Shigella regulation of GSDMD palmitoylation in epithelial cells - Pyroptosis is the first line of host defense that pathogens face upon encountering intestinal epithelial cells. It is an inflammatory form of cell death that leads to the rapid lysis or expulsion of infected epithelial cells and the secretion of pro-inflammatory cytokines, e.g., IL-18. Pyroptosis within human intestinal epithelial cells is primarily activated by the assembly of non-canonical inflammasomes. These complexes serve as platforms for processing and activating caspases, proteases that mediate cytokine and Gasdermin D (GSDMD) processing. The cleavage of GSDMD results in the release of its N-terminal pore-forming domain, GSDMD-NT, which then forms holes in the host cell membranes that mediate the release of cytokines and the flow of ions that eventually lead to cell swelling and lysis via the activity of NinJ1. It was recently demonstrated that the ability of GSDMD to form pores in the plasma membrane of macrophages is dependent on its palmitoylation, a reversible lipid modification mediated by members of the ZHDDC family of palmitoyl acyl-transferases (DHHC- PATs). Using a proximity labeling approach, we have identified a Shigella effector that suppress Shigella- triggered pyroptosis, likely by targeting the ubiquitination and degradation of ZDHHC5, one of the proteins demonstrated to modify GSDMD. These observations provide the first evidence that GSDMD palmitoylation is a major factor in the human innate response to bacterial pathogens. Here, we propose to establish that GSDMD palmitoylation is a major factor in the human innate response to bacterial pathogens and to demonstrate how Shigella flexneri blocks this response to promote their survival in host cells. Insights gained from these studies can inform the development of novel interventions to enhance the host's innate immune response that can be used as new anti-microbial treatment modalities.
