Entry of HIV-1 into target cells requires cell-surface CD4 and additional host cell cofactors. A cofactor required for infection with virus adapted for growth in transformed T-cell lines was recently identified and named fusin. However, fusin does not promote entry of macrophage-tropic viruses, which are believed to be the key pathogenic strains in vivo. The principal cofactor for entry mediated by the envelope glycoproteins of primary macrophage-tropic strains of HIV-1 is CC-CKR-5, a receptor for the β-chemokines RANTES, MIP-1α and MIP-1β.

Identification of a major co-receptor for primary isolates of HIV-1

The attraction of leukocytes to tissues is essential for inflammation and the host response to infection. The process is controlled by chemokines, which are chemotactic cytokines. This review introduces the burgeoning family of cytokines, with special emphasis on their role in the pathophysiology of disease and their potential as targets for therapy. Structure and Function of Chemokines Over 40 chemokines have been identified to date, most of them in the past few years. The relations among chemokines were not initially appreciated, which led to an idiosyncratic nomenclature consisting of many acronyms. When initially identified, these proteins had no known biologic . . .

Chemokines — Chemotactic Cytokines That Mediate Inflammation

The β-chemokines MIP-1α, MIP-1β and RANTES inhibit infection of CD4+ cells by primary, non-syncytium-inducing (NSI) HIV-1 strains at the virus entry stage, and also block env-mediated cell–cell membrane fusion. CD4+ T cells from some HIV-1-exposed uninfected individuals cannot fuse with NSI HIV-1 strains and secrete high levels of β-chemokines. Expression of the β-chemokine receptor CC-CKR-5 in CD4+ , non-permissive human and non-human cells renders them susceptible to infection by NSI strains, and allows env-mediated membrane fusion. CC-CKR-5 is a second receptor for NSI primary viruses.

HIV-1 entry into CD4+ cells is mediated by the chemokine receptor CC-CKR-5.

Homozygous Defect in HIV-1 Coreceptor Accounts for Resistance of Some Multiply-Exposed Individuals to HIV-1 Infection

The entry of human immunodeficiency virus (HIV) into cells requires the sequential interaction of the viral exterior envelope glycoprotein, gp120, with the CD4 glycoprotein and a chemokine receptor on the cell surface. These interactions initiate a fusion of the viral and cellular membranes. Although gp120 can elicit virus-neutralizing antibodies, HIV eludes the immune system. We have solved the X-ray crystal structure at 2.5 A resolution of an HIV-1 gp120 core complexed with a two-domain fragment of human CD4 and an antigen-binding fragment of a neutralizing antibody that blocks chemokine-receptor binding. The structure reveals a cavity-laden CD4-gp120 interface, a conserved binding site for the chemokine receptor, evidence for a conformational change upon CD4 binding, the nature of a CD4-induced antibody epitope, and specific mechanisms for immune evasion. Our results provide a framework for understanding the complex biology of HIV entry into cells and should guide efforts to intervene.

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Structure of an HIV gp120 envelope glycoprotein in complex with the CD4 receptor and a neutralizing human antibody

A cofactor for HIV-1 (human immunodeficiency virus-type 1) fusion and entry was identified with the use of a novel functional complementary DNA (cDNA) cloning strategy. This protein, designated “fusin,” is a putative G protein-coupled receptor with seven transmembrane segments. Recombinant fusin enabled CD4-expressing nonhuman cell types to support HIV-1 Env-mediated cell fusion and HIV-1 infection. Antibodies to fusin blocked cell fusion and infection with normal CD4-positive human target cells. Fusin messenger RNA levels correlated with HIV-1 permissiveness in diverse human cell types. Fusin acted preferentially for T cell line-tropic isolates, in comparison to its activity with macrophage-tropic HIV-1 isolates.

https://science.sciencemag.org/content/sci/272/5263/872.full.pdf

HIV-1 Entry Cofactor: Functional cDNA Cloning of a Seven-Transmembrane, G Protein-Coupled Receptor

A cofactor for HIV-1 (human immunodeficiency virus-type 1) fusion and entry was identified with the use of a novel functional complementary DNA (cDNA) cloning strategy. This protein, designated "fusin," is a putative G protein-coupled receptor with seven transmembrane segments. Recombinant fusin enabled CD4-expressing nonhuman cell types to support HIV-1 Env-mediated cell fusion and HIV-1 infection. Antibodies to fusin blocked cell fusion and infection with normal CD4-positive human target cells. Fusin messenger RNA levels correlated with HIV-1 permissiveness in diverse human cell types. Fusin acted preferentially for T cell line-tropic isolates, in comparison to its activity with macrophage-tropic HIV-1 isolates.

HIV-1 Entry Cofactor: Functional cDNA Cloning of a Seven-Transmembrane, G Protein–Coupled Receptor

The susceptibility to human immunodeficiency virus (HIV) infection depends on the cell surface expression of the human CD4 molecule and a human fusion accessory factor associated with HIV infection (CXCR4). CXCR4 is a member of the 7-transmembrane segment superfamily of G-protein-coupled cell surface molecules. CXCR4 plays an essential role in the membrane fusion step of HIV infection. The establishment of stable, nonhuman cell lines and transgenic mammals having cells that coexpress human CD4 and CXCR4 provides valuable tools for the continuing research of HIV infection and the development of more effective anti-HIV therapeutics. In addition, antibodies against CXCR4, isolated and purified peptide fragments of CXCR4, and CXCR4-binding biologic agents capable of blocking membrane fusion between HIV and target cells represent potential anti-HIV therapeutics.

Cells expressing both human cd4 and cxcr4

The susceptibility of human macrophages to human immunodeficiency virus (HIV) infection depends on cell surface expression of the human CD4 molecule and CC cytokine receptor 5. CCR5 is a member of the 7-transmembrane segment superfamily of G-protein-coupled cell surface molecules. CCR5 plays an essential role in the membrane fusion step of infection by some HIV isolates. The establishment of stable, nonhuman cell lines and transgenic mammals having cells that coexpress human CD4 and CCR5 provides valuable tools for the continuing research of HIV infection. In addition, antibodies which bind to CCR5, CCR5 variants, and CCR5-binding agents, capable of blocking membrane fusion between HIV and target cells represent potential anti-HIV therapeutics for macrophage-tropic strains of HIV.

Edward A. Berger

Papers

HIV-1 Entry Cofactor: Functional cDNA Cloning of a Seven-Transmembrane, G Protein-Coupled Receptor

HIV-1 Entry Cofactor: Functional cDNA Cloning of a Seven-Transmembrane, G Protein–Coupled Receptor

Cells expressing both human cd4 and cxcr4

Cc chemokine receptor 5, antibodies thereto, transgenic animals

Cc chemokine receptor 5 dna, new animal models and therapeutic agents for hiv infection