Quaternary Interaction of the HIV-1 Envelope Trimer with CD4 and Neutralizing Antibodies

Synthetic approaches and application of clinically approved small-molecule Anti-HIV drugs: An update

Application of chemotherapeutic agents to inhibit the HIV replication process has brought about a significant metamorphosis in the landscape of AIDS. Substantial declines in morbidity and mortality rates have been attained, accompanied by notable decreases in healthcare resource utilization. However, treatment modalities do not uniformly inhibit HIV replication in every patient, while the emergence of drug-resistant viral strains poses a substantial obstacle to subsequent therapeutic interventions. Furthermore, chronic administration of therapy may lead to the manifestation of toxicities. These challenges necessitate the exploration of novel pharmacological agents and innovative therapeutic approaches aimed at effectively managing the persistent viral replication characteristic of chronic infection. This review examines the role of clinically approved small-molecule drugs in the treatment of HIV/AIDS, which provides an in-depth analysis of the major classes of small-molecule drugs, including nucleoside/nucleotide reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), integrase inhibitors, entry inhibitors, and pharmacokinetic enhancers. The review mainly discusses the application, synthetic routes, and mechanisms of action of small-molecule drugs employed in the treatment of HIV, as well as their use in combination with antiretroviral therapy, presenting viewpoints on forthcoming avenues in the development of novel anti-HIV drugs.

CD4 is an important host factor for Japanese encephalitis virus entry and replication in PK-15 cells

Japanese encephalitis virus (JEV) is a flavivirus that is spread through mosquito bites and is the leading cause of viral encephalitis in Asia. JEV can infect a variety of cell types; however, crucial receptor molecules remain unclear. The purpose of this study was to determine whether porcine CD4 protein is a receptor protein that impacts JEV entry into PK15 cells and subsequent viral replication. We confirmed the interaction between the JEV E protein and the CD4 protein through Co-IP, virus binding and internalization, antibody blocking, and overexpression and created a PK-15 cell line with CD4 gene knockdown by CRISPR/Cas9. The results show that CD4 interacts with JEV E and that CD4 knockdown cells altered virus adsorption and internalization, drastically reducing virus attachment. The level of viral transcription in CD4 antibody-blocked cells, vs. control cells, was decreased by 49.1%. Based on these results, we believe that CD4 is a receptor protein for JEVs. Furthermore, most viral receptors appear to be associated with lipid rafts, and colocalization studies demonstrate the presence of CD4 protein on lipid rafts. RT‒qPCR and WB results show that virus replication was suppressed in PK-15-CD4KD cells. The difference in viral titer between KD and WT PK-15 cells peaked at 24 h, and the viral titer in WT PK-15 cells was 5.6 × 106, whereas in PK-15-CD4KD cells, it was only 1.8 × 106, a 64% drop, demonstrating that CD4 deficiency has an effect on the process of viral replication. These findings suggest that JEV enters porcine kidney cells via lipid raft-colocalized CD4, and the proliferation process is positively correlated with CD4.

Microsecond dynamics control the HIV-1 envelope conformation

The HIV-1 Envelope (Env) glycoprotein facilitates host cell fusion through a complex series of receptor-induced structural changes. Although significant progress has been made in understanding the structures of various Env conformations and transition intermediates that occur within the millisecond timescale, faster transitions in the microsecond timescale have not yet been observed. In this study, we employed time-resolved, temperature-jump small angle X-ray scattering to monitor structural rearrangements in an HIV-1 Env ectodomain construct with microsecond precision. We detected a transition correlated with Env opening that occurs in the hundreds of microseconds range and another more rapid transition that preceded this opening. Model fitting indicated that the early rapid transition involved an order-to-disorder transition in the trimer apex loop contacts, suggesting that conventional conformation-locking design strategies that target the allosteric machinery may be ineffective in preventing this movement. Utilizing this information, we engineered an envelope that locks the apex loop contacts to the adjacent protomer. This modification resulted in significant angle-of-approach shifts in the interaction of a neutralizing antibody. Our findings imply that blocking the intermediate state could be crucial for inducing antibodies with the appropriate bound state orientation through vaccination.

Characterization of Human Immunodeficiency Virus (HIV-1) Envelope Glycoprotein Variants Selected for Resistance to a CD4-Mimetic Compound

Binding to the host cell receptors CD4 and CCR5/CXCR4 triggers conformational changes in the human immunodeficiency virus (HIV-1) envelope glycoprotein (Env) trimer that promote virus entry. CD4 binding allows the gp120 exterior Env to bind CCR5/CXCR4 and induces a short-lived prehairpin intermediate conformation in the gp41 transmembrane Env. Small-molecule CD4-mimetic compounds (CD4mcs) bind within the conserved Phe-43 cavity of gp120, near the binding site for CD4. CD4mcs like BNM-III-170 inhibit HIV-1 infection by competing with CD4 and by prematurely activating Env, leading to irreversible inactivation. In cell culture, we selected and analyzed variants of the primary HIV-1_AD8 strain resistant to BNM-III-170. Two changes (S375N and I424T) in gp120 residues that flank the Phe-43 cavity each conferred an ~5-fold resistance to BNM-III-170 with minimal fitness cost. A third change (E64G) in layer 1 of the gp120 inner domain resulted in ~100-fold resistance to BNM-III-170, ~2- to 3-fold resistance to soluble CD4-Ig, and a moderate decrease in viral fitness. The gp120 changes additively or synergistically contributed to BNM-III-170 resistance. The sensitivity of the Env variants to BNM-III-170 inhibition of virus entry correlated with their sensitivity to BNM-III-170-induced Env activation and shedding of gp120. Together, the S375N and I424T changes, but not the E64G change, conferred >100-fold and 33-fold resistance to BMS-806 and BMS-529 (temsavir), respectively, potent HIV-1 entry inhibitors that block Env conformational transitions. These studies identify pathways whereby HIV-1 can develop resistance to CD4mcs and conformational blockers, two classes of entry inhibitors that target the conserved gp120 Phe-43 cavity. IMPORTANCE CD4-mimetic compounds (CD4mcs) and conformational blockers like BMS-806 and BMS-529 (temsavir) are small-molecule inhibitors of human immunodeficiency virus (HIV-1) entry into host cells. Although CD4mcs and conformational blockers inhibit HIV-1 entry by different mechanisms, they both target a pocket on the viral envelope glycoprotein (Env) spike that is used for binding to the receptor CD4 and is highly conserved among HIV-1 strains. Our study identifies changes near this pocket that can confer various levels of resistance to the antiviral effects of a CD4mc and conformational blockers. We relate the antiviral potency of a CD4mc against this panel of HIV-1 variants to the ability of the CD4mc to activate changes in Env conformation and to induce the shedding of the gp120 exterior Env from the spike. These findings will guide efforts to improve the potency and breadth of small-molecule HIV-1 entry inhibitors.

HIV Infection and Spread between Th17 Cells

HIV mainly targets CD4+ T cells, from which Th17 cells represent a major cell type, permissive, and are capable of supporting intracellular replication at mucosal sites. Th17 cells possess well-described dual roles, while being central to maintaining gut integrity, these may induce inflammation and contribute to autoimmune disorders; however, Th17 cells’ antiviral function in HIV infection is not completely understood. Th17 cells are star players to HIV-1 pathogenesis and a potential target to prevent or decrease HIV transmission. HIV-1 can be spread among permissive cells via direct cell-to-cell and/or cell-free infection. The debate on which mode of transmission is more efficient is still ongoing without a concrete conclusion yet. Most assessments of virus transmission analyzing either cell-to-cell or cell-free modes use in vitro systems; however, the actual interactions and conditions in vivo are not fully understood. The fact that infected breast milk, semen, and vaginal secretions contain a mix of both cell-free viral particles and infected cells presents an argument for the probability of HIV taking advantage of both modes of transmission to spread. Here, we review important insights and recent findings about the role of Th17 cells during HIV pathogenesis in mucosal surfaces, and the mechanisms of HIV-1 infection spread among T cells in tissues.