The Nlrp3 Inflammasome Suppresses Colorectal Cancer Metastatic Growth in the Liver by Promoting Natural Killer Cell Tumoricidal Activity.

The crosstalk between inflammation and tumorigenesis is now clearly established. However, how inflammation is elicited in the metastatic environment and the corresponding contribution of innate immunity pathways in suppressing tumor growth at secondary sites are poorly understood. Here, we show that mice deficient in Nlrp3 inflammasome components had exacerbated liver colorectal cancer metastatic growth, which was mediated by impaired interleukin-18 (IL-18) signaling. Control of tumor growth was independent of differential cancer cell colonization or proliferation, intestinal microbiota effects, or tumoricidal activity by the adaptive immune system. Instead, the inflammasome-IL-18 pathway impacted maturation of hepatic NK cells, surface expression of the death ligand FasL, and capacity to kill FasL-sensitive tumors. Our results define a regulatory signaling circuit within the innate immune system linking inflammasome activation to effective NK-cell-mediated tumor attack required to suppress colorectal cancer growth in the liver.

Caspase-12, but Not Caspase-11, Inhibits Obesity and Insulin Resistance.

Inflammation is well established to significantly impact metabolic diseases. The inflammatory protease caspase-1 has been implicated in metabolic dysfunction; however, a potential role for the related inflammatory caspases is currently unknown. In this study, we investigated a role for caspase-11 and caspase-12 in obesity and insulin resistance. Loss of caspase-12 in two independently generated mouse strains predisposed mice to develop obesity, metabolic inflammation, and insulin resistance, whereas loss of caspase-11 had no effect. The use of bone marrow chimeras determined that deletion of caspase-12 in the radio-resistant compartment was responsible for this metabolic phenotype. The Nlrp3 inflammasome pathway mediated the metabolic syndrome of caspase-12-deficient mice as ablation of Nlrp3 reversed Casp12(-/-) mice obesity phenotype. Although the majority of people lack a functional caspase-12 because of a T(125) single nucleotide polymorphism that introduces a premature stop codon, a fraction of African descendents express full-length caspase-12. Expression of caspase-12 was linked to decreased systemic and adipose tissue inflammation in a cohort of African American obese children. However, analysis of the Dallas Heart Study African American cohort indicated that the coding T(125)C single nucleotide polymorphism was not associated with metabolic parameters in humans, suggesting that host-specific differences mediate the expressivity of metabolic disease.

The Inflammatory Caspases-1 and -11 Mediate the Pathogenesis of Dermatitis in Sharpin-Deficient Mice.

Chronic proliferative dermatitis in mice (cpdm) is a spontaneous multiorgan inflammatory disorder with pathological hallmarks similar to atopic dermatitis and psoriasis in humans. Cpdm mice lack expression of SHANK-associated RH domain-interacting protein, an adaptor of the linear ubiquitin assembly complex, which acts in the NF-κB pathway to promote inflammation and protect from apoptosis and necroptosis. Although skin inflammation in cpdm mice is driven by TNF- and RIPK1-induced cell death, the contribution of initiating innate immunity sensors and additional inflammatory pathways remains poorly characterized. In this article, we show that inflammasome signaling, including the expression and activation of the inflammatory caspase-1 and -11 and IL-1 family cytokines, was highly upregulated in the skin of cpdm mice prior to overt disease onset. Genetic ablation of caspase-1 and -11 from cpdm mice significantly reduced skin inflammation and delayed disease onset, whereas systemic immunological disease persisted. Loss of Nlrp3 also attenuated skin disease, albeit more variably. Strikingly, induction of apoptosis and necroptosis effectors was sharply decreased in the absence of caspase-1 and -11. These results position the inflammasome as an important initiating signal in skin disease pathogenesis and provide novel insights about inflammasome and cell death effector cross-talk in the context of inflammatory diseases.

TRAIL promotes membrane blebbing, detachment and migration of cells displaying a dysfunctional intrinsic pathway of apoptosis.

Recently, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL/Apo2L) has been shown to be a potential candidate for cancer therapy. TRAIL induces apoptosis in various cancer cells but not in normal tissues. Here we show that HCT116 and SW480 cells with a deficient mitochondrial apoptotic pathway were resistant to TRAIL-induced apoptosis, whereas HCT116 and SW480 cells with a functional mitochondrial apoptotic pathway underwent apoptosis upon exposure to TRAIL. Surprisingly, TRAIL induced phenotypic changes in cells with a dysfunctional mitochondrial apoptotic pathway, including membrane blebbing and a transient loss of adhesion properties to the substratum. Accordingly, TRAIL stimulated the ability of these cells to migrate. This behavior was the consequence of a transient TRAIL-induced ROCK1 cleavage. In addition, we report that Bax-deficient HCT116 cells exposed to TRAIL for a prolonged period lost their sensitivity to TRAIL as a result of downregulation of TRAIL receptor expression, and became resistant to combination of TRAIL and other drugs such as MG-132 and bortezomib. These findings may have important consequences for TRAIL anti-cancer therapy.

Quercetin-mediated Mcl-1 and survivin downregulation restores TRAIL-induced apoptosis in non-Hodgkin's lymphoma B cells.

BACKGROUND: Non-Hodgkin's B-cell lymphomas account for approximately 70% of B-cell lymphomas. While its incidence is dramatically increasing worldwide, the disease is still associated with high morbidity due to ineffectiveness of conventional therapies, creating an urgent need for novel therapeutic approaches. Unconventional compounds, including polyphenols and the cytokine TRAIL, are being extensively studied for their capacity to restore apoptosis in a large number of tumors, including lymphomas. DESIGN AND METHODS: Molecular mechanisms of TRAIL-resistance and reactivation of the apoptotic machinery by quercetin in non-Hodgkin's lymphoma cell lines were determined by Hoescht, flow cytometry, Western blot, qPCR, by use of siRNA or pharmacological inhibitors of the mitochondrial pathway and by immunoprecipitation followed by post-translational modification analysis. RESULTS: Results demonstrate that quercetin, a natural flavonoid, restores TRAIL-induced cell death in resistant transformed follicular lymphoma B-cell lines, despite high Bcl-2 expression levels due to the chromosomal translocation t(14;18). Quercetin rescues mitochondrial activation by inducing the proteasomal degradation of Mcl-1 and by inhibiting survivin expression at the mRNA level, irrespective of p53. Restoration of the TRAIL pathway requires Bax and Bak but is independent of enhanced TRAIL DISC formation. CONCLUSIONS: We demonstrate that inactivation of survivin and Mcl-1 expression by quercetin is sufficient to restore TRAIL sensitivity in resistant non-Hodgkin's lymphoma B cells. Our results suggest, therefore, that combining quercetin with TRAIL treatments may be useful in the treatment of non-Hodgkin's lymphoma.

Peroxynitrite-dependent killing of cancer cells and presentation of released tumor antigens by activated dendritic cells.

Dendritic cells (DCs), essential for the initiation and regulation of adaptive immune responses, have been used as anticancer vaccines. DCs may also directly trigger tumor cell death. In the current study, we have investigated the tumoricidal and immunostimulatory activities of mouse bone marrow-derived DCs. Our results indicate that these cells acquire killing capabilities toward tumor cells only when activated with LPS or Pam3Cys-SK4. Using different transgenic mouse models including inducible NO synthase or GP91 knockout mice, we have further established that LPS- or Pam3Cys-SK4-activated DC killing activity involves peroxynitrites. Importantly, after killing of cancer cells, DCs are capable of engulfing dead tumor cell fragments and of presenting tumor Ags to specific T lymphocytes. Thus, upon specific stimulation, mouse bone marrow-derived DCs can directly kill tumor cells through a novel peroxynitrite-dependent mechanism and participate at virtually all levels of antitumor immune responses, which reinforces their interest in immunotherapy.

CD40 ligand protects from TRAIL-induced apoptosis in follicular lymphomas through NF-kappaB activation and up-regulation of c-FLIP and Bcl-xL.

The TNF family member TRAIL is emerging as a promising cytotoxic molecule for antitumor therapy. However, its mechanism of action and the possible modulation of its effect by the microenvironment in follicular lymphomas (FL) remain unknown. We show here that TRAIL is cytotoxic only against FL B cells and not against normal B cells, and that DR4 is the main receptor involved in the initiation of the apoptotic cascade. However, the engagement of CD40 by its ligand, mainly expressed on a specific germinal center CD4(+) T cell subpopulation, counteracts TRAIL-induced apoptosis in FL B cells. CD40 induces a rapid RNA and protein up-regulation of c-FLIP and Bcl-x(L). The induction of these antiapoptotic molecules as well as the inhibition of TRAIL-induced apoptosis by CD40 is partially abolished when NF-kappaB activity is inhibited by a selective inhibitor, BAY 117085. Thus, the antiapoptotic signaling of CD40, which interferes with TRAIL-induced apoptosis in FL B cells, involves NF-kappaB-mediated induction of c-FLIP and Bcl-x(L) which can respectively interfere with caspase 8 activation or mitochondrial-mediated apoptosis. These findings suggest that a cotreatment with TRAIL and an inhibitor of NF-kappaB signaling or a blocking anti-CD40 Ab could be of great interest in FL therapy.

Differential inhibition of TRAIL-mediated DR5-DISC formation by decoy receptors 1 and 2.

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family that induces cancer cell death by apoptosis with some selectivity. TRAIL-induced apoptosis is mediated by the transmembrane receptors death receptor 4 (DR4) (also known as TRAIL-R1) and DR5 (TRAIL-R2). TRAIL can also bind decoy receptor 1 (DcR1) (TRAIL-R3) and DcR2 (TRAIL-R4) that fail to induce apoptosis since they lack and have a truncated cytoplasmic death domain, respectively. In addition, DcR1 and DcR2 inhibit DR4- and DR5-mediated, TRAIL-induced apoptosis and we demonstrate here that this occurs through distinct mechanisms. While DcR1 prevents the assembly of the death-inducing signaling complex (DISC) by titrating TRAIL within lipid rafts, DcR2 is corecruited with DR5 within the DISC, where it inhibits initiator caspase activation. In addition, DcR2 prevents DR4 recruitment within the DR5 DISC. The specificity of DcR1- and DcR2-mediated TRAIL inhibition reveals an additional level of complexity for the regulation of TRAIL signaling.

The Interleukin (IL)-1R1 pathway is a critical negative regulator of PyMT-mediated mammary tumorigenesis and pulmonary metastasis.

Breast cancer is the most common cancer in women and the second leading cause of female cancer-related deaths worldwide. Inflammation is an established hallmark of tumorigenesis and an important determinant of tumor outcome and response to therapy. With advances in cancer immunotherapy, there is an urgent need to dissect the contribution of specific immune effectors in cancer development. Here, we genetically investigated the role of the Interleukin-1 (IL-1) receptor 1 (IL-1R1) pathway in breast cancer tumorigenesis and metastasis using the MMTV-PyMT mouse model. Our results indicate that IL-1R1 signaling suppresses mammary tumor cell proliferation early in tumorigenesis and curbs breast cancer outgrowth and pulmonary metastasis. We show that PyMT/Il1r1-/- mice had a higher primary tumor burden and increased mortality rate compared with IL-1R1-sufficient PyMT control mice. This phenotype was independent of the inflammatory caspases-1/-11 but driven by IL-1α, as PyMT/Il1a-/- mice phenocopied PyMT/Il1r1-/- mice. Collectively, our results suggest that IL-1α-mediated IL-1R1 signaling is tumor-suppressive in PyMT-driven breast cancer.

Death Receptor-Induced Apoptosis Signalling Regulation by Ezrin Is Cell Type Dependent and Occurs in a DISC-Independent Manner in Colon Cancer Cells.

Ezrin belongs to the ERM (ezrin-radixin-moesin) protein family and has been demonstrated to regulate early steps of Fas receptor signalling in lymphoid cells, but its contribution to TRAIL-induced cell death regulation in adherent cancer cells remains unknown. In this study we report that regulation of FasL and TRAIL-induced cell death by ezrin is cell type dependant. Ezrin is a positive regulator of apoptosis in T-lymphoma cell line Jurkat, but a negative regulator in colon cancer cells. Using ezrin phosphorylation or actin-binding mutants, we provide evidence that negative regulation of death receptor-induced apoptosis by ezrin occurs in a cytoskeleton- and DISC-independent manner, in colon cancer cells. Remarkably, inhibition of apoptosis induced by these ligands was found to be tightly associated with regulation of ezrin phosphorylation on serine 66, the tumor suppressor gene WWOX and activation of PKA. Deficiency in WWOX expression in the liver cancer SK-HEP1 or the pancreatic Mia PaCa-2 cell lines as well as WWOX silencing or modulation of PKA activation by pharmacological regulators, in the colon cancer cell line SW480, abrogated regulation of TRAIL signalling by ezrin. Altogether our results show that death receptor pro-apoptotic signalling regulation by ezrin can occur downstream of the DISC in colon cancer cells.

Cellular inhibitor of apoptosis protein cIAP2 protects against pulmonary tissue necrosis during influenza virus infection to promote host survival.

Cellular inhibitors of apoptosis proteins (cIAPs) are essential regulators of cell death and immunity. The corresponding contributions of IAPs to infectious disease outcomes are relatively unexplored. We find that mice deficient in cIAP2 exhibit increased susceptibility and mortality to influenza A virus infection. The lethality was not due to impaired antiviral immune functions, but rather because of death-receptor-induced programmed necrosis of airway epithelial cells that led to severe bronchiole epithelial degeneration, despite control of viral replication. Pharmacological inhibition of RIPK1 or genetic deletion of Ripk3, both kinases involved in programmed necrosis, rescued cIAP2-deficient mice from influenza-induced lethality. Genetic deletion of the death receptor agonists Fas ligand or TRAIL from the hematopoietic compartment also reversed the susceptibility of cIAP2-deficient mice. Thus, cIAP2-dependent antagonism of RIPK3-mediated programmed necrosis critically protects the host from influenza infection through maintenance of pulmonary tissue homeostasis rather than through pathogen control by the immune system.

Non-apoptotic functions of cell death effectors in inflammation and innate immunity.

Innate immunity and cell death are essential host defense mechanisms. Mounting evidence reveals that these processes are closely linked. The aim of this review is to highlight the close relationship between the pathways governing these processes, particularly how regulators of cell death control the induction of the innate immune response.

Regulating TRAIL receptor-induced cell death at the membrane : a deadly discussion.

The use of TRAIL/APO2L and monoclonal antibodies targeting TRAIL receptors for cancer therapy holds great promise, due to their ability to restore cancer cell sensitivity to apoptosis in association with conventional chemotherapeutic drugs in a large variety of tumors. TRAIL-induced cell death is tightly regulated right from the membrane and at the DISC (Death-Inducing Signaling Complex) level. The following patent and literature review aims to present and highlight recent findings of the deadly discussion that determines tumor cell fate upon TRAIL engagement.

TRAIL-R4 promotes tumor growth and resistance to apoptosis in cervical carcinoma HeLa cells through AKT.

BACKGROUND: TRAIL/Apo2L is a pro-apoptotic ligand of the TNF family that engages the apoptotic machinery through two pro-apoptotic receptors, TRAIL-R1 and TRAIL-R2. This cell death program is tightly controlled by two antagonistic receptors, TRAIL-R3 and TRAIL-R4, both devoid of a functional death domain, an intracellular region of the receptor, required for the recruitment and the activation of initiator caspases. Upon TRAIL-binding, TRAIL-R4 forms a heteromeric complex with the agonistic receptor TRAIL-R2 leading to reduced caspase-8 activation and apoptosis. METHODOLOGY/PRINCIPAL FINDINGS: We provide evidence that TRAIL-R4 can also exhibit, in a ligand independent manner, signaling properties in the cervical carcinoma cell line HeLa, through Akt. Ectopic expression of TRAIL-R4 in HeLa cells induced morphological changes, with cell rounding, loss of adherence and markedly enhanced cell proliferation in vitro and tumor growth in vivo. Disruption of the PI3K/Akt pathway using the pharmacological inhibitor LY294002, siRNA targeting the p85 regulatory subunit of phosphatidylinositol-3 kinase, or by PTEN over-expression, partially restored TRAIL-mediated apoptosis in these cells. Moreover, the Akt inhibitor, LY294002, restituted normal cell proliferation index in HeLa cells expressing TRAIL-R4. CONCLUSIONS/SIGNIFICANCE: Altogether, these results indicate that, besides its ability to directly inhibit TRAIL-induced cell death at the membrane, TRAIL-R4 can also trigger the activation of signaling pathways leading to cell survival and proliferation in HeLa cells. Our findings raise the possibility that TRAIL-R4 may contribute to cervical carcinogenesis.

Multivalent DR5 peptides activate the TRAIL death pathway and exert tumoricidal activity.

Ongoing clinical trials are exploring anticancer approaches based on signaling by TRAIL, a ligand for the cell death receptors DR4 and DR5. In this study, we report on the selective apoptotic effects of multivalent DR5 binding peptides (TRAIL(mim/DR5)) on cancer cells in vitro and in vivo. Surface plasmon resonance revealed up to several thousand-fold increased affinities of TRAIL(mim/DR5)-receptor complexes on generation of divalent and trivalent molecules, the latter of which was achieved with a conformationally restricted adamantane core. Notably, only multivalent molecules triggered a substantial DR5-dependent apoptotic response in vitro. In tumor models derived from human embryonic kidney cells or primary foreskin fibroblasts, TRAIL(mim/DR5) peptides exerted a cancer cell-selective action that could synergize with resveratrol in a manner independent of p53. In a xenograft model of human colon cancer, a divalent TRAIL(mim/DR5) peptide inhibited tumor growth. Our results offer a proof-of-principle for the development of synthetic small molecules to trigger the TRAIL apoptosis pathway for cancer therapy.

TRAIL in cancer therapy: present and future challenges.

Since its identification in 1995, TNF-related apoptosis-inducing ligand (TRAIL) has sparked growing interest in oncology due to its reported ability to selectively trigger cancer cell death. In contrast to other members of the TNF superfamily, TRAIL administration in vivo is safe. The relative absence of toxic side effects of this naturally occurring cytokine, in addition to its antitumoural properties, has led to its preclinical evaluation. However, despite intensive investigations, little is known in regards to the mechanisms underlying TRAIL selectivity or efficiency. An appropriate understanding of its physiological relevance, and of the mechanisms controlling cancer cells escape from TRAIL-induced cell death, will be required to optimally use the cytokine in clinics. The present review focuses on recent advances in the understanding of TRAIL signal transduction and discusses the existing and future challenges of TRAIL-based cancer therapy development.