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.

Association of gp91phox homolog Nox1 with anchorage-independent growth and MAP kinase-activation of transformed human keratinocytes

“…This process was reversed by coexpression of catalase, indicating that hydrogen peroxide is a mediator for tumorigenic conversion (Arnold et al, 2001). These data are consistent with earlier studies implicating the role of ROS in the transformation of rodent fibroblasts (Irani et al, 1997;Schimmel and Bauer, 2002), and keratinocytes (Nakamura et al, 1988).…”

Free Radicals in the Physiological Control of Cell Function

“…ROS are potential carcinogens because they facilitate mutagenesis, tumor promotion, and progression (155, 223,269,410,483). The growth-promoting effects of ROS are related to redox-responsive signaling cascades, some of which have been discussed in section V. A placebocontrolled clinical study of patients with previous adenomatous colonic polyps, i.e., a group with an increased risk for colon cancer and increased proliferative index of colonic crypts, revealed a significant decrease in the proliferative index after treatment with N-acetylcysteine (170).…”

The role of the cellular antioxidant defense in oxidant carcinogenesis.

“…In general, oxidants are cytostatic and cytotoxic, although under exceptional circumstances they can promote growth and facilitate the clonal expansion of initiated cells in carcinogenesis (22,31,46,47). Membrane lipid peroxidation, which causes disruption of membrane integrity, increased permeability to ions, and surface bleb formation as well as chromosomal breakage are major mechanisms leading ultimately to growth inhibition and cell death (3).…”