β-adrenoceptor activation increased VAMP-2 and syntaxin-4 in secretory granules are involved in protein secretion of submandibular gland through the PKA/F-actin pathway.

Chong Ding,Li-Ling Wu,Xin Cong,Guang-Yan Yu,Sheng-Lin Li,Yan Zhang

doi:10.1042/bsr20171142

Abstract

Autologous submandibular gland transplantation is an effective treatment for severe dry eye syndrome. However, the protein secretion in transplanted gland is altered by a mechanism that remains to be elucidated. In the present study, we found that β1-adrenoceptor (β1-AR) and β2-AR expression and the phosphorylation of the downstream molecule protein kinase A (PKA) were elevated in transplanted submandibular glands obtained from epiphora patients. Synaptobrevin/vesicle-associated membrane protein 2 (VAMP-2) interacted with syntaxin-4 and actin in human submandibular gland. The contents of syntaxin-4 and actin interacting with VAMP-2 were increased in transplanted gland. Moreover, VAMP-2 and syntaxin-4 expression in the secretory granule fraction, and VAMP-2 expression in the membrane protein fraction were increased in isoproterenol-treated and transplanted glands. Isoproterenol increased F-actin polymerization in the apical and lateral regions of the cytoplasm in both control and transplanted glands. Inhibiting PKA activity and/or F-actin formation abolished the isoproterenol-enhanced expression of VAMP-2 and syntaxin-4 in the secretory granule fraction and the isoproterenol-enhanced expression of VAMP-2 in the membrane protein fraction. Taken together, these results indicate that the activation of β-ARs induces secretory granules and cell membrane fusion via the interaction of VAMP-2 and syntaxin-4 in a PKA- and F-actin-dependent manner in human submandibular gland. Up-regulated β-ARs might participate in altering protein secretion in transplanted submandibular gland by promoting the interaction of VAMP-2 with syntaxin-4.

Highlights

The release of salivary proteins is primarily evoked by sympathetic neurotransmitter action on β-adrenoceptors (β-ARs), which subsequently activates protein kinase A (PKA) [1]
After the activation of β-ARs and PKA, salivary proteins are released via exocytosis, which is achieved by the interaction of vesicle-anchored soluble N-ethylmaleimide-sensitive fusion attachment protein receptors (v-SNAREs) with target membrane-anchored SNAREs (t-SNAREs) [2,3]
The present study demonstrated that the activation of β-ARs increases synaptobrevin/vesicle-associated membrane protein (VAMP-2) and syntaxin-4 expression in the secretory granule fraction and vesicle-associated membrane proteins (VAMPs)-2 expression in the membrane protein fraction, which was dependent on PKA

Summary

Introduction

The release of salivary proteins is primarily evoked by sympathetic neurotransmitter action on β-adrenoceptors (β-ARs), which subsequently activates protein kinase A (PKA) [1]. After the activation of β-ARs and PKA, salivary proteins are released via exocytosis, which is achieved by the interaction of vesicle-anchored soluble N-ethylmaleimide-sensitive fusion attachment protein receptors (v-SNAREs) with target membrane-anchored SNAREs (t-SNAREs) [2,3]. Amongst these SNAREs, synaptobrevin/vesicle-associated membrane proteins (VAMPs) are v-SNARE family members, whereas syntaxins and synaptosome-associated protein 25 (SNAP-25) homologs are t-SNAREs [4]. VAMP-2, syntaxin-2, syntaxin-4, and SNAP-23, together with cytoskeletal components c 2018 The Author(s)

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