MicroRNA-25/93 induction by Vpu as a mechanism for counteracting MARCH1-restriction on HIV-1 infectivity in macrophages

IMPORTANCE

In order to efficiently produce infectious viral particles, HIV must counter several restrictions exerted by host cell antiviral proteins. MARCH1 is a member of the MARCH protein family that restricts HIV infection by limiting the incorporation of viral envelope glycoproteins into nascent virions. Here, we identified two regulatory RNAs, microRNAs-25 and -93, induced by the HIV-1 accessory protein Vpu, that downregulate MARCH1 mRNA. We also show that Vpu induces these cellular microRNAs in macrophages by hijacking the cellular β-catenin pathway. The notion that HIV-1 has evolved a mechanism to counteract MARCH1 restriction on viral infectivity underlines the importance of MARCH1 in the host antiviral response.

Differential Type-I Interferon Response in Buffy Coat Transcriptome of Individuals Infected with SARS-CoV-2 Gamma and Delta Variants

The innate immune system is the first line of defense against pathogens such as the acute respiratory syndrome coronavirus 2 (SARS-CoV-2). The type I-interferon (IFN) response activation during the initial steps of infection is essential to prevent viral replication and tissue damage. SARS-CoV and SARS-CoV-2 can inhibit this activation, and individuals with a dysregulated IFN-I response are more likely to develop severe disease. Several mutations in different variants of SARS-CoV-2 have shown the potential to interfere with the immune system. Here, we evaluated the buffy coat transcriptome of individuals infected with Gamma or Delta variants of SARS-CoV-2. The Delta transcriptome presents more genes enriched in the innate immune response and Gamma in the adaptive immune response. Interactome and enriched promoter analysis showed that Delta could activate the INF-I response more effectively than Gamma. Two mutations in the N protein and one in the nsp6 protein found exclusively in Gamma have already been described as inhibitors of the interferon response pathway. This indicates that the Gamma variant evolved to evade the IFN-I response. Accordingly, in this work, we showed one of the mechanisms that variants of SARS-CoV-2 can use to avoid or interfere with the host Immune system.

Enzyme Characterization of Pro-virulent SntA, a Cell Wall-Anchored Protein of Streptococcus suis, With Phosphodiesterase Activity on cyclic-di-AMP at a Level Suited to Limit the Innate Immune System

Streptococcus suis and Streptococcus agalactiae evade the innate immune system of the infected host by mechanisms mediated by cell wall-anchored proteins: SntA and CdnP, respectively. The former has been reported to interfere with complement responses, and the latter dampens STING-dependent type-I interferon (IFN) response by hydrolysis of bacterial cyclic-di-AMP (c-di-AMP). Both proteins are homologous but, while CdnP has been studied as a phosphohydrolase, the enzyme activities of SntA have not been investigated. The core structure of SntA was expressed in Escherichia coli as a GST-tagged protein that, after affinity purification, was characterized as phosphohydrolase with a large series of substrates. This included 3′-nucleotides, 2′,3′-cyclic nucleotides, cyclic and linear dinucleotides, and a variety of phosphoanhydride or phosphodiester compounds, most of them previously considered as substrates of E. coli CpdB, a periplasmic protein homologous to SntA and CdnP. Catalytic efficiency was determined for each SntA substrate, either by dividing parameters k_cat/K_M obtained from saturation curves or directly from initial rates at low substrate concentrations when saturation curves could not be obtained. SntA is concluded to act as phosphohydrolase on two groups of substrates with efficiencies higher or lower than ≈ 10⁵ M^–1 s^–1 (average value of the enzyme universe). The group with k_cat/K_M ≥ 10⁵ M^–1 s^–1 (good substrates) includes 3′-nucleotides, 2′,3′-cyclic nucleotides, and linear and cyclic dinucleotides (notably c-di-AMP). Compounds showing efficiencies <10⁴ M^–1 s^–1 are considered poor substrates. Compared with CpdB, SntA is more efficient with its good substrates and less efficient with its poor substrates; therefore, the specificity of SntA is more restrictive. The efficiency of the SntA activity on c-di-AMP is comparable with the activity of CdnP that dampens type-I IFN response, suggesting that this virulence mechanism is also functional in S. suis. SntA modeling revealed that Y530 and Y633 form a sandwich with the nitrogen base of nucleotidic ligands in the substrate-binding site. Mutants Y530A-SntA, Y633A-SntA, and Y530A+Y633A-SntA were obtained and kinetically characterized. For orientation toward the catalytic site, one tyrosine is enough, although this may depend on the substrate being attacked. On the other hand, both tyrosines are required for the efficient binding of good SntA substrates.

Mayaro Virus Replication Restriction and Induction of Muscular Inflammation in Mice Are Dependent on Age, Type-I Interferon Response, and Adaptive Immunity

Mayaro virus (MAYV) is an emergent arbovirus first described in forest regions of the American continent, with recent and increasing notification of urban area circulation. Similar to Chikungunya (CHIKV) and other arthritogenic Alphavirus, MAYV-induced disease shows a high prevalence of persistent arthralgia, and myalgia. Despite this, knowledge regarding pathogenesis and characteristics of host immune response of MAYV infections are still limited. Here, using different ages of wild-type (WT), adult Type I Interferon receptor deficient (IFNAR^-/-), and adult recombination activation gene-1 deficient (RAG^-/-) mice, we have investigated the dependence of age, innate and adaptive immunity for the control of MAYV replication, tissue damage, and inflammation in mice. We have found that MAYV induces clinical signal and replicates in young WT mice, which gain the ability to restrict MAYV replication with aging. In addition, we observed that mice age and type I interferon response are related to restriction of MAYV infection and muscular inflammation in mice. Moreover, MAYV continues to replicate persistently in RAG^-/- mice, being detected at blood and tissues 40 days post infection, indicating that adaptive immunity is essential to MAYV clearance. Despite chronic replication, infected adult RAG^-/- mice did not develop an apparent signal of muscle damage in early and late infection. On the other hand, MAYV infection in young WT and adult IFNAR-/- mice triggers an increase in the expression of pro-inflammatory mediators, such as TNF, IL-6, KC, IL-1β, MCP-1, and RANTES, in muscle tissue, and decreases TGF-β expression, that were not significantly modulated in adult WT and RAG^-/- mice. Taken together, our data demonstrated that age, innate and adaptive immunity are important to restrict MAYV replication and that adaptive immunity is also involved in MAYV-induced tissue damage. These results contribute to the comprehension of MAYV pathogenesis, and describe translational mice models for further studies of MAYV infection, vaccine tests, and therapeutic strategies against this virus.

Modulation of Type-I Interferon Response by hsa-miR-374b-5p During Japanese Encephalitis Virus Infection in Human Microglial Cells

Japanese Encephalitis virus (JEV) is a neurotropic ssRNA virus, belonging to the Flaviviridae family. JEV is one of the leading causes of the viral encephalitis in Southeast-Asian countries. JEV primarily infects neurons however, the microglial activation has been reported to further enhance the neuroinflammation and promote neuronal death. The PI3K/AKT pathway has been reported to play an important role in type-I interferon response via IRF3. Phosphatase and tensin homolog (PTEN), a negative regulator of PI3K/AKT pathway, participates in microglial polarization and neuroinflammation. The microRNAs are small non-coding endogenously expressed RNAs, which regulate the gene expression by binding at 3′ UTR of target gene. The human microglial cells were infected with JEV (JaOArS982 strain) and up-regulation of microRNA; hsa-miR-374b-5p was confirmed by qRT-PCR. The genes in PI3K/AKT pathway, over-expression and knock-down studies of hsa-miR-374b-5p with and without JEV infection were analyzed through immuno blotting. The regulatory role of hsa-miR-374b-5p on the expression of type-I interferon was determined by luciferase assays. JEV infection modulated the expression of hsa-miR-374b-5p and PI3K/AKT pathway via PTEN. The over-expression of hsa-miR-374b-5p suppressed the PTEN while up-regulated the AKT and IRF3 proteins, whereas, the knockdown rescued the PTEN expression and suppressed the AKT and IRF3 proteins. The modulation of hsa-miR-374b-5p regulated the type-I interferon response during JEV infection. In present study, we have shown the modulation of PTEN by hsa-miR-374b-5p, which regulated the PI3K/AKT/IRF3 axis in JEV infected microglial cells.