Susceptibility of HIV-1-TAT transfected cells to undergo apoptosis. Biochemical mechanisms

The effects of HIV-1 Tat protein on mitochondria membrane permeability and apoptosis were analysed in lymphoid cells. In this report we show that stab le-transfected HIV-Tat cells are primed to undergo apoptosis upon serum wit hdrawal. This effect was observed in both the Jhan T cell line and the K562 cells, the latter expressing the bcr-abl chimeric gene, which confers resi stance to apoptosis induced by different stimuli. Using a cytofluorimetric approach we have determined that serum withdrawal induces a disruption of t he transmembrane mitochondrial potential (Delta psi(m)) followed bq an incr ease of reactive oxygen species (ROS) and the subsequent DNA nuclear loss i n K562-Tat cells but not in the K562-pcDNA cell line. These pre-apoptotic e vents were associated with the cleavage of the caspase-3, while the express ion of Bcl-2, Bcl-X-L and Bas proteins was not affected by the presence of Tat, Regardless of the steady state of the Bar protein, we found that in bo th K562 and K562-Tat cells, this protein is located in the nucleus, but aft er serum withdrawal its localization was mainly in the cytoplasm, The activ ity of caspase-3 detected in K562-Tat cells after serum withdrawal parallel ed with the mitochondria permeability transition. Nevertheless, in Jhan-Tat cells the inhibition of this caspase with the specific inhibitor, z-DEVD-c mk, did not affect the disruption of the mitochondria potential induced by serum withdrawal. Interestingly, ae found that HIV-Tat protein accumulates at the mitochondria in the K562-Tat cells cultured under low serum conditio ns, and this mitochondrial localization correlated with the Delta psi(m) di sruption detected in these cells. In addition, HIV-Tat protein synergies wi th protoporphyrin IX (PPIX), a ligand of the mitochondrial benzodiazepine r eceptor, in the induction of apoptosis in both Jhan and K562 cells. Thus, H IV-1 Tat protein may induce apoptosis by a mechanism that involves mitochon drial PT and may contribute to the lymphocyte depletion seen in AIDS patien ts.