Basolateral localisation of KCNQ1 potassium channels in MDCK cells: molecular identification of an N-terminal targeting motif

Abstract

KCNQ1 potassium channels are expressed in many epithelial tissues as well as in the heart. In epithelia KCNQ1 channels play an important role in salt and water transport and the channel has been reported to be located apically in some cell types and basolaterally in others. Here we show that KCNQ1 channels are located basolaterally when expressed in polarised MDCK cells. The basolateral localisation of KCNQ1 is not affected by co-expression of any of the five KCNE β-subunits. We characterise two independent basolateral sorting signals present in the N-terminal tail of KCNQ1. Mutation of the tyrosine residue at position 51 resulted in a non-polarized steady-state distribution of the channel. The importance of tyrosine 51 in basolateral localisation was emphasized by the fact that a short peptide comprising this tyrosine was able to redirect the p75 neurotrophin receptor, an otherwise apically located protein, to the basolateral plasma membrane. Furthermore, a di-leucine-like motif at residues 38-40 (LEL) was found to affect the basolateral localisation of KCNQ1. Mutation of these two leucines resulted in a primarily intracellular localisation of the channel.

Low Incidence of Sudden Cardiac Death in a Swedish Y111C Type 1 Long-QT syndrome Population

“…17 None of the 80 individuals in the study population experienced SCD during the mean follow-up time of 28Ϯ20 years, with a mean of 25Ϯ20 years before the initiation of therapy. This finding is unexpected because the specific Y111C-KCNQ1 mutation has been shown to result in structural and functional effects on the K s channel leading to a severely reduced inward potassium current over the cell membrane in vitro, 9,10 characteristics that suggest a highly malignant mutation.…”

“…9,10 The point mutation (c.332AϾG) leading to an amino acid substitution (Y111C) alters a motif in the N-terminal protein that plays a key role in the trafficking of the K s channel. This alteration results in intracellular retention of the channel that renders it inactive.…”

“…High-risk mutations have been identified within the LQT1 subgroup. [7][8][9][10][11] The Y111C-KCNQ1 (c.332AϾG) mutation has previously been described in 1 patient, a 36-year-old woman, who presented with syncope at the age of 3 years. 3 She experienced Ͼ30 syncopal episodes triggered by emotional or physical stress and had a QT interval, corrected for heart rate, of 520 ms. Electrophysiological studies subsequently demonstrated that the Y111C mutation causes intracellular sequestration of mutated ion channels in the endoplasmic reticulum that renders them inactive.…”

“…3 She experienced Ͼ30 syncopal episodes triggered by emotional or physical stress and had a QT interval, corrected for heart rate, of 520 ms. Electrophysiological studies subsequently demonstrated that the Y111C mutation causes intracellular sequestration of mutated ion channels in the endoplasmic reticulum that renders them inactive. 9 Moreover, the mutation exerts a strong dominantnegative effect on the coexpressed wild-type ion channels encoded by the unaffected allele, 10 leading to a severely reduced inward potassium current in vitro. 9,10 We have observed several Swedish families sharing the same Y111C-KCNQ1 mutation, expressing an apparent benign clinical phenotype.…”

“…9 Moreover, the mutation exerts a strong dominantnegative effect on the coexpressed wild-type ion channels encoded by the unaffected allele, 10 leading to a severely reduced inward potassium current in vitro. 9,10 We have observed several Swedish families sharing the same Y111C-KCNQ1 mutation, expressing an apparent benign clinical phenotype. In this study, we describe the phenotype of a Swedish Y111C population with a focus on life-threatening cardiac events.…”