INHIBITION OF CELL-GROWTH IN NIH 3T3 FIBROBLASTS BY OVEREXPRESSION OFMANGANESE SUPEROXIDE-DISMUTASE - MECHANISTIC STUDIES/

NIH/3T3 mouse fibroblasts were transfected with the cDNA for manganese superoxide dismutase (MnSOD), and two clones overexpressing MnSOD act ivity were subsequently characterized by comparison with parental and control plasmid-transfected cells. One clone with a 1.8-fold increase in MnSOD activity had a 1.5-fold increase in glutathione peroxidase (G PX) activity (increased GPX-adapted clone), while a second clone with a 3-fold increase in MnSOD activity had a 2-fold decrease in copper, z inc superoxide dismutase (CuZnSOD] activity (decreased CuZnSOD-adapted clone). Increased reactive oxygen species (ROS) levels compared with parental or control plasmid-transfected cells were observed in nonsync hronous cells in the increased GPX-adapted clone, but not in the decre ased CuZnSOD-adapted clone. The two MnSOD-overexpressing clones showed different sensitivities to agents that generate oxidative stress. Flo w cytometry analysis of the cell cycle showed altered cell cycle progr ession in both MnSOD-overexpressing clones. During logarithmic growth, both MnSOD-overexpressing clones showed increased mitochondrial membr ane potential compared with parental and control plasmid-transfected c ells. Both MnSOD-overexpressing clones showed a decrease in mitochondr ial mass at the postconfluent phase of growth, suggesting that mitocho ndrial mass may be regulated by MnSOD and/or ROS levels. Our results i ndicate that adaptation of fibroblasts to overexpression of MnSOD can involve more than one mechanism, with the resultant cell phenotype dep endent on the adaptation mechanism utilized by the cell. (C) 1998 Wile y-iiss, Inc.