Mechanisms of Zika virus infection and neuropathogenesis

A spotlight has been focused on the mosquito-borne Zika virus (ZIKV) because of its epidemic outbreak in Brazil and Latin America, as well as the severe neurological manifestations of microcephaly and Guillain–Barré syndrome associated with infection. In this review, we discuss the recent literature on ZIKV-host interactions, including new mechanistic insight concerning the basis of ZIKV-induced neuropathogenesis

Human T Cell Leukemia Virus Type 1 Tax Protein Increases NF-κB Dimer Formation and Antagonizes the Inhibitory Activity of the IκBα Regulatory Protein

AbstractHuman T cell leukemia virus type 1 (HTLV-1) encodes a strong transcriptional transactivator, the Tax protein, that stimulates viral transcription through the long terminal repeat and also stimulates many cellular genes via the activation of host transcription factors. Previous studies have demonstrated that Tax activates NF-κB through binding to the Rel homology domain of NF-κB proteins. Tax was also shown to increase degradation of IκBα resulting in the induction of NF-κB DNA binding activity. We addressed the specificity and function of Tax interaction with members of the NF-κB/IκBα family by using EMSA, protein affinity chromatography, protein–protein crosslinking and co-immunoprecipitation assays. The results of the present study demonstrate that: (1) Tax enhances NF-κB binding to DNA 40- to 100-fold by increasing NF-κB dimer formation which can be detected in the absence of DNA; (2) Tax binds to all NF-κB DNA binding subunitsin vitroand to IκBα; (3) Tax physically associates with IκBαin vivo;and (4) Tax and IκBα have antagonistic effects on NF-κB binding and gene activity. These results suggest that Tax interaction with IκBα interferes with the formation of NF-κB–IκBα complexes and may play a role in targeting IκBα for degradation

NF-κB Protects HIV-1-Infected Myeloid Cells from Apoptosis

AbstractHIV-1 infection of primary monocytic cells and myeloid cell lines results in sustained NF-κB activation. Recently, NF-κB induction has been shown to play a role in protecting cells from programmed cell death. In the present study, we sought to investigate whether constitutive NF-κB activity in chronically HIV-1-infected promonocytic U937 (U9-IIIB) and myeloblastic PLB-985 (PLB-IIIB) cells affects apoptotic signaling. TNFα and cycloheximide caused infected cells to undergo apoptosis more rapidly than parental U937 and PLB-985 cells. Inhibition of TNFα-induced NF-κB activation using the antioxidantN-acetylcysteine (NAC) resulted in increased apoptosis in both U937 and U9-IIIB cells, while preactivation of NF-κB with the non-apoptotic inducer IL-1β caused a relative decrease in apoptosis. Inhibition of constitutive NF-κB activity in U9-IIIB and PLB-IIIB cells also induced apoptosis, suggesting that NF-κB protects cells from a persistent apoptotic signal. TNFα plus NAC treatment resulted in a marked decrease in Bcl-2 protein levels in HIV-1-infected cells, coupled with an increase in Bax protein compared to uninfected cells, suggesting that the difference in susceptibility to TNFα-induced apoptosis may relate to the differences in relative levels of Bcl-2 and Bax. The protective role of NF-κB in blocking TNFα- and HIV-1-induced apoptosis was supported by studies in Jurkat T cells engineered to express IκBα repressor mutants (TD-IκB) under the control of a tetracycline-responsive promoter. Cells underwent apoptosis in response to TNFα only when NF-κB activation was inhibited by TD-IκB expression. As was observed for the U9-IIIB cells, TNFα treatment also induced a marked decrease in Bcl-2 protein levels in TD-IκB expressing cells. These experiments demonstrate that apoptotic signaling is perturbed in HIV-1-infected U9-IIIB cells and indicate that NF-κB activation may play an additional protective role against HIV-1-induced apoptosis in myeloid cells

Host Restriction Factor SAMHD1 Limits Human T Cell Leukemia Virus Type 1 Infection of Monocytes via STING-Mediated Apoptosis

SummaryHuman T cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T cell leukemia and HTLV-1-associated myelopathies. In addition to T cells, HTLV-1 infects cells of the myeloid lineage, which play critical roles in the host innate response to viral infection. Investigating the monocyte depletion observed during HTLV-1 infection, we discovered that primary human monocytes infected with HTLV-1 undergo abortive infection accompanied by apoptosis dependent on SAMHD1, a host restriction factor that hydrolyzes endogenous dNTPs to below the levels required for productive reverse transcription. Reverse transcription intermediates (RTI) produced in the presence of SAMHD1 induced IRF3-mediated antiviral and apoptotic responses. Viral RTIs complexed with the DNA sensor STING to trigger formation of an IRF3-Bax complex leading to apoptosis. This study provides a mechanistic explanation for abortive HTLV-1 infection of monocytes and reports a link between SAMHD1 restriction, HTLV-1 RTI sensing by STING, and initiation of IRF3-Bax driven apoptosis

Differential Regulation of HIV-1 Clade-Specific B, C, and E Long Terminal Repeats by NF-κB and the Tat Transactivator

AbstractThe major group of human immunodeficiency viruses (HIV-1) that comprise the current global pandemic have diversified during their worldwide spread and may be divided into at least 10 distinct subtypes or clades, A through J. Subtype B predominates in North America and Europe, subtype E predominates in Southeast Asia, and subtype C predominates in sub-Saharan Africa. Functional distinctions in long terminal repeat (LTR) architecture among HIV subtypes have been identified, thus raising the possibility that regulatory divergence among the subtypes of HIV-1 has occurred. In addition to the transcriptional specificity of the HIV-1 LTR, productive HIV-1 replication is also dependent upon the viral Tat protein. Therefore, we sought to investigate whether interactions between host signaling pathways and the NF-κB regions of different HIV-1 subtypes, together with subtype-specific interactions between Tat, TAR, and cellular proteins, modulate the efficiency of HIV-1 clade-specific gene transcription. We demonstrate that the NF-κB sites of subtypes B and E both bind NF-κB-related complexes. However, the duplicated κB sites of the C subtype do not compete for NF-κB binding. Also, clade E Tat protein possesses the highest transactivation capacity, regardless of the LTR context. Furthermore, preliminary evidence suggests that the acetylation of subtype-specific Tat proteins may correlate with their transactivation efficiency

Virus-like particle – mediated delivery of the RIG-I agonist M8 induces a type I interferon response and protects cells against viral infection

Virus-Like Particles (VLPs) are nanostructures that share conformation and self-assembly properties with viruses, but lack a viral genome and therefore the infectious capacity. In this study, we produced VLPs by co-expression of VSV glycoprotein (VSV-G) and HIV structural proteins (Gag, Pol) that incorporated a strong sequence-optimized 5’ppp-RNA RIG-I agonist, termed M8. Treatment of target cells with VLPs-M8 generated an antiviral state that conferred resistance against multiple viruses. Interestingly, treatment with VLPs-M8 also elicited a therapeutic effect by inhibiting ongoing viral replication in previously infected cells. Finally, the expression of SARS-CoV-2 Spike glycoprotein on the VLP surface retargeted VLPs to ACE2 expressing cells, thus selectively blocking viral infection in permissive cells. These results highlight the potential of VLPs-M8 as a therapeutic and prophylactic vaccine platform. Overall, these observations indicate that the modification of VLP surface glycoproteins and the incorporation of nucleic acids or therapeutic drugs, will permit modulation of particle tropism, direct specific innate and adaptive immune responses in target tissues, and boost immunogenicity while minimizing off-target effects

A type I interferon autocrine–paracrine loop is involved in Toll-like receptor-induced interleukin-12p70 secretion by dendritic cells

Dendritic cells (DC) produce interleukin-12 (IL-12) in response to Toll-like receptor (TLR) activation. Two major TLR signaling pathways participate in the response to pathogens: the nuclear factor-κB (NF-κB)–dependent pathway leading to inflammatory cytokine secretion including IL-12 and the interferon (IFN)-dependent pathway inducing type I IFN and IFN-regulated genes. Here we show that the two pathways cooperate and are likely both necessary for inducing an optimal response to pathogens. R-848/Resiquimod (TLR7 ligand in the mouse and TLR7/8 ligand in human) synergized with poly(I:C) (TLR3 ligand) or lipopolysaccharide (LPS; TLR4 ligand) in inducing high levels of bioactive IL-12p70 secretion and IFN-β mRNA accumulation by mouse bone marrow–derived DC (BM-DC). Strikingly, IL-12p70 but not IL-12p40 secretion was strongly reduced in BM-DC from STAT1−/− and IFNAR−/− mice. STAT1 tyrosine-phosphorylation, IL-12p35, and IFN-β mRNA accumulation were strongly inhibited in IFNAR−/− BM-DC activated with the TLR ligand combinations. Similar observation were obtained in human TLR8-expressing monocyte-derived DC (moDC) using neutralizing anti-IFNAR2 antibodies, although results also pointed to a possible involvement of IFN-λ1 (also known as IL-29). This suggests that TLR engagement on DC induces endogenous IFNs that further synergize with the NF-κB pathway for optimal IL-12p70 secretion. Moreover, analysis of interferon regulatory factors (IRF) regulation in moDC suggests a role for IRF7/8 in mediating IRF3-independent type I IFN and possibly IL-12p35 synthesis in response to TLR7/8