Editors' ChoiceCell death

Pyroptosis mediator identified

Sci. Signal.  03 Nov 2015:
Vol. 8, Issue 401, pp. ec319
DOI: 10.1126/scisignal.aad7791

Cell death can occur through several distinct mechanisms that are distinguished by the proteins involved and the morphological features of the dying cells. Pyroptosis is a form of cell death that occurs in response to some types of inflammatory signals and involves caspases-1, -11, or -12 in mice or caspases-1, -4, -5, and -12 in humans; cell swelling and lysis; and the release of the proinflammatory cytokine interleukin-1β (IL-1β). When present intracellularly, the bacterial product lipopolysaccharide (LPS) triggers oligomerization and activation of caspase-11 in mice and caspase-4 in humans. Other inflammatory molecules stimulate the inflammasome, which activates caspase-1. Shi et al. and Kayagaki et al. used a gene knockout screen or a mutagenesis screen, respectively, and identified the gene encoding gasdermin D (GSDMD) as necessary for pyroptotic cell death. Both groups found that bone marrow–derived macrophages (BMDMs) lacking functional GSDMD were resistant to death in response to intracellular LPS. However, Shi et al. found that pyroptosis and IL-1β release in response to activators of the inflammasome and caspase-1–mediated death also required GSDMD, whereas the results of Kayagaki et al. indicated that inflammasome-triggered cell death was delayed rather than blocked. As noted by Broz, this may reflect differences in experimental procedures because Shi et al. examined earlier events than those examined by Kayagaki et al. Shi et al. established that GSDMD-deficient cells underwent apoptosis or necroptosis, indicating that GSDMD was specific for pyroptotic death. Both groups determined that caspase-11 cleaved GSDMD, that reintroduction of an Asp275-to-Ala mutant in cells lacking GSDMD failed to restore pyroptosis and IL-1β release, and that expression of the N-terminal fragment resulted in cell death. Shi et al. also reported that caspase-1 and caspase-4 cleaved GSDMD when overexpressed in 293T cells or when used for in vitro assays. By engineering the cleavage site to one recognized by caspase-3 or -7 and expressing this mutated GSDMD in GSDMD–/– Hela cells, Shi et al. showed that the cells underwent cell death in response to stimuli that activate the extrinsic cell death pathway, but that instead of having morphological characteristics of apoptosis, the death response appeared to be mediated by pyroptosis. Kayagaki et al. found that BMDMs lacking components of the inflammasome or caspase-1 exhibited GSDMD cleavage, indicating that cleavage by caspase-11 occurred upstream of formation of the caspase-1–activating inflammasome complex. In addition to finding a key mediator of pyroptotic death, these studies suggest that release of IL-1β, which lacks any known secretory signal, may occur during the cell lysis that occurs during pyroptosis. As noted by Broz, future studies will determine the molecular role of GSDMD in pyroptosis.

J. Shi, Y. Zhao, K. Wang, X. Shi, Y. Wang, H. Huang, Y. Zhuang, T. Cai, F. Wang, F. Shao, Cleavage of GSDMD by inflammatory caspases determines pyroptotic cell death. Nature 526, 660–665 (2015). [PubMed]

N. Kayagaki, I. B. Stowe, B. L. Lee, K. O’Rourke, K. Anderson, Søren Warming, Trinna Cuellar, Benjamin Haley, Merone Roose-Girma, Qui T. Phung, Peter S. Liu, Jennie R. Lill, Hong Li, Jiansheng Wu, Sarah Kummerfeld, Juan Zhang, Wyne P. Lee, Scott J. Snipas, Guy S. Salvesen, Lucy X. Morris, Linda Fitzgerald, Yafei Zhang, Edward M. Bertram, Christopher C. Goodnow, Vishva M. Dixit, Caspase-11 cleaves gasdermin D for non-canonical inflammasome signalling. Nature 526, 666–671 (2015). [PubMed]

P. Broz, Caspase target drives pyroptosis. Nature 526, 642–643 (2015). [PubMed]