Neonatal Diabetes Caused by Mutations in Sulfonylurea Receptor 1: Interplay between Expression and Mg-Nucleotide Gating Defects of ATP-Sensitive Potassium Channels

• Published in: The journal of clinical endocrinology and metabolism Vol. 95; no. 12; pp. E473 - E478
• Main Authors: Zhou, Qing, Garin, Intza, Castaño, Luis, Argente, Jesús, Muñoz-Calvo, Ma. Teresa, Perez de Nanclares, Guiomar, Shyng, Show-Ling
• Format: Journal Article
• Language: English
• Published: United States Endocrine Society 01-12-2010; The Endocrine Society
• Subjects: Amino Acid Substitution; Animals; ATP-Binding Cassette Transporters - genetics; Beta cells; Cell surface; Cercopithecus aethiops; Channel gating; COS Cells; Diabetes mellitus; Diabetes Mellitus - genetics; Gene Expression Regulation; Glucose metabolism; Heterozygote; Humans; Infant, Newborn; Infant, Newborn, Diseases - genetics; Insulin; KATP Channels - physiology; Magnesium - physiology; Membrane potential; Mutation; Neonates; Nucleotides; Original; Potassium channels; Potassium channels (inwardly-rectifying); Potassium Channels, Inwardly Rectifying - genetics; Potassium Channels, Inwardly Rectifying - physiology; Receptors, Drug - genetics; Secretion; sulfonylurea; Sulfonylurea Receptors
• ISSN: 0021-972X; 1945-7197
• DOI: 10.1210/jc.2010-1231

Context: ATP-sensitive potassium (KATP) channels regulate insulin secretion by coupling glucose metabolism to β-cell membrane potential. Gain-of-function mutations in the sulfonylurea receptor 1 (SUR1) or Kir6.2 channel subunit underlie neonatal diabetes.
Objective: 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.
Design: E208K or V324M mutant SUR1 was coexpressed with Kir6.2 in COS cells, and expression and gating properties of the resulting channels were assessed biochemically and electrophysiologically.
Results: Both E208K and V324M augment channel response to MgADP stimulation without altering sensitivity to ATP4− or sulfonylureas. Surprisingly, whereas E208K causes only a small increase in MgADP response consistent with the mild transient diabetes phenotype, V324M causes a severe activating gating defect. Unlike E208K, V324M also impairs channel expression at the cell surface, which is expected to dampen its functional impact on β-cells. When either mutation was combined with a mutation in the second nucleotide binding domain of SUR1 previously shown to abolish Mg-nucleotide response, the activating effect of E208K and V324M was also abolished. Moreover, combination of E208K and V324M results in channels with Mg-nucleotide sensitivity greater than that seen in individual mutations alone.
Conclusion: The results demonstrate that E208K and V324M, located in distinct domains of SUR1, enhance transduction of Mg-nucleotide stimulation from the SUR1 nucleotide binding folds to Kir6.2. Furthermore, they suggest that diabetes severity is determined by interplay between effects of a mutation on channel expression and channel gating.
Characterization of E208K and V324M mutations in sulfonylurea receptor 1 suggests diabetes severity is determined by interplay between effects of mutations on channel expression and channel gating.