Department of Physiology, University of Kentucky, Lexington, Kentucky, USA.
Am J Physiol Cell Physiol. 2011 Jul;301(1):C75-85. doi: 10.1152/ajpcell.00494.2010. Epub 2011 Apr 13.
The human ether-a-go-go related gene (hERG) encodes the voltage-gated K(+) channel that underlies the rapidly activating delayed-rectifier current in cardiac myocytes. hERG is synthesized in the endoplasmic reticulum (ER) as an "immature" N-linked glycoprotein and is terminally glycosylated in the Golgi apparatus. Most hERG missense mutations linked to long QT syndrome type 2 (LQT2) reduce the terminal glycosylation and functional expression. We tested the hypothesis that a distinct pre-Golgi compartment negatively regulates the trafficking of some LQT2 mutations to the Golgi apparatus. We found that treating cells in nocodazole, a microtubule depolymerizing agent, altered the subcellular localization, functional expression, and glycosylation of the LQT2 mutation G601S-hERG differently from wild-type hERG (WT-hERG). G601S-hERG quickly redistributed to peripheral compartments that partially colocalized with KDEL (Lys-Asp-Glu-Leu) chaperones but not calnexin, Sec31, or the ER golgi intermediate compartment (ERGIC). Treating cells in E-4031, a drug that increases the functional expression of G601S-hERG, prevented the accumulation of G601S-hERG to the peripheral compartments and increased G601S-hERG colocalization with the ERGIC. Coexpressing the temperature-sensitive mutant G protein from vesicular stomatitis virus, a mutant N-linked glycoprotein that is retained in the ER, showed it was not restricted to the same peripheral compartments as G601S-hERG at nonpermissive temperatures. We conclude that the trafficking of G601S-hERG is negatively regulated by a microtubule-dependent compartment within the ER. Identifying mechanisms that prevent the sorting or promote the release of LQT2 channels from this compartment may represent a novel therapeutic strategy for LQT2.
人类 ether-a-go-go 相关基因（hERG）编码电压门控 K(+)通道，该通道是心肌细胞中快速激活的延迟整流电流的基础。hERG 在粗面内质网（ER）中作为一种“不成熟”的 N 连接糖蛋白合成，并在高尔基器中进行末端糖基化。大多数与长 QT 综合征 2 型（LQT2）相关的 hERG 错义突变会降低末端糖基化和功能表达。我们测试了这样一个假设，即一个独特的高尔基器前区室负调控某些 LQT2 突变向高尔基器的运输。我们发现，用微管解聚剂 nocodazole 处理细胞会改变 LQT2 突变 G601S-hERG 的亚细胞定位、功能表达和糖基化，与野生型 hERG（WT-hERG）不同。G601S-hERG 迅速重新分布到外周区室，这些区室部分与 KDEL（赖氨酰-天冬氨酰-谷氨酸-亮氨酸）伴侣共定位，但不与 calnexin、Sec31 或内质网高尔基中间区室（ERGIC）共定位。用 E-4031 处理细胞，一种增加 G601S-hERG 功能表达的药物，可防止 G601S-hERG 积累到外周区室，并增加 G601S-hERG 与 ERGIC 的共定位。共表达水疱性口炎病毒的温度敏感型 G 蛋白突变体，一种在 ER 中保留的突变 N 连接糖蛋白，表明它在非允许温度下不局限于与 G601S-hERG 相同的外周区室。我们得出结论，G601S-hERG 的运输受到 ER 中一个微管依赖性区室的负调控。鉴定防止 LQT2 通道从该区室分拣或促进其释放的机制可能代表 LQT2 的一种新的治疗策略。
