Viral protein R upregulates expression of ULBP2 on uninfected bystander cells during HIV-1 infection of primary CD4+ T lymphocytes.

HIV-1 Vpr triggers NK cell-mediated lysis of infected cells by upregulating ULBP2, a ligand of the NKG2D receptor, through activation of the ATR-mediated DNA damage response. Herein, we demonstrate that Vpr augments ULBP2 expression on both infected and uninfected bystander cells during HIV-1 infection of primary CD4+ T lymphocytes. Indeed, the frequency of uninfected bystander cells expressing high levels of ULBP2 was elevated in a Vpr-dependent manner. Nevertheless, the same does not hold true for a Vpr mutant that is not packaged into virions, suggesting the involvement of virion-associated Vpr in this process. Additionally, we show that soluble Vpr has the ability to induce a DNA damage response and to augment cell-surface ULBP2 upon transducing target cells, including T cells, conditions known to promote NK cell-mediated killing. Overall, these findings suggest that Vpr could contribute to CD4+ T cell loss by rendering uninfected bystander cells susceptible to NK cell-mediated killing.