title: Early superoxide dismutase-sensitive event promotes neoplastic transformation in mouse epidermal JB6 cells.
abstract: Evidence has been obtained that implicates the generation of reactive oxygen species as an early and critical event in the promotion of neoplastic transformation in mouse JB6 cells. The time courses for specific inhibition by CuZn-superoxide dismutase (CuZn-SOD) of the 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced promotion of neoplastic transformation in JB6 cells and for changes in antioxidant enzyme activities associated with TPA-exposure were examined. The antipromoting effect of CuZn-SOD was found to be critically dependent on the time of addition of CuZn-SOD relative to the start of a 14-day exposure of cells to TPA. Treatment of JB6 P+ Clone 22 and Clone 41 cells with CuZn-SOD for 18 h before, simultaneously with or up to 1 h after exposure to TPA, all inhibited promotion of transformation maximally. Delay of addition of CuZn-SOD by 2 h or more after the start of TPA treatment resulted in a marked decrease in the promotion inhibitory effect. CuZn-SOD added 24 or 48 h after TPA had no effect on promotion of transformation. Exposure of JB6 cells to 0.2- (superoxide anion radical) generated exogenously by the aerobic xanthine oxidase reaction resulted in promotion of neoplastic transformation that was prevented by concurrent addition of CuZn-SOD. Taken together these studies provide evidence that increased superoxide anion generation within the first 2 h following TPA exposure is an essential event in promotion of transformation in JB6 cells. Upon TPA exposure, JB6 Clone 41 cells exhibited time-specific activity changes in the cellular SOD, glutathione peroxidase (GSH-Px), and catalase. SOD and GSH-Px activities were reduced to 54% and 26% respectively of basal levels within 2 h of TPA treatment. GSH-Px activity recovered to basal levels within 4 h and CuZn-SOD within 48 h. Catalase activity was maximally reduced to 50% of basal within 1 h after TPA treatment and rebounded to greater than basal levels within 4 h. It is postulated that a c-kinase-dependent event induces rapid elevation of superoxide anion following TPA exposure and that this leads to reduced activity of antioxidant enzymes. Since antipromotion by exogenous CuZn-SOD is effective only during the first 2 h following TPA exposure, this suggests that the promotion-relevant 0.2- elevation is transient.
authors.affiliation: Laboratory of Viral Carcinogenesis, National Cancer Institute, Frederick Cancer Research Facility, MD 21701-1013.
authors.forename: Y
authors.initials: Y
authors.lastname: Nakamura
authors.forename: T D
authors.initials: TD
authors.lastname: Gindhart
authors.forename: D
authors.initials: D
authors.lastname: Winterstein
authors.forename: I
authors.initials: I
authors.lastname: Tomita
authors.forename: J L
authors.initials: JL
authors.lastname: Seed
authors.forename: N H
authors.initials: NH
authors.lastname: Colburn
mesh_terms: D000818:Animals; D002273:Carcinogens; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000187:drug effects / Q000201:enzymology*; D005979:Glutathione Peroxidase / Q000037:antagonists & inhibitors; D051379:Mice; D013482:Superoxide Dismutase / Q000037:antagonists & inhibitors*; D013481:Superoxides; D013755:Tetradecanoylphorbol Acetate
chemical_list: D002273:Carcinogens; D013481:Superoxides; D005979:Glutathione Peroxidase; D013482:Superoxide Dismutase; D013755:Tetradecanoylphorbol Acetate