TAT PROTEIN OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 REPRESSES EXPRESSION OF MANGANESE SUPEROXIDE-DISMUTASE IN HELA-CELLS

Using a HeLa cell line stably transfected with the tat gene from human immunodeficiency virus type 1, we have found that the expression of t he regulatory Tat protein suppresses the expression of cellular Mn-con taining superoxide dismutase (Mn-SOD). This enzyme is one of the cell' s primary defenses against oxygen-derived free radicals and is vital f or maintaining a healthy balance between oxidants and antioxidants. Th e parental HeLa cells expressed nearly equivalent amounts of Cu,Zn- an d Mn-SOD isozymes. Those cells expressing the Tat protein, however, co ntained 52% less Mn-SOD activity than parental cells, whereas that of the Cu,Zn enzyme was essentially unchanged. The steady-state levels of Mn-SOD-specific RNAs were also lower in the HeLa-tat cell line than i n the parental line. No difference was seen in the steady-state levels of Cu,Zn-SOD-specific RNAs. In addition to the decreased Mn-SOD activ ity, HeLa-tat cells showed evidence of increased oxidative stress. Car bonyl proteins were markedly higher, and total cellular sulfhydryl con tent decreased in cell extracts at a faster rate, probably reflecting ongoing lipid peroxidation. HeLa and HeLa-tat extracts were incubated with radiolabeled Mn-SOD transcripts, and the reaction products were s ubjected to UV crosslinking, digestion with ribonuclease A, and electr ophoretic analysis. The results suggest a direct interaction between T at protein and Mn-SOD gene transcripts.