposed normalized score algorithm can generate more accurate co-localization results than the spectral angle mapper algorithm. The hyperspectral microscopic imaging technology can enhance the visualization of dual-stained colon sections, improve the contrast and legibility of each stain using their spectral signatures, which is helpful for pathologist performing histological analyses. [ABSTRACT FROM AUTHOR]

Type I IFNs play central roles in innate immunity; however, overproduction of IFN can lead to immunopathology. In this study, we demonstrate that adenosine deaminase acting on RNA 1 (ADAR1), an RNA-editing enzyme induced by IFN, is essential for cells to avoid inappropriate sensing of cytosolic RNA in an inducible knockout cell model—the primary mouse embryo fibroblast derived from ADAR1 lox/lox and Cre-ER mice as well as in HEK293 cells. ADAR1 suppresses viral and cellular RNA detection by retinoic acid–inducible gene I (RIG-I) through its RNA binding rather than its RNA editing activity. dsRNA binds to both ADAR1 and RIG-I, but ADAR1 reduces RIG-I RNA binding. In the absence of ADAR1, cellular RNA stimulates type I IFN production without viral infection or exogenous RNA stimulation. Moreover, we showed in the ADAR1-inducible knockout mice that ADAR1 gene disruption results in high-level IFN production in neuronal tissues—the hallmark of Aicardi–Goutières syndrome, a heritable autoimmune disease recently found to be associated with ADAR1 gene mutations. In summary, this study found that ADAR1 limits cytosolic RNA sensing by RIG-I through its RNA binding activity; therefore, ADAR1 suppresses type I IFN production stimulated by viral and cellular RNAs. These results explain why loss of ADARA1 causes IFN induction and also indicates a mechanism for the involvement of ADAR1 in autoimmune diseases such as Aicardi–Goutières syndrome. [ABSTRACT FROM AUTHOR]

Kaposi's sarcoma-associated herpesvirus (KSHV) is causally linked to several AIDS-related malignancies, including Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease. The interaction of human immunodeficiency virus type 1 (HIV-1) and KSHV has a central role in promoting the aggressive manifestations of AIDS-KS. We have previously shown that negative factor (Nef), a secreted HIV-1 protein, synergizes with KSHV viral interleukin-6 (vIL-6) to promote angiogenesis and tumorigenesis by activating the AKT pathway (X. Zhu, et al., Oncogene, 22 April 2013, http://dx.doi.org/10.103 8/onc.2013.136). Here, we further demonstrated the role of soluble and ectopic Nef in the regulation of KSHV latency. We found that both soluble Nef protein and ectopic expression of Nef by transfection suppressed the expression of KSHV viral lytic mRNA transcripts and proteins and the production of infectious viral particles. MicroRNA (miRNA) microarray analysis identified a number of Nef-regulated miRNAs. Bioinformatics and luciferase reporter analyses showed that one of the Nef-upregulated miRNAs, cellular miRNA 1258 (hsa-miR-1258), directly targeted a seed sequence in the 3' untranslated region (UTR) of the mRNA encoding the major lytic switch protein (RTA), which controls KSHV reactivation from latency. Ectopic expression of hsa-miR-1258 impaired RTA synthesis and enhanced Nef-mediated inhibition of KSHV replication, whereas repression of hsa-miR-1258 has the opposite effect. Mutation of the seed sequence in the RTA 3=UTR abolished downregulation of RTA by hsa-miR-1258. Collectively, these novel findings demonstrate that, by regulating cellular miRNA, Nef may inhibit KSHV replication to promote viral latency and contribute to the pathogenesis of AIDS-related malignancies. [ABSTRACT FROM AUTHOR]