DNA-responsive inflammasomes and their regulators in autoimmunity

Nucleic acid-responsive smart systems for controlled cargo delivery

Stimulus-responsive delivery systems allow controlled, highly regulated, and efficient delivery of various cargos while minimizing side effects. Owing to the unique properties of nucleic acids, including the ability to adopt complex structures by base pairing, their easy synthesis, high specificity, shape memory, and configurability, they have been employed in autonomous molecular motors, logic circuits, reconfigurable nanoplatforms, and catalytic amplifiers. Moreover, the development of nucleic acid (NA)-responsive intelligent delivery vehicles is a rapidly growing field. These vehicles have attracted much attention in recent years due to their programmable, controllable, and reversible properties. In this work, we review several types of NA-responsive controlled delivery vehicles based on locks and keys, including DNA/RNA-responsive, aptamer-responsive, and CRISPR-responsive, and summarize their advantages and limitations.

"Other Than NLRP3" Inflammasomes: Multiple Roles in Brain Disease

Human neuroinflammatory and neurodegenerative diseases, whose prevalence keeps rising, are still unsolved pathobiological/therapeutical problems. Among others, recent etiology hypotheses stressed as their main driver a chronic neuroinflammation, which is mediated by innate immunity-related protein oligomers: the inflammasomes. A panoply of exogenous and/or endogenous harmful agents activates inflammasomes' assembly, signaling, and IL-1β/IL-18 production and neural cells' pyroptotic death. The underlying concept is that inflammasomes' chronic activation advances neurodegeneration while their short-lasting operation restores tissue homeostasis. Hence, from a therapeutic standpoint, it is crucial to understand inflammasomes' regulatory mechanisms. About this, a deluge of recent studies focused on the NLRP3 inflammasome with suggestions that its pharmacologic block would hinder neurodegeneration. Yet hitherto no evidence proves this view. Moreover, known inflammasomes are numerous, and the mechanisms regulating their expression and function may vary with the involved animal species and strains, as well as organs and cells, and the harmful factors triggered as a result. Therefore, while presently leaving out some little-studied inflammasomes, this review focuses on the "other than NLRP3" inflammasomes that participate in neuroinflammation's complex mechanisms: NLRP1, NLRP2, NLRC4, and AIM2. Although human-specific data about them are relatively scant, we stress that only a holistic view including several human brain inflammasomes and other potential pathogenetic drivers will lead to successful therapies for neuroinflammatory and neurodegenerative diseases.

Inhibition of AIM2 inflammasome activation by SOX/ORF37 promotes lytic replication of Kaposi's sarcoma-associated herpesvirus

Inflammasomes are one kind of important innate immune defense against viral and bacterial infections. Several inflammasome-forming sensors detect molecular patterns of invading pathogens and then trigger inflammasome activation and/or pyroptosis in infected cells, and viruses employ unique strategies to hijack or subvert inflammasome activation. Infection with herpesviruses induces the activation of diverse inflammasomes, including AIM2 and IFI16 inflammasomes; however, how Kaposi's sarcoma-associated herpesvirus (KSHV) counteracts inflammasome activation largely remains unclear. Here, we reveal that the KSHV ORF37-encoded SOX protein suppresses AIM2 inflammasome activation independent of its viral DNA exonuclease activity and host mRNA turnover. SOX interacts with the AIM2 HIN domain through the C-terminal Motif VII region and disrupts AIM2:dsDNA polymerization and ASC recruitment and oligomerization. The Y443A or F444A mutation of SOX abolishes the inhibition of AIM2 inflammasome without disrupting SOX nuclease activity, and a short SOX peptide is capable of inhibiting AIM2 inflammasome activation; consequently, infection with SOX-null, Y443A, or F444A Bac16 recombinant viruses results in robust inflammasome activation, suppressed lytic replication, and increased pyroptosis in human lymphatic endothelial cells in an AIM2-dependent manner. These results reveal that KSHV SOX suppresses AIM2 inflammasome activation to promote KSHV lytic replication and inhibit pyroptosis, representing a unique mechanism for evasion of inflammasome activation during KSHV lytic cycle.

Variants in interferon gamma inducible protein 16 (IFI16) and absent in melanoma 2 (AIM2) genes that modulate inflammatory response are associated with periodontitis

OBJECTIVE

Evaluate the association of genetic variants of the interferon gamma inducible protein 16 (IFI16) and absent in melanoma 2 (AIM2) genes with periodontitis.

METHODS

The study involved 117 individuals with periodontitis and 389 without periodontitis, all Brazilians, miscegenated. Individuals with periodontitis presented at least 4 teeth with ≥ 1 site with probing depth ≥ 4 mm; clinical attachment level ≥ 3 mm on the same site and bleeding upon stimulus. Genotyping was performed using the Infinium Multi-Ethnic AMR/AFR-8 Bead Chip focused on Hispanic and African American populations with approximately 2 million markers of the human genome. Multivariate logistic regression was performed to identify associations in additive, dominant and recessive models adjusted for covariates age, obesity, mouth breathing, flossing, asthma, and ancestry.

RESULTS

In IFI16, the rs75985579-A is positively associated with periodontitis in the additive (Odds Ratio adjusted (ORadjusted) 2.65, 95% confidence interval (CI):1.25-5.60, p value: 0.007) and dominant models (ORadjusted 2.56, 95%CI:1.13-5.81, p value: 0.017). In AIM2, the rs76457189-G, is associated negatively with periodontitis in two genetic models evaluated, additive (ORadjusted 0.21, 95%CI:0.05-0.94, p value: 0.022) and dominant (ORadjusted 0.21, 95%CI:0.05-0.94, p value: 0.022).

CONCLUSIONS

These results have shown that variants in the IFI16 and AIM2 genes are associated with periodontitis. Individuals with at least one A (adenine) allele of the rs75985579 (IFI16) are more than twice as likely to have periodontitis, while individuals with the G (guanine) allele of rs76457189 (AIM2) are less likely to be diagnosed with periodontitis, providing a negative association with periodontitis.

Pattern-recognition receptors in endometriosis: A narrative review

Endometriosis is closely associated with ectopic focal inflammation and immunosuppressive microenvironment. Multiple types of pattern recognition receptors (PRRs) are present in the innate immune system, which are able to detect pathogen-associated molecular patterns (PAMPs) and danger-associated molecular patterns (DAMPs) in both intracellular and external environments. However, the exact role of PRRs in endometriosis and the underlying molecular mechanism are unclear. PRRs are necessary for the innate immune system to identify and destroy invasive foreign infectious agents. Mammals mainly have two types of microbial recognition systems. The first one consists of the membrane-bound receptors, such as toll-like receptors (TLRs), which recognize extracellular microorganisms and activate intracellular signals to stimulate immune responses. The second one consists of the intracellular PRRs, including nod-like receptors (NLRs) and antiviral proteins retinoic acid-inducible gene I (RIG-I) and melanoma differentiation-associated gene 5 (MDA-5) with helix enzyme domain. In this review, we mainly focus on the key role of PRRs in the pathological processes associated with endometriosis. PRRs recognize PAMPs and can distinguish pathogenic microorganisms from self, triggering receptor ligand reaction followed by the stimulation of host immune response. Activated immune response promotes the transmission of microbial infection signals to the cells. As endometriosis is characterized by dysregulated inflammation and immune response, PRRs may potentially be involved in the activation of endometriosis-associated inflammation and immune disorders. Toll-like receptor 2 (TLR2), toll-like receptor 3 (TLR3), toll-like receptor 4 (TLR4), nod-like receptor family caspase activation and recruitment domain (CARD) domain containing 5 (NLRC5), nod-like receptor family pyrin domain containing 3 (NLRP3), and c-type lectin receptors (CLRs) play essential roles in endometriosis development by regulating immune and inflammatory responses. Absent in melanoma 2 (AIM2)-like receptors (ALRs) and retinoic acid-inducible gene I-like receptors (RLRs) may be involved in the activation of endometriosis-associated immune and inflammation disorders. PRRs, especially TLRs, may serve as potential therapeutic targets for alleviating pain in endometriosis patients. PRRs and their ligands interact with the innate immune system to enhance inflammation in the stromal cells during endometriosis. Thus, targeting PRRs and their new synthetic ligands may provide new therapeutic options for treating endometriosis.

Comparing the Biological Properties of Double-Stranded DNA Extracted from Human and Porcine Placenta and Salmon Sperm

Background

Double-stranded fragmented extracellular DNA is a participant, inducer, and indicator of various processes occurring in the organism. When investigating the properties of extracellular DNA, the question regarding the specificity of exposure to DNA from different sources has always been raised. The aim of this study was to perform comparative assessment of biological properties of double-stranded DNA obtained from the human placenta, porcine placenta and salmon sperm.

Methods

The intensity of leukocyte-stimulating effect of different dsDNA was assessed in mice after cyclophosphamide-induced cytoreduction. The stimulatory effect of different dsDNA on maturation and functions of human dendritic cells and the intensity of cytokine production by human whole blood cells was analyzed ex vivo. The oxidation level of the dsDNA was also compared.

Results

Human placental DNA exhibited the strongest leukocyte-stimulating effect. DNA extracted from human and porcine placenta exhibited similar stimulatory action on maturation of dendritic cells, allostimulatory capacity, and ability of dendritic cells to induce generation of cytotoxic CD8+CD107a+ T cells in the mixed leukocyte reaction. DNA extracted from salmon sperm stimulated the maturation of dendritic cells, while having no effect on their allostimulatory capacity. DNA extracted from human and porcine placenta was shown to exhibit a stimulatory effect on cytokine secretion by human whole blood cells. The observed differences between the DNA preparations can be caused by the total methylation level and are not related to differences in oxidation level of DNA molecules.

Conclusions

Human placental DNA exhibited the maximum combination of all biological effects.

Cytosolic DNA sensor IFI16 proteins: Potential molecular integrators of interactions among the aging hallmarks

Cellular changes that are linked to aging in humans include genomic instability, telomere attrition, epigenetic alterations, mitochondrial dysfunction, cellular senescence, and altered intercellular communications. The extent of the changes in these aging hallmarks and their interactions with each other are part of the human aging. However, the molecular mechanisms through which the aging hallmarks interact with each other remain unclear. Studies have indicated a potential role for the type I interferon (IFN) and p53-inducible IFI16 proteins in interactions with the aging hallmarks. The IFI16 proteins are members of the PYHIN protein family. Proteins in the family share a DNA-binding domain (the HIN domain) and a protein-protein interaction pyrin domain (PYD). IFI16 proteins are needed for cytosolic DNA-induced activation of the cGAS-STING pathway for type I IFN (IFN-β) expression. The pathway plays an important role in aging-related inflammation (inflammaging). Further, increased levels of the IFI16 proteins potentiate the cell growth inhibitory functions of the p53 and pRb tumor suppressors proteins. Moreover, IFI16 proteins are needed for most aging hallmarks. Therefore, here we discuss how an improved understanding of the role of the IFI16 proteins in integration of the aging hallmarks has potential to improve the human health and lifespan.

DNA and RNA Binding Proteins: From Motifs to Roles in Cancer

DNA and RNA binding proteins (DRBPs) are a broad class of molecules that regulate numerous cellular processes across all living organisms, creating intricate dynamic multilevel networks to control nucleotide metabolism and gene expression. These interactions are highly regulated, and dysregulation contributes to the development of a variety of diseases, including cancer. An increasing number of proteins with DNA and/or RNA binding activities have been identified in recent years, and it is important to understand how their activities are related to the molecular mechanisms of cancer. In addition, many of these proteins have overlapping functions, and it is therefore essential to analyze not only the loss of function of individual factors, but also to group abnormalities into specific types of activities in regard to particular cancer types. In this review, we summarize the classes of DNA-binding, RNA-binding, and DRBPs, drawing particular attention to the similarities and differences between these protein classes. We also perform a cross-search analysis of relevant protein databases, together with our own pipeline, to identify DRBPs involved in cancer. We discuss the most common DRBPs and how they are related to specific cancers, reviewing their biochemical, molecular biological, and cellular properties to highlight their functions and potential as targets for treatment.

Tumor necrosis factor-alpha and interferon-gamma induce inflammasome-mediated corneal endothelial cell death

PURPOSE

Chronic corneal endothelial cell (CEC) loss results in corneal edema and vision loss in conditions such as pseudophakic bullous keratopathy (PBK), Fuchs' dystrophy, and corneal graft failure. Low CEC density has been associated with an elevation of intraocular pro-inflammatory cytokines such as tumor necrosis factor (TNF)-α and interferon (INF)-γ. These cytokines are capable of triggering pyroptosis, a programmed cell death mechanism mediated by the inflammasome, prompting the activation of the pro-inflammatory cytokine interleukin (IL)-1β, the perpetuation of inflammation, and subsequent damage of corneal endothelial tissue. Therefore, the purpose of this study was to determine the deleterious contribution of the inflammasome and pyroptosis to CEC loss.

METHODS

CECs from human donor corneas were treated ex vivo with TNF-α and IFN-γ for 48 h. Levels of caspase-1 and IL-1β were then assayed by ELISA, and the expression of caspase-1 and gasdermin-D (GSDM-D) were confirmed by immunofluorescence. Endothelial cell damage was analyzed by a lactate dehydrogenase (LDH) release assay, and oxidative stress was determined by measuring the levels of reactive oxygen species (ROS) in the culture media.

RESULTS

Inflammasome activation and oxidative stress were elevated in CECs following exposure to TNF-α and IFN-γ, which resulted in cell death by pyroptosis as determined by LDH release which was inhibited by the caspase-1 inhibitor Ac-YVAD-cmk.

CONCLUSION

CEC death is induced by the pro-inflammatory cytokines TNF-α and IFN-γ, which contribute to inflammasome activation. Moreover, the inflammasome is a promising therapeutic target for the treatment of chronic CEC loss.

Absent in melanoma 2 suppresses gastric cancer cell proliferation and migration via inactivation of AKT signaling pathway

Gastric cancer (GC) is the third leading cause of cancer-related mortality worldwide, and poses a great threat to public health. Absent in melanoma 2 (AIM2), a member of the pyrin-HIN family proteins, plays various roles across different types of cancers. However, the possible role of AIM2 in GC, as well as the underling mechanisms, are equivocal and need to be further explored. Herein, we identified that AIM2 expression was significantly down-regulated in GC tissues. Furthermore, loss of AIM2 was significantly associated with tumor size, lymph node metastasis (LNM) and tumor, node, metastases (TNM) staging, as well as poor prognosis in GC patients. Knockdown of AIM2 in GC cells significantly promoted cellular proliferation and migration, whereas AIM2 overexpression did the opposite. Mechanistically, we discovered that AIM2 regulates the AKT signaling pathway. In fact, the enhanced proliferation and migration ability induced by AIM2 knockdown was partially impaired in cells treated with the AKT inhibitor. Overall, our findings suggests that AIM2 is an independent prognostic marker and highlights a new entry point for targeting the AIM2/AKT signaling axis for GC treatment.

Understanding Inflammasomes and PD-1/PD-L1 Crosstalk to Improve Cancer Treatment Efficiency

Inflammasomes and immune checkpoints have been shown to participate in carcinogenesis, cancer growth and response to treatment. Thus, targeting cytokines resulting from inflammasome activation, such as interleukin (IL)-1β, has emerged as a new tool in the therapeutic arsenal. Moreover, the use of checkpoint inhibitors such as anti-PD-1 or anti-PD-L1 has revolutionized the treatment of some cancer patients. However, inflammasome activation and consecutive cytokine release only occurs in some chemotherapeutic treatments and immune checkpoint inhibitors only work for a restricted number of patients, thus limiting the use of therapies targeting these pathways. Expanding knowledge about the inefficiency of these therapies recently brought forward the hypothesis of targeting both pathways. In this review, we provide an overview of the crosstalk between inflammasomes and programmed death-1 (PD-1)/programmed death-ligand 1 (PD-L1) that might explain how these two pathways are mutually dependent, and perhaps why targeting only one of them leads to inefficiency of cancer treatment in some patients.

Type I interferon (IFN)-inducible Absent in Melanoma 2 proteins in neuroinflammation: implications for Alzheimer's disease

Cumulative evidence indicates that activation of innate immune responses in the central nervous system (CNS) induces the expression of type 1 interferons (T1 IFNs), a family of cytokines. The T1 IFNs (IFN-α/β), through activation of the JAK/STAT-signaling in microglia, astrocytes, and neurons, induce the expression of IFN-inducible proteins, which mediate the pro- and anti-inflammatory functions of IFNs. Accordingly, T1 IFN-inducible Absent in Melanoma 2 proteins (murine Aim2 and human AIM2) negatively regulate the expression of TI IFNs and, upon sensing higher levels of cytosolic DNA, assemble the Aim2/AIM2 inflammasome, resulting in activation of caspase-1, pyroptosis, and the secretion of pro-inflammatory cytokines (e.g., IL-1β and IL-18). Of interest, studies have indicated a role for the Aim2/AIM2 proteins in neuroinflammation and neurodegenerative diseases, including Alzheimer's disease (AD). The ability of Aim2/AIM2 proteins to exert pro- and anti-inflammatory effects in CNS may depend upon age, sex hormones, cell-types, and the expression of species-specific negative regulators of the Aim2/AIM2 inflammasome. Therefore, we discuss the role of Aim2/AIM2 proteins in the development of AD. An improved understanding of the role of Absent in Melanoma 2 proteins in AD could identify new approaches to treat patients.

The emerging roles of inflammasome-dependent cytokines in cancer development

In addition to the genomic alterations that occur in malignant cells, the immune system is increasingly appreciated as a critical axis that regulates the rise of neoplasms and the development of primary tumours and metastases. The interaction between inflammatory cell infiltrates and stromal cells in the tumour microenvironment is complex, with inflammation playing both pro- and anti-tumorigenic roles. Inflammasomes are intracellular multi-protein complexes that act as key signalling hubs of the innate immune system. They respond to cellular stress and trauma by promoting activation of caspase-1, a protease that induces a pro-inflammatory cell death mode termed pyroptosis along with the maturation and secretion of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18. Here, we will briefly introduce inflammasome biology with a focus on the dual roles of inflammasome-produced cytokines in cancer development. Despite emerging insight that inflammasomes may promote and suppress cancer development according to the tumour stage and the tumour microenvironment, much remains to be uncovered. Further exploration of inflammasome biology in tumorigenesis should enable the development of novel immunotherapies for cancer patients.

Inflammasome-Dependent Cytokines at the Crossroads of Health and Autoinflammatory Disease

As key regulators of both innate and adaptive immunity, it is unsurprising that the activity of interleukin (IL)-1 cytokine family members is tightly controlled by decoy receptors, antagonists, and a variety of other mechanisms. Additionally, inflammasome-mediated proteolytic maturation is a prominent and distinguishing feature of two important members of this cytokine family, IL-1β and IL-18, because their full-length gene products are biologically inert. Although vital in antimicrobial host defense, deregulated inflammasome signaling is linked with a growing number of autoimmune and autoinflammatory diseases. Here, we focus on introducing the diverse inflammasome types and discussing their causal roles in periodic fever syndromes. Therapies targeting IL-1 or IL-18 show great efficacy in some of these autoinflammatory diseases, although further understanding of the molecular mechanisms leading to unregulated production of these key cytokines is required to benefit more patients.

IFI16 filament formation in salivary epithelial cells shapes the anti-IFI16 immune response in Sjögren's syndrome

IFN-inducible protein 16 (IFI16) is an innate immune sensor that forms filamentous oligomers when activated by double-stranded DNA (dsDNA). Anti-IFI16 autoantibodies occur in patients with Sjögren's syndrome (SS) and associate with severe phenotypic features. We undertook this study to determine whether the structural and functional properties of IFI16 play a role in its status as an SS autoantigen. IFI16 immunostaining in labial salivary glands (LSGs) yielded striking evidence of filamentous IFI16 structures in the cytoplasm of ductal epithelial cells, representing the first microscopic description of IFI16 oligomerization in human tissues, to our knowledge. Transfection of cultured epithelial cells with dsDNA triggered the formation of cytoplasmic IFI16 filaments with similar morphology to those observed in LSGs. We found that a majority of SS anti-IFI16 autoantibodies immunoprecipitate IFI16 more effectively in the oligomeric dsDNA-bound state. Epitopes in the C-terminus of IFI16 are accessible to antibodies in the DNA-bound oligomer and are preferentially targeted by SS sera. Furthermore, cytotoxic lymphocyte granule pathways (highly enriched in the SS gland) induce striking release of IFI16•dsDNA complexes from cultured cells. Our studies reveal that IFI16 is present in a filamentous state in the target tissue of SS and suggest that this property of DNA-induced filament formation contributes to its status as an autoantigen in SS. These studies highlight the role that tissue-specific modifications and immune effector pathways might play in the selection of autoantigens in rheumatic diseases.

A study of single nucleotide polymorphisms in CD157, AIM2 and JARID2 genes in Han Chinese children with autism spectrum disorder

PURPOSE

Autism spectrum disorder (ASD) is a group of developmental brain disorders caused by genetic and environmental factors. The objective of this study was to investigate whether single nucleotide polymorphisms (SNPs) in genes related to immune function were associated with ASD in Chinese Han children.

MATERIALS AND METHODS

A total of 201 children with ASD and 200 age- and gender-matched healthy controls were recruited from September 2012 to June 2106. A TaqMan probe-based approach was used to genotype SNPs corresponding to rs28532698 and rs4301112 in CD157, rs855867 in AIM2, and rs2237126 in JARID2. Case-control and case-only studies were performed to determine the contribution of SNPs to the predisposition of disease and its severity, respectively.

RESULTS

Our results revealed that the genotypes and allele frequencies of these SNPs were not significantly associated with childhood ASD and its severity in this population.

CONCLUSIONS

Results of our study suggest that these SNPs are not predictors of childhood ASD in the Chinese Han population. The discrepant results suggest the predictor roles of SNPs have to be determined in different ethnic populations due to genetic heterogeneity of ASD.

Hypoxia primes human normal prostate epithelial cells and cancer cell lines for the NLRP3 and AIM2 inflammasome activation

The molecular mechanisms by which hypoxia contributes to prostatic chronic inflammation (PCI) remain largely unknown. Because hypoxia stimulates the transcriptional activity of NF-κB, which “primes” cells for inflammasome activation by inducing the expression of NLRP3 or AIM2 receptor and pro-IL-1β, we investigated whether hypoxia could activate the NLRP3 and AIM2 inflammasome in human normal prostate epithelial cells (PrECs) and cancer cell lines. Here we report that hypoxia (1% O₂) treatment of PrECs, prostate cell lines, and a macrophage cell line (THP-1) increased the levels of NLRP3, AIM2, and pro-IL-1β. Further, hypoxia in cells potentiated activation of the NLRP3 and AIM2 inflammasome activity. Notably, hypoxia “primed” cells for NLRP3 and AIM2 inflammasome activation through stimulation of the NF-κB activity. Our observations support the idea that hypoxia in human prostatic tumors contributes to PCI, in part, by priming cells for the activation of NLRP3 and AIM2 inflammasome.

Bypassing Border Control: Nuclear Envelope Rupture in Disease

Recent observations in laminopathy patient cells and cancer cells have revealed that the nuclear envelope (NE) can transiently rupture during interphase. NE rupture leads to an uncoordinated exchange of nuclear and cytoplasmic material, thereby deregulating cellular homeostasis. Moreover, concurrently inflicted DNA damage could prime rupture-prone cells for genome instability. Thus, NE rupture may represent a novel pathogenic mechanism that has far-reaching consequences for cell and organism physiology.

Aging and the Inflammasomes

The inflammasomes are innate immune system sensors that control the activation of caspase-1 and induce inflammation in response to infectious microbes and molecules originating from host proteins, leading to the release of pro-inflammatory cytokines, Il1b and IL18, and a particular inflammatory type of cell death termed pyroptosis. It is broadly considered that chronic inflammation may be a common link in age-related diseases, aging being the greatest risk factor for the development of chronic diseases. In this sense, we discuss the role of inflammasomes in non-infectious inflammation and their interest in aging and age-related diseases.

Papilloma-pseudovirus eradicates intestinal tumours and triples the lifespan of ApcMin/+ mice

Inducing tumour-specific adaptive immunity, such as cytotoxic T lymphocyte (CTL) response, can result in promising antitumour effect against several human malignancies, especially in combination with immune checkpoint blockade strategies. However, little is known whether activation of innate immunity can lead to direct tumoricidal effect. Here, we develop a papilloma pseudovirus-based oral immunotherapeutic approach that shows strong tumoricidal effects in the gut, resulting in an almost tripled lifespan of Apc^Min/+ mice (an animal model of human intestinal tumorigenesis). Mechanistically, these pseudoviruses activate the NLRP3 and AIM2 inflammasomes, leading to caspase-1-mediated tumour regression that is dependent on neither cytotoxic T lymphocytes nor humoral immune response. Blocking caspase-1 activation abrogated the therapeutic effects of the pseudoviruses. Thus, targeting innate immune sensors in tumours by the pseudoviruses might represent a strategy to treat intestinal tumours.

Inflammasomes in Inflammation-Induced Cancer

The inflammasome is an important multiprotein complex that functions during inflammatory immune responses. The activation of inflammasome will lead to the autoactivation of caspase-1 and subsequent cleavage of proIL-1β and proIL-18, which are key sources of inflammatory manifestations. Recently, the roles of inflammasomes in cancers have been extensively explored, especially in inflammation-induced cancers. In different and specific contexts, inflammasomes exhibit distinct and even contrasting effects in cancer development. In some cases, inflammasomes initiate carcinogenesis through the extrinsic pathway and maintain the malignant cancer microenvironment through the intrinsic pathway. On the contrary, inflammasomes also exert anticancer effects by specialized programmed cell death called pyroptosis and immune regulatory functions. The phases and compartments in which inflammasomes are activated strongly influence the final immune effects. We systemically summarize the functions of inflammasomes in inflammation-induced cancers, especially in gastrointestinal and skin cancers. Besides, information about the current therapeutic use of inflammasome-related products and potential future developing directions are also introduced.

AIM2 regulates viability and apoptosis in human colorectal cancer cells via the PI3K/Akt pathway

Absent in melanoma 2 (AIM2) plays an important role in innate immunity as a DNA sensor in the cytoplasm by triggering the assembly of an AIM2 inflammasome that results in caspase-1-mediated inflammatory responses and cell death. In recent years, studies have indicated that AIM2 can suppress cancer cell proliferation, and mutations in the gene encoding AIM2 are frequently identified in patients with colorectal cancer (CRC). However, the mechanism by which AIM2 restricts tumor growth remains unclear. We reconstructed AIM2 expression in HCT116 CRC cells by lentivirus transfection. Using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry, we demonstrated that expression of AIM2 inhibited the viability and increased the apoptosis rate of CRC cells, and cell cycle analysis suggested that AIM2 blocked cell cycle transition from G1 to S phase. Western blot analysis showed that AIM2 promoted apoptosis in CRC cells by suppressing the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway. Our data suggest that AIM2 plays a critical role as a tumor suppressor and might serve as a potential therapeutic target in CRC.

Absent in Melanoma 2 proteins in SLE

Type I interferons (IFN-α/β)-inducible PYRIN and HIN domain-containing protein family includes Absent in Melanoma 2 (murine Aim2 and human AIM2), murine p202, and human PYRIN-only protein 3 (POP3). The generation of Aim2-deficient mice indicated that the Aim2 protein is essential for inflammasome activation, resulting in the secretion of interleukin-1β (IL-1β) and IL-18 and cell death by pyroptosis. Further, Aim2-deficiency also increased constitutive expression of the IFN-β and expression of the p202 protein. Notably, an increased expression of p202 protein in female mice associated with the development of systemic lupus erythematosus (SLE). SLE in patients is characterized by a constitutive increase in serum levels of IFN-α and an increase in the expression IFN-stimulated genes. Recent studies indicate that p202 and POP3 proteins inhibit activation of the Aim2/AIM2 inflammasome and promote IFN-β expression. Therefore, we discuss the role of Aim2/AIM2 proteins in the suppression of type I IFNs production and lupus susceptibility.

Absent in melanoma 2 proteins in the development of cancer

Recent studies utilizing chemical-induced colitis-associated and sporadic colon cancer in mouse models indicated a protective role for absent in melanoma 2 (Aim2) in colon epithelial cells. Accordingly, mutations in the human AIM2 gene have been found in colorectal cancer (CRC), and reduced expression of AIM2 in CRC is associated with its progression. Furthermore, the overexpression of AIM2 protein in human cancer cell lines inhibits cell proliferation. Interferon-inducible Aim2 and AIM2 are members of the PYHIN (PYRIN and HIN domain-containing) protein family and share ~57 % amino acid identity. The family also includes murine p202, human PYRIN-only protein 3, and IFI16, which negatively regulate Aim2/AIM2 functions. Because the CRC incidence and mortality rates are higher among men compared with women and the expression of Aim2/AIM2 proteins and their regulators is dependent upon age, gender, and sex hormones, we discuss the potential roles of Aim2/AIM2 in the development of cancer. An improved understanding of the biological functions of the AIM2 in the development of CRC will likely identify new therapeutic approaches to treat patients.

IFI16, an amplifier of DNA-damage response: Role in cellular senescence and aging-associated inflammatory diseases

DNA-damage induces a DNA-damage response (DDR) in mammalian cells. The response, depending upon the cell-type and the extent of DNA-damage, ultimately results in cell death or cellular senescence. DDR-induced signaling in cells activates the ATM-p53 and ATM-IKKα/β-interferon (IFN)-β signaling pathways, thus leading to an induction of the p53 and IFN-inducible IFI16 gene. Further, upon DNA-damage, DNA accumulates in the cytoplasm, thereby inducing the IFI16 protein and STING-dependent IFN-β production and activation of the IFI16 inflammasome, resulting in the production of proinflammatory cytokines (e.g., IL-1β and IL-18). Increased expression of IFI16 protein in a variety of cell-types promotes cellular senescence. However, reduced expression of IFI16 in cells promotes cell proliferation. Because expression of the IFI16 gene is induced by activation of DNA-damage response in cells and increased levels of IFI16 protein in cells potentiate the p53-mediated transcriptional activation of genes and p53 and pRb-mediated cell cycle arrest, we discuss how an improved understanding of the role of IFI16 protein in cellular senescence and associated inflammatory secretory phenotype is likely to identify the molecular mechanisms that contribute to the development of aging-associated human inflammatory diseases and a failure to cancer therapy.

Toll-like receptor 9 enhances bacterial clearance and limits lung consolidation in murine pneumonia caused by methicillin resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) is an important pathogen in pneumonia, associated with severe lung damage. Tissue injury causes release of Damage Associated Molecular Patterns (DAMPs), which may perpetuate inflammation. DNA has been implicated as a DAMP that activates inflammation through Toll-like receptor (TLR)9. The aim of this study was to evaluate the role of TLR9 in MRSA pneumonia. Wild-type (Wt) and TLR9 knockout (tlr9^-/-) mice were infected intranasally with MRSA USA300 (BK 11540) (5^E7CFU) and euthanized at 6,24,48 or 72 hours for analyses. MRSA pneumonia was associated with profound release of cell-free host DNA in the airways, as reflected by increases in nucleosome and DNA levels in bronchoalveolar lavage fluid (BALF), accompanied by transient detection of pathogen DNA in MRSA-free BALF supernatants. In BALF, as compared to Wt -mice tlr9^-/- mice showed reduced TNFα and IL-6 levels at 6 hours and reduced bacterial clearance at 6 and 24 hours post infection. Furthermore, tlr9^-/- mice exhibited a greater influx of neutrophils in BALF and increased lung consolidation at 24 and 48 hours. This study demonstrates the release of host- and pathogen-derived TLR9 ligands (DNA) into the alveolar space after infection with MRSA via the airways and suggests that TLR9 has pro-inflammatory effects during MRSA pneumonia associated with enhanced bacterial clearance and limitation of lung consolidation.

General Strategies in Inflammasome Biology

The complementary actions of the innate and adaptive immune systems often provide effective host defense against microbial pathogens and harmful environmental agents. Germline-encoded pattern recognition receptors (PRRs) endow the innate immune system with the ability to detect and mount a rapid response against a given threat. Members of several intracellular PRR families, including the nucleotide-binding domain and leucine-rich repeat containing receptors (NLRs), the AIM2-like receptors (ALRs), and the tripartite motif-containing (TRIM) protein Pyrin/TRIM20, nucleate the formation of inflammasomes. These cytosolic scaffolds serve to recruit and oligomerize the cysteine protease caspase-1 in filaments that promote its proximity-induced autoactivation. This oligomerization occurs either directly or indirectly through intervention of the bipartite adaptor protein ASC, apoptosis-associated speck-like protein containing a caspase recruitment domain (CARD), which is needed for the domain interaction. Caspase-1 cleaves the precursors of the inflammatory cytokines interleukin (IL)-1β and IL-18 and triggers their release into the extracellular space, where they act on effector cells to promote both local and systemic immune responses. Additionally, inflammasome activation gives rise to a lytic mode of cell death, named pyroptosis, which is thought to contribute to initial host defense against infection by eliminating replication niches of intracellular pathogens and exposing them to the immune system. Inflammasome-induced host defense responses are the subject of intense investigation, and understanding their physiological roles during infection and the regulatory circuits that are involved is becoming increasingly detailed. Here, we discuss current understanding of the activation mechanisms and biological outcomes of inflammasome activation.

ASC provides a potential link between depression and inflammatory disorders: A clinical study of depressed Iranian medical students

Background and aims AIM2 is a component of inflammasomes which can activate caspase-1 via an adaptor protein (ASC) after pathogen-associated molecular pattern (PAMP) or danger-associated molecular pattern (DAMP) recognition. Activation of caspase-1 is a trigger for the induction of IL-1 and IL-18 which are important pro-inflammatory cytokines. Furthermore, IL-1β, which can regulate inflammatory responses, has also been associated with depression. Previous studies revealed that patients suffering from depression may also have altered immune responses, but the mechanisms underlying this correlation are unclear. Thus, the aim of this study was to determine the mRNA levels of AIM2 and ASC in the peripheral blood mononuclear cells (PBMCs) isolated from Iranian medical students suffering from depression. Materials and methods The participants used for the study included 38 Iranian medical students diagnosed with depression and 43 non-depressed students as a control group. The mRNA levels of AIM2 and ASC were evaluated by quantitative real-time polymerase chain reaction (PCR) using β-actin as a housekeeping gene for the normalization of expression. Results The results showed that mRNA levels of AIM2 were similar in both groups. However, ASC levels were significantly increased in PBMCs isolated from individuals with elevated depressive symptoms when compared to non-depressed participants. Conclusions Based on the current results, it appears that ASC transcript expression may be a surrogate marker for depression and may represent a link between depression and the altered immune responses observed in these categories of individuals with elevated depressive symptoms.

Bisphenol A (BPA) stimulates the interferon signaling and activates the inflammasome activity in myeloid cells

Environmental factors contribute to the development of autoimmune diseases, including systemic lupus erythematosus (SLE), which exhibits a strong female bias (female-to-male ratio 9:1). However, the molecular mechanisms remain largely unknown. Because a feedforward loop between the female sex hormone estrogen (E2) and type I interferon (IFN-α/β)-signaling induces the expression of certain p200-family proteins (such as murine p202 and human IFI16) that regulate innate immune responses and modify lupus susceptibility, we investigated whether treatment of myeloid cells with bisphenol A (BPA), an environmental estrogen, could regulate the p200-family proteins and activate innate immune responses. We found that treatment of murine bone marrow-derived cells (BMCs) and human peripheral blood mononuclear cells with BPA induced the expression of ERα and IFN-β, activated the IFN-signaling, and stimulated the expression of the p202 and IFI16 proteins. Further, the treatment increased levels of the NLRP3 inflammasome and stimulated its activity. Accordingly, BPA-treatment of BMCs from non lupus-prone C57BL/6 and the lupus-prone (NZB×NZW)F1 mice activated the type I IFN-signaling, induced the expression of p202, and activated an inflammasome activity. Our study demonstrates that BPA-induced signaling in the murine and human myeloid cells stimulates the type I IFN-signaling that results in an induction of the p202 and IFI16 innate immune sensors for the cytosolic DNA and activates an inflammasome activity. These observations provide novel molecular insights into the role of environmental BPA exposures in potentiating the development of certain autoimmune diseases such as SLE.

Inflammasomes and human autoimmunity: A comprehensive review

Inflammasomes are multi-protein complexes composed of a NOD-like receptor (NLR)/an AIM-like receptor (ALR), the adapter molecule apoptosis-associated speck-like protein that contains a CARD (ASC), and caspase-1. Active caspase-1 cleaves pro-IL-1β and pro-IL-18 to IL-1β and IL-18, resulting in inflammation. Genetic mutations in inflammasomes were first recognized to result in autoinflammatory diseases, which are characterized by the absence of both autoantibodies and autoreactive-T/B cells. However, there is increasing attention being placed on genetic polymorphisms that are involved in the components of inflammasomes, and these have implications for innate immunity and the natural history of autoimmune diseases. For example, while the NOD-like receptor family, pyrin domain containing 1 (NLRP1) haplotypes contributes to susceptibility to developing vitiligo; there are other single nucleotide polymorphisms (SNPs) that alters the susceptibility and severity of rheumatoid arthritis (RA) and juvenile idiopathic arthritis. Indeed, there are multiple factors that contribute to lowering the threshold of immunity and inflammasomes play a key role in this threshold. For example, IL-1β and IL-18 further perpetuate Th17 responses and endothelial cell damage, which potentiate a number of autoimmune diseases, including synovitis in RA, cardiovascular disease, and systemic lupus erythematosus (SLE). There is also increasing data on the role of innate immunity in experimental autoimmune encephalomyelitis (EAE), in lupus nephritis, and in a variety of autoimmune pathologies in which activation of the innate immune system is the driver for the adaptive system. Indeed, it is likely that the chronic pathology of autoimmunity is mediated in part by otherwise innocent bystander cells, augmented by inflammasomes.

Genomic regulation of senescence and innate immunity signaling in the retinal pigment epithelium

The tumor suppressor p53 is a major regulator of genes important for cell cycle arrest, senescence, apoptosis, and innate immunity, and has recently been implicated in retinal aging. In this study we sought to identify the genetic networks that regulate p53 function in the retina using quantitative trait locus (QTL) analysis. First we examined age-associated changes in the activation and expression levels of p53; known p53 target proteins and markers of innate immune system activation in primary retinal pigment epithelial (RPE) cells that were harvested from young and aged human donors. We observed increased expression of p53, activated caspase-1, CDKN1A, CDKN2A (p16INK4a), TLR4, and IFNα in aged primary RPE cell lines. We used the Hamilton Eye Institute (HEI) retinal dataset ( www.genenetwork.org ) to identify genomic loci that modulate expression of genes in the p53 pathway in recombinant inbred BXD mouse strains using a QTL systems biology-based approach. We identified a significant trans-QTL on chromosome 1 (region 172-177 Mb) that regulates the expression of Cdkn1a. Many of the genes in this QTL locus are involved in innate immune responses, including Fc receptors, interferon-inducible family genes, and formin 2. Importantly, we found an age-related increase in FCGR3A and FMN2 and a decrease in IFI16 levels in RPE cultures. There is a complex multigenic innate immunity locus that controls expression of genes in the p53 pathway in the RPE, which may play an important role in modulating age-related changes in the retina.

Combination of cyclophosphamide and double-stranded DNA demonstrates synergistic toxicity against established xenografts

BACKGROUND

Extracellular double-stranded DNA participates in various processes in an organism. Here we report the suppressive effects of fragmented human double-stranded DNA along or in combination with cyclophosphamide on solid and ascites grafts of mouse Krebs-2 tumor cells and DNA preparation on human breast adenocarcinoma cell line MCF-7.

METHODS

Apoptosis and necrosis were assayed by electrophoretic analysis (DNA nucleosomal fragmentation) and by measurements of LDH levels in ascitic fluid, respectively. DNA internalization into MCF-7 was analyzed by flow cytometry and fluorescence microscopy.

RESULTS

Direct cytotoxic activity of double-stranded DNA (along or in combination with cyclophosphamide) on a solid transplant was demonstrated. This resulted in delayed solid tumor proliferation and partial tumor lysis due to necrosis of the tumor and adjacent tissues. In the case of ascites form of tumor, extensive apoptosis and secondary necrosis were observed. Similarly, MCF-7 cells showed induction of massive apoptosis (up to 45%) as a result of treatments with double-stranded DNA preparation.

CONCLUSIONS

Double-stranded DNA (along or in combination with cyclophosphamide) induces massive apoptosis of Krebs-2 ascite cells and MCF-7 cell line (DNA only). In treated mice it reduces the integrity of gut wall cells and contributes to the development of systemic inflammatory reaction.

Results of multicenter double-blind placebo-controlled phase II clinical trial of Panagen preparation to evaluate its leukostimulatory activity and formation of the adaptive immune response in patients with stage II-IV breast cancer

Background

We performed a multicenter, double-blind, placebo-controlled, phase II clinical trial of human dsDNA-based preparation Panagen in a tablet form. In total, 80 female patients with stage II-IV breast cancer were recruited.

Methods

Patients received three consecutive FAC (5-fluorouracil, doxorubicin and cyclophosphamide) or AC (doxorubicin and cyclophosphamide) adjuvant chemotherapies (3 weeks per course) and 6 tablets of 5 mg Panagen or placebo daily (one tablet every 2–3 hours, 30 mg/day) for 18 days during each chemotherapy course. Statistical analysis was performed using Statistica 6.0 software, and non-parametric analyses, namely Wilcoxon-Mann–Whitney and paired Wilcoxon tests. To describe the results, the following parameters were used: number of observations (n), median, interquartile range, and minimum-maximum range.

Results

Panagen displayed pronounced leukostimulatory and leukoprotective effects when combined with chemotherapy. In an ancillary protocol, anticancer effects of a tablet form of Panagen were analyzed. We show that Panagen helps maintain the pre-therapeutic activity level of innate antitumor immunity and induces formation of a peripheral pool of cytotoxic CD8+ perforin + T-cells. Our 3-year follow-up analysis demonstrates that 24% of patients who received Panagen relapsed or died after the therapy, as compared to 45% in the placebo cohort.

Conclusions

The data collected in this trial set Panagen as a multi-faceted “all-in-one” medicine that is capable of simultaneously sustaining hematopoiesis, sparing the innate immune cells from adverse effects of three consecutive rounds of chemotherapy and boosting individual adaptive immunity. Its unique feature is that it is delivered via gastrointestinal tract and acts through the lymphoid system of intestinal mucosa. Taken together, maintenance of the initial levels of innate immunity, development of adaptive cytotoxic immune response and significantly reduced incidence of relapses 3 years after the therapy argue for the anticancer activity of Panagen.

Trial registration

ClinicalTrials.gov NCT02115984 from 04/07/2014.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1142-z) contains supplementary material, which is available to authorized users.

The roles of interferon-inducible p200 family members IFI16 and p204 in innate immune responses, cell differentiation and proliferation

p204 is a member of the interferon-inducible p200 family proteins in mice. The p200 family has been reported to be multifunctional regulators of cell proliferation, differentiation, apoptosis and senescence. Interferon-inducible protein 16 (IFI16) is regarded as the human ortholog of p204 in several studies. This is possibly due to the similarity of their structures. However the consistency of their functions is still elusive. Currently, an emerging focus has been placed upon the role of the p200 proteins as sensors for microbial DNA in innate immune responses and provides new insights into infections as well as autoimmune diseases. This review specially focuses on IFI16 and p204, the member of p200 family in human and murine respectively, and their pathophysiological roles in innate immune responses, cell differentiation and proliferation.

Inflammasomes

Inflammasomes are large cytosolic multiprotein complexes that assemble in response to detection of infection- or stress-associated stimuli and lead to the activation of caspase-1-mediated inflammatory responses, including cleavage and unconventional secretion of the leaderless proinflammatory cytokines IL-1β and IL-18, and initiation of an inflammatory form of cell death referred to as pyroptosis. Inflammasome activation can be induced by a wide variety of microbial pathogens and generally mediates host defense through activation of rapid inflammatory responses and restriction of pathogen replication. In addition to its role in defense against pathogens, recent studies have suggested that the inflammasome is also a critical regulator of the commensal microbiota in the intestine. Finally, inflammasomes have been widely implicated in the development and progression of various chronic diseases, such as gout, atherosclerosis, and metabolic syndrome. In this perspective, we discuss the role of inflammasomes in infectious and noninfectious inflammation and highlight areas of interest for future studies of inflammasomes in host defense and chronic disease.

Epigenetic regulation of ASC/TMS1 expression: potential role in apoptosis and inflammasome function

Cloning studies have revealed that the apoptosis-associated speck-like protein possessing a caspase-recruiting domain (ASC) and the target of methylation-induced silencing-1 (TMS) are identical proteins. ASC/TMS1 is a bipartite adaptor protein containing the N-terminal pyrin domain and the C-terminal caspase-recruitment domain. There is abundant literature on ASC/TMS1, mostly under the name TMS1, in the epigenetic regulation of apoptosis and carcinogenesis, whereas the abbreviation ASC has been adopted from studies on the assembly of inflammasomes and stimulation of inflammation. There is substantial literature emphasizing that there are common aspects in the regulation of apoptosis and inflammation, which may be related to the function of ASC/TMS1. The region of the transcription start site of ASC/TMS1 gene contains a 600-bp-long CpG island that is highly methylated and the transcription of ASC/TMS1 is repressed in several cancers. However, it is not known whether the ASC/TMS1-dependent epigenetic regulation controls the inflammasome functions and moreover whether this regulation has any role in the inflammation-mediated carcinogenesis or in the pathogenesis of age-related degenerative diseases. We will examine the mechanisms involved in the epigenetic regulation of ASC/TMS1 as well as their significance in the coordination of apoptosis and inflammasome functions. We will also review the role of aberrant methylation of ASC/TMS1 promoter in the function of inflammasomes, a major host defense system, in cellular housekeeping and carcinogenesis.

Structural mechanism of DNA recognition by the p202 HINa domain: insights into the inhibition of Aim2-mediated inflammatory signalling

The HIN-200 family of proteins play significant roles in inflammation-related processes. Among them, AIM2 (absent in melanoma 2) and IFI16 (γ-interferon-inducible protein 16) recognize double-stranded DNA to initiate inflammatory responses. In contrast, p202, a mouse interferon-inducible protein containing two HIN domains (HINa and HINb), has been reported to inhibit Aim2-mediated inflammatory signalling in mouse. To understand the inhibitory mechanism, the crystal structure of the p202 HINa domain in complex with a 20 bp DNA was determined, in which p202 HINa nonspecifically recognizes both strands of DNA through electrostatic attraction. The p202 HINa domain binds DNA more tightly than does AIM2 HIN, and the DNA-binding mode of p202 HINa is different from that of the AIM2 HIN and IFI16 HINb domains. These results, together with the reported data on p202 HINb, lead to an interaction model for full-length p202 and dsDNA which provides a conceivable mechanism for the negative regulation of Aim2 inflammasome activation by p202.

Role of environment and sex differences in the development of autoimmune diseases: a roundtable meeting report

Autoimmune diseases (ADs) impose substantial health and financial burdens in the United States and in many parts of the world. Women are disproportionately affected by many of these disorders, which often contribute to lifelong disabilities. While the number of patients with some ADs appears to be rising, the complexities of conducting epidemiological studies prevent a thorough understanding of the prevalence and incidence of these various conditions. Research on environmental influences of these illnesses is limited, although they are generally hypothesized to result from the interaction of environmental agents in genetically susceptible individuals. Further, there is little known regarding the role of sex and gender in the environmentally influenced mechanisms leading to the development of AD. To address these issues, particularly the roles of environment and sex and gender in ADs and the factors that contribute to the rise in ADs, the Society for Women's Health Research convened an interdisciplinary roundtable of experts from academia, medicine, and government agencies to share their expertise, address knowledge gaps in research, and propose future research recommendations.

Identification of a negative feedback loop between cyclic di-GMP-induced levels of IFI16 and p202 cytosolic DNA sensors and STING

A host type I IFN response is induced by cytosolic sensing of the bacterial second messenger cyclic-di-GMP (c-di-GMP) by STING (stimulator of IFN genes). Because the STING, an adaptor protein, links the cytosolic detection of DNA by the cytosolic DNA sensors such as the IFN-inducible human IFI16 and murine p202 proteins to the TBK1/IRF3 axis, we investigated whether c-di-GMP-induced signaling could regulate expression of IFI16 and p202 proteins. Here, we report that activation of c-di-GMP-induced signaling in human and murine cells increased steady-state levels of IFI16 and p202 proteins. The increase was c-di-GMP concentration- and time-dependent. Unexpectedly, treatment of cells with type I IFN decreased levels of the adaptor protein STING. Therefore, we investigated whether the IFI16 or p202 protein could regulate the expression of STING and activation of the TBK1/IRF3 axis. We found that constitutive knockdown of IFI16 or p202 expression in cells increased steady-state levels of STING. Additionally, the knockdown of IFI16 resulted in activation of the TBK1/IRF3 axis. Accordingly, increased levels of the IFI16 or p202 protein in cells decreased STING levels. Together, our observations identify a novel negative feedback loop between c-di-GMP-induced levels of IFI16 and p202 cytosolic DNA sensors and the adaptor protein STING.

Cutting edge: DNA sensing via the STING adaptor in myeloid dendritic cells induces potent tolerogenic responses

Cytosolic DNA sensing via the stimulator of IFN genes (STING) adaptor incites autoimmunity by inducing type I IFN (IFN-αβ). In this study, we show that DNA is also sensed via STING to suppress immunity by inducing IDO. STING gene ablation abolished IFN-αβ and IDO induction by dendritic cells (DCs) after DNA nanoparticle (DNP) treatment. Marginal zone macrophages, some DCs, and myeloid cells ingested DNPs, but CD11b(+) DCs were the only cells to express IFN-β, whereas CD11b(+) non-DCs were major IL-1β producers. STING ablation also abolished DNP-induced regulatory responses by DCs and regulatory T cells, and hallmark regulatory responses to apoptotic cells were also abrogated. Moreover, systemic cyclic diguanylate monophosphate treatment to activate STING induced selective IFN-β expression by CD11b(+) DCs and suppressed Th1 responses to immunization. Thus, previously unrecognized functional diversity among physiologic innate immune cells regarding DNA sensing via STING is pivotal in driving immune responses to DNA.

AIM2, an IFN-inducible cytosolic DNA sensor, in the development of benign prostate hyperplasia and prostate cancer

Close links have been noted between chronic inflammation of the prostate and the development of human prostatic diseases such as benign prostate hyperplasia (BPH) and prostate cancer. However, the molecular mechanisms that contribute to prostatic inflammation remain largely unexplored. Recent studies have indicated that the IFN-inducible AIM2 protein is a cytosolic DNA sensor in macrophages and keratinocytes. Upon sensing DNA, AIM2 recruits the adaptor ASC and pro-CASP1 to assemble the AIM2 inflammasome. Activation of the AIM2 inflammasome cleaves pro-interleukin (IL)-1β and pro-IL-18 and promotes the secretion of IL-1β and IL-18 proinflammatory cytokines. Given that human prostatic infections are associated with chronic inflammation, the development of BPH is associated with an accumulation of senescent cells with a proinflammatory phenotype, and the development of prostate cancer is associated with the loss of IFN signaling, the role of AIM2 in mediating the formation of prostatic diseases was investigated. It was determined that IFNs (α, β, or γ) induced AIM2 expression in human prostate epithelial cells and cytosolic DNA activated the AIM2 inflammasome. Steady-state levels of the AIM2 mRNA were higher in BPH than in normal prostate tissue. However, the levels of AIM2 mRNA were significantly lower in clinical tumor specimens. Accordingly, constitutive levels of AIM2 mRNA and protein were lower in a subset of prostate cancer cells as compared with BPH cells. Further, the cytosolic DNA activated the AIM2 inflammasome in the androgen receptor-negative PC3 prostate cancer cell line, suggesting that AIM2-mediated events are independent of androgen receptor status.

IMPLICATIONS

The AIM2 inflammasome has a fundamental role in the generation of human prostatic diseases.

Role of inflammasomes and their regulators in prostate cancer initiation, progression and metastasis

Prostate cancer is one of the main cancers that affect men, especially older men. Though there has been considerable progress in understanding the progression of prostate cancer, the drivers of its development need to be studied more comprehensively. The emergence of resistant forms has also increased the clinical challenges involved in the treatment of prostate cancer. Recent evidence has suggested that inflammation might play an important role at various stages of cancer development. This review focuses on inflammasome research that is relevant to prostate cancer and indicates future avenues of study into its effective prevention and treatment through inflammasome regulation. With regard to prostate cancer, such research is still in its early stages. Further study is certainly necessary to gain a broader understanding of prostate cancer development and to create successful therapy solutions.

HPV16 activates the AIM2 inflammasome in keratinocytes

Human papillomaviruses (HPV) are double-stranded DNA viruses, which selectively infect keratinocytes in stratified epithelia. After an initial infection, many patients clear HPV. In some patients, however, HPV persist, and dysfunctional innate immune responses to HPV infection could be involved in the ineffective clearing of these viruses. In this study, the mechanisms of HPV-induced immune responses in keratinocytes were investigated. Binding of viral DNA leads to AIM2 inflammasome activation and IL-1β release, while IFI16 activation results in IFN-β release. Using immunohistochemistry, AIM2 and IFI16-two recently identified sensors for cytosolic DNA-were also detected in HPV positive skin lesions. CISH stainings further confirmed the presence of cytosolic HPV16 DNA in biopsy samples. Moreover, active IL-1β and cleaved caspase-1 were detected in HPV infected skin, suggesting inflammasome activation by viral DNA. In subsequent functional studies, HPV16 DNA triggered IL-1β and IL-18 release via the AIM2 inflammasome in normal human keratinocytes. Although HPV DNA did not induce IFN-β in keratinocytes, IFN-β secretion was observed when AIM2 was blocked. Meanwhile, blocking of IFI16 increased HPV16 DNA-induced IL-1β, but not IL-18, secretion. These findings suggest crosstalk between IFI16 and AIM2 in the immune response to HPV DNA. In sum, novel aspects concerning HPV-induced innate immune responses were identified. Eventually, understanding the mechanisms of HPV-induced inflammasome activation could lead to the development of novel strategies for the prevention and treatment of HPV infections.

Oxidized DNA induces an adaptive response in human fibroblasts

Cell-free DNA (cfDNA) released from dying cells contains a substantial proportion of oxidized nucleotides, thus, forming cfDNA(OX). The levels of cfDNA(OX) are increased in the serum of patients with chronic diseases. Oxidation of DNA turns it into a stress signal. The samples of genomic DNA (gDNA) oxidized by Н2О2in vitro (gDNA(OX)) induce effects similar to that of DNA released from damaged cells. Here we describe the effects of gDNA(OX) on human fibroblasts cultivated in the stressful conditions of serum withdrawal. In these cells, gDNA(OX) evokes an adaptive response that leads to an increase in the rates of survival in serum starving cell populations as well as in populations irradiated at the dose of 1.2Gy. These effects are not seen in control populations of fibroblasts treated with non-modified gDNA. In particular, the exposure to gDNA(OX) leads to a decrease in the expression of the proliferation marker Ki-67 and an increase in levels of РСNА, a decrease in the proportion of subG1- and G2/M cells, a decrease in proportion of cells with double strand breaks (DSBs). Both gDNA(OX) and gDNA suppress the expression of DNA sensors TLR9 and AIM2 and up-regulate nuclear factor-erythroid 2 p45-related factor 2 (NRF2), while only gDNA(OX) inhibits NF-κB signaling. gDNA(OX) is a model for oxidized cfDNA(OX) that is released from the dying tumor cells and being carried to the distant organs. The systemic effects of oxidized DNA have to be taken into account when treating tumors. In particular, the damaged DNA released from irradiated cells may be responsible for an abscopal effects and a bystander mediated adaptive response seen in some cancer patients. These results indicate the necessity for the further study of the effects of oxidized DNA in both in vitro and in vivo systems.

Interferon-inducible Ifi200-family genes as modifiers of lupus susceptibility

Both genetic and environmental factors contribute to the development and progression of systemic lupus erythematosus (SLE), a complex autoimmune disease. The disease exhibits a strong gender bias and develops predominantly in females. Additionally, most SLE patients exhibit increased serum levels of interferon-α (IFN-α) and the "IFN signature". Studies using the mouse models of lupus have identified several lupus susceptibility loci, including the New Zealand Black (NZB)-derived autoimmunity 2 (Nba2) interval on the chromosome 1. The interval, which is syntenic to the human chromosome 1q region, harbors the FcγR family, SLAM/CD2-family, and the IFN-inducible Ifi200-family genes (encoding for the p200-family proteins). Studies involving the B6.Nba2 congenic mice revealed that the development of antinuclear autoantibodies (ANAs) depends on the age, gender, and activation of type I IFN-signaling. Interestingly, recent studies involving the generation of Nba2 subcongenic mouse lines and generation of mice deficient for the Fcgr2b or Aim2 gene within the interval have provided evidence that epistatic interactions among the Nba2 genes contribute to increased lupus susceptibility. Given that the expression of some of the p200-family proteins is differentially regulated by sex hormones and these proteins differentially regulate cytosolic DNA-induced production of type I IFN and proinflammatory cytokines (IL-1β and IL-18), the major known contributors of SLE-associated inflammation, we discuss the recent advancements in our understanding of the role of p200-family proteins in lupus susceptibility modification. An improved understanding of the role of p200-family proteins in the development of autoimmunity is likely to identify new approaches to treat SLE patients.

HIV-1 control in battlegrounds: important host genetic variations for HIV-1 mother-to-child transmission and progression to clinical pediatric AIDS

HIV-1 mother-to-child transmission (MTCT) is the passing of maternal HIV-1 to the offspring during pregnancy, labor and delivery, and/or breastfeeding. HIV-1 MTCT and the evolution to pediatric AIDS are multifactorial, dynamic and variable phenotypic conditions. Both genetic and nongenetic variables can influence susceptibility to HIV-1 MTCT or the rate of progression to clinical pediatric AIDS. In this review, we summarize the current state of knowledge about the roles of genetic variations seen in host immune response genes, and those that have been independently associated, mostly through population genetics of candidate genes, with interindividual susceptibility to HIV-1 MTCT, and progression to pediatric AIDS. We examine common and rare host genetic variations at coding and noncoding polymorphisms, whether functional or not, in agonists and antagonists of the immune response, which have been implicated in HIV-1 control in battlegrounds of cell entry, replication and evolution to AIDS. Further, we point to over 380 single-nucleotide polymorphisms, mostly within the HLA super region, recently identified in unbiased genome-wide association studies of HIV replication and evolution in adults, still unexplored in the context of HIV-1 MTCT, and which are likely to also influence susceptibility to pediatric HIV-1/AIDS.