Antibody-dependent cellular cytotoxicity (ADCC) and antibody-dependent cellular phagocytosis (ADCP) critically contribute to the efficacy of anti-tumor therapeutic antibodies. We report here an unexpected finding that macrophages after ADCP inhibit NK cell-mediated ADCC and T cell-mediated cytotoxicity in breast cancers and lymphomas. Mechanistically, AIM2 is recruited to the phagosomes by FcγR signaling following ADCP and activated by sensing the phagocytosed tumor DNAs through the disrupted phagosomal membrane, which subsequently upregulates PD-L1 and IDO and causes immunosuppression. Combined treatment with anti-HER2 antibody and inhibitors of PD-L1 and IDO enhances anti-tumor immunity and anti-HER2 therapeutic efficacy in mouse models. Furthermore, neoadjuvant trastuzumab therapy significantly upregulates PD-L1 and IDO in the tumor-associated macrophages (TAMs) of HER2

Mammalian cells are equipped with antiviral innate immunity. To survive and grow, human papilloma virus (HPV)-infected cervical cancer cells must overcome this host defense system. However, the precise mechanism whereby cervical cancer cells evade the immunity is not fully understood. We noted that Sirtuin 1 (SIRT1) is overexpressed in HPV-infected cervical cancer cells and hypothesized that SIRT1 counteracts antiviral immunity. Here, we found that cervical cancer cells undergo massive death by SIRT1 knockdown, but this effect is reversed by SIRT1 restoration. SIRT1-knocked-down cells showed representative features of pyroptosis, as well as highly expressed absent in melanoma 2 (AIM2) and its downstream genes related to the inflammasome response. Mechanistically, SIRT1 repressed the NF-κB-driven transcription of the AIM2 gene by destabilizing the RELB mRNA. Interestingly, pyroptotic death signaling in SIRT1-knocked-down cells was transmitted to naïve cervical cancer cells, which was mediated by extracellular vesicles carrying AIM2 inflammasome proteins. Furthermore, the growth of cervical cancer xenografts was significantly inhibited by either SIRT1-targeting siRNAs or SIRT1-knockdown-derived extracellular vesicles. Immunohistochemical analyses showed that SIRT1 expression correlated with poor clinical outcomes in cervical cancer. In conclusion, SIRT1 enabled HPV-infected cervical cancer cells to continue growing by nullifying AIM2 inflammasome-mediated immunity. Without SIRT1, cervical cancer cells could no longer survive because of the derepression of the AIM2 inflammasome. SIRT1 could therefore be a target for the effective treatment of cervical cancer.

Sjögren's syndrome (SS) patients manifest high cell-free DNA (cf-DNA) levels in serum, associated with impaired DNaseI activity. Undegraded DNA may accumulate in tissues and act as an inflammasome-activating signal. Herein, we investigated the occurrence of aberrant DNA build-up in various biologic compartments of SS patients and its correlation with the activity of NLRP3 and AIM2 inflammasomes. For this purpose, we evaluated sera, PBMC, circulating monocytes and salivary glands (SG) from different SS patient subgroups and controls. We found that SS patients at high risk for lymphoma and those with established lymphoma display high serum cf-DNA levels, substantial extranuclear DNA accumulations in PBMC and SG tissues, a unique NLRP3 inflammasome gene signature in PBMC, and significantly increased serum IL-18 and ASC levels. In these patients, the circulating monocytes manifested NLRP3 inflammasome activation and increased response to NLRP3 stimuli, whereas SG-infiltrating macrophages exhibited signs of NLRP3 activation and pyroptosis. Cell-free nucleic acids isolated from patients' sera competently primed the activation of both NLRP3 and AIM2 inflammasomes in healthy monocytes. SS patients also manifested diminished DNaseI activity in serum and DNaseII expression in PBMC, which inversely correlated with indices of inflammasome activation. DNaseII gene-silencing in healthy monocytes led to cytoplasmic DNA deposition and activation of inflammasome-related genes and of caspase1. Our data reveal the occurrence of systemic NLRP3 inflammasome activation in severe SS, which is associated with widespread extranuclear accumulations of inflammagenic DNA and impaired DNA degradation. These findings can provide novel biomarkers and new therapeutic targets for the management of SS patients with adverse outcomes.

Increasing research has indicated that absent in melanoma 2 (AIM2) is aberrantly expressed in several tumor types. However, the association between AIM2 expression and clinicopathological factors or prognosis of patient with colorectal cancer (CRC) remains elusive. In the present study, we first examined the protein and mRNA expression of AIM2 in CRC cell lines by western blotting and quantitative RT-PCR (qRT-PCR). Then, we detected AIM2 expression in CRC tissue using western blotting and immunohistochemistry (IHC) respectively to evaluate its clinicopathological characteristics and prognosis in CRC. Our cytological experiments showed that there was low AIM2 expression in most of the CRC cell lines. Western blotting and IHC indicated that AIM2 expression was obviously lower in the primary CRC tissue than the adjacent normal tissue (P<0.01 and P<0.001). Clinicopathological analysis revealed that low AIM2 expression was significantly associated with some clinicopathological features such as depth of invasion (P=0.020), TNM clinical stage (P=0.013) and lymph node metastasis (P=0.026). Spearman analysis indicated that there was a negative correlation between AIM2 expression and preoperative serum carcino-embryonic antigen (CEA) levels in CRC patients (r=-0.217, P=0.009). Moreover, Kaplan-Meier analysis showed that low expression of AIM2 could lead to a significantly shorter overall survival rate (P=0.001). Cox's proportional hazards model also indicated that the low expression of AIM2 could serve as an independent and significant prognostic factor for survival. Taken together, our findings identify AIM2 as a valuable biomarker for prognosis and a potential therapeutic target for CRC.

Inflammasomes are multi-proteins complex regulating inflammation-associated signaling. While inflammation plays a critical role in cancer cell growth, studies remain uncharacterized on the role of inflammasomes in prostate cancer. Using Gene Expression Omnibus (GEO) public datasets, we screened the expression profiles of inflammasome sensors NLRP3, NLRC4, NLRP6, NRLP12, and AIM2 in prostate tumor tissues, and verified their mRNA level in a panel of prostate cancer cell lines. The selected expression of NLRP3 and NLRP12 inflammasomes was validated, and the clinical association was evaluated in human prostate archival tumor tissues. We observed that the expression of inflammasome sensors was dysregulated at the mRNA level except for the NLRP12. The intensity of NLRP12 immunostaining was significantly higher in malignant prostate as compared to their adjacent benign tissues. In contrast, the NLRP3 immunostaining in prostate tissues was heterogeneous. The inflammasome complex proteins ASC (apoptosis-associated speck-like protein containing a CARD) and pro-caspase-1, as well as its downstream targets IL-1β and IL-18 were confined to aggressive prostate cancer cells. These data suggest an increased expression of NLRP12 in association with prostate cancer and support the role of NLRP12 inflammasome complex regulating inflammatory cytokines in understanding the role of inflammation in the prostate cancer.

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.

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.

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.

BACKGROUND/AIM: Inflammasomes are multiprotein complexes that evoke key inflammatory cascades. The present study evaluated the influence of inflammasome component expression in non-tumorous tissue on postsurgical hepatocellular carcinoma (HCC) prognosis.
MATERIALS AND METHODS: The expressions of candidate genes were investigated using real-time quantitative reverse-transcription polymerase chain reaction in resected HCC cases. In order to identify potential prognostic factors, statistical analyses were performed for each gene.
RESULTS: The expression of nod-like receptor family, pyrin domain containing 3 (NLRP3), nod-like receptor family, CARD domain containing 4 (NLRC4), and absent in melanoma 2 (AIM2) was significantly higher in corresponding normal tissue (CN) compared to those in HCC. High expression of NLRP3, NLRC4, and caspase 1 (CASP1) in CN was significantly correlated with worse overall survival. Furthermore, multivariate analysis revealed that NLRP3 expression in CN greater than the median was an independent prognostic factor for poorer overall survival.
CONCLUSION: High expression of NLRP3, NLRC4, and CASP1 in background non-tumorous liver is significantly correlated with poor prognosis of patients after resection of HCC.

BACKGROUND: This study aimed to screen multiple genes biomarkers based on gene expression data for predicting the survival of ovarian cancer patients.
METHODS: Two microarray data of ovarian cancer samples were collected from The Cancer Genome Atlas (TCGA) database. The data in the training set were used to construct Reactome functional interactions network, which then underwent Markov clustering, supervised principal components, Cox proportional hazard model to screen significantly prognosis related modules. The distinguishing ability of each module for survival was further evaluated by the testing set. Gene Ontology (GO) functional and pathway annotations were performed to identify the roles of genes in each module for ovarian cancer.
RESULTS: The network based approach identified two 7-gene functional interaction modules (31: DCLRE1A, EXO1, KIAA0101, KIN, PCNA, POLD3, POLD2; 35: DKK3, FABP3, IRF1, AIM2, GBP1, GBP2, IRF2) that are associated with prognosis of ovarian cancer patients. These network modules are related to DNA repair, replication, immune and cytokine mediated signaling pathways.
CONCLUSIONS: The two 7-gene expression signatures may be accurate predictors of clinical outcome in patients with ovarian cancer and has the potential to develop new therapeutic strategies for ovarian cancer patients.

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.

Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) is an important adaptor protein for inflammasome activation, mediating the secretion of protumorigenic innate cytokines. However, ASC is also known to trigger apoptosis in tumor cells, acting as a tumor-suppressor gene, which is lost in several human cancers. The aim of this study was to evaluate the clinical significance of ASC in human cutaneous squamous cell carcinoma (SCC). Initially, ASC expression was immunohistochemically evaluated in non-metastic and metastatic SCC. While ASC expression does not correlate with metastatic potential, it correlates with the degree of dedifferentiation. Using methylation specific PCR we were able to demonstrate ASC silencing by promotor specific methylation and impaired inflammasome function in methylated cell lines, linking epigenetic modifications to innate immune activation in keratinocytes. Interestingly, upon ASC restoration by treatment with demethylating agents, we were able to restore AIM2 and NLRP3 activation. In summary, loss of ASC driven tumor development is counterbalanced in the identical cell by the inhibition of pro-tumorigenic inflammation in the tumor cell itself.

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.

NLRs (nucleotide-binding domain leucine-rich repeat proteins or NOD-like receptors) are regulators of inflammation and immunity. A subgroup of NLRs and the innate immune receptor, AIM2 (absent-in-melanoma 2), can induce the assembly of a large caspase-1 activating complex called the inflammasome. Other NLRs regulate key signaling pathways such as NF-kB and MAPK. Since inflammation is a central component of colorectal cancer (CRC), this work was undertaken to analyze NLR and AIM2 expression in human CRC by combining bioinformatics analysis and experimental verification using clinical tissue samples. Additional experiments analyzed the association of (i) gene expression and cancer staging, and (ii) gene expression among inflammasome components.Ten public CRC datasets from the Oncomine® Platform were analyzed. Genes analyzed include NLRP1, NLRP3, NLRP6, NLRP12, NLRC3, NLRC4, NLRC5, NOD1, NOD2 and AIM2. Additionally, forty case-matched cancer samples and adjacent healthy control tissues isolated from a cohort of Chinese CRC patients were profiled.Three patterns of gene expression in CRC are shown. The expression of NLRC3, a checkpoint of inflammation, and the inflammasome components NLRP1, NLRP3, NLRC4 and AIM2 were reduced in CRC. NOD1 and NOD2 expression was increased in CRC, while NLRC5, NLRP6 and NLRP12 showed little difference compared to controls. Reduced expression of NLRC3 in CRC was verified in all available databases analyzed and confirmed with our patient cohort. Furthermore, the extent of NLRC3 and AIM2 gene reduction was correlated with cancer progression. This report reveals the potential value of NLR and AIM2 genes as biomarkers of CRC and cancer progression.

Lynch syndrome is caused by germline mutations of DNA mismatch repair (MMR) genes, most frequently MLH1 and MSH2. Recently, MMR-deficient crypt foci (MMR-DCF) have been identified as a novel lesion which occurs at high frequency in the intestinal mucosa from Lynch syndrome mutation carriers, but very rarely progress to cancer. To shed light on molecular alterations and clinical associations of MMR-DCF, we systematically searched the intestinal mucosa from Lynch syndrome patients for MMR-DCF by immunohistochemistry. The identified lesions were characterised for alterations in microsatellite-bearing genes with proven or suspected role in malignant transformation. We demonstrate that the prevalence of MMR-DCF (mean 0.84 MMR-DCF per 1 cm2 mucosa in the colorectum of Lynch syndrome patients) was significantly associated with patients' age, but not with patients' gender. No MMR-DCF were detectable in the mucosa of patients with sporadic MSI-H colorectal cancer (n = 12). Microsatellite instability of at least one tested marker was detected in 89% of the MMR-DCF examined, indicating an immediate onset of microsatellite instability after MMR gene inactivation. Coding microsatellite mutations were most frequent in the genes HT001 (ASTE1) with 33%, followed by AIM2 (17%) and BAX (10%). Though MMR deficiency alone appears to be insufficient for malignant transformation, it leads to measurable microsatellite instability even in single MMR-deficient crypts. Our data indicate for the first time that the frequency of MMR-DCF increases with patients' age. Similar patterns of coding microsatellite instability in MMR-DCF and MMR-deficient cancers suggest that certain combinations of coding microsatellite mutations, including mutations of the HT001, AIM2 and BAX gene, may contribute to the progression of MMR-deficient lesions into MMR-deficient cancers.

The current study was undertaken with a view to identify differential biomarkers in chewing-tobacco-associated oral cancer tissues in patients of Indian ethnicity. The gene expression profile was analyzed in oral cancer tissues as compared to clinically normal oral buccal mucosa. We examined 30 oral cancer tissues and 27 normal oral tissues with 16 paired samples from contralateral site of the patient and 14 unpaired samples from different oral cancer patients, for whole genome expression using high-throughput IlluminaSentrix Human Ref-8 v2 Expression BeadChip array. The cDNA microarray analysis identified 425 differentially expressed genes with >1.5-fold expression in the oral cancer tissues as compared to normal tissues in the oral cancer patients. Overexpression of 255 genes and downregulation of 170 genes (p < 0.01) were observed. Further, a minimum twofold overexpression was observed in 32 genes and downregulation in 12 genes, in 30-83% of oral cancer patients. Biological pathway analysis using Kyoto Encyclopedia of Genes and Genome Pathway database revealed that the differentially regulated genes were associated with critical biological functions. The biological functions and representative deregulated genes include cell proliferation (AIM2, FAP, TNFSF13B, TMPRSS11A); signal transduction (FOLR2, MME, HTR3B); invasion and metastasis (SPP1, TNFAIP6, EPHB6); differentiation (CLEC4A, ELF5); angiogenesis (CXCL1); apoptosis (GLIPR1, WISP1, DAPL1); and immune responses (CD300A, IFIT2, TREM2); and metabolism (NNMT; ALDH3A1). Besides, several of the genes have been differentially expressed in human cancers including oral cancer. Our data indicated differentially expressed genes in oral cancer tissues and may identify prognostic and therapeutic biomarkers in oral cancers, postvalidation in larger numbers and varied population samples.

Research on innate immune signaling and regulation has recently focused on pathogen recognition receptors (PRRs) and their signaling pathways. Members of PRRs sense diverse microbial invasions or danger signals, and initiate innate immune signaling pathways, leading to proinflammatory cytokines production, which, in turn, instructs adaptive immune response development. Despite the diverse functions employed by innate immune signaling to respond to a variety of different pathogens, the innate immune response must be tightly regulated. Otherwise, aberrant, uncontrolled immune responses will lead to harmful, or even fatal, consequences. Therefore, it is essential to better discern innate immune signaling and many regulators, controlling various signaling pathways, have been identified. In this review, we focus on the recent advances in our understanding of the activation and regulation of innate immune signaling in the host response to pathogens and cancer.

Immune system provides us protection from infectious pathogens and tumors formation during lifetime. Cervical cancer (CC), and its cause, human papillomavirus (HPV) are both challenges for the immune system. We present here evidence of epigenetic activation of immune system genes in CC. Illumina Infinium Human Methylation 450K BeadChip identified genes, which were all significantly hypomethylated in CC tissue versus normal tissue. The GeneMANIA computer program identified a tight network between those genes. The most strongly correlated genes based on their function are immune effectors' process (AIM2, BST2, BTN3A3, and IL12RB1) and response to virus related genes (AIM2, BST2, and IL12RB1). Thus, activation of those genes through demethylation is probably triggered by HPV oncogenes. In conclusion, the immune system of women who do not develop CC is probably activated earlier through DNA demethylation.

The forkhead transcription factor FOXP1 is involved in B-cell development and function and is generally regarded as an oncogene in activated B-cell-like subtype of diffuse large B-cell lymphoma (DLBCL) and mucosa-associated lymphoid tissue lymphoma, lymphomas relying on constitutive nuclear factor κB (NF-κB) activity for survival. However, the mechanism underlying its putative oncogenic activity has not been established. By gene expression microarray, upon overexpression or silencing of FOXP1 in primary human B cells and DLBCL cell lines, combined with chromatin immunoprecipitation followed by next-generation sequencing, we established that FOXP1 directly represses a set of 7 proapoptotic genes. Low expression of these genes, encoding the BH3-only proteins BIK and Harakiri, the p53-regulatory proteins TP63, RASSF6, and TP53INP1, and AIM2 and EAF2, is associated with poor survival in DLBCL patients. In line with these findings, we demonstrated that FOXP1 promotes the expansion of primary mature human B cells by inhibiting caspase-dependent apoptosis, without affecting B-cell proliferation. Furthermore, FOXP1 is dependent upon, and cooperates with, NF-κB signaling to promote B-cell expansion and survival. Taken together, our data indicate that, through direct repression of proapoptotic genes, (aberrant) expression of FOXP1 complements (constitutive) NF-κB activity to promote B-cell survival and can thereby contribute to B-cell homeostasis and lymphomagenesis.

UNLABELLED: 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.

BACKGROUND: Nucleic acid sensing has emerged as one of the important components of the immune system triggering inflammation. The aim of this study is to determine the expression of bacterial DNA sensors, including Toll-like receptor 9 (TLR-9), DNA-dependent activator of interferon-regulatory factors (DAI), and absent in melanoma 2 (AIM2) in chronic periodontitis (CP versus healthy) (H) tissues.
METHODS: Thirty-five CP and 27 H gingival biopsies were included. Real-time quantitative polymerase chain reaction was performed to determine mRNA levels of AIM2, DAI, and TLRs (TLR-1 through TLR-9). The difference in gene expression for each sensor between CP and H tissues was calculated using analysis of covariance. The Spearman test was used to determine correlations among innate receptors. The expression of TLR-9, AIM2, and DAI in gingival tissues was further confirmed using immunohistochemistry.
RESULTS: The present results reveal statistically significant upregulation of TLR-9 (P <0.006), DAI (P <0.001), and TLR-8 (P <0.01) in CP tissues compared to H sites. Although mRNA expression was not changed significantly between groups for other receptors, the present results reveal significant correlations between receptors (P <0.05), suggesting that cooperation between multiple components of the host immune system may influence the overall response. Immunohistochemistry further confirmed expression of TLR-9, AIM2, and DAI in gingival tissues.
CONCLUSIONS: This study highlights a possible role for nucleic acid receptors in periodontal inflammation. Future investigations will determine whether cytoplasmic receptors and their ligands can be targeted to improve clinical outcomes in periodontitis.

TET2 enzymatically converts 5-methyl-cytosine to 5-hydroxymethyl-cytosine, possibly leading to loss of DNA methylation. TET2 mutations are common in myeloid leukemia and were proposed to contribute to leukemogenesis through DNA methylation. To expand on this concept, we studied chronic myelomonocytic leukemia (CMML) samples. TET2 missense or nonsense mutations were detected in 53% (16/30) of patients. In contrast, only 1/30 patient had a mutation in IDH1 or IDH2, and none of them had a mutation in DNMT3A in the sites most frequently mutated in leukemia. Using bisulfite pyrosequencing, global methylation measured by the LINE-1 assay and DNA methylation levels of 10 promoter CpG islands frequently abnormal in myeloid leukemia were not different between TET2 mutants and wild-type CMML cases. This was also true for 9 out of 11 gene promoters reported by others as differentially methylated by TET2 mutations. We found that two non-CpG island promoters, AIM2 and SP140, were hypermethylated in patients with mutant TET2. These were the only two gene promoters (out of 14,475 genes) previously found to be hypermethylated in TET2 mutant cases. However, total 5-methyl-cytosine levels in TET2 mutant cases were significantly higher than TET2 wild-type cases (median = 14.0% and 9.8%, respectively) (p = 0.016). Thus, TET2 mutations affect global methylation in CMML but most of the changes are likely to be outside gene promoters.

The development of oral squamous cell carcinoma (OSCC) is a multistep process that requires the accumulation of genetic alterations. To identify genes responsible for OSCC development, we performed high-density single nucleotide polymorphism array analysis and genome-wide gene expression profiling on OSCC tumors. These analyses indicated that the absent in melanoma 2 (AIM2) gene and the interferon-inducible gene 16 (IFI16) mapped to the hematopoietic interferon-inducible nuclear proteins. The 200-amino-acid repeat gene cluster in the amplified region of chromosome 1q23 is overexpressed in OSCC. Both AIM2 and IFI16 are cytoplasmic double-stranded DNA sensors for innate immunity and act as tumor suppressors in several human cancers. Knockdown of AIM2 or IFI16 in OSCC cells results in the suppression of cell growth and apoptosis, accompanied by the downregulation of nuclear factor kappa-light-chain-enhancer of activated B cells activation. Because all OSCC cell lines have reduced p53 activity, wild-type p53 was introduced in p53-deficient OSCC cells. The expression of wild-type p53 suppressed cell growth and induced apoptosis via suppression of nuclear factor kappa-light-chain-enhancer of activated B cells activity. Finally, the co-expression of AIM2 and IFI16 significantly enhanced cell growth in p53-deficient cells; in contrast, the expression of AIM2 and/or IFI16 in cells bearing wild-type p53 suppressed cell growth. Moreover, AIM2 and IFI16 synergistically enhanced nuclear factor kappa-light-chain-enhancer of activated B cells signaling in p53-deficient cells. Thus, expression of AIM2 and IFI16 may have oncogenic activities in the OSCC cells that have inactivated the p53 system.

Absent in Melanoma 2 (AIM2) is a member of the HIN-200 family of hematopoietic, IFN-inducible, nuclear proteins, associated with both, infection defense and tumor pathology. Recently, AIM2 was found to act as a DNA sensor in innate immunity. In addition, we and others have previously demonstrated a high frequency of AIM2-alterations in microsatellite unstable (MSI-H) tumors. To further elucidate AIM2 function in colorectal tumors, we here addressed AIM2-responsive target genes by microarray based gene expression profiling of 22 244 human genes. A total of 111 transcripts were significantly upregulated, whereas 80 transcripts turned out to be significantly downregulated in HCT116 cells, constitutively expressing AIM2, compared with AIM2-negative cells. Among the upregulated genes that were validated by quantitative PCR and western blotting we recognized several interferon-stimulated genes (ISGs: IFIT1, IFIT2, IFIT3, IFI6, IRF7, ISG15, HLA-DRA, HLA-DRB, TLR3 and CIITA), as well as genes involved in intercellular adhesion and matrix remodeling. Expression of ISGs correlated with expression of AIM2 in 10 different IFN-γ treated colorectal cancer cell lines. Moreover, small interfering RNA-mediated knock-down of AIM2 resulted in reduced expression of HLA-DRA, HLA-DRB and CIITA in IFN-γ-treated cells. IFN-γ independent induction of HLA-DR genes and their encoded proteins was also demonstrated upon doxycyclin-regulated transient induction of AIM2. Luciferase reporter assays revealed induction of the HLA-DR promoter upon AIM2 transfection in different cell lines. STAT-signaling was not involved in IFN-γ independent induction of ISGs, arguing against participation of cytokines released in an autostimulating manner. Our data indicate that AIM2 mediates both IFN-γ dependent and independent induction of several ISGs, including genes encoding the major histocompatibility complex (MHC) class II antigens HLA-DR-α and -β. This suggests a novel role of the IFN/AIM2/ISG cascade likewise in cancer cells.

High level microsatellite instability (MSI-H) occurs in about 15% of colorectal cancer (CRCs), either as sporadic cancers or in the context of hereditary non-polyposis cancer or Lynch syndrome. In MSI-H CRC, mismatch repair deficiency leads to insertion/deletion mutations at coding microsatellites and thus to the translation of frameshift peptides (FSPs). FSPs are potent inductors of T cell responses in vitro and in vivo. The present study aims at the identification of FSP-specific humoral immune responses in MSI-H CRC and Lynch syndrome. Sera from patients with history of MSI-H CRC (n = 69), healthy Lynch syndrome mutation carriers (n = 31) and healthy controls (n = 52) were analyzed for antibodies against FSPs using peptide ELISA. Reactivities were measured against FSPs derived from genes frequently mutated in MSI-H CRCs, AIM2, TGFBR2, CASP5, TAF1B, ZNF294, and MARCKS. Antibody reactivity against FSPs was significantly higher in MSI-H CRC patients than in healthy controls (P = 0.036, Mann-Whitney) and highest in patients with shortest interval between tumor resection and serum sampling. Humoral immune responses in patients were most frequently directed against FSPs derived from mutated TAF1B (11.6%, 8/69) and TGFBR2 (10.1%, 7/69). Low level FSP-specific antibodies were also detected in healthy mutation carriers. Our results show that antibody responses against FSPs are detectable in MSI-H CRC patients and healthy Lynch syndrome mutation carriers. Based on the high number of defined FSP antigens, measuring FSP-specific humoral immune responses is a highly promising tool for future diagnostic application in MSI-H cancer patients.

Approximately 15% of small intestinal adenocarcinomas show inactivation of DNA-mismatch repair (MMR) and display high-level microsatellite instability (MSI-H). MSI-H tumors progress as a result of mutations affecting coding microsatellites (coding microsatellite instability, cMSI) that may result in a functional inactivation of the encoded proteins and provide a selective growth advantage for the affected cell. To investigate the cMSI selection in small intestinal carcinogenesis 56 adenocarcinomas were tested for MSI. Eleven MSI-H carcinomas (19.6%) were identified and subjected to cMSI analysis in 24 potentially tumor relevant genes. Mutation frequencies were similar to those observed in colorectal cancer (CRC). Beside high frequencies of cMSI in TGFbetaR2, ACVR2, and AIM2 we detected MARCKS mutations in 10 out of 11 (91%) tumors with a 30% share of biallelic mutations. Since little is known about MARCKS expression in the intestine, we analyzed MARCKS protein expression in 31 carcinomas. In non-neoplastic mucosa, MARCKS was found to be expressed with a concentration gradient along the crypt-villus axis. In line with cMSI induced functional inactivation of MARCKS, 8 out of 11 MSI-H adenocarcinomas showed regional or complete loss of the protein. In microsatellite stable (MSS) small bowel adenocarcinoma, loss of MARCKS expression was seen in 2 out of 20 tumors (10%). In conclusion, we herein present a cMSI profile of MSI-H small intestinal adenocarcinomas identifying MARCKS as a frequent target of mutation. Loss of MARCKS protein expression suggests a significant role of MARCKS inactivation in the pathogenesis of small intestinal adenocarcinomas.

Absent in melanoma 2 (AIM2) is a member of the interferon-inducible HIN-200 protein family. Recent findings point to a role of AIM2 function in both inflammation and cancer. In response to foreign cytoplasmic DNA, AIM2 forms an inflammasome, resulting in caspase activation in inflammatory cells. Moreover, AIM2 reduces breast cancer cell proliferation and mammary tumor growth in a mouse model and shows a high frequency of frameshift mutations in microsatellite unstable (MSI-H) gastric, endometrial and colorectal cancers. However, the consequences of AIM2 restoration in AIM2-deficient colon cancer cells have not yet been examined. Using different constructs for expression of AIM2 fusion proteins, we found that AIM2 restoration clearly suppressed cell proliferation and viability in HCT116 cells as well as in cell lines derived from other entities. In contrast to previous reports from breast cancer cells, our cell cycle analyses of colon cancer cells revealed that AIM2-mediated inhibition of cell proliferation is associated with accumulation of cells at late S-phase, resulting in G2/M arrest. The latter correlated well with upregulation of cyclin D3 and p21(Waf1/Cip1) as well as with inhibition of cdc2 activity through Tyr-15 phosphorylation. Furthermore, AIM2 restoration affected the adhesion of colorectal cancer cells to fibronectin and stimulated the invasion through extracellular matrix-coated membrane in transwell assays. Consistent with this phenotype, AIM2 induced the expression of invasion-associated genes such as VIM and MCAM, whereas ANXA10 and CDH1 were downregulated. Our data suggest that AIM2 mediates reduction of cell proliferation by cell cycle arrest, thereby conferring an invasive phenotype in colon cancer cells.

Tumors that display a high level of microsatellite instability (MSI-H) accumulate somatic frameshift mutations in several genes. The compensation of this loss of function by transfection represents a suitable approach to tie respective gene deficiency to alterations in cellular characteristics. In view of the emerging significance of cell surface glycans as biochemical signals for presentation/activity of various receptors/integrins and for susceptibility to adhesion/growth-regulatory tissue lectins, we examined the glycophenotype in the MSI-H colon cancer cell line HCT116 for activin type 2 receptor (ACVR2), absent in melanoma 2 (AIM2), and transforming growth factor beta-type 2 receptor (TGFBR2) known to be associated with MSI colorectal carcinogenesis. A panel of probes specific for functional carbohydrate epitopes including human lectins was used to trace changes in cell surface levels, thereby initiating glycan analysis related to MSI. In particular, the presence of core substitutions and branching in N-glycans, the sialylation status of N- and O-glycans, and the presence of Le(a/x)-epitopes were profiled. Transient transfection affected the glycophenotype, depending on the nature of the gene and the probe. The TGFBR2 presence reduced binding of probes specific for a core substitution and increased branch length in N-glycosylation, even reaching a P-value of 0.0016. ACVR2/AIM2 influenced core 1 mucin-type O-glycosylation differentially, upregulation by ACVR2, and downregulation by AIM2. These alterations of cell surface glycosylation by gene products that are not directly associated with the machinery for glycan generation direct attention to pursue analysis of glycosylation in MSI tumor cells on the level of target glycoproteins and open the way for functional studies.

Interferon-inducible IFI16 protein (encoded by IFI16 gene located at 1q21 region) is a member of the p200-protein family. The family includes structurally and functionally-related mouse (for example, p202, p203, and p204 proteins) and human (for example, MNDA, AIM2, and IFIX) proteins. Increased expression of p200-family proteins in a variety of cells is known to inhibit cell cycle progression and modulate cell survival. Consistent with this role of p200-family proteins, increased expression of IFI16 protein in normal human diploid fibroblasts and prostate epithelial cells is associated with cellular senescence-associated permanent cell growth arrest. Furthermore, reduced or loss of IFI16 expression in cells is associated with the development of certain cancers, such as breast and prostate cancer. Interestingly, recent studies have provided evidence that the constitutive and interferon-induced expression of the IFI16 gene varies among individuals and may depend on the race. These studies raise the possibility that alterations (increases or decreases) in the expression of IFI16 protein may contribute to the development of human diseases. In this review, we discuss how our understanding of the regulation of IFI16 expression and its role in cell growth regulation will help elucidate the molecular mechanisms that contribute to the development of various human diseases.

Mismatch repair (MMR) deficiency is a major mechanism of colorectal tumorigenesis that is observed in 10-15% of sporadic colorectal cancers and those associated with the hereditary nonpolyposis colorectal cancer (HNPCC) syndrome. MMR deficiency leads to the accumulation of mutations mainly at short repetitive sequences termed microsatellites, constituting the high level microsatellite instability (MSI-H) phenotype. In recent years, several genes have been described that harbor microsatellites in their coding region (coding microsatellites, cMS) and are frequently affected by mutations in MMR-deficient cancers. However, evidence for a functional role of most of the known cMS-containing genes is missing, and further analyses are needed for a better understanding of MSI tumorigenesis. Here, we examined in detail alterations of the absent in melanoma 2 (AIM2) gene that shows a high frequency of cMS frameshift mutations in MSI-H colorectal, gastric, and endometrial tumors. AIM2 belongs to the HIN-200 family of interferon (IFN)-inducible proteins, its role in colon carcinogenesis, however, is unknown. Sequencing of the entire coding region of AIM2 revealed a high frequency of frameshift and missense mutations in primary MSI-H colon cancers (9/20) and cell lines (9/15). Biallelic AIM2 alterations were detected in 8 MSI-H colon tumors and cell lines. In addition, AIM2 promoter hypermethylation conferred insensitivity to IFN-gamma-induced AIM2 expression of three MSI-H colon cancer cell lines. These results demonstrate that inactivation of AIM2 by genetic and epigenetic mechanisms is frequent in MMR-deficient colorectal cancers, thus suggesting that AIM2 is a mutational target relevant for the progression of MSI-H colorectal cancers.