Glutathiolation regulates tumor necrosis factor-alpha-induced caspase-3 cleavage and apoptosis: key role for glutaredoxin in the death pathway.

Caspase-3 cleavage and activation are known to play central roles in apoptosis. However, the mechanisms that regulate caspase-3 cleavage remain elusive. Glutaredoxin (Grx) is a ubiquitous redox molecule that is unique in its ability to regulate S-glutathiolation (glutathiolation) of proteins. Here we show the essential role of Grx in caspase-3 cleavage via regulation of caspase-3 glutathiolation. Grx activity was significantly upregulated by tumor necrosis factor-alpha in endothelial cells. Small interference RNA knock down of Grx significantly inhibited tumor necrosis factor-alpha-induced endothelial cell death because of attenuated caspase-3 cleavage concomitant with increased caspase-3 glutathiolation. Enhanced caspase-3 cleavage by wild-type Grx overexpression was reversed by catalytically inactive Grx (C22S), demonstrating a requirement for thioltransferase activity. Cysteine-to-serine mutations (C163S, C184S, and C220S) of caspase-3 that were predicted to prevent glutathiolation showed increased cleavage compared with wild-type caspase-3. This inverse correlation between caspase-3 glutathiolation and cleavage was further confirmed by the observation that in vitro glutathiolation of caspase-3 inhibited its cleavage with recombinant caspase-8. Furthermore, Grx association with caspase-3 was decreased by tumor necrosis factor-alpha. These findings demonstrate a novel mechanism of caspase-3 regulation by Grx in tumor necrosis factor-alpha-induced apoptosis.