Mutations of the same conserved glutamate residue in NBD2 of the sulfonylurea receptor 1 subunit of the KATP channel can result in either hyperinsulinism or neonatal diabetes.
The objective of the study was to determine the mechanisms by which two SUR1 mutations, E208K and V324M, associated with transient neonatal diabetes affect KATP channel function.
Activating mutations in genes KCNJ11 and ABCC8, which form the ATP-sensitive K+channel (K(ATP) channel), have been shown to cause transient or permanent neonatal diabetes.
The importance of these interactions is exemplified by the fact that impaired regulation of Kir6.2 by SUR1 results in human disease, with loss-of-function SUR1 mutations causing congenital hyperinsulinism and gain-of-function SUR1 mutations leading to neonatal diabetes.
Here we report that two hyperinsulinism-associated SUR1 missense mutations, R74W and E128K, surprisingly reduce channel inhibition by intracellular ATP, a gating defect expected to yield the opposite disease phenotype neonatal diabetes.
Loss- and gain-of-function mutations in the genes encoding the Kir6.2 and SUR1 subunits of this channel cause hyperinsulinism of infancy and neonatal diabetes, respectively.
Expression of the V59M Kir6.2 mutation in pancreatic beta cells alone is thus sufficient to recapitulate the neonatal diabetes observed in humans. beta-V59M islets also displayed a reduced percentage of beta cells, abnormal morphology, lower insulin content, and decreased expression of Kir6.2, SUR1, and insulin mRNA.
Loss of function mutations in the KCNJ11 and ABCC8 genes that encode for Kir6.2 and SUR1 can cause over-secretion of insulin and result in hyperinsulinism of infancy, while gain of function mutations in KCNJ11 and ABCC8 have recently been described that result in the opposite phenotype of diabetes.Genetic testing is important for patients with hyperinsulinism or neonatal diabetes, as identification of a K(ATP) channel mutation confirms a diagnosis of their disorder.
In contrast to KCNJ11, where only dominant heterozygous mutations have been identified, recessively acting ABCC8 mutations have recently been found in some patients with neonatal diabetes.
Here we investigate the molecular mechanism by which two heterozygous mutations in the second nucleotide-binding domain (NBD2) of SUR1 (R1380L and R1380C) separately cause neonatal diabetes.
Activating mutations in the genes encoding the ATP-sensitive potassium (K(ATP)) channel subunits Kir6.2 and SUR1 are a common cause of neonatal diabetes.
The functional consequence of this ABCC8 mutation mirrors that of KCNJ11 mutations causing neonatal diabetes and provides new insights into the interaction of Kir6.2 and SUR1.