Attenuation of human immunodeficiency virus type 1 cytopathic effect by a mutation affecting the transmembrane envelope glycoprotein

HIV1 cytopathogenicity-genetic difference between direct cytotoxic and fusogenic effect

Formation of large syncytia, rapid cell killing, and early onset of replication are characteristics of the highly cytopathic Zairian virus strain HIV1 NDK compared with the HIV1 LAV prototype. Recombinant provirus molecules derived from cloned infectious DNAs of HIV1 LAV and NDK were constructed by reciprocal exchange of genetic material using conserved restriction sites. Different regions of the HIV1 genome were responsible for variability of the direct single-cell cytotoxic and fusogenic effects. A minimal, provisionally defined portion of genetic information responsible for the higher cytotoxicity of HIV1 NDK compared to the HIV1 LAV prototype was localized in the fragment Spel1042/EcoRl4183, containing the 3'-terminal half of gag and a majority of the pol gene. This region also determined the rapid replication properties of HIV1 NDK. The increased fusogenic potential of HIV1 NDK was associated with the simultaneous presence of HIV1 NDK fragments BssHll255/Spel1042 and EcoRl5278/Xhol8401 which contained the splicing donor, packaging sequence, p18 gag protein, and the HIV env gene. The increase in the direct killing effect but not in the syncytium forming ability of HIV1 NDK correlated with the early onset of replication and rapid spread of HIV1 NDK in cell cultures. The HIV1 NDK fragments BssHll/Spel and EcoRl/Xhol were by themselves necessary but not sufficient to induce formation of large syncytia.

HIV-1 replication and potential targets for intervention

Intense research into fundamental processes of human immunodeficiency syndrome type 1 (HIV-1) replication has yielded knowledge that in many aspects equals or exceeds that of the oncogenic retroviruses. The availability of sensitive virus detection methods has allowed a more thorough characterization of the biology of virus persistence and latency in vivo and removed the dependence on in vitro models. As a clearer picture of the pattern of HIV-1 replication in vivo evolves, it becomes apparent that HIV-1 biology is distinct from that of the prototypic oncogenic retroviruses in several key aspects, particularly with regard to host cell range and determinants of viral permissiveness. In this respect it may be appropriate to examine the lentivirus, rather than the oncovirus model system to better understand the biology and pathogenesis of HIV-1 infection. This synopsis of recent and ongoing research developments in HIV-1 replication and pathogenesis emphasizes the determinants of host cell permissiveness, early events in virus replication, and underlying features in HIV-1 cytopathogenesis. In addition, basic viral replication processes which can be exploited for therapeutic intervention are discussed.

Distinct populations of human immunodeficiency virus type 1 in blood and cerebrospinal fluid

The nucleotide sequence of the gp41 transmembrane protein coding region of human immunodeficiency virus type 1 (HIV-1) proviral DNA obtained from blood and cerebrospinal fluid (CSF) from 6 individuals was determined by direct sequencing of polymerase chain reaction (PCR)-amplified DNA. The direct sequencing approach was performed to avoid errors introduced by Taq polymerase during the amplification reaction. In 3 of 6 paired samples distinct sequence differences between proviral DNA from blood and CSF, ranging from 0.64% to 1.73%, were detected. The greatest diversity (4.2% different amino acids) was found between paired samples of a patient suffering from AIDS encephalopathy, with most of the differences clustering near the carboxy-terminal end of gp41. The results demonstrate that genetically different populations of HIV-1 may be present in different biological compartments and specific neurotropic HIV variants may exist.

Demonstration of two distinct cytopathic effects with syncytium formation-defective human immunodeficiency virus type 1 mutants

The mechanism of human immunodeficiency virus type 1 (HIV-1) cytopathicity is poorly understood and might involve formation of multinucleated giant cells (syncytia), single-cell lysis, or both. In order to determine the contributions of the fusion domain to syncytium formation, single-cell lysis, and viral infectivity and to clarify the molecular details of these events, insertion mutations were made in the portion of env encoding this sequence in the functional HIV-1 proviral clone HXB2. Viruses produced from these mutant clones were found to have a partial (F3) or complete (F6) loss of syncytium-forming ability in acutely infected CEM, Sup T1, and MT4 T-cell lines. During the early stage of acute infection by F6 virus, there was a loss of the syncytial cytopathic effect, which resulted in increased cell viability, and a 1.9- to 2.6-fold increase in virus yield in the cell lines tested. In the late stage of acute infection, the single-cell cytopathic effect of F6 virus was similar to that of the parental HXB2 virus. The F3 and F6 viruses were also found to have a 1.7- to 43-fold reduction in infectivity compared with the HXB2 virus. The mutant F3 and F6 and parental HXB2 envelope proteins were expressed in vaccinia virus, and the mutant envelope proteins were observed to be defective in their ability to form syncytia. BSC-40 cells infected with vaccinia virus recombinants revealed no differences in kinetics of cleavage, cell surface expression, or CD4 binding capacity of the mutant and parental envelope proteins. These results demonstrate that a loss of syncytium formation results in an attenuation of infectivity and a loss of the syncytial cytopathic effect without a loss of single-cell lysis. These mutants may reflect in tissue culture the changes observed in the HIV isolates in vivo during disease progression, which exhibit marked differences in syncytium production.

Disturbance of nuclear transport of proteins in CD4+ cells expressing gp160 of human immunodeficiency virus

An extensive cytopathic effect occurred in the CD4+ cells expressing gp160 of human immunodeficiency virus. A protein capable of nuclear location that was microinjected into such cells was not transported into the nuclei at an early stage when little cytopathic effect had yet to occur.

Effects of changes in gp120-CD4 binding affinity on human immunodeficiency virus type 1 envelope glycoprotein function and soluble CD4 sensitivity

Mutant gp120 glycoproteins exhibiting a range of affinities for CD4 were tested for ability to form syncytia and to complement an env-defective provirus for replication. Surprisingly, gp120 mutants that efficiently induced syncytia and/or complemented virus replication were identified that exhibited marked (up to 50-fold) reductions in CD4-binding ability. Temperature-dependent changes in gp120, which result in a seven- to ninefold increase in affinity for CD4, were shown not to be necessary for subsequent membrane fusion or virus entry events. Mutant glycoproteins demonstrating even relatively small decreases in CD4-binding ability exhibited reduced sensitivity to soluble CD4. The considerable range of CD4-binding affinities tolerated by replication-competent HIV-1 variants has important implications for antiviral strategies directed at the gp120-CD4 interaction.

A structural correlation between lentivirus transmembrane proteins and natural cytolytic peptides

Although oncoviruses and lentiviruses replicate by similar mechanisms, they differ fundamentally in the usual fate of the infected host cell during productive natural infections. Oncoviruses typically establish persistent nonlytic infections in natural host cells, while lentivirus infections characteristically result in a variety of cytopathic effects ultimately leading to death of the target cell. Described here is a unique structural motif consisting of a strongly amphipathic and arginine-rich helical peptide segment in the carboxyl end of lentivirus TM proteins that is structurally similar to the family of cytolytic peptides produced as defensive agents by certain insects and amphibians. Also demonstrated is the lytic nature of synthetic peptides constructed from the transmembrane (TM) protein of human and simian immunodeficiency viruses (HIV and SIV). Thus, it appears that the cytopathic properties of lentiviruses may be in part attributed to the presence of lytic peptides within the TM protein, designated lentivirus lytic peptide (LLP) and that variations in this segment could account for some of the differences observed in the cytopathicity among variants of a particular lentivirus.