An LQT mutant minK alters KvLQT1 trafficking.
Cardiac I(Ks), the slowly activated delayed-rectifier K(+) current, is produced by the protein complex composed of alpha- and beta-subunits: KvLQT1 and minK. Mutations of genes encoding KvLQT1 and minK are responsible for the hereditary long QT syndrome (loci LQT1 and LQT5, respectively). MinK-L51H fails to traffic to the cell surface, thereby failing to produce effective I(Ks). We examined the effects that minK-L51H and an endoplasmic reticulum (ER)-targeted minK (minK-ER) exerted over the electrophysiology and biosynthesis of coexpressed KvLQT1. Both minK-L51H and minK-ER were sequestered primarily in the ER as confirmed by lack of plasma membrane expression. Glycosylation and immunofluorescence patterns of minK-L51H were qualitatively different for minK-ER, suggesting differences in trafficking. Cotransfection with the minK mutants resulted in reduced surface expression of KvLQT1 as assayed by whole cell voltage clamp and immunofluorescence. MinK-L51H reduced current amplitude by 91% compared with wild-type (WT) minK/KvLQT1, and the residual current was identical to KvLQT1 without minK. The phenotype of minK-L51H on I(Ks) was not dominant because coexpressed WT minK rescued the current and surface expression. Collectively, our data suggest that ER quality control prevents minK-L51H/KvLQT1 complexes from trafficking to the plasma membrane, resulting in decreased I(Ks). This is the first demonstration that a minK LQT mutation is capable of conferring trafficking defects onto its associated alpha-subunit.
Krumerman
Andrew
A
Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
Gao
Xiaohong
X
Bian
Jin-Song
JS
Melman
Yonathan F
YF
Kagan
Anna
A
McDonald
Thomas V
TV
D000818:Animals; D016466:CHO Cells; D002451:Cell Compartmentation / Q000235:genetics; D002462:Cell Membrane / Q000378:metabolism*; D006224:Cricetinae; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D006352:Heart Ventricles / Q000378:metabolism / Q000503:physiopathology; D006801:Humans; D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; D008133:Long QT Syndrome / Q000235:genetics* / Q000378:metabolism / Q000503:physiopathology; D008564:Membrane Potentials / Q000235:genetics; D009154:Mutation / Q000235:genetics; D032383:Myocytes, Cardiac / Q000378:metabolism; D018408:Patch-Clamp Techniques; D015221:Potassium Channels / Q000235:genetics* / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated; D011485:Protein Binding / Q000235:genetics; D021381:Protein Transport / Q000235:genetics
D051656:KCNQ Potassium Channels; D051657:KCNQ1 Potassium Channel; C496909:KCNQ1 protein, human; D015221:Potassium Channels; D024642:Potassium Channels, Voltage-Gated