Comparative Analysis of Tat-Dependent and Tat-Deficient Natural Lentiviruses

Y44A Mutation in the Acidic Domain of HIV-2 Tat Impairs Viral Reverse Transcription and LTR-Transactivation

HIV transactivator protein (Tat) plays a pivotal role in viral replication through modulation of cellular transcription factors and transactivation of viral genomic transcription. The effect of HIV-1 Tat on reverse transcription has long been described in the literature, however, that of HIV-2 is understudied. Sequence homology between Tat proteins of HIV-1 and 2 is estimated to be less than 30%, and the main difference lies within their N-terminal region. Here, we describe Y44A-inactivating mutation of HIV-2 Tat, studying its effect on capsid production, reverse transcription, and the efficiency of proviral transcription. Investigation of the mutation was performed using sequence- and structure-based in silico analysis and in vitro experiments. Our results indicate that the Y44A mutant HIV-2 Tat inhibited the activity and expression of RT (reverse transcriptase), in addition to diminishing Tat-dependent LTR (long terminal repeat) transactivation. These findings highlight the functional importance of the acidic domain of HIV-2 Tat in the regulation of reverse transcription and transactivation of the integrated provirions.

The Vif protein of caprine arthritis encephalitis virus inhibits interferon production

Caprine arthritis-encephalitis (CAE) is a chronic progressive infectious disease caused by caprine arthritis-encephalitis virus (CAEV) that seriously threatens the goat industry. Chronic infection and life-long multi-tissue inflammation are the typical features of the disease. Innate antiviral immunity is essential for the host defense system that rapidly recognizes and eliminates invading viruses. Interferon β (IFN-β) is important for innate immunity and regulates immunity against a broad spectrum of viruses. To investigate the details of the IFN-β response to CAEV infection, the effects of six viral proteins and the molecular mechanisms by which they affect IFN-β production were analyzed. Overexpression of DU and Vif promote virus proliferation and inhibit the production of IFN-β. qRT-PCR and luciferase reporter assays showed that overexpression of Vif inhibits the expression of luciferase under the control of the ISRE, NF-κB or IFN-β promoter but does not affect the expression of IFN-β activated by IRF3, indicating that Vif negatively regulates IFN-β production by affecting upstream signal transduction of IRF3. Amino acids 149-164 of Vif were found to be necessary for the inhibitory effect of IFN-β production. Our results indicate that CAEV evades surveillance and clearance by intracellular innate immunity by downregulating IFN-β production.

Mutations in Long Terminal Repeats κB Transcription Factor Binding Sites in Plasma Virus Among South African People Living with HIV-1

HIV-1 subtype C (HIV-1C) is responsible for the majority of infections in sub-Saharan Africa. We selected 63 plasma-derived samples and generated long terminal repeats (LTRs) amplicons from people living with HIV in South Africa to identify transcription factor binding sites. NF-κB plays an important role in regulating the viral gene expression from the viral promoter and controlling viral latency. LTR amplicons were sequenced and phylogenetically analyzed. In our data set, we identified F-κB sites (n = 4; 6%) at position II and (n = 1; 1%) at position I among 63 sequences analyzed. The majority of the sequences identified with H-κB at position II (n = 50; 79%) and position I (n = 55; 87%). Forty-nine (n = 49; 78%) sequences were found to exhibit C-κB site. ZA_LTR052 was identified with a single point mutation. We identified all three NF-κB-binding sites in (n = 44; 70%) the viral promoter-enhancer regions in South African patients.

Prospects in Innate Immune Responses as Potential Control Strategies against Non-Primate Lentiviruses

Lentiviruses are infectious agents of a number of animal species, including sheep, goats, horses, monkeys, cows, and cats, in addition to humans. As in the human case, the host immune response fails to control the establishment of chronic persistent infection that finally leads to a specific disease development. Despite intensive research on the development of lentivirus vaccines, it is still not clear which immune responses can protect against infection. Viral mutations resulting in escape from T-cell or antibody-mediated responses are the basis of the immune failure to control the infection. The innate immune response provides the first line of defense against viral infections in an antigen-independent manner. Antiviral innate responses are conducted by dendritic cells, macrophages, and natural killer cells, often targeted by lentiviruses, and intrinsic antiviral mechanisms exerted by all cells. Intrinsic responses depend on the recognition of the viral pathogen-associated molecular patterns (PAMPs) by pathogen recognition receptors (PRRs), and the signaling cascades leading to an antiviral state by inducing the expression of antiviral proteins, including restriction factors. This review describes the latest advances on innate immunity related to the infection by animal lentiviruses, centered on small ruminant lentiviruses (SRLV), equine infectious anemia virus (EIAV), and feline (FIV) and bovine immunodeficiency viruses (BIV), specifically focusing on the antiviral role of the major restriction factors described thus far.