The tumor necrosis factor (TNF) and TNF receptor (TNFR) gene superfamilies regulate diverse biological functions, including cell proliferation, differentiation, and survival [1] [2] [3]. We have identified a new TNF-related ligand, designated human GITR ligand (hGITRL), and its human receptor (hGITR), an ortholog of the recently discovered murine glucocorticoid-induced TNFR-related (mGITR) protein [4]. The hGITRL gene mapped to chromosome 1q23, near the gene for the TNF homolog Fas/CD95 ligand [5]. The hGITR gene mapped to chromosome 1p36, near a cluster of five genes encoding TNFR homologs [1] [6]. We found hGITRL mRNA in several peripheral tissues, and detected hGITRL protein on cultured vascular endothelial cells. The levels of hGITR mRNA in tissues were generally low; in peripheral blood T cells, however, antigen-receptor stimulation led to a substantial induction of hGITR transcripts. Cotransfection of hGITRL and hGITR in embryonic kidney 293 cells activated the anti-apoptotic transcription factor NF-kappaB, via a pathway that appeared to involve TNFR-associated factor 2 (TRAF2) [7] and NF-kappaB-inducing kinase (NIK) [8]. Cotransfection of hGITRL and hGITR in Jurkat T leukemia cells inhibited antigen-receptor-induced cell death. Thus, hGITRL and hGITR may modulate T lymphocyte survival in peripheral tissues.

Neutrophils are abundant, short-lived leukocytes, and their death by apoptosis is central to hemostasis and the resolution of inflammation, yet the trigger for their entry into apoptosis is unknown. We show here that death receptor signaling, including CD95 death-inducing signaling complex (DISC) formation and caspase 8 activation, occurred early in neutrophil apoptosis. However, death receptor ligation was not required for apoptosis, suggesting a novel mechanism for caspase 8 activation. We detected ceramide generation and clustering of CD95 in lipid rafts early in neutrophil apoptosis, and neutrophil apoptosis and ceramide generation were both significantly inhibited in acid sphingomyelinase knockout (ASM(-/-)) mice compared to wild-type littermates. Further studies revealed that ceramide generation, CD95 clustering, and neutrophil apoptosis were dependent on reactive oxygen species (ROSs) and were preceded by a fall in reduced glutathione levels. We propose that accumulation of ROSs, as a consequence of altered redox status, initiates ligand-independent death receptor signaling via activation of ASM and clustering of preformed DISC components in lipid rafts and is therefore a primary factor limiting neutrophil life span.

Cytomegalovirus (CMV) infection is endemic in Gambian infants, with 62% infected by 3 months and 85% by 12 months of age. We studied the CD8 T-cell responses of infants to CMV following primary infection. CMV-specific CD8 T cells, identified with tetramers, showed a fully differentiated phenotype (CD28(-) CD62L(-) CD95(+) perforin(+) granzyme A(+) Bcl-2(low)). Strikingly, the overall CD8 T-cell population developed a similar phenotype following CMV infection, which persisted for at least 12 months. In contrast, primary infection was accompanied by up-regulation of markers of activation (CD45R0 and HLA-D) on both CMV-specific cells and the overall CD8 T-cell population and division (Ki-67) of specific cells, but neither pattern persisted. At 12 months of age, the CD8 T-cell population of CMV-infected infants was more differentiated than that of uninfected infants. Although the subpopulation of CMV-specific cells remained constant, the CMV peptide-specific gamma interferon response was lower in younger infants and increased with age. As the CD8 T-cell phenotype induced by CMV is indicative of immune dysfunction in the elderly, the existence of a similar phenotype in large numbers of Gambian infants raises the question of whether CMV induces a similarly deleterious effect.

In chemosensitive leukemias and solid tumors, anticancer drugs have been shown to induce apoptosis. Deficiencies in the apoptotic pathways may lead to chemoresistance. Here we report that glutathione (GSH) plays a critical role in activation of apoptosis pathways by CD95 (APO-1/Fas) or anticancer drugs. Upon treatment with anticancer drugs or CD95 triggering, CD95-resistant or Bcl-x(L) overexpressing CEM cells were deficient in activation of apoptosis pathways. CD95-resistant and Bcl-x(L) overexpressing CEM cells exhibited higher intracellular GSH levels in comparison to parental cells. Downregulation of GSH by L-buthionine-(S,R)-sulfoxime (BSO), a specific inhibitor of glutathione synthesis, reversed deficiencies in activation of apoptosis pathways by anticancer drugs or CD95. Interestingly, downregulation of GSH by BSO increased CD95 DISC formation in type I cells. In hybrids of CD95-resistant cells with sensitive cells and hybrids of overexpressing Bcl-x(L) cells with sensitive cells, the phenotype of apoptosis resistance was dominant. Also, in these hybrids, downregulation of GSH reversed CD95- and chemoresistance. We conclude that dominant apoptosis resistance depends, at least in part, on intracellular GSH levels, which may affect apoptosis signaling at different compartments, for example, the death receptor or mitochondria.

Apoptosis of activated peripheral T cells during the termination phase of an immune response is critical to maintain T-cell homeostasis. Activated T cells can be removed by two mechanisms: activation-induced cell death (AICD) and death by neglect. AICD is triggered by death receptors, whereas death by neglect is induced by cytokine withdrawal. CD95 (APO-1/Fas) belongs to the subfamily of death receptors and plays a major role in AICD. In this review, we focus on the molecular mechanisms of AICD, in particular those involving the CD95 system. Moreover, we discuss the relative contribution of AICD and death by neglect to terminate a T-cell immune response. In order to become fully activated, T cells require a second signal provided by antigen-presenting cells. We discuss how these costimulatory signals counteract pro-apoptotic signals and, finally, which signals might protect T cells from death to generate a pool of memory T cells.

The glycosyltransferase, ST6Gal-I, adds sialic acid in an α2-6 linkage to the N-glycans of membrane and secreted glycoproteins. Up-regulation of ST6Gal-I occurs in many cancers, including colon carcinoma, and correlates with metastasis and poor prognosis. However, mechanisms by which ST6Gal-I facilitates tumor progression remain poorly understood due to limited knowledge of enzyme substrates. Herein we identify the death receptor, Fas (CD95), as an ST6Gal-I substrate, and show that α2-6 sialylation of Fas confers protection against Fas-mediated apoptosis. Intriguingly, differences in ST6Gal-I activity do not affect the function of DR4 or DR5 death receptors upon treatment with TRAIL, implicating a selective effect of ST6Gal-I on the Fas receptor. Using ST6Gal-I knockdown and forced overexpression colon carcinoma cell models, we find that α2-6 sialylation of Fas prevents apoptosis stimulated by FasL as well as the Fas-activating antibody, CH11, as evidenced by decreased activation of caspases 8 and 3. We also show that α2-6 sialylation of Fas does not alter the binding of CH11, but rather inhibits the capacity of Fas to induce apoptosis by blocking the association of FADD with Fas cytoplasmic tails, an event that initiates death-inducing signaling complex formation. Furthermore, α2-6 sialylation of Fas inhibits Fas internalization, which is required for apoptotic signaling. Although dysregulated Fas activity is a well known mechanism through which tumors evade apoptosis, the current study is the first to link Fas insensitivity to the actions of a specific sialyltransferase. This finding establishes a new paradigm by which death receptor function is impaired for the self-protection of tumors against apoptosis.

Apoptosis is central for the control and elimination of viral infections. In chronic hepatitis C virus (HCV) infection, enhanced hepatocyte apoptosis and upregulation of the death inducing ligands CD95/Fas, TRAIL and TNFalpha occur. Nevertheless, HCV infection persists in the majority of patients. The impact of apoptosis in chronic HCV infection is not well understood. It may be harmful by triggering liver fibrosis, or essential in interferon (IFN) induced HCV elimination. For virtually all HCV proteins, pro- and anti-apoptotic effects have been described, especially for the core and NS5A protein. To date, it is not known which HCV protein affects apoptosis in vivo and whether the infectious virions act pro- or anti-apoptotic. With the availability of an infectious tissue culture system, we now can address pathophysiologically relevant issues. This review focuses on the effect of HCV infection and different HCV proteins on apoptosis and of the corresponding signaling cascades.

Human immunodeficiency virus, type 1 (HIV-1), vpr gene encodes a 14-kDa virion-associated protein, which exhibits significant effects on human cells. One important property of Vpr is its ability to induce apoptosis during infection. Apoptotic induction is likely to play a role in the pathogenesis of AIDS. However, the pathway of apoptosis is not clearly defined. In this report we investigate the mechanism of apoptosis induced by HIV-1 Vpr using a Vpr pseudotype viral infection system or adeno delivery of Vpr in primary human lymphoid cells and T-cells. With either vector, HIV-1 Vpr induced cell cycle arrest at the G(2)/M phase and apoptosis in lymphoid target cells. Furthermore, we observed that with both vectors, caspase 9, but not caspase 8, was activated following infection of human peripheral blood mononuclear cell with either Vpr-positive HIV virions or adeno-delivered Vpr. Activation of the caspase 9 pathway resulted in caspase 3 activation and apoptosis in human primary cells. These effects were coincident with the disruption of the mitochondrial transmembrane potential and induction of cytochrome c release by Vpr. The Vpr-induced signaling pathway did not induce CD95 or CD95L expression. Bcl-2 overexpressing cells succumb to Vpr-induced apoptosis. These studies illustrate that Vpr induces a mitochondria-dependent apoptotic pathway that is distinct from apoptosis driven by the Fas-FasL pathway.

Apoptosis may be an important mechanism of cell loss in Alzheimer's disease (AD). Experimentally, apoptosis is preceded by nuclear accumulation of p53, and increased expression of Fas (CD95) antigen. In the present study, quantitative Western blot analysis of postmortem frontal and temporal lobe tissue demonstrated significantly higher mean levels of p53 and Fas in AD relative to age-matched controls. Immunohistochemical staining and in situ apoptosis assays demonstrated increased p53 and Fas expression and DNA fragmentation in overlapping populations of cortical neurons, and cortical and white matter glial cells distributed in regions damaged by neurodegeneration. Double-label immunohistochemical staining studies revealed p53 immunoreactivity in: 1) cortical neurons without tau-immunoreactive neurofibrillary tangles; 2) numerous, but not all tau-immunoreactive neuropil neurites and white matter axons; 3) dystrophic fibrils surrounding amyloid-beta-immunoreactive plaques; and 4) glial cells characterized as A2B5+ protoplasmic astrocytes or oligodendrocytes. The prominent distribution of dystrophic p53-immunoreactive processes around amyloid-beta-containing plaques suggests that amyloid deposits are associated with local neuritic degeneration. In addition, the results suggest that many tau-immunoreactive neuritic processes originate from degenerating (p53) as well as regenerating neurons. Finally, apoptosis of glial cells (A2B5+) required to maintain the functional integrity of axons and dendrites may represent an important pathogenic mechanism of axonal loss and synaptic disconnection in AD.

CD95 (APO-1/Fas) is a member of the tumor necrosis factor receptor family, which can trigger apoptosis in a variety of cell types. However, little is known of the mechanisms underlying cell susceptibility to CD95-mediated apoptosis. Here we show that human T cells that are susceptible to CD95-mediated apoptosis, exhibit a constitutive polarized morphology, and that CD95 colocalizes with ezrin at the site of cellular polarization. In fact, CD95 co-immunoprecipitates with ezrin exclusively in lymphoblastoid CD4(+) T cells and primary long-term activated T lymphocytes, which are prone to CD95-mediated apoptosis, but not in short-term activated T lymphocytes, which are refractory to the same stimuli, even expressing equal levels of CD95 on the cell membrane. Pre-treatment with ezrin antisense oligonucleotides specifically protected from the CD95-mediated apoptosis. Moreover, we show that the actin cytoskeleton integrity is essential for this function. These findings strongly suggest that the CD95 cell membrane polarization, through an ezrin-mediated association with the actin cytoskeleton, is a key intracellular mechanism in rendering human T lymphocytes susceptible to the CD95-mediated apoptosis.

Decoy receptor 3 (DcR3) is a newly identified soluble protein that binds to CD95 ligand (CD95L) and inhibits its proapoptotic activity. Here we report that DcR3 is expressed by the majority of long-term and ex vivo malignant glioma cell lines as well as in human glioblastoma in vivo. Expression of DcR3 correlates with the grade of malignancy: 15 of 18 (83%) glioblastomas (WHO grade IV) but none of 11 diffuse astrocytomas (WHO grade II) exhibited DcR3 immunoreactivity. We also demonstrate that human malignant glioma cells engineered to release high amounts of DcR3 into the cell culture supernatant are protected from CD95L-induced apoptotic cell death. In contrast, DcR3 does not confer protection from the death ligand Apo2 ligand (TRAIL). Importantly, ectopic expression of DcR3 resulted in substantial differences in immune cell infiltration in the 9L rat gliosarcoma model. Thus, the infiltration of CD4+ and CD8+ T cells as well as microglia/macrophages into glioma was substantially decreased in DcR3-producing tumors compared with control tumors. Chemotaxis assays revealed that DcR3 counteracts the chemotactic activity of CD95L against microglial cells in vitro. These findings suggest that DcR3 may be involved in the progression and immune evasion of malignant gliomas.

The antitumor ether lipid ET-18-OCH(3) promotes apoptosis in tumor cells through intracellular activation of Fas/CD95. Results of this study showed that ET-18-OCH(3) induces cocapping of Fas and membrane rafts, specialized plasma membrane regions involved in signaling, before the onset of apoptosis in human leukemic cells. Patches of membrane rafts accumulated Fas clusters in leukemic cells treated with ET-18-OCH(3). Sucrose gradient centrifugation of Triton X-100 cell lysates showed that Fas translocated into membrane rafts following ET-18-OCH(3) treatment of T-leukemic Jurkat cells. Disruption of membrane raft integrity by methyl-beta-cyclodextrin or filipin inhibited ET-18-OCH(3)-induced apoptosis in leukemic primary cells and cell lines. Fas clustering was also inhibited by methyl-beta-cyclodextrin. These data indicate that ET-18-OCH(3) reorganizes membrane rafts to trigger apoptosis in human leukemic cells, and that Fas coaggregation with membrane rafts is required for ET-18-OCH(3)-induced apoptosis. This translocation of Fas into membrane rafts may provide a mechanism for amplifying Fas signaling by reorganization of membrane microdomains.

A20 is a Cys2/Cys2 zinc finger protein which is induced by a variety of inflammatory stimuli and which has been characterized as an inhibitor of cell death by a yet unknown mechanism. In order to clarify its molecular mechanism of action, we used the yeast two-hybrid system to screen for proteins that interact with A20. A cDNA fragment was isolated which encoded a portion of a novel protein (TXBP151), which was recently found to be a human T-cell leukemia virus type-I (HTLV-I) Tax-binding protein. The full-length 2386 bp TXBP151 mRNA encodes a protein of 86 kDa. Like A20, overexpression of TXBP151 could inhibit apoptosis induced by tumour necrosis factor (TNF) in NIH3T3 cells. Moreover, transfection of antisense TXBP151 partially abolished the anti-apoptotic effect of A20. Furthermore, apoptosis induced by TNF or CD95 (Fas/APO-1) was associated with proteolysis of TXBP151. This degradation could be inhibited by the broad-spectrum caspase inhibitor zVAD-fmk or by expression of the cowpox virus-derived inhibitor CrmA, suggesting that TXBP151 is a novel substrate for caspase family members. TXBP151 was indeed found to be specifically cleaved in vitro by members of the caspase-3-like subfamily, viz. caspase-3, caspase-6 and caspase-7. Thus TXBP151 appears to be a novel A20-binding protein which might mediate the anti-apoptotic activity of A20, and which can be processed by specific caspases.

Death receptors [Fas/Apo-1/CD95, TNF-R1 [tumour necrosis factor (TNF) receptor 1], DR3 [death receptor 3], TRAIL-R1 [TNF-related apoptosis-inducing ligand receptor 1], TRAIL-R2, DR6, p75-NGFR [p75-nerve growth factor receptor], EDAR [ectodermal dysplasia receptor]] form a subgroup of the TNF-R superfamily that can induce apoptosis (programmed cell death) via a conserved cytoplasmic signalling module termed the death domain. Although death receptors have been recognized mainly as apoptosis inducers, there is growing evidence that these receptors also fulfil a variety of nonapoptotic functions. This review is focused on the molecular mechanisms of apoptotic and non-apoptotic death receptor signalling in light of the phenotype of mice deficient in the various death receptors.

Under pathological conditions, the mode of cell death, apoptosis or necrosis, is relevant for the subsequent fate of the tissue. Cell demise may be shaped by endogenous mediators such as nitric oxide (NO) which interfere with subroutines of the death program. Here we show that apoptosis of Jurkat cells elicited by either staurosporine (STS) or anti-CD95 antibodies in glucose-free medium is converted to necrosis by NO donors. In the presence of NO, release of mitochondrial cytochrome c was delayed and activation of execution caspases was prevented. Stimulated cells died nonetheless. The switch in the mode of cell death was due to NO-dependent failure of mitochondrial energy production. Restoration of intracellular ATP by glucose supplementation recovered the cells' ability to activate caspases and undergo apoptosis. In this system, the apoptosis/necrosis conversion promoted by NO was not mediated by cyclic guanosine monophosphate-dependent mechanisms, poly-(ADP-ribose)-polymerase (PARP) activation, or inhibition of caspases due to S-nitrosylation and glutathione depletion. In contrast, depleting intracellular ATP with rotenone, an inhibitor of mitochondrial complex I mimicked the effect of NO. The findings presented here suggest that NO can decide the shape of cell death by lowering intracellular ATP below the level required to allow the coordinated execution of apoptosis.

Cell cycle machinery controls not only cell growth but also cell survival and death. For example, overexpression of c-Myc or E2F1, which are involved in G1/S transition, causes apoptosis under certain conditions. Furthermore, endogenous E2F1 also participates in apoptosis, as evidenced by the defect of apoptosis in E2F1-deficient mice. Candidate molecules that mediate c-Myc- and E2F1-enhanced apoptosis include p14/p19ARF, ornithine decarboxylase and lactate dehydrogenase-A (for c-Myc) as well as p14/p19ARF, p73, Apaf-1 and caspase-3 (for E2F1). c-Myc also activates the CD95/Fas-FADD-mediated death signal. c-Myc and E2F1 inhibit NF-kappaB activities induced by TNFalpha or reactive oxygen species. Therefore, c-Myc and E2F1 regulate cell growth and death not only by inducing transcription but also by modulating signal transduction pathways.

OBJECTIVE

Death receptors expressed on tumor cells can prevent metastasis formation by inducing apoptosis, but they also can promote migration and invasion. The determinants of death receptor signaling output are poorly defined. Here we investigated the role of oncogenic K-Ras in determining death receptor function and metastatic potential.

METHODS

Isogenic human and mouse colorectal cancer cell lines differing only in the presence or absence of the K-Ras oncogene were tested in apoptosis and invasion assays using CD95 ligand and tumor necrois factor-related apoptosis-inducing ligand (TRAIL) as stimuli. Metastatic potential was assessed by intrasplenic injections of green fluorescent protein- or luciferase-expressing tumor cells, followed by intravital fluorescence microscopy or bioluminescence imaging, and confocal microscopy and immunohistochemistry. Ras-effector pathway control of CD95 output was assessed by an RNA-interference and inhibitor-based approach.

RESULTS

CD95 ligand and TRAIL stimulated invasion of colorectal tumor cells and liver metastases in a K-Ras-dependent fashion. Loss of mutant K-Ras switched CD95 and TRAIL receptors back into apoptosis mode and abrogated metastatic potential. Raf1 was essential for the switch in CD95 function, for tumor cell survival in the liver, and for K-Ras-driven formation of liver metastases. K-Ras and Raf1 suppressed Rho kinase (ROCK)/LIM kinase-mediated phosphorylation of the actin-severing protein cofilin. Overexpression of ROCK or LIM kinase allowed CD95L to induce apoptosis in K-Ras-proficient cells and prevented metastasis formation, whereas their suppression protected K-Ras-deficient cells against apoptosis.

CONCLUSIONS

Oncogenic K-Ras and its effector Raf1 convert death receptors into invasion-inducing receptors by suppressing the ROCK/LIM kinase pathway, and this is essential for K-Ras/Raf1-driven metastasis formation.

A20 is a stress response gene in endothelial cells (ECs). A20 serves a dual cytoprotective function, protecting from tumor necrosis factor (TNF)-mediated apoptosis and inhibiting inflammation via blockade of the transcription factor nuclear factor-kappaB (NF-kappaB). In this study, we evaluated the molecular basis of the cytoprotective function of A20 in EC cultures and questioned whether its protective effect extends beyond TNF to other apoptotic and necrotic stimuli. Our data demonstrate that A20 targets the TNF apoptotic pathway by inhibiting proteolytic cleavage of apical caspases 8 and 2, executioner caspases 3 and 6, Bid cleavage, and release of cytochrome c, thus preserving mitochondrion integrity. A20 also protects from Fas/CD95 and significantly blunts natural killer cell-mediated EC apoptosis by inhibiting caspase 8 activation. In addition to protecting ECs from apoptotic stimuli, A20 safeguards ECs from complement-mediated necrosis. These data demonstrate, for the first time, that the cytoprotective effect of A20 in ECs is not limited to TNF-triggered apoptosis. Rather, A20 affords broad EC protective functions by effectively shutting down cell death pathways initiated by inflammatory and immune offenders.

OBJECTIVE

Apoptosis-related proteins are important molecules for predicting chemotherapy response and prognosis in adult acute myeloid leukemia (AML). However, data on the expression and prognostic impact of these molecules in childhood AML are rare.

METHODS

Using flow cytometry and Western blot analysis, we, therefore, investigated 45 leukemic cell samples from children with de novo AML enrolled and treated within the German AML-BFM93 study for the expression of apoptosis-regulating proteins [CD95, Bcl-2, Bax, Bcl-xL, procaspase-3, X-linked inhibitor of apoptosis protein (XIAP), cellular inhibitor of apoptosis protein-1 (cIAP-1), survivin].

RESULTS

XIAP (P < 0.002) but no other apoptosis regulators showed maturation-dependent expression differences as determined by French-American-British (FAB) morphology with the highest expression levels observed within the immature M0/1 subtypes. XIAP (P < 0.01) and Bcl-xL (P < 0.01) expression was lower in patients with favorable rather than intermediate/poor cytogenetics. After a mean follow-up of 34 months, a shorter overall survival was associated with high expression levels of XIAP [30 (n = 10) versus 41 months (n = 34); P < 0.05] and survivin [27 (n = 10) versus 41 months (n = 34); P < 0.05].

CONCLUSIONS

We conclude that apoptosis-related molecules are associated with maturation stage, cytogenetic risk groups, and therapy outcome in childhood de novo AML. The observed association of XIAP with immature FAB types, intermediate/poor cytogenetics, and poor overall survival should be confirmed within prospective pediatric AML trials.

Trimerization of the Fas receptor (CD95, APO-1), a membrane bound protein, triggers cell death by apoptosis. The main death pathway activated by Fas receptor involves the adaptor protein FADD (for Fas-associated death domain) that connects Fas receptor to the caspase cascade. Anticancer drugs have been shown to enhance both Fas receptor and Fas ligand expression on tumor cells. The contribution of Fas ligand-Fas receptor interactions to the cytotoxic activity of these drugs remains controversial. Here, we show that neither the antagonistic anti-Fas antibody ZB4 nor the Fas-IgG molecule inhibit drug-induced apoptosis in three different cell lines. The expression of Fas ligand on the plasma membrane, which is identified in untreated U937 human leukemic cells but remains undetectable in untreated HT29 and HCT116 human colon cancer cell lines, is not modified by exposure to various cytotoxic agents. These drugs induce the clustering of Fas receptor, as observed by confocal laser scanning microscopy, and its interaction with FADD, as demonstrated by co-immunoprecipitation. Overexpression of FADD by stable transfection sensitizes tumor cells to drug-induced cell death and cytotoxicity, whereas down-regulation of FADD by transient transfection of an antisense construct decreases tumor cell sensitivity to drug-induced apoptosis. These results were confirmed by transient transfection of constructs encoding either a FADD dominant negative mutant or MC159 or E8 viral proteins that inhibit the FADD/caspase-8 pathway. These results suggest that drug-induced cell death involves the Fas/FADD pathway in a Fas ligand-independent fashion.

We have discovered a new and specific cell-killing mechanism mediated by the selective uptake of the antitumor drug 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH(3), Edelfosine) into lipid rafts of tumor cells, followed by its coaggregation with Fas death receptor (also known as APO-1 or CD95) and recruitment of apoptotic molecules into Fas-enriched rafts. Drug sensitivity was dependent on drug uptake and Fas expression, regardless of the presence of other major death receptors, such as tumor necrosis factor (TNF) receptor 1 or TNF-related apoptosis-inducing ligand R2/DR5 in the target cell. Drug microinjection experiments in Fas-deficient and Fas-transfected cells unable to incorporate exogenous ET-18-OCH(3) demonstrated that Fas was intracellularly activated. Partial deletion of the Fas intracellular domain prevented apoptosis. Unlike normal lymphocytes, leukemic T cells incorporated ET-18-OCH(3) into rafts coaggregating with Fas and underwent apoptosis. Fas-associated death domain protein, procaspase-8, procaspase-10, c-Jun amino-terminal kinase, and Bid were recruited into rafts, linking Fas and mitochondrial signaling routes. Clustering of rafts was necessary but not sufficient for ET-18-OCH(3)-mediated cell death, with Fas being required as the apoptosis trigger. ET-18-OCH(3)-mediated apoptosis did not require sphingomyelinase activation. Normal cells, including human and rat hepatocytes, did not incorporate ET-18-OCH(3) and were spared. This mechanism represents the first selective activation of Fas in tumor cells. Our data set a framework for the development of more targeted therapies leading to intracellular Fas activation and recruitment of downstream signaling molecules into Fas-enriched rafts.

The targeted therapeutics sorafenib and vorinostat interact in a synergistic fashion to kill carcinoma cells by activating CD95, and this drug combination is entering phase I evaluation. In this study, we determined how CD95 is activated by treatment with this drug combination. Low doses of sorafenib and vorinostat, but not the individual drugs, rapidly increased reactive oxygen species (ROS), Ca(2+), and ceramide levels in gastrointestinal tumor cells. The production of ROS was reduced in Rho zero cells. Quenching ROS blocked drug-induced CD95 surface localization and apoptosis. ROS generation, CD95 activation, and cell killing was also blocked by quenching of induced Ca(2+) levels or by inhibition of PP2A. Inhibition of acidic sphingomyelinase or de novo ceramide generation blocked the induction of ROS; however, combined inhibition of both acidic sphingomyelinase and de novo ceramide generation was required to block the induction of Ca(2+). Quenching of ROS did not affect drug-induced ceramide/dihydro-ceramide levels, whereas quenching of Ca(2+) reduced the ceramide increase. Sorafenib and vorinostat treatment radiosensitized liver and pancreatic cancer cells, an effect that was suppressed by quenching ROS or knockdown of LASS6. Further, sorafenib and vorinostat treatment suppressed the growth of pancreatic tumors in vivo. Our findings show that induction of cytosolic Ca(2+) by sorafenib and vorinostat is a primary event that elevates dihydroceramide levels, each essential steps in ROS generation that promotes CD95 activation.

Adoptive immunotherapy retargeting T cells to CD19 via a chimeric antigen receptor (CAR) is an investigational treatment capable of inducing complete tumor regression of B-cell malignancies when there is sustained survival of infused cells. T-memory stem cells (TSCM) retain superior potential for long-lived persistence, but challenges exist in manufacturing this T-cell subset because they are rare among circulating lymphocytes. We report a clinically relevant approach to generating CAR+ T cells with preserved TSCM potential using the Sleeping Beauty platform. Because IL-15 is fundamental to T-cell memory, we incorporated its costimulatory properties by coexpressing CAR with a membrane-bound chimeric IL-15 (mbIL15). The mbIL15-CAR T cells signaled through signal transducer and activator of transcription 5 to yield improved T-cell persistence independent of CAR signaling, without apparent autonomous growth or transformation, and achieved potent rejection of CD19+ leukemia. Long-lived T cells were CD45ROnegCCR7+CD95+, phenotypically most similar to TSCM, and possessed a memory-like transcriptional profile. Overall, these results demonstrate that CAR+ T cells can develop long-term persistence with a memory stem-cell phenotype sustained by signaling through mbIL15. This observation warrants evaluation in clinical trials.

The ability to measure human thymic output would be an invaluable tool for the study of the development of the naive T cell repertoire, as well as naive T cell regeneration after intensive cytotoxic chemotherapy or effective antiretroviral therapy of progressive HIV infection. We and others have demonstrated previously that quantification of T cell receptor rearrangement excision circles (TREC) within peripheral T cell populations provides insight into the frequency of recent thymic emigrants (RTE) and, therefore, into thymic function. However, measurement of RTE by this approach is complicated by the fact that TREC levels also are determined by turnover within the naive T cell compartment. Here, we report a phenotypic approach to RTE measurement. We demonstrate that alphaE integrin (CD103) expression is up-regulated very late in thymic development on a subset of CD8(+)/CD4(-) thymocytes and also defines a distinct subset of naive CD8(+) T cells in the periphery. The latter subset is differentiated from circulating CD103(+) mucosa-associated memory T cells by its naive T cell phenotype (CD45RO(-), CD62L(bright), CD27(bright), CD11a(dim), CD95(dim)) and its high concentration of TREC. Indeed, sorted CD103(+) naive CD8(+) cells display higher levels of TREC than their CD103(-) naive counterparts, and these cells demonstrate an age-related decline in frequency that is enhanced significantly by thymectomy. The thymic dependence of this subset and the cells' relatively evanescent presence in the periphery suggest that these cells are a population of RTE and that quantification of their frequency in peripheral blood provides an estimate of the level of ongoing thymopoiesis.