Posttranscriptional regulation of ATA2 transport during liver regeneration.
The recent cloning of ATA2, a cDNA displaying characteristics identical to the System A transporter, has provided the first molecular tool for study of System A-mediated amino acid transport in liver. Despite the 233 +/- 9 and 472 +/- 11% increase in System A transport activity following partial hepatectomy at 6 and 12 h, respectively, the steady-state level of ATA2 mRNA did not show a corresponding marked increase. Examination of the kinetic properties of System A following partial hepatectomy revealed a K(m) of 0.26 +/- 0.04 mM which is consistent with the reported K(m) for ATA2. These results indicate that a System A transporter present in regenerating liver and ATA2 are identical, but that the increase in System A activity following partial hepatectomy does not result from an increase in steady-state levels of ATA2 mRNA. These observations suggest that ATA2-mediated transport of amino acids is regulated at the posttranscriptional level.
Freeman
T L
TL
Department of Internal Medicine, University of Nebraska Medical Center, Omaha, Nebraska, USA.
Mailliard
M E
ME
D026905:Amino Acid Transport Systems; D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism*; D005786:Gene Expression Regulation; D006498:Hepatectomy; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008115:Liver Regeneration / Q000502:physiology*; D008297:Male; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015091:beta-Alanine / Q000031:analogs & derivatives* / Q000493:pharmacokinetics
D026905:Amino Acid Transport Systems; D000596:Amino Acids; D002352:Carrier Proteins; D012333:RNA, Messenger; D015091:beta-Alanine; C012924:2,2-dimethyl-beta-alanine