Glutathione peroxidase-1 inhibits transcription of regenerating islet-derived protein-2 in pancreatic islets

Abstract Our group previously demonstrated that overexpression of selenium-dependent glutathione peroxidase-1 (GPX1) in mice (OE) led to escalated glucose-stimulated insulin secretion and hyperinsulinemia. Because we found a strong correlation of this phenotype with a diminished expression of regenerating islet-derived protein 2 (REG2) in the OE pancreatic islets, the present study was to reveal underlying mechanisms for that down-regulation of REG2 by GPX1 as a major scavenger of reactive oxygen species. We first treated the OE and wild-type (WT) mice and their islets with ROS-generating diquat, streptozotocin, and H 2 O 2 and ROS-scavenging ebselen and N- acetylcysteine (NAC). Their effects on pancreatic and islet REG2 protein and(or) secretion were opposite ( P Reg2 proximate promoter, and found that only activator protein-1 (AP-1) and albumin D box-binding protein (DBP) mRNA and protein levels were affected (elevated) ( P Reg2 expression, their mRNA abundances in the cultured islets were elevated ( P P 2 O 2. Both AP-1 and DBP could bind to the Reg2 promoter at the location of −168 to 0 base pair (bp) in the OE islets. Deleting the AP-1 (−143/-137 and −60/-57 bp) and(or) DBP (−35/-29 bp) binding domains in the Reg2 promoter attenuated and(or) abolished the inhibition of Reg2 promoter activation by ebselen as the GPX1 mimic in βTC-3 cells. In conclusion, the down-regulation of Reg2 expression in the GPX1-overproducing pancreatic islets was mediated by a transcriptional inhibition of the gene through two ROS responsive transcription factors AP-1 and DBP. Our findings reveal GPX1 as a novel regulator of Reg2 expression, and linking these two previously-unrelated proteins will have broad biomedical implications.