Transmembrane protein 168 mutation reduces cardiomyocyte cell surface expression of Nav1.5 through αB-crystallin intracellular dynamics
Transmembrane protein 168 mutation reduces cardiomyocyte cell surface expression of Nav1.5 through αB-crystallin intracellular dynamics
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跨膜蛋白168突变通过αB-晶状体蛋白细胞内动力学降低心肌细胞表面Nav1.5的表达
作者：
Nguyen LKC;Shimizu A;Soh JEC;Komeno M;Sato A;Ogita H
发现跨膜蛋白168（TMEM 168）定位于核膜上。在Brugada综合征患者中发现了TMEM 168的杂合突变（c.1616G>A，p.R539Q）。该突变通过Nedd 4 -2 E3遍在蛋白连接酶诱导的遍在蛋白化和降解来减少心肌细胞钠通道Nav1.5的表达。然而，TMEM 168突变体引起的详细分子机制仍不清楚。在这里，我们证明了小的热休克蛋白α B-晶状体蛋白，它可以结合到Nav1.5和Nedd 4 -2，并干扰这两种蛋白质的协会，强烈地从细胞表面募集到核周区，因为α B-晶状体蛋白与TMEM 168突变体的亲和力比野生型TMEM 168高得多。在HL-1心肌细胞中敲低α B-晶状体蛋白后，尽管Nav1.5的表达减少，但Nav1.5与Nedd 4 -2的相互作用增加。此外，在蛋白酶体抑制剂MG-132的存在下，α B-晶状体蛋白敲低导致的Nav1.5表达的减少被挽救，这表明α B-晶状体蛋白调节的泛素-蛋白酶体系统对于Nav1.5表达的稳定性的重要性。总的来说，Nav1.5、Nedd 4 -2和α B-晶状体蛋白之间分子相互作用的平衡在Nav1.5的心肌细胞表面表达的调节中起作用，而TMEM 168突变体扰乱了这种平衡，导致Nav1.5表达降低。
Transmembrane protein 168 (TMEM168) was found to be localized on the nuclear membrane. A heterozygous mutation (c.1616G>A, p. R539Q) in TMEM168 was identified in patients with Brugada syndrome. This mutation reduced expression of cardiomyocyte sodium channel Nav1.5 via Nedd4-2 E3 ubiquitin ligase-induced ubiquitination and degradation. However, the detailed molecular mechanism provoked by the TMEM168 mutant remains unclear. Here, we demonstrated that small heat shock protein αB-crystallin, which can bind to Nav1.5 and Nedd4-2 and interfere with the association of both proteins, was strongly recruited from the cell surface to the perinuclear region because of the much higher affinity of αB-crystallin with the TMEM168 mutant than with wild-type TMEM168. Following knockdown of αB-crystallin in HL-1 cardiomyocytes, the interaction of Nav1.5 with Nedd4-2 was increased, despite the reduced expression of Nav1.5. Moreover, reduction of Nav1.5 expression by αB-crystallin knockdown was rescued in the presence of a proteasome inhibitor MG-132, suggesting the importance of the αB-crystallin-modulated ubiquitin–proteasome system for the stability of Nav1.5 expression. Collectively, the balance of molecular interactions among Nav1.5, Nedd4-2 and αB-crystallin plays a role in the regulation of cardiomyocyte cell surface expression of Nav1.5, and the TMEM168 mutant disturbs this balance, resulting in a decrease in Nav1.5 expression.