The human immunodeficiency virus-1 Tat protein increases cell proliferation, alters sensitivity to zinc chelator-induced apoptosis, and changes Sp1 DNA binding in HeLa cells

The HIV-1 transcriptional regulatory protein Tat is a pleiotropic factor th at represses expression of the human Mn-superoxide dismutase. Tat increases oxidative stress, as shown by decreased glutathione and NADPH levels. Thes e redox changes enhance proliferation and apoptosis and alter the activity of zinc thiolate-containing proteins such as Spl. Cells stably producing th e Tat protein have an increased proliferation rate, which can be inhibited by pretreatment with the antioxidant mercaptopropionylglycine. Conversely, cells exposed to low concentrations of the oxidant paraquat are stimulated to divide. Intermediate and higher paraquat levels result in increased apop tosis or necrosis, respectively, suggesting that the physiological end poin t depends on the dose of oxidant used. Furthermore, treatment with the zinc chelator (N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamin (TPEN) sensiti zes HeLa-tat cells to apoptosis. In these cells, binding of the zinc-contai ning factor Spl to its DNA sequence is higher than in parental cells. Norma l DNA binding is partially restored by pretreatment with a compound that mi mics superoxide dismutase activity. Interestingly, Sp1-DNA interactions dec rease more rapidly in the HeLa-tat cells after TPEN treatment. HeLa cell ex tracts incubated in the presence of purified Tat protein have increased Spl binding, consistent with the results observed in Tat-transfected cells. Th ese results suggest that the Tat protein, via direct or indirect mechanisms , increases proliferation, sensitizes cells to apoptosis, and changes the c onformation of Spl, affecting its ability to bind to its cognate DNA sequen ce and to retain its zinc. (C) 1999 Academic Press.