Small-molecule inhibition of human immunodeficiency virus type 1 replication by targeting the interaction between Vif and ElonginC

Design, synthesis and biological evaluation of indolizine derivatives as HIV-1 VIF-ElonginC interaction inhibitors

The HIV-1 viral infectivity factor (VIF) protein is essential for viral replication. VIF recruits cellular ElonginB/C-Cullin5 E3 ubiquitin ligase to target the host antiviral protein APOBEC3G (A3G) for proteasomal degradation. Thus, the A3G-Vif-E3 complex represents an attractive target for the development of novel anti-HIV drugs. In this study, we describe the design and synthesis of indolizine derivatives as VIF inhibitors targeting the VIF-ElonginC interaction. Many of the synthesized compounds exhibited obvious inhibition activities of VIF-mediated A3G degradation, and 5 compounds showed improvement of activity compared to the known VIF inhibitor VEC-5 (1) with IC(50) values about 20 μM. The findings described here will be useful for the development of more potent VIF inhibitors.

HIV-1 viral infectivity factor (Vif) alters processive single-stranded DNA scanning of the retroviral restriction factor APOBEC3G

APOBEC3G is a retroviral restriction factor that can inhibit the replication of human immunodeficiency virus, type 1 (HIV-1) in the absence of the viral infectivity factor (Vif) protein. Virion-encapsidated APOBEC3G can deaminate cytosine to uracil in viral (−)DNA, which leads to hypermutation and inactivation of the provirus. APOBEC3G catalyzes these deaminations processively on single-stranded DNA using sliding and jumping movements. Vif is thought to primarily overcome APOBEC3G through an interaction that mediates APOBEC3G ubiquitination and results in its proteasomal degradation. However, Vif may also inhibit APOBEC3G mRNA translation, virion encapsidation, and deamination activity. Here we investigated the molecular mechanism of Vif_IIIB- and Vif_HXB2-mediated inhibition of APOBEC3G deamination activity. Biochemical assays using a model HIV-1 replication assay and synthetic single-stranded or partially double-stranded DNA substrates demonstrated that APOBEC3G has an altered processive mechanism in the presence of Vif. Specifically, Vif_HXB2 inhibited the jumping and Vif_IIIB inhibited the sliding movements of APOBEC3G. The absence of such an effect by Vif on degradation-resistant APOBEC3G D128K indicates that a Vif-APOBEC3G interaction mediates this effect. That the partially processive APOBEC3G was less effective at inducing mutagenesis in a model HIV-1 replication assay suggests that Vif co-encapsidation with APOBEC3G can promote sublethal mutagenesis of HIV-1 proviral DNA.

Host restriction factors in retroviral infection: promises in virus-host interaction

Retroviruses have an intricate life cycle. There is much to be learned from studying retrovirus-host interactions. Among retroviruses, the primate lentiviruses have one of the more complex genome structures with three categories of viral genes: structural, regulatory, and accessory genes. Over time, we have gained increasing understanding of the lentivirus life cycle from studying host factors that support virus replication. Similarly, studies on host restriction factors that inhibit viral replication have also made significant contributions to our knowledge. Here, we review recent progress on the rapidly growing field of restriction factors, focusing on the antiretroviral activities of APOBEC3G, TRIM5, tetherin, SAMHD1, MOV10, and cellular microRNAs (miRNAs), and the counter-activities of Vif, Vpu, Vpr, Vpx, and Nef.

Overexpression of inactive tetherin delGPI mutant inhibits HIV-1 Vpu-mediated antagonism of endogenous tetherin

Tetherin/BST-2/CD317 inhibits HIV-1 release from infected cells, but the viral Vpu protein efficiently antagonizes this antiviral activity through direct interaction between the transmembrane (TM) domains of each protein. Here, we demonstrated that overexpression of an inactive tetherin delGPI mutant, the TM domain of which could competitively block Vpu targeting of endogenous tetherin, potently inhibited HIV-1 release from human tetherin-positive cells in both transient and stable expression conditions. These results also suggest that heterologous dimerization occurred between the delGPI mutant and endogenous tetherin. These findings suggest that blocking the Vpu/tetherin interface may be a novel therapeutic approach against HIV-1 release.

Running loose or getting lost: how HIV-1 counters and capitalizes on APOBEC3-induced mutagenesis through its Vif protein

Human immunodeficiency virus-1 (HIV-1) dynamics reflect an intricate balance within the viruses’ host. The virus relies on host replication factors, but must escape or counter its host’s antiviral restriction factors. The interaction between the HIV-1 protein Vif and many cellular restriction factors from the APOBEC3 protein family is a prominent example of this evolutionary arms race. The viral infectivity factor (Vif) protein largely neutralizes APOBEC3 proteins, which can induce in vivo hypermutations in HIV-1 to the extent of lethal mutagenesis, and ensures the production of viable virus particles. HIV-1 also uses the APOBEC3-Vif interaction to modulate its own mutation rate in harsh or variable environments, and it is a model of adaptation in a coevolutionary setting. Both experimental evidence and the substantiation of the underlying dynamics through coevolutionary models are presented as complementary views of a coevolutionary arms race.

Interplay between CMVs and interferon signaling: implications for pathogenesis and therapeutic intervention

Most human individuals are latently infected with human CMV, a prototypic β-herpesvirus, frequently acquired during early childhood. In the absence of adequate immune control, the otherwise asymptomatic infection causes life-threatening disease. To enable efficient replication and to maintain lifelong latency in immunocompetent hosts, CMVs have evolved numerous molecules mediating immune evasive properties, targeting both innate and adaptive immune responses. Upon infection, cells secrete interferons (IFNs), which initiate an extremely fast signal transduction cascade upon binding to their cognate receptors, culminating in a pronounced change in the cellular gene expression profile. This response leads to the establishment of an intracellular antimicrobial state and to the recruitment, as well as stimulation, of the adaptive immune system. Unfortunately, CMVs impede the IFN system by interfering with its induction, signaling and downstream effector functions. This review aims to present our current understanding of such cytomegaloviral IFN-evasive properties, their pathogenic implications and potential for therapeutic exploitation.