Isoform-specific regulation of HCN4 channels by a family of endoplasmic reticulum proteins
Isoform-specific regulation of HCN4 channels by a family of endoplasmic reticulum proteins
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DOI：
10.1073/pnas.2006238117
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发表时间：
2020-07-28
影响因子：
11.1
通讯作者：
Proenza, Catherine
中科院分区：
文献类型：
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作者：
Peters, Colin H.;Myers, Mallory E.;Proenza, Catherine
可兴奋细胞中的离子通道在大分子复合物中起作用，其中辅助蛋白调节孔形成亚基的生物物理性质。超极化激活的环核苷酸敏感的HCN 4通道是全身细胞膜兴奋性的关键决定因素，包括丘脑皮质神经元和心脏起搏细胞。我们以前的研究表明，HCN 4通道的特性在不同的细胞类型中有很大的差异，这可能是由于内源性辅助蛋白的表达。在这里，我们报告了一个家族的内质网（ER）跨膜蛋白的发现，与HCN 4和调节。类磷脂限制性膜蛋白（LRMP，Jaw 1）和三磷酸肌醇受体相关鸟苷酸激酶底物（IRAG，Mrvi 1，Jaw 1 L）是具有小内质网腔域和大胞浆域的同源蛋白。尽管它们具有同源性，但LRMP和IRAG对HCN 4具有不同的作用。LRMP是一种功能丧失型调节剂，可抑制HCN 4响应cAMP结合的电压依赖性中的典型去极化偏移。相反，IRAG通过在不存在cAMP的情况下使基础电压依赖性去极化而引起HCN 4功能的增益。LRMP和IRAG的作用机制不依赖于traf-ficking和cAMP结合，并且它们对HCN 4亚型具有特异性。我们还发现IRAG在小鼠窦房结中高度表达，计算机建模预测其存在会增加HCN 4电流。我们的研究结果表明，LRMP和IRAG在调节细胞兴奋性中的重要作用，作为工具，以推进机制的理解HCN 4通道功能，并作为可能的scaf-折叠信号通路的协调。
Ion channels in excitable cells function in macromolecular com-plexes in which auxiliary proteins modulate the biophysical properties of the pore-forming subunits. Hyperpolarization-activated, cyclic nucleotide-sensitive HCN4 channels are critical determinants of mem-brane excitability in cells throughout the body, including thalamocort-ical neurons and cardiac pacemaker cells. We previously showed that the properties of HCN4 channels differ dramatically in different cell types, possibly due to the endogenous expression of auxiliary pro-teins. Here, we report the discovery of a family of endoplasmic re-ticulum (ER) transmembrane proteins that associate with and modulate HCN4. Lymphoid-restricted membrane protein (LRMP, Jaw1) and inositol trisphosphate receptor-associated guanylate ki-nase substrate (IRAG, Mrvi1, and Jaw1L) are homologous proteins with small ER luminal domains and large cytoplasmic domains. De-spite their homology, LRMP and IRAG have distinct effects on HCN4. LRMP is a loss-of-function modulator that inhibits the canonical depo-larizing shift in the voltage dependence of HCN4 in response to the binding of cAMP. In contrast, IRAG causes a gain of HCN4 function by depolarizing the basal voltage dependence in the absence of cAMP. The mechanisms of action of LRMP and IRAG are independent of traf-ficking and cAMP binding, and they are specific to the HCN4 isoform. We also found that IRAG is highly expressed in the mouse sinoatrial node where computer modeling predicts that its presence increases HCN4 current. Our results suggest important roles for LRMP and IRAG in the regulation of cellular excitability, as tools for advancing mecha-nistic understanding of HCN4 channel function, and as possible scaf-folds for coordination of signaling pathways.