RESUMO
Programmed cell death contributes to host defense against pathogens. To investigate the relative importance of pyroptosis, necroptosis, and apoptosis during Salmonella infection, we infected mice and macrophages deficient for diverse combinations of caspases-1, -11, -12, and -8 and receptor interacting serine/threonine kinase 3 (RIPK3). Loss of pyroptosis, caspase-8-driven apoptosis, or necroptosis had minor impact on Salmonella control. However, combined deficiency of these cell death pathways caused loss of bacterial control in mice and their macrophages, demonstrating that host defense can employ varying components of several cell death pathways to limit intracellular infections. This flexible use of distinct cell death pathways involved extensive cross-talk between initiators and effectors of pyroptosis and apoptosis, where initiator caspases-1 and -8 also functioned as executioners when all known effectors of cell death were absent. These findings uncover a highly coordinated and flexible cell death system with in-built fail-safe processes that protect the host from intracellular infections.
Assuntos
Apoptose/imunologia , Macrófagos/imunologia , Necroptose/imunologia , Piroptose/imunologia , Infecções por Salmonella/imunologia , Salmonella/imunologia , Animais , Caspase 1/deficiência , Caspase 1/genética , Caspase 12/deficiência , Caspase 12/genética , Caspase 8/genética , Caspases Iniciadoras/deficiência , Caspases Iniciadoras/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Proteína Serina-Treonina Quinases de Interação com Receptores/deficiência , Proteína Serina-Treonina Quinases de Interação com Receptores/genéticaRESUMO
The E3 ligase ARIH2 has an unusual structure and mechanism of elongating ubiquitin chains. To understand its physiological role, we generated gene-targeted mice deficient in ARIH2. ARIH2 deficiency resulted in the embryonic death of C57BL/6 mice. On a mixed genetic background, the lethality was attenuated, with some mice surviving beyond weaning and then succumbing to an aggressive multiorgan inflammatory response. We found that in dendritic cells (DCs), ARIH2 caused degradation of the inhibitor IκBß in the nucleus, which abrogated its ability to sequester, protect and transcriptionally coactivate the transcription factor subunit p65 in the nucleus. Loss of ARIH2 caused dysregulated activation of the transcription factor NF-κB in DCs, which led to lethal activation of the immune system in ARIH2-sufficent mice reconstituted with ARIH2-deficient hematopoietic stem cells. Our data have therapeutic implications for targeting ARIH2 function.
Assuntos
Células Dendríticas/imunologia , Desenvolvimento Embrionário/imunologia , Insuficiência de Múltiplos Órgãos/imunologia , Ubiquitina-Proteína Ligases/fisiologia , Animais , Células Cultivadas , Modelos Animais de Doenças , Desenvolvimento Embrionário/genética , Hematopoese/genética , Humanos , Sistema Imunitário/fisiologia , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Terapia de Alvo Molecular , Insuficiência de Múltiplos Órgãos/genética , NF-kappa B/metabolismo , Ativação Transcricional/imunologia , Ubiquitina-Proteína Ligases/genética , Ubiquitinação/genética , Ubiquitinação/imunologiaRESUMO
The SARS-CoV-2 coronavirus encodes an essential papain-like protease domain as part of its non-structural protein (nsp)-3, namely SARS2 PLpro, that cleaves the viral polyprotein, but also removes ubiquitin-like ISG15 protein modifications as well as, with lower activity, Lys48-linked polyubiquitin. Structures of PLpro bound to ubiquitin and ISG15 reveal that the S1 ubiquitin-binding site is responsible for high ISG15 activity, while the S2 binding site provides Lys48 chain specificity and cleavage efficiency. To identify PLpro inhibitors in a repurposing approach, screening of 3,727 unique approved drugs and clinical compounds against SARS2 PLpro identified no compounds that inhibited PLpro consistently or that could be validated in counterscreens. More promisingly, non-covalent small molecule SARS PLpro inhibitors also target SARS2 PLpro, prevent self-processing of nsp3 in cells and display high potency and excellent antiviral activity in a SARS-CoV-2 infection model.
Assuntos
Antivirais/farmacologia , Proteases 3C de Coronavírus/antagonistas & inibidores , Proteases 3C de Coronavírus/metabolismo , SARS-CoV-2/metabolismo , Ubiquitina/metabolismo , Animais , Sítios de Ligação , Chlorocebus aethiops , Proteases 3C de Coronavírus/química , Proteases 3C de Coronavírus/genética , Cristalografia por Raios X , Citocinas/genética , Avaliação Pré-Clínica de Medicamentos/métodos , Reposicionamento de Medicamentos , Polarização de Fluorescência , Células HEK293 , Humanos , Cinética , Modelos Moleculares , Inibidores de Proteases/farmacologia , Conformação Proteica , SARS-CoV-2/química , SARS-CoV-2/genética , Ubiquitinas/genética , Células VeroRESUMO
Infectious diseases remain a major burden to global health. Despite the implementation of successful vaccination campaigns and efficient drugs, the increasing emergence of pathogenic vaccine or treatment resistance demands novel therapeutic strategies. The development of traditional therapies using small-molecule drugs is based on modulating protein function and activity through the occupation of active sites such as enzyme inhibition or ligand-receptor binding. These prerequisites result in the majority of host and pathogenic disease-relevant, nonenzymatic and structural proteins being labeled "undruggable." Targeted protein degradation (TPD) emerged as a powerful strategy to eliminate proteins of interest including those of the undruggable variety. Proteolysis-targeting chimeras (PROTACs) are rationally designed heterobifunctional small molecules that exploit the cellular ubiquitin-proteasome system to specifically mediate the highly selective and effective degradation of target proteins. PROTACs have shown remarkable results in the degradation of various cancer-associated proteins, and several candidates are already in clinical development. Significantly, PROTAC-mediated TPD holds great potential for targeting and modulating pathogenic proteins, especially in the face of increasing drug resistance to the best-in-class treatments. In this review, we discuss advances in the development of TPD in the context of targeting the host-pathogen interface and speculate on their potential use to combat viral, bacterial, and parasitic infection.
Assuntos
Complexo de Endopeptidases do Proteassoma , Ubiquitina-Proteína Ligases , Complexo de Endopeptidases do Proteassoma/metabolismo , Proteínas/metabolismo , Proteólise , Ubiquitina/metabolismo , Ubiquitina-Proteína Ligases/metabolismo , UbiquitinaçãoRESUMO
The aim of this article is to summarise the virology content presented at the 9th Lorne Infection and Immunity Conference, Australia, in February 2019. The broad program included virology as a key theme, and the commentary herein highlights several key virology presentations at the meeting.
Assuntos
Virologia , Viroses/imunologia , Animais , Austrália , Quirópteros/virologia , Congressos como Assunto , Reservatórios de Doenças/virologia , Humanos , Viroses/prevenção & controle , Viroses/transmissão , Vírus/genética , Vírus/patogenicidadeRESUMO
We have shown that cellular inhibitor of apoptosis proteins (cIAPs) impair clearance of hepatitis B virus (HBV) infection by preventing TNF-mediated killing/death of infected cells. A key question, with profound therapeutic implications, is whether this finding can be translated to the development of drugs that promote elimination of infected cells. Drug inhibitors of cIAPs were developed as cancer therapeutics to promote TNF-mediated tumor killing. These drugs are also known as Smac mimetics, because they mimic the action of the endogenous protein Smac/Diablo that antagonizes cIAP function. Here, we show using an immunocompetent mouse model of chronic HBV infection that birinapant and other Smac mimetics are able to rapidly reduce serum HBV DNA and serum HBV surface antigen, and they promote the elimination of hepatocytes containing HBV core antigen. The efficacy of Smac mimetics in treating HBV infection is dependent on their chemistry, host CD4(+) T cells, and TNF. Birinapant enhances the ability of entecavir, an antiviral nucleoside analog, to reduce viral DNA production in HBV-infected animals. These results indicate that birinapant and other Smac mimetics may have efficacy in treating HBV infection and perhaps, other intracellular infections.
Assuntos
Hepatite B/tratamento farmacológico , Proteínas Inibidoras de Apoptose/antagonistas & inibidores , Animais , Antivirais/farmacologia , Linfócitos T CD4-Positivos/citologia , DNA Viral/sangue , Dipeptídeos/farmacologia , Modelos Animais de Doenças , Guanina/análogos & derivados , Guanina/farmacologia , Hepatite B/metabolismo , Antígenos de Superfície da Hepatite B/sangue , Vírus da Hepatite B , Hepatócitos/citologia , Hepatócitos/metabolismo , Hepatócitos/virologia , Imunofenotipagem , Indóis/farmacologia , Proteínas Inibidoras de Apoptose/metabolismo , Fígado/metabolismo , Camundongos , Camundongos Endogâmicos C3H , Camundongos Endogâmicos C57BL , Microscopia Eletrônica de Varredura , Plasmídeos/metabolismoRESUMO
Hepatitis B virus (HBV) infection can result in a spectrum of outcomes from immune-mediated control to disease progression, cirrhosis, and liver cancer. The host molecular pathways that influence and contribute to these outcomes need to be defined. Using an immunocompetent mouse model of chronic HBV infection, we identified some of the host cellular and molecular factors that impact on infection outcomes. Here, we show that cellular inhibitor of apoptosis proteins (cIAPs) attenuate TNF signaling during hepatitis B infection, and they restrict the death of infected hepatocytes, thus allowing viral persistence. Animals with a liver-specific cIAP1 and total cIAP2 deficiency efficiently control HBV infection compared with WT mice. This phenotype was partly recapitulated in mice that were deficient in cIAP2 alone. These results indicate that antagonizing the function of cIAPs may promote the clearance of HBV infection.
Assuntos
Vírus da Hepatite B , Hepatite B/metabolismo , Proteínas Inibidoras de Apoptose/metabolismo , Ubiquitina-Proteína Ligases/metabolismo , Animais , Proteína 3 com Repetições IAP de Baculovírus , Antígenos CD4/metabolismo , Antígenos CD8/metabolismo , Citocinas/metabolismo , DNA Viral/genética , Modelos Animais de Doenças , Genótipo , Hepatócitos/metabolismo , Hepatócitos/virologia , Imunofenotipagem , Terapia de Imunossupressão , Interferon gama/metabolismo , Fígado/metabolismo , Neoplasias Hepáticas/metabolismo , Neoplasias Hepáticas/virologia , Camundongos , Camundongos Endogâmicos C57BL , Fenótipo , Transdução de Sinais , Fator de Necrose Tumoral alfa/metabolismoRESUMO
The early and mid-career researchers (EMCRs) of scientific communities represent the forefront of research and the future direction in which a field takes. The opinions of this key demographic are not commonly aggregated to audit fields and precisely demonstrate where challenges lie for the future. To address this, we initiated the inaugural International Emerging Researchers Workshop for the global Hepatitis B and Hepatitis D scientific community (75 individuals). The cohort was split into small discussion groups and the significant problems, challenges, and future directions were assessed. Here, we summarise the outcome of these discussions and outline the future directions suggested by the EMCR community. We show an effective approach to gauging and accumulating the ideas of EMCRs and provide a succinct summary of the significant gaps remaining in the Hepatitis B and Hepatitis D field.
Assuntos
Hepatite B , Hepatite D , Humanos , Hepatite B/virologia , Hepatite D/virologia , Pesquisa Biomédica , Pesquisadores , Vírus da Hepatite BRESUMO
Human norovirus is the leading cause of acute gastroenteritis worldwide, however despite the significance of this pathogen, we have a limited understanding of how noroviruses cause disease, and modulate the innate immune response. Programmed cell death (PCD) is an important part of the innate response to invading pathogens, but little is known about how specific PCD pathways contribute to norovirus replication. Here, we reveal that murine norovirus (MNV) virus-induced PCD in macrophages correlates with the release of infectious virus. We subsequently show, genetically and chemically, that MNV-induced cell death and viral replication occurs independent of the activity of inflammatory mediators. Further analysis revealed that MNV infection promotes the cleavage of apoptotic caspase-3 and PARP. Correspondingly, pan-caspase inhibition, or BAX and BAK deficiency, perturbed viral replication rates and delayed virus release and cell death. These results provide new insights into how MNV harnesses cell death to increase viral burden.
Assuntos
Infecções por Caliciviridae , Norovirus , Camundongos , Humanos , Animais , Macrófagos , Apoptose , Imunidade Inata , Norovirus/fisiologia , Replicação ViralRESUMO
Multiple omics analyzes of Vaccinia virus (VACV) infection have defined molecular characteristics of poxvirus biology. However, little is known about the monkeypox (mpox) virus (MPXV) in humans, which has a different disease manifestation despite its high sequence similarity to VACV. Here, we perform an in-depth multi-omics analysis of the transcriptome, proteome, and phosphoproteome signatures of MPXV-infected primary human fibroblasts to gain insights into the virus-host interplay. In addition to expected perturbations of immune-related pathways, we uncover regulation of the HIPPO and TGF-ß pathways. We identify dynamic phosphorylation of both host and viral proteins, which suggests that MAPKs are key regulators of differential phosphorylation in MPXV-infected cells. Among the viral proteins, we find dynamic phosphorylation of H5 that influenced the binding of H5 to dsDNA. Our extensive dataset highlights signaling events and hotspots perturbed by MPXV, extending the current knowledge on poxviruses. We use integrated pathway analysis and drug-target prediction approaches to identify potential drug targets that affect virus growth. Functionally, we exemplify the utility of this approach by identifying inhibitors of MTOR, CHUK/IKBKB, and splicing factor kinases with potent antiviral efficacy against MPXV and VACV.
Assuntos
Fibroblastos , Monkeypox virus , Mpox , Proteínas Virais , Humanos , Monkeypox virus/genética , Fosforilação , Mpox/virologia , Mpox/metabolismo , Fibroblastos/virologia , Fibroblastos/metabolismo , Proteínas Virais/metabolismo , Proteínas Virais/genética , Proteoma/metabolismo , Interações Hospedeiro-Patógeno , Transdução de Sinais , Proteômica/métodos , Transcriptoma , Antivirais/farmacologia , MultiômicaRESUMO
Emerging RNA viruses, including SARS-CoV-2, continue to be a major threat. Cell entry of SARS-CoV-2 particles via the endosomal pathway involves cysteine cathepsins. Due to ubiquitous expression, cathepsin L (CatL) is considered a promising drug target in the context of different viral and lysosome-related diseases. We characterized the anti-SARS-CoV-2 activity of a set of carbonyl- and succinyl epoxide-based inhibitors, which were previously identified as inhibitors of cathepsins or related cysteine proteases. Calpain inhibitor XII, MG-101, and CatL inhibitor IV possess antiviral activity in the very low nanomolar EC50 range in Vero E6 cells and inhibit CatL in the picomolar Ki range. We show a relevant off-target effect of CatL inhibition by the coronavirus main protease α-ketoamide inhibitor 13b. Crystal structures of CatL in complex with 14 compounds at resolutions better than 2 Å present a solid basis for structure-guided understanding and optimization of CatL inhibitors toward protease drug development.
Assuntos
Antivirais , Catepsina L , SARS-CoV-2 , Catepsina L/antagonistas & inibidores , Catepsina L/metabolismo , Antivirais/farmacologia , Antivirais/química , Antivirais/síntese química , Animais , Chlorocebus aethiops , Células Vero , SARS-CoV-2/efeitos dos fármacos , Humanos , Relação Estrutura-Atividade , Inibidores de Cisteína Proteinase/farmacologia , Inibidores de Cisteína Proteinase/química , Inibidores de Cisteína Proteinase/síntese química , Cristalografia por Raios X , Inibidores de Proteases/farmacologia , Inibidores de Proteases/química , Inibidores de Proteases/síntese química , Inibidores de Proteases/metabolismo , Modelos MolecularesRESUMO
Titanium dioxide (TiO2) shows significant potential as a self-cleaning material to inactivate severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and prevent virus transmission. This study provides insights into the impact of UV-A light on the photocatalytic inactivation of adsorbed SARS-CoV-2 virus-like particles (VLPs) on a TiO2 surface at the molecular and atomic levels. X-ray photoelectron spectroscopy, combined with density functional theory calculations, reveals that spike proteins can adsorb on TiO2 predominantly via their amine and amide functional groups in their amino acids blocks. We employ atomic force microscopy and grazing-incidence small-angle X-ray scattering (GISAXS) to investigate the molecular-scale morphological changes during the inactivation of VLPs on TiO2 under light irradiation. Notably, in situ measurements reveal photoinduced morphological changes of VLPs, resulting in increased particle diameters. These results suggest that the denaturation of structural proteins induced by UV irradiation and oxidation of the virus structure through photocatalytic reactions can take place on the TiO2 surface. The in situ GISAXS measurements under an N2 atmosphere reveal that the virus morphology remains intact under UV light. This provides evidence that the presence of both oxygen and UV light is necessary to initiate photocatalytic reactions on the surface and subsequently inactivate the adsorbed viruses. The chemical insights into the virus inactivation process obtained in this study contribute significantly to the development of solid materials for the inactivation of enveloped viruses.
Assuntos
SARS-CoV-2 , Titânio , Raios Ultravioleta , Titânio/química , Titânio/efeitos da radiação , SARS-CoV-2/efeitos da radiação , SARS-CoV-2/química , Inativação de Vírus/efeitos da radiação , Inativação de Vírus/efeitos dos fármacos , Humanos , Glicoproteína da Espícula de Coronavírus/química , Glicoproteína da Espícula de Coronavírus/metabolismo , COVID-19/virologia , COVID-19/prevenção & controle , Adsorção , Propriedades de SuperfícieRESUMO
We investigated the adsorption of severe acute respiratory syndrome corona virus 2 (SARS-CoV-2), the virus responsible for the current pandemic, on the surface of the model catalyst TiO2(101) using atomic force microscopy, transmission electron microscopy, fluorescence microscopy, and X-ray photoelectron spectroscopy, accompanied by density functional theory calculations. Three different methods were employed to inactivate the virus after it was loaded on the surface of TiO2(101): (i) ethanol, (ii) thermal, and (iii) UV treatments. Microscopic studies demonstrate that the denatured spike proteins and other proteins in the virus structure readsorb on the surface of TiO2 under thermal and UV treatments. The interaction of the virus with the surface of TiO2 was different for the thermally and UV treated samples compared to the sample inactivated via ethanol treatment. AFM and TEM results on the UV-treated sample suggested that the adsorbed viral particles undergo damage and photocatalytic oxidation at the surface of TiO2(101) which can affect the structural proteins of SARS-CoV-2 and denature the spike proteins in 30 min. The role of Pd nanoparticles (NPs) was investigated in the interaction between SARS-CoV-2 and TiO2(101). The presence of Pd NPs enhanced the adsorption of the virus due to the possible interaction of the spike protein with the NPs. This study is the first investigation of the interaction of SARS-CoV-2 with the surface of single crystalline TiO2(101) as a potential candidate for virus deactivation applications. Clarification of the interaction of the virus with the surface of semiconductor oxides will aid in obtaining a deeper understanding of the chemical processes involved in photoinactivation of microorganisms, which is important for the design of effective photocatalysts for air purification and self-cleaning materials.
Assuntos
COVID-19 , SARS-CoV-2 , Adsorção , Proteínas , Glicoproteína da Espícula de Coronavírus , Titânio/químicaRESUMO
Across the globe, 2-3% of humans carry the p.Ser132Pro single nucleotide polymorphism in MLKL, the terminal effector protein of the inflammatory form of programmed cell death, necroptosis. Here we show that this substitution confers a gain in necroptotic function in human cells, with more rapid accumulation of activated MLKLS132P in biological membranes and MLKLS132P overriding pharmacological and endogenous inhibition of MLKL. In mouse cells, the equivalent Mlkl S131P mutation confers a gene dosage dependent reduction in sensitivity to TNF-induced necroptosis in both hematopoietic and non-hematopoietic cells, but enhanced sensitivity to IFN-ß induced death in non-hematopoietic cells. In vivo, MlklS131P homozygosity reduces the capacity to clear Salmonella from major organs and retards recovery of hematopoietic stem cells. Thus, by dysregulating necroptosis, the S131P substitution impairs the return to homeostasis after systemic challenge. Present day carriers of the MLKL S132P polymorphism may be the key to understanding how MLKL and necroptosis modulate the progression of complex polygenic human disease.
Assuntos
Apoptose , Proteínas Quinases , Humanos , Animais , Camundongos , Fosforilação , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Membrana Celular/metabolismo , Mutação , Fatores de Transcrição/metabolismo , Proteína Serina-Treonina Quinases de Interação com Receptores/metabolismoRESUMO
Several drug screening campaigns identified Calpeptin as a drug candidate against SARS-CoV-2. Initially reported to target the viral main protease (Mpro), its moderate activity in Mpro inhibition assays hints at a second target. Indeed, we show that Calpeptin is an extremely potent cysteine cathepsin inhibitor, a finding additionally supported by X-ray crystallography. Cell infection assays proved Calpeptin's efficacy against SARS-CoV-2. Treatment of SARS-CoV-2-infected Golden Syrian hamsters with sulfonated Calpeptin at a dose of 1 mg/kg body weight reduces the viral load in the trachea. Despite a higher risk of side effects, an intrinsic advantage in targeting host proteins is their mutational stability in contrast to highly mutable viral targets. Here we show that the inhibition of cathepsins, a protein family of the host organism, by calpeptin is a promising approach for the treatment of SARS-CoV-2 and potentially other viral infections.
Assuntos
COVID-19 , Humanos , SARS-CoV-2/metabolismo , Catepsinas , Antivirais/farmacologia , Antivirais/uso terapêutico , Antivirais/química , Inibidores de Proteases/farmacologia , Cisteína Endopeptidases/metabolismoRESUMO
BACKGROUND & AIMS: Approved therapies for chronic hepatitis B include systemic administration of interferon (IFN)-alfa and inhibitors of hepatitis B virus (HBV) reverse-transcription. Systemic application of IFN-alfa is limited by side effects. Reverse-transcriptase inhibitors effectively control HBV replication, but rarely eliminate the virus and can select drug-resistant variants. We aimed to develop an alternative therapeutic approach that combines gene silencing with induction of IFN in the liver. METHODS: To stimulate an immune response while inhibiting HBV activity, we designed 3 small interfering (si)RNAs that target highly conserved sequences and multiple HBV transcripts of all genotypes. A 5'-triphosphate (3p) was added to the siRNAs, turning them into a ligand for the cytosolic helicase retinoic acid-inducible protein I, which becomes activated and induces expression of type-I IFNs. Antiviral activity was investigated in cell lines that replicate HBV, in HBV-infected primary human hepatocytes, and in HBV transgenic mice. RESULTS: 3p-double-stranded RNA (3p-RNA) activated retinoic acid-inducible protein I, induced a strong type I IFN response (expression of IFN-ß) in liver cells and showed transient but strong antiviral activity. Bifunctional, HBV-specific, 3p-siRNAs controlled replication of HBV more efficiently and for longer periods of time than 3p-RNAs without silencing capacity or siRNAs that targeted identical sequences but did not contain 3p. CONCLUSIONS: HBV-specific 3p-siRNAs are bifunctional antiviral molecules that induce production of type I IFNs in the liver and target HBV RNAs to inhibit viral replication.
Assuntos
Vírus da Hepatite B/efeitos dos fármacos , Vírus da Hepatite B/genética , Hepatite B/virologia , Interferência de RNA , RNA Interferente Pequeno/genética , RNA Interferente Pequeno/farmacologia , Replicação Viral/efeitos dos fármacos , 2',5'-Oligoadenilato Sintetase/metabolismo , Animais , Células Hep G2 , Hepatite B/metabolismo , Hepatite B/patologia , Vírus da Hepatite B/fisiologia , Humanos , Interferon Tipo I/metabolismo , Interferon-alfa/metabolismo , Interferon beta/metabolismo , Camundongos , Camundongos Transgênicos , Fosforilação/genética , RNA Interferente Pequeno/química , Proteínas Recombinantes , Reação em Cadeia da Polimerase Via Transcriptase Reversa , Transativadores/metabolismo , Fatores de Transcrição/metabolismo , Transfecção , Carga Viral/efeitos dos fármacos , Replicação Viral/genética , Replicação Viral/fisiologiaRESUMO
Pathogen recognition and TNF receptors signal via receptor interacting serine/threonine kinase-3 (RIPK3) to cause cell death, including MLKL-mediated necroptosis and caspase-8-dependent apoptosis. However, the post-translational control of RIPK3 is not fully understood. Using mass-spectrometry, we identified that RIPK3 is ubiquitylated on K469. The expression of mutant RIPK3 K469R demonstrated that RIPK3 ubiquitylation can limit both RIPK3-mediated apoptosis and necroptosis. The enhanced cell death of overexpressed RIPK3 K469R and activated endogenous RIPK3 correlated with an overall increase in RIPK3 ubiquitylation. Ripk3 K469R/K469R mice challenged with Salmonella displayed enhanced bacterial loads and reduced serum IFNγ. However, Ripk3 K469R/K469R macrophages and dermal fibroblasts were not sensitized to RIPK3-mediated apoptotic or necroptotic signaling suggesting that, in these cells, there is functional redundancy with alternate RIPK3 ubiquitin-modified sites. Consistent with this idea, the mutation of other ubiquitylated RIPK3 residues also increased RIPK3 hyper-ubiquitylation and cell death. Therefore, the targeted ubiquitylation of RIPK3 may act as either a brake or accelerator of RIPK3-dependent killing.
RESUMO
Targeting the potent immunosuppressive properties of FOXP3+ regulatory T cells (Tregs) has substantial therapeutic potential for treating autoimmune and inflammatory diseases. Yet, the molecular mechanisms controlling Treg homeostasis, particularly during inflammation, remain unclear. We report that caspase-8 is a central regulator of Treg homeostasis in a context-specific manner that is decisive during immune responses. In mouse genetic models, targeting caspase-8 in Tregs led to accumulation of effector Tregs resistant to apoptotic cell death. Conversely, inflammation induced the MLKL-dependent necroptosis of caspase-8-deficient lymphoid and tissue Tregs, which enhanced immunity to a variety of chronic infections to promote clearance of viral or parasitic pathogens. However, improved immunity came at the risk of lethal inflammation in overwhelming infections. Caspase-8 inhibition using a clinical-stage compound revealed that human Tregs have heightened sensitivity to necroptosis compared with conventional T cells. These findings reveal a fundamental mechanism in Tregs that could be targeted to manipulate the balance between immune tolerance versus response for therapeutic benefit.
Assuntos
Caspase 8/metabolismo , Tolerância Imunológica , Linfócitos T Reguladores , Animais , Homeostase , Inflamação/metabolismo , CamundongosRESUMO
Interleukin-1ß (IL-1ß) is activated by inflammasome-associated caspase-1 in rare autoinflammatory conditions and in a variety of other inflammatory diseases. Therefore, IL-1ß activity must be fine-tuned to enable anti-microbial responses whilst limiting collateral damage. Here, we show that precursor IL-1ß is rapidly turned over by the proteasome and this correlates with its decoration by K11-linked, K63-linked and K48-linked ubiquitin chains. The ubiquitylation of IL-1ß is not just a degradation signal triggered by inflammasome priming and activating stimuli, but also limits IL-1ß cleavage by caspase-1. IL-1ß K133 is modified by ubiquitin and forms a salt bridge with IL-1ß D129. Loss of IL-1ß K133 ubiquitylation, or disruption of the K133:D129 electrostatic interaction, stabilizes IL-1ß. Accordingly, Il1bK133R/K133R mice have increased levels of precursor IL-1ß upon inflammasome priming and increased production of bioactive IL-1ß, both in vitro and in response to LPS injection. These findings identify mechanisms that can limit IL-1ß activity and safeguard against damaging inflammation.
Assuntos
Caspase 1/genética , Inflamassomos/genética , Interleucina-1beta/genética , Complexo de Endopeptidases do Proteassoma/genética , Processamento de Proteína Pós-Traducional , Animais , Caspase 1/imunologia , Células HEK293 , Humanos , Inflamassomos/imunologia , Inflamação , Interleucina-1beta/imunologia , Lipopolissacarídeos/administração & dosagem , Macrófagos/imunologia , Macrófagos/patologia , Camundongos , Camundongos Knockout , Cultura Primária de Células , Complexo de Endopeptidases do Proteassoma/imunologia , Proteólise , Espécies Reativas de Oxigênio/imunologia , Espécies Reativas de Oxigênio/metabolismo , Transdução de Sinais , Ubiquitina/genética , Ubiquitina/imunologia , UbiquitinaçãoRESUMO
A major unmet clinical need is a therapeutic capable of removing hepatitis B virus (HBV) genome from the liver of infected individuals to reduce their risk of developing liver cancer. A strategy to deliver such a therapy could utilize the ability to target and promote apoptosis of infected hepatocytes. Presently there is no clinically relevant strategy that has been shown to effectively remove persistent episomal covalently closed circular HBV DNA (cccDNA) from the nucleus of hepatocytes. We used linearized single genome length HBV DNA of various genotypes to establish a cccDNA-like reservoir in immunocompetent mice and showed that clinical-stage orally administered drugs that antagonize the function of cellular inhibitor of apoptosis proteins can eliminate HBV replication and episomal HBV genome in the liver. Primary human liver organoid models were used to confirm the clinical relevance of these results. This study underscores a clinically tenable strategy for the potential elimination of chronic HBV reservoirs in patients.