Human immunodeficiency virus type 1 Tat protein impairs selenoglutathione peroxidase expression and activity by a mechanism independent of cellular selenium uptake: Consequences on cellular resistance to UV-A radiation

The expression of the HIV-1 Tat protein in HeLa cells resulted in a 2.5-fol d decrease in the activity of the antioxidant enzyme glutathione peroxidase (GPX), This decrease seemed not to be due to a disturbance in selenium (Se ) uptake, Indeed, the intracellular level of Se was similar in parental and tat-transfected cells. A Se enrichment of the medium did not lead to an id entical GPX activity in both cell lines, suggesting a disturbance in Se uti lization, Total intracellular Se-75 selenoproteins were analyzed. Several q uantitative differences were observed between parental and tat-transfected cells. Mainly, cytoplasmic glutathione peroxidase and a 15-kDa selenoprotei n were decreased in HeLa-tat cells, while phospholipid hydroperoxide glutat hione peroxidase and low-molecular-mass selenocompounds were increased. Thi oredoxin reductase activity and total levels of Se-75-labeled proteins were not different between the two cell types. The effect of Tat on GPX mRNA le vels was also analyzed. Northern blots revealed a threefold decrease in the GPX/glyceraldehyde phosphate dehydrogenase mRNA ratio in HeLa-tat versus w ild type cells. By deregulating the intracellular oxidant/antioxidant balan ce, the Tat protein amplified UV sensitivity. The LD50 for ultraviolet radi ation A was 90 J/cm(2) for HeLa cells and only 65 J/cm(2) for HeLa-tat cell s. The oxidative stress occurring in the Tat-expressing cells and demonstra ted by the diminished ratio of reduced glutathione/oxidized glutathione was not correlated with the intracellular metal content, Cellular iron and cop per levels were significantly decreased in HeLa-tat cells, All these distur bances, as well as the previously described decrease in Mn superoxide dismu tase activity, are part of the viral strategy to modify the redox potential of cells and may have important consequences for patients, (C) 2001 Academ ic Press.