SYT1 Knockout Cell Line (HEK293)

ANO1 plays a crucial role in determining numerous physiological functions, including epithelial secretion, yet its regulatory mechanisms remain incompletely understood. Here, we describe a fundamental dynamic regulation of ANO1 surface expression and Ca-dependent gating via the cAMP/PKA pathway at the STIM1 ER/PM junctions. At these junctions, STIM1 assembles AC-AKAP-PKA complexes, while E-Syt1 mediates formation of ANO1-VAPA-IRBIT-E-Syt1-AC8-AKAP5-PKA complex, that phosphorylates ANO1 S673, increasing ANO1 Ca affinity. Within these complexes, the Ca and cAMP pathways act synergistically to enhance ANO1 function. By contrast, E-Syt2 dissociates the ANO1-VAPA interaction, forming ANO1-IRBIT-E-Syt2-AC6-AKAP11-PKA complex that phosphorylates ANO1 S221, which markedly reduces ANO1 Ca affinity. The effects of the E-Syts are primarily mediated by their reciprocal regulation of junctional PI(4)P, PI(4,5)P and PtdSer. Accordingly, IRBIT deletion in mice impairs receptor-stimulated activation of ANO1 and fluid secretion. These findings should have broad implications for ANO1 roles and functions across various tissues.

Synaptotagmin-7 (Syt7) plays direct or redundant Ca2+ sensor roles in multiple forms of vesicle exocytosis in synapses. Here, we show that Syt7 is a redundant Ca2+ sensor with Syt1/Doc2 to drive spontaneous glutamate release, which functions uniquely to activate the postsynaptic GluN2B-containing NMDARs that significantly contribute to mental illness. In mouse hippocampal neurons lacking Syt1/Doc2, Syt7 inactivation largely diminishes spontaneous release. Using 2 approaches, including measuring Ca2+ dose response and substituting extracellular Ca2+ with Sr2+, we detect that Syt7 directly triggers spontaneous release via its Ca2+ binding motif to activate GluN2B-NMDARs. Furthermore, modifying the localization of Syt7 in the active zone still allows Syt7 to drive spontaneous release, but the GluN2B-NMDAR activity is abolished. Finally, Syt7 SNPs identified in bipolar disorder patients destroy the function of Syt7 in spontaneous release in patient iPSC-derived and mouse hippocampal neurons. Therefore, Syt7 could contribute to neuropsychiatric disorders through driving spontaneous glutamate release.