Effect of glutathione depletion on caspase-3 independent apoptosis pathway induced by curcumin in Jurkat cells

Curcumin, a yellow pigment from Curcuma longa, exhibits anti-inflammatory, antitumor, and antioxidative properties. Although its precise mode of action has not been elucidated so far, numerous studies have shown that curcumin may induce apoptosis in normal and cancer cells. Previously, we showed that in Jurkat cells curcumin induced nontypical apoptosis-like pathway, which was independent of mitochondria and caspase-3. Now we show that the inhibition of caspase-3 by curcumin, which is accompanied by attenuation of internucleosomal DNA fragmentation, may be due to elevation of glutathione, which increased in curcumin-treated cells to 130% of control. We have demonstrated that glutathione depletion does not itself induce apoptosis in Jurkat cells; though, it can release cytochrome c from mitochondria and caspase-3 from inhibition by curcumin, as shown by Western blot. The level of Bcl-2 protein was not affected by glutathione depletion even upon curcumin treatment. Altogether, our results show that in Jurkat cells curcumin prevents glutathione decrease, thus protecting cells against caspase-3 activation and oligonucleosomal DNA fragmentation. On the other hand, it induces nonclassical apoptosis via a still-unrecognized mechanism, which leads to chromatin degradation and high-molecular-weight DNA fragmentation.