Inflammasome is an intracellular signaling complex of the innate immune system. 
Activation of inflammasomes promotes the secretion of interleukin 1β (IL-1β) and 
IL-18 and triggers pyroptosis. Caspase-1 and -11 (or -4/5 in human) in the 
canonical and non-canonical inflammasome pathways, respectively, are crucial for 
inflammasome-mediated inflammatory responses. Here we report that gasdermin D 
(GSDMD) is another crucial component of inflammasomes. We discovered the 
presence of GSDMD protein in nigericin-induced NLRP3 inflammasomes by a 
quantitative mass spectrometry-based analysis. Gene deletion of GSDMD 
demonstrated that GSDMD is required for pyroptosis and for the secretion but not 
proteolytic maturation of IL-1β in both canonical and non-canonical inflammasome 
responses. It was known that GSDMD is a substrate of caspase-1 and we showed its 
cleavage at the predicted site during inflammasome activation and that this 
cleavage was required for pyroptosis and IL-1β secretion. Expression of the 
N-terminal proteolytic fragment of GSDMD can trigger cell death and N-terminal 
modification such as tagging with Flag sequence disrupted the function of GSDMD. 
We also found that pro-caspase-1 is capable of processing GSDMD and ASC is not 
essential for GSDMD to function. Further analyses of LPS plus nigericin- or 
Salmonella typhimurium-treated macrophage cell lines and primary cells showed 
that apoptosis became apparent in Gsdmd(-/-) cells, indicating a suppression of 
apoptosis by pyroptosis. The induction of apoptosis required NLRP3 or other 
inflammasome receptors and ASC, and caspase-1 may partially contribute to the 
activation of apoptotic caspases in Gsdmd(-/-) cells. These data provide new 
insights into the molecular mechanisms of pyroptosis and reveal an unexpected 
interplay between apoptosis and pyroptosis.