bims-cediti 2025-11-09 papers

Issue of 2025–11–09
seven papers selected by
Kateryna Shkarina, Universität Bonn

EMBO J. 2025 Nov 05.

Structural insights into the atypical filament assembly of pyrin domain-containing IFI16.

Archit Garg, Ewa Niedzialkowska, Jeffrey J Zhou, Jasper Moh, Edward H Egelman, Jungsan Sohn.

In response to various intracellular stress or damage-associated signals, inflammasomes can be activated and trigger a pyroptotic cell death process through the sequential assembly of structurally compatible and interacting filamentous oligomers involving the pyrin domains (PYD) of important inflammasome components. The PYD-containing interferon-inducible protein 16 (IFI16) has been suggested as a viral DNA sensor that can induce inflammasome formation, but it also has other inflammasome-independent functions, including interferon production. Here, the cryo-EM structure of the filament assembled by the PYD of human IFI16 reveals a helical architecture distinct from inflammasome PYD filaments. In silico interface energy calculations suggest that the helical architecture of the IFI16PYD filament prevents interactions with inflammasome PYD filaments. Biochemical and cell biology experiments consistently demonstrate that IFI16 does not directly interact with inflammasome pyrin domains. Together, our results provide insights into the structural basis of the inflammasome-independent functions of IFI16, and also show that strict architectural compatibility requirements for interactions contribute to the signal transduction specificity in inflammasome signaling.

Keywords: Cryo-EM; Inflammasomes; Innate Immune System; Interferon-inducible Protein 16; Pyrin Domain

DOI: https://doi.org/10.1038/s44318-025-00626-7

J Virol. 2025 Nov 05. e0102025

Human cytomegalovirus-triggered necroptosis is suppressed by sequestration of MLKL in the nucleus of infected monocytes.

Brittany W Geiler, Shima Moradpour, Ben B Chauder, Dilruba Akter, Gary C Chan.

The systemic spread of human cytomegalovirus (HCMV) is associated with severe morbidity and mortality in immunocompromised and immunonaïve patients. Hematogenous dissemination of HCMV to different organ sites is facilitated by peripheral blood monocytes. Circulating monocytes have a short lifespan due, in part, to their intrinsic biological programming to initiate caspase-8-mediated apoptosis upon entry into the circulation from the bone marrow. We previously reported that HCMV extends the lifespan of infected monocytes by blocking procaspase-8 cleavage, yet the precise viral mechanism responsible for suppressing caspase-8 activity remains unknown. Here, we demonstrate that HCMV entry into monocytes rapidly increases the abundance of the anti-apoptotic cellular FLICE-like inhibitory protein long (cFLIPL), which prevents procaspase-8 cleavage into active caspase-8. However, others have demonstrated that inhibition of caspase-8 opens a "trapdoor" cell death response termed necroptosis. Accordingly, we found that increased levels of cFLIPL, along with a co-stimulatory signal from Toll-like receptor 3, activate the receptor-interacting protein kinase 3 responsible for initiating necroptosis. Despite the triggering of the necroptotic cascade within infected monocytes, the final execution of this death pathway is thwarted by nuclear sequestering of mixed lineage kinase domain-like pseudokinase, the executioner of necroptosis. Together, our data reveal a multitude of countermeasures employed by HCMV to obstruct cellular antiviral death responses within infected monocytes.IMPORTANCEHuman cytomegalovirus (HCMV) is highly prevalent in the adult population, with a seroprevalence of 50%-80% in the United States. Although immunocompetent individuals are generally asymptomatic, HCMV infection can cause multiorgan disease in immunocompromised and immunonaïve patients. Peripheral blood monocytes are responsible for the systemic dissemination of HCMV. However, the inherently short lifespan of monocytes, combined with the induction of antiviral cellular death responses, requires HCMV to circumvent cell death pathways to allow for viral spread. In this work, we show that HCMV induces cFLIPL levels to inhibit caspase-8-mediated apoptosis. However, the inhibition of apoptosis, combined with TLR3 activation, triggers a secondary cell death pathway termed necroptosis. As a countermeasure to block necroptosis, HCMV sequesters MLKL within the nucleus of infected monocytes. Defining the precise mechanisms through which HCMV stimulates survival will provide insight into novel therapeutics able to target infected monocytes.

Keywords: apoptosis; cytomegalovirus; monocytes; necroptosis

DOI: https://doi.org/10.1128/jvi.01020-25

Adv Sci (Weinh). 2025 Nov 04. e07381

Secondary Necrosis Following Caspase-Activation can Occur Independently of Gasdermin E.

Shubhangi Gavali, Francesca Maremonti, Wulf Tonnus, Florian Gembardt, Marlena Nastassja Schlecht, Karolin Flade, Anne von Mässenhausen, Stephen W G Tait, Stefan R Bornstein, Andreas Linkermann.

Regulated necrosis is a known direct consequence of activation of the necroptosis- and pyroptosis- pathways, but may also result from apoptosis in a process referred to as secondary necrosis. Apoptosis is well understood to be mediated by caspase activation, but the mechanisms that lead to plasma membrane rupture in secondary necrosis remain considerably obscure. Recent data suggested a caspase-mediated cleavage of gasdermin E (GSDME), a member of the gasdermin family. Here, apoptosis induced by diphtheria toxin (DT) is employed as a novel tool to study secondary necrosis. In addition, cisplatin and anti-Fas monoclonal antibody Jo2 are employed to study secondary necrosis in cell culture and in vivo, respectively. Despite prominent, yet epiphenomenal cleavage of GSDME, it is demonstrated that silencing or CRISPR/Cas9-mediated knockout of GSDME does not compromise the kinetics of secondary necrosis induced by DT or cisplatin. During Jo2-induced acute liver toxicity in mice, GSDME expressed in the necrotic liver is detected predominantly in its uncleaved form. In conclusion, the hypothesis of GSDME to be a central mediator of secondary necrosis in these model systems is disproved.

Keywords: B cell lymphoma 2 (BCL2); death receptor; immunotoxins; regulated necrosis

DOI: https://doi.org/10.1002/advs.202507381

Front Immunol. 2025 ;16 1666184

Phospholipase D1 is a critical mediator of neutrophil extracellular trap formation and venous thrombosis.

Ryosuke Aihara, Masatomo Takahashi, Kenji Morino, Keisuke Matsubara, Kazufumi Kunimura, Akihiko Nishikimi, Yoshihiro Izumi, Takeshi Bamba, Yoshinori Fukui, Takehito Uruno.

Neutrophil extracellular traps (NETs) are a host defense mechanism whereby activated neutrophils release decondensed chromatin and antimicrobial proteins into the extracellular space to trap and kill invading pathogens. While effective in clearing pathogens, NETs also pose pathological risks by exposing self-DNA, histones, granular enzymes, and reactive oxygen species (ROS), contributing to pathologies such as autoimmune diseases, inflammatory disorders, and thrombosis. Here, we identify phospholipase D1 (PLD1), a lipid-signaling enzyme that generates phosphatidic acid (PA), as a critical regulator of ROS generation and NET formation in murine neutrophils. Using both PLD1-deficient neutrophils and a selective inhibitor, we demonstrate that PLD1 is essential for NET release. Notably, exogenous PA alone is sufficient to trigger robust ROS production and NET formation. In vivo, PLD1-deficient mice fail to generate ROS in an acute lung inflammation model and are protected from venous thrombosis. These findings identify PLD1 and PA as key upstream regulators of NET formation and suggest that pharmacological inhibition of PLD1 could provide a potential avenue for early intervention in NET-related diseases such as venous thrombosis.

Keywords: deep vein thrombosis; neutrophil extracellular trap; phosphatidic acid; phospholipase D1; reactive oxygen species

DOI: https://doi.org/10.3389/fimmu.2025.1666184

Nat Commun. 2025 Nov 04. 16(1): 9742

The Salmonella pathogenicity island 1 injectisome reprograms host cell translation to evade the inflammatory response.

George Wood, Rebecca Johnson, Jessica Powell, Owain J Bryant, Filip Lastovka, Matthew P Brember, Panagiotis Tourlomousis, John P Carr, Clare E Bryant, Betty Y W Chung.

During bacterial infection both the host cell and its invader must rapidly divert resources to synthesize specific proteins. For the host, these factors may be needed for innate immune responses, including programmed cell death, and in the bacteria newly synthesized proteins may include survival factors that counteract host defences. Salmonella is an important bacterial pathogen that invades and multiplies within host cells. It is well established that epithelial cell invasion is dependent upon the Salmonella pathogenicity island 1 (SPI-1) type III injectisome, a biological needle that penetrates host cells and injects effectors that promote bacterial internalization. However, the importance of the SPI-1 injectisome in infection of professional phagocytes such as macrophages, the predominant host cell type supporting systemic infection, is less clear. Through time-resolved parallel transcriptomic and translatomic studies of macrophage infection, we reveal SPI-1 injectisome-dependent infection of macrophages triggers rapid translation of transcription factors, including Early Growth Response 1 (EGR1). Despite EGR1's short half-life, its swift synthesis, driven by untranslated regions of its mRNA, is sufficient to inhibit the transcription of pro-inflammatory genes; this restrains inflammation and macrophage death which would otherwise abort systemic infection. This demonstrates the importance of translational activation in host-pathogen dynamics during bacterial infection.

DOI: https://doi.org/10.1038/s41467-025-64744-w

Scand J Immunol. 2025 Nov;102(5): e70060

Innate Immunity and Inflammation: Conuersim Between PAMPS and DAMPS.

Balachandran Ravindran.

The current conundrum of inflammation is that exogenous pathogen-associated molecular patterns (PAMPs) from microbial sources or endogenous damage-associated molecular patterns (DAMPs) released during trauma/tissue injury generate host inflammatory response independently or in a synergistic manner. The 'discussion' highlights several confounders in the in vitro investigations reported in the literature and argues in favour of addressing the issue only in in vivo model systems, such as germ-free animals that are free of microbiota and hence PAMPs, in which response to DAMPs can be precisely studied. Based on the available literature, the 'discussion forum' proposes that host innate immune responses leading to the induction of inflammatory molecules by PAMPs and DAMPs are interdependent and biologically inactive in isolation, and that their threshold and context would be critical determining factors for acute or chronic inflammation.

Keywords: DAMPs; PAMPs; inflammation; innate immunity; tissue damage; wound healing

DOI: https://doi.org/10.1111/sji.70060

Nat Commun. 2025 Nov 07. 16(1): 9827

The methyl-CpG-binding protein 2 inhibits cGAS-associated signaling.

The detection of cytosolic dsDNA by the cyclic GMP-AMP synthase (cGAS) is tightly regulated to avoid pathological inflammatory responses. Here, we show that the methyl-CpG-binding protein 2 (MeCP2), a major transcriptional regulator, controls dsDNA-associated inflammatory responses. The presence of cytosolic dsDNA promotes MeCP2 export from the nucleus to the cytosol where it interacts with dsDNA, dampening detection by cGAS. MeCP2 export partially phenocopies MeCP2 deficiency, leading to innate immune activation and enforcing an antiviral state. Finally, MeCP2 displacement from the nucleus following dsDNA stimulation disrupts its canonical function, leading to the reactivation of otherwise repressed genes, such as endogenous retroelements. Re-expression of the latter leads to the accumulation of DNA species feeding cGAS-dependent signalling. We thus establish a direct role of MeCP2 in the regulation of the breadth and nature of dsDNA-associated inflammatory responses and suggest targeting dsDNA-associated pathways or endogenous retroelements as therapeutic options for patients with MeCP2 deficiency.

DOI: https://doi.org/10.1038/s41467-025-65713-z