Different prooxidant levels stimulate growth, trigger apoptosis, or produce necrosis of insulin-secreting RINm5F cells. The role of intracellular polyamines.

Increasing concentrations (1-100 microM) of the redox cycling quinone, 2,3-dimethoxy-1,4-naphthoquinone (DMNQ), stimulated growth, triggered apoptosis, or caused necrosis of pancreatic RINm5F cells, depending on the dose and duration of the exposure. Following the exposure of RINm5F cells to 10 microM DMNQ, ornithine decarboxylase activity and polyamine biosynthesis increased. This was accompanied by enhanced cell proliferation. Conversely, exposure to 30 microM DMNQ for 3 h resulted in the inhibition of ornithine decarboxylase, intracellular polyamine depletion, and apoptotic cell killing. Pretreatment of the cultures with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate, restored polyamine levels and prevented apoptosis. Exposure to the same DMNQ concentration for only 1 h, with subsequent re-incubation in growth medium, neither caused polyamine depletion nor resulted in apoptosis. Finally, exposure to an even higher DMNQ concentration (100 microM) for either 1 or 3 h caused rapid intracellular Ca2+ overload, ATP, NAD+, and glutathione depletion, and extensive DNA single strand breakage, which resulted in necrotic cell death. Our results show that a disturbance of polyamine biosynthesis occurred prior to cell growth or apoptosis elicited by oxidative stress. In addition, we show that effects as opposite as cell proliferation and deletion, by either apoptosis or necrosis, can be induced, in the same system, by varying the exposure to a prooxidant.