Functional analysis of novel KCNQ2 mutations found in patients with Benign Familial Neonatal Convulsions.
Benign Familial Neonatal Convulsions (BFNC) are a rare epilepsy disorder with an autosomal-dominant inheritance. It is linked to mutations in the potassium channel genes KCNQ2 and KCNQ3. These encode for Kv7.2 and Kv7.3 potassium ion channels, which produce an M-current that regulates the potential firing action in neurons through modulation of the membrane potential. We report on the biophysical and biochemical properties of V589X, T359K and P410fs12X mutant-KCNQ2 ion channels that were detected in three BFNC families. Mutant KCNQ2 cDNAs were co-expressed with WT-KCNQ2 and KCNQ3 cDNAs in HEK293 cells to mimic heterozygous expression of the KCNQ2 mutations in BFNC patients. The resulting potassium currents were measured using patch-clamp techniques and showed an approximately 75% reduction in current and a depolarized shift in the voltage dependence of activation. Furthermore, the time-constant of activation of M-currents in cells expressing T359K and P410fs12X was slower compared to cells expressing only wild-type proteins. Immunofluorescent labeling of HEK293 cells stably expressing GFP-tagged KCNQ2-WT or mutant alpha-subunits indicated cell surface expression of WT, V589X and T359K mutants, suggesting a loss-of-function, while P410fs12X was predominantly retained in the ER and sub-cellular compartments outside the ER suggesting an effectively haplo-insufficient effect.
Volkers
Linda
L
Complex Genetics Section, DBG-Department of Medical Genetics, University Medical Center Utrecht, The Netherlands.
Rook
Martin B
MB
Das
Joost H G
JH
Verbeek
Nienke E
NE
Groenewegen
W Antoinette
WA
van Kempen
Marjan J A
MJ
Lindhout
Dick
D
Koeleman
Bobby P C
BP
D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D020936:Epilepsy, Benign Neonatal / Q000235:genetics*; D005190:Family; D005260:Female; D005455:Fluorescent Antibody Technique; D049452:Green Fluorescent Proteins; D006801:Humans; D051658:KCNQ2 Potassium Channel / Q000235:genetics* / Q000378:metabolism*; D051659:KCNQ3 Potassium Channel / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D009154:Mutation; D020125:Mutation, Missense; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
D051658:KCNQ2 Potassium Channel; C496914:KCNQ2 protein, human; D051659:KCNQ3 Potassium Channel; C496916:KCNQ3 protein, human; D049452:Green Fluorescent Proteins; D011188:Potassium