Characterization of the human biliverdin reductase gene structure and regulatory elements: promoter activity is enhanced by hypoxia and suppressed by TNF‐α‐activated NF‐κB

Abstract

hBVR is a Ser/Thr/Tyr kinase/scaffold protein/transcription factor/intracellular transporter of regulators. hBVR is an upstream activator of the insulin/IGF-1/MAPK/PI3K signaling pathway, and of NF-kappaB. As a reductase, it converts biliverdin to the antioxidant, bilirubin. hBVR gene has 8 exons; exon 1 is not translated. We report the characterization of hBVR promoter and its negative and positive regulation, respectively, by TNF-alpha and hypoxia. The 5' end of exon 1 was defined by primer extension analyses; deletion of an inhibitor sequence 350-425 bp upstream of this exon enhanced the promoter activity. One of two NF-kappaB binding sites in the 836-bp promoter was functional; the P65 subunit of NF-kappaB and TNF-alpha acted as inhibitors. On the basis of EMSA and ChIP assays, TNF-alpha treatment increases binding of NF-kappaB to its regulatory element. Overexpression of IkappaB increased hBVR mRNA. Biliverdin, but not bilirubin, was as effective as TNF-alpha in inhibiting hBVR promoter activity. Only one of 4 hypoxia responsive elements (HREs) bound to HIF-1alpha and ARNT expressed in HEK293A cells. An abasic site was introduced at the 3' G of the HRE. This element bound HIF-1 in the gel shift and in in-cell luciferase assays. hBVR was detected in the nucleus at 1, 2, and 4 h after hypoxia (1% O(2)), at which times its kinase and reductase activities were increased. Because hypoxia positively influences hBVR promoter and phosphorylation and TNF-alpha activated NF-kappaB inhibits the promoter, while biliverdin inhibits both NF-kappaB activity and hBVR promoter, we propose a regulatory mechanism for NF-kappaB by hypoxia and TNF-alpha centered on hBVR/biliverdin.

Intraperitoneally administered biliverdin protects against UVB-induced skin photo-damage in hairless mice

“…Accordingly, inhibition of UV-irradiation induced inflammatory cytokines secretion is important to protect skin from photo-damage. Recently, several studies have shown that BVD is rapidly converted by BVR to bilirubin, resulting in decreased release of proinflammatory cytokines, such as IL-12, IL-6, and TNF-a in animals [44]. In the present study, the proinflammatory cytokine IL-6 increased in the UVB group, and BVD treatment diminished IL-6 expression, thereby preventing the skin inflammation mediated by UVB-induced oxidative stress.…”

Elucidating the Role of Biliverdin Reductase in the Expression of Heme Oxygenase-1 as a Cytoprotective Response to Stress

“…pro-inflammatory and pro-proliferative targets (Gibbs et al, 2010). Consistent with the possibility that BVR regulates the activity of NFκB, TNF--mediated stimulation caused NFκB to act as a repressor of BVR expression which demonstrates that BVR is competitive with the inflammation process mediated by TNF-through activation of NFκB.…”

“…When BVR was over-expressed in HEK 293 and MCF-7 cells, the cells were arrested in G 1 /G o stage . Furthermore, over-expression of BVR also protected cells from NFκB-mediated proliferation after stimulation with TNF- (Gibbs et al, 2010). These findings are consistent with a number of studies that have used various cell types (HEK293 (Miralem et al, 2005), HeLa (Ahmad et al, 2002), cardiomyocytes (Pachori et al, 2007) and renal epithelial cells (Young et al, 2009)) to show that the inhibition of BVR expression using interference RNA resulted in apoptosis after the cells were challenged with arsenite, hydrogen peroxide, hypoxia/reoxygenation, and angiotensin II, respectively.…”

Characterization of heme oxygenase and biliverdin reductase gene expression in zebrafish (Danio rerio): Basal expression and response to pro-oxidant exposures

“…For example, both rat and human BVRa gene promoters contain regulatory elements for NFκB and HIF-1α (Gibbs et al ., 2010) which is in agreement with human BVRa being activated by hypoxia (Salim et al ., 2001) and inhibited by NFκB (Gibbs et al ., 2010). These results are consistent with the observation of four HRE motifs in the proximal promoter region of the zebrafish bvra gene (Figure 11).…”

“…These results are consistent with the observation of four HRE motifs in the proximal promoter region of the zebrafish bvra gene (Figure 11). Additionally, computer analysis of the human BVRa promoter suggested numerous candidate regulatory elements including the aryl hydrocarbon receptor (AHR) and heat shock factor 1 (HSF-1) (Gibbs et al , 2010). Interestingly, both bilirubin and biliverdin have also been implicated in the activation of the AHR pathway (Sinal and Bend, 1997; Phelan et al ., 1998).…”