Classification and rescue of ROMK mutations underlying hyperprostaglandin E syndrome/antenatal Bartter syndrome.
BACKGROUND
Mutations in the renal K+ channel ROMK (Kir 1.1) cause hyperprostaglandin E syndrome/antenatal Bartter syndrome (HPS/aBS), a severe tubular disorder leading to renal salt and water wasting. Several studies confirmed the predominance of alterations of current properties in ROMK mutants. However, in most of these studies, analysis was restricted to nonmammalian cells and electrophysiologic methods. Therefore, for the majority of ROMK mutations, disturbances in protein trafficking remained unclear. The aim of the present study was the evaluation of different pathogenic mechanisms of 20 naturally occurring ROMK mutations with consecutive classification into mutational classes and identification of distinct rescue mechanisms according to the underlying defect.


METHODS
Mutated ROMK potassium channels were expressed in Xenopus oocytes and a human kidney cell line and analyzed by two electrode voltage clamp analysis, immunofluorescence, and Western blot analysis.


RESULTS
We identified 14 out of 20 ROMK mutations that did not reach the cell surface, indicating defective membrane trafficking. High expression levels rescued six out of 14 ROMK mutants, leading to significant K+ currents. In addition, two early inframe stop mutations could be rescued by aminoglycosides, resulting in full-length ROMK and correct trafficking to the plasma membrane in a subset of transfected cells.


CONCLUSIONS
In contrast to previous reports, most of the investigated ROMK mutations displayed a trafficking defect that might be rescued by pharmacologic agents acting as molecular chaperones. The evaluation of different disease-causing mechanisms will be essential for establishing new and more specific therapeutic strategies for HPS/aBS patients.
Peters
Melanie
M
Department of Pediatrics, Philipps University Marburg, Marburg, Germany.
Ermert
Saskia
S
Jeck
Nikola
N
Derst
Christian
C
Pechmann
Ulla
U
Weber
Stefanie
S
Schlingmann
Karl P
KP
Seyberth
Hannsjoerg W
HW
Waldegger
Siegfried
S
Konrad
Martin
M
D000818:Animals; D001477:Bartter Syndrome / Q000235:genetics*; D002460:Cell Line; D018388:Codon, Terminator; D004252:DNA Mutational Analysis; D004594:Electrophysiology; D005315:Fetal Diseases / Q000235:genetics*; D005839:Gentamicins / Q000494:pharmacology; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D009154:Mutation; D009865:Oocytes / Q000378:metabolism; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D011458:Prostaglandins E / Q000378:metabolism*; D051381:Rats; D013194:Staining and Labeling; D013577:Syndrome; D014981:Xenopus
D018388:Codon, Terminator; D005839:Gentamicins; C086989:KCNJ1 protein, human; C510692:Kcnj1 protein, rat; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D011458:Prostaglandins E