The glucose-6-phosphatase catalytic subunit gene family comprises three members, G6PC, G6PC2 and G6PC3. G6PC is predominantly expressed in liver where it catalyses the terminal step in the gluconeogenic and glycogenolytic pathways, namely the hydrolysis of glucose-6-phosphate (G6P) to glucose and inorganic phosphate. G6PC2, initially known as IGRP, is ~50% identical at the amino acid level to G6PC but it is expressed specifically in pancreatic islets. G6PC2 also hydrolyses G6P, though at a much lower rate than G6PC. This is consistent with the observation that deletion of the G6PC2 gene in mice results in decreased fasting blood glucose levels, suggesting that G6PC2 normally opposes the action of glucokinase in islets and lowers intracellular G6P concentrations and consequently glucose-stimulated insulin secretion. Two recent genome wide association (GWA) studies have linked single nucleotide polymorphisms (SNPs) in the G6PC2 gene to variations in fasting blood glucose levels in humans, a parameter that is linearly correlated with cardiovascular-associated mortality. Our preliminary data strongly support the hypothesis that sequence variations in the G6PC2 gene, rather than surrounding genes, contribute to elevated fasting blood glucose levels and hence cardiovascular-associated mortality. This project is therefore at a more advanced stage relative to many other GWA studies where disease-associated SNPs have been reported but the disease-associated genes remain to be identified. The goal of the experiments proposed in this application is to extend the GWA studies by functionally characterizing the effects of G6PC2 gene variants on transcription (Aim 1) and splicing (Aim 2). Our initial experiments have shown that two SNPs in the G6PC2 promoter affect G6PC2 fusion gene transcription. In addition, our sequence analyses suggest that the G6PC2 SNP that was first linked to variations in fasting blood glucose is located in a branch point, a key cis-acting element controlling pre-mRNA splicing.
| Baerenwald, D A; Bonnefond, A; Bouatia-Naji, N et al. (2013) Multiple functional polymorphisms in the G6PC2 gene contribute to the association with higher fasting plasma glucose levels. Diabetologia 56:1306-16 |
| Bouatia-Naji, Nabila; Bonnefond, Amélie; Baerenwald, Devin A et al. (2010) Genetic and functional assessment of the role of the rs13431652-A and rs573225-A alleles in the G6PC2 promoter that are strongly associated with elevated fasting glucose levels. Diabetes 59:2662-71 |
