SNAP23

The trafficking of aquaporin 5 (AQP5) is critical for salivary secretion. Synaptosomal-associated protein 23 (SNAP23) is an important regulator in the process of membrane fusion. However, the role of SNAP23 on AQP5 trafficking has not been explored. Botulinum toxin type A (BoNT/A) is a bacterial toxin that effectively treats sialorrhea. We previously reported that BoNT/A induced AQP5 redistribution in cultured acinar cells, but the mechanism remained unclear. In this study, SNAP23 was predominantly localized to the plasma membrane of acinar cells in the rat submandibular gland (SMG) and colocalized with AQP5 at the apical membrane of acinar cells. In stable GFP-AQP5-transfected SMG-C6 cells, the acetylcholine receptor agonist carbachol (CCh) induced trafficking of AQP5 from intracellular vesicles to the apical membrane. Furthermore, SNAP23 knockdown by siRNA significantly inhibited CCh-induced AQP5 trafficking, whereas this inhibitory effect was reversed by SNAP23 re-expression, indicating that SNAP23 was essential in AQP5 trafficking. More importantly, BoNT/A inhibited salivary secretion from SMGs, and the underlying mechanism involved that BoNT/A blocked CCh-triggered AQP5 trafficking by decreasing SNAP23 in acinar cells. Taken together, these results identified a crucial role for SNAP23 in AQP5 trafficking and provided new insights into the mechanism of BoNT/A in treating sialorrhea and thereby a theoretical basis for clinical applications.

Phagosome formation and maturation reportedly occur via sequential membrane fusion events mediated by synaptosomal-associated protein of 23 kDa (SNAP23), a plasma membrane-localized soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) family. Vesicle-associated membrane protein 5 (VAMP5), also a plasmalemma SNARE, interacts with SNAP23; however, its precise function in phagocytosis in macrophages remains elusive. To elucidate this aspect, we investigated the characteristics of macrophages in the presence of VAMP5 overexpression or knockdown and found that VAMP5 participates in Fcγ receptor-mediated phagosome formation, although not directly in phagosome maturation. Overexpressed VAMP5 was localized to the early phagosomal membrane but no longer localized to the lysosomal-associated membrane protein 1-positive maturing phagosomal membrane. Analyses using compound-based selective inhibitors demonstrated that VAMP5 dissociation from early phagosomes occurs in a clathrin- and dynamin-dependent manner and is indispensable for SNAP23 function in subsequent membrane fusion during phagosome maturation. Accordingly, to the best of our knowledge, we demonstrate, for the first time, that VAMP5 exerts an immunologically critical function during phagosome formation and maturation via SNARE-based membrane trafficking in macrophages.

The COG complex is implicated in the tethering of retrograde intra-Golgi vesicles, which involves vesicular tethering and SNAREs. SNARE complexes mediate the inva-sion and metastasis of cancer cells through MMPs which activate growth factors for ECM frag-ments by binding to integrin receptors. Increasing MMPs is in line with YKL40 since YKL40 is linked to promoting angiogenesis through VEGF and can increase ovarian cancer (OC) resistance to chemotropic and cell migration.

The aim of this study is an assessment of siRNA-COG3 on proliferation, invasion, and apoptosis of OC cells. In addition, siRNA-COG3 may prevent the growth of OC cancer in mice with tumors.

Primary OC cell lines will be treated with siRNA-COG3 to assay YKL40 and identified angiogenesis by Tube-like structure formation in HOMECs. The Golgi morphology was analyzed using Immunofluorescence microscopy. Furthermore, the effects of siRNA-COG3 on the prolifer-ation and apoptosis of cells were evaluated using MTT and TUNEL assays. Clones of the HOSEpiC OC cell line were subcutaneously implanted in FVB/N mice. Mice were treated after two weeks of injection of cells using siRNA-COG3. Tumor development suppression was detected by D-luciferin. RT-PCR and western blotting analyses were applied to determine COG3, MT1-MMP, SNAP23, and YKL40 expression to investigate the effects of COG3 gene knockdown.

siRNA-COG3 exhibited a substantial effect in suppressing tumor growth in mice. It dra-matically reduced OC cell proliferation and triggered apoptosis (all p < 0.01). Inhibition of COG3, YKL-40, and MT1-MPP led to suppression of angiogenesis and reduction of microvessel density through SNAP23 in OC cells.

Overall, by knockdown of the COG3 gene, MT1-MMP and YKL40 were dropped, leading to suppressed angiogenesis along with decreasing migration and proliferation. SiRNA-COG3 may be an ideal agent to consider for clinical trial assessment therapy for OC, especially when an antiangiogenic SNAR-pathway targeting drug.