We have reported that a cytoplasmic protein Cu, Zn-SOD,undergoes glycation, fragmentation, and inactivation under diabetic conditions and aging. We have examined effects of glycated Cu, Zn-SOD on DNA damage. We found that cloned DNA was fragmented by incubation with glycated Cu, Zn-SOD.This fragmentation was also observed in nulcear DNA isolated from cells. Metal ion chelators and hydorxyl radical scavengers inhibited the DNA fragmentation, suggesting the involvement of the Fenton reaction mediated by glycated Cu, Zn-SOD and released Cu^<2+> in this reaction.
We also established human Cu, Zn-SOD expression system using baculovirus and insect cells, and produced three mutant enzymes (Gly41Asp, His43Arg, Gly85Arg) related to amyotrophic lateral sclerosis (ALS) as well as wild-type enzyme and purified them. Gly85Arg mutant exhibited similar activity to the wild-type enzyme, but activities of Gly41Asp and His43Arg were decreased to nearly a half of it. Structural unstability and inactivation of mutant enzymes by hydrogen peroxide may be a cause of the decreased activities, suggesting that ALS may be induced by this decreased activity in mutant enzymes.
A mitochondrial enzyme Mn-SOD is induced by TNF and IL-1 and scavenges reactive oxygen species produced by treatment with cytokines. Our results show that not only Mn-SOD bur also some antioxidative enzymes including Cu, Zn-SOD,catalase, glutathione-S-transferase, are suppressed by treatment with TGF-beta. These results suggest that TGB-beta-induced apoptosis is triggered by the reduction of antioxidative enyzme activities.