TAT-EXPRESSING JURKAT CELLS SHOW AN INCREASED RESISTANCE TO DIFFERENTAPOPTOTIC STIMULI, INCLUDING ACUTE HUMAN IMMUNODEFICIENCY VIRUS-TYPE I (HIV-1) INFECTION

Human CD4(+) T lymphoblastoid Jurkat cells were stably transfected wit h two different plasmid vectors containing the cDNA of human immunodef iciency virus-type 1 (HIV-1) tat gene under the control of either the promoter of simian virus 40 (pRPneo/tat) or the long terminal repeat r egion of SL3 murine leukaemia virus (pRPneo/SL3/tat). Both pRPneo/tat and pRPneo/SL3/tat Jurkat cell lines showed a constant and high produc tion of bioactive Tat in transient co-transfection assays with an HIV- 1 long terminal repeat (LTR)-chloramphenicol acetyltransferase (CAT) r eporter plasmid. Tat-positive and mock-transfected Jurkat cells were c ultured with various cytotoxic agents, which have been associated to t he progressive loss of CD4 T-lymphocytes characteristic of HIV-1 disea se. In the presence of recombinant tumour necrosis factor-alpha (TNF-a lpha), anti-fas antibody, Leu3a anti-CD4 antibody, the percentage of a poptosis, evaluated in a 24-72 h short-term assay, was lower (P < 0.05 ) in tat-positive Jurkat cells than in mock-transfected controls. The low susceptibility to the cytotoxic activity of TNF-alpha and anti-fas antibody of tat-transfected cells was confirmed by counting viable ce lls up to 15 d of culture. Also, recombinant Tat protein was able to p revent the increase of apoptosis induced in mock-transfected Jurkat by TNF-alpha. Of note, tat-expressing cells showed a better survival wit h respect to mock-transfected control cells even when acutely infected with high doses (500 000 cpm of reverse transcriptase) of HIV-1 (stra in IIIB) or treated with heat-inactivated HIV-1. These data demonstrat e that the expression of the regulatory HIV-1 Tat protein is able to r escue Jurkat lymphoblastoid cells from apoptosis induced by a variety of cytotoxic agents. Since Tat protein expression is restricted to the initial phases of an active HIV-1 replication, the anti-apoptotic eff ect of Tat could have the physiological significance of selectively pr otecting HIV-1 producing cells from death, at least for the time neces sary to allow virus production and spreading.