ANISOOSMOTIC REGULATION OF HEPATIC GENE-EXPRESSION

The effect of anisoosmolarity on the abundance of various mRNA species was examined in perfused rat liver and H4IIE rat hepatoma cells, Hype rosmotic exposure (385 mosmol/l) of isolated rat livers increased mRNA levels for tyrosine aminotransferase (TAT) by 246% and those for phos phoenolpyruvate carboxykinase (PEPCK) by 186%,whereas hypoosmotic expo sure (225 mosmol/l) decreased their levels to 43% and 42%, respectivel y, mRNA levels for fructose-1,6-bisphosphatase (FBP), argininosuccinat e lyase (ASL), argininosuccinate synthetase (ASS), glutamine synthetas e (GS), glutaminase (GA) and glucokinase (GK) were largely unaffected, In H4IIE cells the modulation of TAT and PEPCK mRNA levels by anisoos motic exposure was similar to that found in perfused rat liver, ASL an d glutaminase mRNA levels were influenced in an opposite manner. The e ffects of anisoosmolarity on PEPCK mRNA levels in H4IIE cells were lar gely abolished in the presence of the protein kinase inhibitors H-7, H -89 and HA-1004, Other protein kinase inhibitors such as Go-6850, KN-6 2, Rp-8-CPT-cAMPS, rapamycin, wortmannin, genistein or herbimycin did not prevent the osmosensitivity of PEPCK mRNA levels, Also pertussis a nd cholera toxin, vanadate and colchicine did not affect the osmosensi tivity of PEPCK mRNA levels. The data suggest that anisoosmotic exposu re acts on the levels of some but not all mRNA species and that this a ction may involve changes in protein phosphorylation, They further ind icate that the recently identified osmosensitive signal transduction p athway which involves a G-protein and tyrosine kinase dependent activa tion of mitogen-activated protein kinases is apparently not involved i n the osmoregulation of PEPCK mRNA levels.