Dual role of the HIV-1 vpr protein in the modulation of the apoptotic response of T cells.

We investigated the effect of vpr, physiologically expressed during the course of an acute HIV-1 infection, on the response of infected cells to apoptotic stimuli as well as on the HIV-induced apoptosis. At 48 h after infection, Jurkat cells exhibited a lower susceptibility to undergo apoptosis with respect to uninfected cells. This effect was not observed following infection with either a vpr-mutated virus or a wild-type strain in the presence of antisense oligodeoxynucleotides targeted at vpr mRNA. Single-cell analysis, aimed at simultaneously identifying apoptotic and infected cells, revealed that resistance to apoptosis correlated with productive infection. Notably, vpr-dependent protection from induced apoptosis was also observed in HIV-1-infected PBMC. In contrast, at later stages of infection, a marked increase in the number of cells spontaneously undergoing apoptosis was detected in infected cultures. This virus-induced apoptosis involved vpr expression and predominantly occurred in productively infected cells. These results indicate that HIV-1 vpr can exert opposite roles in the regulation of apoptosis, which may depend on the level of its intracellular expression at different stages of HIV-1 infection. The dual function of vpr represents a novel mechanism in the complex strategy evolved by HIV to influence the turnover of T lymphocytes leading to either viral persistence or virus release and spreading.