NLRP3 suppresses NK cell-mediated responses to carcinogen-induced tumors and metastases

Caspase-1 from Human Myeloid-Derived Suppressor Cells Can Promote T Cell-Independent Tumor Proliferation

Immunosuppressive myeloid-derived suppressive cells (MDSCs) are characterized by their phenotypic and functional heterogeneity. To better define their T cell-independent functions within the tumor, sorted monocytic CD14⁺CD11b⁺HLA-DR^low/- MDSCs (mMDSC) from squamous cell carcinoma patients showed upregulated caspase-1 activity, which was associated with increased IL1β and IL18 expression. In vitro studies demonstrated that mMDSCs promoted caspase-1-dependent proliferation of multiple squamous carcinoma cell lines in both human and murine systems. In vivo, growth rates of B16, MOC1, and Panc02 were significantly blunted in chimeric mice adoptively transferred with caspase-1 null bone marrow cells under T cell-depleted conditions. Adoptive transfer of wild-type Gr-1⁺CD11b⁺ MDSCs from tumor-bearing mice reversed this antitumor response, whereas caspase-1 inhibiting thalidomide-treated MDSCs phenocopied the antitumor response found in caspase-1 null mice. We further hypothesized that MDSC caspase-1 activity could promote tumor-intrinsic MyD88-dependent carcinogenesis. In mice with wild-type caspase-1, MyD88-silenced tumors displayed reduced growth rate, but in chimeric mice with caspase-1 null bone marrow cells, MyD88-silenced tumors did not display differential tumor growth rate. When we queried the TCGA database, we found that caspase-1 expression is correlated with overall survival in squamous cell carcinoma patients. Taken together, our findings demonstrated that caspase-1 in MDSCs is a direct T cell-independent mediator of tumor proliferation. Cancer Immunol Res; 6(5); 566-77. ©2018 AACR.

The inflammasome: an emerging therapeutic oncotarget for cancer prevention

Deregulated inflammation is considered to be one of the hallmarks of cancer initiation and development regulation. Emerging evidence indicates that the inflammasome plays a central role in regulating immune cells and cytokines related to cancer. The inflammasome is a multimeric complex consisting of NOD-like receptors (NLRs) and responds to a variety of endogenous (damage-associated molecular patterns) and exogenous (pathogen-associated molecular patterns) stimuli. Several lines of evidence suggests that in cancer the inflammasome is positively associated with characteristics such as elevated levels of IL-1β and IL-18, activation of NF-κB signaling, enhanced mitochondrial oxidative stress, and activation of autophagic process. A number of NLRs, such as NLRP3 and NLRC4 are also highlighted in carcinogenesis and closely correlate to chemoresponse and prognosis. Although conflicting evidence suggested the duplex role of inflammasome in cancer development, the phenomenon might be attributed to NLRs difference, cell and tissue type, cancer stage, and specific experimental conditions. Given the promising role of inflammasome in mediating cancer development, precise elucidation of its signaling network and pathological significance may lead to novel therapeutic options for malignancy therapy and prevention.

Inflammasome and Cancer

The current chapter focuses on the role of inflammasome in cancer prevention and development. Emerging evidence suggested that inflammasome is closely correlated with elevated levels of IL-1β and IL-18, activation of NF-κB signaling, enhanced mitochondrial oxidative stress, and activation of autophagic process in cancer. Meanwhile, inflammasome component NOD-like receptors (NLRs) are also involved in carcinogenesis and closely correlated to chemoresponse and prognosis. Although several lines indicated the duplex role of inflammasome in cancer development, the phenomenon might be attributed to NLR difference, cell and tissue type, cancer stage, and specific experimental conditions. Designation of inflammasome targeting strategy has become a novel tool for cancer prevention or treatment.

Inflammasome Adaptor ASC Suppresses Apoptosis of Gastric Cancer Cells by an IL18-Mediated Inflammation-Independent Mechanism

Inflammasomes are key regulators of innate immunity in chronic inflammatory disorders and autoimmune diseases, but their role in inflammation-associated tumorigenesis remains ill-defined. Here we reveal a protumorigenic role in gastric cancer for the key inflammasome adaptor apoptosis-related speck-like protein containing a CARD (ASC) and its effector cytokine IL18. Genetic ablation of ASC in the gp130^F/F spontaneous mouse model of intestinal-type gastric cancer suppressed tumorigenesis by augmenting caspase-8-like apoptosis in the gastric epithelium, independently from effects on myeloid cells and mucosal inflammation. This phenotype was characterized by reduced activation of caspase-1 and NF-κB activation and reduced expression of mature IL18, but not IL1β, in gastric tumors. Genetic ablation of IL18 in the same model also suppressed gastric tumorigenesis, whereas blockade of IL1β and IL1α activity upon genetic ablation of the IL1 receptor had no effect. The specific protumorigenic role for IL18 was associated with high IL18 gene expression in the gastric tumor epithelium compared with IL1β, which was preferentially expressed in immune cells. Supporting an epithelial-specific role for IL18, we found it to be highly secreted from human gastric cancer cell lines. Moreover, IL18 blockade either by a neutralizing anti-IL18 antibody or by CRISPR/Cas9-driven deletion of ASC augmented apoptosis in human gastric cancer cells. In clinical specimens of human gastric cancer tumors, we observed a significant positive correlation between elevated mature IL18 protein and ASC mRNA levels. Collectively, our findings reveal the ASC/IL18 signaling axis as a candidate therapeutic target in gastric cancer.Significance: Inflammasome activation that elevates IL18 helps drive gastric cancer by protecting cancer cells against apoptosis, with potential implications for new therapeutic strategies in this setting. Cancer Res; 78(5); 1293-307. ©2017 AACR.

Complement Receptor 3 Has Negative Impact on Tumor Surveillance through Suppression of Natural Killer Cell Function

Complement receptor 3 (CR3) is expressed abundantly on natural killer (NK) cells; however, whether it plays roles in NK cell-dependent tumor surveillance is largely unknown. Here, we show that CR3 is an important negative regulator of NK cell function, which has negative impact on tumor surveillance. Mice deficient in CR3 (CD11b^-/- mice) exhibited a more activated NK phenotype and had enhanced NK-dependent tumor killing. In a B16-luc melanoma-induced lung tumor growth and metastasis model, mice deficient in CR3 had reduced tumor growth and metastases, compared with WT mice. In addition, adaptive transfer of NK cells lacking CR3 (into NK-deficient mice) mediated more efficient suppression of tumor growth and metastases, compared with the transfer of CR3 sufficient NK cells, suggesting that CR3 can impair tumor surveillance through suppression of NK cell function. In vitro analyses showed that engagement of CR3 with iC3b (classical CR3 ligand) on NK cells negatively regulated NK cell activity and effector functions (i.e. direct tumor cell killing, antibody-dependent NK-mediated tumor killing). Cell signaling analyses showed that iC3b stimulation caused activation of Src homology 2 domain-containing inositol-5-phosphatase-1 (SHIP-1) and JNK, and suppression of ERK in NK cells, supporting that iC3b mediates negative regulation of NK cell function through its effects on SHIP-1, JNK, and ERK signal transduction pathways. Thus, our findings demonstrate a previously unknown role for CR3 in dysregulation of NK-dependent tumor surveillance and suggest that the iC3b/CR3 signaling is a critical negative regulator of NK cell function and may represent a new target for preserving NK cell function in cancer patients and improving NK cell-based therapy.

MiR-22 sustains NLRP3 expression and attenuates H. pylori-induced gastric carcinogenesis

Chronic inflammation is the primary cause of gastric cancer (GC). NLRP3, as an important inflammasome component, has crucial roles in initiating inflammation. However, the potential roles of NLRP3 in GC is unknown. Here, we show that NLRP3 expression is markedly upregulated in GC, which promotes NLRP3 inflammasome activation and interleukin-1β (IL-1β) secretion in macrophages. In addition, NLRP3 binds to cyclin-D1 (CCND1) promoter and promotes its transcription in gastric epithelial cells. Consequently, NLRP3 enhances epithelial cells proliferation and GC tumorigenesis. Furthermore, we identify miR-22, which is constitutively expressed in gastric mucosa, as a suppressor of NLRP3. MiR-22 directly targets NLRP3 and attenuates its oncogenic effects in vitro and in vivo. However, Helicobacter pylori (H. pylori) infection suppresses miR-22 expression, while enhances NLRP3 expression, and that triggers uncontrolled proliferation of epithelial cells and the emergence of GC. Thus, our research describes a mechanism by which miR-22 suppresses NLRP3 and maintains homeostasis of gastric microenvironments and suggests miR-22 as a potential target for the intervention of GC.

NLRP3 inflammasome activation plays a carcinogenic role through effector cytokine IL-18 in lymphoma

Inflammasomes play important roles in the pathogenesis of tumors, but the roles of NLRP3 inflammasome in the lymphoma remain unclear. Activated NLRP3 inflammasome induces the maturation of its effector cytokine IL-18 which functions in the development of cancer. Here, we investigated the polymorphism and expression of NLRP3 inflammasome related genes and explored their function in lymphoma. We found that IL-18 (rs1946518) and NFκB94 ins/del (rs28362491) contributed to lymphoma susceptibility and allele G in IL-18 was significantly associated with the risk of lymphoma. The mRNA and plasma expression levels of IL-18 were significantly elevated in primary lymphoma patients and decreased after remission. NLRP3 inflammasome could be activated by ATP plus LPS in lymphoma cells accompanied with the increasing expression of NLRP3-related genes. NLRP3 inflammasome activation reduced the dexamethasone-induced proliferation-inhibiting effect by promoting cells into S phase. NLRP3 inflammasome activation promoted lymphoma cells proliferation and inhibited apoptosis through up-regulation of c-myc and bcl-2, and down-regulation of TP53 and bax, and then reduced the anti-tumor effect of dexamethasone. Similar with the activation of NLRP3, the effector cytokine IL-18 also had the proliferation-promoting, apoptosis-inhibiting and resistance-reducing effects on lymphoma cells via shifting the balance of c-myc/TP53 and bcl-2/bax. Moreover, neutralizing IL-18 has the opposite effects. In conclusion, NLRP3 inflammasome contributes to the susceptibility and plays a carcinogenic role through its effector cytokine IL-18 in lymphoma.

Control of Metastasis by NK Cells

The metastatic spread of malignant cells to distant anatomical locations is a prominent cause of cancer-related death. Metastasis is governed by cancer-cell-intrinsic mechanisms that enable neoplastic cells to invade the local microenvironment, reach the circulation, and colonize distant sites, including the so-called epithelial-to-mesenchymal transition. Moreover, metastasis is regulated by microenvironmental and systemic processes, such as immunosurveillance. Here, we outline the cancer-cell-intrinsic and -extrinsic factors that regulate metastasis, discuss the key role of natural killer (NK) cells in the control of metastatic dissemination, and present potential therapeutic approaches to prevent or target metastatic disease by harnessing NK cells.

Immunological Consequences of Epithelial-Mesenchymal Transition in Tumor Progression

Microenvironments that tumor cells encounter are different during the stages of cancer progression-primary tumor, metastasis, and at the metastatic site. This suggests potential differences in immune surveillance of primary tumor and metastasis. Epithelial-mesenchymal transition (EMT) is a key reversible process in which cancer cells transition into highly motile and invasive cells for dissemination. Only a tiny proportion successfully metastasize, supporting the notion of metastasis-specific immune surveillance. EMT involves extensive molecular reprogramming of cells conferring many clinically relevant features to cancer cells and affects tumor cell interactions within the tumor microenvironment. We review the impact of tumor immune infiltrates on tumor cell EMT and the consequences of EMT in shaping the immune microenvironment of tumors. The usefulness of EMT as a model to investigate metastasis-specific immune surveillance mechanisms are also explored. Finally, we discuss potential implications of EMT for tumor immunogenicity, as well as current immunotherapies and future strategies.

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.

Inflammasome as a Therapeutic Target for Cancer Prevention and Treatment

Chronic inflammation is a critical modulator of carcinogenesis through secretion of inflammatory cytokines, which leads to the formation of an inflammatory microenvironment. In this process, the inflammasome plays an important role in the expression and activation of interleukin (IL)-1β and IL-18 to promote cancer development. The inflammasome is a multiprotein complex consisting of several nucleotide-binding domain and leucine-rich repeat containing receptor, adaptor proteins, and caspase 1 (CASP1). It senses the various intracellular (damage-associated molecular patterns) and extracellular (pathogen-associated molecular patterns) stimuli. A primed inflammasome recruits adaptor proteins, activates CASP1 to enhance the proteolytic cleavage of pro-IL-1β and IL-18, and sends the signal to respond to each insult. Depending on stimuli and cell contexts, several inflammasomes are closely associated with the initiation and promotion of carcinogenesis. In contrast, inflammasomes also show an ambivalent effect on carcinogenesis by enhancing inflammatory cell death (pyroptosis) and repairing damaged tissues. Although the inflammasome plays a controversial role in carcinogenesis, it may be a promising target for human cancer prevention and treatment. A more in-depth study on the role of the inflammasome in carcinogenesis, based on stimuli, cell contexts, and cancer stages, can lead to the development of novel therapeutic strategies against malignant human cancers.

The role of NLRP3 inflammasome in 5-fluorouracil resistance of oral squamous cell carcinoma

Background

5-Fluorouracil (5-FU) is a widely used drug for the therapy of cancer. However, the chemoresistance of tumor cells to 5-FU usually limits its clinical effectiveness. In this study, we explored the role of NLRP3 inflammasome in 5-FU resistance of oral squamous cell carcinoma (OSCC).

Methods

The mRNA and protein expression levels of NLRP3, Caspase1 and IL-1β in resected OSCC specimens or cell lines were measured respectively by quantitative real time-PCR (qRT-PCR) and western blot. NLRP3 and Ki-67 expression in paraffin-embedded OSCC tissues was determined by immunohistochemistry. The correlation between 5-FU treatment and the expression and activation of NLRP3 inflammasome was further examined by evaluating NLRP3 and IL-1β expression in OSCC cell lines without or with NLRP3 knocked down. Cell viabilities of OSCC cells were determined by the MTT assay. Apoptosis and intracellular reactive oxygen species (ROS) of OSCC cells induced by 5-FU were measured by the flow cytometer. The carcinogen-induced tongue squamous carcinoma mice model was established by continuous oral administration of 4-nitroquinoline 1-oxide in wild-type BALB/c, Nlrp3^−/− and Caspase1^−/− mice. Tumor incidence were observed and tumor area were evaluated.

Results

In the clinical analysis, expression and activation of NLRP3 inflammasome was clearly increased in OSCC tissues of patients who received 5-FU-based chemotherapy. Multivariate Cox regression analysis revealed that this high expression was significantly correlated with tumor stage and differentiation, and was associated with poor prognosis. Moreover, 5-FU treatment increased expression and activation of NLRP3 inflammasome in OSCC cells in a cell culture system and xenograft mouse model. Silencing of NLRP3 expression significantly inhibited OSCC cell proliferation and enhanced 5-FU-induced apoptosis of OSCC cells. Further investigation showed that intracellular ROS induced by 5-FU promoted the expression and activation of NLRP3 inflammasome and increased the production of interleukin (IL)-1β, which then mediated the chemoresistance. With the carcinogen-induced OSCC model, we found less and later tumor incidence in Nlrp3^−/− and Caspase1^−/− mice than wild-type mice. And greater decrease of tumor area was observed in the gene deficient mice treated with 5-FU.

Conclusions

Our findings suggest that NLRP3 inflammasome promoted 5-FU resistance of OSCC both in vitro and in vivo, and targeting the ROS/NLRP3 inflammasome/IL-1β signaling pathway may help 5-FU-based adjuvant chemotherapy of OSCC.

The inhibition of NLRP3 signaling attenuates liver injury in an α-galactosylceramide-induced hepatitis model

Inflammasomes are involved in innate immune responses. Several NOD-Like receptors (NLRs) participate in the formation of inflammasomes. NACHT, LRR and PYD domains-containing protein 3 (NALP3) belongs to the NLR family and recognizes adenosine triphosphate (ATP), crystals, and Reactive Oxygen Species (ROS). This study examined the effect of inflammasomes on alpha-galactosylceramide (GalCer)-induced liver injury using NALP3-knockout (KO) mice. GalCer administration induced inflammasome activation and IL-1β-maturation. In NALP3-KO mice treated with GalCer, serum ALT levels were significantly reduced compared with those in GalCer-treated WT mice. Histological examination revealed decreased necrosis in NALP3-KO mice compared with WT mice, consistent with ALT levels. Expression of proinflammatory cytokines (such as IL-6, and TNF-α) and chemokines was also significantly suppressed in NALP3-KO mice. Moreover, flow cytometry analysis revealed fewer infiltrating immune cells in the livers of GalCer-treated NALP3-KO mice. Inportantly, the frequency of MDSCs (CD11b⁺Gr-1^int cells), which suppress the immune response, was significantly increased in GalCer-treated NALP3-KO mice. In conclusion, NALP3 inhibition attenuated liver injury in GalCer-induced hepatitis. The inhibition of NALP3 signaling coused be a therapeutic target in immune-mediated liver injury.

NLRP1 promotes tumor growth by enhancing inflammasome activation and suppressing apoptosis in metastatic melanoma

Inflammasomes are mediators of inflammation, and constitutively activated NLRP3 inflammasomes have been linked to IL-1β-mediated tumorigenesis in human melanoma. Whereas NLRP3 regulation of caspase-1 activation requires the adaptor protein ASC, caspase-1 activation by another danger-signaling sensor NLRP1 does not require ASC because NLRP1 contains a C-terminal CARD domain that facilitates direct caspase-1 activation via CARD-CARD interaction. We hypothesized that NLRP1 has additional biological activities besides IL-1β maturation and investigated its role in melanoma tumorigenesis. NLRP1 expression in melanoma was confirmed by analysis of 216 melanoma tumors and 13 human melanoma cell lines. Unlike monocytic THP-1 cells with prominent nuclear localization of NLRP1, melanoma cells expressed NLRP1 mainly in the cytoplasm. Knocking down NLRP1 revealed a tumor promoting property of NLRP1 both in vitro and in vivo. Mechanistic studies showed that caspase-1 activity, IL-1β production, IL-1β secretion, and NF-kB activity were reduced by knocking down of NLRP1 in human metastatic melanoma cell lines 1205Lu and HS294T, indicating that NLRP1 inflammasomes are active in metastatic melanoma. However, unlike previous reports showing that NLRP1 enhances pyroptosis in macrophages, NLRP1 in melanoma behaved differently in the context of cell death. Knocking down NLRP1 increased caspase-2, -9, and -3/7 activities and promoted apoptosis in human melanoma cells. Immunoprecipitation revealed interaction of NLRP1 with CARD-containing caspase-2 and -9, whereas NLRP3 lacking a CARD motif did not interact with the caspases. Consistent with these findings, NLRP1 activation but not NLRP3 activation reduced caspase-2, -9, and -3/7 activities and provided protection against apoptosis in human melanoma cells, suggesting a suppressive role of NLRP1 in caspase-3/7 activation and apoptosis via interaction with caspase-2 and -9. In summary, we showed that NLRP1 promotes melanoma growth by enhancing inflammasome activation and suppressing apoptotic pathways. Our study demonstrates a tumor-promoting role of NLRP1 in cancer cells.

Inflammasomes and Cancer

Inflammation affects all stages of tumorigenesis. A key signaling pathway leading to acute and chronic inflammation is through activation of the caspase-1 inflammasome. Inflammasome complexes are assembled on activation of certain nucleotide-binding domain, leucine-rich repeat-containing proteins (NLR), AIM2-like receptors, or pyrin. Of these, NLRP1, NLRP3, NLRC4, NLRP6, and AIM2 influence the pathogenesis of cancer by modulating innate and adaptive immune responses, cell death, proliferation, and/or the gut microbiota. Activation of the inflammasome and IL18 signaling pathways is largely protective in colitis-associated colorectal cancer, whereas excessive inflammation driven by the inflammasome or the IL1 signaling pathways promotes breast cancer, fibrosarcoma, gastric carcinoma, and lung metastasis in a context-dependent manner. The clinical relevance of inflammasomes in multiple forms of cancer highlights their therapeutic promise as molecular targets. In this review, we explore the crossroads between inflammasomes and the development of various tumors and discuss possible therapeutic values in targeting the inflammasome for the prevention and treatment of cancer. Cancer Immunol Res; 5(2); 94-99. ©2017 AACR.

Proteoglycan neofunctions: regulation of inflammation and autophagy in cancer biology

Inflammation and autophagy have emerged as prominent issues in the context of proteoglycan signaling. In particular, two small, leucine-rich proteoglycans, biglycan and decorin, play pivotal roles in the regulation of these vital cellular pathways and, as such, are intrinsically involved in cancer initiation and progression. In this minireview, we will address novel functions of biglycan and decorin in inflammation and autophagy, and analyze new emerging signaling events triggered by these proteoglycans, which directly or indirectly modulate these processes. We will critically discuss the dual role of proteoglycan-driven inflammation and autophagy in tumor biology, and delineate the potential mechanisms through which soluble extracellular matrix constituents affect the microenvironment associated with inflammatory and neoplastic diseases.

Dietary Emulsifier-Induced Low-Grade Inflammation Promotes Colon Carcinogenesis

The increased risks conferred by inflammatory bowel disease (IBD) to the development of colorectal cancer gave rise to the term "colitis-associated cancer" and the concept that inflammation promotes colon tumorigenesis. A condition more common than IBD is low-grade inflammation, which correlates with altered gut microbiota composition and metabolic syndrome, both present in many cases of colorectal cancer. Recent findings suggest that low-grade inflammation in the intestine is promoted by consumption of dietary emulsifiers, a ubiquitous component of processed foods, which alter the composition of gut microbiota. Here, we demonstrate in a preclinical model of colitis-induced colorectal cancer that regular consumption of dietary emulsifiers, carboxymethylcellulose or polysorbate-80, exacerbated tumor development. Enhanced tumor development was associated with an altered microbiota metagenome characterized by elevated levels of lipopolysaccharide and flagellin. We found that emulsifier-induced alterations in the microbiome were necessary and sufficient to drive alterations in major proliferation and apoptosis signaling pathways thought to govern tumor development. Overall, our findings support the concept that perturbations in host-microbiota interactions that cause low-grade gut inflammation can promote colon carcinogenesis. Cancer Res; 77(1); 27-40. ©2016 AACR.

Transcriptional regulation of inflammasome-associated pattern recognition receptors, and the relevance to disease pathogenesis

Over the last decade it has emerged that inflammasome complexes provide a pivotal platform for the host innate immune system to respond to exogenous infectious microbes (viruses, bacteria, fungi) and non-infectious environmental agents (cigarette smoke, pollution), as well as endogenous "danger" signals. Upon the canonical activation of inflammasomes, a key effector function is to catalyze, via caspase-1, the maturation of the potent pro-inflammatory cytokines interleukin (IL)-1β and IL-18, which, in addition to chronic inflammatory responses have also been intimately linked to the inflammatory form of lytic cell death, pyroptosis. However, recent evidence suggests that inflammasomes exhibit marked pleiotropism beyond their canonical functions, whereby their activation can also influence a large number of cellular responses including proliferation, apoptosis, autophagy and metabolism. It is therefore not surprising that the dysregulated expression and/or activation of inflammasomes is increasingly implicated in numerous disease states, such as chronic auto-inflammatory and autoimmune disorders, metabolic syndrome, neurodegenerative and cardiovascular diseases, as well as cancer. In this review we will highlight recent advancements in our understanding of the transcriptional regulation of genes encoding inflammasome-associated innate immune receptors, and the impact on a variety of cellular responses during disease pathogenesis.

Improved Efficacy of Neoadjuvant Compared to Adjuvant Immunotherapy to Eradicate Metastatic Disease

Immunotherapy has recently entered a renaissance phase with the approval of multiple agents for the treatment of cancer. Immunotherapy stands ready to join traditional modalities, including surgery, chemotherapy, radiation, and hormone therapy, as a pillar of cancer treatment. Although immunotherapy has begun to have success in advanced cancer treatment, its scheduling and efficacy with surgery to treat earlier stages of cancer and prevent distant metastases have not been systematically examined. Here, we have used two models of spontaneously metastatic breast cancers in mice to illustrate the significantly greater therapeutic power of neoadjuvant, compared with adjuvant, immunotherapies in the context of primary tumor resection. Elevated and sustained peripheral tumor-specific immune responses underpinned the outcome, and blood sampling of tumor-specific CD8⁺ T cells immediately prior to and post surgery may provide a predictor of outcome. These data now provide a strong rationale to extensively test and compare neoadjuvant immunotherapy in humans.

SIGNIFICANCE

We demonstrate the significantly greater therapeutic efficacy of neoadjuvant, compared with adjuvant, immunotherapies to eradicate distant metastases following primary tumor resection. Elevated and sustained peripheral tumor-specific immune responses underpinned the outcome, and blood sampling of tumor-specific CD8⁺ T cells immediately prior to and post surgery may provide a predictor of outcome. Cancer Discov; 6(12); 1382-99. ©2016 AACR.See related commentary by Melero et al., p. 1312This article is highlighted in the In This Issue feature, p. 1293.

Recent Advances of the NLRP3 Inflammasome in Central Nervous System Disorders

Inflammasomes are multiprotein complexes that trigger the activation of caspases-1 and subsequently the maturation of proinflammatory cytokines interleukin-1β and interleukin-18. These cytokines play a critical role in mediating inflammation and innate immunity response. Among various inflammasome complexes, the NLRP3 inflammasome is the best characterized, which has been demonstrated as a crucial role in various diseases. Here, we review recently described mechanisms that are involved in the activation and regulation of NLRP3 inflammasome. In addition, we summarize the recent researches on the role of NLRP3 inflammasome in central nervous system (CNS) diseases, including traumatic brain injury, ischemic stroke and hemorrhagic stroke, brain tumor, neurodegenerative diseases, and other CNS diseases. In conclusion, the NLRP3 inflammasome may be a promising therapeutic target for these CNS diseases.

Decreased NK-cell tumour immunosurveillance consequent to JAK inhibition enhances metastasis in breast cancer models

The JAK/STAT pathway is an attractive target for breast cancer therapy due to its frequent activation, and clinical trials evaluating JAK inhibitors (JAKi) in advanced breast cancer are ongoing. Using patient biopsies and preclinical models of breast cancer, we demonstrate that the JAK/STAT pathway is active in metastasis. Unexpectedly, blocking the pathway with JAKi enhances the metastatic burden in experimental and orthotopic models of breast cancer metastasis. We demonstrate that this prometastatic effect is due to the immunosuppressive activity of JAKi with ensuing impairment of NK-cell-mediated anti-tumour immunity. Furthermore, we show that immunostimulation with IL-15 overcomes the enhancing effect of JAKi on metastasis formation. Our findings highlight the importance of evaluating the effect of targeted therapy on the tumour environment. The impact of JAKi on NK cells and the potential value of immunostimulators to overcome the weakened tumour immunosurveillance, are worthwhile considering in the clinical setting of breast cancer.

JAK inhibitors are currently undergoing evaluation in clinical trials for advanced breast cancer. Here, the authors show that JAK pathway inhibition increases metastasis in mouse models of breast cancer by impairing NK anti-tumour activity and that these side effects can be overcome by addition of IL-15.

From Inflammation to Prostate Cancer: The Role of Inflammasomes

Inflammation-associated studies entice specific attention due to inflammation's role in multiple stages of prostate cancer development. However, mechanistic regulation of inflammation inciting prostate cancer remains largely uncharacterized. A focused class of inflammatory regulators known as inflammasomes has recently gained attention in cancer development. Inflammasomes are a multiprotein complex that drives a cascade of proinflammatory cytokines regulating various cellular activities. Inflammasomes activation is linked with infection, stress, or danger signals, which are common events within the prostate gland. In this study, we review the potential of inflammasomes in understanding the role of inflammation in prostate cancer.

Mouse Models of Tumor Immunotherapy

Immunotherapy is now evolving into a major therapeutic option for cancer patients. Such clinical advances also promote massive interest in the search for novel immunotherapy targets, and to understand the mechanism of action of current drugs. It is projected that a series of novel immunotherapy agents will be developed and assessed for their therapeutic activity. In light of this, in vivo experimental mouse models that recapitulate human malignancies serve as valuable tools to validate the efficacy and safety profile of immunotherapy agents, before their transition into clinical trials. In this review, we will discuss the major classes of experimental mouse models of cancer commonly used for immunotherapy assessment and provide examples to guide the selection of appropriate models. We present some new data concerning the utility of a carcinogen-induced tumor model for comparing immunotherapies and combining immunotherapy with chemotherapy. We will also highlight some recent advances in experimental modeling of human malignancies in mice that are leading towards personalized therapy in patients.

Bench to bedside: NK cells and control of metastasis

Natural killer (NK) cells play a critical role in host immune responses against tumor growth and metastasis. The numerous mechanisms used by NK cells to regulate and control cancer metastasis include interactions with tumor cells via specific receptors and ligands as well as direct cytotoxicity and cytokine-induced effector mechanisms. NK cells also play a role in tumor immunosurveillance and inhibition of metastases formation by recognition and killing of tumor cells. In this review, we provide an overview of the molecular mechanisms of NK cell responses against tumor metastases and discuss multiple strategies by which tumors evade NK cell-mediated surveillance. With an increasing understanding of the molecular mechanisms driving NK cell activity, there is a growing potential for the development of new cancer immunotherapies. Here we provide a historical background on NK cell-based therapies and discuss the implications of recent and ongoing clinical trials using novel NK cell-based immunotherapy.

Transcriptional regulation of myeloid-derived suppressor cells

Myeloid-derived suppressor cells are a heterogeneous group of pathologically activated immature cells that play a major role in the negative regulation of the immune response in cancer, autoimmunity, many chronic infections, and inflammatory conditions, as well as in the regulation of tumor angiogenesis, tumor cell invasion, and metastases. Accumulation of myeloid-derived suppressor cells is governed by a network of transcriptional regulators that could be combined into 2 partially overlapping groups: factors promoting myelopoiesis and preventing differentiation of mature myeloid cells and factors promoting pathologic activation of myeloid-derived suppressor cells. In this review, we discuss the specific nature of these factors and their impact on myeloid-derived suppressor cell development.

Resveratrol inhibits NLRP3 inflammasome activation by preserving mitochondrial integrity and augmenting autophagy

The NLRP3 inflammasome is a caspase-1-containing multi-protein complex that controls the release of IL-1β and plays important roles in the development of inflammatory disease. Here, we report that resveratrol, a polyphenolic compound naturally produced by plants, inhibits NLRP3 inflammasome-derived IL-1β secretion and pyroptosis in macrophages. Resveratrol inhibits the activation step of the NLRP3 inflammasome by suppressing mitochondrial damage. Resveratrol also induces autophagy by activating p38, and macrophages treated with an autophagy inhibitor are resistant to the suppressive effects of resveratrol. In addition, resveratrol administration mitigates glomerular proliferation, glomerular sclerosis, and glomerular inflammation in a mouse model of progressive IgA nephropathy. These findings were associated with decreased renal mononuclear leukocyte infiltration, reduced renal superoxide anion levels, and inhibited renal NLRP3 inflammasome activation. Our data indicate that resveratrol suppresses NLRP3 inflammasome activation by preserving mitochondrial integrity and by augmenting autophagy.

NK cells require IL-28R for optimal in vivo activity

Natural killer (NK) cells are naturally circulating innate lymphoid cells that protect against tumor initiation and metastasis and contribute to immunopathology during inflammation. The signals that prime NK cells are not completely understood, and, although the importance of IFN type I is well recognized, the role of type III IFN is comparatively very poorly studied. IL-28R-deficient mice were resistant to LPS and cecal ligation puncture-induced septic shock, and hallmark cytokines in these disease models were dysregulated in the absence of IL-28R. IL-28R-deficient mice were more sensitive to experimental tumor metastasis and carcinogen-induced tumor formation than WT mice, and additional blockade of interferon alpha/beta receptor 1 (IFNAR1), but not IFN-γ, further enhanced metastasis and tumor development. IL-28R-deficient mice were also more susceptible to growth of the NK cell-sensitive lymphoma, RMAs. Specific loss of IL-28R in NK cells transferred into lymphocyte-deficient mice resulted in reduced LPS-induced IFN-γ levels and enhanced tumor metastasis. Therefore, by using IL-28R-deficient mice, which are unable to signal type III IFN-λ, we demonstrate for the first time, to our knowledge, the ability of IFN-λ to directly regulate NK cell effector functions in vivo, alone and in the context of IFN-αβ.

Differential expression of inflammasomes in lung cancer cell lines and tissues

As pivotal elements involved in inflammation, inflammasomes represent a group of multiprotein complexes triggering the maturation of proinflammatory cytokine interleukin (IL)-1β and IL-18. Although the importance of the inflammasomes in inflammatory diseases is well appreciated, a precise characterization of their expressions in lung cancer remains obscure. This study aimed to determine the expressions of inflammasomes in various lung cancer cell lines and tissues to understand their potential roles in lung cancer. Our findings showed that inflammasome components were markedly upregulated in lung cancer and elicited the maturation of IL-1β and IL-18. In addition, enormous variations in subtypes and levels of inflammasomes were detected in lung cancers depending on their histological type and grading, invasion ability, as well as chemoresistance. Generally, AIM2 inflammasome was overexpressed in nonsmall cell lung cancer (NSCLC), while NLRP3 inflammasome was upregulated in lung adenocarcinoma (ADC) and small cell lung cancer (SCLC). The high-metastatic or cisplatin-sensitive NSCLC cells expressed more inflammasome components and products than their counterpart low-metastatic or cisplatin-resistant NSCLC cells, respectively. In resected lung cancer tissues, high-grade ADC expressed more inflammasome components and products than low-grade ADC. Together, these findings suggest that inflammasomes may be crucial biomarkers for lung cancer as well as potential modulators of the biological behaviors of lung cancer. Further, pharmacotherapeutics targeting inflammasomes might be novel adjuvant therapy strategies for lung cancer.

NK Cells and Cancer Immunoediting

Natural killer (NK) cells are innate lymphoid cells (ILC) known for their ability to recognize and rapidly eliminate infected or transformed cells. Consequently, NK cells are fundamental for host protection against virus infections and malignancies. Even though the critical role of NK cells in cancer immunosurveillance was suspected years ago, the underlying mechanisms took time to be unraveled. Today, it is clear that anti-tumor functions of NK cells are tightly regulated and expand far beyond the simple killing of malignant cells. In spite of tremendous steps made in understanding the NK cell biology, further work is warranted to fully exploit the anticancer potential of these cells. Indeed, tumor-mediated immune suppression hampers NK cell activity, thus complicating their stimulation for therapeutic purposes. Herein, we review the current knowledge of NK cell functions in anti-tumor immunity . We discuss NK cell activity in the cancer immunoediting process with particular emphasis on the elimination and escape phases.

Inflammasome activation is critical to the protective immune response during chemically induced squamous cell carcinoma

Chronic inflammation affects most stages of tumorigenesis, including initiation, promotion, malignant differentiation, invasion and metastasis. Inflammasomes have been described as involved with persistent inflammation and are known to exert both pro and antitumour effects. We evaluated the influence of apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC) and caspase (CASP)-1 in the antitumor immune response using a multistage model of squamous cell carcinoma (SCC) development. Absence of ASC and CASP-1 resulted in an earlier incidence and increased number of papilloma. Loss of inflammassome function in mice resulted in decreased presence of natural killer (NK), dendritic (DC), CD4⁺, CD8⁺ and CD45RB⁺ T cells in the tumor lesions as well as in lymph nodes (LN) compared with WT mice. Increased percentage of CD4⁺CD25⁺Foxp3⁺ T cells was associated with association with inflammasome loss of function. Moreover, significant differences were also found with neutrophils and macrophage infiltrating the lesions. Myeloperoxidase (MPO), but not elastase (ELA), activity oscillated among the groups during the SCC development. Levels of proinflammatory cytokines IL-1β, IL-18, Tumor Necrosis Factor (TNF)-α and Interferon (IFN)-γ were decreased in the tumor microenvironment in the absence of inflammasome proteins. These observations suggest a link between inflammasome function and SCC tumorigenesis, indicating an important role for inflammasome activation in the control of SCC development.

Transcriptional regulation of pattern recognition receptors by Jak/STAT signaling, and the implications for disease pathogenesis

Cytokines are well known for their pleiotropism, affecting a large number of cellular responses, including proliferation, survival, functional maturation, and immunomodulation. It is, therefore, not surprising that both the deregulated expression of cytokines and the subsequent activation of their downstream signaling pathways is a common feature of many cancers, as well as chronic inflammatory, autoimmune, metabolic, and cardiovascular diseases. In this regard, activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway is the predominant intracellular signaling event triggered by cytokines, with STAT1 and STAT3 having the greatest diversity of biological functions among the 7 known members of the STAT family of latent transcription factors. Notably, over recent years, it has emerged that STAT1 and STAT3 are employed by various cytokines to manipulate the signal output of heterologous receptors of the innate immune system, namely pattern recognition receptors (PRRs), with both immune and nonimmune (eg, oncogenic, metabolic) cellular processes being affected. This review highlights these pivotal advancements in our understanding of how a cross talk between cytokine and PRR signaling networks can impact on a variety of cellular responses during disease pathogenesis, and the potential therapeutic implications of targeting these networks.

NOD-Like Receptors: Master Regulators of Inflammation and Cancer

Cytosolic NOD-like receptors (NLRs) have been associated with human diseases including infections, cancer, and autoimmune and inflammatory disorders. These innate immune pattern recognition molecules are essential for controlling inflammatory mechanisms through induction of cytokines, chemokines, and anti-microbial genes. Upon activation, some NLRs form multi-protein complexes called inflammasomes, while others orchestrate caspase-independent nuclear factor kappa B (NF-κB) and mitogen activated protein kinase (MAPK) signaling. Moreover, NLRs and their downstream signaling components engage in an intricate crosstalk with cell death and autophagy pathways, both critical processes for cancer development. Recently, increasing evidence has extended the concept that chronic inflammation caused by abberant NLR signaling is a powerful driver of carcinogenesis, where it abets genetic mutations, tumor growth, and progression. In this review, we explore the rapidly expanding area of research regarding the expression and functions of NLRs in different types of cancers. Furthermore, we particularly focus on how maintaining tissue homeostasis and regulating tissue repair may provide a logical platform for understanding the liaisons between the NLR-driven inflammatory responses and cancer. Finally, we outline novel therapeutic approaches that target NLR signaling and speculate how these could be developed as potential pharmaceutical alternatives for cancer treatment.

Luteoloside suppresses proliferation and metastasis of hepatocellular carcinoma cells by inhibition of NLRP3 inflammasome

The inflammasome is a multi-protein complex which when activated regulates caspase-1 activation and IL-1β secretion. Inflammasome activation is mediated by NLR proteins that respond to stimuli. Among NLRs, NLRP3 senses the widest array of stimuli. NLRP3 inflammasome plays an important role in the development of many cancer types. However, Whether NLRP3 inflammasome plays an important role in the process of hepatocellular carcinoma (HCC) is still unknown. Here, the anticancer effect of luteoloside, a naturally occurring flavonoid isolated from the medicinal plant Gentiana macrophylla, against HCC cells and the underlying mechanisms were investigated. Luteoloside significantly inhibited the proliferation of HCC cells in vitro and in vivo. Live-cell imaging and transwell assays showed that the migration and invasive capacities of HCC cells, which were treated with luteoloside, were significantly inhibited compared with the control cells. The inhibitory effect of luteoloside on metastasis was also observed in vivo in male BALB/c-nu/nu mouse lung metastasis model. Further studies showed that luteoloside could significantly reduce the intracellular reactive oxygen species (ROS) accumulation. The decreased levels of ROS induced by luteoloside was accompanied by decrease in expression of NLRP3 inflammasome resulting in decrease in proteolytic cleavage of caspase-1. Inactivation of caspase-1 by luteoloside resulted in inhibition of IL-1β. Thus, luteoloside exerts its inhibitory effect on proliferation, invasion and metastasis of HCC cells through inhibition of NLRP3 inflammasome. Our results indicate that luteoloside can be a potential therapeutic agent not only as an adjuvant therapy for HCC, but also, in the control and prevention of metastatic HCC.

Inflammasomes in cancer: a double-edged sword

Chronic inflammatory responses have long been observed to be associated with various types of cancer and play decisive roles at different stages of cancer development. Inflammasomes, which are potent inducers of interleukin (IL)-1β and IL-18 during inflammation, are large protein complexes typically consisting of a Nod-like receptor (NLR), the adapter protein ASC, and Caspase-1. During malignant transformation or cancer therapy, the inflammasomes are postulated to become activated in response to danger signals arising from the tumors or from therapy-induced damage to the tumor or healthy tissue. The activation of inflammasomes plays diverse and sometimes contrasting roles in cancer promotion and therapy depending on the specific context. Here we summarize the role of different inflammasome complexes in cancer progression and therapy. Inflammasome components and pathways may provide novel targets to treat certain types of cancer; however, using such agents should be cautiously evaluated due to the complex roles that inflammasomes and pro-inflammatory cytokines play in immunity.

Yin and yang of tumor inflammation: how innate immune suppressors shape the tumor microenvironments

Pattern recognition-mediated sensing systems direct host immunity towards either antitumor immunosurveillance or protumorigenic inflammation. These activities imply dual and conflicting roles in the regulation of tumor-associated inflammation. On the one hand, recent evidence has revealed that several signaling components and cell-surface receptors suppress innate immune signals and constitute a negative feedback machinery preventing excess and continuous inflammation within tumor microenvironments. On the other hand, these same components also negatively regulate intrinsic tumorigenic activities by targeting nuclear factor-kappaB (NF-κB)-mediated antiapoptotic and inflammatory signals. Furthermore, the activation status of innate immune suppressors may reflect the functional plasticity of interactions between tumor cells and innate immune cells and determine whether tumor inflammation supports anti- or pro-tumorigenic responses. Thus, innate immune suppressors may provide valuable information about the immunogenic or tumorigenic status of tumor-associated inflammation thereby serving as potential biomarkers that predict tumor progression. Comprehensive analysis for identifying general and unique features of each innate immune suppressor in the regulation of tumor inflammation should explore the development of new biomarkers for improving future therapeutic strategies.

Beneficial and Detrimental Roles of NLRs in Carcinogenesis

Inflammation plays a critical role in tumorigenesis and can contribute to oncogenic mutations, tumor promotion, and angiogenesis. Tumor-promoting inflammation is driven by many factors including the presence of the pro-inflammatory cytokines interleukin (IL)-1β and IL-18. One major source of IL-1β and IL-18 secretion is through the activation of inflammasomes. Inflammasomes are multi-protein complexes that upon activation lead to the processing and secretion of IL-1β and IL-18 mediated by the cysteine protease caspase-1. Several inflammasomes, including NLRP3, NLRC4, and NLRP6, have been implicated in tumorigenesis. However, inflammasomes play divergent roles in different types of cancer reflecting the complexity of inflammation during tumorigenesis. Understanding the role of inflammasome activation during specific stages of tumorigenesis and also during cancer immunotherapy will help identify novel therapeutic targets that could improve treatment strategies for cancer patients. Here we will discuss recent advances in understanding the mechanism by which NLRs regulate carcinogenesis.

Thymoquinone suppresses metastasis of melanoma cells by inhibition of NLRP3 inflammasome

The inflammasome is a multi-protein complex which when activated regulates caspase-1 activation and IL-1β and IL-18 secretion. The NLRP3 (NACHT, LRR, and pyrin domain-containing protein 3) inflammasome is constitutively assembled and activated in human melanoma cells. We have examined the inhibitory effect of thymoquinone (2-isopropyl-5-methylbenzo-1,4-quinone), a major ingredient of black seed obtained from the plant Nigella sativa on metastatic human (A375) and mouse (B16F10) melanoma cell lines. We have assessed whether thymoquinone inhibits metastasis of melanoma cells by targeting NLRP3 subunit of inflammasomes. Using an in vitro cell migration assay, we found that thymoquinone inhibited the migration of both human and mouse melanoma cells. The inhibitory effect of thymoquinone on metastasis was also observed in vivo in B16F10 mouse melanoma model. The inhibition of migration of melanoma cells by thymoquinone was accompanied by a decrease in expression of NLRP3 inflammasome resulting in decrease in proteolytic cleavage of caspase-1. Inactivation of caspase-1 by thymoquinone resulted in inhibition of IL-1β and IL-18. Treatment of mouse melanoma cells with thymoquinone also inhibited NF-κB activity. Furthermore, inhibition of reactive oxygen species (ROS) by thymoquinone resulted in partial inactivation of NLRP3 inflammasome. Thus, thymoquinone exerts its inhibitory effect on migration of human and mouse melanoma cells by inhibition of NLRP3 inflammasome. Thus, our results indicate that thymoquinone can be a potential immunotherapeutic agent not only as an adjuvant therapy for melanoma, but also, in the control and prevention of metastatic melanoma.

Natural killer cells in non-hematopoietic malignancies

Natural killer (NK) cells belong to the innate immune system and were initially described functionallywise by their spontaneous cytotoxic potential against transformed or virus-infected cells. A delicate balance between activating and inhibiting receptors regulates NK cell tolerance. A better understanding of tissue resident NK cells, of NK cell maturation stages and migration patterns has evolved allowing a thoughtful evaluation of their modus operandi. While evidence has been brought up for their relevance as gate keepers in some hematopoietic malignancies, the role of NK cells against progression and dissemination of solid tumors remains questionable. Hence, many studies pointed out the functional defects of the rare NK cell infiltrates found in tumor beds and the lack of efficacy of adoptively transferred NK cells in patients. However, several preclinical evidences suggest their anti-metastatic role in a variety of mouse tumor models. In the present review, we discuss NK cell functions according to their maturation stage and environmental milieu, the receptor/ligand interactions dictating tumor cell recognition and recapitulate translational studies aimed at deciphering their prognostic or predictive role against human solid malignancies.