DUSP8过表达通过JNK/p38 MAPK通路来改善LPS诱导的巨噬细胞炎症反应

双特异性磷酸酶8（dual-specificity phosphatase 8, DUSP8）是双特异性蛋白磷酸酶家族的成员之一,被报道参与多个疾病发生过程。然而,DUSP8是否参与巨噬细胞等免疫细胞炎性应答过程,目前仍未有研究证实。本研究旨在检测DUSP8在脂多糖(LPS)诱导的巨噬细胞炎症反应中的表达,并探讨过表达DUSP8在巨噬细胞炎症反应的作用。利用100 ng/mL LPS刺激野生型C57BL/6小鼠骨髓来源巨噬细胞（bone marrow derived macrophage,BMDM）,分别在不同时间点收取细胞,实时PCR和Western 印迹检测发现LPS处理后,BMDM中DUSP8的表达水平明显降低（P<0.05）,且在12 h达到最低值;随后,分别转染DUSP8过表达载体（DUSP8-EGFP）和对照载体（EGFP）于BMDM,Western 印迹检测发现DUSP8-EGFP转染能够显著上调DUSP8的表达水平（P<0.05）;进一步用流式细胞术(flow cytometry, FCM)检测发现DUSP8过表达使巨噬细胞表面分子CD80和CD86的表达显著下调（P<0.05）;同时,中性红吞噬实验结果显示,DUSP8过表达后巨噬细胞的吞噬能力明显降低（P<0.05）;此外,ELISA (enzyme linked immunosorbent assay)检测结果显示,过表达DUSP8显著降低IL-1β,IL-6的表达水平（P<0.05）;最后,Western 印迹结果显示,JNK和p38 MAPK的磷酸化水平在DUSP8过表达组中明显降低（P<0.05）。以上表明,DUSP8过表达可显著改善LPS诱导的巨噬细胞炎症反应,其机制主要通过抑制JNK和p38 MAPK的活化。     

AIM2/ASC triggers caspase-8-dependent apoptosis in Francisella-infected caspase-1-deficient macrophages

The inflammasome is a signalling platform leading to caspase-1 activation. Caspase-1 causes pyroptosis, a necrotic-like cell death. AIM2 is an inflammasome sensor for cytosolic DNA. The adaptor molecule ASC mediates AIM2-dependent caspase-1 activation. To date, no function besides caspase-1 activation has been ascribed to the AIM2/ASC complex. Here, by comparing the effect of gene inactivation at different levels of the inflammasome pathway, we uncovered a novel cell death pathway activated in an AIM2/ASC-dependent manner. Francisella tularensis, the agent of tularaemia, triggers AIM2/ASC-dependent caspase-3-mediated apoptosis in caspase-1-deficient macrophages. We further show that AIM2 engagement leads to ASC-dependent, caspase-1-independent activation of caspase-8 and caspase-9 and that caspase-1-independent death is reverted upon caspase-8 inhibition. Caspase-8 interacts with ASC and active caspase-8 specifically colocalizes with the AIM2/ASC speck thus identifying the AIM2/ASC complex as a novel caspase-8 activation platform. Furthermore, we demonstrate that caspase-1-independent apoptosis requires the activation of caspase-9 and of the intrinsic pathway in a typical type II cell manner. Finally, we identify the AIM2/ASC-dependent caspase-1-independent pathway as an innate immune mechanism able to restrict bacterial replication in vitro and control IFN-γ levels in vivo in Casp1(KO) mice. This work underscores the crosstalk between inflammasome components and the apoptotic machinery and highlights the versatility of the pathway, which can switch from pyroptosis to apoptosis.     

The central inflammasome adaptor protein ASC activates the inflammasome after transition from a soluble to an insoluble state

Apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD) (ASC) is a 22 kDa protein that functions as the central adaptor for inflammasome assembly. ASC forms insoluble specks in monocytes undergoing pyroptosis, and the polymerization of ASC provides a template of CARDs that leads to proximity-mediated autoactivation of caspase-1 in canonical inflammasomes. However, specks are insoluble protein complexes, and solubility is typically important for protein function. Therefore, we sought to define whether ASC specks comprise active inflammasome complexes or are simply the end stage of exhausted ASC polymers. Using a THP-1 cell–lysing model of caspase-1 activation that is ASC dependent, we compared caspase-1 activation induced by preassembled insoluble ASC specks and soluble monomeric forms of ASC. Unexpectedly, after controlling for the concentration dependence of ASC oligomerization, we found that only insoluble forms of ASC promoted caspase-1 autocatalysis. This link to insolubility was recapitulated with recombinant ASC. We show that purified recombinant ASC spontaneously precipitated and was functional, whereas the maltose-binding protein–ASC fusion to ASC (promoting enhanced solubility) was inactive until induced to insolubility by binding to amylose beads. This functional link to insolubility also held true for the Y146A mutation of the CARD of ASC, which avoids insolubility and caspase-1 activation. Thus, we conclude that the role of ASC insolubility in inflammasome function is inextricably linked to its pyrin domain–mediated and CARD-mediated polymerizations. These findings will support future studies into the molecular mechanisms controlling ASC solubility.     

The Lysosome Rupture-activated TAK1-JNK Pathway Regulates NLRP3 Inflammasome Activation

Lysosome rupture triggers NLRP3 inflammasome activation in macrophages. However, the underlying mechanism is not fully understood. Here we showed that the TAK1-JNK pathway, a MAPK signaling pathway, is activated through lysosome rupture and that this activation is necessary for the complete activation of the NLRP3 inflammasome through the oligomerization of an adapter protein, apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC). We also revealed that the activation of the TAK1-JNK pathway is sustained through Ca²⁺ ions and that calcium/calmodulin-dependent protein kinase type II functions upstream of the TAK1-JNK pathway and specifically regulates lysosome rupture-induced NLRP3 inflammasome activation. These data suggest a novel role for the TAK1-JNK pathway as a critical regulator of NLRP3 inflammasome activation.     

Glutathione peroxidase-1 deficiency augments proinflammatory cytokine-induced redox signaling and human endothelial cell activation

Glutathione peroxidase-1 (GPx-1) is a crucial antioxidant enzyme, the deficiency of which promotes atherogenesis. Accordingly, we examined the mechanisms by which GPx-1 deficiency enhances endothelial cell activation and inflammation. In human microvascular endothelial cells, we found that GPx-1 deficiency augments intercellular adhesion molecule-1 (ICAM-1) and vascular cell adhesion molecule-1 (VCAM-1) expression by redox-dependent mechanisms that involve NFκB. Suppression of GPx-1 enhanced TNF-α-induced ROS production and ICAM-1 expression, whereas overexpression of GPx-1 attenuated these TNF-α-mediated responses. GPx-1 deficiency prolonged TNF-α-induced IκBα degradation and activation of ERK1/2 and JNK. JNK or NFκB inhibition attenuated TNF-α induction of ICAM-1 and VCAM-1 expression in GPx-1-deficient and control cells, whereas ERK1/2 inhibition attenuated only VCAM-1 expression. To analyze further signaling pathways involved in GPx-1-mediated protection from TNF-α-induced ROS, we performed microarray analysis of human microvascular endothelial cells treated with TNF-α in the presence and absence of GPx-1. Among the genes whose expression changed significantly, dual specificity phosphatase 4 (DUSP4), encoding an antagonist of MAPK signaling, was down-regulated by GPx-1 suppression. Targeted DUSP4 knockdown enhanced TNF-α-mediated ERK1/2 pathway activation and resulted in increased adhesion molecule expression, indicating that GPx-1 deficiency may augment TNF-α-mediated events, in part, by regulating DUSP4.     

Gasdermin D is an executor of pyroptosis and required for interleukin-1β secretion

Inflammasome is an intracellular signaling complex of the innate immune system. Activation of inflammasomes promotes the secretion of interleukin 1β (IL-1β) and IL-18 and triggers pyroptosis. Caspase-1 and -11 (or -4/5 in human) in the canonical and non-canonical inflammasome pathways, respectively, are crucial for inflammasome-mediated inflammatory responses. Here we report that gasdermin D (GSDMD) is another crucial component of inflammasomes. We discovered the presence of GSDMD protein in nigericin-induced NLRP3 inflammasomes by a quantitative mass spectrometry-based analysis. Gene deletion of GSDMD demonstrated that GSDMD is required for pyroptosis and for the secretion but not proteolytic maturation of IL-1β in both canonical and non-canonical inflammasome responses. It was known that GSDMD is a substrate of caspase-1 and we showed its cleavage at the predicted site during inflammasome activation and that this cleavage was required for pyroptosis and IL-1β secretion. Expression of the N-terminal proteolytic fragment of GSDMD can trigger cell death and N-terminal modification such as tagging with Flag sequence disrupted the function of GSDMD. We also found that pro-caspase-1 is capable of processing GSDMD and ASC is not essential for GSDMD to function. Further analyses of LPS plus nigericin- or Salmonella typhimurium-treated macrophage cell lines and primary cells showed that apoptosis became apparent in Gsdmd^−/− cells, indicating a suppression of apoptosis by pyroptosis. The induction of apoptosis required NLRP3 or other inflammasome receptors and ASC, and caspase-1 may partially contribute to the activation of apoptotic caspases in Gsdmd^−/− cells. These data provide new insights into the molecular mechanisms of pyroptosis and reveal an unexpected interplay between apoptosis and pyroptosis.     

poly(dA:dT)促进体外培养的人绒毛组织AIM2炎性体活化

目的:在妊娠过程中,胎盘可能暴露于多种病原微生物,威胁胎儿正常生长发育。为探讨人胎盘绒毛组织是否表达AIM2炎性体成员基因以及人胎盘组织的AIM2炎性体的活化形式。方法:以THP-1细胞来源的RNA和蛋白作为阳性对照,分别应用RT-PCR和Western blot方法检测人早孕期胎盘绒毛组织中AIM2炎性体两个相关基因AIM2和ASC的表达。分离和体外培养人胎盘绒毛膜组织,并用不同浓度的poly(d A:d T)进行转染,处理24小时后,分别收集组织培养上清和蛋白裂解液,Western blot检测蛋白裂解液中caspase-1的活化,ELISA检测培养上清中IL-1β的分泌。结果:RT-PCR和Western blot结果均显示人早孕期胎盘绒毛组织组成性表达AIM2炎性体相关基因AIM2和ASC。同时,体外培养的人胎盘绒毛组织在转染5μg/m L poly(d A:d T)后,caspase-1剪切片段p10显著增多,培养上清中IL-1β分泌也显著增多(P0.01)。结论:人胎盘绒毛组织存在功能性的AIM2炎性体,能够被胞内双链DNA活化。     

Mycobacterium abscessus activates the NLRP3 inflammasome via Dectin-1-Syk and p62/SQSTM1

Numerous atypical mycobacteria, including Mycobacterium abscessus (Mabc), cause nontuberculous mycobacterial infections, which present a serious public health threat. Inflammasome activation is involved in host defense and the pathogenesis of autoimmune diseases. However, inflammasome activation has not been widely characterized in human macrophages infected with atypical mycobacteria. Here, we demonstrate that Mabc robustly activates the nucleotide binding and oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3) inflammasome via dectin-1/Syk-dependent signaling and the cytoplasmic scaffold protein p62/SQSTM1 (p62) in human macrophages. Both dectin-1 and Toll-like receptor 2 (TLR2) were required for Mabc-induced mRNA expression of pro-interleukin (IL)-1β, cathelicidin human cationic antimicrobial protein-18/LL-37 and β-defensin 4 (DEFB4). Dectin-1-dependent Syk signaling, but not that of MyD88, led to the activation of caspase-1 and secretion of IL-1β through the activation of an NLRP3/apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) inflammasome. Additionally, potassium efflux was required for Mabc-induced NLRP3/ASC inflammasome activation. Furthermore, Mabc-induced p62 expression was critically involved in NLRP3 inflammasome activation in human macrophages. Finally, NLRP3/ASC was critical for the inflammasome in antimicrobial responses to Mabc infection. Taken together, these data demonstrate the induction mechanism of the NLRP3/ASC inflammasome and its role in innate immunity to Mabc infection.     

AIM2 and NLRP3 inflammasomes activate both apoptotic and pyroptotic death pathways via ASC

Inflammasomes are protein complexes assembled upon recognition of infection or cell damage signals, and serve as platforms for clustering and activation of procaspase-1. Oligomerisation of initiating proteins such as AIM2 (absent in melanoma-2) and NLRP3 (NOD-like receptor family, pyrin domain-containing-3) recruits procaspase-1 via the inflammasome adapter molecule ASC (apoptosis-associated speck-like protein containing a CARD). Active caspase-1 is responsible for rapid lytic cell death termed pyroptosis. Here we show that AIM2 and NLRP3 inflammasomes activate caspase-8 and -1, leading to both apoptotic and pyroptotic cell death. The AIM2 inflammasome is activated by cytosolic DNA. The balance between pyroptosis and apoptosis depended upon the amount of DNA, with apoptosis seen at lower transfected DNA concentrations. Pyroptosis had a higher threshold for activation, and dominated at high DNA concentrations because it happens more rapidly. Gene knockdown showed caspase-8 to be the apical caspase in the AIM2- and NLRP3-dependent apoptotic pathways, with little or no requirement for caspase-9. Procaspase-8 localised to ASC inflammasome ‘specks'' in cells, and bound directly to the pyrin domain of ASC. Thus caspase-8 is an integral part of the inflammasome, and this extends the relevance of the inflammasome to cell types that do not express caspase-1.     

Apoptosis-associated speck-like protein (ASC) controls Legionella pneumophila infection in human monocytes

The ability of Legionella pneumophila to cause pneumonia is determined by its capability to evade the immune system and grow within human monocytes and their derived macrophages. Human monocytes efficiently activate caspase-1 in response to Salmonella but not to L. pneumophila. The molecular mechanism for the lack of inflammasome activation during L. pneumophila infection is unknown. Evaluation of the expression of several inflammasome components in human monocytes during L. pneumophila infection revealed that the expression of the apoptosis-associated speck-like protein (ASC) and the NOD-like receptor NLRC4 are significantly down-regulated in human monocytes. Exogenous expression of ASC maintained the protein level constant during L. pneumophila infection and conveyed caspase-1 activation and restricted the growth of the pathogen. Further depletion of ASC with siRNA was accompanied with improved NF-κB activation and enhanced L. pneumophila growth. Therefore, our data demonstrate that L. pneumophila manipulates ASC levels to evade inflammasome activation and grow in human monocytes. By targeting ASC, L. pneumophila modulates the inflammasome, the apoptosome, and NF-κB pathway simultaneously.     

PTP inhibitor IV protects JNK kinase activity by inhibiting dual-specificity phosphatase 14 (DUSP14)

Protein phosphorylation plays critical roles in the regulation of protein activity and cell signaling. The level of protein phosphorylation is controlled by protein kinases and protein tyrosine phosphatases (PTPs). Disturbance of the equilibrium between protein kinase and PTP activities results in abnormal protein phosphorylation, which has been linked to the etiology of several diseases, including cancer. In this study, we screened protein tyrosine phosphatases (PTPs) by in vitro phosphatase assays to identify PTPs that are inhibited by bis (4-trifluoromethyl-sulfonamidophenyl, TFMS)-1,4-diisopropylbenzene (PTP inhibitor IV). PTP inhibitor IV inhibited DUSP14 phosphatase activity. Kinetic studies with PTP inhibitor IV and DUSP14 revealed a competitive inhibition, suggesting that PTP inhibitor IV binds to the catalytic site of DUSP14. PTP inhibitor IV effectively and specifically inhibited DUSP14-mediated dephosphorylation of JNK, a member of the mitogen-activated protein kinase (MAPK) family.     

DUSP1 is involved in the progression of small cell carcinoma of the prostate

Small cell carcinoma of the prostate (SCCP) is a rare and the most aggressive variant of prostate cancer. There is no effective cure or treatment for SCCP. Therefore, there is an urgent need for new therapy to improve the prognosis of patients with SCCP. DUSP1 is a dual specific phosphatase with an increasingly recognized in tumor biology. Altered expression of DUSP1 induced changes in the expression of genes involved in various biological pathways, including cell-cell signaling and angiogenesis. To understand more about the role of DUSP1 in SCCP, we evaluated the biological function and associated regulatory mechanism of DUSP1. In this study, DUSP1 was significantly down-regulated in human SCCP compared with the non-carcinoma tissues (P < 0.05). Overexpression of DUSP1 was found to suppress MAPK signaling and cell proliferation in PC-3 cells. Additionally, silencing of DUSP1 enhanced MAPK signaling and PC-3 cell proliferation. Moreover, it was observed that DUSP1 blocked the phosphorylation of p38 MAPK induced by anisomycin. Taken together, this investigation suggests that DUSP1 is involved in the progression of SCCP and may provide a new therapeutic target for SCCP treatment.     

IFI16 acts as a nuclear pathogen sensor to induce the inflammasome in response to Kaposi Sarcoma-associated herpesvirus infection

Inflammasomes are cytoplasmic sensors of foreign molecules, including pathogens, and function to induce caspase-1 activation and IL-1β cytokine maturation. Whether such a mechanism exists in the nucleus and is effective against nuclear replicating pathogens is unknown. Nuclear replicating herpesvirus KSHV is associated with Kaposi Sarcoma, an angioproliferative tumor characterized by an inflammatory microenvironment including IL-1β. We demonstrate that during KSHV infection of endothelial cells, interferon gamma-inducible protein 16 (IFI16) interacts with the adaptor molecule ASC and procaspase-1 to form a functional inflammasome. This complex was initially detected in the nucleus and subsequently in the perinuclear area. KSHV gene expression and/or latent KSHV genome is required for inflammasome activation and IFI16 colocalizes with the KSHV genome in the infected cell nucleus. Caspase-1 activation by KSHV was reduced by IFI16 and ASC silencing. Our studies reveal IFI16 as a nuclear pathogen sensor and demonstrate that the inflammasome also functions in the nucleus.     

ASC, Ipaf and Cryopyrin/Nalp3: bona fide intracellular adapters of the caspase-1 inflammasome

The adapter molecules ASC, Ipaf and Cryopyrin/Nalp3 have each been proposed to regulate caspase-1 within a multi-protein complex called the "inflammasome". Activation of caspase-1 leads to the cleavage and activation of pro-inflammatory cytokines such as interleukin (IL)-1beta and IL-18. The analysis of mice deficient in ASC, Ipaf and Cryopyrin/Nalp3 has revealed that the inflammasome is a dynamic entity that is assembled from different adapters in a stimulus-dependent manner.     

NSC-87877, inhibitor of SHP-1/2 PTPs, inhibits dual-specificity phosphatase 26 (DUSP26)

Protein phosphorylation plays critical roles in many regulatory mechanisms controlling cell activities and thus involved in various diseases. The cellular equilibrium of phosphorylation is regulated through the actions of protein kinases and phosphatases. Therefore, these regulatory proteins have emerged as promising targets for drug development. In this study, we screened protein tyrosine phosphatases (PTPs) by in vitro phosphatase assays to identify PTPs that are inhibited by 8-hydroxy-7-(6-sulfonaphthalen-2-yl)diazenyl-quinoline-5-sulfonic acid (NSC-87877), a potent inhibitor of SHP-1 and SHP-2 PTPs. Phosphatase activity of dual-specificity protein phosphatase 26 (DUSP26) was decreased by the inhibitor in a dose-dependent manner. Kinetic studies with NSC-87877 and DUSP26 revealed a competitive inhibition. NSC-87877 effectively inhibited DUSP26-mediated dephosphorylation of p38, a member of mitogen-activated protein kinase (MAPK) family. Since DUSP26 is involved in survival of anaplastic thyroid cancer (ATC) cells, NSC-87877 could be a therapeutic reagent for treating ATC.     

Serum amyloid A activates the NLRP3 inflammasome via P2X7 receptor and a cathepsin B-sensitive pathway

Serum amyloid A (SAA) is an acute-phase protein, the serum levels of which can increase up to 1000-fold during inflammation. SAA has a pathogenic role in amyloid A-type amyloidosis, and increased serum levels of SAA correlate with the risk for cardiovascular diseases. IL-1β is a key proinflammatory cytokine, and its secretion is strictly controlled by the inflammasomes. We studied the role of SAA in the regulation of IL-1β production and activation of the inflammasome cascade in human and mouse macrophages, as well as in THP-1 cells. SAA could provide a signal for the induction of pro-IL-1β expression and for inflammasome activation, resulting in secretion of mature IL-1β. Blocking TLR2 and TLR4 attenuated SAA-induced expression of IL1B, whereas inhibition of caspase-1 and the ATP receptor P2X(7) abrogated the release of mature IL-1β. NLRP3 inflammasome consists of the NLRP3 receptor and the adaptor protein apoptosis-associated speck-like protein containing CARD (a caspase-recruitment domain) (ASC). SAA-mediated IL-1β secretion was markedly reduced in ASC(-/-) macrophages, and silencing NLRP3 decreased IL-1β secretion, confirming NLRP3 as the SAA-responsive inflammasome. Inflammasome activation was dependent on cathepsin B activity, but it was not associated with lysosomal destabilization. SAA also induced secretion of cathepsin B and ASC. In conclusion, SAA can induce the expression of pro-IL-1β and activation of the NLRP3 inflammasome via P2X(7) receptor and a cathepsin B-sensitive pathway. Thus, during systemic inflammation, SAA may promote the production of IL-1β in tissues. Furthermore, the SAA-induced secretion of active cathepsin B may lead to extracellular processing of SAA and, thus, potentially to the development of amyloid A amyloidosis.     

Reconstituted NALP1 inflammasome reveals two-step mechanism of caspase-1 activation

Interleukin (IL)-1beta maturation is accomplished by caspase-1-mediated proteolysis, an essential element of innate immunity. NLRs constitute a recently recognized family of caspase-1-activating proteins, which contain a nucleotide-binding oligomerization domain and leucine-rich repeat (LRR) domains and which assemble into multiprotein complexes to create caspase-1-activating platforms called "inflammasomes." Using purified recombinant proteins, we have reconstituted the NALP1 inflammasome and have characterized the requirements for inflammasome assembly and caspase-1 activation. Oligomerization of NALP1 and activation of caspase-1 occur via a two-step mechanism, requiring microbial product, muramyl-dipeptide, a component of peptidoglycan, followed by ribonucleoside triphosphates. Caspase-1 activation by NALP1 does not require but is enhanced by adaptor protein ASC. The findings provide the biochemical basis for understanding how inflammasome assembly and function are regulated, and shed light on NALP1 as a direct sensor of bacterial components in host defense against pathogens.     

Varicella-zoster virus infection triggers formation of an interleukin-1β (IL-1β)-processing inflammasome complex

Innate cellular immunity is the immediate host response against pathogens, and activation of innate immunity also modulates the induction of adaptive immunity. The nucleotide-binding oligomerization domain (NOD)-like receptors (NLRs) are a family of intracellular receptors that recognize conserved patterns associated with intracellular pathogens, but information about their role in the host defense against DNA viruses is limited. Here we report that varicella-zoster virus (VZV), an alphaherpesvirus that is the causative agent of varicella and herpes zoster, induces formation of the NLRP3 inflammasome and the associated processing of the proinflammatory cytokine IL-1β by activated caspase-1 in infected cells. NLRP3 inflammasome formation was induced in VZV-infected human THP-1 cells, which are a transformed monocyte cell line, primary lung fibroblasts, and melanoma cells. Absent in melanoma gene-2 (AIM2) is an interferon-inducible protein that can form an alternative inflammasome complex with caspase-1 in virus-infected cells. Experiments in VZV-infected melanoma cells showed that NLRP3 protein recruits the adaptor protein ASC and caspase-1 to form an NLRP3 inflammasome complex independent of AIM2 protein and in the absence of free radical reactive oxygen species release. NLRP3 was also expressed extensively in infected skin xenografts in the severe combined immunodeficiency mouse model of VZV pathogenesis in vivo. We conclude that NLRP3 inflammasome formation is an innate cellular response to infection with this common pathogenic human herpesvirus.