The Rab11-family interacting protein 2 is an important regulator of inflammatory cell death in human macrophages

Abstract

Abstract Evidence that membrane trafficking and anchoring at the trans-Golgi network is important for NLRP3 inflammasome activation is now emerging. The Rab11-family interacting protein 2 (FIP2) is a key regulator of intracellular vesicle trafficking and has been shown to bind to a number of phosphatidylinositol phosphate (PtdIns) species, including PtdIns4P that is prevalent in the membranes of the Golgi apparatus. Here we report a role of FIP2 in NLRP3 inflammasome activation downstream of TLR4. High resolution confocal microscopy data revealed that FIP2 was resident in the Golgi and the trans-Golgi-network. In LPS primed and Nigericin treated cells, FIP2 was frequently observed on specks containing the inflammasome adaptor ASC. FIP2 positive ASC-specks were observed in mouse macrophages, THP-1 monocytes, primary human monocytes and macrophages. In addition, FIP2 showed a marked co-localisation with Caspase-1 in Golgi. Also, FIP2 co-localised with NLRP3 in additional cellular compartments. Indeed, co-immunoprecipitation studies in HEK293 cells showed that FIP2 could bind both NLRP3 and Caspase-1. Moreover, FIP2 silenced THP-1 monocytes showed impaired ASC-speck formation and marked reduction in secretion of cleaved IL1-β and Caspase-1. Similar results were found when FIP2 silenced THP-1 cells were LPS primed and treated with virulent clinical isolates of uropathogenic Escherichia coli (UPEC). Together these data show that FIP2 is a regulator of NLRP3 inflammasome assembly and activation.