Date of this Version
Yu et al. Page 1-30
Thioredoxin (Trx) is an important redox regulator with cytosolic Trx1 and mitochondrial Trx2 isozymes. Trx has multi-physiological functions in cells and its bioavailability is negatively controlled through active site binding to a specific thioredoxin binding protein (TBP-2). This paper describes the delicate balance between TBP-2 and Trx, and the effect of overexpression of TBP-2 in the human lens epithelial cells. Cells overexpressing TBP-2 (TBP-2 OE) showed a 7- fold increase of TBP-2, and a nearly 40% suppression of Trx activity but no change in Trx expression. The TBP-2 OE cells grew slower and their population decreased to 30% by day 7. Cell cycle analysis showed that TBP-2 OE cells arrested at the G2-M stage, and that they displayed low expressions of the cell cycle elements P-cdc2 (Y15), cdc2, cdc25A and cdc25C. Furthermore, TBP-2 OE cells were more sensitive to oxidation. Under H2O2 (200 μM, 24 hrs) treatment, these cells lost 80% viability and became highly apoptotic. Brief oxidative stress (200 μM, 30 min) to TBP-2 OE cells disrupted the Trx anti-apoptotic function by dissociating the cytosolic and mitochondrial Trx-ASK binding complexes. The same H2O2-treated cells also showed activated ASK (P-ASK), Bax, lowered Bcl2, cytochrome c release, and elevated caspase 3/7 activities. We conclude from these studies that high cellular levels of TBP-2 can potentially suppress Trx bioavailability and increase oxidation sensitivity. Overexpression of TBP-2 also causes slow growth by mitotic arrest, and apoptosis by activating the ASK death pathway.
Biochemistry, Biophysics, and Structural Biology Commons, Cell and Developmental Biology Commons, Immunology and Infectious Disease Commons, Medical Sciences Commons, Veterinary Microbiology and Immunobiology Commons, Veterinary Pathology and Pathobiology Commons