Evidence for a regulatory protein involved in the increased activity of system A for neutral amino acid transport in osmotically stressed mammalian cells.
System A for neutral amino acid transport is increased by hypertonic shock in NBL-1 cells previously induced to express system A activity by amino acid starvation. The hypertonicity-mediated effect can be blocked by cycloheximide but is insensitive to tunicamycin. The activity induced may be inactivated irreversibly by the addition of system A substrates, by a rapid mechanism insensitive to cycloheximide. In CHO-K1 cells, hypertonicity increases system A activity, as has been shown in NBL-1 cells. This effect is additive to the activity produced by derepression of system A by amino acid starvation and is insensitive to tunicamycin. Furthermore, the alanine-resistant mutant CHO-K1 alar4, which bears a mutation affecting the regulatory gene R1, involved in the derepression of system A activity after amino acid starvation, is still able to respond to the hypertonic shock by increasing system A activity to a level similar to that described in hypertonicity-induced derepressed CHO-K1 (wild type) cells. These results suggest (i) that the hypertonicity-mediated increase of system A activity occurs through a mechanism other than that involved in system A derepression and (ii) that a regulatory protein coded by an osmotically sensitive gene is responsible for further activation of preexisting A carriers.
Ruiz-Montasell
B
B
Departament de Bioquímica i Fisiologia, Universitat de Barcelona, Spain.
Gómez-Angelats
M
M
Casado
F J
FJ
Felipe
A
A
McGivan
J D
JD
Pastor-Anglada
M
M
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D016466:CHO Cells; D002417:Cattle; D002460:Cell Line; D002999:Clone Cells; D006224:Cricetinae; D003470:Culture Media; D003609:Dactinomycin / Q000494:pharmacology; D004848:Epithelium / Q000378:metabolism; D005809:Genes, Regulator; D006982:Hypertonic Solutions; D007668:Kidney; D007700:Kinetics; D008954:Models, Biological; D012333:RNA, Messenger / Q000378:metabolism; D013395:Sucrose / Q000494:pharmacology; D014415:Tunicamycin / Q000494:pharmacology
D000596:Amino Acids; D003470:Culture Media; D006982:Hypertonic Solutions; D012333:RNA, Messenger; D014415:Tunicamycin; D003609:Dactinomycin; D013395:Sucrose