Human NLRP11 function in non-canonical inflammasome activation by bacterial pathogen LPS

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The gram-negative bacterial outer membrane glycolipid lipopolysaccharide (LPS) is recognized by both the cell surface TLR4 complex and cytosolic sensors. Recognition of bacterial LPS in the cytosol induces the activation of the caspase-4/caspase-5 (CASP4/5, human) or CASP11 (mouse) inflammasome, signaling platforms that trigger pyroptotic cell death. The dogma for recognition of bacterial LPS, based on the simplest interpretation of non-physiological data showing that CASP4/11 bind bacterial LPS in vitro, is that cytosolic bacterial LPS is directly sensed by CASP4/11 rather than by a pattern recognition receptor. We recently found that NLRP11, a poorly characterized primate-specific member of a family of pattern recognition receptors, is a pattern recognition receptor for cytosolic bacterial LPS. We found that efficient cell death induced by cytosolic bacterial LPS in human macrophages depends on NLRP11 function in the CASP4 inflammasome pathway. We initially identified NLRP11 in a genome-wide screen of human myeloid-derived cells for factors that promote cell death during infection with the gram- negative bacterial pathogen Shigella flexneri. We propose to leverage our findings to uncover mechanisms of NLRP11 function in cytosolic bacterial LPS-triggered activation of the human CASP4 inflammasome, including the role of variants of S. flexneri LPS in this process. 1. Define determinants of host-pathogen interaction of NLRP11 with bacterial LPS and caspase(s) and of NLRP11 specificity for caspase(s). We will define the molecular domains and sequences that mediate bacterial LPS interaction with NLRP11 and NLRP11 with CASP4. 2. Determine mechanisms of host NLRP11-mediated activation of CASP4 in response to cytosolic bacterial pathogens and cytosolic bacterial LPS. We will test our hypothesis that resting state NLRP11 is autoinhibited and activated NLRP11 triggers CASP4 activation by proximity-induced dimerization and will test the requirements for bacterial LPS in NLRP11 activation. 3. Test whether host NLRP11 recognition is modulated by specific LPS modifications or modes of LPS delivery by gram-negative bacterial pathogens. We will determine the role of selected modifications of LPS from S. flexneri on its recognition by NLRP11 and on NLRP11-dependent CASP4 activation and will test our hypothesis that NLRP11 is most critical to CASP4 responses when S. flexneri LPS is in micelle-reducing conditions. Our focus is to determine mechanisms of cytosolic bacterial LPS-triggered NLRP11-mediated activation of the human CASP4 inflammasome. We are uniquely positioned to accomplish these goals. Our insights are likely to have broad implications for gram-negative pathogenesis and thus be of great interest to the pathogenesis community.