Opposing effects of polysulfides and thioredoxin on apoptosis through caspase persulfidation

Abstract

Hydrogen sulfide has been implicated in a large number of physiological processes including cell survival and death, encouraging research into its mechanisms of action and therapeutic potential. Results from recent studies suggest that the cellular effects of hydrogen sulfide are mediated in part by sulfane sulfur species, including persulfides and polysulfides. In the present study, we investigated the apoptosis-modulating effects of polysulfides, especially on the caspase cascade, which mediates the intrinsic apoptotic pathway. Biochemical analyses revealed that organic or synthetic polysulfides strongly and rapidly inhibit the enzymatic activity of caspase-3, a major effector protease in apoptosis. We attributed the caspase-3 inhibition to persulfidation of its catalytic cysteine. In apoptotically stimulated HeLa cells, short-term exposure to polysulfides triggered the persulfidation and deactivation of cleaved caspase-3. These effects were antagonized by the thioredoxin/thioredoxin reductase system (Trx/TrxR). Trx/TrxR restored the activity of polysulfide-inactivated caspase-3 in vitro, and TrxR inhibition potentiated polysulfide-mediated suppression of caspase-3 activity in situ. We further found that under conditions of low TrxR activity, early cell exposure to polysulfides leads to enhanced persulfidation of initiator caspase-9 and decreases apoptosis. Notably, we show that the proenzymes procaspase-3 and -9 are basally persulfidated in resting (unstimulated) cells and become depersulfidated during their processing and activation. Inhibition of TrxR attenuated the depersulfidation and activation of caspase-9. Taken together, our results reveal that polysulfides target the caspase-9/3 cascade and thereby suppress cancer cell apoptosis, and highlight the role of Trx/TrxR-mediated depersulfidation in enabling caspase activation.

Oxidants, Antioxidants and Thiol Redox Switches in the Control of Regulated Cell Death Pathways

“…The Trx/TrxR system mediates caspase depersulfidation, a process required for protease activation. Of particular interest, the new findings show that procaspase-3 and -9 are constitutively persulfidated in resting HeLa cells and undergo Trx/TrxR-dependent depersulfidation during their processing and activation in response to an apoptotic stimulus [63]. These observations support the idea that persulfidation serves as a safeguard mechanism in apoptosis, whereby Trx-catalyzed persulfide removal is necessary to enable caspase activation and propagation of the apoptotic signal.…”

“…New evidence shows that thiol persulfidation regulates the activity of caspase-3 and -9 [63]. Specifically, exposure of HeLa cancer cells to polysulfides triggers the persulfidation and deactivation of cleaved caspase-3 and -9.…”

Dimethyl Trisulfide Diminishes Traumatic Neuropathic Pain Acting on TRPA1 Receptors in Mice

“…However, polysulfides react potentially with any thiol groups of proteins and change the protein function. A multitude of proteins have been reported to be modulated by polysulfides, including actin, glyceraldehyde-3-phosphate dehydrogenase (GAPDH), nuclear factor κB (NF-κB), ATP-sensitive potassium channel (KATP), protein tyrosine phosphatase 1B (PTP1B), Kelch-like ECH-associated protein-1 (Keap1) and phosphatase and tensin homolog (PTEN) [ 39 , 40 ]. Divergent actions of DMTS on numerous proteins at different levels of the organism might evoke opposing effects in macrophages.…”

Interactions of zinc- and redox-signaling pathways

“…One site involves the catalytic site of caspase 9, in particular the catalytic histidine (His 237) and cysteine (Cys 287) residues, whereas the other site comprises a cysteine residue (Cys 272) that is located away from the catalytic site [ 229 ]. Aside of their inhibition by zinc, caspases can also be regulated by oxidative modifications, such as glutathionylation [ 230 ], nitrosylation [ 231 ] or persulfidation [ 232 ]. Caspase 3 was shown to be inhibited by micromolar concentrations of GSSG (IC 50 : 75 μM), due to glutathionylation of the cysteine residues Cys 45 on p12 subunit and Cys 135 on p17 subunit (active site), whereby the inhibition is reversible by the addition of reducing agents, such as GSH [ 230 ].…”