Abstract
Interleukin-1β (IL-1β) is a critical regulator of the inflammatory response. IL-1β is not secreted through the conventional ER–Golgi route of protein secretion, and to date its mechanism of release has been unknown. Crucially, its secretion depends upon the processing of a precursor form following the activation of the multimolecular inflammasome complex. Using a novel and reversible pharmacological inhibitor of the IL-1β release process, in combination with biochemical, biophysical, and real-time single-cell confocal microscopy with macrophage cells expressing Venus-labelled IL-1β, we have discovered that the secretion of IL-1β after inflammasome activation requires membrane permeabilisation, and occurs in parallel with the death of the secreting cell. Thus, in macrophages the release of IL-1β in response to inflammasome activation appears to be a secretory process independent of nonspecific leakage of proteins during cell death. The mechanism of membrane permeabilisation leading to IL-1β release is distinct from the unconventional secretory mechanism employed by its structural homologues fibroblast growth factor 2 (FGF2) or IL-1α, a process that involves the formation of membrane pores but does not result in cell death. These discoveries reveal key processes at the initiation of an inflammatory response and deliver new insights into the mechanisms of protein release.
Highlights
Stimulation to activate cytosolic pattern recognition receptor (PRR), often of the NLR (Nucleotide-binding domain and Leucine-rich repeat containing Receptor) family, to form large multiprotein complexes called inflammasomes.[3]
Using the canonical inducer of NLRP3 inflammasome activation, extracellular ATP, we previously reported that release of IL-1β preceded that of the cell death marker lactate dehydrogenase (LDH) from primary peritoneal macrophages.[12]
We used sensitive single-cell quantitative approaches in addition to new pharmacological interventions with membrane stabilising reagents to show that in response to NLRP3 inflammasome activation, the secretion of IL-1β from macrophages depended upon permeabilisation of the plasma membrane, occurred concomitantly with cell death, and was distinct from the specific formation of translocation pores utilised by fibroblast growth factor 2 (FGF2)
Summary
Stimulation (signal 2) to activate cytosolic PRRs, often of the NLR (Nucleotide-binding domain and Leucine-rich repeat containing Receptor) family, to form large multiprotein complexes called inflammasomes.[3]. Following a recent review of the literature, we have postulated that there are a number of possible mechanisms through which IL-1β could exit the cell.[5] Potential secretory mechanisms include its release through the regulated secretion of lysosomes,[6] the shedding of microvesicles from the plasma membrane,[7] or its direct release across a hyperpermeable plasma membrane.[8] This last mechanism is perhaps related to cell death that in many instances is linked to IL-1β secretion. We used sensitive single-cell quantitative approaches in addition to new pharmacological interventions with membrane stabilising reagents to show that in response to NLRP3 inflammasome activation, the secretion of IL-1β from macrophages depended upon permeabilisation of the plasma membrane, occurred concomitantly with cell death, and was distinct from the specific formation of translocation pores utilised by FGF2
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
