Molecular Mechanism of Heme Oxygenase-1 Gene Induction by Activation of the Protein Kinase A-Dependent Signaling Pathway

Abstract

Heme oxygenase-1 (HO-1) is the inducible isoform of the rate-limiting enzyme of heme degradation and is induced by a host of oxidative stress stimuli. We have previously demonstrated that HO-1 mRNA expression is up-regulated by the second messenger Bt₂cAMP in primary rat hepatocytes cultures. The HO-1 induction by Bt₂cAMP occurred transcriptionally via activation of the protein kinase A-dependent signaling pathway. To examine the cis-acting regulatory elements (REs) responsive to Bt₂cAMP and glucagon, luciferase constructs of the rat HO-1 gene were tested in transiently transfected primary rat hepatocyte cultures. A functional RE wasidentified in the HO-1 5′-flanking promoter region between position −664 and −657 from the cap side which was previously termed HO-1 cAMP RE (CRE)/activating protein-1 (AP-1) element. In electrophoretic mobility shift assays the HO-1 CRE/AP-1 element specifically bound to the recombinant transcription factor CRE binding protein (CREB) and formed a specific DNA-protein complex with nuclear extracts of rat hepatocyte cultures which was unchanged by the treatment with Bt₂cAMP or glucagon. Since the HO-1 CRE/AP-1 element is also involved in HO-1 gene activation by the protein kinase G-dependent signaling pathway this regulatory site may be a crucial nuclear target for potential pharmacological interventions.