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PubMed1996

Regulation of the gluconeogenic phosphoenolpyruvate carboxykinase and glycolytic aldolase A gene expression by O2 in rat hepatocyte cultures. Involvement of hydrogen peroxide as mediator in the response to O2.

Heme proteins acting as oxidases which produce H2O2 have been proposed to function as O2 sensors. In order to find out whether the modulation by O2 of PCK gene activation and the stimulation of the ALD A gene by venous O2 operate via H2O2, the effects of different concentrations of H2O2 and catalase as H2O2 scavenger were studied in rat hepatocyte cultures under different O2 tensions. Primary hepatocytes were treated with 0.1 nM glucagon, 50 microM H2O2 and/or 100 micrograms/ml catalase each at arterial O2 or venous pO2. PCK mRNA was induced by glucagon maximally under arterial O2 and only half maximally under venous O2. ALD A mRNA was induced only by venous O2. H2O2 enhanced the induction of PCK mRNA to similar levels under venous O2 tensions and the induction of ALD A mRNA under both O2 was completely inhibited. Addition of catalase antagonized the actions of H2O2 completely. These findings support the hypothesis that an H2O2-generating heme protein is involved in the O2 sensing system regulating gluconeogenic and glycolytic gene expression in response to O2.

Animals↗
PubMed1996

Differences in DNA-binding efficiency of Sp1 to aldolase and pyruvate kinase promoter correlate with altered redox states in resting and proliferating rat thymocytes.

Thymocytes induce their glycolytic enzymes as they undergo transition from the resting to the proliferating state. Corresponding increases in mRNA levels point to a transcriptional regulation. Electrophoretic mobility shift assays revealed that the DNA-binding efficiency of Sp1 is increased when nuclear extracts from proliferating compared to resting rat thymocytes were used. Here we demonstrate that hydrogen peroxide, added to nuclear extract from proliferating cells, decreases the Sp1 DNA-binding activity, whereas in nuclear extracts from resting cells dithioerythritol fully restores DNA-binding efficiency. Moreover we show that in contrast to resting thymocytes, production of reactive peroxide anions upon priming with phorbol 12-myristate 13-acetate is nearly abolished in the proliferating cells. From these results we propose that reactive oxygen intermediates affect the interaction of the Sp1 transcription factor with its consensus sequence and subsequently regulate glycolytic gene expression.

Animals↗