title: Regulation of the human taurine transporter by oxidative stress in retinal pigment epithelial cells stably transformed to overexpress aldose reductase.
abstract: In diabetes, overexpression of aldose reductase (AR) and consequent glucose-induced impairment of antioxidant defense systems may predispose to oxidative stress and the development of diabetic complications, but the mechanisms are poorly understood. Taurine (2-aminoethanesulfonic acid) functions as an antioxidant, osmolyte, and calcium modulator such that its intracellular depletion could promote cytotoxicity in diabetes. The relationships of oxidative stress and basal AR gene expression to Na+-taurine cotransporter (TT) gene expression, protein abundance, and TT activity were therefore explored in low AR-expressing human retinal pigment epithelial (RPE) 47 cells and RPE 47 cells stably transformed to overexpress AR (RPE 75). Changes in TT gene expression were determined using a 4.6-kb TT promoter-luciferase fusion gene. Compared with RPE 47 cells, in high AR-expressing RPE 75 cells, TT promoter activity was decreased by 46%, which was prevented by an AR inhibitor. TT promoter activity increased up to 900% by prooxidant exposure, which was associated with increased TT peptide abundance and taurine transport. However, induction of TT promoter activity by oxidative stress was attenuated in high AR-expressing cells and partially corrected by AR inhibitor. Finally, exposure of RPE 75 cells to high glucose increased oxidative stress, but down-regulated TT expression. These studies demonstrate for the first time that the TT is regulated by oxidative stress and that overexpression of AR and high glucose impair this response. Abnormal expression of AR may therefore impair antioxidant defense, which may determine tissue susceptibility to chronic diabetic complications.
authors.affiliation: Department of Internal Medicine, University of Michigan, Ann Arbor, MI, USA.
authors.forename: Eitaro
authors.initials: E
authors.lastname: Nakashima
authors.forename: Rodica
authors.initials: R
authors.lastname: Pop-Busui
authors.forename: Roberto
authors.initials: R
authors.lastname: Towns
authors.forename: Thommey P
authors.initials: TP
authors.lastname: Thomas
authors.forename: Yoshiuki
authors.initials: Y
authors.lastname: Hosaka
authors.forename: Jiro
authors.initials: J
authors.lastname: Nakamura
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Greene
authors.forename: Paul D
authors.initials: PD
authors.lastname: Killen
authors.forename: Justin
authors.initials: J
authors.lastname: Schroeder
authors.forename: Dennis D
authors.initials: DD
authors.lastname: Larkin
authors.forename: Yuk Lam
authors.initials: YL
authors.lastname: Ho
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Stevens
mesh_terms: D000449:Aldehyde Reductase / Q000235:genetics* / Q000378:metabolism*; D002478:Cells, Cultured; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects; D016678:Genome / Q000235:genetics; D005947:Glucose / Q000494:pharmacology; D006801:Humans; D008315:Malondialdehyde / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D018384:Oxidative Stress; D010857:Pigment Epithelium of Eye / Q000166:cytology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D014162:Transfection; D000099247:Taurine Transporters
chemical_list: D000449:Aldehyde Reductase; D018076:DNA, Complementary; D005947:Glucose; D008315:Malondialdehyde; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D000099247:Taurine Transporters