Insights into the regulation of glucokinase from novel mutational mechanisms causing pancreatic beta-cell dysfunction
Lead Research Organisation:
University of Oxford
Department Name: Nuffield Dept of Clinical Medicine
Abstract
Glucokinase plays an important role in insulin secretion and is a current therapeutic target for diabetes. Patients with faults in the gene encoding this protein can have either diabetes or raised fasting blood glucose that is usually treated by diet alone or low blood glucose levels which are usually treated with diazoxide.
It is not understood how all of these faulty proteins result in low or high blood glucose values in patients. This study aims to investigate the mechanisms by which the defective genes cause diabetes or low blood glucose. Recently it has been discovered that some faults in genes do not cause disease because they change the protein; but that they affect the intermediate step of RNA processing that prevents or alters protein synthesis. My study will look at whether this is true for glucokinase gene defects. I will also look to see if some defects in genes cause disease because they prevent the glucokinase protein from being regulated by other proteins. This work is important because it will help interpret genetic test results and will also increase our understanding of an important drug target for the development of therapeutic agents to treat diabetes.
It is not understood how all of these faulty proteins result in low or high blood glucose values in patients. This study aims to investigate the mechanisms by which the defective genes cause diabetes or low blood glucose. Recently it has been discovered that some faults in genes do not cause disease because they change the protein; but that they affect the intermediate step of RNA processing that prevents or alters protein synthesis. My study will look at whether this is true for glucokinase gene defects. I will also look to see if some defects in genes cause disease because they prevent the glucokinase protein from being regulated by other proteins. This work is important because it will help interpret genetic test results and will also increase our understanding of an important drug target for the development of therapeutic agents to treat diabetes.
Technical Summary
Glucokinase plays a central role in the regulation of insulin secretion. Variation within the glucokinase (GCK) gene is causally-related to a range of phenotypes reflecting beta-cell dysfunction including monogenic diabetes (MODY), hyperinsulinaemic hypoglycaemia (HI), glucose levels and birth weight. GCK activators represent an emerging therapeutic option for type 2 diabetes.
The more than 200 GCK mutations so far implicated in monogenic conditions are widely-distributed across the gene. Molecular diagnostic testing is well-established in both MODY and HI, as identification of a GCK mutation provides information highly-relevant to the clinical management of the proband and their family.
In addition to the clinical and physiological insights, the detailed functional analysis of GCK mutations has provided important clues into the function, structure and regulation of this key enzyme. To date, GCK mutations have been shown to display a range of mutational mechanisms including kinetic inactivation (causing MODY), activation (in HI) and thermal-lability. However, my own preliminary work has identified a number of clearly-pathogenic mutations for which routine kinetic studies have failed to demonstrate a molecular basis for pathogenicity, or where kinetic studies may actually be misleading. I have also identified and characterised a large number of families segregating GCK-like MODY in whom extensive resequencing has failed to identify GCK mutations; and HI cases in whom all known genetic causes have been excluded.
A range of mutational mechanisms may be operating in these individuals: including abnormalities of RNA processing, disruptions of the interactions between GCK and regulatory/binding partners, copy number variation (CNV), and/or mutations in genes encoding regulatory partners of GCK. A detailed understanding of the molecular mechanisms involved will not only add novel clues to the regulation and function of GCK: it is also critical for appropriate clinical management.
The aims of this project are:
(i) to perform a systematic assessment of a selected group of 34 GCK-MODY mutations to identify the mutational mechanisms responsible: this will involve studies of mRNA processing, enzyme kinetics, interaction dynamics and mRNA and protein stability.
(ii) to determine the role of CNV in GCK-related phenotypes;
(iii) to investigate the role of mutations in the gene(s) encoding important islet GCK- regulatory proteins in beta-cell dysfunction.
This work should provide: (i) improved clinical diagnostics for families with monogenic diabetes and HI; (ii) insights into fundamental mechanisms of beta-cell regulation and function (relevant to all forms of diabetes); and (iii) the potential for novel, improved therapeutic tools for manipulation of beta-cell function.
The more than 200 GCK mutations so far implicated in monogenic conditions are widely-distributed across the gene. Molecular diagnostic testing is well-established in both MODY and HI, as identification of a GCK mutation provides information highly-relevant to the clinical management of the proband and their family.
In addition to the clinical and physiological insights, the detailed functional analysis of GCK mutations has provided important clues into the function, structure and regulation of this key enzyme. To date, GCK mutations have been shown to display a range of mutational mechanisms including kinetic inactivation (causing MODY), activation (in HI) and thermal-lability. However, my own preliminary work has identified a number of clearly-pathogenic mutations for which routine kinetic studies have failed to demonstrate a molecular basis for pathogenicity, or where kinetic studies may actually be misleading. I have also identified and characterised a large number of families segregating GCK-like MODY in whom extensive resequencing has failed to identify GCK mutations; and HI cases in whom all known genetic causes have been excluded.
A range of mutational mechanisms may be operating in these individuals: including abnormalities of RNA processing, disruptions of the interactions between GCK and regulatory/binding partners, copy number variation (CNV), and/or mutations in genes encoding regulatory partners of GCK. A detailed understanding of the molecular mechanisms involved will not only add novel clues to the regulation and function of GCK: it is also critical for appropriate clinical management.
The aims of this project are:
(i) to perform a systematic assessment of a selected group of 34 GCK-MODY mutations to identify the mutational mechanisms responsible: this will involve studies of mRNA processing, enzyme kinetics, interaction dynamics and mRNA and protein stability.
(ii) to determine the role of CNV in GCK-related phenotypes;
(iii) to investigate the role of mutations in the gene(s) encoding important islet GCK- regulatory proteins in beta-cell dysfunction.
This work should provide: (i) improved clinical diagnostics for families with monogenic diabetes and HI; (ii) insights into fundamental mechanisms of beta-cell regulation and function (relevant to all forms of diabetes); and (iii) the potential for novel, improved therapeutic tools for manipulation of beta-cell function.
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| Anna Gloyn (Principal Investigator) |