The intracellular chloride channel proteins CLIC1 and CLIC4 induce IL-1β transcription and activate the NLRP3 inflammasome

The NLRP3 inflammasome is a multiprotein complex that regulates the activation of caspase-1 leading to the maturation of the proinflammatory cytokines IL-1 beta and IL-18 and promoting pyroptosis. Classically, the NLRP3 inflammasome in murine macrophages is activated by the recognition of pathogen-associated molecular patterns and by many structurally unrelated factors. Understanding the precise mechanism of NLRP3 activation by such a wide array of stimuli remains elusive, but several signaling events, including cytosolic efflux and influx of select ions, have been suggested. Accordingly, several studies have indicated a role of anion channels in NLRP3 inflammasome assembly, but their direct involvement has not been shown. Here, we report that the chloride intracellular channel proteins CLIC1 and CLIC4 participate in the regulation of the NLRP3 inflammasome. Confocal microscopy and cell fractionation experiments revealed that upon LPS stimulation of macrophages, CLIC1 and CLIC4 translocated into the nucleus and cellular membrane. In LPS/ATP-stimulated bone marrow-derived macrophages (BMDMs), CLIC1 or CLIC4 siRNA transfection impaired transcription of IL-1 beta, ASC speck formation, and secretion of mature IL-1 beta. Collectively, our results demonstrate that CLIC1 and CLIC4 participate both in the priming signal for IL-1 beta and in NLRP3 activation.