Association of the P441L KCNQ1 variant with severity of long QT syndrome and risk of cardiac events

Figures

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  FIGURE 1. Characterization of long QT syndrome type 1 in a patient with the P441L variant of KCNQ1 (potassium voltage-gated channel, subfamily Q member 1). (A) Patient electrocardiogram showing the corrected QT interval (QTc) interval is prolonged to 797 ms. (B) Sanger sequencing data showing the novel KCNQ1 mutation of C1322T in the P441L variant. Sequence analysis of genomic KCNQ1 obtained from the blood of the patient reveals a heterozygote missense mutation (C→T) at position 1322 of the KCNQ1 coding region (C1322T). (C) Schematic representation of KCNQ1 protein with the P441L variant; proline is replaced by leucine at position 441 of the cytoplasmic C-terminal domain (P441L). Created with BioRender.com. (D) Partial amino acid sequences of different species KCNQ1 homologs aligned at the position corresponding to tyrosine 441 of human KCNQ1 (arrow). Number, the position of the last amino acid of each partial sequence. The conserved motif is outlined in black.

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  FIGURE 2. KCNQ1 P441L variant protein trafficking in the absence or presence of KCNE1 (potassium voltage-gated channel subfamily E regulatory subunit 1), and the interaction between the KCNQ1 P441L variant and KCNE1 proteins. (A–C) Representative confocal microscopy images and line plots showing the cellular distribution of wild-type and P441L variant KCNQ1 proteins in HEK293 cells. Scale bar, 10 μm. KCNQ1 was tagged with EGFP at the N-terminus and thus is shown as green fluorescence. Red fluorescence indicates the endoplasmic reticulum (ER); blue fluorescence, 4′,6-diamidino-2-phenylindole (DAPI), indicates cell nuclei. Line plots in panel (C) represent profiles plotted from left to right (L–R) to display the relative red and green fluorescence intensities obtained at the orange lines shown in the merged images. (D) Representative Western blot images showing fractionation assay results indicating that compared with the wild-type KCNQ1-EGFP (WT) protein level, the P441L-EGFP (P441L) protein level is significantly lower in the cell membrane but significantly increased in the cytoplasm. (E–G) Representative confocal microscopy images and line plots showing the cellular distribution of WT and…

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  FIGURE 3. Properties of KCNQ1 and P441L mutant whole-cell currents in HEK293 cells. (A) The 4-s test pulse voltage protocol (top) and representative current traces from HEK293 cells expressing empty vectors, KCNQ1-EGFP, or P441L-EGFP. (B) Summary data showing whole-cell current–voltage relationships of HEK293 cells expressing empty vectors, KCNQ1-EGFP, or P441L-EGFP. Data are shown as the mean ± SEM, n = 6, *P < 0.05 vs. KCNQ1-EGFP. (C) Representative current traces from HEK293 cells co-expressing KCNQ1-EGFP/KCNE1-mCherry or P441L-EGFP/KCNE1-mCherry. (D) Summary data showing whole-cell current–voltage relationships of HEK293 cells expressing empty vector, KCNQ1-EGFP/KCNE1-mCherry, or P441L-EGFP/KCNE1-mCherry. Data are shown as the mean ± SEM, n = 6, *P < 0.05 KCNQ1-EGFP/KCNE1-mCherry vs. P441L-EGFP/KCNE1-mCherry; #P < 0.05 Empty vector vs. P441L-EGFP/KCNE1-mCherry.