Vpr R36W and R77Q Mutations Alter HIV-1 Replication and Cytotoxicity in T Lymphocytes

Chronic immune inflammation (CII) is a characteristic symptom of HIV-1 infection that contributes to acquired immunodeficiency syndrome (AIDS) progression 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 disease progression are poorly understood. Mutations in the Viral Protein R (Vpr) have been suggested to have a direct impact on disease progression. Studies have shown that Vpr interacts with both host and viral factors; these interactions affect cellular activities such as cell cycle progression and enhancement of apoptosis. The Vpr mutants R36W and R77Q have been associated with RP and LTNP phenotypes, respectively; however, these findings are still controversial. This study sheds light on 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. Our results show a replication enhancement of the R36W mutant (increased viral load and percentage of p24+ cells) 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 or R36W viruses. Since necrosis is associated with the release of pro-inflammatory factors, the R36 mutation could lead to more robust CII and the RP phenotype. Conversely, the R77Q mutation leads to apoptosis, potentially avoiding CII and leading to a LTNP phenotype. Thus, Vpr mutations may impact HIV-1 related progression to AIDS.