Redox status of thioredoxin-1 (TRX1) determines the sensitivity of human liver carcinoma cells (HepG2) to arsenic trioxide-induced cell death

Abstract

Intracellular redox homeostasis plays a critical role in determining tumor cells' sensitivity to drug-induced apoptosis. Here we investigated the role of thioredoxin-1 (TRX1), a key component of redox regulation, in arsenic trioxide (As 2 O 3 )-induced apoptosis. Over-expression of wild-type TRX1 in HepG 2 cells led to the inhibition of As 2 O 3 -induced cytochrome c (cyto c) release, caspase activation and apoptosis, and down-regulation of TRX1 expression by RNAi sensitized HepG 2 cells to As 2 O 3 -induced apoptosis. Interestingly, mutation of the active site of TRX1 from Cys 32/35 to Ser 32/35 converted this molecule from an apoptotic protector to an apoptotic promoter. In an effort to understand the mechanisms of this conversion, we used isolated mitochondria from mouse liver and found that recombinant wild-type TRX1 could protect mitochondria from the apoptotic changes. In contrast, the mutant form of TRX1 alone elicited mitochondria-related apoptotic changes, including the mitochondrial permeability transition pore (mPTP) opening, loss of mitochondrial membrane potential, and cyto c release from mitochondria. These apoptotic effects were inhibited by cyclosporine A (CsA), indicating that mutant TRX1 targeted to mPTP. Alteration of TRX1 from its reduced form to oxidized form in vivo by 2,4-dinitrochlorobenzene (DNCB), a specific inhibitor of TRX reductase, also sensitized HepG 2 cells to As 2 O 3 -induced apoptosis. These data suggest that TRX1 plays a central role in regulating apoptosis by blocking cyto c release, and inactivation of TRX1 by either mutation or oxidization of the active site cysteines may sensitize tumor cells to As 2 O 3 -induced apoptosis.

Arsenic trioxide-induced cytotoxicity in small cell lung cancer via altered redox homeostasis and mitochondrial integrity

“…In H841 cell line model, ATO downregulated both reduced and oxidative form of Trx1 without affecting redox status. This is discrepant from previous report, which indicated that ATO could inhibit thioredoxin reductase and consequently decrease the reduced form of Trx1 (68). Although the activity or expression of thioredoxin reductase has not been measured, our findings suggest that ATO targets the total Trx1 rather than just the reduced form in H841 cells.…”

“…Thioredoxin system was reported to be an important target of ATO in some cancers (26,68). In H841 cell line model, ATO downregulated both reduced and oxidative form of Trx1 without affecting redox status.…”

Low 8-oxo-7,8-dihydro-2′-deoxyguanosine levels and influence of genetic background in an Andean population exposed to high levels of arsenic

“…TXN is reduced by thioredoxin reductases 1 and 2 (TXNRD1, TXNRD2), and oxidized to TXNS 2 by peroxiredoxin 2 (via reduction of H 2 O 2 ). TXN are not only an antioxidant but also could influence arsenic related effects by its role in arsenic metabolism and apoptosis [28,29]. GSH is also a substrate in conjugation reactions to a number of different xenobiotics, thereby promoting their elimination.…”

Different Pathways Are Involved in Arsenic-Trioxide-Induced Cell Proliferation and Growth Inhibition in Human Keratinocytes

“…Cellular events of arsenic-induced apoptosis have been associated with the redox status of thioredoxin-1 and cytochrome c, which facilitate mitochondrial permeability [7,8] . In addition, the cell cycle and its regulation play an important role in arsenic-induced apoptosis.…”