Nitric oxide stimulates insulin gene transcription in pancreatic β-cells

https://doi.org/10.1016/j.bbrc.2006.12.127Get rights and content

Abstract

Recent studies have identified a positive role for nitric oxide (NO) in the regulation of pancreatic β-cell function. The aim of this study was to determine the effects of short-term exposure to NO on β-cell gene expression and the activity of the transcription factor PDX-1. NO stimulated the activity of the insulin gene promoter in Min6 β-cells and endogenous insulin mRNA levels in both Min6 and isolated islets of Langerhans. Addition of wortmannin prior to NO stimulation blocked the observed increases in insulin gene promoter activity. Although NO addition stimulated the phosphorylation of p38, inhibition by SB203580 did not block the effect of NO on the insulin gene promoter. NO addition also stimulated both the nuclear accumulation and the DNA binding activity of PDX-1. This study has shown that over 24 h, NO stimulates insulin gene expression, PI-3-kinase activity and the activity of the critical β-cell transcription factor PDX-1.

Section snippets

Materials and methods

Cell culture. Min6, a β-cell line derived from transgenic mice expressing the SV40 large T antigen under the control of the rat insulin gene promoter [13] were cultured in DMEM containing 5 mM glucose, supplemented with 15% heat-inactivated foetal calf serum.

Plasmids and transfections. Min6 cells were transfected using Lipofectamine (Invitrogen) as previously described [7]. Plasmids were prepared using the Endotoxin-Free Maxiprep kit (Qiagen). The construct pGL-LUC200 is based on the basic pGL2

NO stimulates insulin gene promoter activity in Min6 β-cells

Normal physiological concentrations of NO are in the nanomolar to micromolar range, with a maximal physiological concentration of 1–5 μM [17]. To examine the short-term effects of NO on β-cell function in the present study, we utilised a concentration of 5 μM. To investigate the effect of NO on insulin gene promoter activity, Min6 cells were transfected with the construct Luc200, which contains a 200 bp fragment of the human insulin gene promoter upstream of the firefly luciferase reporter gene,

Discussion

To date, studies examining the effects of NO on pancreatic β-cell function have largely focused on the long-term detrimental effects of this free radical on cell survival and the role of NO in the promotion of apoptosis. The aim of the present study was to examine the short-term effects of NO on pancreatic β-cell gene regulation, and the activity of the key transcription factor PDX-1. Our analysis has shown that NO stimulates the activity of the insulin gene promoter over a 24 h timecourse, with

Acknowledgments

This work was supported in part by Eli Lilly. S.C.C. was supported by the Newcastle upon Tyne NHS Hospitals Trust. W.M.M. was supported by a CDA from the Juvenile Diabetes Research Foundation. H.R. was supported by a Biotechnology and Biological Sciences Research Council CASE studentship. Work in the CSB laboratory is supported by the Biotechnology and Biological Sciences Research Council.

References (27)

Cited by (19)

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    Nitrite increased mRNA expression of insulin1 and insulin2 in isolated pancreatic islets as well as expression of proinsulin and C-peptide in pancreatic tissue; these data indicate that nitrite increases insulin synthesis in Type 2 diabetic rats. Similar to our results, it has been shown that nitrite increases insulin content in pancreatic islets in Type 2 diabetic rats [12] and NO increases insulin mRNA levels in isolated islets from male Wistar rats and in Min6 β-cell line; in fact NO stimulates insulin gene promoter via phosphoinositide 3-kinase signaling pathway [25]. In addition, C-peptide, an indicator of β-cell function [26], increases NO production [27] and blood flow in pancreatic β-cells [28] that may be involved in higher insulin production after nitrite administration.

  • Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

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    The role of NO in insulin secretion is controversial; iNOS-derived NO decreases, while eNOS-derived NO increases insulin secretion [32,111]. In addition, NO stimulates the activity of the insulin gene promoter, with comparable increases in endogenous insulin mRNA levels in both Min6 β-cells (a pancreatic β-cell line derived from transgenic mouse expressing the large T-antigen of SV40 [112]) and isolated rat islets of Langerhans [113]. Both glucose and insulin increase NO production in β-cells [114]; glucose-induced NO production at physiological concentrations increases insulin secretion, however, higher NO levels inhibit insulin secretion [114].

  • Establishment of pancreatic microenvironment model of ER stress: Quercetin attenuates β-cell apoptosis by invoking nitric oxide-cGMP signaling in endothelial cells

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    The use of small molecules that enhance NO∙ availability including statins and Ang-converting enzyme inhibitors as a potential therapeutic approach in preventing and treating the vascular complications of diabetes has been reported earlier [37]. Moreover, a short-term exposure to NO∙ showed a pro-survival effect in pancreatic β-cells under ER stress and also enhanced the levels of insulin [38]. In recent years the compounds which act as eNOS modulators have gained importance in the therapeutic aspects.

  • Nitrite increases glucose-stimulated insulin secretion and islet insulin content in obese type 2 diabetic male rats

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    Similar to our results, a direct relation has been reported between insulin content and GSIS in pancreatic islets [43,44]. The stimulatory effect of nitrite on insulin content may be due to increased insulin gene transcription by NO, as has previously been reported [45]. Another possible explanation for increased islet insulin content following nitrite administration is the inhibition of insulin-degrading enzyme (IDE), a ubiquitously expressed cytosolic protease, by S-nitrosylation [42].

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