title: Overexpression of thioredoxin-binding protein 2 increases oxidation sensitivity and apoptosis in human lens epithelial cells.
abstract: Thioredoxin (Trx) is an important redox regulator with cytosolic Trx1 and mitochondrial Trx2 isozymes. Trx has multiple 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 human lens epithelial cells. Cells overexpressing TBP-2 (TBP-2 OE) showed a sevenfold increase in 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 expression of the cell cycle elements P-cdc2(Y15), cdc2, cdc25A, and cdc25C. Furthermore, TBP-2 OE cells were more sensitive to oxidation. Under H2O2 (200μM, 24h) treatment, these cells lost 80% viability and became highly apoptotic. Brief oxidative stress (200μM, 30min) to TBP-2 OE cells disrupted the Trx antiapoptotic function by dissociating the cytosolic and mitochondrial Trx-ASK binding complexes. The same H2O2-treated cells also showed activated ASK (P-ASK), increased Bax, lowered Bcl-2, cytochrome c release, and elevated caspase 3/7 activity. 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.
authors.affiliation: Eye Center of the Second Affiliated Hospital, Medical College of Zhejiang University, Hangzhou, China.
authors.forename: Yibo
authors.initials: Y
authors.lastname: Yu
authors.forename: Kuiyi
authors.initials: K
authors.lastname: Xing
authors.forename: Rilwan
authors.initials: R
authors.lastname: Badamas
authors.forename: Charles A
authors.initials: CA
authors.lastname: Kuszynski
authors.forename: Hongli
authors.initials: H
authors.lastname: Wu
authors.forename: Marjorie F
authors.initials: MF
authors.lastname: Lou
mesh_terms: D017209:Apoptosis; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D020169:Caspases / Q000378:metabolism; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002460:Cell Line; D002465:Cell Movement; D049109:Cell Proliferation; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007908:Lens, Crystalline / Q000378:metabolism*; D059566:M Phase Cell Cycle Checkpoints; D008928:Mitochondria / Q000378:metabolism; D016877:Oxidants / Q000494:pharmacology; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D034622:RNA Interference; D013879:Thioredoxins / Q000378:metabolism*; D051028:bcl-2-Associated X Protein / Q000378:metabolism
chemical_list: C494826:BAX protein, human; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C485678:DBF4 protein, human; D016877:Oxidants; D019253:Proto-Oncogene Proteins c-bcl-2; C486715:TXNIP protein, human; D051028:bcl-2-Associated X Protein; D013879:Thioredoxins; D045304:Cytochromes c; D006861:Hydrogen Peroxide; D020169:Caspases