title: Enhancement of L-cystine transport activity and its relation to xCT gene induction at the blood-brain barrier by diethyl maleate treatment.
abstract: The purpose of the present study was to elucidate the mechanism of enhancement of L-cystine uptake at the blood-brain barrier (BBB). The uptake of [(14)C]L-cystine and [(3)H]L-glutamic acid (L-Glu) was determined using a mouse brain endothelial cell line (MBEC4) as an in vitro BBB model. The mRNA levels of L-cystine/L-Glu exchanger, system x(c)(-), which consists of xCT and 4F2hc, were determined by quantitative real-time reverse transcription-polymerase chain reaction analysis. The [(14)C]L-cystine uptake by MBEC4 cells appeared to be mediated via an Na(+)-independent saturable process. The corresponding Michaelis-Menten constant (K(m)) was 63.7 microM. In the presence of L-Glu, there was competitive inhibition with an inhibition constant (K(i)) of 83.5 microM. [(3)H]L-Glu uptake in the absence of Na(+) was saturable with a K(m) of 48.1 microM, and it exhibited competitive inhibition with a K(i) of 24.9 microM in the presence of L-cystine. The mutual inhibition between L-cystine and L-Glu and the type of inhibition suggest that system x(c)(-) operates in MBEC4 cells. The xCT and 4F2hc mRNAs were expressed in MBEC4 cells and, following diethyl maleate (DEM) treatment, the xCT mRNA level and L-cystine uptake in MBEC4 cells were enhanced in parallel with an increase in DEM concentration (up to 500 microM). Concomitantly, the glutathione concentration in MBEC4 cells was increased. In conclusion, system x(c)(-)-mediated L-cystine uptake takes place in MBEC4 cells. L-Cystine transport via system x(c)(-) at the BBB is likely to be induced under oxidative stress conditions following DEM treatment due to enhanced transcription of the xCT gene.
authors.affiliation: Faculty of Pharmaceutical Sciences, Toyama Medical and Pharmaceutical University, Toyama, Japan.
authors.forename: Ken-Ichi
authors.initials: K
authors.lastname: Hosoya
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Tomi
authors.forename: Sumio
authors.initials: S
authors.lastname: Ohtsuki
authors.forename: Hitomi
authors.initials: H
authors.lastname: Takanaga
authors.forename: Shigeki
authors.initials: S
authors.lastname: Saeki
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Kanai
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Endou
authors.forename: Mikihiko
authors.initials: M
authors.lastname: Naito
authors.forename: Takashi
authors.initials: T
authors.lastname: Tsuruo
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Terasaki
mesh_terms: D000465:Algorithms; D027182:Amino Acid Transport System y+; D000818:Animals; D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000187:drug effects*; D002352:Carrier Proteins / Q000235:genetics*; D002478:Cells, Cultured; D003553:Cystine / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D018698:Glutamic Acid / Q000378:metabolism; D005978:Glutathione / Q000378:metabolism; D007700:Kinetics; D008297:Male; D008298:Maleates / Q000494:pharmacology*; D051379:Mice; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012964:Sodium / Q000502:physiology; D013268:Stimulation, Chemical; D015533:Transcriptional Activation
chemical_list: D027182:Amino Acid Transport System y+; D002352:Carrier Proteins; D008298:Maleates; D012333:RNA, Messenger; C492255:Slc7a11 protein, mouse; D018698:Glutamic Acid; D003553:Cystine; D012964:Sodium; C014476:diethyl maleate; D005978:Glutathione