title: Overexpression of glutathione S-transferase II and multidrug resistance transport proteins is associated with acquired tolerance to inorganic arsenic.
abstract: Recent work shows that long-term exposure to low levels of arsenite induces malignant transformation in a rat liver epithelial cell line. Importantly, these chronic arsenic-exposed (CAsE) cells also develop self-tolerance to acute arsenic exposure. Tolerance is accompanied by reduced cellular arsenic accumulation, suggesting a mechanistic basis for reduced arsenic sensitivity. The present study examined the role of xenobiotic export pumps in acquired arsenic tolerance. Microarray analysis of CAsE cells showed increased expression of the genes encoding for glutathione S-transferase Pi (GST-Pi), multidrug resistance-associated protein genes (MRP1/MRP2, which encode for the efflux transporter Mrp1/Mrp2) and the multidrug resistance gene (MDR1, which encodes for the efflux transporter P-glycoprotein). These findings were confirmed at the transcription level by reverse transcription-polymerase chain reaction and at the translation level by Western-blot analysis. Acquired arsenic tolerance was abolished when cells were exposed to ethacrynic acid (an inhibitor of GST-Pi), buthionine sulfoximine (a glutathione synthesis inhibitor), MK571 (a specific inhibitor for Mrps), and PSC833 (a specific inhibitor for P-glycoprotein) in dose-dependent fashions. MK571, PSC833, and buthionine sulfoximine markedly increased cellular arsenic accumulation. Consistent with a role for multidrug resistance efflux pumps in arsenic resistance, CAsE cells were found to be cross-resistant to cytotoxicity of several anticancer drugs, such as vinblastine, doxorubicin, actinomycin-D, and cisplatin, that are also substrates for Mrps and P-glycoprotein. Thus, acquired tolerance to arsenic is associated with increased expression GST-Pi, Mrp1/Mrp2 and P-glycoprotein, which function together to reduce cellular arsenic accumulation.
authors.affiliation: Laboratory of Comparative Carcinogenesis, National Cancer Institute at National Institute for Environmental Health Sciences, Research Triangle Park, North Carolina, USA.
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: H
authors.initials: H
authors.lastname: Chen
authors.forename: D S
authors.initials: DS
authors.lastname: Miller
authors.forename: J E
authors.initials: JE
authors.lastname: Saavedra
authors.forename: L K
authors.initials: LK
authors.lastname: Keefer
authors.forename: D R
authors.initials: DR
authors.lastname: Johnson
authors.forename: C D
authors.initials: CD
authors.lastname: Klaassen
authors.forename: M P
authors.initials: MP
authors.lastname: Waalkes
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000378:metabolism; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000818:Animals; D001151:Arsenic / Q000633:toxicity*; D020261:Arsenic Poisoning; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004351:Drug Resistance; D018432:Drug Resistance, Multiple / Q000502:physiology*; D005982:Glutathione Transferase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D020411:Oligonucleotide Array Sequence Analysis; D051381:Rats; D011916:Rats, Inbred F344
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018528:ATP-Binding Cassette Transporters; D001151:Arsenic; D005982:Glutathione Transferase; D027425:ATP-Binding Cassette, Sub-Family C Proteins; C041116:leukotriene-C4 synthase