Biliverdin reductase, a novel regulator for induction of activating transcription factor-2 and heme oxygenase-1.

Biliverdin IXalpha reductase (BVR) catalyzes reduction of the HO activity product, biliverdin, to bilirubin. hBVR is a serine/threonine kinase that contains a bZip domain. Presently, regulation of gene expression by hBVR was examined. 293A cells were infected with adenovirus-doxycycline (Ad-Dox)-inducible hBVR cDNA. High level expression of hBVR was determined at mRNA, protein, and activity levels 8 h after induction. Cell signal transduction microarray analysis of cells infected with expression or with the control Ad-inverted (INV)-hBVR vector identified ATF-2 among several up-regulated genes. ATF-2 is a bZip transcription factor for activation of cAMP response element (CRE) and a dimeric partner to c-jun in MAPK pathway that regulates the stress protein, HO-1, expression. Northern and Western blot analyses showed increases of approximately 10-fold in ATF-2 mRNA and protein at 16 and 24 h after Dox addition. Ad-INV-hBVR did not effect ATF-2 expression. In hBVR-infected cells, levels of HO-1 mRNA and protein were increased. In vitro translated hBVR and nuclear extract containing hBVR in gel mobility-shift assay bound to AP-1 sites in the ATF-2 promoter region and to an oligonucleotide containing the CRE site. Both bindings could be competed out by excess unlabeled probe; in the presence of hBVR antibody, they displayed shifted bands. Co-transfection of hBVR with ATF-2 or c-jun promoters caused a severalfold increase in luciferase activity. hBVR modulation of ATF-2 and HO-1 expression suggests it has a potential role in regulation of AP-1 and cAMP-regulated genes and a role in cell signaling. We propose that increased expression of the protein can be used to alter the gene expression profile in the cell.