HIV-1 Vpr increases viral expression by manipulation of the cell cycle: a mechanism for selection of Vpr in vivo.

The human immunodeficiency virus type 1 (HIV-1) encodes a protein, called Vpr, that prevents proliferation of infected cells by arresting them in G2 of the cell cycle. This Vpr-mediated cell-cycle arrest is also conserved among highly divergent simian immunodeficiency viruses, suggesting an important role in the virus life cycle. However, it has been unclear how this could be a selective advantage for the virus. Here we provide evidence that expression of the viral genome is optimal in the G2 phase of the cell cycle, and that Vpr increases virus production by delaying cells at the point of the cell cycle where the long terminal repeat (LTR) is most active. Although Vpr is selected against when virus is adapted to tissue culture, we show that selection for Vpr function in vivo occurs in both humans and chimpanzees infected with HIV-1. These results suggest a novel mechanism for maximizing virus production in the face of rapid killing of infected target cells.

The human immunodeficiency virus type 1 vpr gene prevents cell proliferation during chronic infection.

Human immunodeficiency virus type 1 (HIV-1) is a retrovirus that can cause extensive cytopathicity in T cells. However, long-term productive infection of T-cell lines has been described. Here we show that although Vpr has no effect on the initial cytopathic effect of HIV-1, viruses that contain an intact vpr gene are unable to establish a chronic infection of T cells. However, virus with a mutated vpr gene can readily establish such long-term cultures. The effect of Vpr is independent of the env gene and the nef gene. Furthermore, expression of Vpr alone affects the progression of cells in the cell cycle. These results suggest that HIV-1 has evolved a viral gene to prevent chronic infection of T cells.

Human immunodeficiency virus type 1 cell cycle control: Vpr is cytostatic and mediates G2 accumulation by a mechanism which differs from DNA damage checkpoint control.

Vpr is a 96-amino-acid protein encoded by human immunodeficiency virus type 1 (HIV-1) that prevents proliferation of infected cells. We have established a system for infection of 100% of a T-cell population with HIV and use this system to show that within the context of HIV-1 infection, Vpr is primarily cytostatic rather than cytotoxic. Vpr acts upstream of dephosphorylation of the mitotic cyclin-dependent kinase, and causes infected cells to accumulate in the G2 stage of the cell cycle. However, some HIV-1 infected cells increase in ploidy and size, accumulating DNA to an 8N level. Furthermore, the mechanism of the Vpr mitotic block is qualitatively different from that of G2 DNA damage checkpoint control.

Indicator cell lines for detection of primary strains of human and simian immunodeficiency viruses.

CCR5 and CXCR4 are the two major coreceptors that have been identified for human immunodeficiency virus (HIV) entry. We have modified several beta-galactosidase-based HIV indicator cell lines to express CCR5 and/or CXCR4. Using these new reagents, we have been able to detect all primary isolates tested using one or both of these cell lines. However, there is large variation in the absolute viral infectivity among primary strains. Furthermore, all HIV strains are capable of causing syncytia in the indicator cells when the coreceptor is present regardless of whether they had previously been characterized as "syncytia-inducing" or "non-syncytium-inducing."

Uracil DNA glycosylase specifically interacts with Vpr of both human immunodeficiency virus type 1 and simian immunodeficiency virus of sooty mangabeys, but binding does not correlate with cell cycle arrest.

The Vpr protein encoded by human immunodeficiency virus type 1 (HIV-1) is important for growth of virus in macrophages and prevents infected cells from passing into mitosis (G2 arrest). The cellular target for these functions is not known, but Vpr of HIV-1 and the related Vpr from simian immunodeficiency virus of sooty mangabeys (SIV(SM)) bind the DNA repair enzyme UNG, while the Vpx protein of SIV(SM) does not. Nonetheless, a mutational analysis of Vpr showed that binding to UNG is neither necessary nor sufficient for the effect of Vpr on the cell cycle.