Modulation of the glucagon-dependent activation of the phosphoenolpyruvate carboxykinase gene by oxygen in rat hepatocyte cultures. Evidence for a heme protein as oxygen sensor.
The glucagon-dependent activation of the phosphoenolpyruvate carboxykinase (PCK) gene is modulated by oxygen. It was proposed that heme proteins might function as O2 sensors; their actions are impaired after replacement of the central Fe2+ ion by Co2+ and inhibition of heme synthesis by succinylacetone (SA). Therefore, the effects of CoCl2 and SA, alone and in combination, on the glucagon-dependent induction of PCK activity and PCK mRNA were investigated at different physiological oxygen tensions in primary rat hepatocyte cultures. The cells were exposed to 50 microM CoCl2 and/or 2 mM SA from 4-24 h. After addition of fresh media without CoCl2 or SA, PCK was induced with 1 nM glucagon. PCK activity and PCK mRNA were elevated to 100% at 16% O2 and to about 65% at 8% O2. CoCl2 reduced these increases to about 45% at 16% O2 and to about 35% at 8% O2. SA lowered the inductions to about 50% and 40% each at 16% and 8% O2. CoCl2 plus SA diminished the elevations to about 5% at both oxygen tensions. In the presence of CoCl2 and/or SA, ornithine decarboxylase induction by insulin was not impaired; lactate dehydrogenase did not leak from the cells, which in electron microscopical inspections had normal cell structures. These findings support the hypothesis that a heme protein is involved in the activation of the PCK gene and that it acts as an O2 sensor.
Kietzmann
T
T
Institut für Biochemie und Molekulare Zellbiologie, Göttingen, Germany.
Schmidt
H
H
Probst
I
I
Jungermann
K
K
D000818:Animals; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D003035:Cobalt / Q000494:pharmacology; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D005934:Glucagon / Q000494:pharmacology*; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008099:Liver / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D010100:Oxygen / Q000494:pharmacology*; D010313:Partial Pressure; D010729:Phosphoenolpyruvate Carboxykinase (GTP) / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar
D012333:RNA, Messenger; D003035:Cobalt; D005934:Glucagon; D007770:L-Lactate Dehydrogenase; D010729:Phosphoenolpyruvate Carboxykinase (GTP); C018021:cobaltous chloride; D010100:Oxygen