title: The methylmercury-L-cysteine conjugate is a substrate for the L-type large neutral amino acid transporter.
abstract: Methylmercury (MeHg) is a potent neurotoxin. The mechanism(s) that governs MeHg transport across the blood-brain barrier and other biological membranes remains unclear. This study addressed the role of the L-type large neutral amino acid transporter, LAT1, in MeHg transport. Studies were carried out in CHO-k1 cells. Over-expression of LAT1 in these cells was associated with enhanced uptake of [(14)C]-MeHg when treated with L-cysteine, but not with the D-cysteine conjugate. In the presence of excess L-methionine, a substrate for LAT1, L-cysteine-conjugated [(14)C]-MeHg uptake was significantly attenuated. Treatment of LAT-1 over-expressing CHO-k1 cells with L-cysteine-conjugated MeHg was also associated with increased leakage of lactate dehydrogenase into the media as well as reduced cell viability measured by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. In contrast, knock-down of LAT1 decreased the uptake of l-cysteine-conjugated MeHg and attenuated the effects of MeHg on lactate dehydrogenase leakage and CHO-k1 cell viability. These results indicate that the MeHg-L-cysteine conjugate is a substrate for the neutral amino acid transporter, LAT1, which actively transports MeHg across membranes.
authors.affiliation: Department of Pediatrics, Kennedy Center for Research on human Development, Vanderbilt University Medical Center, Nashville, Tennessee 37232, USA.
authors.forename: Zhaobao
authors.initials: Z
authors.lastname: Yin
authors.forename: Haiyan
authors.initials: H
authors.lastname: Jiang
authors.forename: Tore
authors.initials: T
authors.lastname: Syversen
authors.forename: João B T
authors.initials: JB
authors.lastname: Rocha
authors.forename: Marcelo
authors.initials: M
authors.lastname: Farina
authors.forename: Michael
authors.initials: M
authors.lastname: Aschner
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D016466:CHO Cells; D002247:Carbon Isotopes / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D006224:Cricetinae; D003412:Cricetulus; D003545:Cysteine / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D027283:Large Neutral Amino Acid-Transporter 1 / Q000235:genetics / Q000378:metabolism*; D008767:Methylmercury Compounds / Q000378:metabolism* / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000494:pharmacology; D013778:Tetrazolium Salts; D013844:Thiazoles; D014162:Transfection / Q000379:methods
chemical_list: D002247:Carbon Isotopes; D027283:Large Neutral Amino Acid-Transporter 1; D008767:Methylmercury Compounds; D034741:RNA, Small Interfering; D013778:Tetrazolium Salts; D013844:Thiazoles; D007770:L-Lactate Dehydrogenase; C022616:thiazolyl blue; D003545:Cysteine
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