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 o f System A-mediated amino acid transport in liver. Despite the 233 +/- 9 an d 472 +/- 11% increase in System A transport activity following partial hep atectomy at 6 and 12 h, respectively, the steady-state level of ATA2 mRNA d id not show a corresponding marked increase. Examination of the kinetic pro perties 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 ATA 2 are identical, but that the increase in System A activity following parti al hepatectomy does not result from an increase in steady-state levels of A TA2 mRNA. These observations suggest that ATA2-mediated transport of amino acids is regulated at the posttranscriptional level. (C) 2000 Academic Pres s.