Activation of Reg gene, a gene for insulin-producing beta -cell regeneration: poly(ADP-ribose) polymerase binds Reg promoter and regulates the transcription by autopoly(ADP-ribosyl)ation.

Abstract

The regeneration of pancreatic islet beta cells is important for the prevention and cure of diabetes mellitus. We have demonstrated that the administration of poly(ADP-ribose) synthetase/polymerase (PARP) inhibitors such as nicotinamide to 90% depancreatized rats induces islet regeneration. From the regenerating islet-derived cDNA library, we have isolated Reg (regenerating gene) and demonstrated that Reg protein induces beta-cell replication via the Reg receptor and ameliorates experimental diabetes. However, the mechanism by which Reg gene is activated in beta cells has been elusive. In this study, we found that the combined addition of IL-6 and dexamethasone induced the expression of Reg gene in beta cells and that PARP inhibitors enhanced the expression. Reporter gene assays revealed that the -81 approximately -70 region (TGCCCCTCCCAT) of the Reg gene promoter is a cis-element for the expression of Reg gene. Gel mobility shift assays showed that the active transcriptional DNA/protein complex was formed by the stimulation with IL-6 and dexamethasone. Surprisingly, PARP bound to the cis-element and was involved in the active transcriptional DNA/protein complex. The DNA/protein complex formation was inhibited depending on the autopoly(ADP-ribosyl)ation of PARP in the complex. Thus, PARP inhibitors enhance the DNA/protein complex formation for Reg gene transcription and stabilize the complex by inhibiting the autopoly(ADP-ribosyl)ation of PARP.