Human ether-a-go-go-related gene mutation L539fs/47-hERG leads to cell apoptosis through the endoplasmic reticulum stress pathway

Abstract

Congenital long QT syndrome (LQTS) is a cardiac channelopathy that often results in fatal arrhythmias. LQTS mutations not only lead to abnormal myocardial electrical activities but are associated with heart contraction abnormalities, cardiomyopathy and congenital heart defects. In vivo and in vitro studies have found that LQTS mutations are associated with cardiomyocyte apoptosis, cardiac developmental disorders and even embryonic mortality. Cardiac delayed rectifier potassium channel dysfunction due to the human ether-a-go-go-related gene (hERG) mutation causes congenital LQTS type 2. The majority of LQTS 2 mutations are characterized by mutant protein accumulation in the endoplasmic reticulum (ER). Unfolded or misfolded protein retention in the ER causes an unfolded protein reaction, which is characteristic of ER stress (ERS). Therefore, the present study hypothesized that LQTS mutations can cause cardiac structural abnormalities via ERS-mediated cardiomyocyte apoptosis. To test this hypothesis, 293 cells were transiently transfected with an L539fs/47-hERG plasmid to generate an LQTS 2 model. L539fs/47-hERG is an LQTS 2 mutation, which consists of a 19-bp deletion at 1619-1637 and a point mutation at 1692. Using confocal laser scanning microscopy analysis, it was verified that the L539fs/47-hERG protein was retained in the ER. Hoechst 33342 apoptosis staining indicated that apoptosis was increased in the L539fs/47-hERG-transfected cells, and this be reversed by treatment with 4-phenyl butyric acid. Western blot analysis revealed increased expression levels of the ERS chaperone glucose regulated protein 78 and pro-apoptotic ERS-induced factors, including protein kinase R-like endoplasmic reticulum kinase, eukaryotic translation-initiation factor-2α and C/EBP homologous protein, in the L539fs/47-hERG-transfected cells. The B-cell lymphoma (Bcl-2)-associated X protein/Bcl-2 ratio and caspase-12 were also increased in the mutated cells. These results demonstrate that L539fs/47-hERG induces cell apoptosis and the potential molecular mechanism involves the activation of ERS and ERS-mediated cell apoptosis.