Sarkar Paramita, Lüscher Benjamin P, Ye Zengyou, Chung Woo Young, Abtahi Ava Movahed, Zheng Changyu, Lee Min Goo, Varga Árpád, Pallagi Petra, Maléth József, Ahuja Malini, Muallem Shmuel
Epithelial Signaling and Transport Section, National Institute of Dental Craniofacial Research, National Institutes of Health, Bethesda, MD, 20892, USA.
Department of Hematology and Central Hematological Laboratory, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland.
EMBO J. 2025 May 27. doi: 10.1038/s44318-025-00470-9.
Endoplasmic reticulum/plasma membrane (ER/PM) junctions are a major site of cellular signal transduction including in epithelia; however, whether their lipid membrane environment affects junctional ion transporters function remains unclear. Here, we show that epithelial secretion is governed by phosphatidylserine (PtdSer) levels in ER/PM nanodomains, specified by the antagonistic action of the lipid transfer proteins E-Syt3 and ORP5, which transduce cAMP signals to the chloride channel CFTR and activate the sodium-bicarbonate cotransporter NBCe1-B by IRBIT. Lipid transfer by E-Syt3, along with restricted plasma membrane localization by the E-Syt3 C2C domain, are essential for E-Syt3 function, as removal of PtdSer from junctions by E-Syt3 dissociated the cAMP signaling pathway complex, preventing CFTR activation, and prevented NBCe1-B activation by IRBIT. CFTR and NBCe1-B PtdSer sensor domains responded to PtdSer reduction by E-Syt3; which was reversed by exogenous PtdSer or by PtdSer supplied by ORP5. In mice, E-Syt3 depletion improved chloride flux and fluid secretion in salivary glands and isolated pancreatic ducts. These findings provide a framework for understanding the role of junctional lipids in the assembly of functional ion protein complexes and cellular communication at epithelial signaling hubs.
内质网/质膜（ER/PM）连接是细胞信号转导的主要部位，包括在上皮细胞中；然而，它们的脂膜环境是否会影响连接离子转运蛋白的功能仍不清楚。在这里，我们表明上皮分泌受ER/PM纳米结构域中磷脂酰丝氨酸（PtdSer）水平的调控，这是由脂转运蛋白E-Syt3和ORP5的拮抗作用所决定的，它们将cAMP信号转导至氯离子通道CFTR，并通过IRBIT激活钠-碳酸氢根共转运体NBCe1-B。E-Syt3的脂转运作用，以及E-Syt3 C2C结构域对质膜定位的限制，对于E-Syt3的功能至关重要，因为E-Syt3从连接部位去除PtdSer会使cAMP信号通路复合物解离，阻止CFTR激活，并阻止IRBIT对NBCe1-B的激活。CFTR和NBCe1-B的PtdSer传感结构域对E-Syt3导致的PtdSer减少有反应；外源性PtdSer或ORP5提供的PtdSer可使其逆转。在小鼠中，E-Syt3的缺失改善了唾液腺和分离的胰管中的氯离子通量和液体分泌。这些发现为理解连接脂质在功能性离子蛋白复合物组装以及上皮信号枢纽处细胞通讯中的作用提供了一个框架。
