Overproduction of human Mn-superoxide dismutase modulates tert-butylhydroperoxide(tbooH)-induced apoptosis in transformed CHO cells

Manganese superoxide dismutase (MnSOD) is a nuclear encoded mitochondrial matrix enzyme that scavenges superoxide radicals (O-2(-)). The sense and antisense human MnSOD and cDNA under the transcriptional control of a human beta-actin promoter were introduced into Chinese hamster ovary (CHO) cells by lipofectin transfection with recombinant plasmids containing a neomycin selectable marker. MnSOD activity increased about four-fold in cells transfected with sense MnSOD cDNA and decreased to similar to 30% in cells transfected with antisense MnSOD cDNA as compared with controls. Overexpression of the MnSOD gene did not alter CuZnSOD or glutathione peroxidase (GPx) activities. Upon exposure of the cells to tert-butylhydroperoxide (tbooH) (10(-4)M), which can induce programmed cell death (PCD) or apoptosis, GPx activity increased mainly in cells transfected with sense MnSOD cDNA. In conclusion, the induction of apoptosis by tbooH exposure was selectively delayed in these cells expressing sense MnSOD. CHO cells expressing antisense MnSOD gene were more sensitive to tbooH cytotoxity than control cells. These results suggest that raised GPx activity may confer protection against tbooH-induced apoptosis in human MnSOD transformed cells.