Title: The methylmercury-L-cysteine conjugate is a substrate for the L-type large neutral amino acid transporter.

Authors: Yin, Zhaobao; Jiang, Haiyan; Syversen, Tore; Rocha, João B T; Farina, Marcelo; Aschner, Michael

Published In J Neurochem, (2008 Nov)

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.

PubMed ID: 18793329

MeSH Terms: Analysis of Variance; Animals; CHO Cells; Carbon Isotopes/metabolism; Cell Survival/drug effects; Cricetinae; Cricetulus; Cysteine/metabolism*; Cysteine/pharmacology; Humans; L-Lactate Dehydrogenase/metabolism; Large Neutral Amino Acid-Transporter 1/genetics; Large Neutral Amino Acid-Transporter 1/metabolism*; Methylmercury Compounds/metabolism*; Methylmercury Compounds/pharmacology; RNA, Small Interfering/pharmacology; Tetrazolium Salts; Thiazoles; Transfection/methods