Escape from the dominant HLA-B27-restricted cytotoxic T-lymphocyte response in Gag is associated with a dramatic reduction in human immunodeficiency virus type 1 replication.

Human leukocyte antigen (HLA)-B27-positive subjects are uncommon in their ability to control infection with human immunodeficiency virus type 1 (HIV-1). However, late viral escape from a narrowly directed immunodominant Gag-specific CD8(+) T-lymphocyte (CTL) response has been linked to AIDS progression in these individuals. Identifying the mechanism of the immune-mediated control may provide critical insights into HIV-1 vaccine development.

Analysis of human cell heterokaryons demonstrates that target cell restriction of cyclosporine-resistant human immunodeficiency virus type 1 mutants is genetically dominant.

The host cell protein cyclophilin A (CypA) binds to CA of human immunodeficiency virus type 1 (HIV-1) and promotes HIV-1 infection of target cells. Disruption of the CypA-CA interaction, either by mutation of the CA residue at G89 or P90 or with the immunosuppressive drug cyclosporine (CsA), reduces HIV-1 infection. Two CA mutants, A92E and G94D, previously were identified by selection for growth of wild-type HIV-1 in cultures of CD4(+) HeLa cell cultures containing CsA.

Maturation-dependent human immunodeficiency virus type 1 particle fusion requires a carboxyl-terminal region of the gp41 cytoplasmic tail.

Lentiviruses, including human immunodeficiency virus type 1 (HIV-1), typically encode fusion glycoproteins with long cytoplasmic tails (CTs). We previously reported that immature HIV-1 particles are inhibited for fusion with target cells by a mechanism requiring the 152-amino-acid CT of gp41. The gp41 CT was also shown to mediate the detergent-resistant association of the HIV-1 envelope glycoprotein complex with immature HIV-1 particles, indicating that the gp41 CT forms a stable complex with Gag in immature virions.

A mutation in alpha helix 3 of CA renders human immunodeficiency virus type 1 cyclosporin A resistant and dependent: rescue by a second-site substitution in a distal region of CA.

The replication of many isolates of human immunodeficiency virus type 1 (HIV-1) is enhanced by binding of the host cell protein cyclophilin A (CypA) to the viral capsid protein (CA). The immunosuppressive drug cyclosporine A (CsA) and its nonimmunosuppressive analogs bind with high affinity to CypA and inhibit HIV-1 replication. Previous studies have identified two mutations, A92E and G94D, in the CypA-binding loop of CA that confer the ability of HIV-1 to replicate in the presence of CsA.

Selective restriction of Nef-defective human immunodeficiency virus type 1 by a proteasome-dependent mechanism.

The Nef protein enhances human immunodeficiency virus type 1 (HIV-1) infectivity by facilitating an early postentry step in the virus life cycle. We report here that the addition of MG132 or lactacystin, each a specific inhibitor of cellular proteasome activity, preferentially enhances cellular permissiveness to infection by Nef-defective versus wild-type HIV-1. Pseudotyping by the glycoprotein of vesicular stomatitis virus rendered Nef-defective HIV-1 particles minimally responsive to the enhancing effects of proteasome inhibitors.

Human immunodeficiency virus type 1 resistance to the small molecule maturation inhibitor 3-O-(3',3'-dimethylsuccinyl)-betulinic acid is conferred by a variety of single amino acid substitutions at the CA-SP1 cleavage site in Gag.

The compound 3-O-(3',3'-dimethylsuccinyl)-betulinic acid (DSB) potently and specifically inhibits human immunodeficiency virus type 1 (HIV-1) replication by delaying the cleavage of the CA-SP1 junction in Gag, leading to impaired maturation of the viral core. In this study, we investigated HIV-1 resistance to DSB by analyzing HIV-1 mutants encoding a variety of individual amino acid substitutions in the CA-SP1 cleavage site. Three of the substitutions were lethal to HIV-1 replication owing to a deleterious effect on particle assembly.

Analysis of HIV-1-X4 fusion with immature dendritic cells identifies a specific restriction that is independent of CXCR4 levels.

Immature dendritic cells (iDCs) are likely to be among the first targets of HIV infection during sexual transmission. We analyzed whether the relatively inefficient viral replication in iDCs could be attributed to specific restrictions during the viral life cycle. Using iDCs from a panel of donors, we set out to compare their capacity to support infection and propagation of X4- and R5-tropic viruses.

Viral and cellular factors that regulate HIV-1 uncoating.

Purpose Of Review: The immediate events in HIV-1 infection following fusion of HIV-1 particles with the target cells are poorly defined and difficult to study. It is generally thought that the viral capsid undergoes a disassembly process that has broadly been referred to as uncoating. The recent identification of species-specific host restriction factors that target the viral capsid has sparked new interest in retroviral uncoating.

Saturation of TRIM5 alpha-mediated restriction of HIV-1 infection depends on the stability of the incoming viral capsid.

HIV-1 infection is restricted at a post-entry stage in some simian cell lines by species-specific variants of TRIM5 alpha. Restriction targets the viral capsid protein (CA) and results in attenuated reverse transcription. TRIM5 alpha restriction can be inhibited by the addition of noninfectious virus-like particles (VLPs), thus rendering cells permissive for infection by an HIV-1 reporter virus.

Evidence for a functional link between uncoating of the human immunodeficiency virus type 1 core and nuclear import of the viral preintegration complex.

Human immunodeficiency virus type 1 (HIV-1) particles begin their replication upon fusion with the plasma membrane of target cells and release of the viral core into the host cell cytoplasm. Soon thereafter, the viral capsid, which is composed of a polymer of the CA protein, disassociates from the internal ribonucleoprotein complex. While this disassembly process remains poorly understood, the available evidence indicates that proper uncoating of the core is a key step in infection.

A mutation in the human immunodeficiency virus type 1 Gag protein destabilizes the interaction of the envelope protein subunits gp120 and gp41.

The Gag protein of human immunodeficiency virus type 1 (HIV-1) associates with the envelope protein complex during virus assembly. The available evidence indicates that this interaction involves recognition of the gp41 cytoplasmic tail (CT) by the matrix protein (MA) region of Pr55(Gag). Here we show that substitution of Asp for Leu at position 49 (L49D) in MA results in a specific reduction in particle-associated gp120 without affecting the levels of gp41.

Maturation of the viral core enhances the fusion of HIV-1 particles with primary human T cells and monocyte-derived macrophages.

HIV-1 infection requires fusion of viral and cellular membranes in a reaction catalyzed by the viral envelope proteins gp120 and gp41. We recently reported that efficient HIV-1 particle fusion with target cells is linked to maturation of the viral core by an activity of the gp41 cytoplasmic domain. Here, we show that maturation enhances the fusion of a variety of recombinant viruses bearing primary and laboratory-adapted Env proteins with primary human CD4+ T cells.

Inhibition of HIV-1 maturation via drug association with the viral Gag protein in immature HIV-1 particles.

The small molecule 3-O-(3',3'-dimethylsuccinyl)-betulinic acid (DSB) potently inhibits human immunodeficiency virus, type 1 (HIV-1) replication by interfering with proteolytic cleavage of the viral Gag protein at a specific site. Here we have demonstrated that the antiviral mechanism involves the association of DSB with Gag at a 1:1 stoichiometry within immature HIV-1 particles. The binding was specific, as mutations in Gag that confer resistance to DSB inhibited the association, which could be competed by DSB but not by the inactive compound betulinic acid.

Antimicrobial peptides from amphibian skin potently inhibit human immunodeficiency virus infection and transfer of virus from dendritic cells to T cells.

Topical antimicrobicides hold great promise in reducing human immunodeficiency virus (HIV) transmission. Amphibian skin provides a rich source of broad-spectrum antimicrobial peptides including some that have antiviral activity. We tested 14 peptides derived from diverse amphibian species for the capacity to inhibit HIV infection.

Betulinic acid derivatives as HIV-1 antivirals.

Betulinic acid (BA) derivatives are low molecular weight organic compounds synthesized from a plant-derived natural product. Several BA derivatives are potent and highly selective inhibitors of HIV-1. Depending on the specific side-chain modification, these compounds function by inhibiting HIV fusion or, as recently demonstrated, by interfering with a specific step in HIV-1 maturation.

Structural requirements for recognition of the human immunodeficiency virus type 1 core during host restriction in owl monkey cells.

Human immunodeficiency virus type 1 (HIV-1) infection of simian cells is restricted at an early postentry step by host factors whose mechanism of action is unclear. These factors target the viral capsid protein (CA) and attenuate reverse transcription, suggesting that they bind to the HIV-1 core and interfere with its uncoating. To identify the relevant binding determinants in the capsid, we tested the capacity of viruses containing Gag cleavage site mutations and amino acid substitutions in CA to inhibit restriction of a wild type HIV-1 reporter virus in owl monkey cells.

The direct measurement of embryogenic volume and nucleo-cytoplasmic ratio during mouse pre-implantation development.

After fertilization, the mammalian conceptus undergoes cleavage, a process of cell proliferation in the absence of interphase growth. It is not known when cleavage ends and gives way to fully replicative cell cycles with a stable nucleo-cytoplasmic ratio. We have used two-photon excitation and confocal microscopy to measure directly volumes and nucleo-cytoplasmic ratios of whole murine concepti and their individual constituent blastomeres during pre-implantation development up to the early uterine attachment stage (day 5).

A cell-based screen for drugs to treat Huntington's disease.

We have developed a medium-throughput cell-based assay to screen drugs for Huntington's disease (HD). The assay measures the ability of drugs to protect cultured neuronal (PC12) cells from death caused by an expanded polyglutamine (poly Q) form of huntingtin exon 1. Using this assay, we have blindly screened a library of 1040 compounds compiled by the NINDS: the NIH Custom Collection (NCC).

The sequence of the CA-SP1 junction accounts for the differential sensitivity of HIV-1 and SIV to the small molecule maturation inhibitor 3-O-{3',3'-dimethylsuccinyl}-betulinic acid.

Background: Despite the effectiveness of currently available antiretroviral therapies in the treatment of HIV-1 infection, a continuing need exists for novel compounds that can be used in combination with existing drugs to slow the emergence of drug-resistant viruses. We previously reported that the small molecule 3-O-{3',3'-dimethylsuccinyl}-betulinic acid (DSB) specifically inhibits HIV-1 replication by delaying the processing of the CA-SP1 junction in Pr55Gag. By contrast, SIVmac239 replicates efficiently in the presence of high concentrations of DSB.

Nef stimulates human immunodeficiency virus type 1 replication in primary T cells by enhancing virion-associated gp120 levels: coreceptor-dependent requirement for Nef in viral replication.

The Nef protein enhances human immunodeficiency virus type 1 (HIV-1) replication through an unknown mechanism. We and others have previously reported that efficient HIV-1 replication in activated primary CD4(+) T cells depends on the ability of Nef to downregulate CD4 from the cell surface. Here we demonstrate that Nef greatly enhances the infectivity of HIV-1 particles produced in primary T cells.

Coupling of human immunodeficiency virus type 1 fusion to virion maturation: a novel role of the gp41 cytoplasmic tail.

Retrovirus particles are not infectious until they undergo proteolytic maturation to form a functional core. Here we report a link between human immunodeficiency virus type 1 (HIV-1) core maturation and the ability of the virus to fuse with target cells. Using a recently developed reporter assay of HIV-1 virus-cell fusion, we show that immature HIV-1 particles are 5- to 10-fold less active for fusion with target cells than are mature virions.

Assembly properties of the human immunodeficiency virus type 1 CA protein.

During retroviral maturation, the CA protein oligomerizes to form a closed capsid that surrounds the viral genome. We have previously identified a series of deleterious surface mutations within human immunodeficiency virus type 1 (HIV-1) CA that alter infectivity, replication, and assembly in vivo. For this study, 27 recombinant CA proteins harboring 34 different mutations were tested for the ability to assemble into helical cylinders in vitro.

Bifunctional anti-human immunodeficiency virus type 1 small molecules with two novel mechanisms of action.

A class of betulinic acid derivatives was synthesized to target two critical steps in the human immunodeficiency virus type 1 (HIV-1) replication cycle, entry and maturation. Each mechanism of HIV-1 inhibition is distinct from clinically available anti-HIV therapeutics. The viral determinants of the antientry and antimaturation activities are the bridging sheet of HIV-1 gp120 and the P24/p2 cleavage site, respectively.

Small-molecule inhibition of human immunodeficiency virus type 1 replication by specific targeting of the final step of virion maturation.

Despite the effectiveness of currently available human immunodeficiency virus type 1 (HIV-1) therapies, a continuing need exists for new drugs to treat HIV-1 infection. We investigated the mechanism by which 3-O-[3',3'-dimethylsuccinyl]-betulinic acid (DSB) inhibits HIV-1 replication. DSB functions at a late stage of the virus life cycle but does not inhibit the HIV-1 protease in vitro or interfere with virus assembly or release.