A mutation in the TMD0-L0 region of sulfonylurea receptor-1 (L225P) causes permanent neonatal diabetes mellitus (PNDM).
OBJECTIVE
We sought to examine the molecular mechanisms underlying permanenent neonatal diabetes mellitus (PNDM) in a patient with a heterozygous de novo L225P mutation in the L0 region of the sulfonylurea receptor (SUR)1, the regulatory subunit of the pancreatic ATP-sensitive K(+) channel (K(ATP) channel).


METHODS
The effects of L225P on the properties of recombinant K(ATP) channels in transfected COS cells were assessed by patch-clamp experiments on excised membrane patches and by macroscopic Rb-flux experiments in intact cells.


RESULTS
L225P-containing K(ATP) channels were significantly more active in the intact cell than in wild-type channels. In excised membrane patches, L225P increased channel sensitivity to stimulatory Mg nucleotides without altering intrinsic gating or channel inhibition by ATP in the absence of Mg(2+). The effects of L225P were abolished by SUR1 mutations that prevent nucleotide hydrolysis at the nucleotide binding folds. L225P did not alter channel inhibition by sulfonylurea drugs, and, consistent with this, the patient responded to treatment with oral sulfonylureas.


CONCLUSIONS
L225P underlies K(ATP) channel overactivity and PNDM by specifically increasing Mg-nucleotide stimulation of the channel, consistent with recent reports of mechanistically similar PNDM-causing mutations in SUR1. The mutation does not affect sulfonylurea sensitivity, and the patient is successfully treated with sulfonylureas.
Masia
Ricard
R
Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, MO 63110, USA.
De Leon
Diva D
DD
MacMullen
Courtney
C
McKnight
Heather
H
Stanley
Charles A
CA
Nichols
Colin G
CG
D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000502:physiology; D019943:Amino Acid Substitution; D000818:Animals; D019556:COS Cells; D002522:Chlorocebus aethiops; D003922:Diabetes Mellitus, Type 1 / Q000235:genetics* / Q000503:physiopathology; D004594:Electrophysiology; D005091:Exons; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D020641:Polymorphism, Single Nucleotide; D015221:Potassium Channels / Q000235:genetics* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying / Q000235:genetics* / Q000502:physiology; D011955:Receptors, Drug / Q000235:genetics* / Q000502:physiology; D064233:Sulfonylurea Receptors; D014162:Transfection
C577507:ABCC8 protein, human; D018528:ATP-Binding Cassette Transporters; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011955:Receptors, Drug; D064233:Sulfonylurea Receptors