Neonatal diabetes caused by mutations in sulfonylurea receptor 1: interplay between expression and Mg-nucleotide gating defects of ATP-sensitive potassium channels.
BACKGROUND
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.


METHODS
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.


CONCLUSIONS
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.
Zhou
Qing
Q
Department of Biochemistry and Molecular Biology, Oregon Health & Science University, 3181 S.W. Sam Jackson Park Road, Portland, Oregon 97239, USA.
Garin
Intza
I
Castaño
Luis
L
Argente
Jesús
J
Muñoz-Calvo
Ma Teresa
MT
Perez de Nanclares
Guiomar
G
Shyng
Show-Ling
SL
D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003920:Diabetes Mellitus / Q000235:genetics*; D005786:Gene Expression Regulation; D006579:Heterozygote; D006801:Humans; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000235:genetics*; D054086:KATP Channels / Q000502:physiology*; D008274:Magnesium / Q000502:physiology; D009154:Mutation; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000502:physiology; D011955:Receptors, Drug / Q000235:genetics*; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel
D018528:ATP-Binding Cassette Transporters; D054086:KATP Channels; D008274:Magnesium; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors; D000099161:Kcnj11 Channel; C577507:ABCC8 protein, human
Neuron. 1999 Mar;22(3):537-48
10197533
Nature. 2006 Mar 23;440(7083):470-6
16554807
J Physiol. 1997 Oct 1;504 ( Pt 1):35-45
9350615
J Mol Cell Cardiol. 2005 Jul;39(1):79-98
15978905
EMBO J. 2003 Aug 1;22(15):3833-43
12881418
J Clin Invest. 2000 Oct;106(7):897-906
11018078
Diabetes. 2007 May;56(5):1357-62
17317760
Am J Physiol Endocrinol Metab. 2007 Oct;293(4):E880-9
17652156
J Biol Chem. 2003 Oct 24;278(43):41577-80
12941953
Endocr Rev. 1999 Apr;20(2):101-35
10204114
J Clin Invest. 2008 Aug;118(8):2877-86
18596924
Am J Hum Genet. 2007 Aug;81(2):375-82
17668386
Diabetes. 2007 Jul;56(7):1930-7
17446535
Diabetes. 2007 Jun;56(6):1737-41
17389331
Proc Natl Acad Sci U S A. 2001 Feb 27;98(5):2882-7
11226335
J Biol Chem. 2009 Mar 20;284(12):7951-9
19151370
Diabetes. 2005 Sep;54(9):2645-54
16123353
Diabetes. 2007 Sep;56(9):2339-48
17575084
Hum Mutat. 2009 Feb;30(2):170-80
18767144
Diabetes. 2006 Jun;55(6):1738-46
16731837