Biomedical subjects

Elaine R Thomas

Publications and source records attributed to Elaine R Thomas.

5 recordsLinked to original sources

PubMed2006

Macrophage entry mediated by HIV Envs from brain and lymphoid tissues is determined by the capacity to use low CD4 levels and overall efficiency of fusion.

HIV infects macrophages and microglia in the central nervous system (CNS), which express lower levels of CD4 than CD4+ T cells in peripheral blood. To investigate mechanisms of HIV neurotropism, full-length env genes were cloned from autopsy brain and lymphoid tissues from 4 AIDS patients with HIV-associated dementia (HAD). Characterization of 55 functional Env clones demonstrated that Envs with reduced dependence on CD4 for fusion and viral entry are more frequent in brain compared to lymphoid tissue. Envs that mediated efficient entry into macrophages were frequent in brain but were also present in lymphoid tissue. For most Envs, entry into macrophages correlated with overall fusion activity at all levels of CD4 and CCR5. gp160 nucleotide sequences were compartmentalized in brain versus lymphoid tissue within each patient. Proline at position 308 in the V3 loop of gp120 was associated with brain compartmentalization in 3 patients, but mutagenesis studies suggested that P308 alone does not contribute to reduced CD4 dependence or macrophage-tropism. These results suggest that HIV adaptation to replicate in the CNS selects for Envs with reduced CD4 dependence and increased fusion activity. Macrophage-tropic Envs are frequent in brain but are also present in lymphoid tissues of AIDS patients with HAD, and entry into macrophages in the CNS and other tissues is dependent on the ability to use low receptor levels and overall efficiency of fusion.

AIDS Dementia Complex↗

PubMed2006

The HIV Env variant N283 enhances macrophage tropism and is associated with brain infection and dementia.

HIV infects tissue macrophages and brain microglia, which express lower levels of CD4 and CCR5 than CD4+ T cells in peripheral blood. Mechanisms that enhance HIV tropism for macrophages in the CNS and other tissues are not well understood. Here, we identify an HIV envelope glycoprotein (Env) variant in the CD4-binding site of gp120, Asn 283 (N283), that is present at a high frequency in brain tissues from AIDS patients with HIV-associated dementia (HAD). N283 increases gp120 affinity for CD4 by decreasing the gp120-CD4 dissociation rate, enhancing the capacity of HIV Envs to use low levels of CD4 for virus entry and increasing viral replication in macrophages and microglia. Structural modeling suggests that the enhanced ability of Envs with N283 to use low levels of CD4 is due to a hydrogen bond formed with Gln 40 of CD4. N283 is significantly more frequent in brain-derived Envs from HAD patients (41%; n=330) compared with non-HAD patients (8%; n=151; P<0.001). These findings suggest that the macrophage-tropic HIV Env variant N283 is associated with brain infection and dementia in vivo, representing an example of a HIV variant associated with a specific AIDS-related complication.

AIDS Dementia Complex↗

PubMed2006

A zinc-binding region in Vif binds Cul5 and determines cullin selection.

Human immunodeficiency virus-1 (HIV-1) Vif overcomes the anti-viral activity of APOBEC3G by targeting it for ubiquitination via a Cullin 5-ElonginB-ElonginC (Cul5-EloBC) E3 ligase. Vif associates with Cul5-EloBC through a BC-box motif that binds EloC, but the mechanism by which Vif selectively recruits Cul5 is poorly understood. Here we report that a region of Vif (residues 100-142) upstream of the BC-box binds selectively to Cul5 in the absence of EloC. This region contains a zinc coordination site HX5CX17-18CX3-5H (HCCH), with His/Cys residues at positions 108, 114, 133, and 139 coordinating one zinc ion. The HCCH zinc coordination site, which is conserved among primate lentivirus Vif proteins, does not correspond to any known class of zinc-binding motif. Mutations of His/Cys residues in the HCCH motif impair zinc coordination, Cul5 binding, and APOBEC3G degradation. Mutations of conserved hydrophobic residues (Ile-120, Ala-123, and Leu-124) located between the two Cys residues in the HCCH motif disrupt binding of the zinc-coordinating region to Cul5 and inhibit APOBEC3G degradation. The Vif binding site maps to the first cullin repeat in the N terminus of Cul5. These data suggest that the zinc-binding region in Vif is a novel cullin interaction domain that mediates selective binding to Cul5. We propose that the HCCH zinc-binding motif facilitates Vif-Cul5 binding by playing a structural role in positioning hydrophobic residues for direct contact with Cul5.

APOBEC Deaminases↗

PubMed2006

Mechanisms of HIV-1 neurotropism.

Human immunodeficiency virus type 1 (HIV) infects macrophages and microglia in the CNS and frequently causes neurocognitive impairment. Although antiviral therapy generally reduces the viral load in the CNS and improves HIV-associated neurological dysfunction, most current antiviral drugs have poor CNS penetrance and cannot completely suppress viral replication. Furthermore, drug-resistance mutations can evolve independently in the CNS. Thus, a long-lived viral reservoir persists in macrophages and microglia in the brain despite antiviral therapy. This review discusses mechanisms underlying the neurotropism of HIV, focusing on the role of the HIV envelope glycoproteins and their interactions with CD4 and the chemokine receptors CCR5 and CXCR4. We review data from studies of neurotropic HIV derived from the brains of patients with HIV-associated neurocognitive impairment as well as studies of nonhuman primate models. Understanding mechanisms that underlie HIV neurotropism and neurovirulence is critical for development of therapeutics to inhibit CNS infection and preventing neurological injury in HIV-infected individuals.

Animals↗

PubMed2003

CD4-dependent and CD4-independent HIV-2: consequences for neutralization.

BACKGROUND: HIV-2 is less pathogenic than HIV-1. In contrast to HIV-1, many isolates of HIV-2, including primary isolates, can infect cells independently of CD4. OBJECTIVE: To compare the sensitivity of CD4-dependent and CD4-independent isolates of HIV-2 to antibody-mediated neutralization. METHODS: The neutralization sensitivity of CD4-dependent and CD4-independent molecular clones of HIV-2 to a panel of HIV-2-positive serum samples was tested. Monoclonal antibodies to various epitopes across the viral envelope were used to determine whether a specific epitope conferred neutralization sensitivity. Neutralization sensitivity of primary isolates of HIV-2 able to infect in the absence of cellular CD4 was also investigated. Antibody binding to sensitive and resistant envelopes was analysed using enzyme-linked immunosorbent assay and flow cytometry. RESULTS: CD4-independent ROD B was highly sensitive to neutralization by HIV-2-positive sera compared with the CD4-dependent isolate ROD A. Induction of ROD A to infect CD4-negative cells by soluble CD4 rendered it equally sensitive to antibody neutralization. Similarly, primary X4, R5 or dual-tropic isolates of HIV-2 were significantly more susceptible to neutralization when utilizing a CD4-independent route of infection. Neutralization sensitivity was not epitope specific but several conformation-dependent antibodies accentuated this phenotype. Antibody binding to monomeric or oligomeric envelope did not correlate with neutralization sensitivity. CONCLUSIONS: HIV-2 isolates utilizing a CD4-independent route of infection are more sensitive to antibody-mediated neutralization. Cellular CD4 may protect HIV-2 from neutralization. This sensitivity to neutralization may, in part, explain the lower virus load and slower progression to disease in HIV-2-infected individuals.

Antibodies, Monoclonal↗