EVIDENCE FOR SECRETION OF CYTOSOLIC CUZN SUPEROXIDE-DISMUTASE BY HEP G2 CELLS AND HUMAN FIBROBLASTS

The role so far ascribed to intracellular CuZn superoxide dismutase is that of an intracellular scavenger of oxygen radicals. However, other functions of cytosolic CuZn superoxide dismutase have been hypothesiz ed. For example, CuZn superoxide dismutase incubated with rat hepatocy te cells in culture inhibits 3-hydroxy-3methylglutaryl CoA reductase, thereby reducing cholesterol synthesis. We recently demonstrated the p resence of surface membrane receptors for CuZn superoxide dismutase, s uggesting possible autocrine or paracrine activities. The aim of the p resent study was to investigate whether cytosolic CuZn superoxide dism utase can be secreted by human hepatocarcinoma and fibroblast cells li nes. Proteins in human hepatocellular carcinoma (Hep G2) cells and hum an fibroblasts were biosynthetically labelled with [S-35]-cysteine; th en cell lysates and media were immunoprecipitated with rabbit polyclon al anti-human CuZn superoxide dismutase antibodies and separated by 12 % polyacrylamide gel electrophoresis. Both Hep G2 cells and human fibr oblasts produce and secrete CuZn superoxide dismutase which was detect able in cells and medium as a single protein band with the same electr ophoretic mobility as human erythrocyte CuZn superoxide dismutase. The se data suggest that CuZn superoxide dismutase, an enzyme thus far con sidered to be located exclusively intracellularly is secreted by at le ast two cell lines. This is consistent with autocrine or paracrine rol es for CuZn superoxide dismutase. (C) 1996 Elsevier Science Ltd