Sanchez-Conde, F. G. | Search bioRxiv

bioRxiv2025

Sudden Death-Associated KCNH2 Variants Have Opposing Effects on hERG1NP Function

hERG1NP is a non-conducting subdomain of the full-length hERG1 channel that is expressed in the nuclei of developing cardiomyocytes. From the nucleus, hERG1NP modulates gating and expression of the full-length hERG1 channel. hERG1NP variants are linked with sudden death in the young, but the impact of these variants on hERG1NP activity has not been studied. To determine the effect of hERG1NP variants on hERG1NP activity, we measured hERG1NP intracellular localization and modulation of membrane current from the full-length hERG1a channel in HEK293 cells. The wildtype hERG1NP suppressed both hERG1a current (IhERG) and protein. We then screened six hERG1NP variants for changes in either intracellular targeting or modulation of hERG1a current. Two variants, R885C and R1047L, disrupted hERG1NP activity by altering nuclear transport or abolishing both IhERG current suppression and nuclear targeting, respectively. Two additional variants, G1036D and Q1068R, enhanced hERG1NP activity by depolarizing hERG1as voltage dependence of activation via accelerated channel deactivation and recovery from inactivation. Lastly, two variants had no effect: R1035W and R1069S. This work demonstrates that hERG1NP variants associated with sudden death in the young can trigger both loss-of-function and gain-of-function effects on hERG1NP. Additional work is needed to identify specific pathogenic mechanisms of hERG1NP variants.

cell biology↗

bioRxiv2022

KCNH2 encodes a nuclear-targeted polypeptide that mediates hERG1 channel gating and expression

KCNH2 encodes hERG1, the voltage-gated potassium channel that conducts the rapid delayed rectifier potassium current (IKr) in human cardiac tissue. hERG1 is one of the first channels expressed during early cardiac development, and its dysfunction is associated with intrauterine fetal death, sudden infant death syndrome, cardiac arrhythmia, and sudden cardiac death. Here, we identified a novel hERG1 polypeptide (hERG1NP) that is targeted to the nuclei of immature cardiac cells, including hiPSC-CMs and neonatal rat cardiomyocytes. The nuclear hERG1NP immunofluorescent signal is diminished in matured hiPSC-CMs and absent from adult rat cardiomyocytes. Antibodies targeting distinct hERG1 channel epitopes demonstrated that the hERG1NP signal maps to the hERG1 distal C-terminal domain. KCNH2 deletion using CRISPR simultaneously abolished IKr and the hERG1NP signal in hiPSC-CMs. We then identified a putative nuclear localization sequence (NLS) within the distal hERG1 C-terminus, 883-RQRKRKLSFR-892. Interestingly, the distal C-terminal domain was targeted almost exclusively to the nuclei when overexpressed HEK293 cells. Conversely, deleting the NLS from the distal peptide abolished nuclear targeting. Similarly, blocking or {beta}1 karyopherin activity diminished nuclear targeting. Finally, overexpressing the putative hERG1NP peptide in the nuclei of HEK cells significantly reduced hERG1a current density, compared to cells expressing the NLS-deficient hERG1NP or GFP. These data identify a developmentally regulated polypeptide encoded by KCNH2, hERG1NP, whose presence in the nucleus indirectly modulates hERG1 current magnitude and kinetics.

cell biology↗