Abstract
Heme oxygenase-1 (HO-1) is the inducible form of the rate-limiting enzyme of heme degradation; it regulates the cellular content of heme. To investigate the role of the cAMP-dependent protein kinase (PKA) signaling pathway on hepatic HO-1 gene expression, primary rat hepatocyte cultures were treated with the PKA-stimulating agents dibutyryl-cAMP (Bt2cAMP), forskolin, and glucagon. HO-1 mRNA levels were induced by these agents in a time-dependent manner with a transient maximum after 6 hr of treatment. The induction of HO-1 was dose dependent, reaching a maximum at concentrations of 250 μm Bt2cAMP and 50 nm glucagon, respectively. The accumulation of HO-1 mRNA correlated with increased levels of HO-1 protein as determined by Western blot analysis. The Bt2cAMP-dependent induction of HO-1 mRNA expression was prevented by pretreatment with the PKA inhibitor KT5720 but not with the protein kinase G inhibitor KT5823. HO-1 mRNA induction by CdCl2 and heme was differentially affected by Bt2cAMP. Up-regulation of the HO-1 gene by Bt2cAMP occurred on the transcriptional level as determined by nuclear run-off assay and blocking of the Bt2cAMP-dependent induction of HO-1 mRNA by actinomycin D. Treatment with Bt2cAMP increased the half-life of HO-1 mRNA from 4.7 to 5.5 hr. Taken together, the results of the current study demonstrate that HO-1 gene expression is induced by activation of the cAMP signal transduction pathway via a transcriptional mechanism in primary rat hepatocyte cultures.
Footnotes
- Received September 2, 1997.
- Accepted December 4, 1997.
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Send reprint requests to: Stephan Immenschuh, M.D., Zentrum für Innere Medizin, Abteilung Gastroenterologie und Endokrinologie, Georg-August Universität Göttingen, Robert-Koch Str. 40, 37075 Göttingen, Germany. E-mail:simmens{at}gwdg.de
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↵1 Current affiliation: Zentrum für Innere Medizin, Abteilung Gastroenterologie und Endokrinologie, Georg-August Universität Göttingen, 37075 Göttingen, Germany.
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This study was supported by National Institutes of Health Grants DK30203 and DK30664 (U.M.-E.), the Children’s Blood Foundation of the New York Hospital (U.M.-E.), and Deutsche Forschungsgemeinschaft Grants Im 20/2–1 (S.I.) and SFB 402 (T.K.).
- The American Society for Pharmacology and Experimental Therapeutics
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