Project description:The process of pyroptosis is mediated by inflammasomes and a downstream effector known as gasdermin D (GSDMD). Upon cleavage by inflammasome-associated caspases, the N-terminal domain of GSDMD forms membrane pores that promote cytolysis. Numerous proteins promote GSDMD cleavage, but none are known to be required for pore formation after GSDMD cleavage. Herein, we report a forward genetic screen that identified the Ragulator-Rag complex as being necessary for GSDMD pore formation and pyroptosis in macrophages. Mechanistic analysis revealed that Ragulator-Rag is not required for GSDMD cleavage upon inflammasome activation, but rather promotes GSDMD oligomerization in the plasma membrane. Defects in GSDMD oligomerization and pore formation can be rescued by mitochondrial poisons that stimulate reactive oxygen species (ROS) production, and ROS modulation impacts the ability of inflammasome pathways to promote pore formation downstream of GSDMD cleavage. These findings reveal an unexpected link between key regulators of immunity (inflammasome-GSDMD) and metabolism (Ragulator-Rag).
Project description:The process of pyroptosis is mediated by inflammasomes and a downstream effector known as gasdermin D (GSDMD). Upon cleavage by inflammasome-associated caspases, the N-terminal domain of GSDMD forms membrane pores that promote cytolysis. Numerous proteins promote GSDMD cleavage, but none are known to be required for pore formation after GSDMD cleavage. Herein, we report a forward genetic screen that identified the Ragulator-Rag complex as being necessary for GSDMD pore formation and pyroptosis in macrophages. Mechanistic analysis revealed that Ragulator-Rag is not required for GSDMD cleavage upon inflammasome activation but rather promotes GSDMD oligomerization in the plasma membrane. Defects in GSDMD oligomerization and pore formation can be rescued by mitochondrial poisons that stimulate reactive oxygen species (ROS) production, and ROS modulation impacts the ability of inflammasome pathways to promote pore formation downstream of GSDMD cleavage. These findings reveal an unexpected link between key regulators of immunity (inflammasome-GSDMD) and metabolism (Ragulator-Rag).
Project description:The type I interferon (IFN) response is a pivotal transcription program in the host innate immunity against infectious viruses that induces a multitude of interferon-stimulated genes (ISGs) to antagonize every stage of viral replication. Aberrant IFN response often leads to enhanced viral susceptibility or autoimmune conditions. Accordingly, type I IFN induction is tightly regulated from viral recognition to signaling propagation and transcriptional activation to cytokine production. Lysosomes, which are essential organelles for cellular homeostasis and metabolic signaling, play an evolutionarily conserved role in viral clearance. Through their degradative capacity and recycling function, lysosomes facilitate the containment and destruction of viral particles or debris delivered via endocytic, autophagic, and phagocytic routes. Despite the central role of lysosomes in virus-host interactions, it remains unclear whether type I IFN induction requires direct lysosomal input. Here, we identified the lysosomal scaffold Ragulator as crucial for IFN-β transcriptional activation through an antiviral screen using a GFP-expressing Influenza A virus as a readout. Independent of their known roles in mTORC1 regulation, the Ragulator-dependent antiviral response requires downstream heterodimeric Rag GTPases that alter their nucleotide-loading states to establish the IFN-I gene signature. Depleting Ragulator or Rag GTPases causes exhaustion of a regulatory pool of interferon-regulator factors (IRFs), leading to abrogated Ifnb1 transcription, IFN-β secretion, and ISG response, thereby enhancing susceptibility to viral infections both in cells and in vivo. Thus, our findings reveal a new role for lysosomes in the nuclear transcription of antiviral innate immunity.
Project description:The type I interferon (IFN) response is a pivotal transcription program in the host innate immunity against infectious viruses that induces a multitude of interferon-stimulated genes (ISGs) to antagonize every stage of viral replication. Aberrant IFN response often leads to enhanced viral susceptibility or autoimmune conditions. Accordingly, type I IFN induction is tightly regulated from viral recognition to signaling propagation and transcriptional activation to cytokine production. Lysosomes, which are essential organelles for cellular homeostasis and metabolic signaling, play an evolutionarily conserved role in viral clearance. Through their degradative capacity and recycling function, lysosomes facilitate the containment and destruction of viral particles or debris delivered via endocytic, autophagic, and phagocytic routes. Despite the central role of lysosomes in virus-host interactions, it remains unclear whether type I IFN induction requires direct lysosomal input. Here, we identified the lysosomal scaffold Ragulator as crucial for IFN-β transcriptional activation through an antiviral screen using a GFP-expressing Influenza A virus as a readout. Independent of their known roles in mTORC1 regulation, the Ragulator-dependent antiviral response requires downstream heterodimeric Rag GTPases that alter their nucleotide-loading states to establish the IFN-I gene signature. Depleting Ragulator or Rag GTPases causes exhaustion of a regulatory pool of interferon-regulator factors (IRFs), leading to abrogated Ifnb1 transcription, IFN-β secretion, and ISG response, thereby enhancing susceptibility to viral infections both in cells and in vivo. Thus, our findings reveal a new role for lysosomes in the nuclear transcription of antiviral innate immunity.
Project description:Alcoholic hepatitis (AH) continues to be a disease with high mortality and no efficacious medical treatment. Although severe AH is presented as acute on chronic liver failure, what underlies this transition from chronic alcoholic steatohepatitis (ASH) to AH, is largely unknown. To address this question, unbiased RNA-seq and proteomic analyses were performed on livers of the recently developed AH mouse model which exhibits the shift to AH from chronic ASH upon weekly alcohol binge, and these results are compared with gene expression profiling data from AH patients. This cross-analysis has identified Casp11 (CASP4 in man) as a commonly upregulated gene known to be involved in non-canonical inflammasome pathway. Immunoblotting confirms CASP11/4 activation in AH mice but not in chronic ASH. Gasdermin-D (GSDMD) which induces pyroptosis (lytic cell death caused by bacterial infection) downstream of CASP11/4 activation, is also activated in AH livers. CASP11 deficiency reduces GSDMD activation, bacterial load in the liver, and the severity of AH. Conversely, the deficiency of IL-18, the key anti-microbial cytokine, aggravates hepatic bacterial load, GSDMD activation, and AH. Further, hepatocyte-specific expression of constitutively active GSDMD worsens hepatocellular lytic death and PMN inflammation. These results implicate pyroptosis induced by CASP11/4-GSDMD pathway in the pathogenesis of AH.
Project description:Gasdermin D (GSDMD) is the executioner of pyroptosis, which is important for host defense against pathogen infection. After activation, caspase-mediated cleavage of GSDMD liberates an N-terminal fragment (GSDMD-NT), which oligomerizes and forms pores in the plasma membrane, leading to cell death and subsequent release of proinflammatory cytokines. How this process is spatiotemporally controlled to promote pyroptosis in cells has been a fundamental, unaddressed question. Here, we identify GSDMD as a substrate for reversible S-palmitoylation on cysteine 192 (Cys192) in response to lipopolysaccharide (LPS) stimulation. We found that the palmitoyl acyltransferase DHHC7palmitoylates GSDMD to direct its cleavage by caspases in pyroptosis by promoting the interaction of GSDMD and caspases. We further show that after GSDMD cleavage, palmitoylation of GSDMD-NTpromotes its plasma membrane translocation and binding, and then acyl protein thioesterase 2 (APT2) depalmitoylates GSDMD-NT to unmask the Cys192 residue to promote oxidation-mediated oligomerization and pyroptosis. Perturbation of either palmitoylation or depalmitoylation suppresses pyroptosis, extends the survival of mice from LPS-induced lethal septic shock and sensitizes mice to bacterial infection. Thus. our findings reveal a model through which a palmitoylation-depalmitoylationrelay spatially and temporally controls GSDMD activation in pyroptosis.
Project description:Gasdermin D (GSDMD) is the executioner of pyroptosis, which is important for host defense against pathogen infection. After activation, caspase-mediated cleavage of GSDMD liberates an N-terminal fragment (GSDMD-NT), which oligomerizes and forms pores in the plasma membrane, leading to cell death and subsequent release of proinflammatory cytokines. How this process is spatiotemporally controlled to promote pyroptosis in cells has been a fundamental, unaddressed question. Here, we identify GSDMD as a substrate for reversible S-palmitoylation on cysteine 192 (Cys192) in response to lipopolysaccharide (LPS) stimulation. We found that the palmitoyl acyltransferase DHHC7palmitoylates GSDMD to direct its cleavage by caspases in pyroptosis by promoting the interaction of GSDMD and caspases. We further show that after GSDMD cleavage, palmitoylation of GSDMD-NTpromotes its plasma membrane translocation and binding, and then acyl protein thioesterase 2 (APT2) depalmitoylates GSDMD-NT to unmask the Cys192 residue to promote oxidation-mediated oligomerization and pyroptosis. Perturbation of either palmitoylation or depalmitoylation suppresses pyroptosis, extends the survival of mice from LPS-induced lethal septic shock and sensitizes mice to bacterial infection. Thus. our findings reveal a model through which a palmitoylation-depalmitoylationrelay spatially and temporally controls GSDMD activation in pyroptosis.