Long QT syndrome-associated I593R mutation in HERG potassium channel activates ER stress pathways

Hereditary long QT syndrome is a fatal arrhythmia associated with gene mutations in potassium and sodium channels that are expressed in ventricle. By employing heterologous expression and making comparisons to cells expressing wild-type human-ether-a-go-go-related protein (HERG), a potassium channel that contributes to I(Kr) current in ventricular cardiomyocytes, we demonstrate activation of an elevated endoplasmic reticulum (ER) stress response by the mutant I593R HERG potassium channel implicated in long QT syndrome type 2. I593R HERG is trafficking-impaired and forms Triton-insoluble aggregates. Expression of I593R HERG activates the unfolded protein response pathway and, separately, NF-kappaB signaling. ATF6, the activating transcription factor of the unfolded protein response pathway, is processed into the active transcription factor in the cells expressing I593R HERG. Consistent with ATF6 activation, the ER chaperones/calcium-binding proteins Grp78, Grp94, and calreticulin are elevated in I593R HERG-expressing cells. Coexpression of I593R HERG with wild-type HERG also results in ER stress pathway activation. By eliciting downstream links in signal transduction pathways associated with ER stress, expression of mutant trafficking impaired ion channels may contribute to disease etiology mechanisms that augment those associated with attenuated ion flux.