Reversion of the lethal phenotype of an HIV-1 integrase mutant virus by overexpression of the same integrase mutant protein

The human immunodeficiency virus type 1 (HIV-1) integrase (IN) is essential for integration of viral DNA into host cell chromatin. We have reported previously (Priet, S., Navarro, J. M., Gros, N., Querat, G., and Sire, J. (2003) J. Biol. Chem. 278, 4566-4571) that IN also plays a role in the packaging of the host uracil DNA glycosylase UNG2 into viral particles and that the region of IN encompassing residues 170-180 was responsible for the interaction with UNG2 and for its packaging into virions. In this work, we aimed to investigate the replication of HIV-1 viruses rendered deficient in virion-associated UNG2 by single or double point mutations in the region 170-180 of IN. We show that the L172A/K173A IN mutant virus was deficient for UNG2 packaging and was defective for replication because of a blockage at the stage of proviral DNA integration in host cell DNA. In vitro assays using long term repeat mimics, however, demonstrate that the L172A/K173A IN mutant was catalytically active. Moreover, trans-complementation experiments show that the viral propagation of L172A/K173A viruses could be rescued by the overexpression of Vpr.L172A/K173A IN fusion protein in a dose-dependent manner and that this rescue is independent of UNG2 packaging. Altogether, our data indicate that L172A/K173A mutations of IN induce a subtle defect in the function of IN, which nevertheless dramatically impairs viral replication. Unexpectedly, this blockage of replication could be overcome by forcing the packaging of higher amounts of this same mutated integrase. This is the first study reporting that blockage of the integration process of HIV-1 provirus carrying a mutation of IN could be alleviated by increasing amounts of IN even carrying the same mutations.     

High-level expression of active HIV-1 integrase from a synthetic gene in human cells.

A synthetic gene encoding for HIV-1 integrase was designed to circumvent the intrinsic instability and the repressor elements present in the wild-type gene. High-level expression of HIV-1 integrase was obtained in various human cell lines independently of viral accessory proteins. A human 293T cell line was selected that stably expresses HIV-1 integrase and has growth kinetics comparable to the parental cell line. The enzyme was localized in the nucleus and remained stably associated with the chromosomes during mitosis. Lentiviral vector particles carrying the inactivating D64V mutation in the integrase gene were capable of stably transducing 293T cells when complemented in the producer cells with integrase expressed from the synthetic gene. When the cell line that stably expresses integrase was infected with the defective viral particles, complementation of integrase activity was detected as well. Expression of active HIV-1 integrase in human cells will facilitate the study of the interplay between host and viral factors during integration.     

Inhibition of early steps of HIV-1 replication by SNF5/Ini1

To replicate, human immunodeficiency virus, type 1 (HIV-1) needs to integrate a cDNA copy of its RNA genome into a chromosome of the host cell, a step controlled by the viral integrase (IN) protein. Viral integration involves the participation of several cellular proteins. SNF5/Ini1, a subunit of the SWI/SNF chromatin remodeling complex, was the first cofactor identified to interact with IN. We report here that SNF5/Ini1 interferes with early steps of HIV-1 replication. Inhibition of SNF5/Ini1 expression by RNA interference increases HIV-1 replication. Using quantitative PCR, we show that both the 2-long terminal repeat circle and integrated DNA forms accumulate upon SNF5/Ini1 knock down. By yeast two-hybrid assay, we screened a library of HIV-1 IN random mutants obtained by PCR random mutagenesis using SNF5/Ini1 as prey. Two different mutants of interaction, IN E69G and IN K71R, were impaired for SNF5/Ini1 interaction. The E69G substitution completely abolished integrase catalytic activity, leading to a replication-defective virus. On the contrary, IN K71R retained in vitro integrase activity. K71R substitution stimulates viral replication and results in higher infectious titers. Taken together, these results suggest that, by interacting with IN, SNF5/Ini1 interferes with early steps of HIV-1 infection.     

Regulation of expression and activity of the yeast transcription factor ADR1.

Disruption of ADR1, a positive regulatory gene in the yeast Saccharomyces cerevisiae, abolished derepression of ADH2 but did not affect glucose repression of ADH2 or cell viability. The ADR1 mRNA was 5 kilobases long and had an unusually long leader containing 509 nucleotides. ADR1 mRNA levels were regulated by the carbon source in a strain-dependent fashion. beta-Galactosidase levels measured in strains carrying an ADR1-lacZ gene fusion paralleled ADR1 and ADR1-lacZ mRNA levels, indicating a lack of translational regulation of ADR1 mRNA. ADH2 was regulated by the carbon source to the same extent in all strains examined and showed complete dependence on ADR1 as well. The expression of ADR1 mRNA and an ADR1-beta-galactosidase fusion protein during glucose repression suggested that the activity of the ADR1 protein is regulated at the posttranslational level to properly regulate ADH2 expression. The ADR1-beta-galactosidase fusion protein was able to activate ADH2 expression during glucose repression but showed significantly higher levels of activation upon derepression. A similar result was obtained when ADR1 was present on a multicopy plasmid. These results suggest that low-level expression of ADR1 is required to maintain glucose repression of ADH2 and are consistent with the hypothesis that ADR1 is regulated at the posttranslational level.     

Stereospecificity of reactions catalyzed by HIV-1 integrase

The retroviral integrase catalyzes two successive chemical reactions essential for integration of the retroviral genome into a host chromosome: 3' end processing, in which a dinucleotide is cleaved from each 3' end of the viral DNA; and the integration reaction itself, in which the resulting recessed 3' ends of the viral DNA are joined to the host DNA. We have examined the stereospecificity of human immunodeficiency virus type 1 integrase for phosphorothioate substrates in these reactions and in a third reaction, disintegration, which is macroscopically the reverse of integration. Integrase preferentially catalyzed end processing and integration of a substrate with the (R(p))-phosphorothioate stereoisomer at the reaction center and disintegration of a substrate with an (S(p))-phosphorothiate at the reaction center. These results suggest a model for the architecture of the active site of integrase, and its interactions with key features of the viral and target DNA.     

Modulating HIV-1 replication by RNA interference directed against human transcription elongation factor SPT5

Background

Dendritic cell (DC) transmission of human immunodeficiency virus (HIV) to CD4+ T cells occurs across a point of cell-cell contact referred to as the infectious synapse. The relationship between the infectious synapse and the classically defined immunological synapse is not currently understood. We have recently demonstrated that human B cells expressing exogenous DC-SIGN, DC-specific intercellular adhesion molecule-3 (ICAM-3)-grabbing nonintegrin, efficiently transmit captured HIV type 1 (HIV-1) to CD4+ T cells. K562, another human cell line of hematopoietic origin that has been extensively used in functional analyses of DC-SIGN and related molecules, lacks the principal molecules involved in the formation of immunological synaptic junctions, namely major histocompatibility complex (MHC) class II molecules and leukocyte function-associated antigen-1 (LFA-1). We thus examined whether K562 erythroleukemic cells could recapitulate efficient DC-SIGN-mediated HIV-1 transmission (DMHT).

Results

Here we demonstrate that DMHT requires cell-cell contact. Despite similar expression of functional DC-SIGN, K562/DC-SIGN cells were inefficient in the transmission of HIV-1 to CD4+ T cells when compared with Raji/DC-SIGN cells. Expression of MHC class II molecules or LFA-1 on K562/DC-SIGN cells was insufficient to rescue HIV-1 transmission efficiency. Strikingly, we observed that co-culture of K562 cells with Raji/DC-SIGN cells impaired DMHT to CD4+ T cells. The K562 cell inhibition of transmission was not directly exerted on the CD4+ T cell targets and required contact between K562 and Raji/DC-SIGN cells.

Conclusions

DMHT is cell type dependent and requires cell-cell contact. We also find that the cellular milieu can negatively regulate DC-SIGN transmission of HIV-1 in trans.