SNAP‐23 and VAMP‐3 contribute to the release of IL‐6 and TNFα from a human synovial sarcoma cell line

Abstract

Fibroblast-like synoviocytes are important mediators of inflammatory joint damage in arthritis through the release of cytokines, but it is unknown whether their exocytosis from these particular cells is SNARE-dependent. Here, the complement of soluble N-ethylmaleimide-sensitive factor attachment protein receptors (SNAREs) in human synovial sarcoma cells (SW982) was examined with respect to the secretion of interleukin-6 (IL-6) and tumour necrosis factor α (TNFα), before and after knockdown of a synaptosome-associated protein of molecular mass 23 kDa (SNAP-23) or the vesicle-associated membrane protein 3 (VAMP-3). Wild-type SW982 cells expressed SNAP-23, VAMP-3, syntaxin isoforms 2-4 and synaptic vesicle protein 2C (SV2C). These cells showed Ca²⁺-dependent secretion of IL-6 and TNFα when stimulated by interleukin-1β (IL-1β) or in combination with K⁺ depolarization. Specific knockdown of SNAP-23 or VAMP-3 decreased the exocytosis of IL-6 and TNFα; the reduced expression of SNAP-23 caused accumulation of SV2 in the peri-nuclear area. A monoclonal antibody specific for VAMP-3 precipitated SNAP-23 and syntaxin-2 (and syntaxin-3 to a lesser extent). The formation of SDS-resistant complexes by SNAP-23 and VAMP-3 was reduced upon knockdown of SNAP-23. Although the syntaxin isoforms 2, 3 and 4 are expressed in SW982 cells, knockdown of each did not affect the release of cytokines. Collectively, these results show that SNAP-23 and VAMP-3 participate in IL-1β-induced Ca²⁺-dependent release of IL-6 and TNFα from SW982 cells.