Abstract
The accessory protein Vpr of Human Immunodeficiency Virus type 1 (HIV-1) enhances replication of the virus in macrophages (1-7). Virus particle packaged Vpr is released in target cells shortly after entry, suggesting it is required early in infection (8, 9). Why it is required for infection of macrophages and not cycling T-cells and why it induces G2/M arrest in cycling cells are unknown. Here we observe, by co-immunoprecipitation assay, an interaction between Vpr and endogenous REAF (RNA-associated Early-stage Antiviral Factor, RPRD2), a protein shown previously to potently restrict HIV infection(10). After HIV-1 infects macrophages, within 30 minutes of viral entry, Vpr induces the degradation of REAF. Subsequently, as replication continues, REAF expression is upregulated – a response which is curtailed by Vpr. REAF is more highly expressed in differentiated macrophages than in cycling T-cells. Expression in cycling cells is cell-cycle dependent and knockdown induces cell-cycle perturbation. Therefore, our results support the long held hypothesis that Vpr induces the degradation of a factor involved in the cell cycle that impedes HIV infection in macrophages.
Summary Human Immunodeficiency Virus type 1 (HIV-1) has so called accessory proteins which modulate the activity of host proteins, enabling efficient replication of the virus. The precise function of one such accessory protein, Vpr, has so far not been revealed. REAF is a host protein that limits the capacity of HIV-1 to infect cells. Here, we show that Vpr interacts with REAF. Shortly after infection, only when Vpr is present, REAF is degraded in primary macrophages. Vpr further curtails the cells subsequent increase in REAF production. Additionally, when the ability of cell to produce REAF is prevented, the population accumulates in the G2/M phase of the cell cycle. In infection, Vpr sends cells into G2/M arrest. This study therefore supports the long held hypothesis that Vpr is responsible for the degradation of a cellular factor involved in the cell cycle and one which impedes the completion of HIV-1 replication.