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Streptococcus gallolyticus subsp. gallolyticus (SGG), an opportunistic gram-positive pathogen responsible for septicemia and endocarditis in the elderly, is often associated with colon cancer (CRC). In this work, we investigated the oncogenic role ofSGGstrain UCN34 using the azoxymethane (AOM)-induced CRC modelin vivo, organoid formationex vivoand proteomic and phosphoproteomic analyses from murine colons. We showed thatSGGUCN34 accelerates colon tumor development in the murine CRC model. Full proteome and phosphoproteome analysis of murine colons chronically colonized bySGGUCN34 or the closely related non-pathogenicS. gallolyticus subsp. macedonicus(SGM) revealed that 164 proteins and 725 phosphorylation sites were differentially regulated following colonization bySGGUCN34. Ingenuity Pathway Analysis (IPA) indicates a pro-tumoral shift specifically induced following colonization bySGGUCN34, as most proteins and phosphoproteins identified were associated with digestive cancer. Comprehensive analysis of the altered phosphoproteins using ROMA software revealed significantly elevated activities in several cancer hallmark pathways affecting tumoral cells and their microenvironment, i.e. MAPK (ERK, JNK and p38), mTOR and integrin/ILK/actin signaling, inSGGUCN34 colonized colon. Importantly, analysis of protein arrays of human colon tumors colonized withSGGshowed up-regulation of PI3K/Akt/mTOR and MAPK pathways, providing clinical relevance to our findings. To testSGG’s capacity to induce pre-cancerous transformation of the murine colonic epithelium, we grewex vivoorganoids which revealed unusual structures with compact morphology following exposure toSGG. Taken together, our results reveal that the oncogenic role ofSGGUCN34 is associated with activation of multiple cancer-related signaling pathways.Author SummaryColorectal cancer is the third most common cause of cancer mortality worldwide. The colon is a very singular organ, colonized by a vast and complex community of microorganisms, known as the gut microbiota. Strong evidence supports a role of the microbiota in colon cancer development.Streptococcus gallolyticussubsp.gallolyticus(SGG), a gut commensal, was one of the first bacteria to be associated with colorectal cancer. A better understanding of the role ofSGGin colon cancer development is critical to developing novel strategies to improve clinical diagnosis and treatment of this disease. Here, using a global proteomic analysis of mouse colonic tissue colonized bySGG, we show that over 90% of the proteins with altered levels are involved in cancer.SGGcolonization promotes autocrine and paracrine pro-tumor signals contributing to transformation of the colonic epithelium but also modifying the stromal microenvironment, which in turn sustains tumor development. Importantly, two tumor hallmark pathways (PI3K/Akt/mTOR and MAPK) identified in our mouse model were also found in human colon tumor biopsies colonized bySGG, strengthening the clinical relevance to our study.

International audience; After birth, the intestine undergoes major changes to shift from an immature proliferative state to a functional intestinal barrier. By combining inducible lineage tracing and transcriptomics in mouse models, we identify a prodifferentiation PDGFRαHigh intestinal stromal lineage originating from postnatal LTβR+ perivascular stromal progenitors. The genetic blockage of this lineage increased the intestinal stem cell pool while decreasing epithelial and immune maturation at weaning age, leading to reduced postnatal growth and dysregulated repair responses. Ablating PDGFRα in the LTBR stromal lineage demonstrates that PDGFRα has a major impact on the lineage fate and function, inducing a transcriptomic switch from prostemness genes, such as Rspo3 and Grem1, to prodifferentiation factors, including BMPs, retinoic acid, and laminins, and on spatial organization within the crypt-villus and repair responses. Our results show that the PDGFRα-induced transcriptomic switch in intestinal stromal cells is required in the first weeks after birth to coordinate postnatal intestinal maturation and function.

Summary Innate lymphoid cells (ILCs) have been shown to be significantly affected in the small intestine lamina propria and secondary lymphoid organs (SLOs) of conventional lymphopenic mice. How ILCs are regulated by adaptive immunity in SLOs remains unclear. In T cell-deficient mice, ILC2s are significantly increased in the mesenteric lymph nodes (MLNs) at the expense of CCR6+ ILC3s, which are nonetheless increased in the peripheral lymph nodes (PLNs). Here, we show that T cells regulate lymph node-resident ILCs in a tissue- and subset-specific way. First, reducing microbial colonization from birth restored CCR6+ ILC3s in the MLNs of T cell-deficient mice. In contrast, T cell reconstitution resulted in the contraction of both MLNs ILC2s and PLNs ILC3s, whereas antagonizing microbial colonization from birth had no impact on these populations. Finally, the accumulation of MLNs ILC2s was partly regulated by T cells through stroma-derived IL-33., Graphical abstract, Highlights • T cells differentially regulate ILC homeostasis in PLNs and MLNs • MLNs ILC3 homeostasis is regulated by T cells in a microbiota- and age-dependent way • T cells indirectly regulate stroma-derived IL-33 in MLNs • IL-33 participates in the regulation of MLNs ILC2 homeostasis by T cells, Immunology; Components of the Immune System; Microbiome

Highlights • Perivascular mesenchymal cells include pericytes, adventitial fibroblasts and mesenchymal stromal cells. • Perivascular mesenchymal cells have roles in the recruitment and/or activity of specific immune populations. • Subsets of perivascular mesenchymal cells act as progenitors for specialized stromal cells essential in repair and immunity. • Dysregulation of the perivascular niche contribute to chronic inflammation and fibrosis., The mesenchymal microenvironment is increasingly recognized as a major player in immunity. Here we focus on mesenchymal cells located within or in proximity to the blood vessels wall, which include pericytes, adventitial fibroblasts and mesenchymal stromal cells. We discuss recent evidence that these cells play a role in tissue homeostasis, immunity and inflammatory pathologies by multiple mechanisms, including vascular modulation, leucocyte migration, activation or survival in the perivascular space and differentiation into specialized ‘effector’ mesenchymal cells essential for tissue repair and immunity, such as myofibroblasts and lymphoid stromal cells. When dysregulated, these responses contribute to inflammatory and fibrotic diseases.

International audience; The proper tissue-specific regulation of gene expression is essential for development and homeostasis in metazoans. However, the illegitimate expression of normally tissue-restricted genes-like testis- or placenta-specific genes-is frequently observed in tumors; this promotes transformation, but also allows immunotherapy. Two important questions are: how is the expression of these genes controlled in healthy cells? And how is this altered in cancer? To address these questions, we used an unbiased approach to test the ability of 350 distinct genetic or epigenetic perturbations to induce the illegitimate expression of over 40 tissue-restricted genes in primary human cells. We find that almost all of these genes are remarkably resistant to reactivation by a single alteration in signaling pathways or chromatin regulation. However, a few genes differ and are more readily activated; one is the placenta-expressed gene ADAM12, which promotes invasion. Using cellular systems, an animal model, and bioinformatics, we find that a non-canonical but druggable TGF-β/KAT2A/TAK1 axis controls ADAM12 induction in normal and cancer cells. More broadly, our data show that illegitimate gene expression in cancer is an heterogeneous phenomenon, with a few genes activatable by simple events, and most genes likely requiring a combination of events to become reactivated.

Listeria monocytogenes (Lm) crosses the intestinal villus barrier via goblet cells (GCs). Disson et al. show that Lm infection of Peyer’s patch myeloid cells signals to villus stromal cells, leading to a decrease of GCs expressing luminally accessible E-cadherin, thereby blocking villus infection while favoring colitis., The foodborne pathogen Listeria monocytogenes (Lm) crosses the intestinal villus epithelium via goblet cells (GCs) upon the interaction of Lm surface protein InlA with its receptor E-cadherin. Here, we show that Lm infection accelerates intestinal villus epithelium renewal while decreasing the number of GCs expressing luminally accessible E-cadherin, thereby locking Lm portal of entry. This novel innate immune response to an enteropathogen is triggered by the infection of Peyer’s patch CX3CR1+ cells and the ensuing production of IL-23. It requires STAT3 phosphorylation in epithelial cells in response to IL-22 and IL-11 expressed by lamina propria gp38+ stromal cells. Lm-induced IFN-γ signaling and STAT1 phosphorylation in epithelial cells is also critical for Lm-associated intestinal epithelium response. GC depletion also leads to a decrease in colon mucus barrier thickness, thereby increasing host susceptibility to colitis. This study unveils a novel innate immune response to an enteropathogen, which implicates gp38+ stromal cells and locks intestinal villus invasion, but favors colitis., Graphical Abstract

Enhancing anti-tumor immunity and preventing tumor escape are efficient strategies to increase the efficacy of therapeutic cancer vaccines. However, the treatment of advanced tumors remains difficult, mainly due to the immunosuppressive tumor microenvironment. Regulatory T cells and myeloid-derived suppressor cells have been extensively studied, and their role in suppressing tumor immunity is now well established. In contrast, the role of B lymphocytes in tumor immunity remains unclear because B cells can promote tumor immunity or display regulatory functions to control excessive inflammation, mainly through IL-10 secretion. Here, in a mouse model of HPV-related cancer, we demonstrate that B cells accumulated in the draining lymph node of tumor-bearing mice, due to a prolonged survival, and showed a decreased expression of MHC class II and CD86 molecules and an increased expression of Ly6A/E, PD-L1 and CD39, suggesting potential immunoregulatory properties. However, B cells from tumor-bearing mice did not show an increased ability to secrete IL-10 and a deficiency in IL-10 production did not impair tumor growth. In contrast, in B cell-deficient μMT mice, tumor rejection occurred due to a strong T cell-dependent anti-tumor response. Genetic analysis based on single nucleotide polymorphisms identified genetic variants associated with tumor rejection in μMT mice, which could potentially affect reactive oxygen species production and NK cell activity. Our results demonstrate that B cells play a detrimental role in anti-tumor immunity and suggest that targeting B cells could enhance the anti-tumor response and improve the efficacy of therapeutic cancer vaccines.

International audience; The ability to repair tissues is essential for the survival of organisms. In chronic settings, the failure of the repair process to terminate results in overproduction of collagen, a pathology known as fibrosis, which compromises organ recovery and impairs function. The origin of the collagen-overproducing cell has been debated for years. Here we review recent insights gained from the use of lineage tracing approaches in several organs. The resulting evidence points toward specific subsets of tissue-resident mesenchymal cells, mainly localized in a perivascular position, as the major source for collagen-producing cells after injury. We discuss these findings in view of the functional heterogeneity of mesenchymal cells of the perivascular niche, which have essential vascular, immune, and regenerative functions that need to be preserved for efficient repair.

International audience; The intestinal epithelium represents the most vigorously renewing adult tissue in mammals and intestinal stem cells (ISCs) fuel this process. Two main features characterized the ISCs: (i) their capacity of self-renewing and persisting over the entire lifetime of the organism; (ii) their multipotency, therefore allowing them to generate the multiple cell types present in the intestine. These features depend upon intrinsic program of the ISCs, but especially from signals that ISCs receive from their surrounding microenvironment: the niche. Three main actors have been described until now as being part of the ISC niche: Paneth cells, mesenchymal stromal cells, and the microbiota. This chapter highlights the recent advances in defining the niche of ISCs at homeostasis and under stress conditions.

International audience; Neisseria meningitidis is a life-threatening human bacterial pathogen responsible for pneumonia, sepsis, and meningitis. Meningococcal strains with reduced susceptibility to penicillin G (Pen(I)) carry a mutated penicillin-binding protein (PBP2) resulting in a modified peptidoglycan structure. Despite their antibiotic resistance, Pen(I) strains have failed to expand clonally. We analyzed the biological consequences of PBP2 alteration among clinical meningococcal strains and found that peptidoglycan modifications of the Pen(I) strain resulted in diminished in vitro Nod1-dependent proinflammatory activity. In an influenza virus-meningococcal sequential mouse model mimicking human disease, wild-type meningococci induced a Nod1-dependent inflammatory response, colonizing the lungs and surviving in the blood. In contrast, isogenic Pen(I) strains were attenuated for such response and were out-competed by meningococci sensitive to penicillin G. Our results suggest that antibiotic resistance imposes a cost to the success of the pathogen and may potentially explain the lack of clonal expansion of Pen(I) strains.

International audience; Chikungunya virus (CHIKV) is the causative agent of an outbreak that began in La Réunion in 2005 and remains a major public health concern in India, Southeast Asia, and southern Europe. CHIKV is transmitted to humans by mosquitoes and the associated disease is characterized by fever, myalgia, arthralgia, and rash. As viral load in infected patients declines before the appearance of neutralizing antibodies, we studied the role of type I interferon (IFN) in CHIKV pathogenesis. Based on human studies and mouse experimentation, we show that CHIKV does not directly stimulate type I IFN production in immune cells. Instead, infected nonhematopoietic cells sense viral RNA in a Cardif-dependent manner and participate in the control of infection through their production of type I IFNs. Although the Cardif signaling pathway contributes to the immune response, we also find evidence for a MyD88-dependent sensor that is critical for preventing viral dissemination. Moreover, we demonstrate that IFN-alpha/beta receptor (IFNAR) expression is required in the periphery but not on immune cells, as IFNAR(-/-)-->WT bone marrow chimeras are capable of clearing the infection, whereas WT-->IFNAR(-/-) chimeras succumb. This study defines an essential role for type I IFN, produced via cooperation between multiple host sensors and acting directly on nonhematopoietic cells, in the control of CHIKV.

ADAM (a disintegrin and metalloproteinase) proteins have a predominant role in the protein ectodomain shedding of membrane-bound molecules. ADAMs have emerged as critical regulators of cell-cell signaling during development and homeostasis, and are believed to contribute to pathologies, such as cancer, where their regulation is altered. ADAM9 is consistently overexpressed in various human cancers, and plays a role in tumorigenesis in mouse models. ADAM9 cleaves and releases a number of molecules with important roles in tumorigenesis and angiogenesis, such as EGF, FGFR2iiib, Tie-2, Flk-1, EphB4, CD40, VCAM-1, and VE-cadherin, and could represent a potential therapeutic target in tumors where it is highly expressed. This review provides an overview of ADAM9 with a major focus on its contribution to tumorigenesis. Its role in the shedding of cell surface molecules will be discussed along with emerging aspects of regulation and possible functions in cancer development.

The thymus represents the “cradle” for T cell development, with thymic stroma providing multiple soluble and membrane cues to developing thymocytes. Although IL-7 is recognized as an essential factor for thymopoiesis, the “environmental niche” of thymic IL-7 activity remains poorly characterized in vivo. Using bacterial artificial chromosome transgenic mice in which YFP is under control of IL-7 promoter, we identify a subset of thymic epithelial cells (TECs) that co-express YFP and high levels of Il7 transcripts (IL-7 hi cells). IL-7 hi TECs arise during early fetal development, persist throughout life, and co-express homeostatic chemokines ( Ccl19 , Ccl25 , Cxcl12 ) and cytokines ( Il15 ) that are critical for normal thymopoiesis. In the adult thymus, IL-7 hi cells localize to the cortico-medullary junction and display traits of both cortical and medullary TECs. Interestingly, the frequency of IL-7 hi cells decreases with age, suggesting a mechanism for the age-related thymic involution that is associated with declining IL-7 levels. Our temporal-spatial analysis of IL-7-producing cells in the thymus in vivo suggests that thymic IL-7 levels are dynamically regulated under distinct physiological conditions. This IL-7 reporter mouse provides a valuable tool to further dissect the mechanisms that govern thymic IL-7 expression in vivo.

The nuclear hormone receptor retinoic acid receptor-related orphan receptor gamma t (RORgamma t) is required for the generation of T helper 17 cells expressing the proinflammatory cytokine interleukin (IL)-17. In vivo, however, less than half of RORgamma t(+) T cells express IL-17. We report here that RORgamma t(+) T alphabeta cells include Foxp3(+) cells that coexist with IL-17-producing RORgamma t(+) T alphabeta cells in all tissues examined. The Foxp3(+) RORgamma t(+) T alphabeta express IL-10 and CCL20, and function as regulatory T cells. Furthermore, the ratio of Foxp3(+) to IL-17-producing RORgamma t(+) T alphabeta cells remains remarkably constant in mice enduring infection and inflammation. This equilibrium is tuned in favor of IL-10 production by Foxp3 and CCL20, and in favor of IL-17 production by IL-6 and IL-23. In the lung and skin, the largest population of RORgamma t(+) T cells express the gammadelta T cell receptor and produce the highest levels of IL-17 independently of IL-6. Thus, potentially antagonistic proinflammatory IL-17-producing and regulatory Foxp3(+) RORgamma t(+) T cells coexist and are tightly controlled, suggesting that a perturbed equilibrium in RORgamma t(+) T cells might lead to decreased immunoreactivity or, in contrast, to pathological inflammation.

ADAM9 is a membrane-anchored metalloprotease that is markedly up-regulated in several human carcinomas. Here, we show that ADAM9 is similarly up-regulated in mouse models for prostate, breast, and intestinal carcinoma. To assess whether ADAM9 is critical for the pathogenesis of prostate carcinoma, one of the most common cancers in men, we evaluated how loss of ADAM9 affects tumorigenesis in W10 mice, a mouse model for this disease. In the absence of ADAM9, most tumors in 50-week-old W10 mice were well differentiated, whereas littermate controls expressing wild-type ADAM9 had predominantly poorly differentiated, and in some cases significantly larger, tumors. Moreover, gain-of-function experiments in which ADAM9 was overexpressed in mouse prostate epithelium resulted in significant abnormalities, including epithelial hyperplasia at 4 to 6 months of age, and prostatic intraepithelial neoplasia after 1 year. A potential underlying mechanism for the role of ADAM9 in prostate cancer emerged from cell-based assays: ADAM9 can cleave and release epidermal growth factor and FGFR2iiib from cells, both of which have pivotal functions in the pathogenesis of this disease. Taken together, these results suggest that ADAM9 contributes to the pathogenesis of prostate cancer and potentially also other carcinomas, raising the possibility that ADAM9 might be a good target for antitumor drugs.

International audience; Mesenchymal stromal cells in lymphoid organs, also called lymphoid stromal cells (LSCs), play a pivotal role in immunity by forming specialized microenvironments that provide signals for leukocyte migration, positioning, and survival. Best characterized in lymphoid organs, LSCs are also abundant in the intestinal mucosa, which harbors a rich repertoire of immune cells. However, the lack of efficient procedures for isolation and purification of LSCs from the intestine has been a major limitation to their characterization. Here we report a new method to efficiently isolate, in addition to immune cells, viable lymphoid stromal cells and other stromal subsets from the intestinal lamina propria for subsequent phenotypic and functional analysis.

International audience; Profibrotic cells that develop upon injury generate permanent scar tissue and impair organ recovery, though their origin and fate are unclear. Here we show that transient expression of ADAM12 (a disintegrin and metalloprotease 12) identifies a distinct proinflammatory subset of platelet-derived growth factor receptor-α-positive stromal cells that are activated upon acute injury in the muscle and dermis. By inducible genetic fate mapping, we demonstrate in vivo that injury-induced ADAM12(+) cells are specific progenitors of a major fraction of collagen-overproducing cells generated during scarring, which are progressively eliminated during healing. Genetic ablation of ADAM12(+) cells, or knockdown of ADAM12, is sufficient to limit generation of profibrotic cells and interstitial collagen accumulation. ADAM12(+) cells induced upon injury are developmentally distinct from muscle and skin lineage cells and are derived from fetal ADAM12(+) cells programmed during vascular wall development. Thus, our data identify injury-activated profibrotic progenitors residing in the perivascular space that can be targeted through ADAM12 to limit tissue scarring.

International audience; It has been recognized that macroautophagy constitutes an important survival mechanism that allows both the maintenance of cellular homeostasis and the regulation of programmed cell death pathways (e.g., apoptosis). Although several pathogens have been described to induce autophagy, the prosurvival function of this process in infectious models remains poorly characterized. Our recent studies on chikungunya virus (CHIKV), the causative agent of major epidemics in India, Southeast Asia and southern Europe, reveal a novel mechanism by which autophagy limits the cytopathic effects of CHIKV by impinging upon virus-induced cell death pathways.

Comment in Words of wisdom. Re: Preexisting BCG-specific T cells improve intravesical immunotherapy for bladder cancer. [Eur Urol. 2012] Bladder cancer: Pre-existing immunity to BCG can boost clinical response to intravesical therapy. [Nat Rev Urol. 2012]; International audience; Therapeutic intravesical instillation of bacillus Calmette-Guérin (BCG) is effective at triggering inflammation and eliciting successful tumor immunity in patients with non-muscle invasive bladder cancer, with 50 to 70% clinical response. Therapeutic success relies on repeated instillations of live BCG administered as adjuvant therapy shortly after tumor resection; however, the precise mechanisms remain unclear. Using an experimental model, we demonstrate that after a single instillation, BCG could disseminate to bladder draining lymph nodes and prime interferon-γ-producing T cells. Nonetheless, repeated instillations with live BCG were necessary for a robust T cell infiltration into the bladder. Parenteral exposure to BCG before instillation overcame this requirement; after the first intravesical instillation, BCG triggered a more robust acute inflammatory process and accelerated T cell entry into the bladder, as compared to the standard protocol. Moreover, parenteral exposure to BCG before intravesical treatment of an orthotopic tumor markedly improved response to therapy. Indeed, patients with sustained preexisting immunity to BCG showed a significant improvement in recurrence-free survival. Together, these data suggest that monitoring patients' response to purified protein derivative, and, in their absence, boosting BCG responses by parenteral exposure before intravesical treatment initiation, may be a safe and effective means of improving intravesical BCG-induced clinical responses

An imbalance between proliferation and apoptosis is important in tumor progression. Endothelin-1 (ET-1) has vasoconstricting and mitogenic activities and may be involved in apoptosis regulation. We found that ET-1 and FasL systems were colocalized in human colon tumors and that ET-1 was secreted by human (HT-29, SW480) and rat (PROb, REGb) colon carcinoma cell lines. Bosentan, a mixed endothelin-A- and -B- (ET(A)/ET(B)) receptor antagonist, potentiated FasL- (APO-1, CD95) induced apoptosis in these cells. The specific inhibition of enzymes involved in ceramide production did not restore survival of cells exposed to FasL and bosentan. Inhibition of PKC with bisindolylmaleimide IX enhanced FasL-induced apoptosis in HT-29, PROb and REGb cells in the absence of bosentan. These results suggest that ET-1 is an autocrine survival factor able to protect colon carcinoma cells against FasL-induced apoptosis, involving the protein kinase C (PKC) but not the sphingomyelin-ceramide signaling transduction pathways.

Stromal cells in lymphoid tissues regulate lymphocyte recruitment and survival through the expression of specific chemokines and cytokines. During inflammation, the same signals recruit lymphocytes to the site of injury; however, the “lymphoid” stromal (LS) cells producing these signals remain poorly characterized. We find that mouse inflammatory lesions and tumors develop gp38+ LS cells, in recapitulation of the development of LS cells early during the ontogeny of lymphoid organs and the intestine, and express a set of genes that promotes the development of lymphocyte-permissive tissues. These gp38+ LS cells are induced by a robust pathway that requires myeloid cells but not known Toll- or NOD-like receptors, the inflammasome, or adaptive immunity. Parabiosis and inducible genetic cell fate mapping experiments indicate that local precursors, presumably resident fibroblasts rather that circulating precursors, massively proliferate and give rise to LS cells during inflammation. Our results show that LS cells are both programmed during ontogeny and reinduced during inflammation.

It is recognised that stromal cells determine cancer progression. We have previously shown that active TGFbeta produced by rat colon carcinoma cells modulated NO production in rat endothelial cells. To elucidate the role of TGFbeta and NO in the mechanisms of interaction of colon carcinoma cells with stromal cells and in cancer progression, we transfected REGb cells, a regressive colon carcinoma clone secreting latent TGFbeta, with a cDNA encoding for a constitutively-secreted active TGFbeta. Out of 20 injected rats only one tumour progressed, which was resected and sub-cultured (ReBeta cells). ReBeta cells secreted high levels of active TGFbeta. The adhesive properties of REGb and Rebeta cells to endothelial cells were similar, showing that the secretion of active TGFbeta is not involved in tumour cell adhesion to endothelial cells. ReBeta, but not REGb, cell culture supernatants inhibited cytokine-dependent NO secretion by endothelial cells, but inhibition of NO production was similar in co-cultures of REGb or ReBeta cells with endothelial cells. Therefore, secretion of active TGFbeta regulated endothelial NO synthase activity when tumour cells were distant from, but not in direct contact with, endothelial cells. However, only ReBeta cells inhibited cytokine-dependent secretion of NO in coculture with macrophages, indicating that the active-TGFbeta-NO axis confers an advantage for tumour cells in their interaction with macrophages rather than endothelial cells in cancer progression.

Imbalanced proliferation and apoptosis is important in tumor progression. Endothelin (ET)-1, a 21-amino-acid peptide with vasoconstricting and mitogenic activities, has been shown to be involved in the regulation of apoptosis. Progressive and regressive rat colon (PROb and REGb cells) carcinoma cell lines express the components of the ET-1 system (preproET-1, ET-converting enzyme and ET-receptors) and secrete ET-1. These cells also express the Fas(APO-1, CD95)/FasL system, but are resistant to FasL-induced apoptosis. We thus addressed the role of ET-1 in FasL-dependent cell death. Bosentan, a mixed ET(A)/ET(B) receptor antagonist, potentiated FasL-induced apoptosis in these cells. At low concentrations (10(-13) to 10(-10) M), ET-1 dose-dependently reversed bosentan-induced apoptosis. Bosentan sensitization to FasL-induced apoptosis was not mediated by increased expression of Fas receptor and was blocked by the caspase inhibitor zVAD-fmk. The specific inhibition of enzymes involved in ceramide production did not restore survival of cells exposed to FasL and bosentan. Our results suggest that ET-1 is a survival factor able to protect in vitro colon carcinoma cells against FasL-induced apoptosis.

Endothelin-1 (ET-1) is a powerful mitogenic and/or anti-apoptotic peptide produced by many cancer cells. To evaluate the potential role of the endothelin system in glioblastoma we first determined the cellular distribution of the mRNA and proteins of the components of the endothelin system, preproendothelin-1 (PPET-1), endothelin-converting enzyme-1 (ECE-1), and ET(A) and ET(B) receptors in human glioblastoma tissue and glioblastoma cell lines. PPET-1, ECE-1, and ET(A) receptor were highly expressed in glioblastoma vessels and in some scattered glioblastoma areas whereas ET(B) receptor was mainly found in cancer cells. This suggests that glioblastoma vessels constitute an important source of ET-1 that acts on cancer cells via the ET(B) receptor. Four human glioblastoma cell lines expressed mRNA for all of the components of the ET-1 pathway. Bosentan, a mixed ET(A) and ET(B) receptor antagonist, induced apoptosis in these cell lines in a dose-dependent manner. Apoptosis was potentiated by Fas Ligand (APO-1L, CD95L), a pro-apoptotic peptide, only in LNZ308 cells, corresponding to the known functional Fas expression in these cell lines. LNZ308 cells also expressed the long and short forms of the cellular FLICE/caspase-8 inhibitory protein (FLIP). Bosentan and a protein kinase C inhibitor down-regulated short FLIP in these cells. ET-1 induced transient phosphorylation of extracellular signal-regulated kinase but did not induce long-term thymidine incorporation in LNZ308 glioblastoma cells. These results suggest that, in glioblastoma cells, ET-1, mainly acting via the ET(B) receptor, is a survival/antiapoptotic factor produced by tumor vasculature, but not a proliferation factor, involving protein kinase C and extracellular signal-regulated kinase pathways, and stabilization of the short form of FLIP.

Chikungunya virus induces autophagy by triggering ER and oxidative stress, and this autophagy restricts apoptosis and viral propagation., Autophagy is an important survival pathway and can participate in the host response to infection. Studying Chikungunya virus (CHIKV), the causative agent of a major epidemic in India, Southeast Asia, and southern Europe, we reveal a novel mechanism by which autophagy limits cell death and mortality after infection. We use biochemical studies and single cell multispectral assays to demonstrate that direct infection triggers both apoptosis and autophagy. CHIKV-induced autophagy is mediated by the independent induction of endoplasmic reticulum and oxidative stress pathways. These cellular responses delay apoptotic cell death by inducing the IRE1α–XBP-1 pathway in conjunction with ROS-mediated mTOR inhibition. Silencing of autophagy genes resulted in enhanced intrinsic and extrinsic apoptosis, favoring viral propagation in cultured cells. Providing in vivo evidence for the relevance of our findings, Atg16LHM mice, which display reduced levels of autophagy, exhibited increased lethality and showed a higher sensitivity to CHIKV-induced apoptosis. Based on kinetic studies and the observation that features of apoptosis and autophagy were mutually exclusive, we conclude that autophagy inhibits caspase-dependent cell death but is ultimately overwhelmed by viral replication. Our study suggests that inducers of autophagy may limit the pathogenesis of acute Chikungunya disease.