Functional expression of A glutamine transporter responsive to down-regulation by lipopolysaccharide through reduced promoter activity in cultured rat neocortical astrocytes.
The prevailing view is that the glutamine (Gln) transporter (GlnT/ATA1/SAT1/SNAT1) is a member of the system A transporter superfamily with the ability to fuel the glutamate/Gln cycle at nerve terminals in glutamatergic neurons. Semiquantitative reverse transcription-polymerase chain reaction revealed similarly high expression of mRNA for GlnT by rat brain neocortical astrocytes as well as neurons, with progressively lower expression by cerebellar astrocytes, hippocampal astrocytes, and whole-brain microglia in culture. [(3)H]Gln was accumulated in a temperature-dependent manner with a saturable profile in both cultured neocortical neurons and astrocytes, whereas biochemical and pharmacological analyses on [(3)H]Gln accumulation revealed the expression of both system A and system L transporters by cultured neocortical neurons and astrocytes. Exposure to lipopolysaccharide (LPS) for 24 hr resulted in a significant decrease in both GlnT mRNA expression and [(3)H]Gln accumulation, with a concomitant drastic increase in nitrite formation in cultured neocortical astrocytes. Moreover, LPS significantly inhibited the promoter activity of GlnT in the astrocytic cell line C6 glioma cells as well as primary rat neocortical astrocytes in culture. These results suggest that activation by LPS would lead to down-regulation of the expression of GlnT responsible for the incorporation of extracellular Gln into intracellular spaces across plasma membranes through the inhibition of its promoter activity in cultured rat neocortical astrocytes.
Laboratory of Molecular Pharmacology, Division of Pharmaceutical Sciences, Kanazawa University Graduate School of Natural Science and Technology, Kanazawa, Japan.
Masato
M
Ogura
Noritaka
N
Nakamichi
Katsura
K
Takano
Hirotaka
H
Oikawa
Yuki
Y
Kambe
Yu
Y
Ohno
Hideo
H
Taniura
Yukio
Y
Yoneda
D026924:Amino Acid Transport System A / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D002478:Cells, Cultured; D015536:Down-Regulation / Q000187:drug effects / Q000235:genetics*; D004660:Encephalitis / Q000139:chemically induced / Q000235:genetics / Q000378:metabolism; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000096:biosynthesis; D008070:Lipopolysaccharides / Q000494:pharmacology; D008969:Molecular Sequence Data; D019579:Neocortex / Q000166:cytology; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D026924:Amino Acid Transport System A; D002352:Carrier Proteins; D008070:Lipopolysaccharides; D012333:RNA, Messenger; C486716:Slc38a1 protein, rat; C037853:glutamine transport proteins; D018698:Glutamic Acid