Department of Genetic Medicine and Regenerative Therapeutics, Institute of Regenerative Medicine and Biofunction, Tottori University, Japan.
Circ Res. 2011 Feb 18;108(4):458-68. doi: 10.1161/CIRCRESAHA.110.227835. Epub 2010 Dec 23.
The human ether-a-go-go-related gene (hERG) encodes the α subunit of the potassium current I(Kr). It is highly expressed in cardiomyocytes and its mutations cause long QT syndrome type 2. Heat shock protein (Hsp)70 is known to promote maturation of hERG. Hsp70 and heat shock cognate (Hsc70) 70 has been suggested to play a similar function. However, Hsc70 has recently been reported to counteract Hsp70.
We investigated whether Hsc70 counteracts Hsp70 in the control of wild-type and mutant hERG stability.
Coexpression of Hsp70 with hERG in HEK293 cells suppressed hERG ubiquitination and increased the levels of both immature and mature forms of hERG. Immunocytochemistry revealed increased levels of hERG in the endoplasmic reticulum and on the cell surface. Electrophysiological studies showed increased I(Kr). All these effects of Hsp70 were abolished by Hsc70 coexpression. Heat shock treatment of HL-1 mouse cardiomyocytes induced endogenous Hsp70, switched mouse ERG associated with Hsc70 to Hsp70, increased I(Kr), and shortened action potential duration. Channels with disease-causing missense mutations in intracellular domains had a higher binding capacity to Hsc70 than wild-type channels and channels with mutations in the pore region. Knockdown of Hsc70 by small interfering RNA or heat shock prevented degradation of mutant hERG proteins with mutations in intracellular domains.
These results indicate reciprocal control of hERG stability by Hsp70 and Hsc70. Hsc70 is a potential target in the treatment of LQT2 resulting from missense hERG mutations.
人类 ether-a-go-go 相关基因（hERG）编码钾电流 I（Kr）的α亚基。它在心肌细胞中高度表达，其突变可导致长 QT 综合征 2 型。热休克蛋白（Hsp）70 已知可促进 hERG 的成熟。热休克同源物（Hsc70）70 已被证明具有类似的功能。然而，最近有报道称 Hsc70 可拮抗 Hsp70。
我们研究了 Hsc70 是否在控制野生型和突变型 hERG 稳定性方面拮抗 Hsp70。
在 HEK293 细胞中，hERG 与 Hsp70 的共表达抑制了 hERG 的泛素化，并增加了 hERG 的未成熟和成熟形式的水平。免疫细胞化学显示 hERG 在内质网和细胞表面的水平增加。电生理研究显示 I（Kr）增加。Hsc70 的共表达消除了 Hsp70 的所有这些作用。HL-1 小鼠心肌细胞的热休克处理诱导内源性 Hsp70，将与 Hsc70 相关的小鼠 ERG 切换到 Hsp70，增加 I（Kr），并缩短动作电位持续时间。与细胞内结构域的致病错义突变相关的通道与野生型通道和孔区突变的通道相比，具有更高的与 Hsc70 的结合能力。通过小干扰 RNA 或热休克敲低 Hsc70 可防止具有细胞内结构域突变的突变型 hERG 蛋白降解。
这些结果表明 hERG 稳定性受 Hsp70 和 Hsc70 的相互控制。Hsc70 是治疗由 hERG 错义突变引起的 LQT2 的潜在靶点。
