Nt antigen recognized by IgE bound to the FceRI receptor, mast cells become activated, resulting in the activation of a series of signaling cascades [3]. Mast cell activation leads to degranulation of preformed mediators and the production of de novo synthesized mediators such as cytokines, chemokines and lipid mediators [3,4,5]. The release of preformed and newly synthesized mediators can cause profound inflammatory effects in allergic diseases [6]. Mast cell degranulation, like other intracellular trafficking processes, depends on the interaction of vesicular v-SNAREs (soluble N-ethylmaleimide-sensitive fusion factor attachment protein receptor) and target t-SNAREs to form a core complex that catalyses membrane fusion. The Sec1/Munc18 (SM) family is essential in intracellular trafficking through interaction with SNAREs [7]. This SM-SNARE interaction is involved in compound exocytosis that requires the fusion of docked secretory granules with the plasma membrane [8,9]. In the case of mast cell degranulation, many proteins are involved, including SNARE proteins (such as syntaxin-3 [10], syntaxin-4 [11], SNAP-23 [11,12], VAMP-2 [13], VAMP-7 [10], and VAMP-8 [11]), and SM family proteins (such as STXBP2, STXBP3) [9], among others.The SM family includes at least seven mammalian members: syntaxin binding protein (STXBP)1, STXBP2, STXBP3, VPS33A, VPS33B, VPS45, and SLY1. The STXBPs are functionally homologous to yeast Sec1p and function at the plasma membrane where they bind to the closed conformation of syntaxin 1? [14]. STXBP1 can play different roles in exocytosis regulated by various cellular machineries [15]. STXBP1 acts, along with STXBP2, to support the function of wide range of syntaxins and brings syntaxin-1 to the plasma membrane by binding the closed conformation of the protein [16]. STXBP1 also mediates synaptic vesicle docking and priming through direct binding to SNARE complexes [17,18,19,20], and leads to the subsequent calcium-mediated initiation of fusion [17,21,22,23]. Apart from its regulatory roles in vesicle docking, priming, and fusion, STXBP1 has been shown to bind double-stranded DNA and localize to ITI 007 biological activity neuronal nuclei [19]. It was proposed as a putative shuttle protein between the cytoplasm and the nucleus in neurons [19]. STXBP1 was shown to regulate neurite outgrowth from neurons through regulating cone filopodia [24], and negatively regulates insulin secretion by stabilizing syntaxin-1A in a closed conformation during vesicle priming [25]. Mutations in the STXBP1 gene have been shown to be associated with a wide spectrum of epileptic disorders and intellectual disabilities, including early infantile epileptic encephalopathy, 
as well as symptomatic generalized, partial, and nonsyndromic epilepsy [26,27,28,29,30,31]. STXBP1 and its interaction with syntaxin-1A have been well studied in neurons [32,33]. STXBP1 is phosphorylated by PKC in vitro and in vivo, and isSTXBP1 Is Not BIBS39 Required for Allergycritical for vesical secretion [34,35]. Mechanisms of mast cell degranulation share many similar features of vesical secretion as those present in neurons, such as PKC activation [36], and involvement of SNARE proteins (syntaxin-3 [10], syntaxin-4 [11], SNAP-23 [11,12], VAMP-2 [13], VAMP-7 [10], and VAMP-8 [11]) and SM family proteins (STXBP2, STXBP3) [9]. However, a role of STXBP1 in mast cells has not been previously investigated. In this study, we used liver-derived mast cells (LMCs) from STXBP1-deficient mice to examine wheth.Nt antigen recognized by IgE bound to the FceRI receptor, mast cells become activated, resulting in the activation of a series of signaling cascades [3]. Mast cell activation leads to degranulation of preformed mediators and the production of de novo synthesized mediators such as cytokines, chemokines and lipid mediators [3,4,5]. The release of preformed and newly synthesized mediators can cause profound inflammatory effects in allergic diseases [6]. Mast cell degranulation, like other intracellular trafficking processes, depends on the interaction of vesicular v-SNAREs (soluble N-ethylmaleimide-sensitive fusion factor attachment protein receptor) and target t-SNAREs to form a core complex that catalyses membrane fusion. The Sec1/Munc18 (SM) family is essential in intracellular trafficking through interaction with SNAREs [7]. This SM-SNARE interaction is involved in compound exocytosis that requires the fusion of docked secretory granules with the plasma membrane [8,9]. In the case of mast cell degranulation, many proteins are involved, including SNARE proteins (such as syntaxin-3 [10], syntaxin-4 [11], SNAP-23 [11,12], VAMP-2 [13], VAMP-7 [10], and VAMP-8 [11]), and SM family proteins (such as STXBP2, STXBP3) [9], among others.The SM family includes at least seven mammalian members: syntaxin binding protein (STXBP)1, STXBP2, STXBP3, VPS33A, VPS33B, VPS45, and SLY1. The STXBPs are functionally homologous to yeast Sec1p and function at the plasma membrane where they bind to the closed conformation of syntaxin 1? [14]. STXBP1 can play different roles in exocytosis regulated by various cellular machineries [15]. STXBP1 acts, along with STXBP2, to support the function of wide range of syntaxins and brings syntaxin-1 to the plasma membrane by binding the closed conformation of the protein [16]. STXBP1 also mediates synaptic vesicle docking and priming through direct binding to SNARE complexes [17,18,19,20], and leads to the subsequent calcium-mediated initiation of fusion [17,21,22,23]. Apart from its regulatory roles in vesicle docking, priming, and fusion, STXBP1 has been shown to bind double-stranded DNA and localize to neuronal nuclei [19]. It was proposed as a putative shuttle protein between the cytoplasm and the nucleus in neurons [19]. STXBP1 was shown to regulate neurite outgrowth from neurons through regulating cone filopodia [24], and negatively regulates insulin secretion by stabilizing syntaxin-1A in a closed conformation during vesicle priming [25]. Mutations in the STXBP1 gene have been shown to be associated with a wide spectrum of epileptic disorders and intellectual disabilities, including early infantile epileptic encephalopathy, as well as symptomatic generalized, partial, and nonsyndromic epilepsy [26,27,28,29,30,31]. STXBP1 and its interaction with syntaxin-1A have been well studied in neurons [32,33]. STXBP1 is phosphorylated by PKC in vitro and in vivo, and isSTXBP1 Is Not Required for Allergycritical for vesical secretion [34,35]. Mechanisms of mast cell 
degranulation share many similar features of vesical secretion as those present in neurons, such as PKC activation [36], and involvement of SNARE proteins (syntaxin-3 [10], syntaxin-4 [11], SNAP-23 [11,12], VAMP-2 [13], VAMP-7 [10], and VAMP-8 [11]) and SM family proteins (STXBP2, STXBP3) [9]. However, a role of STXBP1 in mast cells has not been previously investigated. In this study, we used liver-derived mast cells (LMCs) from STXBP1-deficient mice to examine wheth.