The improved effect of hypothermic cultivation on thefunctional expression of human cardiac Kv1.5 channels

本文研究了低温暴露对人Kv1.5（hKv1.5）通道活性、表达、降解和定位的影响。在表达hKv1.5的CHO细胞中，与37℃下观察到的电流相比，在降温培养（28℃）下电流显著增加。Western印迹分析证实，hKv1.5的蛋白水平（未成熟和成熟蛋白）显着升高，在低温条件下。蛋白酶体抑制剂MG 132处理显著增加了37℃下未成熟（但不是成熟）的hKv 1.5蛋白; MG 132暴露后，低温条件下未成熟或成熟的hKv 1.5蛋白均无变化，因此表明在降低的温度下成熟的hKv 1.5蛋白的增强可能不是由于蛋白水解的抑制。28℃培养的HEK细胞表面hKv1.5荧光信号较37℃培养的HEK细胞明显增强。重要的是，低温处理显着转移的亚细胞分布的成熟hKv1.5轻馏分，这表明相当大的重叠与trans-Golgi组件。最后，低温处理还挽救了运输缺陷型hKv1.5突变体（I502 A，I508 A，位于孔区域）的蛋白表达和功能电流。这些结果表明，低温暴露稳定的蛋白质在细胞器官，调节其再循环运输，从而增强功能hKv1.5电流。

We herein investigated the effect of low temperature exposure in the channel activity, expression, degradation and localization of human Kv1.5 (hKv1.5). In hKv1.5-expressing CHO cells, the currents significantly increased at a reduced temperature cultivation (28℃) in comparison to those observed at 37℃. A Western blot analysis confirmed that the protein levels (immature and mature proteins) of hKv1.5 were significantly elevated under hypothermic conditions. The treatment with a proteasome inhibitor, MG132, significantly increased the immature (but not the mature) hKv1.5 protein at 37℃; there were no changes in either the immature or mature hKv1.5 proteins at low temperature conditions after MG132 exposure, thus indicating that the enhancement of the mature hKv1.5 protein at reduced temperature may not result from the inhibition of proteolysis. Moreover, the hKv1.5 fluorescence signal in the HEK cells increased significantly on the cell surface at 28℃ versus those cultured at 37℃. Importantly, the low temperature treatment markedly shifted the subcellular distribution of the mature hKv1.5 lighter fractions, which showed considerable overlap with the trans-Golgi component. Finally, the hypothermic treatment also rescued the protein expression and functional currents of trafficking-defective hKv1.5 mutants (I502A, I508A, located in the pore region). These results indicate that low temperature exposure stabilizes the protein in the cellular organs, modulates its recycling trafficking, thus enhancing functional hKv1.5 currents.