Autophosphorylation at serine 166 regulates RIP kinase 1-mediated cell death and inflammation

Raver1 links Ripk1 RNA splicing to caspase-8-mediated pyroptotic cell death, inflammation, and pathogen resistance

Multiple cell death and inflammatory signaling pathways converge on two critical factors: receptor-interacting serine/threonine kinase 1 (RIPK1) and caspase-8. Careful regulation of these molecules is critical to control apoptosis, pyroptosis, and inflammation. Here, we found a pivotal role of Raver1 as an essential regulator of Ripk1 pre-mRNA splicing, expression, and functionality and the subsequent caspase-8-dependent inflammatory cell death. We show that Raver1 influences mRNA diversity primarily by repressing alternative exon inclusion. Macrophages from Raver1-deficient mice exhibit altered splicing of Ripk1. As a result, Raver1-deficient primary macrophages display diminished cell death and decreased interleukin-18 and interleukin-1ß production, when infected with Yersinia bacteria, or by restraining TGF-ß-activated kinase 1 or IKKβ in the presence of lipopolysaccharide, tumor necrosis factor family members, or interferon-γ. These responses are accompanied by reduced activation of caspase-8, Gasdermin D and E, and caspase-1 in the absence of Raver1. Consequently, Raver1-deficient mice showed heightened susceptibility to Yersinia infection. Raver1 and RIPK1 also controlled the expression and function of the C-type lectin receptor Mincle. Our study underscores the critical regulatory role of Raver1 in modulating innate immune responses and highlights its significance in directing in vivo and in vitro inflammatory processes.

RIPK1 in necroptosis and recent progress in related pharmaceutics

Necroptosis is a programmed form of cell death. Receptor-interacting serine/threonine protein kinase l (RIPK1) is a crucial protein kinase that regulates the necroptosis pathway. Increased expression of death receptor family ligands such as tumor necrosis factor (TNF) increases the susceptibility of cells to apoptosis and necroptosis. RIPK1, RIPK3, and mixed-lineage kinase-like domain (MLKL) proteins mediate necrosis. RIPK1-mediated necroptosis further promotes cell death and inflammation in the pathogenesis of liver injury, skin diseases, and neurodegenerative diseases. The N-terminal kinase domain of RIPK1 is significant in the induction of cell death and can be used as a vital drug target for inhibitors. In this paper, we outline the pathways of necroptosis and the role RIPK1 plays in them and suggest that targeting RIPK1 in therapy may help to inhibit multiple cell death pathways.

Innate Immune Sensors and Cell Death-Frontiers Coordinating Homeostasis, Immunity, and Inflammation in Skin

The skin provides a life-sustaining interface between the body and the external environment. A dynamic communication among immune and non-immune cells in the skin is essential to ensure body homeostasis. Dysregulated cellular communication can lead to the manifestation of inflammatory skin conditions. In this review, we will focus on the following two key frontiers in the skin: innate immune sensors and cell death, as well as their cellular crosstalk in the context of skin homeostasis and inflammation. This review will highlight the recent advancements and mechanisms of how these pathways integrate signals and orchestrate skin immunity, focusing on inflammatory skin diseases and skin infections in mice and humans.

Protein shapeshifting in necroptotic cell death signaling

Necroptosis is a mode of programmed cell death executed by the mixed lineage kinase domain-like (MLKL) pseudokinase following its activation by the upstream receptor-interacting protein kinase-3 (RIPK3), subsequent to activation of death, Toll-like, and pathogen receptors. The pathway originates in innate immunity, although interest has surged in therapeutically targeting necroptosis owing to its dysregulation in inflammatory diseases. Here, we explore how protein conformation and higher order assembly of the pathway effectors - Z-DNA-binding protein-1 (ZBP1), RIPK1, RIPK3, and MLKL - can be modulated by post-translational modifications, such as phosphorylation, ubiquitylation, and lipidation, and intermolecular interactions to tune activities and modulate necroptotic signaling flux. As molecular level knowledge of cell death signaling grows, we anticipate targeting the conformations of key necrosomal effector proteins will emerge as new avenues for drug development.

Loss of SGK1 supports metastatic colonization in hepatocellular carcinoma by promoting resistance to T cell-mediated immunity

BACKGROUND & AIMS

Immune evasion by tumor cells is a principal obstacle to effectively targeting metastasis in hepatocellular carcinoma (HCC). However, the specific molecular mechanisms facilitating immune escape during metastatic seeding are not fully elucidated.

METHODS

Utilizing in vivo CRISPR library screening in murine HCC metastasis models under conditions of both intact and depleted T cell immunity, we identified genes critical to tumor immune evasion during metastatic colonization, and investigated intrinsic mechanisms by several experimental approaches.

RESULTS

Our screens identified Sgk1 as an essential suppressor of metastatic colonization under T cell immunosurveillance. Sgk1-deficient tumor cells displayed significantly enhanced metastatic capacity in the presence of CD8+ T cells, underscoring the role of Sgk1 in regulating immune escape. Clinical analyses corroborated these findings, showing markedly lower SGK1 expression in circulating tumor cells and metastatic lesions relative to matched primary tumors in HCC patients, with low SGK1 expression associating with compromised T cell function and poorer clinical outcomes. Mechanistically, Sgk1 inactivation in tumor cells attenuated CD8+ T cell-mediated, RIPK1-dependent necroptosis-a cell death pathway essential for cytotoxic T cell-mediated restriction of metastasis. Loss of Sgk1 consequently enabled tumor cells to circumvent T cell-induced cytotoxicity, thereby promoting metastatic colonization. Furthermore, the outgrowth of Sgk1-deficient metastatic cells induced a microenvironmental shift toward terminal T cell exhaustion, establishing conditions conducive to sustained immune evasion.

CONCLUSIONS

These findings establish SGK1 as a crucial regulator of immune-mediated control over metastatic growth in HCC. SGK1 expression in metastatic lesions may serve as a predictive biomarker for response to immune checkpoint inhibitors, presenting new avenues for therapeutic intervention to overcome immune resistance in metastatic HCC.

IMPACT AND IMPLICATIONS

Despite metastasis is a common occurrence and lethal determinant in cancers, the mechanism underlying tumor immune evasion during metastatic seeding is unclear. Our study reveals that loss of Sgk1 renders metastatic tumor cells survival advantages against antitumor immune response by abrogating CD8+ T cell-induced RIPK1-dependent necroptosis. Growth of Sgk1-silenced metastasis led to infiltration of terminally exhausted CD8+ T cells, which could be reversed by immune checkpoint inhibitors administered at early stage of metastatic seeding. These findings provide valuable insights into potential therapeutic strategies targeting resistance to T cell immunity in cancer metastasis.

A systematic approach to identify gaps in neuroimmunology: TNF-α and fear learning deficits, a worked example

BACKGROUND

The pathophysiology of several neurodegenerative and neuropsychiatric disorders is linked to an altered immune system. However, it is often unclear how the immune system specifically affects these disorders since neuroimmune interactions are very complex. In this paper, we introduce an adjusted version of the adverse outcome pathway (AOP) approach from toxicology to the field of neuroimmunology. A review of the effect of TNF-α on fear learning deficits is used as a worked example to demonstrate how an AOP approach can help identify gaps of knowledge and crucial steps in the pathophysiology of neuroimmunological disorders.

METHODS

The AOP was constructed in five steps. First, the adverse outcome was formulated clearly and specifically. Second, the link between the molecular initiating event and the adverse outcome was established with a preliminary literature search in the Medline database. Third, a systematic literature search was performed in which we identified 95 relevant articles. Fourth, the main biological processes and relevant key events were identified. Fifth, the links between key events were determined and an AOP network was constructed.

RESULTS

We identified three pathways through which TNF-α may affect fear learning. First, TNF-α receptor activation increases NF-κB levels which increases oxidative stress levels and reduces the activity of glutamate transporters. This alters the synaptic plasticity which is associated with impaired fear acquisition, consolidation, and fear extinction. Second, activation of TNF-α receptors increases the expression and capacity of the serotonin transporter which is linked to impaired fear acquisition, expression, and extinction. Third, TNF-α receptor 1 activation can induce necroptosis, leading to neuroinflammation which is linked to fear learning deficits.

CONCLUSION

To successfully apply the AOP approach in neuroimmunology we recommend defining adverse outcomes more precisely, establishing stronger connections between key events from various biological processes, incorporating feedforward and feedback loops, and identifying more mechanistic knowledge in later key events. These adjustments are needed to map the complex processes within the field of neuroimmunology and to identify gaps of knowledge.

Anti-inflammatory and cytoprotective polypharmacology of Canephron N reveals targeting of the IKK-NF-κB and p38-MK2-RIPK1 axes

Urinary tract infections are among the most frequently occurring forms of infection, and inflammation and tissue damage contribute significantly to symptoms, e.g., dysuria and urge. Canephron N is an orally bioavailable herbal medicine with anti-inflammatory, spasmolytic, anti-adhesive, and anti-nociceptive therapeutic effects that is approved for the treatment of uncomplicated urinary tract infections. Here, we used renal tubular epithelial HK-2 cells to study the anti-inflammatory and cytoprotective effects and molecular mechanisms of its active component, BNO 2103. BNO 2103 suppressed nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) activation by lipopolysaccharide (LPS) and tumor necrosis factor alpha (TNFα) and prevented inhibitory κB kinase (IKK)-dependent phosphorylation and degradation of inhibitor of nuclear factor kappa B alpha (IκBα). BNO 2103 also suppressed the inflammation-specific S536 phosphorylation of the NF-κB subunit p65 and the production of a specific set of inflammatory cytokines. Unlike other NF-κB inhibitors, BNO 2103 demonstrated cytoprotection against TNFα-induced cytotoxicity. Our data suggest that BNO 2103 acts primarily through the mitogen-activated protein kinase p38 (p38 MAPK)-MAPK-activated protein kinase 2 (MK2) axis by promoting receptor-interacting serine/threonine protein kinase 1 (RIPK1) phosphorylation at S320. Simultaneously, it suppresses S166 autophosphorylation and subsequent activation of RIPK1, which is required for apoptotic and necroptotic responses to TNFα. This study confirms Canephron N as an effective alternative to traditional anti-inflammatory drugs and provides initial evidence of its ability to inhibit apoptosis and necroptosis in the urogenital system. It also presents a detailed pathway investigation that identifies the specific targets of Canephron N within the NF-κB signaling cascade.

Raver1 links Ripk1 RNA splicing to caspase-8-mediated pyroptotic cell death, inflammation, and pathogen resistance

Multiple cell death and inflammatory signaling pathways converge on two critical factors: receptor interacting serine/threonine kinase 1 (RIPK1) and caspase-8. Careful regulation of these molecules is critical to control apoptosis, pyroptosis and inflammation. Here we discovered a pivotal role of Raver1 as an essential regulator of Ripk1 pre-mRNA splicing, expression, and functionality, and the subsequent caspase-8-dependent inflammatory cell death. Macrophages from Raver1 -deficient mice exhibit altered splicing of Ripk1 , accompanied by diminished cell death and reduced activation of caspase-8, Gasdermin D and E, caspase-1, as well as decreased interleukin-18 (IL-18) and IL-1ß production. These effects were triggered by Yersinia bacteria, or by restraining TAK1 or IKKβ in the presence of LPS, TNF family members, or IFNγ. Consequently, animals lacking Raver1 showed heightened susceptibility to Yersinia infection. Raver1 and RIPK1 also controlled the expression and function of the C-type lectin receptor Mincle. Our study underscores the critical regulatory role of Raver1 in modulating innate immune responses and highlights its significance in directing in vivo and in vitro inflammatory processes.

Significance

Caspase-8 and the kinase RIPK1 are at focal points of several inflammation and cell death pathways. Thus, a careful regulation of their actions is needed. Our work identifies the RNA splicing factor Raver1 as a critical factor directing the splicing of Ripk1 in order to modulate RIPK1/caspase-8-driven pyroptosis, apoptosis and inflammation. Raver1 is central for macrophage responses to Yersinia bacteria, initiated after blockade of kinases TAK1 and IKK, measured as activation of RIPK1, caspase-8, Gasdermin D, caspase-3, IL-1ß and IL-18. Importantly, Raver1 is necessary for host resistance to Yersinia infection in vivo . We propose that Raver1 is key for correct tuning of RIPK1-caspase-8 dependent processes.

Palmitoylation licenses RIPK1 kinase activity and cytotoxicity in the TNF pathway

Tumor necrosis factor (TNF)-induced receptor-interacting serine/threonine protein kinase 1 (RIPK1)-mediated cell death, including apoptosis and necroptosis, is increasingly recognized as a major driver of inflammatory diseases. Cell death checkpoints normally suppress RIPK1 kinase to safeguard the organism from its detrimental consequences. However, the mechanisms licensing RIPK1 kinase activity when a protective checkpoint is disabled remain unclear. Here, we identified S-palmitoylation as a licensing modification for RIPK1 kinase. TNF induces RIPK1 palmitoylation, mediated by DHHC5 and dependent on K63-linked ubiquitination of RIPK1, which enhances RIPK1 kinase activity by promoting the homo-interaction of its kinase domain and promotes cell death upon cell death checkpoint blockade. Furthermore, DHHC5 is amplified by fatty acid in the livers of mice with metabolic dysfunction-associated steatohepatitis, contributing to increased RIPK1 cytotoxicity observed in this condition. Our findings reveal that ubiquitination-dependent palmitoylation licenses RIPK1 kinase activity to induce downstream cell death signaling and suggest RIPK1 palmitoylation as a feasible target for inflammatory diseases.

Large-scale characterization of drug mechanism of action using proteome-wide thermal shift assays

In response to an ever-increasing demand of new small molecules therapeutics, numerous chemical and genetic tools have been developed to interrogate compound mechanism of action. Owing to its ability to approximate compound-dependent changes in thermal stability, the proteome-wide thermal shift assay has emerged as a powerful tool in this arsenal. The most recent iterations have drastically improved the overall efficiency of these assays, providing an opportunity to screen compounds at a previously unprecedented rate. Taking advantage of this advance, we quantified more than one million thermal stability measurements in response to multiple classes of therapeutic and tool compounds (96 compounds in living cells and 70 compounds in lysates). When interrogating the dataset as a whole, approximately 80% of compounds (with quantifiable targets) caused a significant change in the thermal stability of an annotated target. There was also a wealth of evidence portending off-target engagement despite the extensive use of the compounds in the laboratory and/or clinic. Finally, the combined application of cell- and lysate-based assays, aided in the classification of primary (direct ligand binding) and secondary (indirect) changes in thermal stability. Overall, this study highlights the value of these assays in the drug development process by affording an unbiased and reliable assessment of compound mechanism of action.

Regulated cell death in chronic kidney disease: current evidence and future clinical perspectives

Chronic kidney disease (CKD) is the progressive loss of kidney function/structure over a period of at least 3 months. It is characterised histologically by the triad of cell loss, inflammation and fibrosis. This literature review focuses on the forms of cell death that trigger downstream inflammation and fibrosis, collectively called regulated cell death (RCD) pathways. Discrete forms of RCD have emerged as central mediators of CKD pathology. In particular, pathways of regulated necrosis - including mitochondrial permeability transition pore (mPTP)-mediated necrosis, necroptosis, ferroptosis and pyroptosis - have been shown to mediate kidney pathology directly or through the release of danger signals that trigger a pro-inflammatory response, further amplifying tissue injury in a cellular process called necroinflammation. Despite accumulating evidence in pre-clinical models, no clinical studies have yet targeted these RCD modes in human CKD. The review summarizes recent advances in our understanding of RCD pathways in CKD, looks at inter-relations between the pathways (with the emphasis on propagation of death signals) and the evidence for therapeutic targeting of molecules in the RCD pathways to prevent or treat CKD.

CD14 is a decision-maker between Fas-mediated death and inflammation

Signaling through classical death receptor Fas was mainly appreciated as a pro-death pathway until recent reports characterized pro-inflammatory outcomes of Fas-mediated activation in pathological contexts. How Fas signaling can switch to pro-inflammatory activation is poorly understood. Herein, we report that in macrophages and neutrophils, the Toll-like receptor (TLR) adapter CD14 determines the inflammatory output of Fas-mediated signaling. Our findings propose CD14 as a crucial chaperone of Fas receptor internalization in macrophages and neutrophils, resulting in Cd14-/- myeloid cells that are protected from FasL-induced apoptosis, activate nuclear factor κB (NF-κB), and release cytokines in response. As in TLR signaling, CD14 is also required for Fas to signal through the adaptor TRIF (TIR-domain-containing adapter-inducing interferon-β) and induce a pro-death complex. Our findings demonstrate that CD14 availability can determine the switch between Fas-mediated pro-death and pro-inflammatory outcomes by internalizing the receptor.

Significance of Programmed Cell Death Pathways in Neurodegenerative Diseases

Programmed cell death (PCD) is a form of cell death distinct from accidental cell death (ACD) and is also referred to as regulated cell death (RCD). Typically, PCD signaling events are precisely regulated by various biomolecules in both spatial and temporal contexts to promote neuronal development, establish neural architecture, and shape the central nervous system (CNS), although the role of PCD extends beyond the CNS. Abnormalities in PCD signaling cascades contribute to the irreversible loss of neuronal cells and function, leading to the onset and progression of neurodegenerative diseases. In this review, we summarize the molecular processes and features of different modalities of PCD, including apoptosis, necroptosis, pyroptosis, ferroptosis, cuproptosis, and other novel forms of PCD, and their effects on the pathogenesis of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), spinal muscular atrophy (SMA), multiple sclerosis (MS), traumatic brain injury (TBI), and stroke. Additionally, we examine the key factors involved in these PCD signaling pathways and discuss the potential for their development as therapeutic targets and strategies. Therefore, therapeutic strategies targeting the inhibition or facilitation of PCD signaling pathways offer a promising approach for clinical applications in treating neurodegenerative diseases.

Bioactivated Glucoraphanin Modulates Genes Involved in Necroptosis on Motor-Neuron-like Nsc-34: A Transcriptomic Study

Research on bioactive compounds has grown recently due to their health benefits and limited adverse effects, particularly in reducing the risk of chronic diseases, including neurodegenerative conditions. According to these observations, this study investigates the activity of sulforaphane (RS-GRA) on an in vitro model of differentiated NSC-34 cells. We performed a transcriptomic analysis at various time points (24 h, 48 h, and 72 h) and RS-GRA concentrations (1 µM, 5 µM, and 10 µM) to identify molecular pathways influenced by this compound and the effects of dosage and prolonged exposure. We found 39 differentially expressed genes consistently up- or downregulated across all conditions. Notably, Nfe2l2, Slc1a5, Slc7a11, Slc6a9, Slc6a5, Sod1, and Sod2 genes were consistently upregulated, while Ripk1, Glul, Ripk3, and Mlkl genes were downregulated. Pathway perturbation analysis showed that the overall dysregulation of these genes results in a significant increase in redox pathway activity (adjusted p-value 1.11 × 10-3) and a significant inhibition of the necroptosis pathway (adjusted p-value 4.64 × 10-3). These findings suggest RS-GRA's potential as an adjuvant in neurodegenerative disease treatment, as both increased redox activity and necroptosis inhibition may be beneficial in this context. Furthermore, our data suggest two possible administration strategies, namely an acute approach with higher dosages and a chronic approach with lower dosages.

ASIC1/RIP1 accelerates atherosclerosis via disrupting lipophagy

INTRODUCTION

Atherosclerosis, a major contributor to cardiovascular disease, remains a significant health concern worldwide. While previous research has shown that acid-sensing ion channel 1 (ASIC1) impedes macrophage cholesterol efflux, its precise role in atherogenesis and the underlying mechanisms have remained elusive.

OBJECTIVES

This study aimed to investigate the role of ASIC1 in atherosclerosis and its underlying mechanisms.

METHODS

First, data from a single-cell RNA sequencing (scRNA-seq) database were used to explore the relationships between ASIC1 differential expression and lipophagy in human atherosclerotic lesions. Finally, we validated the role of ASIC1/RIP1 signaling in lipophagy in vivo (human and mice) and in vitro (RAW264.7 and HTP-1 cells).

RESULT

Our results demonstrated a significant increase in ASIC1 protein levels within CD68+ macrophages in both human aortic lesions and AopE-/- mouse lesion areas compared to nonlesion regions. Concurrently, there was a notable decrease in lipophagy, a crucial process for lipid metabolism. In vitro assays further elucidated that ASIC1 interaction with RIP1 (receptor-interacting protein 1) promoted the phosphorylation of RIP1 at serine 166 and transcription factor EB (TFEB) at serine 142, leading to disrupted lipophagy and increased lipid accumulation. Intriguingly, all these events were reversed upon ASIC1 deficiency and RIP1 inhibition. Furthermore, in ApoE-/- mouse models of atherosclerosis, silencing ASIC1 expression or inhibiting RIP1 activation not only significantly attenuated atherogenesis but also restored TFEB-mediated lipophagy in aortic tissues. This was evidenced by reduced TFEB Ser-142 phosphorylation, decreased LC3II and LAMP1 protein expression, increased numbers of lipophagosomes, and a decrease in lipid droplets.

CONCLUSION

Our findings unveil the critical role of macrophage ASIC1 in interacting with RIP1 to inhibit lipophagy, thereby promoting atherogenesis. Targeting ASIC1 represents a promising therapeutic avenue for the treatment of atherosclerosis.

Modulation of extrinsic apoptotic pathway by intracellular glycosylation

The importance of post-translational modifications (PTMs), particularly O-GlcNAcylation, of cytoplasmic proteins in apoptosis has been neglected for quite a while. Modification of cytoplasmic proteins by a single N-acetylglucosamine sugar is a dynamic and reversible PTM exhibiting properties more like phosphorylation than classical O- and N-linked glycosylation. Due to the sparse information existing, we have only limited understanding of how GlcNAcylation affects cell death. Deciphering the role of GlcNAcylation in cell fate may provide further understanding of cell fate decisions. This review focus on the modulation of extrinsic apoptotic pathway via GlcNAcylation carried out by O-GlcNAc transferase (OGT) or by other bacterial effector proteins.

VIK-Mediated Auxin Signaling Regulates Lateral Root Development in Arabidopsis

The crucial role of TIR1-receptor-mediated gene transcription regulation in auxin signaling has long been established. In recent years, the significant role of protein phosphorylation modifications in auxin signal transduction has gradually emerged. To further elucidate the significant role of protein phosphorylation modifications in auxin signaling, a phosphoproteomic analysis in conjunction with auxin treatment has identified an auxin activated Mitogen-activated Protein Kinase Kinase Kinase (MAPKKK) VH1-INTERACTING Kinase (VIK), which plays an important role in auxin-induced lateral root (LR) development. In the vik mutant, auxin-induced LR development is significantly attenuated. Further investigations show that VIK interacts separately with the positive regulator of LR development, LATERAL ORGAN BOUNDARIES-DOMAIN18 (LBD18), and the negative regulator of LR emergence, Ethylene Responsive Factor 13 (ERF13). VIK directly phosphorylates and stabilizes the positive transcription factor LBD18 in LR formation. In the meantime, VIK directly phosphorylates the negative regulator ERF13 at Ser168 and Ser172 sites, causing its degradation and releasing the repression by ERF13 on LR emergence. In summary, VIK-mediated auxin signaling regulates LR development by enhancing the protein stability of LBD18 and inducing the degradation of ERF13, respectively.

Targeting necroptosis: a promising avenue for respiratory disease treatment

Respiratory diseases are a growing concern in public health because of their potential to endanger the global community. Cell death contributes critically to the pathophysiology of respiratory diseases. Recent evidence indicates that necroptosis, a unique form of programmed cell death (PCD), plays a vital role in the molecular mechanisms underlying respiratory diseases, distinguishing it from apoptosis and conventional necrosis. Necroptosis is a type of inflammatory cell death governed by receptor-interacting serine/threonine protein kinase 1 (RIPK1), RIPK3, and mixed-lineage kinase domain-like protein (MLKL), resulting in the release of intracellular contents and inflammatory factors capable of initiating an inflammatory response in adjacent tissues. These necroinflammatory conditions can result in significant organ dysfunction and long-lasting tissue damage within the lungs. Despite evidence linking necroptosis to various respiratory diseases, there are currently no specific alternative treatments that target this mechanism. This review provides a comprehensive overview of the most recent advancements in understanding the significance and mechanisms of necroptosis. Specifically, this review emphasizes the intricate association between necroptosis and respiratory diseases, highlighting the potential use of necroptosis as an innovative therapeutic approach for treating these conditions.

Non-canonical autophosphorylation of RIPK1 drives timely pyroptosis to control Yersinia infection

Caspase-8-dependent pyroptosis has been shown to mediate host protection from Yersinia infection. For this mode of cell death, the kinase activity of receptor-interacting protein kinase 1 (RIPK1) is required, but the autophosphorylation sites required to drive caspase-8 activation have not been determined. Here, we show that non-canonical autophosphorylation of RIPK1 at threonine 169 (T169) is necessary for caspase-8-mediated pyroptosis. Mice with alanine in the T169 position are highly susceptible to Yersinia dissemination. Mechanistically, the delayed formation of a complex containing RIPK1, ZBP1, Fas-associated protein with death domain (FADD), and caspase-8 abrogates caspase-8 maturation in T169A mice and leads to the eventual activation of RIPK3-dependent necroptosis in vivo; however, this is insufficient to protect the host, suggesting that timely pyroptosis during early response is specifically required to control infection. These results position RIPK1 T169 phosphorylation as a driver of pyroptotic cell death critical for host defense.

Large-scale characterization of drug mechanism of action using proteome-wide thermal shift assays

In response to an ever-increasing demand of new small molecules therapeutics, numerous chemical and genetic tools have been developed to interrogate compound mechanism of action. Owing to its ability to approximate compound-dependent changes in thermal stability, the proteome-wide thermal shift assay has emerged as a powerful tool in this arsenal. The most recent iterations have drastically improved the overall efficiency of these assays, providing an opportunity to screen compounds at a previously unprecedented rate. Taking advantage of this advance, we quantified more than one million thermal stability measurements in response to multiple classes of therapeutic and tool compounds (96 compounds in living cells and 70 compounds in lysates). When interrogating the dataset as a whole, approximately 80% of compounds (with quantifiable targets) caused a significant change in the thermal stability of an annotated target. There was also a wealth of evidence portending off-target engagement despite the extensive use of the compounds in the laboratory and/or clinic. Finally, the combined application of cell- and lysate-based assays, aided in the classification of primary (direct ligand binding) and secondary (indirect) changes in thermal stability. Overall, this study highlights the value of these assays in the drug development process by affording an unbiased and reliable assessment of compound mechanism of action.

TBK1 and IKKε protect target cells from IFNγ-mediated T cell killing via an inflammatory apoptotic mechanism

Cytotoxic T cells produce interferon gamma (IFNγ), which plays a critical role in anti-microbial and anti-tumor responses. However, it is not clear whether T cell-derived IFNγ directly kills infected and tumor target cells, and how this may be regulated. Here, we report that target cell expression of the kinases TBK1 and IKKε regulate IFNγ cytotoxicity by suppressing the ability of T cell-derived IFNγ to kill target cells. In tumor targets lacking TBK1 and IKKε, IFNγ induces expression of TNFR1 and the Z-nucleic acid sensor, ZBP1, to trigger RIPK1-dependent apoptosis, largely in a target cell-autonomous manner. Unexpectedly, IFNγ, which is not known to signal to NFκB, induces hyperactivation of NFκB in TBK1 and IKKε double-deficient cells. TBK1 and IKKε suppress IKKα/β activity and in their absence, IFNγ induces elevated NFκB-dependent expression of inflammatory chemokines and cytokines. Apoptosis is thought to be non-inflammatory, but our observations demonstrate that IFNγ can induce an inflammatory form of apoptosis, and this is suppressed by TBK1 and IKKε. The two kinases provide a critical connection between innate and adaptive immunological responses by regulating three key responses: (1) phosphorylation of IRF3/7 to induce type I IFN; (2) inhibition of RIPK1-dependent death; and (3) inhibition of NFκB-dependent inflammation. We propose that these kinases evolved these functions such that their inhibition by pathogens attempting to block type I IFN expression would enable IFNγ to trigger apoptosis accompanied by an alternative inflammatory response. Our findings show that loss of TBK1 and IKKε in target cells sensitizes them to inflammatory apoptosis induced by T cell-derived IFNγ.

Blockade of IKK signaling induces RIPK1-independent apoptosis in human macrophages

Regulated cell death in response to microbial infection plays an important role in immune defense and is triggered by pathogen disruption of essential cellular pathways. Gram-negative bacterial pathogens in the Yersinia genus disrupt NF-κB signaling via translocated effectors injected by a type III secretion system, thereby preventing induction of cytokine production and antimicrobial defense. In murine models of infection, Yersinia blockade of NF-κB signaling triggers cell-extrinsic apoptosis through Receptor Interacting Serine-Threonine Protein Kinase 1 (RIPK1) and caspase-8, which is required for bacterial clearance and host survival. Unexpectedly, we find that human macrophages undergo apoptosis independently of RIPK1 in response to Yersinia or chemical blockade of IKKβ. Instead, IKK blockade led to decreased cFLIP expression, and overexpression of cFLIP contributed to protection from IKK blockade-induced apoptosis in human macrophages. We found that IKK blockade also induces RIPK1 kinase activity-independent apoptosis in human T cells and human pancreatic cells. Altogether, our data indicate that, in contrast to murine cells, blockade of IKK activity in human cells triggers a distinct apoptosis pathway that is independent of RIPK1 kinase activity. These findings have implications for the contribution of RIPK1 to cell death in human cells and the efficacy of RIPK1 inhibition in human diseases.

Impact of protein and small molecule interactions on kinase conformations

Protein kinases act as central molecular switches in the control of cellular functions. Alterations in the regulation and function of protein kinases may provoke diseases including cancer. In this study we investigate the conformational states of such disease-associated kinases using the high sensitivity of the kinase conformation (KinCon) reporter system. We first track BRAF kinase activity conformational changes upon melanoma drug binding. Second, we also use the KinCon reporter technology to examine the impact of regulatory protein interactions on LKB1 kinase tumor suppressor functions. Third, we explore the conformational dynamics of RIP kinases in response to TNF pathway activation and small molecule interactions. Finally, we show that CDK4/6 interactions with regulatory proteins alter conformations which remain unaffected in the presence of clinically applied inhibitors. Apart from its predictive value, the KinCon technology helps to identify cellular factors that impact drug efficacies. The understanding of the structural dynamics of full-length protein kinases when interacting with small molecule inhibitors or regulatory proteins is crucial for designing more effective therapeutic strategies.

A RIPK1-specific PROTAC degrader achieves potent antitumor activity by enhancing immunogenic cell death

Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) functions as a critical stress sentinel that coordinates cell survival, inflammation, and immunogenic cell death (ICD). Although the catalytic function of RIPK1 is required to trigger cell death, its non-catalytic scaffold function mediates strong pro-survival signaling. Accordingly, cancer cells can hijack RIPK1 to block necroptosis and evade immune detection. We generated a small-molecule proteolysis-targeting chimera (PROTAC) that selectively degraded human and murine RIPK1. PROTAC-mediated depletion of RIPK1 deregulated TNFR1 and TLR3/4 signaling hubs, accentuating the output of NF-κB, MAPK, and IFN signaling. Additionally, RIPK1 degradation simultaneously promoted RIPK3 activation and necroptosis induction. We further demonstrated that RIPK1 degradation enhanced the immunostimulatory effects of radio- and immunotherapy by sensitizing cancer cells to treatment-induced TNF and interferons. This promoted ICD, antitumor immunity, and durable treatment responses. Consequently, targeting RIPK1 by PROTACs emerges as a promising approach to overcome radio- or immunotherapy resistance and enhance anticancer therapies.

Regulation of RIPK1 Phosphorylation: Implications for Inflammation, Cell Death, and Therapeutic Interventions

Receptor-interacting protein kinase 1 (RIPK1) plays a crucial role in controlling inflammation and cell death. Its function is tightly controlled through post-translational modifications, enabling its dynamic switch between promoting cell survival and triggering cell death. Phosphorylation of RIPK1 at various sites serves as a critical mechanism for regulating its activity, exerting either activating or inhibitory effects. Perturbations in RIPK1 phosphorylation status have profound implications for the development of severe inflammatory diseases in humans. This review explores the intricate regulation of RIPK1 phosphorylation and dephosphorylation and highlights the potential of targeting RIPK1 phosphorylation as a promising therapeutic strategy for mitigating human diseases.

The role of RIPK1 in chronic obstructive pulmonary disease

Necroptosis has emerged as one of the crucial pathological processes involved in the regulation of cell death and inflammation in chronic obstructive pulmonary disease (COPD). Airway epithelial necroptosis is closely linked to COPD pathogenesis. Necroptotic lung cells can release damage-associated molecular patterns (DAMPs) that can initiate a robust inflammatory response. However, the underlying mechanism of necroptosis in COPD is still not clearly understood. Therefore, we aimed to explore the roles and mechanisms of receptor-interacting serine/threonine-protein kinase 1 (RIPK1)-mediated necroptosis in the regulation of inflammatory responses in COPD to provide insights into RIPK1-inhibitor drug discovery efforts and their therapeutic benefits in COPD.

The role of mitochondrial damage-associated molecular patterns in acute pancreatitis

Acute pancreatitis (AP) is one of the most common gastrointestinal tract diseases with significant morbidity and mortality. Current treatments remain unspecific and supportive due to the severity and clinical course of AP, which can fluctuate rapidly and unpredictably. Mitochondria, cellular power plant to produce energy, are involved in a variety of physiological or pathological activities in human body. There is a growing evidence indicating that mitochondria damage-associated molecular patterns (mtDAMPs) play an important role in pathogenesis and progression of AP. With the pro-inflammatory properties, released mtDAMPs may damage pancreatic cells by binding with receptors, activating downstream molecules and releasing inflammatory factors. This review focuses on the possible interaction between AP and mtDAMPs, which include cytochrome c (Cyt c), mitochondrial transcription factor A (TFAM), mitochondrial DNA (mtDNA), cardiolipin (CL), adenosine triphosphate (ATP) and succinate, with focus on experimental research and potential therapeutic targets in clinical practice. Preventing or diminishing the release of mtDAMPs or targeting the mtDAMPs receptors might have a role in AP progression.

Rotavirus non-structural protein 4 usurps host cellular RIPK1-RIPK3 complex to induce MLKL-dependent necroptotic cell death

The dynamic interface between invading viral pathogens and programmed cell death (PCD) of the host is a finely regulated process. Host cellular demise at the end of the viral life cycle ensures the release of progeny virions to initiate new infection cycles. Rotavirus (RV), a diarrheagenic virus with double-stranded RNA genome, has been reported to trigger different types of PCD such as apoptosis and pyroptosis in a highly regulated way to successfully disseminate progeny virions. Recently our lab also showed that induction of MLKL-driven programmed necroptosis by RV. However, the host cellular machinery involved in RV-induced necroptosis and the upstream viral trigger responsible for it remained unaddressed. In the present study, the signalling upstream of MLKL-driven necroptosis has been delineated where the involvement of Receptor interacting serine/threonine kinase 3 (RIPK3) and 1 (RIPK1) from the host side and RV non-structural protein 4 (NSP4) as the viral trigger for necroptosis has been shown. Interestingly, RV-NSP4 was found to be an integral component of the necrosome complex by interacting with RIPK1, thereby bypassing the requirement of RIPK1 kinase activity. Subsequently, NSP4-driven elevated cytosolic Ca2+ concentration and Ca2+-binding to NSP4 lead further to RHIM domain-dependent RIPK1-RIPK3 interaction, RIPK3-dependent MLKL phosphorylation, and eventual necroptosis. Overall, this study presents the interplay between RV-NSP4 and the host cellular necrosome complex to induce necroptotic death of host cells.

The protein phosphatase PP6 promotes RIPK1-dependent PANoptosis

BACKGROUND

The innate immune system serves as the first line of host defense. Transforming growth factor-β-activated kinase 1 (TAK1) is a key regulator of innate immunity, cell survival, and cellular homeostasis. Because of its importance in immunity, several pathogens have evolved to carry TAK1 inhibitors. In response, hosts have evolved to sense TAK1 inhibition and induce robust lytic cell death, PANoptosis, mediated by the RIPK1-PANoptosome. PANoptosis is a unique innate immune inflammatory lytic cell death pathway initiated by an innate immune sensor and driven by caspases and RIPKs. While PANoptosis can be beneficial to clear pathogens, excess activation is linked to pathology. Therefore, understanding the molecular mechanisms regulating TAK1 inhibitor (TAK1i)-induced PANoptosis is central to our understanding of RIPK1 in health and disease.

RESULTS

In this study, by analyzing results from a cell death-based CRISPR screen, we identified protein phosphatase 6 (PP6) holoenzyme components as regulators of TAK1i-induced PANoptosis. Loss of the PP6 enzymatic component, PPP6C, significantly reduced TAK1i-induced PANoptosis. Additionally, the PP6 regulatory subunits PPP6R1, PPP6R2, and PPP6R3 had redundant roles in regulating TAK1i-induced PANoptosis, and their combined depletion was required to block TAK1i-induced cell death. Mechanistically, PPP6C and its regulatory subunits promoted the pro-death S166 auto-phosphorylation of RIPK1 and led to a reduction in the pro-survival S321 phosphorylation.

CONCLUSIONS

Overall, our findings demonstrate a key requirement for the phosphatase PP6 complex in the activation of TAK1i-induced, RIPK1-dependent PANoptosis, suggesting this complex could be therapeutically targeted in inflammatory conditions.

Targeting the TNF/IAP pathway synergizes with anti-CD3 immunotherapy in T-cell acute lymphoblastic leukemia

ABSTRACT

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy. Current treatments, based on intensive chemotherapy regimens provide overall survival rates of ∼85% in children and <50% in adults, calling the search of new therapeutic options. We previously reported that targeting the T-cell receptor (TCR) in T-ALL with anti-CD3 (αCD3) monoclonal antibodies (mAbs) enforces a molecular program akin to thymic negative selection, a major developmental checkpoint in normal T-cell development; induces leukemic cell death; and impairs leukemia progression to ultimately improve host survival. However, αCD3 monotherapy resulted in relapse. To find out actionable targets able to re-enforce leukemic cells' vulnerability to αCD3 mAbs, including the clinically relevant teplizumab, we identified the molecular program induced by αCD3 mAbs in patient-derived xenografts derived from T-ALL cases. Using large-scale transcriptomic analysis, we found prominent expression of tumor necrosis factor α (TNFα), lymphotoxin α (LTα), and multiple components of the "TNFα via NF-κB signaling" pathway in anti-CD3-treated T-ALL. We show in vivo that etanercept, a sink for TNFα/LTα, enhances αCD3 antileukemic properties, indicating that TNF/TNF receptor (TNFR) survival pathways interferes with TCR-induced leukemic cell death. However, suppression of TNF-mediated survival and switch to TNFR-mediated cell death through inhibition of cellular inhibitor of apoptosis protein-1/2 (cIAP1/2) with the second mitochondrial-derived activator of caspases (SMAC) mimetic birinapant synergizes with αCD3 to impair leukemia expansion in a receptor-interacting serine/threonine-protein kinase 1-dependent manner and improve mice survival. Thus, our results advocate the use of either TNFα/LTα inhibitors, or birinapant/other SMAC mimetics to improve anti-CD3 immunotherapy in T-ALL.

Emerging role of immunogenic cell death in cancer immunotherapy

Cancer immunotherapy, such as immune checkpoint blockade (ICB), has emerged as a groundbreaking approach for effective cancer treatment. Despite its considerable potential, clinical studies have indicated that the current response rate to cancer immunotherapy is suboptimal, primarily attributed to low immunogenicity in certain types of malignant tumors. Immunogenic cell death (ICD) represents a form of regulated cell death (RCD) capable of enhancing tumor immunogenicity and activating tumor-specific innate and adaptive immune responses in immunocompetent hosts. Therefore, gaining a deeper understanding of ICD and its evolution is crucial for developing more effective cancer therapeutic strategies. This review focuses exclusively on both historical and recent discoveries related to ICD modes and their mechanistic insights, particularly within the context of cancer immunotherapy. Our recent findings are also highlighted, revealing a mode of ICD induction facilitated by atypical interferon (IFN)-stimulated genes (ISGs), including polo-like kinase 2 (PLK2), during hyperactive type I IFN signaling. The review concludes by discussing the therapeutic potential of ICD, with special attention to its relevance in both preclinical and clinical settings within the field of cancer immunotherapy.

Protein phosphorylation and kinases: Potential therapeutic targets in necroptosis

Necroptosis is a pivotal contributor to the pathogenesis of various human diseases, including those affecting the nervous system, cardiovascular system, pulmonary system, and kidneys. Extensive investigations have elucidated the mechanisms and physiological ramifications of necroptosis. Among these, protein phosphorylation emerges as a paramount regulatory process, facilitating the activation or inhibition of specific proteins through the addition of phosphate groups to their corresponding amino acid residues. Currently, the targeting of kinases has gained recognition as a firmly established and efficacious therapeutic approach for diverse diseases, notably cancer. In this comprehensive review, we elucidate the intricate role of phosphorylation in governing key molecular players in the necroptotic pathway. Moreover, we provide an in-depth analysis of recent advancements in the development of kinase inhibitors aimed at modulating necroptosis. Lastly, we deliberate on the prospects and challenges associated with the utilization of kinase inhibitors to modulate necroptotic processes.

Immunogenic cell death in cancer: targeting necroptosis to induce antitumour immunity

Most metastatic cancers remain incurable due to the emergence of apoptosis-resistant clones, fuelled by intratumour heterogeneity and tumour evolution. To improve treatment, therapies should not only kill cancer cells but also activate the immune system against the tumour to eliminate any residual cancer cells that survive treatment. While current cancer therapies rely heavily on apoptosis - a largely immunologically silent form of cell death - there is growing interest in harnessing immunogenic forms of cell death such as necroptosis. Unlike apoptosis, necroptosis generates second messengers that act on immune cells in the tumour microenvironment, alerting them of danger. This lytic form of cell death optimizes the provision of antigens and adjuvanticity for immune cells, potentially boosting anticancer treatment approaches by combining cellular suicide and immune response approaches. In this Review, we discuss the mechanisms of necroptosis and how it activates antigen-presenting cells, drives cross-priming of CD8+ T cells and induces antitumour immune responses. We also examine the opportunities and potential drawbacks of such strategies for exposing cancer cells to immunological attacks.

Biallelic human SHARPIN loss of function induces autoinflammation and immunodeficiency

The linear ubiquitin assembly complex (LUBAC) consists of HOIP, HOIL-1 and SHARPIN and is essential for proper immune responses. Individuals with HOIP and HOIL-1 deficiencies present with severe immunodeficiency, autoinflammation and glycogen storage disease. In mice, the loss of Sharpin leads to severe dermatitis due to excessive keratinocyte cell death. Here, we report two individuals with SHARPIN deficiency who manifest autoinflammatory symptoms but unexpectedly no dermatological problems. Fibroblasts and B cells from these individuals showed attenuated canonical NF-κB responses and a propensity for cell death mediated by TNF superfamily members. Both SHARPIN-deficient and HOIP-deficient individuals showed a substantial reduction of secondary lymphoid germinal center B cell development. Treatment of one SHARPIN-deficient individual with anti-TNF therapies led to complete clinical and transcriptomic resolution of autoinflammation. These findings underscore the critical function of the LUBAC as a gatekeeper for cell death-mediated immune dysregulation in humans.

A guide to cell death pathways

Regulated cell death mediated by dedicated molecular machines, known as programmed cell death, plays important roles in health and disease. Apoptosis, necroptosis and pyroptosis are three such programmed cell death modalities. The caspase family of cysteine proteases serve as key regulators of programmed cell death. During apoptosis, a cascade of caspase activation mediates signal transduction and cellular destruction, whereas pyroptosis occurs when activated caspases cleave gasdermins, which can then form pores in the plasma membrane. Necroptosis, a form of caspase-independent programmed necrosis mediated by RIPK3 and MLKL, is inhibited by caspase-8-mediated cleavage of RIPK1. Disruption of cellular homeostatic mechanisms that are essential for cell survival, such as normal ionic and redox balance and lysosomal flux, can also induce cell death without invoking programmed cell death mechanisms. Excitotoxicity, ferroptosis and lysosomal cell death are examples of such cell death modes. In this Review, we provide an overview of the major cell death mechanisms, highlighting the latest insights into their complex regulation and execution, and their relevance to human diseases.

RIPK3 signaling and its role in regulated cell death and diseases

Receptor-interacting protein kinase 3 (RIPK3), a member of the receptor-interacting protein kinase (RIPK) family with serine/threonine protein kinase activity, interacts with RIPK1 to generate necrosomes, which trigger caspase-independent programmed necrosis. As a vital component of necrosomes, RIPK3 plays an indispensable role in necroptosis, which is crucial for human life and health. In addition, RIPK3 participates in the pathological process of several infections, aseptic inflammatory diseases, and tumors (including tumor-promoting and -suppressive activities) by regulating autophagy, cell proliferation, and the metabolism and production of chemokines/cytokines. This review summarizes the recent research progress of the regulators of the RIPK3 signaling pathway and discusses the potential role of RIPK3/necroptosis in the aetiopathogenesis of various diseases. An in-depth understanding of the mechanisms and functions of RIPK3 may facilitate the development of novel therapeutic strategies.

Cellular heterogeneity in TNF/TNFR1 signalling: live cell imaging of cell fate decisions in single cells

Cellular responses to TNF are inherently heterogeneous within an isogenic cell population and across different cell types. TNF promotes cell survival by activating pro-inflammatory NF-κB and MAPK signalling pathways but may also trigger apoptosis and necroptosis. Following TNF stimulation, the fate of individual cells is governed by the balance of pro-survival and pro-apoptotic signalling pathways. To elucidate the molecular mechanisms driving heterogenous responses to TNF, quantifying TNF/TNFR1 signalling at the single-cell level is crucial. Fluorescence live-cell imaging techniques offer real-time, dynamic insights into molecular processes in single cells, allowing for detection of rapid and transient changes, as well as identification of subpopulations, that are likely to be missed with traditional endpoint assays. Whilst fluorescence live-cell imaging has been employed extensively to investigate TNF-induced inflammation and TNF-induced cell death, it has been underutilised in studying the role of TNF/TNFR1 signalling pathway crosstalk in guiding cell-fate decisions in single cells. Here, we outline the various opportunities for pathway crosstalk during TNF/TNFR1 signalling and how these interactions may govern heterogenous responses to TNF. We also advocate for the use of live-cell imaging techniques to elucidate the molecular processes driving cell-to-cell variability in single cells. Understanding and overcoming cellular heterogeneity in response to TNF and modulators of the TNF/TNFR1 signalling pathway could lead to the development of targeted therapies for various diseases associated with aberrant TNF/TNFR1 signalling, such as rheumatoid arthritis, metabolic syndrome, and cancer.

RIP3 in Necroptosis: Underlying Contributions to Traumatic Brain Injury

Traumatic brain injury (TBI) is a global public safety issue that poses a threat to death, characterized by high fatality rates, severe injuries and low recovery rates. There is growing evidence that necroptosis regulates the pathophysiological processes of a variety of diseases, particularly those affecting the central nervous system. Thus, moderate necroptosis inhibition may be helpful in the management of TBI. Receptor-interacting protein kinase (RIP) 3 is a key mediator in the necroptosis, and its absence helps restore the microenvironment at the injured site and improve cognitive impairment after TBI. In this report, we review different domains of RIP3, multiple analyses of necroptosis, and associations between necroptosis and TBI, RIP3, RIP1, and mixed lineage kinase domain-like. Next, we elucidate the potential involvement of RIP3 in TBI and highlight how RIP3 deficiency enhances neuronal function.

Mediators of necroptosis: from cell death to metabolic regulation

Necroptosis, a programmed cell death mechanism distinct from apoptosis, has garnered attention for its role in various pathological conditions. While initially recognized for its involvement in cell death, recent research has revealed that key necroptotic mediators, including receptor-interacting protein kinases (RIPKs) and mixed lineage kinase domain-like protein (MLKL), possess additional functions that go beyond inducing cell demise. These functions encompass influencing critical aspects of metabolic regulation, such as energy metabolism, glucose homeostasis, and lipid metabolism. Dysregulated necroptosis has been implicated in metabolic diseases, including obesity, diabetes, metabolic dysfunction-associated steatotic liver disease (MASLD) and alcohol-associated liver disease (ALD), contributing to chronic inflammation and tissue damage. This review provides insight into the multifaceted role of necroptosis, encompassing both cell death and these extra-necroptotic functions, in the context of metabolic diseases. Understanding this intricate interplay is crucial for developing targeted therapeutic strategies in diseases that currently lack effective treatments.

Cell death

Cell death supports morphogenesis during development and homeostasis after birth by removing damaged or obsolete cells. It also curtails the spread of pathogens by eliminating infected cells. Cell death can be induced by the genetically programmed suicide mechanisms of apoptosis, necroptosis, and pyroptosis, or it can be a consequence of dysregulated metabolism, as in ferroptosis. Here, we review the signaling mechanisms underlying each cell-death pathway, discuss how impaired or excessive activation of the distinct cell-death processes can promote disease, and highlight existing and potential therapies for redressing imbalances in cell death in cancer and other diseases.

Helicobacter pylori PldA modulates TNFR1-mediated p38 signaling pathways to regulate macrophage responses for its survival

Helicobacter pylori, a dominant member of the gastric microbiota was associated with various gastrointestinal diseases and presents a significant challenge due to increasing antibiotic resistance. This study identifies H. pylori's phospholipase A (PldA) as a critical factor in modulating host macrophage responses, facilitating H. pylori 's evasion of the immune system and persistence. PldA alters membrane lipids through reversible acylation and deacylation, affecting their structure and function. We found that PldA incorporates lysophosphatidylethanolamine into macrophage membranes, disrupting their bilayer structure and impairing TNFR1-mediated p38-MK2 signaling. This disruption results in reduced macrophage autophagy and elevated RIP1-dependent apoptosis, thereby enhancing H. pylori survival, a mechanism also observed in multidrug-resistant strains. Pharmacological inhibition of PldA significantly decreases H. pylori viability and increases macrophage survival. In vivo studies corroborate PldA's essential role in H. pylori persistence and immune cell recruitment. Our findings position PldA as a pivotal element in H. pylori pathogenesis through TNFR1-mediated membrane modulation, offering a promising therapeutic target to counteract bacterial resistance.

Roles of RIPK1 as a stress sentinel coordinating cell survival and immunogenic cell death

Cell death and inflammation are closely linked arms of the innate immune response to combat infection and tissue malfunction. Recent advancements in our understanding of the intricate signals originating from dying cells have revealed that cell death serves as more than just an end point. It facilitates the exchange of information between the dying cell and cells of the tissue microenvironment, particularly immune cells, alerting and recruiting them to the site of disturbance. Receptor-interacting serine/threonine-protein kinase 1 (RIPK1) is emerging as a critical stress sentinel that functions as a molecular switch, governing cellular survival, inflammatory responses and immunogenic cell death signalling. Its tight regulation involves multiple layers of post-translational modifications. In this Review, we discuss the molecular mechanisms that regulate RIPK1 to maintain homeostasis and cellular survival in healthy cells, yet drive cell death in a context-dependent manner. We address how RIPK1 mutations or aberrant regulation is associated with inflammatory and autoimmune disorders and cancer. Moreover, we tease apart what is known about catalytic and non-catalytic roles of RIPK1 and discuss the successes and pitfalls of current strategies that aim to target RIPK1 in the clinic.

PTEN-induced kinase 1 exerts protective effects in diabetic kidney disease by attenuating mitochondrial dysfunction and necroptosis

Mitochondrial dysfunction plays a pivotal role in diabetic kidney disease initiation and progression. PTEN-induced serine/threonine kinase 1 (PINK1) is a core organizer of mitochondrial quality control; however, its function in diabetic kidney disease remains controversial. Here, we aimed to investigate the pathophysiological roles of PINK1 in diabetic tubulopathy, focusing on its effects on mitochondrial homeostasis and tubular cell necroptosis, which is a specialized form of regulated cell death. PINK1-knockout mice showed more severe diabetes-induced tubular injury, interstitial fibrosis, and albuminuria. The expression of profibrotic cytokines significantly increased in the kidneys of diabetic Pink1-/- mice, which eventually culminated in aggravated interstitial fibrosis. Additionally, the knockdown of PINK1 in HKC-8 cells upregulated the fibrosis-associated proteins, and these effects were rescued by PINK1 overexpression. PINK1 deficiency was also associated with exaggerated hyperglycemia-induced mitochondrial dysfunction and defective mitophagic activity, whereas PINK1 overexpression ameliorated these negative effects and restored mitochondrial homeostasis. Mitochondrial reactive oxygen species triggered tubular cell necroptosis under hyperglycemic conditions, which was aggravated by PINK1 deficiency and improved by its overexpression. In conclusion, PINK1 plays a pivotal role in suppressing mitochondrial dysfunction and tubular cell necroptosis under high glucose conditions and exerts protective effects in diabetic kidney disease.

Effect of doramectin on programmed cell death pathway in glioma cells

PURPOSE

Doramectin (DRM) is a kind of avermectin drugs, and it has been shown that DRM has anti-cancer effects. However, the molecular mechanism of DRM in programmed cell death (PCD) aspects is still unclear. The objective of this study was to confirm whether DRM induced PCD in glioma cells.

METHODS

In this experiment, the MTT assay and Ki-67 assay were used to detect in vitro cell viability and in vivo tumor proliferation. Then, the effect of DRM on PCD was analyzed by transcriptome comparison. Next, Endogenous apoptosis was detected by transmission electron microscopy (TEM), the DNA gel electrophoresis, JC-1 assay, western blotting and qRT-PCR. Meanwhile, necroptosis was detected by TEM, Hoechst 33342, FITC and PI staining assay, western blotting.

RESULTS

We found DRM induced apoptosis through Bcl-2/Bax/Caspase-3 pathway. And, DRM induced ROS overproduction, then ROS caused necroptosis through RIPK1/RIPK3/MLKL pathway, Mitochondria acted as a bridge between the two pathways.

CONCLUSION

Our research provided new insight with the function of anti-cancer of DRM. These results demonstrated DRM may be used as potential therapeutic agents inducing apoptosis and necroptosis for cancer therapy.

Tyrosine phosphorylation of IRF3 by BLK facilitates its sufficient activation and innate antiviral response

Viral infection triggers the activation of transcription factor IRF3, and its activity is precisely regulated for robust antiviral immune response and effective pathogen clearance. However, how full activation of IRF3 is achieved has not been well defined. Herein, we identified BLK as a key kinase that positively modulates IRF3-dependent signaling cascades and executes a pre-eminent antiviral effect. BLK deficiency attenuates RNA or DNA virus-induced ISRE activation, interferon production and the cellular antiviral response in human and murine cells, whereas overexpression of BLK has the opposite effects. BLK-deficient mice exhibit lower serum cytokine levels and higher lethality after VSV infection. Moreover, BLK deficiency impairs the secretion of downstream antiviral cytokines and promotes Senecavirus A (SVA) proliferation, thereby supporting SVA-induced oncolysis in an in vivo xenograft tumor model. Mechanistically, viral infection triggers BLK autophosphorylation at tyrosine 309. Subsequently, activated BLK directly binds and phosphorylates IRF3 at tyrosine 107, which further promotes TBK1-induced IRF3 S386 and S396 phosphorylation, facilitating sufficient IRF3 activation and downstream antiviral response. Collectively, our findings suggest that targeting BLK enhances viral clearance via specifically regulating IRF3 phosphorylation by a previously undefined mechanism.

Quizartinib inhibits necroptosis by targeting receptor-interacting serine/threonine protein kinase 1

Systemic inflammatory response syndrome (SIRS), at least in part driven by necroptosis, is characterized by life-threatening multiple organ failure. Blocking the progression of SIRS and consequent multiple organ dysfunction is challenging. Receptor-interacting serine/threonine protein kinase 1 (RIPK1) is an important cell death and inflammatory mediator, making it a potential treatment target in several diseases. Here, using a drug repurposing approach, we show that inhibiting RIPK1 is also an effective treatment for SIRS. We performed cell-based high-throughput drug screening of an US Food and Drug Administration (FDA)-approved drug library that contains 1953 drugs to identify effective inhibitors of necroptotic cell death by SYTOX green staining. Dose-response validation of the top candidate, quizartinib, was conducted in two cell lines of HT-22 and MEFs. The effect of quizartinib on necroptosis-related proteins was evaluated using western blotting, immunoprecipitation, and an in vitro RIPK1 kinase assay. The in vivo effects of quizartinib were assessed in a murine tumor necrosis factor α (TNFα)-induced SIRS model. High-throughput screening identified quizartinib as the top "hit" in the compound library that rescued cells from necroptosis in vitro. Quizartinib inhibited necroptosis by directly inhibiting RIPK1 kinase activity and blocking downstream complex IIb formation. Furthermore, quizartinib protected mice against TNFα-induced SIRS. Quizartinib, as an FDA-approved drug with proven safety and efficacy, was repurposed for targeted inhibition of RIPK1. This work provides essential preclinical data for transferring quizartinib to the treatment of RIPK1-dependent necroptosis-induced inflammatory diseases, including SIRS.

TAK1 Improves Cognitive Function via Suppressing RIPK1-Driven Neuronal Apoptosis and Necroptosis in Rats with Chronic Hypertension

Chronic hypertension is a major risk factor for cognitive impairment, which can promote neuroinflammation and neuronal loss in the central nervous system. Transforming growth factor β-activated kinase 1 (TAK1) is a key molecular component in determining cell fate and can be activated by inflammatory cytokines. This study aimed to investigate the role of TAK1 in mediating neuronal survival in the cerebral cortex and hippocampus under chronic hypertensive conditions. To that end, we used stroke-prone renovascular hypertension rats (RHRSP) as chronic hypertension models. Adeno-associated virus (AAV) designed to overexpress or knock down TAK1 expression were injected into the lateral ventricles of rats and the subsequent effects on cognitive function and neuronal survival under chronic hypertensive conditions were assessed. We found that, TAK1 knockdown in RHRSP markedly increased neuronal apoptosis and necroptosis and induced cognitive impairment, which could be reversed by Nec-1s, an inhibitor of receptor interacting protein kinase 1 (RIPK1). In contrast, overexpression of TAK1 in RHRSP significantly suppressed neuronal apoptosis and necroptosis and improved cognitive function. Further knockdown of TAK1 in sham-operated rats received similar phenotype with RHRSP. The results have been verified in vitro. In this study, we provide in vivo and in vitro evidence that TAK1 improves cognitive function by suppressing RIPK1-driven neuronal apoptosis and necroptosis in rats with chronic hypertension.

Molecular basis for nuclear accumulation and targeting of the inhibitor of apoptosis BIRC2

The inhibitor of apoptosis protein BIRC2 regulates fundamental cell death and survival signaling pathways. Here we show that BIRC2 accumulates in the nucleus via binding of its second and third BIR domains, BIRC2BIR2 and BIRC2BIR3, to the histone H3 tail and report the structure of the BIRC2BIR3-H3 complex. RNA-seq analysis reveals that the genes involved in interferon and defense response signaling and cell-cycle regulation are most affected by depletion of BIRC2. Overexpression of BIRC2 delays DNA damage repair and recovery of the cell-cycle progression. We describe the structural mechanism for targeting of BIRC2BIR3 by a potent but biochemically uncharacterized small molecule inhibitor LCL161 and demonstrate that LCL161 disrupts the association of endogenous BIRC2 with H3 and stimulates cell death in cancer cells. We further show that LCL161 mediates degradation of BIRC2 in human immunodeficiency virus type 1-infected human CD4+ T cells. Our findings provide mechanistic insights into the nuclear accumulation of and blocking BIRC2.

A phase I randomized, double-blinded, placebo-controlled study assessing the safety and pharmacokinetics of RIPK1 inhibitor GFH312 in healthy subjects

Receptor-interacting protein kinase 1 (RIPK1) mediates necroptosis and inflammation in various pathophysiologies, emerging as a pharmacological target for neurodegenerative and inflammatory indications. This phase I, first-in-human, placebo-controlled study evaluated the safety, pharmacokinetics (PKs), and pharmacodynamics (PDs) of GFH312, an RIPK1 inhibitor, in healthy adults. Subjects received GFH312 as a single ascending dose up to 500 mg (part I) or once-daily repeated doses up to 200 mg for 14 days (part II). PKs were assessed using plasma and cerebrospinal fluid (CSF); PDs were assessed by phospho-RIPK1 levels. Seventy-six subjects were enrolled between April 2021 and June 2022: 38 (part I) and 19 (part II) received GFH312; 14 and five received placebo, respectively. At least one treatment-emergent adverse event (TEAE) occurred in 42.1% (part I) and 63.2% (part II) of subjects receiving GFH312, compared with 42.9% and 40.0% of subjects receiving placebo, respectively. The most common TEAE was headache (21.1%). Two treatment-related TEAEs were reported in part I and four in part II. No serious TEAEs were reported. Systemic absorption was rapid; exposure (area under the concentration-time curve from time zero to the last measurable concentration and maximum plasma concentration) increased with dose level. The GFH312 CSF concentration post 100 mg single dose was approximately fourfold higher than the half maximal inhibitory concentration of human monocyte-derived macrophages necroptosis with expected central nervous system penetration. Subjects receiving GFH312 had decreased phospho-RIPK1 levels in peripheral blood mononuclear cells postdose. In conclusion, GFH312 was well-tolerated and demonstrated RIPK1 inhibition in healthy subjects. Ongoing studies will inform the use of GFH312 in potential indications.

IFNγ Causes Keratinocyte Necroptosis in Acute Graft-Versus-Host Disease

Epidermal keratinocytes form the first-line cellular barrier of the skin for protection against external injuries and maintenance of local tissue homeostasis. Expression of ZBP1 was shown to cause necroptotic keratinocyte cell death and skin inflammation in mice. We sought to characterize the relevance of ZBP1 and necroptosis in human keratinocytes and type 1-driven cutaneous acute graft-versus-host disease. in this study, we identify ZBP1 expression, necroptosis, and interface dermatitis as being the hallmarks of acute graft-versus-host disease. ZBP1 expression was dependent on leukocyte-derived IFNγ, and interference with IFNγ signaling by Jak inhibition prevented cell death. In predominantly IL-17-driven psoriasis, both ZBP1 expression and necroptosis could not be detected. Of note, in contrast to the signaling in mice, ZBP1 signaling in human keratinocytes was not affected by RIPK1's presence. These findings show that ZBP1 drives inflammation in IFNγ-dominant type 1 immune responses in human skin and may further point to a general role of ZBP1-mediated necroptosis.