Restoration of absent in melanoma 2 (AIM2) induces G2/M cell cycle arrest and promotes invasion of colorectal cancer cells

New insights into nucleic acid sensor AIM2: The potential benefit in targeted therapy for cancer

The AIM2 inflammasome represents a multifaceted oligomeric protein complex within the innate immune system, with the capacity to perceive double-stranded DNA (dsDNA) and engage in diverse physiological reactions and disease contexts, including cancer. While originally conceived as a discerning DNA sensor, AIM2 has demonstrated its capability to discern various nucleic acid variations, encompassing RNA and DNA-RNA hybrids. Through its interaction with nucleic acids, AIM2 orchestrates the assembly of a complex involving multiple proteins, aptly named the AIM2 inflammasome, which facilitates the enzymatic cleavage of proinflammatory cytokines, namely pro-IL-1β and pro-IL-18. This process, in turn, underpins its pivotal biological role. In this review, we provide a systematic summary and discussion of the latest advancements in AIM2 sensing various types of nucleic acids. Additionally, we discuss the modulation of AIM2 activation, which can cause cell death, including pyroptosis, apoptosis, and autophagic cell death. Finally, we fully illustrate the evidence for the dual role of AIM2 in different cancer types, including both anti-tumorigenic and pro-tumorigenic functions. Considering the above information, we uncover the therapeutic promise of modulating the AIM2 inflammasome in cancer treatment.

The implication of pyroptosis in cancer immunology: Current advances and prospects

Pyroptosis is a regulated cell death pathway involved in numerous human diseases, especially malignant tumors. Recent studies have identified multiple pyroptosis-associated signaling molecules, like caspases, gasdermin family and inflammasomes. In addition, increasing in vitro and in vivo studies have shown the significant linkage between pyroptosis and immune regulation of cancers. Pyroptosis-associated biomarkers regulate the infiltration of tumor immune cells, such as CD4+ and CD8+ T cells, thus strengthening the sensitivity to therapeutic strategies. In this review, we explained the relationship between pyroptosis and cancer immunology and focused on the significance of pyroptosis in immune regulation. We also proposed the future application of pyroptosis-associated biomarkers in basic research and clinical practices to address malignant behaviors. Exploration of the underlying mechanisms and biological functions of pyroptosis is critical for immune response and cancer immunotherapy.

Macrophage IL-1β contributes to tumorigenesis through paracrine AIM2 inflammasome activation in the tumor microenvironment

Intracellular recognition of self and non-self -nucleic acids can result in the initiation of effective pro-inflammatory and anti-tumorigenic responses. We hypothesized that macrophages can be activated by tumor-derived nucleic acids to induce inflammasome activation in the tumor microenvironment. We show that tumor conditioned media (CM) can induce IL-1β production, indicative of inflammasome activation in primed macrophages. This could be partially dependent on caspase 1/11, AIM2 and NLRP3. IL-1β enhances tumor cell proliferation, migration and invasion while coculture of tumor cells with macrophages enhances the proliferation of tumor cells, which is AIM2 and caspase 1/11 dependent. Furthermore, we have identified that DNA-RNA hybrids could be the nucleic acid form which activates AIM2 inflammasome at a higher sensitivity as compared to dsDNA. Taken together, the tumor-secretome stimulates an innate immune pathway in macrophages which promotes paracrine cancer growth and may be a key tumorigenic pathway in cancer. Broader understanding on the mechanisms of nucleic acid recognition and interaction with innate immune signaling pathway will help us to better appreciate its potential application in diagnostic and therapeutic benefit in cancer.

Pyroptosis and its role in cancer

Programmed cell death (PCD) is mediated by specific genes that encode signals. It can balance cell survival and death. Pyroptosis is a type of inflammatory, caspase-dependent PCD mediated by gasdermin proteins, which function in pore formation, cell expansion, and plasma membrane rupture, followed by the release of intracellular contents. Pyroptosis is mediated by caspase-1/3/4/5/11 and is primarily divided into the classical pathway, which is dependent on caspase-1, and the non-classical pathway, which is dependent on caspase-4/5/11. Inflammasomes play a vital role in these processes. The various components of the pyroptosis pathway are related to the occurrence, invasion, and metastasis of tumors. Research on pyroptosis has revealed new options for tumor treatment. This article summarizes the recent research progress on the molecular mechanism of pyroptosis, the relationship between the various components of the pyroptosis pathway and cancer, and the applications and prospects of pyroptosis in anticancer therapy.

Pan-cancer analysis of AIM2 inflammasomes with potential implications for immunotherapy in human cancer: A bulk omics research and single cell sequencing validation

Background

The absent in melanoma 2 (AIM2) inflammasome is a multi-protein platform that recognizes aberrant cytoplasmic double-stranded DNA(dsDNA) and induces cytokine maturation, release, and pyroptosis. Some studies found that the AIM2 inflammasome was a double-edged sword in many cancers. However, there have been fewer studies on AIM2 inflammasomes in pan-cancer.

Methods

Gene expression was analyzed using The Cancer Genome Atlas (TCGA) database and The Genotype-Tissue Expression (GTEx) database. Immunohistochemistry (IHC) was used to validate the expression of the AIM2. We used the survival curve to explore the prognostic significance of the AIM2 inflammasomes in pan-cancer. Mutations and methylation of AIM2 inflammasome-related genes (AIM2i-RGs) were also comprehensively analyzed. Single sample gene set enrichment analysis was used to calculate the AIM2 inflammasomes score and explore the correlation of the AIM2 inflammasomes score with immune-related genes and immune infiltrations. The function of AIM2 inflammasomes in pan-cancer was analyzed at the single-cell level. Single-cell transcriptome sequencing (scRNA-seq) data was used to assess the activation state of the AIM2 inflammasomes in the tumor microenvironment.

Results

We found that AIM2i-RGs were aberrantly expressed in tumors and were strongly associated with prognosis. In pan-cancer, the expression of AIM2i-RGs was positively associated with copy number variation and negatively associated with methylation. In AIM2i-RGs, missense mutations were the predominant type of single nucleotide polymorphism. Moreover, we found that the drugs dimethyloxallyl glycine (DMOG) and Z-LNle-CHO may be sensitive to the AIM2 inflammasomes. The AIM2 inflammasomes score was significantly and positively correlated with the tumor immunity score and the stroma score. In most tumors, the AIM2 inflammasomes score was significantly and positively correlated with CD8+ T cell abundance in the tumor microenvironment. Additionally, the AIM2 inflammasomes score was significantly correlated with immune checkpoint genes in pan-cancer as well as immune checkpoint therapy-related markers including tumor mutational burden (TMB), microsatellite instability(MSI), and tumor immune dysfunction and exclusion(TIDE). scRNA-seq analysis suggested that AIM2 inflammasomes differ significantly among different cells in the tumor microenvironment. IHC confirmed low expression of AIM2 in colorectal cancer.

Discussion

AIM2 inflammasomes may be a new target for future tumor therapy It is likely involved in tumor development, and its high expression may serve as a predictor of tumor immunotherapy efficacy.

No Time to Die: How Kidney Cancer Evades Cell Death

The understanding of the pathogenesis of renal cell carcinoma led to the development of targeted therapies, which dramatically changed the overall survival rate. Nonetheless, despite innovative lines of therapy accessible to patients, the prognosis remains severe in most cases. Kidney cancer rarely shows mutations in the genes coding for proteins involved in programmed cell death, including p53. In this paper, we show that the molecular machinery responsible for different forms of cell death, such as apoptosis, ferroptosis, pyroptosis, and necroptosis, which are somehow impaired in kidney cancer to allow cancer cell growth and development, was reactivated by targeted pharmacological intervention. The aim of the present review was to summarize the modality of programmed cell death in the pathogenesis of renal cell carcinoma, showing in vitro and in vivo evidence of their potential role in controlling kidney cancer growth, and highlighting their possible therapeutic value.

Pyroptosis Regulators and Tumor Microenvironment Infiltration Characterization in Clear Cell Renal Cell Carcinoma

Background

It is well known that chronic inflammation can promote the occurrence and progression of cancer. As a type of proinflammatory death, pyroptosis can recast a suitable microenvironment to promote tumor growth. However, the potential role of pyroptosis in clear cell renal cell carcinoma (ccRCC) remains unclear.

Methods

The transcriptome expression profile and mutation profile data of ccRCC with clinical characteristics included in this study were obtained from The Cancer Genome Atlas (TCGA) and Gene Expression Omnibus (GEO) databases. Consensus clustering was used for clustering. Gene set enrichment analysis (GSEA) analysis were applied to evaluate the biological mechanisms. Single sample gene set enrichment analysis (ssGSEA) was applied for evaluating the proportion of various immune infiltrating cells. The ESTIMATE algorithm was involved to compute the immune microenvironment scores.

Results

Among the 17 pyroptosis regulators, a total of 15 pyroptosis regulators were differential expressed between tumor and normal tissues, in which 12 of them emerged strong correlations with prognoses. According to the pyroptosis components, the ccRCC patients were divided into four pyroptosis subtypes with different clinical, molecular, and pathway characteristics. Compared with other clusters, cluster B showed the pyroptosis heat phenotype, while cluster D represented the pyroptosis cold phenotype with poor overall survival. In addition, we performed principal component analysis (PCA) on the differential genes between clusters to construct the pyroptosis index. Furthermore, the pyroptosis index was significantly correlated with survival in different tumor mutation statuses and different grades and stages. Besides, the expression of pyroptosis-related regulators was related to the infiltration of immune cells and the expression of immune checkpoints, among which AIM2 was considered as the most significant immune-related pyroptosis regulator. Ultimately, we found that AIM2 was related to the immune activation pathway and was significantly overexpressed in tumor tissues.

Conclusion

This study revealed that pyroptosis regulators and pyroptosis index played an important role in the development and prognoses of ccRCC. Moreover, AIM2 can be used as a predictor of the response of immunotherapy. Assessing the pyroptosis patterns may help evaluate the tumor status and guide immunotherapy strategies.

AIM2 inhibits the proliferation, invasion and migration, and promotes the apoptosis of osteosarcoma cells by inactivating the PI3K/AKT/mTOR signaling pathway

Osteosarcoma is a primary bone tumor that mainly occurs in children and adolescents. Absent in melanoma 2 (AIM2) has been demonstrated to be involved in regulating the occurrence and development of cancer, exerting oncogenic and pro-cancer effects; however, its role in osteosarcoma is poorly understood. The present study aimed to explore the function and molecular mechanism of AIM2 in the progression of osteosarcoma. In the present study, AIM2 expression was predicted using the Cancer Cell Line Encyclopedia database and examined in several osteosarcoma cell lines using reverse transcription-quantitative PCR and western blotting. Following AIM2 overexpression, cell proliferation and apoptosis were examined using Cell Counting Kit-8, colony formation and TUNEL staining assays. The expression levels of proteins related to apoptosis, epithelial-mesenchymal transition (EMT) and the PI3K/AKT/mTOR signaling pathway were determined by western blotting. Additionally, cell invasion and migration were assessed using Transwell and wound healing assays. After addition of the PI3K/AKT/mTOR signaling pathway inhibitor LY294002 or activator 740Y-P, cell function analysis was performed. The results demonstrated that AIM2 was expressed at low levels in osteosarcoma cell lines. AIM2 overexpression inhibited proliferation, invasion, migration and EMT, and promoted apoptosis in osteosarcoma cells. Furthermore, the levels of phosphorylated (p)-PI3K, p-AKT and p-mTOR were markedly downregulated following AIM2 overexpression. Furthermore, LY294002 treatment had the same effects as AIM2 upregulation on osteosarcoma cell proliferation, apoptosis, invasion, migration and EMT. By contrast, 740Y-P reversed the effects of AIM2 overexpression on the behavior of osteosarcoma cells. Overall, the findings of the present study demonstrated that AIM2 may inhibit the progression of osteosarcoma by inactivating the PI3K/AKT/mTOR signaling pathway, and suggested that AIM2 may be a promising marker for the treatment of osteosarcoma.

Comprehensive analysis of pyroptosis regulators and tumor immune microenvironment in clear cell renal cell carcinoma

Background

Increasing evidence has indicated that pyroptosis could regulate the tumor immune microenvironment (TIME) to affect the tumor development. As a highly immunogenic tumor, clear cell renal cell carcinoma (ccRCC) can benefit from immunotherapy, but related research on pyroptosis in the TIME of ccRCC is still deficient.

Methods

Available data derived from TCGA and GEO databases were analyzed to identify the different expression profiles of pyroptosis in ccRCC and normal tissues, and the correlation of pyroptosis regulators with TIME was evaluated in ccRCC.

Results

According to consensus clustering analysis, two differential expression levels of subtypes were identified to affect patient prognosis, and were related to histological tumor stage and grade. Immune cells were calculated by the CIBERSORT algorithm. Higher infiltrated levels of B cells naive, T cells CD4 memory resting, NK cells resting, monocytes, macrophages were observed in Cluster 1, while higher infiltrated levels of CD8⁺ T cells, T follicular helper cells, and Tregs were observed in Cluster 2. Gene set enrichment analysis indicated that Cluster 2 was enriched in multiple immune-related pathways, including the JAK-STAT signaling pathway. Moreover, overexpression of eight immune checkpoints was related to ccRCC development, especially in Cluster 2. As four potentially key pyroptosis regulators, AIM2, CASP5, NOD2, and GZMB were confirmed to be upregulated in ccRCC by RT-qPCR analysis and further verified by the HPA database. Further pan-cancer analysis suggested that these four pyroptosis regulators were differentially expressed and related to the TIME in multiple cancers.

Conclusion

The present study provided a comprehensive view of pyroptosis regulators in the TIME of ccRCC, which may provide potential value for immunotherapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-021-02384-y.

AIM2 Suppresses Inflammation and Epithelial Cell Proliferation during Glomerulonephritis

Absent in melanoma-2 (AIM2) is an inflammasome-forming innate immune sensor for dsDNA but also exhibits inflammasome-independent functions such as restricting cellular proliferation. AIM2 is expressed in the kidney, but its localization and function are not fully characterized. In normal human glomeruli, AIM2 localized to podocytes. In patients with glomerulonephritis, AIM2 expression increased in CD44⁺-activated parietal epithelial cells within glomerular crescents. To explore AIM2 effects in glomerular disease, studies in Aim2 ^-/- mice were performed. Aim2^-/- glomeruli showed reduced expression of Wilm tumor gene-1 (WT1), WT1-driven podocyte genes, and increased proliferation in outgrowth assays. In a nephrotoxic serum (NTS)-induced glomerulonephritis model, Aim2^-/- (B6) mice exhibited more severe glomerular crescent formation, tubular injury, inflammation, and proteinuria compared with wild-type controls. Inflammasome activation markers were absent in both Aim2 ^-/- and wild-type kidneys, despite an increased inflammatory transcriptomic signature in Aim2 ^-/- mice. Aim2 ^-/- mice also demonstrated dysregulated cellular proliferation and an increase in CD44⁺ parietal epithelial cells during glomerulonephritis. The augmented inflammation and epithelial cell proliferation in Aim2 ^-/- (B6) mice was not due to genetic background, as Aim2 ^-/- (B6.129) mice demonstrated a similar phenotype during NTS glomerulonephritis. The AIM2-like receptor (ALR) locus was necessary for the inflammatory glomerulonephritis phenotype observed in Aim2 ^-/- mice, as NTS-treated ALR ^-/- mice displayed equal levels of injury as wild-type controls. Podocyte outgrowth from ALR ^-/- glomeruli was still increased, however, confirming that the ALR locus is dispensable for AIM2 effects on epithelial cell proliferation. These results identify a noncanonical role for AIM2 in suppressing inflammation and epithelial cell proliferation during glomerulonephritis.

Nuclear AIM2-Like Receptors Drive Genotoxic Tissue Injury by Inhibiting DNA Repair

Radiation is an essential preparative procedure for bone marrow (BM) transplantation and cancer treatment. The therapeutic efficacy of radiation and associated toxicity varies from patient to patient, making it difficult to prescribe an optimal patient-specific irradiation dose. The molecular determinants of radiation response remain unclear. AIM2-like receptors (ALRs) are key players in innate immunity and determine the course of infections, inflammatory diseases, senescence, and cancer. Here it is reported that mice lacking ALRs are resistant to irradiation-induced BM injury. It is shown that nuclear ALRs are inhibitors of DNA repair, thereby accelerate genome destabilization, micronuclei generation, and cell death, and that this novel function is uncoupled from their role in innate immunity. Mechanistically, ALRs bind to and interfere with chromatin decompaction vital for DNA repair. The finding uncovers ALRs as targets for new interventions against genotoxic tissue injury and as possible biomarkers for predicting the outcome of radio/chemotherapy.

Pyroptosis Patterns Characterized by Distinct Tumor Microenvironment Infiltration Landscapes in Gastric Cancer

BACKGROUND

The potential role of pyroptosis in tumor microenvironment (TME) reprogramming and immunotherapy has received increasing attention. As most studies have concentrated on a single TME cell type or a single pyroptosis regulator (PR), the overall TME cell-infiltrating characteristics mediated by the integrated roles of multiple PRs have not been comprehensively recognized.

METHODS

This study curated 33 PRs and conducted consensus clustering to identify distinct pyroptosis patterns in gastric cancer (GC) patients. A single-sample gene set enrichment analysis algorithm was used to quantify the infiltration density of TME immune cells and the enrichment scores of well-defined biological signatures. The pyroptosis patterns of individuals were quantified using a principal component analysis algorithm called the pyroptosis score (PS).

RESULTS

Three distinct pyroptosis patterns with significant survival differences were identified from 1422 GC samples; these patterns were closely associated with three TME cell-infiltrating landscapes-namely, the immune-inflamed, immune-excluded, and immune-desert phenotypes. The PS model generated on the basis of the pyroptosis pattern-related signature genes could accurately predict the TME status, existing molecular subtypes, genetic variation, therapeutic response, and clinical outcome; among which, a relatively high PS was highly consistent with immune activation, molecular subtypes with survival advantages, high tumor mutation burden, high microsatellite instability, and other favorable characteristics. In particular, from the Cancer Genome Atlas database, the PS model exhibited significant prognostic relevance in a pan-cancer analysis, and patients with a relatively high PS exhibited durable therapeutic advantages and better prognostic benefits in anti-PD1/L1 therapy.

CONCLUSIONS

This study demonstrates that pyroptosis is prominently correlated with TME diversity and complexity, and quantification of the pyroptosis patterns of individuals will enhance our cognition of TME infiltration landscapes and help in formulating more effective immunotherapeutic strategies.

The complex role of AIM2 in autoimmune diseases and cancers

Absent in melanoma 2 (AIM2) is a novel member of interferon (IFN)-inducible PYHIN proteins. In innate immune cells, AIM2 servers as a cytoplasmic double-stranded DNA sensor, playing a crucial role in the initiation of the innate immune response as a component of the inflammasome. AIM2 expression is increased in patients with systemic lupus erythematosus (SLE), psoriasis, and primary Sjogren's syndrome, indicating that AIM2 might be involved in the pathogenesis of autoimmune diseases. Meanwhile, AIM2 also plays an antitumorigenesis role in an inflammasome independent-manner. In melanoma, AIM2 is initially identified as a tumor suppressor factor. However, AIM2 is also found to contribute to lung tumorigenesis via the inflammasome-dependent release of interleukin 1β and regulation of mitochondrial dynamics. Additionally, AIM2 reciprocally dampening the cGAS-STING pathway causes immunosuppression of macrophages and evasion of antitumor immunity during antibody treatment. To summarize the complicated effect and role of AIM2 in autoimmune diseases and cancers, herein, we provide an overview of the emerging research progress on the function and regulatory pathway of AIM2 in innate and adaptive immune cells, as well as tumor cells, and discuss its pathogenic role in autoimmune diseases, such as SLE, psoriasis, primary Sjogren's syndrome, and cancers, such as melanomas, non-small-cell lung cancer, colon cancer, hepatocellular carcinoma, renal carcinoma, and so on, hopefully providing potential therapeutic and diagnostic strategies for clinical use.

The role of innate immune signals in antitumor immunity

Innate immunity serves as a first line of defense against infectious agents, and germ-line-encoded pattern recognition receptors detect stressed and infected cells and elicit potent effector activities that accomplish efficient microbe containment. Recent evidence demonstrates that these pattern-sensing systems are also applicable to the recognition of tumor-derived stress-related factors. In particular, toll-like receptors and cytosolic sensors for DNA and RNA recognition utilize endogenous host elements containing microbial components, danger-associated molecules, and/or nucleic acids to stimulate innate signaling pathways and generate protective immune responses against nascent tumors in animal models and humans. In this review, we describe recent advances and perspectives about antitumor mechanisms and clinical application of innate immune signals and pathways.

AIM2 inhibits colorectal cancer cell proliferation and migration through suppression of Gli1

Colorectal cancer (CRC) is a common malignant tumor and is one of the leading causes of cancer-related deaths worldwide. Absent in melanoma 2 (AIM2), as a member of the pyrin-HIN family proteins, plays contentious roles in different types of cancers. In the present work, we provide evidence that AIM2 was commonly downregulated in human CRC and loss of AIM2 significantly correlated with tumor size, depth of invasion, lymph node metastasis (LNM) and TNM (Tumor, Node, Metastases) stage in patients suffering from CRC. AIM2 knockdown promoted CRC cell proliferation, migration and epithelial-mesenchymal transition (EMT) progress, whereas AIM2 overexpression did the opposite. AIM2 inhibited glioma-associated oncogene-1 (Gli1) expression through Smoothened homolog (SMO)-independent pathway and regulated CRC cell proliferation and migration in a Gli1-dependent manner. Moreover, AIM2 could modulate Protein kinase B (AKT)/mechanistic target of rapamycin (mTOR) signaling pathway and the increased Gli1 expression and EMT progress induced by AIM2 depletion was reversed after incubation with AKT inhibitor Ly294002 in CRC cells. In conclusion, our results define AIM2 as a novel regulator of Gli1 in CRC cell growth and metastasis, and suggest that the AIM2/AKT/mTOR/Gli1 signaling axis may serve as a potential target for treatment of CRC.

Immunobiology and structural biology of AIM2 inflammasome

Absent in melanoma 2 (AIM2) is a cytoplasmic sensor that upon recognizing double-stranded DNA assembles with apoptosis-associated speck-like protein containing a CARD (ASC) and procaspase-1 to form the multi-protein complex AIM2 inflammasome. Double-stranded DNA from bacterial, viral, or host cellular origins triggers AIM2 inflammasome assembly and activation, ultimately resulting in secretion of proinflammatory cytokines and pyroptotic cell death in order to eliminate microbial infection. Many pathogens therefore evade or suppress AIM2 inflammasome to establish infection. On the other hand, AIM2 activation is tightly controlled by multiple cellular factors to prevent autoinflammation. Extensive structural studies have captured the molecular details of multiple steps in AIM2 inflammasome assembly. The structures collectively revealed a nucleated polymerization mechanism that not only pervades each step of AIM2 inflammasome assembly, but also underlies assembly of other inflammasomes and complexes in immune signaling. In this article, we briefly review the identification of AIM2 as a cytoplasmic DNA sensor, summarize the importance of AIM2 inflammasome in infections and diseases, and discuss the molecular mechanisms of AIM2 assembly, activation, and regulation using recent cellular, biochemical, and structural results.

CCL19 suppresses gastric cancer cell proliferation, migration, and invasion through the CCL19/CCR7/AIM2 pathway

Absent in melanoma 2 (AIM2) has been reported to be an important inflammasome component that exerts tumor suppression in several tumors. However, whether CCL19/CCR7/AIM2 is involved in the progression of GC still remains unclear. Quantitative real-time and ELISA assay were used to determine the expressions of AIM2, CCL19 and CCR7 in GC tissues and cell lines. CCK-8, Edu staining, flow cytometry, Transwell assay, and tumorigenesis in nude mice were used to explore the function of AIM2 and CCL19 in vitro and in vivo. Apoptosis and inflammation-related biomarkers were detected by Western blot and ELISA assay. H&E staining was used to assess the histological changes in the subcutaneous tumor model. Immunohistochemistry (IHC) was used to evaluate the expression of Ki-67. We found that expression levels of AIM2, CCL19 and CCR7 were obviously lower in early GC tissues than those in progressive GC tissues. In vitro assays revealed that CCL19 treatment could enhance the suppressive effects of AIM2 overexpression on cell proliferation, migration, and invasion through CCR7. An in vivo assay also demonstrated that silencing of AIM2 reversed the suppressive effects of CCL19 on tumor growth. Collectively, CCL19 overexpression significantly inhibited GC cell proliferation and tumor growth in vitro and in vivo by up-regulating the CCR7/AIM2 pathway. Thus, CCL19 activated CCR7/AIM2 signaling pathway and it may be a potential therapeutic approach for GC therapy.

Role of inflammasomes in the pathogenesis of periodontal disease and therapeutics

Inflammasomes are a group of multimolecular intracellular complexes assembled around several innate immune proteins. Recognition of a diverse range of microbial, stress and damage signals by inflammasomes results in direct activation of caspase‐1, which subsequently induces the only known form of secretion of active interleukin‐1β and interleukin‐18. Although the importance of interleukin‐1β in the periodontium is not questioned, the impact of inflammasomes in periodontal disease and its potential for therapeutics in periodontology is still in its very early stages. Increasing evidence in preclinical models and human data strongly implicate the involvement of inflammasomes in a number of inflammatory, autoinflammatory and autoimmune disorders. Here we review: (a) the currently known inflammasome functions, (b) clinical/preclinical data supporting inflammasome involvement in the context of periodontal and comorbid diseases and (c) potential therapies targeting inflammasomes. To clarify further the inflammasome involvement in periodontitis, we present analyses of data from a large clinical study (n = 5809) that measured the gingival crevicular fluid‐interleukin‐1β and grouped the participants based on current periodontal disease classifications. We review data on 4910 European‐Americans that correlate 16 polymorphisms in the interleukin‐1B region with high gingival crevicular fluid‐interleukin‐1β levels. We show that inflammasome components are increased in diseased periodontal tissues and that the caspase‐1 inhibitor, VX‐765, inhibits ~50% of alveolar bone loss in experimental periodontitis. The literature review further supports that although patients clinically present with the same phenotype, the disease that develops probably has different underlying biological pathways. The current data indicate that inflammasomes have a role in periodontal disease pathogenesis. Understanding the contribution of different inflammasomes to disease development and distinct patient susceptibility will probably translate into improved, personalized therapies.

The hepatoprotective effects of XCHD and MgIG against methotrexate-induced liver injury and inflammation in rats through suppressing the activation of AIM2 inflammasomes

BACKGROUND

Recent studies have shown that drug-induced liver injury may be related to the immune response activated by drugs. A cytosolic dsDNA inflammasome called absent in melanoma 2 (AIM2) was found to be associated with aseptic inflammation. The present study aimed to explore the effects of on the liver injury and inflammation in methotrexate (Mtx)-induced rats.

METHODS

Sprague Dawley (SD) rats were selected and classified into 4 groups randomly, includes control group, Mtx group, Mtx-Xiaochaihu decoction (XCHD) group and Mtx-magnesium isoglycyrrhizinate (MgIG) group. Light microscopy was used to examine histological specimens after hematoxylin-eosin (HE) staining. The AST levels in liver tissue and blood serum ALT in the rats were assessed with enzyme linked immunosorbent assay (ELISA). Then AIM2 expression and inflammatory factors, including caspase-1, IL-18, and IL-1β, in the liver biopsy specimens of rats were detected by immunohistochemistry. Furthermore, the correlation between inflammatory and AIM2 expression factors was comprehensively analyzed.

RESULTS

Functional and structural hepatotoxicity can be caused by the exposure to Mtx, which was supported by the improved biochemical marker levels and the worse histopathological changes in liver tissue. Compared with the Mtx group, the levels of liver enzymes ALT and AST, histological deterioration in the liver tissues were effectively decreased by XCHD and MgIG treatment, respectively. In addition, the expression of AIM2, caspase-1 and IL-1β was observably higher in the Mtx group, which was apparently inhibited in the Mtx-XCHD and Mtx-MgIG groups. There was no obvious change in IL-18 expression among four groups. AIM2 expression were positively associated with the severity of liver inflammation and had a higher relevance with caspase-1 expression.

CONCLUSIONS

AIM2 inflammasome in hepatocytes has a significant effect on the development of Mtx-induced liver injury, which can be ameliorated by both XCHD and MgIG treatment. The latent mechanism and potential signal pathway require further study.

PYHIN Proteins and HPV: Role in the Pathogenesis of Head and Neck Squamous Cell Carcinoma

In the last decades, the human papillomavirus (HPV) emerged as an etiological cause of head and neck squamous cell carcinoma (HNSCC), especially in the oropharynx. The role of two intracellular DNA sensors, which belong to the PYHIN family (interferon-inducible protein 16 (IFI16) and absent in melanoma 2 protein (AIM2)), has been analyzed in relation to HPV infection and head and neck carcinogenesis. In particular, IFI16 and AIM2 expression depends on HPV infection in HNSCC. They represent viral restriction factors and are key components of the intrinsic immunity activated against different viruses, including HPV. This review analyzed and summarized the recent findings about the role of PYHIN proteins in HPV⁺ and HPV⁻ HNSCC.

Benzene metabolites trigger pyroptosis and contribute to haematotoxicity via TET2 directly regulating the Aim2/Casp1 pathway

Background

Long term low-dose benzene exposure leads to the inhibition of haematopoiesis. However, the underlying mechanisms remained poorly defined, especially mediated by early effector molecules.

Methods

Here, we first found in mRNA microarray that pyroptotic classic genes (Casp1, 4, 5, and IL1β) were up-regulated and represented dose-dependent differential expression in controls, low-dose benzene-exposed and chronic benzene-poisoned workers, and the expression of Casp1 and IL1β were confirmed in low-dose benzene-exposed workers and was accompanied with elevated potent proinflammatory IL1β. In vitro studies showed that benzene metabolites induced AHH-1 cell pyroptosis through activating Aim2/Casp1 pathway with the increased expression of GSDMD. Meanwhile, TET2 overexpression was elevated in vivo and in vitro and it was positively correlated with IL1β. Further, we verified that pyroptosis caused by 1,4-BQ could be ameliorated in vitro by RNAi or pretreatment with Dimethyloxalylglycine (DMOG), the inhibitor of TET2.

Findings

Exposure to benzene can trigger pyroptosis via TET2 directly regulating the Aim2/Casp1 signaling pathway to cause haematotoxicity.

Interpretation

Benzene metabolites induced pyroptotic cell death through activation of the Aim2/Casp1 pathway which can be regulated by Tet2 overexpression. Tet2 may be a potential risk factor and is implicated in the development of benzene-related diseases.

Fund

National Natural Science Foundation of China; the Support Project of High–level Teachers in Beijing Municipal Universities in the Period of 13th Five–year Plan; Beijing Natural Science Foundation Program and Scientific Research Key Program of Beijing Municipal Commission of Education.

Role of AIM2 inflammasome in inflammatory diseases, cancer and infection

AIM2 is a cytosolic innate immune receptor which recognizes double-stranded DNA (dsDNA) released during cellular perturbation and pathogenic assault. AIM2 recognition of dsDNA leads to the assembly of a large multiprotein oligomeric complex termed the inflammasome. This inflammasome assembly leads to the secretion of bioactive interleukin-1β (IL-1β) and IL-18 and induction of an inflammatory form of cell death called pyroptosis. Sensing of dsDNA by AIM2 in the cytosol is crucial to mediate protection against the invading pathogens including bacteria, virus, fungi and parasites. AIM2 also responds to dsDNA released from damaged host cells, resulting in the secretion of the effector cytokines thereby driving the progression of sterile inflammatory diseases such as skin disease, neuronal disease, chronic kidney disease, cardiovascular disease and diabetes. Additionally, the protection mediated by AIM2 in the development of colorectal cancer depends on its ability to regulate epithelial cell proliferation and gut microbiota in maintaining intestinal homeostasis independently of the effector cytokines. In this review, we will highlight the recent progress on the role of the AIM2 inflammasome as a guardian of cellular integrity in modulating chronic inflammatory diseases, cancer and infection.

Absent in melanoma 2 suppresses epithelial-mesenchymal transition via Akt and inflammasome pathways in human colorectal cancer cells

Absent in melanoma 2 (AIM2) is a critical component in natural immunity system and is closely related to cancer initiation and development. It has been shown that AIM2 inhibited colorectal cancer (CRC) development and cell proliferation. It remains unresolved how AIM2 acts on CRC metastasis. In this study, we assessed migration, invasion ability, and epithelial-mesenchymal transition (EMT) program upon AIM2 overexpression or knockdown in human CRC cells. Transwell assay demonstrated that upregulation of AIM2 reduced cell migration and invasion. Epithelial marker E-cadherin was augmented and mesenchymal markers vimentin, as well as Snail, were examined decreased by Western blot, real-time polymerase chain reaction, and immunofluorescence. Correspondingly, knockdown of AIM2 led to a reverse consequence. In addition, AIM2 regulated Akt phosphorylation and effects of AIM2 on cell invasion and EMT were recovered after administration of Akt inhibitor, suggesting that AIM2 suppressed EMT dependent on Akt pathway. In addition, caspase-1 inhibitor exposure indicated that AIM2 abrogated EMT through the inflammasome pathway as well. In summary, AIM2 suppressed EMT via Akt and inflammasome pathways in human CRC cells.

Ribosomal DNA as DAMPs Signal for MCF7 Cancer Cells

Introduction: The cell free ribosomal DNA (cf-rDNA) is accrued in the total pool of cell free DNA (cfDNA) in some non-cancer diseases and demonstrates DAMPs characteristics. The major research questions: (1) How does cell free rDNA content change in breast cancer; (2) What type of response in the MCF7 breast cancer cells is caused by cf-rDNA; and (3) What type of DNA sensors (TLR9 or AIM2) is stimulated in MCF7 in response to the action of cf-rDNA?

Materials and Methods: CfDNA and gDNA were isolated from the blood plasma and the cells derived from 38 breast cancer patients and 20 healthy female controls. The rDNA content in DNA was determined using non-radioactive quantitative hybridization. In order to explore the rDNA influence on MCF7 breast cancer cells, the model constructs (GC-DNAs) were applied: pBR322-rDNA plasmid (rDNA inset 5836 bp long) and pBR322 vector. ROS generation, DNA damage, cell cycle, expression of TLR9, AIM2, NF-kB, STAT3, and RNA for 44 genes affecting the cancer cell viability were evaluated. The methods used: RT-qPCR, fluorescent microscopy, immunoassay, flow cytometry, and siRNA technology.

Results: The ratio R = cf-rDNA/g-rDNA for the cases was higher than for the controls (median 3.4 vs. 0.8, p < 10⁻⁸). In MCF7, GC-DNAs induce a ROS burst, DNA damage response, and augmentation of NF-kB and STAT3 activity. The number of the apoptotic cells decreases, while the number of cells with an instable genome (G2/M– arrest, micronuclei) increase. Expression of anti-apoptotic genes (BCL2, BCL2A1, BCL2L1, BIRC3, MDM2) is elevated, while expression of pro-apoptotic genes (BAX, BID, BAD, PMAIP1, BBC3) is lowered. The cells response for pBR322-rDNA is much more intense and develops much faster, than response for pBR322, and is realized through activation of TLR9- MyD88 - NF-kB- signaling. This difference in response speed is owing to the heightened oxidability of pBR322-rDNA and better ability to penetrate the cell. Induction of TLR9 expression in MCF7 is followed by blocking AIM2 expression.

Conclusion: (1) Ribosomal DNA accumulates in cfDNA of breast cancer patients; (2) Cell free rDNA induce DNA damage response and stimulates cells survival, including cells with an instable genome; (3) Cell free rDNA triggers TLR9- MyD88- NF-kB- signaling, with significantly repressing the expression of AIM2.

Decrease of AIM2 mediated by luteolin contributes to non-small cell lung cancer treatment

Non-small cell lung cancer (NSCLC) is one of the most common malignancies in the world. Although extensive studies showed that luteolin exhibited antitumor effects against NSCLC, the mechanism has not been fully established. In the present study, we found that luteolin significantly reduced the expression of absent in melanoma 2 (AIM2) at both mRNA and protein levels leading to the suppression of AIM2 inflammasome activation, which induced G2/M phase arrest and inhibited epithelial–mesenchymal transition (EMT) in NSCLC. Furthermore, the inhibitory effects of luteolin on NSCLC cells were abolished by the knockdown of AIM2. On the contrary, the antitumor effects of luteolin could be notably reversed by the overexpression of AIM2. In addition, luteolin reduced poly(dA:dT)-induced caspase-1 activation and IL-1β cleavage in NSCLC cells. These findings suggested that AIM2 was essential to luteolin-mediated antitumor effects. The antitumor effects of luteolin, which were closely associated with AIM2, were also confirmed in the A549 and H460 xenograft mouse models. Collectively, our study displayed that the antitumor effects of luteolin on NSCLC were AIM2 dependent and the downregulation of AIM2 might be an effective way for NSCLC treatment.

AIM2 deficiency reduces the development of hepatocellular carcinoma in mice

Chronic liver inflammation is crucial in the pathogenesis of hepatocellular carcinoma (HCC). Activation of the inflammasome complex is a key inflammatory process that has been associated with different liver diseases, but its role in HCC development remains largely unexplored. Here we analyzed the impact of different inflammasome components, including absent in melanoma 2 (AIM2) and NOD-like receptor family pyrin domain containing 3 (NLRP3), in the development of diethylnitrosamine (DEN)-induced HCC in mice. Genetic inactivation of AIM2, but not NLRP3, reduces liver damage and HCC development in this model. AIM2 deficiency ameliorates inflammasome activation, liver inflammation and proliferative responses during HCC initiation. We also identified that AIM2 is highly expressed in Kupffer cells, and that AIM2-mediated production of IL-1β by these cells is enhanced after DEN-induced liver damage. Our data indicate that AIM2 promotes inflammation during carcinogenic liver injury and that it contributes to genotoxic HCC development in mice, thereby recognizing AIM2 as a potential therapeutic target in this disease.

H1/pAIM2 nanoparticles exert anti-tumour effects that is associated with the inflammasome activation in renal carcinoma

Renal cell carcinoma (RCC) is a high metastasis tumour with less effective treatment available currently. Absent in melanoma 2 (AIM2) as a tumour suppressor might be used as a potential therapeutic target for RCC treatment. Here, we found that AIM2 expression was significantly decreased in RCC patient specimens and renal carcinoma cell lines (786‐O and OSRC‐2). To establish a safe and effective AIM2 gene delivery system, we formed the nanoparticles consisting of a folate grafted PEI600‐CyD (H1) nanoparticle‐mediated AIM2 gene (H1/pAIM2) as an effective delivery agent. Delivery of H1/pAIM2 in renal carcinoma cells could remarkably increase the expression of AIM2, and subsequently decrease cell proliferation, migration, and invasion as well as enhance cell apoptosis. In order to evaluate the therapeutic efficacy of AIM2 in vivo, H1/pAIM2 nanoparticles were injected intratumorally into 786‐O‐xenograft mice. Administration of H1/pAIM2 nanoparticles could inhibit the tumour growth as evidenced by reduced tumour volume and weight. Furthermore, Blockade of inflammasome activation triggered by H1/pAIM2 nanoparticles using inflammasome inhibitor YVAD‐CMK abrogated the anti‐tumoral activities of H1/AIM2. These results indicated the therapeutic effect of H1/pAIM2 nanoparticles was mainly attributable to its capability to enhance the inflammasome activation. H1/AIM2 nanoparticles might act as an efficient therapeutic approach for RCC treatment.

Tumor cell-specific AIM2 regulates growth and invasion of cutaneous squamous cell carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the most common metastatic skin cancer. Inflammation is a typical feature in cSCC progression. Analysis of the expression of inflammasome components in cSCC cell lines and normal human epidermal keratinocytes revealed upregulation of the expression of AIM2 mRNA and protein in cSCC cells. Elevated levels of AIM2 mRNA were noted in cSCCs in vivo compared with normal skin. Strong and moderate tumor cell specific expression of AIM2 was detected with immunohistochemistry (IHC) in sporadic human cSCCs in vivo, whereas expression of AIM2 was moderate in cSCC in situ (cSCCIS) and low or absent in actinic keratosis (AK) and normal skin. IHC of cSCCs, cSCCIS and AKs from organ transplant recipients also revealed strong and moderate tumor cell specific expression of AIM2 in cSCCs. Knockdown of AIM2 resulted in reduction in viability of cSCC cells and onset of apoptosis. RNA-seq and pathway analysis after knockdown of AIM2 in cSCC cells revealed downregulation of the biofunction category Cell cycle and upregulation of the biofunction category Cell Death and Survival. Knockdown of AIM2 also resulted in reduction in invasion of cSCC cells and downregulation in production of invasion proteinases MMP1 and MMP13. Knockdown of AIM2 resulted in suppression of growth and vascularization of cSCC xenografts in vivo. These results provide evidence for the role of AIM2 in the progression of cSCC and identify AIM2 inflammasome function as a potential therapeutic target in these invasive and metastatic tumors.

ASC contributes to metastasis of oral cavity squamous cell carcinoma

ASC (Apoptosis-associated Speck-like protein containing a CARD) acts as a platform protein in the inflammasome cascade of some cancer types. However, its potential involvement in OSCC (oral cavity squamous cell carcinoma) has not yet been determined. Here, we investigated the potential role of ASC in OSCC. RT-qPCR analysis of 20 paired tumor and adjacent normal tissue samples revealed that the mRNA levels of ASC, along with IL-1β, CASP1, and NLRP3 in ASC-associated NLRP3 inflammasome were significantly elevated in OSCC tissues. Immunohistochemical staining of these four proteins in 111 clinical specimens revealed that high-level expression of ASC was significantly associated with tumor stage, node stage (p=0.001), overall stage (p<0.001), extracapsular spread (p<0.001), perineural invasion (p=0.004) and tumor depth (p<0.001). Kaplan-Meier survival analysis further revealed that high-level ASC expression was correlated with poorer overall survival (p=0.001), disease-specific survival (p<0.001) and disease-free survival (p<0.001). Studies using OSCC cell lines indicated that high-level ASC expression enhanced cell migration and invasion, and experiments using an orthotropic nude mouse model confirmed that ASC overexpression induced metastasis of OSCC cells. This is the first report to show that ASC contributes to OSCC metastasis, and that high-level ASC expression is a marker for poor prognosis in OSCC patients.

CD146 positive human dental pulp stem cells promote regeneration of dentin/pulp-like structures

CD146 and STRO-1 are endothelial biomarkers that are co-expressed on the cellular membranes of blood vessels within human dental pulp tissue. This study characterized the percentage of dentin-like structures produced by CD146-positive (CD146⁺) human dental pulp stem cells (DPSCs), compared with their CD146-negative (CD146^-) counterparts. DPSC populations were enriched using magnetic-activated cell sorting (MACS), yielding CD146⁺ and CD146^- cells, as well as mixtures composed of 25% CD146⁺ cells and 75% CD146^- cells (CD146^+/-). Cell growth assays indicated that CD146⁺ cells exhibit an approximate 3-4 h difference in doubling time, compared with CD146^- cells. Cell cycle distributions were determined by flow cytometry analysis. The low percentage of CD146⁺ cells' DNA content in G₀/G₁ phase were compared with CD146^- and non-separated cells. In contrast to CD146^- and non-separated cells, prompt mineralization was observed in CD146⁺ cells. Subsequently, qRT-PCR revealed high mRNA expression of CD146 and Alkaline phosphatase in mineralization-induced CD146⁺ cells. CD146⁺ cells were also observed high adipogenic ability by Oil red O staining. Histological examinations revealed an increased area of dentin/pulp-like structures in transplanted CD146⁺ cells, compared with CD146^- and CD146^+/- cells. Immunohistochemical studies detected dentin matrix protein-1 (DMP1) and dentin sialophosphoprotein (DSPP), as well as human mitochondria, in transplanted DPSCs. Co-expression of CD146 and GFP indicated that CD146 was expressed in transplanted CD146⁺ cells. CD146⁺ cells may promote mineralization and generate dentin/pulp-like structures, suggesting a role in self-renewal of stem cells and dental pulp regenerative therapy.

Loss of AIM2 expression promotes hepatocarcinoma progression through activation of mTOR-S6K1 pathway

Absent in melanoma (AIM2) is a member of the interferon-inducible HIN-200 protein family and is recently recognized to play an important dual role in both innate immunity and tumor pathology. However, the role of AIM2 in the development of hepatocellular carcinoma (HCC) remains to be clarified. Here we showed that AIM2 expression was significantly decreased in liver cancer tissues, and loss of its expression was significantly correlated with more advanced tumor progression. Exogenous overexpression of AIM2 in HCC cells suppressed mammalian target of rapamycin (mTOR)-S6K1 pathway and further inhibited proliferation, colony formation and invasion of HCC cells. On the contrary, block of AIM2 in HCC cells induced (mTOR)-S6K1 pathway activation and thus promoted HCC progression. Treatment with mTOR pathway inhibitor rapamycin further verified its contribution to HCC progression in AIM2 absent HCC cells. Thus, these data suggested that AIM2 played a critical role as a tumor suppressor and might serve as a potential therapeutic target for future development of AIM2-based gene therapy for human liver cancer. This study also paves a new avenue to treat AIM2-deficient cancer by suppression of mTOR.

The Goldilocks Conundrum: NLR Inflammasome Modulation of Gastrointestinal Inflammation during Inflammatory Bowel Disease

Recent advances have revealed significant insight into inflammatory bowel disease (IBD) pathobiology. Ulcerative colitis and Crohn's disease, the chronic relapsing clinical manifestations of IBD, are complex disorders with genetic and environmental influences. These diseases are associated with the dysregulation of immune tolerance, excessive inflammation, and damage to the epithelial cell barrier. Increasing evidence indicates that pattern recognition receptors, including Toll-like receptors (TLRs) and nucleotide-binding domain and leucine-rich repeat-containing proteins (NLRs), function to maintain immune system homeostasis, modulate the gastrointestinal microbiome, and promote proper intestinal epithelial cell regeneration and repair. New insights have revealed that NLR family members are essential components in maintaining this immune system homeostasis. To date, the vast majority of studies associated with NLRs have focused on family members that form a multiprotein signaling platform called the inflammasome. These signaling complexes are responsible for the cleavage and activation of the potent pleotropic cytokines IL-1β and IL-18, and they facilitate a unique form of cell death defined as pyroptosis. In this review, we summarize the current paradigms associated with NLR inflammasome maintenance of immune system homeostasis in the gastrointestinal system. New concepts related to canonical and noncanonical inflammasome signaling, as well as the implications of classical and alternative inflammasomes in IBD pathogenesis, are also reviewed.

A noncanonical function of cGAMP in inflammasome priming and activation

IFN-I signaling and inflammasome activation are two innate pathways important for combatting a variety of pathogens. Swanson et al. show that cGAMP activates the inflammasome in addition to IFN-I, and that the activation of both is needed to control infection by a DNA virus.

Recognition of pathogen-associated molecular patterns and danger-associated molecular patterns by host cells is an important step in innate immune activation. The DNA sensor cyclic guanosine monophosphate–adenosine monophosphate (cGAMP) synthase (cGAS) binds to DNA and produces cGAMP, which in turn binds to stimulator of interferon genes (STING) to activate IFN-I. Here we show that cGAMP has a noncanonical function in inflammasome activation in human and mouse cells. Inflammasome activation requires two signals, both of which are activated by cGAMP. cGAMP alone enhances expression of inflammasome components through IFN-I, providing the priming signal. Additionally, when combined with a priming signal, cGAMP activates the inflammasome through an AIM2, NLRP3, ASC, and caspase-1 dependent process. These two cGAMP-mediated functions, priming and activation, have differential requirements for STING. Temporally, cGAMP induction of IFN-I precedes inflammasome activation, which then occurs when IFN-I is waning. In mice, cGAS/cGAMP amplify both inflammasome and IFN-I to control murine cytomegalovirus. Thus, cGAMP activates the inflammasome in addition to IFN-I, and activation of both is needed to control infection by a DNA virus.

The multifaceted roles of inflammasome proteins in cancer

PURPOSE OF REVIEW

Inflammasomes are major actors of the innate immune system, through their regulation of inflammatory caspases and maturation of IL-1β and IL-18. These multiprotein complexes have been shown to play major roles in inflammatory and metabolic diseases and have more recently been implicated in tumor development and dissemination. In this review, we address these recent findings, focusing particularly on colorectal cancer (CRC) initiation and tumor dissemination.

RECENT FINDINGS

Based mostly on loss-of-function experiments in mouse models, paradoxical results were obtained as both protumoral and antitumoral activities were reported. Moreover, several studies report major inflammasome-independent functions for some of these innate receptor proteins such as absent in melanoma 2, nod-like receptor family pyrin containing 3 (NLRP3) or nod-like receptor family CARD containing 4 (NLRC4), functions exerted in epithelial cells as well as in immune cells.

SUMMARY

The current review summarizes recent findings on the implication of inflammasomes and of absent in melanoma 2, NLRC4 and NLRP3 inflammasome-independent functions in cancer development and dissemination. Although contradictory in certain aspects, these studies highlight a lack of understanding of their mechanistic functions and regulations in cancer and the need for further investigations.

HBx-mediated decrease of AIM2 contributes to hepatocellular carcinoma metastasis

Tumor metastasis is responsible for the high mortality rates in patients with hepatocellular carcinoma (HCC). Absent in melanoma 2 (AIM2) has been implicated in inflammation and carcinogenesis, although its role in HCC metastasis remains unknown. In the present study, we show that AIM2 protein expression was noticeably reduced in HCC cell lines and clinical samples. A reduction in AIM2 was closely associated with higher serum AFP levels, vascular invasion, poor tumor differentiation, an incomplete tumor capsule and unfavorable postsurgical survival odds. In vitro studies demonstrated that AIM2 expression was modulated by hepatitis B virus X protein (HBx) at transcriptional and post-translational levels. HBx overexpression markedly blocked the expression of AIM2 at mRNA and protein levels by enhancing the stability of Enhancer of zeste homolog 2 (EZH2). Furthermore, HBx interacted with AIM2, resulting in an increase of AIM2 degradation via ubiquitination induction. Functionally, knockdown of AIM2 enhanced cell migration, formation of cell pseudopodium, wound healing and tumor metastasis, whereas reintroduction of AIM2 attenuated these functions. The loss of AIM2 induced the activation of epithelial-mesenchymal transition (EMT). Fibronectin 1 (FN1) was found to be a downstream effector of AIM2, with its expression reversely modulated by AIM2. Silencing of FN1 significantly halted cell migration induced by AIM2 depletion. These data demonstrate that HBx-induced loss of AIM2 is associated with poor outcomes and facilitates HCC metastasis by triggering the EMT process. The results of the present study therefore suggest that AIM2 is a potential prognostic biomarker in hepatitis B virus-related HCC, as well as a possible therapeutic target for tumor metastasis.

Inflammasomes in Myeloid Cells: Warriors Within

The inflammasome is a large multimeric protein complex comprising an effector protein that demonstrates specificity for a variety of activators or ligands; an adaptor molecule; and procaspase-1, which is converted to caspase-1 upon inflammasome activation. Inflammasomes are expressed primarily by myeloid cells and are located within the cell. The macromolecular inflammasome structure can be visualized by cryo-electron microscopy. This complex has been found to play a role in a variety of disease models in mice, and several have been genetically linked to human diseases. In most cases, the effector protein is a member of the NLR (nucleotide-binding domain leucine-rich repeat-containing) or NOD (nucleotide oligomerization domain)-like receptor protein family. However, other effectors have also been described, with the most notable being AIM-2 (absent in melanoma 2), which recognizes DNA to elicit inflammasome function. This review will focus on the role of the inflammasome in myeloid cells and its role in health and disease.

Nucleic acid sensing pattern recognition receptors in the development of colorectal cancer and colitis

Colorectal cancer (CRC) is a leading cause of cancer-related deaths that is often associated with inflammation initiated by activation of pattern recognition receptors (PRRs). Nucleic acid sensing PRRs are one of the major subsets of PRRs that sense nucleic acid (DNA and RNA), mainly including some members of Toll-like receptors (TLR3, 7, 8, 9), AIM2-like receptors (AIM2, IFI16), STING, cGAS, RNA polymerase III, and DExD/H box nucleic acid helicases (such as RIG-I like receptors (RIG-I, MDA5, LPG2), DDX1, 3, 5, 7, 17, 21, 41, 60, and DHX9, 36). Activation of these receptors eventually leads to the release of cytokines and activation of immune cells, which are well known to play crucial roles in host defense against intracellular bacterial and virus infection. However, the functions of these nucleic acid sensing PRRs in the other diseases such as CRC and colitis remain largely unknown. Recent studies indicated that nucleic acid sensing PRRs contribute to CRC and/or colitis development, and therapeutic modulation of nucleic acid sensing PRRs may reduce the risk of CRC development. However, until now, a comprehensive review on the role of nucleic acid sensing PRRs in CRC and colitis is still lacking. This review provided an overview of the roles as well as the mechanisms of these nucleic acid sensing PRRs (AIM2, STING, cGAS, RIG-I and its downstream molecules, DDX3, 5, 6,17, and DHX9, 36) in CRC and colitis, which may aid the diagnosis, therapy, and prognostic prediction of CRC and colitis.

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.

Review Article. Absent in melanoma 2 (AIM2) in the intestine: diverging actions with converging consequences

The intestinal mucosa is a difficult environment to maintain homeostasis as it is constantly challenged by microbial and food antigens. Maintaining an intact epithelial barrier, a continuous turnover of intestinal epithelial cells and normobiosis of the gut microbiota are essential components to prevent intestinal diseases such as inflammatory bowel diseases (IBD) and colorectal cancer (CRC). Inflammasomes are critical immune regulators that are involved in all of these processes. They are multiprotein complexes able to assemble upon interaction with a noxious stimulus that will subsequently lead to caspase-1 activation. Activated caspase-1 will orchestrate the maturation and release of proinflammatory cytokines IL-1β and IL-18, and induce pyroptosis, an inflammatory form of cell death. Both cytokine release and pyroptosis are initiated after detection of molecular patterns by a distinct inflammasome sensor protein. Absent in melanoma 2 (AIM2) is such an inflammasome sensor that specifically responds to the presence of double stranded DNA (dsDNA) in the cytoplasm, leading to the recruitment and activation of caspase-1. Recent studies revealed additional roles of AIM2 in controlling epithelial cell proliferation, tight junction expression and the microbiome. Therefore, AIM2 plays a significant role in maintaining intestinal homeostasis. This review focuses on the multifunctional role of AIM2 in intestinal homeostasis by regulating intestinal immunity and preventing colorectal cancer development.

Sensing of dangerous DNA

The presence of damaged and microbial DNA can pose a threat to the survival of organisms. Cells express various sensors that recognize specific aspects of such potentially dangerous DNA. Recognition of damaged or microbial DNA by sensors induces cellular processes that are important for DNA repair and inflammation. Here, we review recent evidence that the cellular response to DNA damage and microbial DNA are tightly intertwined. We also discuss insights into the parameters that enable DNA sensors to distinguish damaged and microbial DNA from DNA present in healthy cells.

A five-gene expression signature to predict progression in T1G3 bladder cancer

OBJECTIVE

The aim of this study was to analyze tumour gene expression profiles of progressive and non-progressive T1G3 bladder cancer (BC) patients to develop a gene expression signature to predict tumour progression.

METHODS

Retrospective, multicenter study of 96 T1G3 BC patients without carcinoma in situ (CIS) who underwent a transurethral resection. Formalin-fixed paraffin-embedded tissue samples were collected. Global gene expression patterns were analyzed in 21 selected samples from progressive and non-progressive T1G3 BC patients using Illumina microarrays. Expression levels of 94 genes selected based on microarray data and based on literature were studied by quantitative polymerase chain reaction (qPCR) in an independent series of 75 progressive and non-progressive T1G3 BC patients. Univariate logistic regression was used to identify individual predictors. A variable selection method was used to develop a multiplex biomarker model. Discrimination of the model was measured by area under the receiver-operating characteristic curve. Interaction networks between the genes of the model were built by GeneMANIA Cytoscape plugin.

RESULTS

A total of 1294 genes were found differentially expressed between progressive and non-progressive patients. Differential expression of 15 genes was validated by qPCR in an additional set of samples. A five-gene expression signature (ANXA10, DAB2, HYAL2, SPOCD1, and MAP4K1) discriminated progressive from non-progressive T1G3 BC patients with a sensitivity of 79% and a specificity of 86% (AUC = 0.83). Direct interactions between the five genes of the model were not found.

CONCLUSIONS

Progressive and non-progressive T1G3 bladder tumours have shown different gene expression patterns. To identify T1G3 BC patients with a high risk of progression, a five-gene expression signature has been developed.

Invasive Cell Fate Requires G1 Cell-Cycle Arrest and Histone Deacetylase-Mediated Changes in Gene Expression

Despite critical roles in development and cancer, the mechanisms that specify invasive cellular behavior are poorly understood. Through a screen of transcription factors in Caenorhabditis elegans, we identified G1 cell-cycle arrest as a precisely regulated requirement of the anchor cell (AC) invasion program. We show that the nuclear receptor nhr-67/tlx directs the AC into G1 arrest in part through regulation of the cyclin-dependent kinase inhibitor cki-1. Loss of nhr-67 resulted in non-invasive, mitotic ACs that failed to express matrix metalloproteinases or actin regulators and lack invadopodia, F-actin-rich membrane protrusions that facilitate invasion. We further show that G1 arrest is necessary for the histone deacetylase HDA-1, a key regulator of differentiation, to promote pro-invasive gene expression and invadopodia formation. Together, these results suggest that invasive cell fate requires G1 arrest and that strategies targeting both G1-arrested and actively cycling cells may be needed to halt metastatic cancer.

AIM2 inflammasome in infection, cancer, and autoimmunity: Role in DNA sensing, inflammation, and innate immunity

Recognition of DNA by the cell is an important immunological signature that marks the initiation of an innate immune response. AIM2 is a cytoplasmic sensor that recognizes dsDNA of microbial or host origin. Upon binding to DNA, AIM2 assembles a multiprotein complex called the inflammasome, which drives pyroptosis and proteolytic cleavage of the proinflammatory cytokines pro-IL-1β and pro-IL-18. Release of microbial DNA into the cytoplasm during infection by Francisella, Listeria, Mycobacterium, mouse cytomegalovirus, vaccinia virus, Aspergillus, and Plasmodium species leads to activation of the AIM2 inflammasome. In contrast, inappropriate recognition of cytoplasmic self-DNA by AIM2 contributes to the development of psoriasis, dermatitis, arthritis, and other autoimmune and inflammatory diseases. Inflammasome-independent functions of AIM2 have also been described, including the regulation of the intestinal stem cell proliferation and the gut microbiota ecology in the control of colorectal cancer. In this review we provide an overview of the latest research on AIM2 inflammasome and its role in infection, cancer, and autoimmunity.

NLR-regulated pathways in cancer: opportunities and obstacles for therapeutic interventions

NLRs (nucleotide-binding domain, leucine-rich repeat containing receptors) are pattern recognition receptors associated with immunity and inflammation in response to endogenous and exogenous pathogen and damage associated molecular patterns (PAMPs and DAMPs respectively). Dysregulated NLR function is associated with several diseases including cancers, metabolic diseases, autoimmune disorders and autoinflammatory syndromes. In the last decade, distinct cell and organ specific roles for NLRs have been identified however; their roles in cancer initiation, development and progression remain controversial. This review summarizes the emerging role of NLRs in cancer and their possible future as targets for cancer therapeutics.