Regulation of System B0 amino-acid-transport activity in the renal epithelial cell line NBL-1 and concomitant changes in SAAT1 hybridizing transcripts.
alpha-(Methylamino)isobutyric acid (MeAIB) insensitive Na(+)-dependent alanine transport activity in the bovine kidney cell line NBL-1 was increased upon amino acid starvation (> or = 20% over control levels). When L-phenylalanine (3 mM) was included in the starvation medium the increase was further enhanced (> or = 85% over control levels). In cells grown in control medium the Vmax, for MeAIB-insensitive Na+/alanine co-transport was found to be 6.0 +/- 0.7 nmol/3 min per mg (Km 41 +/- 12 microM) and for L-phenylalanine-treated amino-acid-starved cells the Vmax. was 21 +/- 5 nmol/3 min per mg (Km 92 +/- 40 microM). The increase in Vmax. was prevented by cycloheximide. Substrate specificity analysis identified the L-phenylalanine-induced transport system as System B0. [35S]Methionine labelling of cells during the amino acid starvation/phenylalanine treatments resulted in the differential labelling of a protein of 78 kDa. Northern-blot analysis using a SAAT1-specific probe revealed the presence of a new transcript (3.2 kb) in RNA extracted from cells incubated in amino acid starvation medium with L-phenylalanine included. The present findings suggest a novel means of control for System B0 by the use of physiological stress. It is also proposed that SAAT1 and System-B0 transcripts have considerable sequence similarity.
Plakidou-Dymock
S
S
Department of Biochemistry, University of Bristol, School of Medical Sciences, U.K.
Tanner
M J
MJ
McGivan
J D
JD
D000409:Alanine / Q000378:metabolism; D026923:Amino Acid Transport Systems, Basic; D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids / Q000008:administration & dosage / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002417:Cattle; D002460:Cell Line; D003470:Culture Media; D015342:DNA Probes; D004848:Epithelium / Q000378:metabolism; D007668:Kidney / Q000378:metabolism*; D007700:Kinetics; D008715:Methionine / Q000378:metabolism; D010649:Phenylalanine / Q000494:pharmacology; D012313:RNA / Q000032:analysis; D012964:Sodium / Q000494:pharmacology; D015091:beta-Alanine / Q000031:analogs & derivatives / Q000494:pharmacology
D026923:Amino Acid Transport Systems, Basic; D026921:Amino Acid Transport Systems, Neutral; D000596:Amino Acids; D002352:Carrier Proteins; D003470:Culture Media; D015342:DNA Probes; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine; D010649:Phenylalanine; D012313:RNA; D012964:Sodium; D008715:Methionine; D000409:Alanine