Cellular Mechanism for the Pharmacological Correction of hERG Mutations Linked to the Long QT Syndrome

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The human Ether-a-go-go Related Gene (hERG) encodes Kv11.1 and underlies the rapidly activating delayed rectifier K+ current in the heart, and loss-of-function hERG mutations cause the type 2 long QT syndrome (LQT2). The majority of LQT2-linked missense mutations decrease the trafficking of Kv11.1. An important finding is drugs that bind to Kv11.1 and block current (IKv11.1) can correct the trafficking for most of these mutations (pharmacological correction). We tested the hypothesis that pharmacological correction increases the trafficking of mutant LQT2 channels from the Endoplasmic Reticulum (ER). Voltage-clamping and Western blotting experiments of HEK293 cells expressing the trafficking-deficient LQT2 mutation G601S showed that pharmacological correction still occurred in cells treated with the protein synthesis inhibitor cycloheximide. Confocal analyses of HEK293 cells stably expressing wild type Kv11.1 or G601S showed that G601S is selectively stored in an intermediate ER compartment with BAP31. The intermediate BAP31 compartment does not overlap with the perinuclear ER compartment, transitional ER compartment, or the ER Golgi Intermediate Compartment. Treating cells in E-4031, a drug that corrects G601S trafficking, decreased G601S co-localization with intermediate BAP31 compartment and increased G601S immunostaining at the cell surface membrane. Additional experiments showed that treating cell in E-4031 for as little as 30 min was sufficient to caused the pharmacological correction of IKv11.1 for many hours. Together these data demonstrate that a steady-state subpopulation of LQT2 channels is stored separately in the BAP31 transitional ER compartment and their functional expression is readily corrected by E-4031 treatment.