title: High levels of thioredoxin reductase 1 modulate drug-specific cytotoxic efficacy.
abstract: The selenoprotein thioredoxin reductase 1 (TrxR1) is currently recognized as a plausible anticancer drug target. Here we analyzed the effects of TrxR1 targeting in the human A549 lung carcinoma cell line, having a very high basal TrxR1 expression. We determined the total cellular TrxR activity to be 271.4 +/- 39.5 nmol min(-1) per milligram of total protein, which by far exceeded the total thioredoxin activity (39.2 +/- 3.5 nmol min(-1) per milligram of total protein). Knocking down TrxR1 by approx 90% using siRNA gave only a slight effect on cell growth, irrespective of concurrent glutathione depletion (> or = 98% decrease), and no increase in cell death or distorted cell cycle phase distributions. This apparent lack of phenotype could probably be explained by Trx functions being maintained by the remaining TrxR1 activity. TrxR1 knockdown nonetheless yielded drug-specific modulation of cytotoxic efficacy in response to various chemotherapeutic agents. No changes in response upon exposure to auranofin or juglone were seen after TrxR1 knockdown, whereas sensitivity to 1-chloro-2,4-dinitrobenzene or menadione became markedly increased. In contrast, a virtually complete resistance to cisplatin using concentrations up to 20 microM appeared upon TrxR1 knockdown. The results suggest that high overexpression of TrxR has an impact not necessarily linked to Trx function that nonetheless modulates drug-specific cytotoxic responses.
authors.affiliation: Division of Biochemistry, Department of Medical Biochemistry and Biophysics, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
authors.forename: Sofi E
authors.initials: SE
authors.lastname: Eriksson
authors.forename: Stefanie
authors.initials: S
authors.lastname: Prast-Nielsen
authors.forename: Emilie
authors.initials: E
authors.lastname: Flaberg
authors.forename: Laszlo
authors.initials: L
authors.lastname: Szekely
authors.forename: Elias S J
authors.initials: ES
authors.lastname: Arnér
mesh_terms: D000230:Adenocarcinoma / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D001310:Auranofin / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D048708:Cell Growth Processes / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D002945:Cisplatin / Q000494:pharmacology; D004137:Dinitrochlorobenzene / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm / Q000187:drug effects / Q000235:genetics; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy* / Q000201:enzymology / Q000235:genetics / Q000473:pathology; D009285:Naphthoquinones / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D054481:Thioredoxin Reductase 1 / Q000235:genetics / Q000378:metabolism*; D024483:Vitamin K 3 / Q000494:pharmacology
chemical_list: D004137:Dinitrochlorobenzene; D009285:Naphthoquinones; D034741:RNA, Small Interfering; D001310:Auranofin; D024483:Vitamin K 3; D054481:Thioredoxin Reductase 1; D002945:Cisplatin; C005134:juglone