THE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 TAT PROTEIN UP-REGULATES BCL-2 GENE-EXPRESSION IN JURKAT T-CELL LINES AND PRIMARY PERIPHERAL-BLOOD MONONUCLEAR-CELLS

The regulatory Tat protein of human immunodeficiency virus type-1 (HIV -1) exerts a pleyotropic activity on the survival and proliferation of different cell types in culture, In this report, we investigated the effect of either endogenous or exogenous Tat on Bcl-2 proto-oncogene e xpression and cell survival in Jurkat T-cell lines and primary periphe ral blood mononuclear cells, Stable and transient transfections of Jur kat cells with the cDNA of tat and a plasmid containing Bcl-2 promoter in front of CAT (Bcl-2 Pr/CAT) stimulated CAT activity and showed an increase of Bcl-2 mRNA and protein expression, This effect was specifi cally related to tat, because Jurkat cells transfected with the cDNA o f tat in antisense orientation, tat carrying a mutation in the amino a cid cys(22)-gly(22), or the control vector alone (pRPneo-SL3) did not show any significant difference in Bcl-2 promoter activity with respec t to parental Jurkat cells. We also observed a specific correlation be tween tat-induced Bcl-2 gene expression and inhibition of apoptosis in duced by serum withdrawal, Our results suggest that the structural int egrity of the activation domain of Tat was required for the promotion of the Bcl-2 promoter and Jurkat cell survival, because a single mutat ion in the aminoacid cys(22) was sufficient to completely block the up regulation of Bcl-2 and inhibition of apoptosis. Moreover, picomolar c oncentrations of native or recombinant Tat were able to upregulate Bcl -2 expression both in Jurkat and primary peripheral blood mononuclear cells, suggesting that extracellular Tat, actively released by infecte d cells, may also play a significant role in suppressing apoptosis, An aberrant cell survival of lymphoid cells consequent to the upregulati on of Bcl-2 may represent an additional pathogenetic mechanism that co uld help explain both the dysregulated immune response and the frequen t occurrence of hyperplastic/neoplastic disorders in HIV-1-seropositiv e individuals. (C) by The American Society of Hematology.