Acidosis-sensing glutamine pump SNAT2 determines amino acid levels and mammalian target of rapamycin signalling to protein synthesis in L6 muscle cells.
Wasting of lean tissue as a consequence of metabolic acidosis is a serious problem in patients with chronic renal failure. A possible contributor is inhibition by low pH of the System A (SNAT2) transporter, which carries the amino acid L-glutamine (L-Gln) into muscle cells. The aim of this study was to determine the effect of selective SNAT2 inhibition on intracellular amino acid profiles and amino acid-dependent signaling through mammalian target of rapamycin in L6 skeletal muscle cells. Inhibition of SNAT2 with the selective competitive substrate methylaminoisobutyrate, metabolic acidosis (pH 7.1), or silencing SNAT2 expression with small interfering RNA all depleted intracellular L-Gln. SNAT2 inhibition also indirectly depleted other amino acids whose intracellular concentrations are maintained by the L-Gln gradient across the plasma membrane, notably the anabolic amino acid L-leucine. Consequently, SNAT2 inhibition strongly impaired signaling through mammalian target of rapamycin to ribosomal protein S6 kinase, ribosomal protein S6, and 4E-BP1, leading to impairment of protein synthesis comparable with that induced by rapamycin. It is concluded that even though SNAT2 is only one of several L-Gln transporters in muscle, it may determine intracellular anabolic amino acid levels, regulating the amino acid signaling that affects protein mass, nucleotide/nucleic acid metabolism, and cell growth.
Evans
Kate
K
Department of Infection, Immunity and Inflammation, University of Leicester, John Walls Renal Unit, Leicester General Hospital, Leicester, United Kingdom.
Nasim
Zeerak
Z
Brown
Jeremy
J
Butler
Heather
H
Kauser
Samira
S
Varoqui
Hélène
H
Erickson
Jeffrey D
JD
Herbert
Terence P
TP
Bevington
Alan
A
D000138:Acidosis / Q000378:metabolism*; D026924:Amino Acid Transport System A; D026905:Amino Acid Transport Systems / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D020868:Gene Silencing; D006863:Hydrogen-Ion Concentration; D008954:Models, Biological; D032342:Muscle Cells / Q000378:metabolism*; D014176:Protein Biosynthesis / Q000235:genetics*; D011494:Protein Kinases / Q000502:physiology*; D051381:Rats; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D015091:beta-Alanine / Q000031:analogs & derivatives / Q000494:pharmacology
D026924:Amino Acid Transport System A; D026905:Amino Acid Transport Systems; D000596:Amino Acids; D002352:Carrier Proteins; C412568:Slc38a2 protein, rat; C037853:glutamine transport proteins; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D011494:Protein Kinases; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases