INDUCTION OF APOPTOSIS AT DIFFERENT OXYGEN-TENSIONS - EVIDENCE THAT OXYGEN RADICALS DO NOT MEDIATE APOPTOTIC SIGNALING

Apoptosis has been hypothesized to be mediated through the induction o f free radicals via oxidate pathways. Furthermore, it has been propose d that Bcl-2 acts to inhibit apoptosis induced by a wide variety of st imuli by preventing the production of oxygen-derived free radicals. Si nce the generation of oxygen free radicals is dependent upon oxygen co ncentration, this hypothesis would lead to the prediction that the con centration of oxygen should affect the induction of apoptosis. In orde r to test this prediciton, we have examined the induction of apoptosis in T-lymphoma cell lines S49.1 and WEHI 7.1 by dexamethasone and by w ithdrawal of serum from myc-immortalized fiblasts in 95% oxygen, atmos pheric oxygen (20%), and hypoxic conditions of up to 125-fold less oxg en. Culture in 95% oxygen induced apoptosis in all cells tested, confi rming that oxidative damage can lead to apoptosis. However, for one ce ll line, WEHI 7.1, hypoxia also induced apoptosis. Furthermore, for th e other cell lines tested, induction of apoptosis by either dexamethas one or by serum withdrawal was not affected by hypoxia. These results are not consistent with the hypothesis that apoptosis is mediated via oxygen-generate free radical formation.