The secretory pathway-resident SNARE Sec22b regulates nitric oxide and cytokine production in dendritic cells

Soluble NSF attachment receptor (SNARE) proteins regulate the vesicle transport machinery in phagocytic cells. Within the secretory pathway, Sec22b is an ER-Golgi intermediate compartment (ERGIC)-resident SNARE that controls phagosome maturation and function in macrophages and dendritic cells. The ERGIC controls the release of cytokines and may impact that of nitric oxide (NO), the latter of which is synthesized by the Golgi-active inducible nitric oxide synthase (iNOS). Whether the ERGIC SNARE Sec22b controls NO and cytokine secretion, is unknown. Using bone marrow-derived dendritic cells (BMDC), we demonstrated that iNOS colocalizes with ERGIC/Golgi markers, notably Sec22b and its partner syntaxin-5 (Stx5), in the cytoplasm and at the phagosome. Pharmacological blockade of the secretory pathway hindered NO and cytokine release, and inhibited NFκB translocation to the nucleus. Importantly, RNAi-mediated silencing of Sec22b revealed that NO and cytokine production were abrogated at the protein and mRNA levels. This correlated with deregulated mitogen-activated protein kinase (MAPK) signalling and reduced nuclear translocation of NFκB. Collectively, our data unveiled a novel function for the ERGIC, and its resident SNARE Sec22b, in the release of inflammatory mediators.