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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
Author(s) -
Kietzmann Thomas,
Schmidt Helga,
Probst Irmelin,
Jungermann Kurt
Publication year - 1992
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/0014-5793(92)81113-z
Subject(s) - phosphoenolpyruvate carboxykinase , glucagon , hepatocyte , chemistry , heme , cytosol , oxygen , lactate dehydrogenase , medicine , microbiology and biotechnology , endocrinology , biochemistry , enzyme , biology , hormone , in vitro , organic chemistry
The glucagon‐dependent activation of the phosphoenolpyruvate carboxykinase (PCK) gene is modulated by oxygen. It was proposed that heme proteins might function as O 2 sensors; their actions are impaired after replacement of the central Fe 2+ ion by Co 2+ and inhibition of heme synthesis by succinylacetone (SA). Therefore, the effects of CoCl 2 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 μM CoCl 2 and/or 2 mM SA from 4–24 h. After addition of fresh media without CoCl 2 or SA, PCK was induced with 1 nM glucagon, PCK activity and PCK mRNA were elevated to 100% at 16% O 2 and to about 63% at 8% O 2 , CoCl 2 reduced these increases to about 45% at 16% O 2 and to about 35% at 8% O 2 . SA lowered the inductions to about 50% and 40% each at 16% and 8% O 2 . CoCl 2 plus SA diminished the elevations to about 5% at both oxygen tensions. In the presence of CoCl 2 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 O 2 sensor.