Biology subjects

Kagan, J. C.

Publications and source records attributed to Kagan, J. C..

13 recordsLinked to original sources

bioRxiv2026

NLRP11 promotes non-canonical inflammasome activation in human macrophages by enhancing caspase-4 recognition of cytosolic lipopolysaccharide

Innate immune detection of Gram-negative bacteria depends on sensing of cytosolic lipopolysaccharide (cLPS) by the non-canonical inflammasome, mediated in humans by NLRP11 and caspase-4 (CASP4). Activation of this pathway in human macrophages triggers gasdermin-D activation and pyroptotic cell death. Although CASP4 directly binds LPS in vitro, additional host factors are required for efficient activation in vivo. Here, we show that NLRP11, a primate-specific pattern recognition receptor, facilitates CASP4 recognition of cLPS and promotes non-canonical inflammasome activation. NLRP11 functions upstream CASP4, forming an ASC-independent complex that requires a conserved CASP4 p20 residue, binds cLPS, and enhances CASP4-dependent LPS recognition. Mutational analyses demonstrate that in human macrophages, in addition to LPS binding and CASP4 catalytic activity, CASP4 interaction with NLRP11 is essential for efficient pyroptosis. Together, these findings establish NLRP11 as a primate-specific determinant that enhances CASP4-mediated cLPS detection and non-canonical inflammasome activation, revealing a mechanism for human-specific regulation of innate immunity.

immunology↗

bioRxiv2025

NINJ1 is activated by Mycobacterium tuberculosis ESX-1 secreted effector EsxA and mediates necrosis of infected human macrophages

Lytic cell death contributes to tissue damage and dissemination during Mycobacterium tuberculosis (Mtb) infection, yet the mechanisms governing plasma membrane rupture (PMR) remain incompletely defined. Here, we identify Ninjurin-1 (NINJ1), a mediator of PMR, as a central effector of macrophage lysis during Mtb infection. Mtb infection induced NINJ1 oligomerization, and genetic deletion or pharmacological inhibition of NINJ1 markedly reduced lactate dehydrogenase (LDH) release. Cytokine secretion was largely preserved in NINJ1-deficient macrophages, with the exception of CXCL10. Unexpectedly, inhibition of pyroptosis, apoptosis, necroptosis, and ferroptosis - individually or in combination - did not prevent NINJ1 activation or PMR, indicating that Mtb-induced membrane rupture proceeds independently of canonical regulated cell death pathways. However, NINJ1 oligomerization and PMR required the Mtb ESX-1 secretion system, identifying a bacterial virulence determinant as a critical upstream trigger. Although osmoprotective PEG partially reduced LDH release, neither calcium signaling nor cell swelling accounted for NINJ1-dependent PMR in Mtb-infected macrophages. Together, these findings establish NINJ1 as a key executioner of Mtb-induced lytic cell death and reveal an ESX-1-dependent pathway of PMR that is uncoupled from canonical host cell death programs. TeaserNINJ1 mediates plasma membrane rupture of macrophages infected with Mycobacterium tuberculosis

microbiology↗

bioRxiv2025

Wall teichoic acid is required for DNA-triggered innate immune receptor activation by Staphylococcus aureus

Receptors that stimulate inflammation are commonly activated by ligands that are buried within microbial cells. The mechanisms that facilitate immunostimulatory ligand release from microbes during infection are largely undefined. Using the pathogen Staphylococcus aureus, we describe wall teichoic acid (WTA) as a critical mediator of DNA release from bacterial cells during infection. Mechanistically, we found that the -glycosylated form of WTA, generated by the enzyme TarM, is the primary mediator of bacterial DNA release within macrophages. This process is antagonized by the enzyme O-acetyltransferase, which prevents WTA attachment to peptidoglycan. This competition among peptidoglycan modifying enzymes determines activation of cytosolic DNA receptors AIM2 and cGAS. WTA therefore operates as a meta-regulator of inflammation, by controlling the availability of microbial ligands that stimulate innate immunity.

immunology↗

bioRxiv2024

LPS binding caspase activation and recruitment domains (CARDs) are bipartite lipid binding modules

Caspase-11 is an innate immune pattern recognition receptor (PRR) that detects cytosolic bacterial lipopolysaccharides (LPS) through its caspase activation and recruitment domain (CARD), triggering inflammatory cell death known as pyroptosis. Caspase-11 also detects eukaryotic (i.e. self) lipids. This observation raises the question of whether common or distinct mechanisms govern the interactions with self and nonself lipids. In this study, using biochemical, computational, and cell-based assays, we report that the caspase-11 CARD functions as a bipartite lipid-binding module. Distinct regions within the CARD bind to phosphate groups and long acyl chains of self and nonself lipids. Self-lipid binding capability is conserved across numerous caspase-11 homologs and orthologs. The symmetry in self and nonself lipid detection mechanisms enabled us to engineer an LPS-binding domain de novo, using an ancestral CARD-like domain present in the fish Amphilophus citrinellus. These findings offer critical insights into the molecular basis of LPS recognition by caspase-11 and highlight the fundamental and likely inseparable relationship between self and nonself discrimination.

immunology↗

bioRxiv2024

Control of Inflammatory Response by Tissue Microenvironment

Inflammation is an essential defense response but operates at the cost of normal tissue functions. Whether and how the negative impact of inflammation is monitored remains largely unknown. Acidification of the tissue microenvironment is associated with inflammation. Here we investigated whether macrophages sense tissue acidification to adjust inflammatory responses. We found that acidic pH restructured the inflammatory response of macrophages in a gene-specific manner. We identified mammalian BRD4 as a novel intracellular pH sensor. Acidic pH disrupts the transcription condensates containing BRD4 and MED1, via histidine-enriched intrinsically disordered regions. Crucially, a decrease in macrophage intracellular pH is necessary and sufficient to regulate transcriptional condensates in vitro and in vivo, acting as negative feedback to regulate the inflammatory response. Collectively, these findings uncovered a pH-dependent switch in transcriptional condensates that enables environment-dependent control of inflammation, with a broader implication for calibrating the magnitude and quality of inflammation by the inflammatory cost. HighlightsO_LIAcidic pH regulates a switch-like gene-specific inflammatory response in macrophages C_LIO_LIAcidic pH impacts chromatin remodeling and transcription circuits to control inflammatory programs C_LIO_LIBRD4 transcriptional condensates are regulated by intracellular pH via the histidine-enriched intrinsically disordered region C_LIO_LITissue inflammation decreases intracellular pH and disrupts BRD4 condensates as a negative feedback C_LI

immunology↗

bioRxiv2023

ROS-dependent palmitoylation is an obligate licensing modification for GSDMD pore formation

Gasdermin D (GSDMD) is the common effector for cytokine secretion and pyroptosis downstream of inflammasome activation by forming large transmembrane pores upon cleavage by inflammatory caspases. Here we report the surprising finding that GSDMD cleavage is not sufficient for its pore formation. Instead, GSDMD is lipidated by S-palmitoylation at Cys191 upon inflammasome activation, and only palmitoylated GSDMD N-terminal domain (GSDMD-NT) is capable of membrane translocation and pore formation, suggesting that palmitoylation licenses GSDMD activation. Treatment by the palmitoylation inhibitor 2-bromopalmitate and alanine mutation of Cys191 abrogate GSDMD membrane localization, cytokine secretion, and cell death, without affecting GSDMD cleavage. Because palmitoylation is formed by a reversible thioester bond sensitive to free thiols, we tested if GSDMD palmitoylation is regulated by cellular redox state. Lipopolysaccharide (LPS) mildly and LPS plus the NLRP3 inflammasome activator nigericin markedly elevate reactive oxygen species (ROS) and GSDMD palmitoylation, suggesting that these two processes are coupled. Manipulation of cellular ROS by its activators and quenchers augment and abolish, respectively, GSDMD palmitoylation, GSDMD pore formation and cell death. We discover that zDHHC5 and zDHHC9 are the major palmitoyl transferases that mediate GSDMD palmitoylation, and when cleaved, recombinant and partly palmitoylated GSDMD is 10-fold more active in pore formation than bacterially expressed, unpalmitoylated GSDMD, evidenced by liposome leakage assay. Finally, other GSDM family members are also palmitoylated, suggesting that ROS stress and palmitoylation may be a general switch for the activation of this pore-forming family. One-Sentence SummaryGSDMD palmitoylation is induced by ROS and required for pore formation

immunology↗

bioRxiv2022

Correction of age-associated defects in dendritic cell functions enables CD4+ T cells to eradicate tumors in the elderly

Defective host defenses later in life are associated with changes in immune system activity. The means to correct immune defects to ensure immunity in the elderly are undefined. In this study, we found that CD8+ T cells, which are necessary for anti-tumor immunity in young mice, are not required to eradicate the same cancers later in life. Rather, CD4+ T cells drive anti-tumor immunity in elderly mice. The generation of anti-tumor CD4+ T cells requires multiple dendritic cell (DC) activities that are elicited by immune agonists known as hyperactivators, but not by adjuvants that model those used clinically. DC hyperactivators correct age-associated defects in DC migration and T cell co-stimulation while enabling NLRP3 inflammasome activities within living cells. These combined activities enable DCs to induce TH1-skewed T cells that persist into old age and eliminate implantable tumors. These results raise the possibility of correcting age-associated immune defects through DC manipulation.

immunology↗

bioRxiv2022

STING is a common driver of type I interferon responses to diverse bacteria in macrophages

Central to health and disease are innate immune receptors that bind bacterial molecules to initiate inflammation and host defense. Beyond pathogens and their membrane disruptive activities, mechanisms enabling bacterial molecules to access innate immune receptors in the cytoplasm are unknown. Here, we describe the cytoplasmic cyclic dinucleotide (CDN)-binding protein STING as a common bacterial sensor. Irrespective of virulence and after bacteriolysis in phagolysosomes, CDNs produced during infections with evolutionarily diverse bacteria activate STING. Of the several known CDN transporters, two supported bacteria-induced STING activation. We propose a connection between phagocytosis and STING that ensures host-bacteria interactions result in STING activation.

immunology↗

bioRxiv2022

The pore-forming protein gasdermin D is a cellular redox sensor

Reactive oxygen species (ROS) affect inflammation and immunity in a multitude of ways, in particular in the context of the signaling pathways that determine cell fate. Inflammasomes are multiprotein cytoplasmic complexes whose pyroptosis-inducing activities are controlled by ROS. Our knowledge of how ROS mediates inflammasome activities is largely based on studies of the initiating events in these pathways. Herein, we show that ROS controls the terminal events in the pyroptosis pathways. We found that ROS oxidizes the protein gasdermin D (GSDMD) and promotes its assembly into a death-inducing pore forming complex. Mechanistically, ROS enhances GSDMD-mediated pyroptosis in an intrinsic manner, likely through oxidative modification of a specific cysteine residue (C192). Diverse ROS sources promote GSDMD oxidation, ranging from homeostatic control via the Ragulator-Rag complex, to inducible control via diverse microbial products and environmental toxins. These findings expand the steps in the inflammasome pathway that are controlled by ROS and suggest that GSDMD operates as a pyroptosis-inducing redox sensor.

immunology↗

bioRxiv2022

Three functionally distinct classes of cGAS proteins in nature revealed by self-DNA-induced interferon responses

Innate immune pattern recognition receptors (PRRs) emerged early in evolution. It is generally assumed that structurally homologous proteins in distinct species will operate via similar mechanisms. We tested this prediction through the study of interferon responses to self-DNA by the enzymatic PRR cyclic GMP-AMP synthase (cGAS). Contrary to expectations, we identified three functional classes of this PRR in mammals. Class 1 proteins (including human) contained a catalytic domain that was intrinsically self-DNA reactive and stimulated interferon responses in diverse cell types. This reactivity was prevented by an upstream N-terminal domain. Class 2 and 3 proteins were either not self-DNA reactive (including chimpanzee) or included proteins whose N-terminal domain promoted self-DNA reactivity (mouse). While self-DNA reactivity of Class 1 cGAS was linked to an ability to access intra-mitochondrial DNA, mitochondrial localization was not associated with other classes. These studies reveal unexpected diversity in the mechanisms of self-DNA reactivity of a PRR. One Sentence SummaryThe regulation of self-DNA reactivity of cGAS is evolutionarily diverse in mammals.

immunology↗

bioRxiv2022

Human cytomegalovirus vMIA inhibits MAVS oligomerization at peroxisomes in an MFF-dependent manner

Upon intracellular recognition of viral RNA, RIG-I-like proteins interact with MAVS at peroxisomes and mitochondria, inducing its oligomerization and the downstream production of direct antiviral effectors. The human cytomegalovirus (HCMV) is able to specifically evade this antiviral response, via its antiapoptotic protein vMIA. Besides suppressing the programmed cell death of infected cells, vMIA inhibits the antiviral signalling at mitochondria by inducing the organelles fragmentation, consequently hindering the interaction between MAVS and the endoplasmic reticulum protein STING. Here, we demonstrate that vMIA interferes with the peroxisomal antiviral signalling via a distinct mechanism that is independent of the organelles morphology and does not affect STING. vMIA interacts with MAVS at peroxisomes and inhibits its oligomerization, restraining downstream signalling, in an MFF-dependent manner. This study also demonstrates that vMIA is totally dependent on the organelles fission machinery to induce peroxisomal fragmentation, while this dependency is not observed at mitochondria. Furthermore, although we demonstrate that vMIA is also able to inhibit MAVS oligomerization at mitochondria, our results indicate that this process, such as the whole vMIA-mediated inhibition of the mitochondrial antiviral response, is independent of MFF. These observed differences in the mechanisms of action of vMIA towards both organelles, likely reflect their intrinsic differences and roles throughout the viral infection. This study uncovers specific molecular mechanisms that may be further explored as targets for antiviral therapy and highlights the relevance of peroxisomes as platforms for antiviral signalling against HCMV.

cell biology↗

bioRxiv2020

Evolution-inspired dissection of caspase activities enables the redesign of caspase-4 into an LPS sensing interleukin-1 converting enzyme

Innate immune signaling pathways comprise multiple proteins that promote inflammation. This multistep means of information transfer suggests that complexity is a prerequisite for pathway design. Herein, we examined this possibility by studying caspases that regulate inflammasome-dependent inflammation. Several caspases differ in their ability to recognize bacterial LPS and cleave interleukin-1{beta} (IL-1{beta}). No caspase is known to contain both activities, yet distinct caspases with complementary activities bookend an LPS-induced pathway to IL-1{beta} cleavage. Using unique caspases present in carnivorans as a guide, we identified molecular determinants of IL-1{beta} cleavage specificity within caspase-1. This knowledge enabled the redesign of human caspase-4 to operate as a one-protein signaling pathway, which intrinsically links LPS detection to IL-1{beta} cleavage and release, independent of inflammasomes. Strikingly, cat caspase-4 displays the activities of redesigned human caspase-4. These findings illustrate natural signaling pathway diversity and highlight how multistep innate immune pathways can be condensed into a single protein.

immunology↗

bioRxiv2020

Downstream of gasdermin D cleavage, a Ragulator-Rag-mTORC1 pathway promotes pore formation and pyroptosis

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 are recognized to promote GSDMD cleavage, but none are known to be required for pore formation after GSDMD cleavage. Herein, we report a forward genetic screen that was designed to identify regulators of pyroptosis that act downstream of GSDMD cleavage. This screen identified several components of the Ragulator-Rag complex, which is known for its metabolic control of mTOR. Mechanistic studies revealed that Ragulator-Rag is not necessary for GSDMD localization to the plasma membrane, but is necessary for pore formation and mitochondrial inactivation. Downstream of Ragulator-Rag is mTORC1, which we found to promote pyroptosis in response to diverse natural stimuli, including infection. GSDMD therefore requires a Ragulator-Rag-mTORC1 pathway in order to form pores and execute pyroptosis.

immunology↗