Death Receptor CD95 Research Articles

Proximity Ligation Assay (PLA) to Evaluate DISC and MISC Composition.

Distribution of the death receptor CD95 into lipid rafts (aggregation) and/or its internalization may contribute to the implementation of the apoptotic signal at the detriment of the non-apoptotic signaling pathway [1-6]. Also CD95 can form different protein complexes via dynamic protein-protein interactions (PPIs) according to its interaction with soluble or transmembrane CD95L. Therefore, spatiotemporal identification of these PPIs is pivotal to anticipate the signaling pathway implemented in cells stimulated with different forms of CD95L. Also, many disorders result from dysfunctions in terms of PPI subcellular distribution and/or their intensity, rendering evaluation of these features crucial to better understand pathogenesis.In situ proximity ligation assay (PLA) is a methodology that offers the possibility to identify PPIs and to determine where these PPIs occur in subcellular location (Fig. 1). Moreover, based on imaging, this method allows a quantification of PPIs at the cellular level and with a higher specificity than classical immunofluorescence assays. We here describe PLA used to confirm CD95/FADD interaction, a protocol that may serve to highlight other CD95 partners.

Cell death-independent activities of the death receptors CD95, TRAILR1, and TRAILR2.

Since their identification more than 20 years ago, the death receptors CD95, TRAILR1, and TRAILR2 have been intensively studied with respect to their cell death-inducing activities. These receptors, however, can also trigger a variety of cell death-independent cellular responses reaching from the activation of proinflammatory gene transcription programs over the stimulation of proliferation and differentiation to induction of cell migration. The cell death-inducing signaling mechanisms of CD95 and the TRAIL death receptors are well understood. In contrast, despite the increasing recognition of the biological and pathophysiological relevance of the cell death-independent activities of CD95, TRAILR1, and TRAILR2, the corresponding signaling mechanisms are less understood and give no fully coherent picture. This review is focused on the cell death-independent activities of CD95 and the TRAIL death receptors and addresses mainly three questions: (a) how are these receptors linked to noncell death pathways at the molecular level, (b) which factors determine the balance of cell death and cell death-independent activities of CD95 and the TRAIL death receptors at the cellular level, and (c) what are the consequences of the cell death-independent functions of these receptors for their role in cancer and inflammatory diseases.

A Bak-dependent mitochondrial amplification step contributes to Smac mimetic/glucocorticoid-induced necroptosis.

Necroptosis is a form of programmed cell death that critically depends on RIP3 and MLKL. However, the contribution of mitochondria to necroptosis is still poorly understood. In the present study, we discovered that mitochondrial perturbations play a critical role in Smac mimetic/Dexamethasone (Dexa)-induced necroptosis independently of death receptor ligands. We demonstrate that the Smac mimetic BV6 and Dexa cooperate to trigger necroptotic cell death in acute lymphoblastic leukemia (ALL) cells that are deficient in caspase activation due to absent caspase-8 expression or pharmacological inhibition by the caspase inhibitor zVAD.fmk, since genetic silencing or pharmacological inhibition of RIP3 or MLKL significantly rescue BV6/Dexa-induced necroptosis. In addition, RIP3 or MLKL knockout mouse embryonic fibroblasts (MEFs) are protected from BV6/Dexa/zVAD.fmk-induced cell death. In contrast, antagonistic antibodies against the death receptor ligands TNFα, TRAIL or CD95 ligand fail to rescue BV6/Dexa-triggered cell death. Kinetic studies revealed that prior to cell death BV6/Dexa treatment causes hyperpolarization of the mitochondrial membrane potential (MMP) followed by loss of MMP, reactive oxygen species (ROS) production, Bak activation and disruption of mitochondrial respiration. Importantly, knockdown of Bak significantly reduces BV6/Dexa-induced loss of MMP and delays cell death, but not ROS production, whereas ROS scavengers attenuate Bak activation, indicating that ROS production occurs upstream of BV6/Dexa-mediated Bak activation. Consistently, BV6/Dexa treatment causes oxidative thiol modifications of Bak protein. Intriguingly, knockdown or knockout of RIP3 or MLKL protect ALL cells or MEFs from BV6/Dexa-induced ROS production, Bak activation, drop of MMP and disruption of mitochondrial respiration, demonstrating that these mitochondrial events depend on RIP3 and MLKL. Thus, mitochondria might serve as an amplification step in BV6/Dexa-induced necroptosis. These findings provide new insights into the role of mitochondrial dysfunctions during necroptosis and have important implications for the development of novel treatment approaches to overcome apoptosis resistance in ALL.

ANTI-APOPTOTIC EFFECT OF CD95 RECEPTOR IN NA VE CD8+ T-LYMPHOCYTES IN CHILDREN WITH ACUTE INFECTIOUS MONONUCLEOSIS

Acute infectious mononucleosis is a widespread viral disease, which most often manifests in childhood. The development of acute infectious mononucleosis is accompanied by the change of the CD4+/CD8+ T-lymphocytes ratio and the increase of the virus-specific CD8+ cytotoxic T-lymphocytes number. One of the T-lymphocytes number regulation mechanisms is the modulation of their progenitor cells apoptosis. The death receptor CD95 takes part in the regulation of T-lymphocytes apoptosis, including naïve T-cells. We studied the effect of CD95 receptor activation on apoptosis of naïve CD4+ and naïve cytotoxic CD8+ T-lymphocytes in healthy children and children with acute infectious mononucleosis. In this study children with acute infectious mononucleosis at the age of 9 to 16 years were included. For comparison healthy children of the same age with no clinical and laboratory signs of the disease were used. Naïve CD4+ and naïve cytotoxic CD8+ T-lymphocytes were isolated by negative magnetic immunoseparation. The analysis of naïve T-cells apoptosis and the CD95 receptor surface expression density was performed by using the flow cytometry analysis. The analysis of T-cells was performed in three variants: freshly isolated naïve CD4+ T-lymphocytes and naïve cytotoxic CD8+ T-lymphocytes, and also cells after 24 hours of the cultivation with anti-CD95 monoclonal antibodies or without them. In healthy children both CD95– and CD95+ naïve CD4+ T-lymphocytes underwent apoptosis. In children with acute infectious mononucleosis CD95– naïve CD4+ T-lymphocytes lost their susceptibility to apoptosis induction. In healthy children and children with acute infectious mononucleosis CD95– naïve cytotoxic CD8+ T-lymphocytes were resistant to apoptosis in contrast to CD95+ naïve CD4+ T-lymphocytes. In healthy children CD95 receptor did not induce apoptosis of isolated naïve CD4+ T-lymphocytes and naïve cytotoxic CD8+ T-lymphocytes. In children with acute infectious mononucleosis CD95 receptor was involved in inhibition of apoptosis of naïve cytotoxic CD8+ T-lymphocytes and did not effect on the level of apoptosis of naïve CD4+ T-lymphocytes. We suggest that CD95-dependent suppression of naïve cytotoxic CD8+ T-lymphocytes apoptosis is a protective mechanism for the maintenance of a sufficient number of cytotoxic T-lymphocytes in the blood for the realization of effective antiviral immune response.

CD95-mediated apoptosis in Burkitt's lymphoma B-cells is associated with Pim-1 down-regulation

B-cells of the high-grade non-Hodgkin lymphoma Burkitt's lymphoma (BL) overexpress survival oncoproteins, including the proviral integration site for Moloney murine leukaemia virus kinase (Pim)-1, and become apoptosis resistant. Activated death receptor CD95 after ligation with anti-CD95 monoclonal antibody (mAb) resulted in the regression of BL via induction of apoptosis, suggesting a decrease of survival protein expression. Here, CD95-mediated apoptotic pathways in BL B-cell lines (Raji and Daudi) following treatment with anti-CD95 mAb was investigated with the cause-and-effects on pim-1 gene expression, in comparison with leukemic cell line (K562) used as CD95-negative cells. Immunohistochemical staining for CD95 and Pim-1 was performed, and the effects of anti-CD95 mAb on apoptotic signalling using western blotting, on caspase activity and cell survival of BL B-cell and leukemic cell lines were determined. We showed that Raji cells expressed more CD95 receptors than Daudi cells. Half of each population underwent apoptosis accompanied by decreased cell viability after anti-CD95 mAb treatment. Distinct extrinsic and intrinsic CD95-mediated apoptotic pathways in Raji and Daudi cells were revealed by high caspase activity and mitochondrial outer membrane permeabilization, respectively. We observed decreased Pim-1 transcript and protein expression levels with increased heat-shock protein (Hsp)70 and decreased Hsp90 expression in anti-CD95 mAb-treated cells. Throughout the study, K562 cells did not undergo apoptosis upon anti-CD95 mAb treatment. Pim-1 knockdown following to stable transfection with plasmid vectors induced apoptosis and decreased viability of BL and K562 cells. Therefore, CD95-mediated apoptosis induces Pim-1 down-regulation in BL B-cells, but Pim-1 down-regulation cannot fully eradicate BL and leukaemia.

Ligand stimulation of CD95 induces activation of Plk3 followed by phosphorylation of caspase-8

Upon interaction of the CD95 receptor with its ligand, sequential association of the adaptor molecule FADD (MORT1), pro-forms of caspases-8/10, and the caspase-8/10 regulator c-FLIP leads to the formation of a death-inducing signaling complex. Here, we identify polo-like kinase (Plk) 3 as a new interaction partner of the death receptor CD95. The enzymatic activity of Plk3 increases following interaction of the CD95 receptor with its ligand. Knockout (KO) or knockdown of caspase-8, CD95 or FADD prevents activation of Plk3 upon CD95 stimulation, suggesting a requirement of a functional DISC for Plk3 activation. Furthermore, we identify caspase-8 as a new substrate for Plk3. Phosphorylation occurs on T273 and results in stimulation of caspase-8 proapoptotic function. Stimulation of CD95 in cells expressing a non-phosphorylatable caspase-8-T273A mutant in a rescue experiment or in Plk3-KO cells generated by CRISPR/Cas9 reduces the processing of caspase-8 prominently. Low T273 phosphorylation correlates significantly with low Plk3 expression in a cohort of 95 anal tumor patients. Our data suggest a novel mechanism of kinase activation within the Plk family and propose a new model for the stimulation of the extrinsic death pathway in tumors with high Plk3 expression.

Manipulations of the TNF-Receptor Affinity and Oligomerization Characterized by Fluorescence Lifetime Measurements

Tumor necrosis factor (TNF) receptor 1 (TNFR1) and Death Receptor 5 (DR5) are members of the TNF receptor superfamily that are activated by binding to their ligands, TNFα and TNF-related apoptosis-inducing ligand (TRAIL) respectively. The TNFα-TNFR1 signaling pathway culminates with NF-κB activation and inflammatory response. The TRAIL-DR5 signaling pathway culminates in apoptosis. Recently, we have shown that TRAIL-induced apoptosis is initiated through the formation of large and highly structured networks held together by receptor dimers. In our current work, we use fluorescence lifetime measurements to study TNFR1. As an initial control to validate our approach, we monitored receptor-receptor binding affinity as a function of temperature and detergent concentration. Here, we have extended these initial studies to include investigation of the role of cholesterol and cytochalasin B. We have recently shown that cholesterol depletion in cells does not inhibit the formation of DR5 networks but, interestingly, does fail to initiate apoptosis. Others have shown that disruption of actin cytoskeleton by cytochalasin B in death receptor CD95, another member of the TNF receptor superfamily, induces and enhances apoptosis. Our lifetime measurements are used to investigate any potential connection between these cell-level observations and the biophysics of TNF-Receptor oligomerization.

Increased extrafollicular expression of the B-cell stimulatory molecule CD70 in HIV-1-infected individuals.

CD70 molecules expressed by activated T cells provide potent B cell stimulatory signals. We hypothesized that an altered CD70 expression might contribute to B cell abnormalities during HIV-1 infection. CD70 expression and the functional and migratory properties of the CD4CD70 T lymphocytes were analyzed in HIV-1-infected patients and in humanized mice. Correlations were tested between CD70 expression and features of B-cell activation, apoptosis sensitivity and functional exhaustion. CD4CD70 T cells were analyzed in cohorts of CD4 T-cell lymphopenic, viremic or nonlymphopenic, nonviremic HIV-1-infected patients and in noninfected individuals. CD70 upregulation was also followed in HIV-1-infected humanized mice. CD38, CD95, LAIR1 and PD-1 expressions were monitored on B-cell subpopulations, Ki67 was assessed to estimate B-cell proliferation and antibody levels were measured in plasma. Blood CD4CD70 T-cell frequencies increased in response to CD4 T-cell depletion or high viremia levels as a possible consequence of increased activation and proliferation in this subset. CD4CD70 T cells produced T-helper 1-type cytokines and expressed chemokine receptors mobilizing toward sites of inflammation but not to lymphoid follicles. High CD70 expression was observed in HIV-1-infected humanized mice at extrafollicular sites (peritoneum, bone-marrow). CD4CD70 T-cell frequencies correlated with the expression of the activation marker CD38 and the death receptor CD95 on various memory B-cell subsets, with B-cell proliferation and with plasma IgG levels. CD4CD70 T cells may contribute to B cell hyperactivation and accelerated memory B-cell turnover during HIV-1 infection.

The tragic fate of group 3 innate lymphoid cells during HIV-1 infection.

HIV-1 infection usually leads to systemic chronic inflammation that is associated with gut microbial translocation. The recently defined group 3 innate lymphoid cells (ILC3s) are critical for maintenance of intestinal barrier function; however, it is not clear whether and how HIV-1 infection influences the function of these cells. In this issue of the JCI, Zhang and colleagues present compelling evidence that the survival and function of ILC3s are dramatically impaired by HIV-1 infection. The authors provide evidence that HIV-1 infection induces persistent activation of plasmacytoid dendritic cells (pDCs) and production of type I IFNs, which together increase expression of death receptor CD95 on ILC3s and thereby promote subsequent ILC3 apoptosis. Together, these results identify a mechanism that explains the impaired intestinal barrier function that results from chronic HIV-1 infection and shed light on the role of pDCs in HIV-1 immunopathogenesis and therapy.

Abstract LB-094: Regorafenib and sildenafil interact to kill tumor cells

Abstract The present studies were to determine whether the multi-kinase inhibitor sorafenib or its derivative regorafenib interacted with phosphodiesterase 5 (PDE5) inhibitors such as sildenafil (Viagra) to kill tumor cells. PDE5 and PDGFR (alpha and beta) were over-expressed in liver tumors compared to normal liver tissue. In multiple cell types in vitro sorafenib/regorafenib and PDE5 inhibitors interacted in a greater than additive fashion to cause tumor cell death. Knock down of PDE5 or of PDGFR (alpha and beta) recapitulated the effects of the individual drugs. The drug combination increased ROS/RNS levels that were causal in cell killing. RNS stimulated the activation of the death receptor CD95 as well as the formation of autophagosomes and autolysosomes. Inhibition of CD95 / FADD / caspase 8 signaling suppressed drug combination toxicity. Knock down of ULK-1, Beclin1 or ATG5 suppressed drug combination lethality. The drug combination inactivated ERK, AKT, p70 S6K and mTOR and activated JNK. The drug combination also reduced mTOR protein expression. Activation of ERK or AKT was modestly protective whereas re-expression of an activated mTOR protein or inhibition of JNK signaling almost abolished drug combination toxicity. Sildenafil and sorafenib / regorafenib interacted in vivo to suppress xenograft tumor growth using liver and colon cancer cells. PDE5 inhibitors and sorafenib / regorafenib are FDA approved agents, and our data is now being translated into the clinic for further determination as to whether this drug combination is a useful anti-tumor therapy for solid tumor patients. Citation Format: Mehrad Tavallai, Laurence Booth, Jane L. Roberts, Andrew Poklepovic, Paul Dent. Regorafenib and sildenafil interact to kill tumor cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr LB-094. doi:10.1158/1538-7445.AM2015-LB-094

Modulation of SIV and HIV DNA vaccine immunity by Fas-FasL signaling.

Signaling through the Fas/Apo-1/CD95 death receptor is known to affect virus-specific cell-mediated immune (CMI) responses. We tested whether modulating the Fas-apoptotic pathway can enhance immune responses to DNA vaccination or lymphocytic choriomeningitis virus (LCMV) infection. Mice were electroporated with plasmids expressing a variety of pro- or anti-apoptotic molecules related to Fas signaling and then either LCMV-infected or injected with plasmid DNA expressing SIV or HIV antigens. Whereas Fas or FasL knockout mice had improved CMI, down-regulation of Fas or FasL by shRNA or antibody failed to improve CMI and was accompanied by increases in regulatory T cells (Treg). Two “adjuvant” plasmids were discovered that significantly enhanced plasmid immunizations. The adjuvant effects of Fas-associated death domain (FADD) and of cellular FLICE-inhibitory protein (cFLIP) were consistently accompanied by increased effector memory T lymphocytes and increased T cell proliferation. This adjuvant effect was also observed when comparing murine infections with LCMV-Armstrong and its persisting variant LCMV-Clone 13. LCMV-Armstrong was cleared in 100% of mice nine days after infection, while LCMV-Clone 13 persisted in all mice. However, half of the mice pre-electroporated with FADD or cFLIP plasmids were able to clear LCMV-Clone 13 by day nine, and, in the case of cFLIP, increased viral clearance was accompanied by higher CMI. Our studies imply that molecules in the Fas pathway are likely to affect a number of events in addition to the apoptosis of cells involved in immunity.

Lipid rafts and raft-mediated supramolecular entities in the regulation of CD95 death receptor apoptotic signaling.

Membrane lipid rafts are highly ordered membrane domains enriched in cholesterol, sphingolipids and gangliosides that have the property to segregate and concentrate proteins. Lipid and protein composition of lipid rafts differs from that of the surrounding membrane, thus providing sorting platforms and hubs for signal transduction molecules, including CD95 death receptor-mediated signaling. CD95 can be recruited to rafts in a reversible way through S-palmitoylation following activation of cells with its physiological cognate ligand as well as with a wide variety of inducers, including several antitumor drugs through ligand-independent intracellular mechanisms. CD95 translocation to rafts can be modulated pharmacologically, thus becoming a target for the treatment of apoptosis-defective diseases, such as cancer. CD95-mediated signaling largely depends on protein-protein interactions, and the recruitment and concentration of CD95 and distinct downstream apoptotic molecules in membrane raft domains, forming raft-based supramolecular entities that act as hubs for apoptotic signaling molecules, favors the generation and amplification of apoptotic signals. Efficient CD95-mediated apoptosis involves CD95 and raft internalization, as well as the involvement of different subcellular organelles. In this review, we briefly summarize and discuss the involvement of lipid rafts in the regulation of CD95-mediated apoptosis that may provide a new avenue for cancer therapy.

Tauroursodeoxycholate Protects Rat Hepatocytes from Bile Acid-Induced Apoptosis via β1-Integrin- and Protein Kinase A-Dependent Mechanisms

Background/Aims: Ursodeoxycholic acid, which in vivo is rapidly converted into its taurine conjugate, is frequently used for the treatment of cholestatic liver disease. Apart from its choleretic effects, tauroursodeoxycholate (TUDC) can protect hepatocytes from bile acid-induced apoptosis, but the mechanisms underlying its anti-apoptotic effects are poorly understood. Methods: These mechanisms were investigated in perfused rat liver and isolated rat hepatocytes. Results: It was found that TUDC inhibited the glycochenodeoxycholate (GCDC)-induced activation of the CD95 death receptor at the level of association between CD95 and the epidermal growth factor receptor. This was due to a rapid TUDC-induced β₁-integrin-dependent cyclic AMP (cAMP) signal with induction of the dual specificity mitogen-activated protein (MAP) kinase phosphatase 1 (MKP-1), which prevented GCDC-induced phosphorylation of mitogen-activated protein kinase kinase 4 (MKK4) and c-jun-NH₂-terminal kinase (JNK) activation. Furthermore, TUDC induced a protein kinase A (PKA)-mediated serine/threonine phosphorylation of the CD95, which was recently identified as an internalization signal for CD95. Furthermore, TUDC inhibited GCDC-induced CD95 targeting to the plasma membrane in a β₁-integrin-and PKA-dependent manner. In line with this, the β₁-integrin siRNA knockdown in sodium taurocholate cotransporting polypeptide (Ntcp)-transfected HepG2 cells abolished the protective effect of TUDC against GCDC-induced apoptosis. Conclusion: TUDC exerts its anti-apoptotic effect via a β₁-integrin-mediated formation of cAMP, which prevents CD95 activation by hydrophobic bile acids at the levels of JNK activation and CD95 serine/threonine phosphorylation.

Regulation of OSU-03012 toxicity by ER stress proteins and ER stress-inducing drugs.

The present studies examined the toxic interaction between the non-coxib celecoxib derivative OSU-03012 and phosphodiesterase 5 (PDE5) inhibitors, and also determined the roles of endoplasmic reticulum stress response regulators in cell survival. PDE5 inhibitors interacted in a greater than additive fashion with OSU-03012 to kill parental glioma and stem-like glioma cells. Knockdown of the endoplasmic reticulum stress response proteins IRE1 or XBP1 enhanced the lethality of OSU-03012, and of [OSU-03012 + PDE5 inhibitor] treatment. Pan-caspase and caspase-9 inhibition did not alter OSU-03012 lethality but did abolish enhanced killing in the absence of IRE1 or XBP1. Expression of the mitochondrial protective protein BCL-XL or the caspase-8 inhibitor c-FLIP-s, or knockdown of death receptor CD95 or the death receptor caspase-8 linker protein FADD, suppressed killing by [OSU-03012 + PDE5 inhibitor] treatment. CD95 activation was blocked by the nitric oxide synthase inhibitor L-NAME. Knockdown of the autophagy regulatory proteins Beclin1 or ATG5 protected the cells from OSU-03012 and from [OSU-03012 + PDE5 inhibitor] toxicity. Knockdown of IRE1 enhanced OSU-03012/[OSU-03012 + PDE5 inhibitor]-induced JNK activation, and inhibition of JNK suppressed the elevated killing caused by IRE1 knockdown. Knockdown of CD95 blunted JNK activation. Collectively, our data demonstrate that PDE5 inhibitors recruit death receptor signaling to enhance OSU-03012 toxicity in glioblastoma multiforme (GBM) cells.

Induction of death receptor CD95 and co-stimulatory molecules CD80 and CD86 by meningococcal capsular polysaccharide-loaded vaccine nanoparticles.

Neisseria meningitidis is a leading cause of bacterial meningitis and sepsis, and its capsular polysaccharides (CPS) are a major virulence factor in meningococcal infections and form the basis for serogroup designation and protective vaccines. We formulated a novel nanovaccine containing meningococcal CPS as an antigen encapsulated in albumin-based nanoparticles (NPs) that does not require chemical conjugation to a protein carrier. These nanoparticles are taken up by antigen-presenting cells and act as antigen depot by slowly releasing the antigen. In this study, we determined the ability of CPS-loaded vaccine nanoparticles to induce co-stimulatory molecules, namely CD80, CD86, and CD95 that impact effective antigen presentation. Co-stimulatory molecule gene induction and surface expression on macrophages and dendritic cells pulsed with meningococcal CPS-loaded nanoparticles were investigated using gene array and flow cytometry methods. Meningococcal CPS-loaded NP significantly induced the surface protein expression of CD80 and CD86, markers of dendritic cell maturation, in human THP-1 macrophages and in murine dendritic cells DC2.4 in a dose-dependent manner. The massive upregulation was also observed at the gene expression. However, high dose of CPS-loaded NP, but not empty NP, induced the expression of death receptor CD95 (Fas) leading to reduced TNF-α release and reduction in cell viability. The data suggest that high expression of CD95 may lead to death of antigen-presenting cells and consequently suboptimal immune responses to vaccine. The CPS-loaded NP induces the expression of co-stimulatory molecules and acts as antigen depot and can spare antigen dose, highly desirable criteria for vaccine formulations.

Loss of the death receptor CD95 (Fas) expression by dendritic cells protects from a chronic viral infection.

Chronic viral infections incapacitate adaptive immune responses by "exhausting" virus-specific T cells, inducing their deletion and reducing productive T-cell memory. Viral infection rapidly induces death receptor CD95 (Fas) expression by dendritic cells (DCs), making them susceptible to elimination by the immune response. Lymphocytic choriomeningitis virus (LCMV) clone 13, which normally establishes a chronic infection, is rapidly cleared in C57Black6/J mice with conditional deletion of Fas in DCs. The immune response to LCMV is characterized by an extended survival of virus-specific effector T cells. Moreover, transfer of Fas-negative DCs from noninfected mice to preinfected animals results in either complete clearance of the virus or a significant reduction of viral titers. Thus, DC-specific Fas expression plays a role in regulation of antiviral responses and suggests a strategy for stimulation of T cells in chronically infected animals and humans to achieve the clearance of persistent viruses.

Synergistic Cooperation Between Sunitinib and Cisplatin Promotes Apoptotic Cell Death in Human Medullary Thyroid Cancer

Tyrosine kinase inhibitors represent a new treatment option for patients with advanced medullary thyroid cancer (MTC). However, cures have not been achieved with current available agents used in monotherapy. Because RET has been shown to negatively regulate CD95 death receptor activation in preclinical models of RET-dependent MTC, we investigated the potential of the combination approach with the RET-targeting tyrosine kinase inhibitor sunitinib and cisplatin to enhance apoptosis activation through the extrinsic pathway. The effects of sunitinib and cisplatin were examined in human MTC cell lines harboring oncogenic RET mutations. Experiments were designed to determine drug effects on RET signaling, cell growth, apoptosis, autophagy, and tumor growth in mice and to investigate the mechanisms of the drug interaction. Sunitinib and cisplatin synergistically inhibited the growth of MZ-CRC-1 cells harboring the RET M918T activating mutation. The combination enhanced apoptosis activation through CD95-mediated, caspase-8-dependent pathway. Moreover, sunitinib induced a severe perturbation of the autophagic flux characterized by autophagosome accumulation and a remarkable lysosomal dysfunction, which was further enhanced, with lysosomal leakage induction, by cisplatin. Administration of the drug combination to mice xenografted with MZ-CRC-1 cells improved the antitumor efficacy, as compared with single-agent treatments, inducing complete responses in 30% of the treated mice, a significant increase in caspase-3 activation (P < .01 vs cisplatin, and P < .0005 vs sunitinib) and apoptosis in tumor cells. Addition of cisplatin to sunitinib potentiates apoptotic cell death and has promising preclinical activity in MTCs harboring the RET M918T oncogene.

Abstract A64: Synergistic cooperation between sunitinib and cisplatin promotes apoptotic cell death in human medullary thyroid cancer.

Abstract Recent clinical trials with tyrosine kinase inhibitors (TKIs) have demonstrated therapeutic benefit in patients with advanced medullary thyroid cancer (MTC), a disease poorly responsive to conventional chemotherapy. However, new therapeutic strategies are needed to obtain complete durable responses. The RET TK receptor, which is deeply implicated in the pathogenesis of both inherited and sporadic MTCs, is a major target of most TKIs under clinical investigation in MTC. RET germline mutations represent the pathogenic drivers of MEN2 syndromes and somatic oncogenic mutations of RET are present in 30-50% of sporadic MTCs. Since RET has been shown to negatively regulate CD95 death receptor activation in preclinical models of RET-dependent MTC, we investigated the therapeutic potential of the combination of the RET targeting TKI sunitinib with cisplatin, a known activator of the apoptotic extrinsic pathway. Experiments were designed to determine the effects of the drug combination in human MTC cell lines harboring oncogenic RET mutations. RET signaling, cell growth, apoptosis, autophagy, tumor growth in mice, and the mechanisms underlying the drug interaction were investigated using standardized methods. Assessment of the drug interaction was carried out by the Combination Index method. Sunitinib and cisplatin synergistically inhibited the growth of MZ-CRC-1 cells harboring the RET M918T activating mutation typical of the vast majority of MEN2B-associated and sporadic MTCs. The combination enhanced apoptosis activation through CD95-mediated, caspase-8 dependent, pathway. Moreover, sunitinib induced a severe perturbation of the autophagic flux characterized by autophagosome accumulation and a remarkable lysosomal dysfunction which was further enhanced, with lysosomal leakage induction, by cisplatin. Administration of the drug combination to mice xenografted with MZCRC-1 cells significantly improved the antitumor efficacy, as compared to single agent treatments, enhancing tumor growth inhibition and inducing complete responses in 30% of treated mice. In addition, a significant increase in caspase-3 activation (P&amp;lt;0.01 vs cisplatin, P&amp;lt;0.0005 vs sunitinib) and apoptosis was observed in tumor cells. Overall, these findings indicate that addition of cisplatin to sunitinib potentiates drug induced cell death in MTC cells through a mechanism involving both the apoptotic and the autophagic/lysosomal systems, and has promising preclinical activity in MTCs harboring the RET M918T oncogene. Citation Information: Mol Cancer Ther 2013;12(11 Suppl):A64. Citation Format: Alessia Lopergolo, Valentina Nicolini, Denis Cominetti, Marco Folini, Paola Perego, Vittoria Castiglioni, Eugenio Scanziani, Maria Grazia Borrello, Nadia Zaffaroni, Giuliana Cassinelli, Cinzia Lanzi. Synergistic cooperation between sunitinib and cisplatin promotes apoptotic cell death in human medullary thyroid cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr A64.

Innate immunity in the Grid2 Lc/+ mouse model of cerebellar neurodegeneration: glial CD95/CD95L plays a non-apoptotic role in persistent neuron loss-associated inflammatory reactions in the cerebellum

BackgroundThere is growing evidence that the death receptor CD95 has a wider role in non-apoptotic functions. In the brain, it may contribute to neural death and to the associated inflammatory reaction via a non-apoptotic pathway. Brain injury triggers an inflammatory reaction in which the CD95/CD95L system acts principally through peripheral cells recruited to the lesion. In cases of inflammation within the brain, with no blood–brain barrier leakage, the role of the CD95/CD95L system is thus unclear. We investigated the possible role of CD95 and CD95L in such conditions, by studying the relationships between glial cell activation, neuron death and CD95/CD95L expression in the cerebellum of the Lurcher (Grid2Lc/+) mutant mouse, a model of cerebellar neurodegeneration.MethodsGlial cells in slices of wild-type and Lurcher mouse cerebella were observed by light microscopy at various ages overlapping periods of neuron loss and of pre- and post-neurodegeneration. Subcellular organization was studied by electron microscopy. We assessed CD95 levels by western blotting, RT-PCR and glial cell cultures. The levels of CD95L and IL-6 were studied by ELISA and a biological assay, respectively.ResultsIn the Grid2Lc/+cerebellum, neuron loss triggers a typical, but abnormally persistent, inflammatory reaction. We identified two phases of astrogliosis: an early burst of large glial cell activation, peaking at postnatal days 25 to 26, coinciding with peak cerebellar neuron loss, followed by a long period of slow decline indicating that the strength of the glial reaction is modulated by neuron mortality rates. Comparisons of time-courses of glial cell activation, cytokine production and neuron loss revealed that the number of surviving neurons decreased as CD95 increased. Thus, CD95 cannot be directly involved in neuron death, and its role must be limited to a contribution to the inflammatory reaction. The upregulation of CD95 likely on astrocytes coincides with increases in the levels of IL-6, a cytokine produced principally by astrocytes, and soluble CD95L.ConclusionsThese results suggest that CD95 and soluble CD95L contribute, via non-apoptotic signaling, to the inflammatory reaction initiated early in neuron death within the Grid2Lc/+ cerebellum.

Essential roles of PKA, iNOS, CD95/CD95L, and terminal caspases in suppression of eosinopoiesis by PGE2 and other cAMP-elevating agents.

Up- and downregulation of eosinopoiesis control pulmonary eosinophilia in human asthma. In mice, eosinopoiesis is suppressed in vitro by prostaglandin E2 (PGE2) and in vivo by diethylcarbamazine, through a proapoptotic mechanism sequentially requiring inducible NO synthase (iNOS) and the ligand for death receptor CD95 (CD95L). We examined the roles of iNOS, cAMP-mediated signaling, caspases, and CD95L/CD95 in suppression of eosinopoiesis by PGE2 and other agents signaling through cAMP. Bone-marrow collected from BALB/c mice, or from iNOS-, CD95-, or CD95L-deficient mutants (and wild-type controls), was cultured with interleukin-5 (IL-5), alone or associated with PGE2, cAMP-inducing/mimetic agents, caspase inhibitor zVAD-fmk, iNOS inhibitor aminoguanidine, or combinations thereof, and eosinopoiesis was evaluated at various times. PGE2, added up to 24 hours of culture, dose-dependently suppressed eosinopoiesis, by inducing apoptosis. This effect was (a) paralleled by induction of iNOS in eosinophils; (b) duplicated by sodium nitroprusside, isoproterenol, and cAMP-inducing/mimetic agents; (c) prevented by protein kinase A inhibition. NO was produced through iNOS by dibutyryl-cAMP-stimulated bone-marrow. Overall, PGE2 and isoproterenol shared a requirement for four effector elements (iNOS, CD95L, CD95, and terminal caspases), which together define a pathway targeted by several soluble up- and downmodulators of eosinopoiesis, including drugs, mediators of inflammation, and cytokines.