title: KCNJ10 mutations display differential sensitivity to heteromerisation with KCNJ16.
abstract: OBJECTIVE
  Mutations in the inwardly-rectifying K(+)-channel KCNJ10/Kir4.1 cause autosomal recessive EAST syndrome (epilepsy, ataxia, sensorineural deafness and tubulopathy). KCNJ10 is expressed in the distal convoluted tubule of the kidney, stria vascularis of the inner ear and brain glial cells. Patients diagnosed clinically with EAST syndrome were genotyped and mutations in KCNJ10 were studied functionally.
  
  
  METHODS
  Patient DNA was amplified and sequenced, and new mutations were identified. Mutant and wild-type KCNJ10 constructs were cloned and heterologously expressed in Xenopus oocytes. Whole-cell K(+) currents were measured by 2-electrode voltage clamping and channel expression was analysed by Western blotting.
  
  
  RESULTS
  We identified 3 homozygous mutations in KCNJ10 (p.F75C, p.A167V and p.V91fs197X), with mutation p.A167V previously reported in a compound heterozygous state. Oocytes expressing wild-type human KCNJ10 showed inwardly rectified currents, which were significantly reduced in all of the mutants (p < 0.001). Specific inhibition of KCNJ10 currents by Ba(2+) demonstrated a large residual function in p.A167V only, which was not compatible with causing disease. However, co-expression with KCNJ16 abolished function in these heteromeric channels almost completely.
  
  
  CONCLUSIONS
  This study provides an explanation for the pathophysiology of the p.A167V KCNJ10 mutation, which had previously not been considered pathogenic on its own. These findings provide evidence for the functional cooperation of KCNJ10 and KCNJ16. Thus, in vitro ascertainment of KCNJ10 function may necessitate co-expression with KCNJ16.
authors.affiliation: Department of Neuroscience, Physiology and Pharmacology, University College London, London, UK.
authors.forename: Sophie
authors.initials: S
authors.lastname: Parrock
authors.forename: Sofia
authors.initials: S
authors.lastname: Hussain
authors.forename: Naomi
authors.initials: N
authors.lastname: Issler
authors.forename: Ann-Marie
authors.initials: AM
authors.lastname: Differ
authors.forename: Nicholas
authors.initials: N
authors.lastname: Lench
authors.forename: Stefano
authors.initials: S
authors.lastname: Guarino
authors.forename: Michiel J S
authors.initials: MJ
authors.lastname: Oosterveld
authors.forename: Mandy
authors.initials: M
authors.lastname: Keijzer-Veen
authors.forename: Eva
authors.initials: E
authors.lastname: Brilstra
authors.forename: Hester
authors.initials: H
authors.lastname: van Wieringen
authors.forename: A Yvette
authors.initials: AY
authors.lastname: Konijnenberg
authors.forename: Sarah
authors.initials: S
authors.lastname: Amin-Rasip
authors.forename: Simona
authors.initials: S
authors.lastname: Dumitriu
authors.forename: Enriko
authors.initials: E
authors.lastname: Klootwijk
authors.forename: Nine
authors.initials: N
authors.lastname: Knoers
authors.forename: Detlef
authors.initials: D
authors.lastname: Bockenhauer
authors.forename: Robert
authors.initials: R
authors.lastname: Kleta
authors.forename: Anselm A
authors.initials: AA
authors.lastname: Zdebik
mesh_terms: D000409:Alanine / Q000235:genetics; D000818:Animals; D005260:Female; D005838:Genotype; D006319:Hearing Loss, Sensorineural / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D008607:Intellectual Disability / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D009865:Oocytes / Q000378:metabolism; D018408:Patch-Clamp Techniques; D017354:Point Mutation; D024661:Potassium Channels, Inwardly Rectifying / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D055503:Protein Multimerization; D012640:Seizures / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D017422:Sequence Analysis, DNA; D014633:Valine / Q000235:genetics; D014981:Xenopus; D000098854:Kcnj10 Channel; D000097062:Kir5.1 Channel
chemical_list: D000409:Alanine; D024661:Potassium Channels, Inwardly Rectifying; D014633:Valine; D000098854:Kcnj10 Channel; C576242:KCNJ16 protein, human; D000097062:Kir5.1 Channel