title: Functional characterization of a novel KCNJ11 in frame mutation-deletion associated with infancy-onset diabetes and a mild form of intermediate DEND: a battle between K(ATP) gain of channel activity and loss of channel expression.
abstract: ATP-sensitive potassium (K(ATP)) channels are widely distributed in various tissues and cell types where they couple cell metabolism to cell excitability. Gain of channel function (GOF) mutations in the genes encoding Kir6.2 (KCNJ11) or the associated regulatory ssulfonylurea receptor 1 subunit (ABCC8), cause developmental delay, epilepsy and neonatal diabetes (DEND) due to suppressed cell excitability in pancreatic β-cells and neurons. The objective of this study was to determine the molecular basis of infancy-onset diabetes and a mild form of intermediate DEND, resulting from a novel KCNJ11 in frame mutation plus deletion. The naturally occurring Kir6.2 mutation plus deletion (Ser225Thr, Pro226_Pro232del) as well as the isolated S225T mutation or isolated del226-232 deletion were coexpressed with SUR1 in COS cells in homozygous or heterozygous states. The protein expression and gating effects of the resulting channels were assessed biochemically and electrophysiologically. For both the deletion and point mutations, simulated heterozygous expression resulted in overall increased conductance in intact cells in basal conditions and rightward shifted ATP dose-response curves in excised patches, due to increased intrinsic open probability. Interestingly, homomeric channels for the combined deletion/mutation, or for the deletion alone, showed dramatically reduced channel expression at the cell membrane, which would underlie a reduced function in vivo. These results demonstrate that both the mis-sense mutation and the deleted region in the Kir6.2 subunit are important for control of the intrinsic channel gating and suggest that the clinical presentation could be affected by the competition between loss-of-function by reduced trafficking and enhanced channel gating.
authors.affiliation: Department of Cell Biology and Physiology, and Center for the Investigation of Membrane Excitability Diseases, Washington University School of Medicine, St. Louis, Missouri, United States of America.
authors.forename: Yu-Wen
authors.initials: YW
authors.lastname: Lin
authors.forename: Anlong
authors.initials: A
authors.lastname: Li
authors.forename: Valeria
authors.initials: V
authors.lastname: Grasso
authors.forename: Domenica
authors.initials: D
authors.lastname: Battaglia
authors.forename: Antonino
authors.initials: A
authors.lastname: Crinò
authors.forename: Carlo
authors.initials: C
authors.lastname: Colombo
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Barbetti
authors.forename: Colin G
authors.initials: CG
authors.lastname: Nichols
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D017668:Age of Onset; D000818:Animals; D019556:COS Cells; D002648:Child; D002522:Chlorocebus aethiops; D003920:Diabetes Mellitus / Q000235:genetics* / Q000503:physiopathology; D004827:Epilepsy / Q000235:genetics* / Q000503:physiopathology; D006579:Heterozygote; D006801:Humans; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000235:genetics* / Q000503:physiopathology; D015640:Ion Channel Gating / Q000187:drug effects; D008297:Male; D051379:Mice; D008958:Models, Molecular; D050505:Mutant Proteins / Q000378:metabolism; D018408:Patch-Clamp Techniques; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000378:metabolism*; D055503:Protein Multimerization / Q000187:drug effects; D021122:Protein Subunits / Q000378:metabolism; D011596:Psychomotor Disorders / Q000235:genetics* / Q000503:physiopathology; D017384:Sequence Deletion / Q000235:genetics*; D040681:Structural Homology, Protein; D000099161:Kcnj11 Channel
chemical_list: D000255:Adenosine Triphosphate; D050505:Mutant Proteins; D024661:Potassium Channels, Inwardly Rectifying; D021122:Protein Subunits; D000099161:Kcnj11 Channel