Changes in CuZn-superoxide dismutase during induced differentiation of murine erythroleukemia cells

Superoxide dismutase (SOD) activity in murine erythroleukemia cells (MELC) was determined during differentiation induced by hexamethylene bisacetamide. SOD levels in hexamethylene bisacetamide-treated MELC were about twice as high as those of controls. Dose response and kinetic experiments have shown that SOD activity variations are closely related to the amount of inducer and the duration of treatment in culture. Moreover, phorbol 12-myristate 13-acetate, which inhibits hexamethylene bisacetamide-induced MELC maturation, was also effective in reducing the extent of the SOD increase. SOD changes mainly involved the CuZn form of the enzyme, having a molecular weight of about 32,000 and a striking sensitivity to cyanide inhibition. In addition, the isoelectrophoretic analysis of CuZn-SOD from both treated and untreated cells yielded an identical pattern. This suggests that quantitative rather than qualitative enzyme changes occurred during MELC terminal division. SOD levels are directly related to the degree of differentiation and particularly to the amount of cytosolic hemoglobin, whose synthesis in committed cells is paralleled by a rise in enzyme activity. The SOD increase represents a distinctive marker of erythroleukemia maturation and might tentatively be interpreted as a cellular response to oxidative stress from hemoglobin autoxidation.