The inflammasome and its regulation

Inflammasomes, multiprotein platforms of caspase-1 activation, are assembled in response to a number of exogenous and endogenous danger signals, leading to the production of pro-inflammatory cytokines and induction of inflammatory cell death through the activation of caspase-1. Inflammasomes have been implicated in a wide range of physiological and pathological processes, including host defense against microbial pathogens, maintenance of intestinal homeostasis, and even development of inflammatory disorders. Thus, inflammasomes can be both beneficial and detrimental, and understanding the mechanisms involved in inflammasome activation may provide a better approach to prevent the harmful effects of the inflammatory response. Although inflammasome complexes are formed via protein-protein interactions between their components, accumulating evidence suggests that inflammasome activation is positively and negatively regulated by ligand-binding receptors, accessory proteins, other caspases, cytokines, kinases/phosphatases, redox sensors, ion homeostasis, second messengers, organelles, cytoskeleton, and autophagy, among others. Moreover, inflammasome activation can result in the formation of another caspase-1-activating protein complex, the ASC speck/pyroptosome, which is also tightly controlled. In this review, we discuss how the assembly of inflammasomes and ASC speck is regulated by complex mechanisms. Recent findings on effector functions and biological roles of inflammasomes also are summarized.