In vivo redox state of human thioredoxin and redox shift by the histone deacetylase inhibitor suberoylanilide hydroxamic acid (SAHA).

The cytosolic thioredoxin (Trx1) system is essential for maintaining a reduced intracellular environment, via reduced Trx1 acting as a general protein disulfide reductase. Trx1 is implicated in cell signaling such as proliferation, DNA synthesis, enzyme activation, cell cycle regulation, transcription, gene activation, and prevention of apoptosis. Human Trx1 contains the active-site cysteines, Cys32 and Cys35, and three additional structural cysteines, Cys62, Cys69, and Cys73, that regulate Trx1 structure and activity via a second disulfide formation, S-glutathionylation or S-nitrosylation. The present study uses an electrophoretic redox Western blot method to analyze the oxidation state of Trx1 in vivo separating the protein-changed isoform following alkylation with iodoacetic acid in 8M urea. Treatment with the histone deacetylase inhibitor SAHA increased Trx1 inhibitor thioredoxin interacting protein (Txnip) levels, decreased Trx1 activity, and switched the Trx1 oxidation state toward a more oxidized one, as a result of complex formation with Trx1, and increased reactive oxygen species (ROS). SAHA is currently in clinical trials for cancer treatment, and one possible mechanism for its anticancer effect is via effects on the Trx1 system. Determining the exact oxidation state of human cytosolic Trx1 may be useful in developing and evaluating cancer drugs and antioxidant agents.