Transcriptional Regulation of Cyclooxygenase-2 Gene in Pancreatic β-Cells

Abstract

Prostaglandin E 2 (PGE 2 ) has been shown to negatively affect pancreatic ␤-cell function, and its inducible synthesis is mediated in part by cycloxygenase-2 (COX-2). Regulation of basal and inducible COX-2 gene expression in pancreatic ␤-cells is not fully understood. In this report, we used pancreatic ␤-cells (RINm5F) to explore the molecular mechanisms regulating COX-2 promoter activity. Through deletion analysis of a ؊907/؉70-bp 5 upstream region of the mouse COX-2 gene, we identified an inhibition domain (؊804/؊371) and an activation domain (؊371/؉70). The highest promoter activity was seen when the promoter was reduced to ؊371 bp. Several cis-acting elements were selected for site-directed mutations in the activation domain. We identified three sites that were essential for basal COX-2 promoter activity: 1) CCAAT/enhancer-binding protein (C/EBP), 2) aryl hydrocarbon receptor (AhR), and 3) cAMP response element-binding protein (CREB). Single mutation of each individual site inhibited 70 -80% of basal COX-2 promoter activity. Double mutation of the AhR and CREBbinding sites showed synergy in repressing COX-2 promoter activity as did mutation of all three sites. We demonstrated that the transcription factors from RINm5F nuclear extracts specifically bound to oligonucleotides containing C/EBP, AhR, or CREB consensus sites. Forskolin, an activator of adenyl cyclase, increased COX-2 promoter activity via the CREB site. COX-2 promoter activity was also increased by 2,3,7,8-tetrachlorodibenzo-p-dioxin, an AhR activator, through the AhR site. Both forskolin and 2,3,7,8-tetrachlorodibenzo-p-dioxin increased COX-2 mRNA in a dose-dependent manner. We consider these three transcriptional regulators of COX-2 expression to be potential targets for the prevention of ␤-cell damage mediated by PGE 2 .

Harpagoside suppresses lipopolysaccharide-induced iNOS and COX-2 expression through inhibition of NF-κB activation

“…This discrepancy suggests that the ability of harpagoside to attenuate NF-B activity is cell and/or stimulus specific. Cell type and stimulus dependence was in fact demonstrated for transcriptional regulation of COX-2, which is mediated distinctly by the binding of inducible transcriptional factors to cis-acting elements in the COX-2 promoter (Yang and Bleich, 2004). Interestingly, the whole extracts of Harpagophytum were shown to attenuate NF-B translocation to the nucleus in rat mesangial cells (Kaszkin et al, 2004) indicating the involvement of other active components in the extract.…”

Synergism of aromatic amines and benzo[a]pyrene in induction of Ah receptor-dependent genes

“…In this study, we analysed RNA expression of CYP1A1, COX-2 and UGT1, which are known to be induced via the Ah receptor (Ma and Lu 2007;Kawajiri and Fujii-Kuriyama 2007;Yang and Bleich 2004;Degner et al 2007;Zhou et al 2005;Mackenzie et al 2003). 4-ABP did not induce CYP1A1, COX-2 or UGT1 up to concentrations of 50 M. In contrast to 4-ABP, B[a]P is known to be a strong inducer of CYP1A1 which acts via the Ah receptor (Ma and Lu 2007).…”

Recruitment of CREB1 and Histone Deacetylase 2 (HDAC2) to the Mouse Ltbp-1 Promoter Regulates its Constitutive Expression in a Dioxin Receptor-dependent Manner

“…48,49 To analyse the importance of XRE and CRE on Ltbp-1 promoter activity, we have produced constructs containing deletions of these conserved elements and performed luciferase activity assays in Hepa 1 cells (Fig. 3a, upper).…”