Vpr R36w and R77Q Mutations Alter HIV-1 Replication and Cytotoxicity in T Lymphocytes

Abstract Background: Acquired immunodeficiency syndrome (AIDS) is caused when HIV depletes CD4+ helper T cell levels in infected patients. Distinct AIDS development rates have shown that there are Rapid Progressor (RP) and Long-Term Non-Progressor (LTNP) patients, but the circumstances governing these differences in the kinetics of helper T cell depletion are poorly understood. Mutations in the Viral Protein R (Vpr) gene have been suggested to have a direct impact on helper T cell depletion. Interactions of Vpr with both host and viral factors affect cellular activities such as cell cycle progression and apoptosis. The Vpr mutants R36W and R77Q have been associated with RP and LTNP phenotypes, respectively; however, these findings are still controversial. This study examines the effects that Vpr mutations have in the context of HIV-1 infection of the HUT78 T cell line, using replication-competent CXCR4-tropic virus strains. Results: Our results show a replication enhancement of the R36W mutant accompanied by increased cytotoxicity. Interestingly, the R77Q mutant showed a unique enhancement of apoptosis (measured by Annexin V and TUNEL staining) and G2 cell cycle arrest; these effects were not seen with WT, R36W or Vpr null viruses. Thus, point mutations in Vpr can exhibit profound differences in mechanisms and rates of cell killing. Conclusions: The vpr gene is thought to be an important virulence factor in Human Immunodeficiency Virus type 1 (HIV-1). Vpr polymorphisms have been associated with different rates of AIDS progression. However, there is controversy about the cytopathic and virulence phenotypes of Vpr mutants, with contradictory conclusions about the same mutants. Here, we examine the replication capacity, apoptotic induction, and G2 cell cycle arrest phenotypes of three vpr mutants compared to wild-type HIV-1. One mutant associated with rapid AIDS progression replicated more efficiently and killed cells more rapidly than wild-type HIV-1. Another mutant associated with slow AIDS progression triggered apoptosis more efficiently than wild-type HIV-1 and showed significant levels of G2 cell cycle arrest. These results shed additional light on the role of vpr polymorphisms in T cell killing by HIV-1 and may help to explain the role of Vpr in different rates of AIDS progression.