Interleukin 1 beta-converting enzyme related proteases/caspases are involved in TRAIL-induced apoptosis of myeloma and leukemia cells

On the TRAIL to apoptosis

Apoptosis in mammalian cells can be initiated through two major interrelated pathways, one involving engagement of the TNF family of death receptors, the other involving the release of cytochrome c from mitochondria. Unlike other members of the TNF ligand family, TNF-related apoptosis-inducing ligand (TRAIL) preferentially induces apoptosis in tumor cell lines, but not in normal cells, suggesting that TRAIL could potentially represent a powerful cancer therapeutic. Recent experiments have revealed that one of the key regulators of TRAIL expression in lymphocytes is the NF-kappa B transcription factors. Several TRAIL receptors have been identified: two of these receptors TRAIL-R1/DR4 and TRAIL-R2/DR5 contain cytoplasmic death domains and signal apoptosis, while two other decoy receptors, TRAIL-R3/DcR1 and TRAIL-R4/DcR2 lack a functional death domain and do not mediate apoptosis. Many cancer cell lines preferentially express TRAIL-R1 and TRAIL-R2, suggesting differential regulation of the death and decoy receptors. Further knowledge of the regulation and physiological role of TRAIL and TRAIL receptors may aid in the rational design of regimens that utilize the TRAIL signaling pathway to eliminate tumor cells.

TRAIL enhances thymidine kinase/ganciclovir gene therapy of neuroblastoma cells

The clinical benefit of suicide gene therapy of tumors has been marginal, mostly due to the low gene transfer efficiency in vivo. The death-inducing ligand, TRAIL, effectively kills many tumor cell types, while sparing most normal tissues. We hypothesized that TRAIL may enhance HSV thymidine kinase/ganciclovir (TK/GCV) gene therapy of tumor cells by augmenting both target and bystander cell kill. Human SH-EP neuroblastoma cells expressing TK as well as bystander cells were effectively killed by apoptosis, and their clonogenicity was ablated following GCV. Human TRAIL enhanced TK/GCV-induced cell death and decreased clonogenicity of TK-expressing cells and also of bystander cells. Cooperation between TRAIL and TK/GCV depended both on caspase activation and on mitochondrial apoptogenic function because both the broad-spectrum caspase inhibitor zVAD.fmk and overexpression of Bcl-2 decreased enhancement of cell kill by TRAIL. Facilitation of TRAIL signalling by up-regulation of TRAIL receptors did not contribute to enhancement because cell surface expression of the agonistic TRAIL receptors 1 and 2 was not increased by TK/GCV. In conclusion, the concerted activation of caspases and the mitochondrial amplification of caspase activation by TK/GCV may explain the cooperative effect of TK/GCV and TRAIL on the kill of neuroblastoma cells. Because combined treatment also augmented the bystander cell kill, the addition of TRAIL may increase the efficacy of TK/GCV gene therapy of neuroblastoma.

Negative regulation of erythroblast maturation by Fas-L(+)/TRAIL(+) highly malignant plasma cells: a major pathogenetic mechanism of anemia in multiple myeloma

Multiple myeloma (MM) is associated with severe normochromic/normocytic anemia. This study demonstrates that the abnormal up-regulation of apoptogenic receptors, including both Fas ligand (L) and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), by highly malignant myeloma cells is involved in the pathogenesis of the ineffective erythropoiesis and chronic exhaustion of the erythroid matrix. By measuring Fas-L and TRAIL in plasma cells and the content of glycophorin A (GpA) in erythroblasts from a cohort of 28 untreated, newly diagnosed patients with MM and 7 with monoclonal gammopathy of undetermined significance (MGUS), selected in relation to their peripheral hemoglobin values, results showed that both receptors occurred at high levels in 15 severely anemic MM patients. Their marrow erythropoietic component was low and included predominantly immature GpA(+dim) erythroblasts, in contrast with the higher relative numbers of mature GpA(+bright) erythroid cells observed in the nonanemic patients and those with MGUS. In cocultures with autologous Fas-L(+)/TRAIL(+) myeloma cells, the expanded GpA(+dim) erythroid population underwent prompt apoptosis after direct exposure to malignant plasma cells, whereas erythroblasts from nonanemic patients were scarcely affected. The evidence that Fas-L(+)/TRAIL(+) malignant plasma cells prime erythroblast apoptosis by direct cytotoxicity was also supported by the increase of FLICE in fresh immature GpA(+dim) erythroid cells, whereas ICE and caspase-10 increased in subsequent maturative forms. In addition, GATA-1, a survival factor for erythroid precursors, was remarkably down-regulated in fresh erythroblasts from the severely anemic patients. These results indicate that progressive destruction of the erythroid matrix in aggressive MM is due to cytotoxic mechanisms based on the up-regulation in myeloma cells of Fas-L, TRAIL, or both. It is conceivable that the altered regulation of these receptors defines a peculiar cytotoxic phenotype that drives the progression of aggressive MM.

Low glucose-enhanced TRAIL cytotoxicity is mediated through the ceramide-Akt-FLIP pathway

To examine whether the tumor microenvironment alters cytokine-induced cytotoxicity, human prostate adenocarcinoma DU-145 cells were exposed to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and/or glucose deprivation, a common characteristic of the tumor microenvironment. TRAIL alone reduced cell survival in a dose-dependent manner. Glucose deprivation alone induced no cytotoxicity within 4 h. However, the combination of TRAIL (50 ng/ml) and glucose deprivation for 4 h increased cell death and PARP cleavage by promoting activation of caspase-8 and caspase-3, relative to that of TRAIL alone. Similar results were observed in human colorectal carcinoma CX-1 cells. Data from immunoblotting analysis reveal that glucose deprivation-enhanced TRAIL cytotoxicity is inversely related to the intracellular level of FLICE inhibitory protein (FLIP) but not that of death receptor 5 (DR5). Results from mass spectrometry show that glucose deprivation elevates ceramide. The elevation of ceramide may cause dephosphorylation of Akt and maintain dephosphorylation of Akt in the presence of TRAIL and then subsequently down-regulate the expression of FLIP. Taken together, the present studies suggest that glucose deprivation enhances TRAIL-induced cytotoxicity through the ceramide-Akt-FLIP pathway.

Potentiation of the sensitivity of renal cell carcinoma cells to TRAIL-mediated apoptosis by subtoxic concentrations of 5-fluorouracil

Cytotoxic chemotherapy has shown little antitumour activity against renal cell carcinoma (RCC). Although immunotherapy is relatively effective against RCC, the response rate is approximately 20%. Therefore, there is an urgent need to increase this response rate. Tumour necrosis factor-related apoptosis-inducing ligand (TRAIL/Apo-2L) is one member of the tumour necrosis factor ligand family that selectively induces apoptosis of cancer cells. Since several cytotoxic anticancer drugs including 5-fluorouracil (5-FU) also mediate apoptosis, we reasoned that combined treatment of cancer cells with TRAIL and drugs might result in synergy and overcome the resistance of the cancer cell. This study has examined whether TRAIL can synergise with 5-FU in both cytotoxic and apoptotic assays against drug-resistant RCC cells. Cytotoxicity was determined by an 1-day microculture tetrazolium dye assay. Synergy was assessed by isobolographic analysis. Treatment of Caki-1 cells with TRAIL in combination with 5-FU resulted in a synergistic cytotoxic effect. Synergy was also achieved in freshly derived RCC cells from 3 patients. The enhanced cytotoxicity was obtained irrespective of the sequence of the treatment, but the highest cytotoxicity was observed when Caki-1 cells were treated with TRAIL and 5-FU simultaneously. The synergy achieved in cytotoxicity with TRAIL and 5-FU was shown to be due to apoptosis. The mechanisms responsible for the synergistic cytotoxicity and apoptosis were examined. Treatment of Caki-1 cells with 5-FU enhanced the expression of p53 and bax, but had no effect on the expression of bcl-2. Incubation of Caki-1 cells with TRAIL enhanced the intracellular accumulation of 5-FU and 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP). Treatment of Caki-1 cells with TRAIL downregulated the expression of thymidylate synthase (TS) and dihydropyrimidine dehydrogenase (DPD) modestly, and upregulated the expression of orotate phosphoribosyltransferase (OPRT). However, the expression level of thymidine phosphorylase (TP) was not affected by TRAIL. This study demonstrates that combined treatment of RCC cells with TRAIL and 5-FU overcomes their resistance. The sensitisation obtained with freshly isolated RCC cells required low subtoxic concentrations of 5-FU. These findings support the potential application in vivo of a combination of TRAIL and 5-FU in the treatment of TRAIL/5-FU-resistant RCC.

Neuronal survival and cell death signaling pathways

Neuronal viability is maintained through a complex interacting network of signaling pathways that can be perturbed in response to a multitude of cellular stresses. A shift in the balance of signaling pathways after stress or in response to pathology can have drastic consequences for the function or the fate of a neuron. There is significant evidence that acutely injured and degenerating neurons may die by an active mechanism of cell death. This process involves the activation of discrete signaling pathways that ultimately compromise mitochondrial structure, energy metabolism and nuclear integrity. In this review we examine recent evidence pertaining to the presence and activation of anti- and pro-cell death regulatory pathways in nervous system injury and degeneration.

Actinomycin D and gemcitabine synergistically sensitize androgen-independent prostate cancer cells to Apo2L/TRAIL-mediated apoptosis

The cytotoxic efficacy and kinetics involved in sensitization of Apo2L/TRAIL-resistant, androgen-independent prostate cancer cells to Apo2L/TRAIL or tumor necrosis factor-alpha or Fas ligand-mediated apoptosis were tested using subclinical concentrations of actinomycin D, paclitaxel, cisplatinum, gemcitabine, and radiation in CL-1, LNCaP, DU-145, and PC3 prostate cancer cell lines. CL-1 cells expressed all four Apo2L/TRAIL receptors and were resistant to Apo2L/TRAIL-mediated apoptosis (1-5,000 ng/mL) and to the sensitizers when given alone. Pretreatment with actinomycin D followed by Apo2L/TRAIL or tumor necrosis factor-alpha or anti-Fas CH-11 monoclonal antibody, but not in the reverse order, induced apoptosis in all cell lines. Synergistic sensitization in CL-1 cells was shown also with gemcitabine but not with cisplatinum, VP-16, paclitaxel, or radiation. Incubating the Apo2L/TRAIL-resistant CL-1, LNCaP, DU-145, and PC3 cell lines with 100 ng/mL actinomycin D for 4 hours followed by Apo2L/TRAIL for 24 hours resulted in 45.4 +/- 10.3%, 58.8 +/- 3.6%, 53.4 +/- 1.4%, and 84.2 +/- 8.4% apoptosis, respectively. Prolonging the sensitization time to 24 hours followed by 20 hours of incubation with Apo2L/TRAIL further enhanced the killing activity against CL-1 cells to 89 +/- 1% (delta = 60%, synergistic ratio = 3.1). This killing has a biphasic pattern that was contributed to by apoptosis (83%) and necrosis (17%) at 10 hours (peak) and 40% and 60%, respectively, at 20 hours. These results suggest that prostate cancer cells' resistance to Apo2L/TRAIL-mediated apoptosis can be reversed and synergy is achieved by sensitization of tumor cells with subclinical concentrations of actinomycin D or gemcitabine and may be useful clinically for the treatment of metastatic hormone- and drug-refractory prostate cancer.

The differential sensitivity of Bc1-2-overexpressing human breast tumor cells to TRAIL or doxorubicin-induced apoptosis is dependent on Bc1-2 protein levels

Bc1-2 protein is a potent anti-apoptotic protein that inhibits a mitochondria-operated pathway of apoptosis in many cells. DNA damaging agents and death receptor ligands can activate this mitochondrial apoptotic mechanism. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been suggested to escape from the inhibitory action of Bc1-2 protein. We show that in human breast tumor MCF-7 cells, TRAIL induced a mitochondrial pathway of apoptosis that involved cytochrome c release from mitochondria and activation of caspase 9. The DNA damaging drug doxorubicin also activated this mitochondria-regulated mechanism of apoptosis, which was inhibited in Bc1-2-overexpressing cells. We also demonstrate that in MCF-7 cells Bc1-2 might confer resistance to TRAIL-induced apoptosis, depending on the expression levels of the anti-apoptotic protein. These results indicate that enhanced expression of Bc1-2 in tumor cells can render these cells less sensitive not only to chemotherapeutic drugs but also to TRAIL.

Cytotoxic activity of human dendritic cells is differentially regulated by double-stranded RNA and CD40 ligand

The main function of dendritic cells (DCs) is to induce adaptive immune response through Ag presentation and specific T lymphocyte activation. However, IFN-alpha- or IFN-gamma-stimulated CD11c+ blood DCs and IFN-beta-stimulated monocyte-derived DCs were recently reported to express functional TNF-related apoptosis-inducing ligand (TRAIL), suggesting that DCs may become cytotoxic effector cells of innate immunity upon appropriate stimulation. In this study, we investigate whether dsRNA and CD40 ligand (CD40L), that were characterized as potent inducers of DC maturation, could also stimulate or modulate DC cytotoxicity toward tumoral cells. We observed that dsRNA, but not CD40L, is a potent inducer of TRAIL expression in human monocyte-derived DCs. As revealed by cytotoxicity assays, DCs acquire the ability to kill tumoral cells via the TRAIL pathway when treated with dsRNA. More precisely, dsRNA is shown to induce IFN-beta synthesis that consecutively mediates TRAIL expression by the DCs. In contrast, we demonstrate that TRAIL expression in dsRNA- or IFN-alpha-treated DCs is potently inhibited after CD40L stimulation. Unexpectedly, CD40L-activated DCs still developed cytotoxicity toward tumoral cells. This latter appeared to be partly mediated by TNF-alpha induction and a yet unidentified pathway. Altogether, these results demonstrate that dsRNA and CD40L, that were originally characterized as maturation signals for DCs, also stimulate their cytotoxicity that is mediated through TRAIL-dependent or -independent mechanisms.

Apo2L/TRAIL and Bcl-2-related proteins regulate type I interferon-induced apoptosis in multiple myeloma

It has been reported that interferons (IFNs) may have antitumor activity in multiple myeloma (MM). The mechanism for their effect on MM, however, remains elusive. This study shows that IFN-alpha and -beta, but not -gamma, induce apoptosis characterized by Annexin V positivity, nuclear fragmentation and condensation, and loss of clonogenicity in 3 MM cell lines (U266, RPMI-8266, and NCI-H929), and in plasma cells from 10 patients with MM. Apo2 ligand (Apo2L, also TRAIL) induction was one of the earliest events following IFN administration in U266 cells. Treatment of these cells with TRAIL, but not with Fas agonistic antibodies, induces apoptosis. Cell death induced by IFNs and Apo2L in U266 cells was partially blocked by a dominant-negative Apo2L receptor, DR5, demonstrating the functional significance of Apo2L induction. This study shows that IFNs activate caspases and the mitochondrial-dependent apoptotic pathway, possibly mediated by Apo2L production. Thus, IFN-alpha and -beta induce cytochrome c release from mitochondria starting at 12 hours, with an amplified release seen at 48 hours. Moreover, Bid cleavage precedes the initial cytochrome c release, whereas the late, amplified cytochrome c release coincides with changes in levels of Bcl-2, Bcl-X(L), and reduction of mitochondrial membrane potential. These results link the Apo2L induction and modulation of Bcl-2 family proteins to mitochondrial dysfunction. Furthermore, IFNs and Apo2L induce cell death of CD38(+)/CD45(-/dim) plasma cells, without significant effect on nonplasma blood cells, in a caspase and Bcl-2 cleavage-dependent manner. These results warrant further clinical studies with IFNs and Apo2L in MM.

Inhibition of TRAIL-induced apoptosis and forced internalization of TRAIL receptor 1 by adenovirus proteins

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis through two receptors, TRAIL-R1 (also known as death receptor 4) and TRAIL-R2 (also known as death receptor 5), that are members of the TNF receptor superfamily of death domain-containing receptors. We show that human adenovirus type 5 encodes three proteins, named RID (previously named E3-10.4K/14.5K), E3-14.7K, and E1B-19K, that independently inhibit TRAIL-induced apoptosis of infected human cells. This conclusion was derived from studies using wild-type adenovirus, adenovirus replication-competent mutants that lack one or more of the RID, E3-14.7K, and E1B-19K genes, and adenovirus E1-minus replication-defective vectors that express all E3 genes, RID plus E3-14.7K only, RID only, or E3-14.7K only. RID inhibits TRAIL-induced apoptosis when cells are sensitized to TRAIL either by adenovirus infection or treatment with cycloheximide. RID induces the internalization of TRAIL-R1 from the cell surface, as shown by flow cytometry and indirect immunofluorescence for TRAIL-R1. TRAIL-R1 was internalized in distinct vesicles which are very likely to be endosomes and lysosomes. TRAIL-R1 is degraded, as indicated by the disappearance of the TRAIL-R1 immunofluorescence signal. Degradation was inhibited by bafilomycin A1, a drug that prevents acidification of vesicles and the sorting of receptors from late endosomes to lysosomes, implying that degradation occurs in lysosomes. RID was also shown previously to internalize and degrade another death domain receptor, Fas, and to prevent apoptosis through Fas and the TNF receptor. RID was shown previously to force the internalization and degradation of the epidermal growth factor receptor. E1B-19K was shown previously to block apoptosis through Fas, and both E1B-19K and E3-14.7K were found to prevent apoptosis through the TNF receptor. These findings suggest that the receptors for TRAIL, Fas ligand, and TNF play a role in limiting virus infections. The ability of adenovirus to inhibit killing through these receptors may prolong acute and persistent infections.

Killing effect of TNF-related apoptosis inducing ligand regulated by tetracycline on gastric cancer cell line NCI-N87

AIM: To clone the cDNA fragment of human TRAIL (TNF-related apoptosis inducing ligand) into a tetracycline-regulated gene expression system, the RevTet-On system, transduce expression vectors into a gastric carcinoma cell line-NCI-N87 and examine the effects of controlled expression of TRAIL in vitro on the gastric carcinoma cells.

METHODS: The full-length cDNA of TRAIL was inserted into a vector under the control of the tetracycline-responsive element (TRE) to obtain the plasmid pRevTRE-TRAIL, which was transfected into a packaging cell line PT67. In addition, vector pRev-Tet On and pRevTRE were also transfected into PT67 separately. After hygromycin and G418 selection, the viral titer was determined. The medium containing retroviral vectors was collected and used to transduce a gastric carcinoma cell line NCI-N87. The resulting cell line NCI-N87-Tet On TRE-TRAIL and a control cell line, NCI-N87 Tet On-TRE, were established. TRAIL expression in the cell line was induced by incubating cells with doxycycline (Dox), which is a tetracycline analogue. The killing effect on gastric carcinoma cells was analyzed after induction.

RESULTS: The recombinant plasmid pRev-TRE-TRAIL was constructed. After hygromycin or G418 selection, the producer cell lines PT67-TRE, PT67-TRE-TRAIL and PT67-Tet On were obtained, with titers of about 10⁸ CFU·L^-1. By transducing NCI-N87 cells with retroviral vectors from these cell lines, stable cell lines NCI-N87-Tet On TRE-TRAIL (NN3T) and control cell line NCI-N87-Tet On TRE (NN2T) were established. The growth curves of the selected cell lines were the same with the wild type NCI-N87. When Dox was added, cell death was obvious in the test groups (29%-77%), whereas no difference was observed in control and wild type cell lines. With the addition of a medium from the test group, human leukemia cell line Jurkat was activated till death (83%), indicating the secretion of active TRAIL proteins from the test cells to the medium.

CONCLUSION: With the use of the RevTet-On system, a regulated expression system for TRAIL was constructed. Using this system, the selected killing effect of TRAIL on gastric carcinoma cell line NCI-N87 could be observed.

Potential and caveats of TRAIL in cancer therapy

Induction of apoptosis in tumor cells is a major goal for chemotherapy and radiation treatment strategies. However, disordered gene expression often leads to apoptosis resistance rendering tumor cells insensitive to various conventional treatments. TNF-related apoptosis-inducing ligand (TRAIL) is a recently identified cytokine of the TNF superfamily that induces apoptosis in tumor cells upon binding to different receptors. Remarkably, the majority of tumor cell lines are sensitive to TRAIL-induced apoptosis, while most nontransformed cell types are TRAIL-resistant. Furthermore, a combination treatment of TRAIL with ionizing irradiation or chemotherapeutic agents induces apoptosis in a highly synergistic manner, particularly in those cells that are otherwise resistant to a sole treatment. In contrast to other TNF members, TRAIL apparently does not exert overt systemic toxicity in murine and primate models, although unexpected concerns about a potential hepatotoxicity of TRAIL have been recently raised. While the molecular mechanisms of TRAIL sensitivity and resistance are poorly understood, TRAIL seems to be a promising biological agent for combination therapy with chemotherapeutic drugs or irradiation.

Receptor binding cancer antigen expressed on SiSo cells, a novel regulator of apoptosis of erythroid progenitor cells

To better understand the control of apoptosis during erythropoiesis, this study investigated the role of a novel tumor-associated antigen, RCAS1 (receptor binding cancer antigen expressed on SiSo cells), with regard to the regulation of apoptosis of erythroid progenitor cells. Erythroid colony-forming cells (ECFCs) purified from human peripheral blood were used. Binding experiments of RCAS1 showed that ECFCs abundantly expressed receptors (RCAS1R) for RCAS1 and that the degree of binding of RCAS1 to the receptors diminished rapidly during erythroid maturation in vitro. When the soluble form of RCAS1 was added to the cultures, ECFCs underwent apoptosis, including collapse of the mitochondrial transmembrane potential, and activation of caspases 8 and 3. The addition of an anti-Fas blocking antibody or Fas-Fc failed to reduce the apoptosis induced by RCAS1, thereby indicating that effects of RCAS1 are independent of Fas activation. When binding of RCAS1 to normal bone marrow cells was analyzed, RCAS1R was evident on cells with an immature erythroid phenotype (transferrin receptor+/glycophorin A−) but not with a mature phenotype (transferrin receptor−/glycophorin A+). Histochemical staining revealed the expression of RCAS1 in the cytoplasm of bone marrow macrophages. These findings indicate that RCAS1, which is mainly produced by macrophages in hematopoietic tissue, may have a crucial role in controlling erythropoiesis by modulating apoptosis of erythroid progenitor cells via a Fas-independent mechanism.

Pancreatic adenocarcinoma cell lines show variable susceptibility to TRAIL-mediated cell death

BACKGROUND AND AIMS

Programmed cell death via the Fas receptor/Fas Ligand and DR4, DR5/TRAIL plays a major role in tumor escape and elimination mechanisms. It also promises to be an effective therapy alternative for aggressive tumors, as has been recently shown for colon, breast, and lung cancer cells. We attempted to clarify the role of these molecules in aggressivity of pancreatic carcinomas and to identify possible pathways as targets for therapy.

METHODS

Five pancreatic cell lines were investigated for the expression of FasL/Fas, DcR3, DR4, DR5/TRAIL, DcR1, DcR2, and other death pathways related molecules such as Bax, bcl-xL, bcl-2, FADD, and caspase-3 by flow cytometry, immunoblotting, and RT/PCR, both semiquantitative and real time (TaqMan). The susceptibility of these cell lines to apoptosis mediated by recombinant TRAIL was investigated. The effect of therapeutic agents (gemcitabine) on their susceptibility to TRAIL induced apoptosis was studied as well.

RESULTS

Pancreatic adenocarcinomas expressed high levels of apoptosis-inducing receptors and ligands. They showed differential susceptibility to cell death induced by TRAIL, despite expressing intact receptors and signaling machineries. Treatment with commonly used therapeutic agents did not augment their susceptibility to apoptosis. This could be explained by the fact that they expressed differentially high levels of decoy receptors, as well as molecules known as inhibitors of apoptosis.

CONCLUSIONS

The data suggest that pancreatic carcinoma cells have developed different mechanisms to evade the immune system. One is the expression of nonfunctional receptors, decoy receptors, and molecules that block cell death, such as bcl2 and bcl-xL. The second is the expression of apoptosis-inducing ligands, such as TRAIL, that could induce cell death of immune cells. The success in treating malignant tumors by recombinant TRAIL might apply to some but not all pancreatic tumors because of their differential resistance to TRAIL-induced cell death.

Transfection of caspase-3 in the caspase-3–deficient Hodgkin's disease cell line, KMH2, results in enhanced sensitivity to CD95-, TRAIL-, and ARA-C–induced apoptosis

BACKGROUND

CD95(Fas/apo-1) is a cell surface protein member of the tumor necrosis factor receptor family that serves an important role in the induction of apoptosis in several cell types. Although expression of CD95 has been detected on Hodgkin/Reed Sternberg (HRS) cells in situ, our understanding of the biological significance of this molecule in Hodgkin's disease (HD) is limited.

DESIGN

We analyzed both CD95-related apoptotic signaling and its effects on the expression of several factors involved in the regulation of apoptotic mechanisms including: caspase-3, caspase-8, bcl-2, bcl-x, and Bax in HD cell lines (L-428, L-540, HDLM-2, HS-445, and KM-H2).

RESULTS

HD cell lines showed similar expression levels of CD95 and all but KM-H2 demonstrated variable increases in apoptosis after CD95 stimulation by the agonistic monoclonal antibody, CH11. There was no significant correlation between CD95 sensitivity and constitutive expression levels of caspase-8, bcl-2, bcl-x, and Bax. Caspase-3 transcript was demonstrated by reverse transcriptase polymerase chain reaction (RT-PCR) in all cell lines but protein was at low to nearly undetectable levels in KM-H2 cells. Transfection of KM-H2 cells with pro-caspase-3 resulted in a markedly enhanced apoptotic response to CD95 stimulation that was blocked by pretreatment with the caspase-3 inhibitor, DEVD-FMK. In addition, pro-caspase-3-transfected KM-H2 cells showed significantly increased sensitivity to other caspase-3-dependent apoptotic stimuli, including the death-inducing ligand, TRAIL, and the chemotherapeutic agent, Ara-C.

CONCLUSION

These data demonstrate that caspase-3 expression plays an important role in CD95-mediated apoptosis in HD cell lines. Furthermore, lack of or decreased expression of caspase-3 in HD cells impairs their apoptotic response not only to CD95 but also to other caspase-3-dependent apoptotic stimuli.

Regression of human mammary adenocarcinoma by systemic administration of a recombinant gene encoding the hFlex-TRAIL fusion protein

The tumor necrosis factor (TNF)-related apoptosis-inducing ligand, TRAIL, is a new member of the TNF family. It can specifically induce apoptosis in a variety of human tumors. To investigate the possibility of employing the TRAIL gene for systemic cancer therapy, we constructed a recombinant gene encoding the soluble form of the human Flt3L gene (hFlex) at the 5' end and the human TRAIL gene at the 3' end. Such design allows the TRAIL gene product to be secreted into the body circulation. We have also demonstrated that the addition of an isoleucine zipper to the N-terminal of TRAIL greatly enhanced the trimerization of the fusion protein and dramatically increased its anti-tumor activity. The fusion protein reached the level of 16-38 microg/ml in the serum after a single administration of the recombinant gene by hydrodynamic-based gene delivery in mice. A high level of the fusion protein correlated with the regression of a human breast tumor established in SCID mice. No apparent toxicity was observed in the SCID mouse model. In addition, the fusion protein caused an expansion of the dendritic cell population in the C57BL/6 recipient mice, indicating that the hFlex component of the fusion protein was functional. Thus, the hFlex-TRAIL fusion protein may provide a novel approach, with the possible involvement of dendritic cell-mediated anti-cancer immunity, for the treatment of TRAIL-sensitive tumors.

Expression and function of death receptors and their natural ligands in the intestine

The tumor necrosis factor receptor (TNFR) family is a still-growing group of homologous transmembrane proteins, some of which bear an intracellular "death domain" and are able to directly mediate apoptosis. Apoptosis is induced upon trimerization of the receptors by their natural ligands' constituting the complementary TNF family. The best-characterized apoptosis-mediating TNFR family member is CD95 (APO-1/Fas). CD95 is functionally expressed on the basolateral surface of colonic epithelial cells regardless of their position along the crypt axis. The biological significance of this CD95 expression in the gut, however, is still under discussion. Although it is unlikely that the CD95/CD95L system is involved in the physiologic regeneration of the intestinal epithelium, this system may play an important role in the pathogenesis of inflammatory bowel diseases. In contrast to the normal epithelium, colon carcinoma cell lines are mostly resistant to CD95-induced apoptosis. The detection of CD95L expression in colon carcinoma cell lines has led to the concept of carcinomas as "immunoprivileged sites," where invading immune cells are killed by CD95L-expressing tumor cells. A more recently described member of the TNF family is TRAIL, which is also able to induce apoptosis. As yet, four TRAIL receptors have been cloned, two of which (TRAIL-R1 and 2) bear a death domain and mediate apoptosis, whereas two others (TRAIL-R3 and 4) lack (functional) death domains and are supposed to act as decoy receptors. Because many tumor cell lines in vitro are sensitive to TRAIL-induced apoptosis while their normal counterparts are not, TRAIL is currently under discussion as a possible anticancer therapeutic agent.

Activation of protein kinase C inhibits TRAIL-induced caspases activation, mitochondrial events and apoptosis in a human leukemic T cell line

TRAIL causes apoptosis in numerous types of tumor cells. However, the mechanisms regulating TRAIL-induced apoptosis remain to be elucidated. We have investigated the role of PKC in regulating TRAIL-induced mitochondrial events and apoptosis in the Jurkat T cell line. We found a caspase-dependent decline in mitochondrial membrane potential and translocation of cytochrome c from mitochondria into the cytosol in response to TRAIL. Both these events were prevented by PKC activation. Moreover, PKC activation considerably reduced the activation of caspases, PARP cleavage and apoptosis when induced upon TRAIL treatment. MAPK activation was involved in the mechanism of PKC-mediated inhibition of TRAIL-induced cytochrome c release from mitochondria. Furthermore, inhibition of the MAPK pathway partially reversed the PKC-mediated inhibition of TRAIL-induced apoptosis. Besides, PKC activation may also inhibit the TRAIL-induced apoptosis through a MAPK-independent mechanism. Altogether, these results indicate a negative role of PKC in the regulation of apoptotic signals generated upon TRAIL receptor activation.

Enhanced sensitivity of bladder cancer cells to tumor necrosis factor related apoptosis inducing ligand mediated apoptosis by cisplatin and carboplatin

PURPOSE

The development and acquisition of multiple drug resistance in cancer cells are a consequence of cancer chemotherapy and remain a major obstacle in treatment. Therefore, there is an obvious need for alternative approaches, such as immunotherapy and gene therapy. Tumor necrosis factor related apoptosis inducing ligand (TRAIL) is one of the tumor necrosis factor ligand families and it selectively induces apoptosis against cancer cells. Several cytotoxic anticancer drugs also mediate apoptosis and may share the common intracellular pathways leading to apoptosis. We reasoned that combination treatment of cancer cells with TRAIL and drugs may overcome this resistance. We evaluated whether bladder cancer cells are sensitive to TRAIL mediated cytotoxicity and whether TRAIL may synergize with anticancer agents in cytotoxicity and apoptosis against bladder cancer cells.

MATERIALS AND METHODS

Cytotoxicity was determined by a 1-day microculture tetrazolium dye assay. Synergy was assessed by isobolographic analysis.

RESULTS

Human T24 bladder cancer line was relatively resistant to TRAIL and TRAIL was not cytotoxic against normal bladder cells. Treatment of T24 cells with TRAIL in combination with 5-fluorouracil or mitomycin C did not overcome resistance to these agents. However, treatment of T24 cells with a combination of TRAIL and cisplatin resulted in a synergistic cytotoxic effect. Synergy was also achieved in the cisplatin resistant T24 line (T24/CDDP), 2 other bladder cancer lines and 3 freshly derived bladder cancer cells. The combination of TRAIL and carboplatin resulted in a synergistic cytotoxic effect on T24 cells. However, the combination of TRAIL and trans-diamminedichloroplatinum (II) resulted in an antagonistic cytotoxic effect. The synergy achieved in cytotoxicity with TRAIL and cisplatin was also achieved in apoptosis. Treating T24 cells with cisplatin enhanced the expression of bax but not bcl-2. Incubation of T24 cells with TRAIL increased the intracellular accumulation of cisplatin.

CONCLUSIONS

This study demonstrates that combination treatment of bladder cancer cells with TRAIL and cisplatin overcomes their resistance. The sensitization obtained with established cisplatin resistant and freshly isolated bladder cancer cells required low subtoxic concentrations of cisplatin, supporting the in vivo potential application of a combination of TRAIL and cisplatin for treating TRAIL resistant and cisplatin resistant bladder cancer.

Mechanisms underlying hypoxia-induced neuronal apoptosis

In vivo models of cerebral hypoxia-ischemia have shown that neuronal death may occur via necrosis or apoptosis. Necrosis is, in general, a rapidly occurring form of cell death that has been attributed, in part, to alterations in ionic homeostasis. In contrast, apoptosis is a delayed form of cell death that occurs as the result of activation of a genetic program. In the past decade, we have learned considerably about the mechanisms underlying apoptotic neuronal death following cerebral hypoxia-ischemia. With this growth in knowledge, we are coming to the realization that apoptosis and necrosis, although morphologically distinct, are likely part of a continuum of cell death with similar operative mechanisms. For example, following hypoxia-ischemia, excitatory amino acid release and alterations in ionic homeostasis contribute to both necrotic and apoptotic neuronal death. However, apoptosis is distinguished from necrosis in that gene activation is the predominant mechanism regulating cell survival. Following hypoxic-ischemic episodes in the brain, genes that promote as well as inhibit apoptosis are activated. It is the balance in the expression of pro- and anti-apoptotic genes that likely determines the fate of neurons exposed to hypoxia. The balance in expression of pro- and anti-apoptotic genes may also account for the regional differences in vulnerability to hypoxic insults. In this review, we will examine the known mechanisms underlying apoptosis in neurons exposed to hypoxia and hypoxia-ischemia.

Resistance to TRAIL-induced apoptosis in primitive neuroectodermal brain tumor cells correlates with a loss of caspase-8 expression

TNF-related apoptosis-inducing ligand (TRAIL) is a potent inducer of apoptosis in adult malignant glioma and various other human solid tumor models but not in normal tissues. To characterize the TRAIL death pathway in childhood primitive neuroectodermal brain tumor (PNET), 8 human PNET cell lines were tested for TRAIL-induced apoptosis. TRAIL-sensitivity of the PNET cell lines was correlated with mRNA expression levels of TRAIL, its agonistic (TRAIL-R1, TRAIL-R2) and antagonistic (TRAIL-R3, TRAIL-R4) receptors, cellular FLICE-like inhibitory protein (cFLIP), caspase-3 and caspase-8. Three of 8 PNET cell lines tested were susceptible to TRAIL-induced apoptosis. Sensitivity to TRAIL-induced apoptosis did not correlate with mRNA expression of TRAIL receptors or cFLIP. However, all TRAIL-sensitive PNET cell lines expressed caspase-8 mRNA and protein, while none of the five TRAIL-resistant PNET cell lines expressed caspase-8 protein. Treatment with the methyltransferase inhibitor 5-aza-2'-deoxycytidine restored mRNA expression of caspase-8 and TRAIL-sensitivity in formerly TRAIL-resistant PNET cells, suggesting that gene methylation inhibits caspase-8 transcription in these cells. We conclude, that loss of caspase-8 mRNA is an important mechanism of TRAIL-resistance in PNET cells. Treatment with recombinant soluble TRAIL, possibly in combination with methyltransferase inhibitors, represents a promising therapeutic approach for PNET that deserves further investigation.

Induction of apoptosis in glioma cell lines by TRAIL/Apo-2l

TRAIL/Apo-2L, a novel cytokine, is a member of the tumor necrosis factor (TNF) family and serves as an extracellular signal triggering apoptosis. TRAIL/Apo-2L is capable of killing various transformed cells but not unstimulated primary T cells. In this study, five human glioma cells (U87, U118, U178, U563, and A172) were examined for their susceptibility to the apoptotic effects of TRAIL/Apo-2L. TRAIL/Apo-2L cDNA was isolated by RT-PCR, and recombinant TRAIL/Apo-2L protein was purified by the pMAL-c2 system (New England Biolabs, Beverly, MA). Exposure of A172 cells to bacterially expressed soluble TRAIL/Apo-2L fusion protein at a concentration of 1 microg/ml resulted in significant cell death over a 24-h period. Three experiments were performed to suggest that the TRAIL/Apo-2L killing was through the induction of apoptosis of A172 target cells. In addition, the expression of TRAIL/Apo-2L in different glioma cells was found to be variable, and TRAIL/Apo-2L-induced apoptosis was in a cell type-dependent manner. Some correlation between the susceptibility to TRAIL/Apo-2L and the expression level of one of its cognate receptors, DR4, was observed. In addition, cycloheximide worked synergistically with TRAIL/Apo-2L to induce apoptosis in glioma cells.

Death of the autoimmune thyrocyte: is it pushed or does it jump?

Programmed cell death or apoptosis is central both in physiology during development and in disease. The mechanism of apoptosis is under the control of antiapoptotic survival genes of the Bcl-2 family and proapoptotic death receptors of the TNF superfamily (Fas, TNFR, TRAILR). Following death signal, the death receptor binds to its own receptor and initiates, through binding of adaptors, a cascade of events mediated by the autoproteolytic activation of specific enzymes called caspases. This enzyme activation is ultimately responsible for the dissembly of basic nuclear and cytoplasmic cell structures leading to cell death. In certain cell systems, antiapoptotic genes of the Bcl-2 family prevent the proapoptotic pathway. One of their roles is to maintain mitochondrial function integrity. In autoimmune destructive thyroiditis high levels of apoptosis have been demonstrated particularly within the destructed follicles near the infiltrated areas in comparison to Graves' disease and non autoimmune glands. In Hashimoto's thyroiditis Fas expression has been found increased on thyrocytes and in vitro can be modulated by proinflammatory cytokines. FasL expression on thyrocytes remains controversial. Thyroid cells from Graves' disease and multinodular glands are known to kill Fas expressing target cells although Hashimoto's thyrocytes are not efficient effector cells. Intrathyroidal lymphocytes from Hashimoto's thyroids maintain functional killer activity. These findings would suggest that intrathyroidal lymphocytes could be responsible for thyrocyte death in vivo. Whether this mechanism is Fas/FasL, TRAIL/TRAILR dependent can not be confirmed as specific blocking reagents were not able to inhibit cell induced death. In Hashimoto's thyroiditis an impairment of Bcl-2 and Bcl-X anitapoptotic genes on thyrocytes has also been detected. Bcl-X expression can be down-regulated in vitro by incubation with cytokines. These findings suggest that thyrocyte death may not exclusively be the result of specific interactions between death receptor and their ligands but it may involve simultaneous impairment of protective genes of the Bcl-2 family. Whether the impairment of the Bcl-2 family is a direct consequence of environmental stimuli or is the result of an intrinsic thyrocyte (mitochondrial?) alteration is as yet not known.

Failure of Bcl-2 to block cytochrome c redistribution during TRAIL-induced apoptosis

Tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF family of cytokines that promotes apoptosis and NF-kappaB activation. Here we show that recombinant hu-TRAIL initiates the activation of multiple caspases, the loss of mitochondrial transmembrane potential, the cleavage of BID and the redistribution of mitochondrial cytochrome c. However, whereas Bcl-2 efficiently blocked UV radiation-induced cytochrome c release and consequent apoptosis of CEM cells, it failed to do either in the context of TRAIL treatment. Thus, TRAIL engages a death pathway that is at least partially routed via the mitochondria, but in contrast with other stimuli that engage this pathway, TRAIL-induced cytochrome c release is not regulated by Bcl-2.

A unique zinc-binding site revealed by a high-resolution X-ray structure of homotrimeric Apo2L/TRAIL

Apoptosis-inducing ligand 2 (Apo2L, also called TRAIL), a member of the tumor necrosis factor (TNF) family, induces apoptosis in a variety of human tumor cell lines but not in normal cells [Wiley, S. R., Schooley, K., Smolak, P. J., Din, W. S., Huang, C.-P., Nicholl, J. K., Sutherland, G. R., Smith, T. D., Rauch, C., Smith, C. A., and Goodwin, R. G. (1995) Immunity 3, 673-682; Pitti, R. M., Marsters, S. A., Ruppert, S., Donahue, C. J., Moore, A., and Ashkenazi, A. (1996) J. Biol. Chem. 271, 12687-12690]. Here we describe the structure of Apo2L at 1.3 A resolution and use alanine-scanning mutagenesis to map the receptor contact regions. The structure reveals a homotrimeric protein that resembles TNF with receptor-binding epitopes at the interface between monomers. A zinc ion is buried at the trimer interface, coordinated by the single cysteine residue of each monomer. The zinc ion is required for maintaining the native structure and stability and, hence, the biological activity of Apo2L. This is the first example of metal-dependent oligomerization and function of a cytokine.

Locoregional Apo2L/TRAIL eradicates intracranial human malignant glioma xenografts in athymic mice in the absence of neurotoxicity

Glioblastoma multiforme is a lethal neoplasm refractory to radiochemotherapy. Although glioma cells undergo apoptosis when exposed to the death ligand, CD95 (Fas/APO-1) ligand, the therapeutic use of CD95L is considered impossible because of lethal side effects. Here, we report that the locoregional application of Apo2 ligand (Apo2L) exerts strong antitumor activity on preestablished intracranially growing human U87MG glioma xenografts in athymic mice. Two repetitive intratumoral injections of 2 microg Apo2L resulted in long-term survival of mice (>100 days), whereas the median survival of mock-treated mice was 36 days. The assessment of tumor volumes at 21 and 35 days after inoculation showed complete eradication of glioma xenografts in Apo2L-treated mice. Histology and TUNEL assay confirmed the induction of apoptosis by Apo2L in glioma cells in vivo. Importantly, the intracerebral injection of Apo2L does not result in acute or delayed neurotoxicity. We propose that a phase 1 trial of intralesional Apo2L therapy for human glioblastoma multiforme is warranted.

TRAIL causes cleavage of bid by caspase-8 and loss of mitochondrial membrane potential resulting in apoptosis in BJAB cells

A new member of the TNF family, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), has been shown to induce apoptosis. However, the mechanism for TRAIL-induced apoptosis remains to be clarified. SDS-PAGE and Western blot analysis showed that cleavage of Bid was induced by a 1-h incubation of BJAB cells with TRAIL and was blocked by a caspase-8 inhibitor. Flow cytometry demonstrated that loss of mitochondrial membrane potential in BJAB cells began about 1.5 h after the treatment with TRAIL and was apparent at 2 h in comparison with the control. DNA ladder formation, which is characteristic for apoptosis, in the cells treated with TRAIL was detected at 2 h and observed most effectively at 3 h. The time course study suggests that TRAIL causes cleavage of Bid via activation of caspase-8, subsequently the loss of mitochondrial membrane potential, resulting in apoptosis in BJAB cells.

Interleukin-1 protects transformed keratinocytes from tumor necrosis factor-related apoptosis-inducing ligand- and CD95-induced apoptosis but not from ultraviolet radiation-induced apoptosis

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), a new member of the tumor necrosis factor (TNF) family, induces apoptosis primarily of transformed cells. Interleukin-1 was previously found to protect the keratinocyte cell line KB from TRAIL-induced apoptosis, thus we studied whether interleukin-1 also protects from other apoptotic stimuli (ultraviolet radiation (UV), CD95-ligand). Interleukin-1 rescued KB cells from TRAIL- and CD95-induced apoptosis, which was critically dependent on nuclear factor kappaB, because cells transfected with a super-repressor form of the nuclear factor kappaB inhibitor IkappaB were less protected. In contrast, UV-mediated apoptosis was not only not prevented by interleukin-1 but even enhanced. This opposite effect of interleukin-1 was also observed for the expression of the inhibitor of apoptosis proteins (IAP). Whereas TRAIL- and CD95-mediated suppression of IAP expression was partially reversed by interleukin-1, UV-mediated down-regulation of IAPs was not reversed but even further enhanced. Increased apoptosis induced by interleukin-1 plus UV was accompanied by excessive TNFalpha release, implying that enhanced cytotoxicity is due to the additive effect of these two apoptotic stimuli. Accordingly, enhanced apoptosis was reduced by blocking the TNF receptor-1. The opposite effects of interleukin-1 indicate that different mechanisms are involved in UV-induced apoptosis compared with CD95- and TRAIL-mediated apoptosis. Furthermore, the data suggest that whether a signal acts in an antiapoptotic way or not does not only depend on the signal itself but also on the stimulus causing apoptosis.

Triggering cell death: the crystal structure of Apo2L/TRAIL in a complex with death receptor 5

Formation of a complex between Apo2L (also called TRAIL) and its signaling receptors, DR4 and DR5, triggers apoptosis by inducing the oligomerization of intracellular death domains. We report the crystal structure of the complex between Apo2L and the ectodomain of DR5. The structure shows three elongated receptors snuggled into long crevices between pairs of monomers of the homotrimeric ligand. The interface is divided into two distinct patches, one near the bottom of the complex close to the receptor cell surface and one near the top. Both patches contain residues that are critical for high-affinity binding. A comparison to the structure of the lymphotoxin-receptor complex suggests general principles of binding and specificity for ligand recognition in the TNF receptor superfamily.

Regulation of APO-2 ligand/trail expression in NK cells-involvement in NK cell-mediated cytotoxicity

Apo-2L is a new member of the tumour necrosis factor (TNF) family shown to induce apoptosis in a number of tumour cell lines. Apo-2L mRNA is expressed by numerous human tissues. Here we report that Apo-2L is expressed and utilized by human Natural Killer (NK) cells. NK cells were shown to express surface Apo-2L in response to interleukin 2 (IL-2) activation, and this response was restricted to the CD3(-)population of the NK cells. Apo-2L mRNA and intracellular Apo-2L were present in both CD3(-)and CD3(+)NK cells; however, increased expression in response to IL-2 was only observed in CD3(-)CD56(+)cells. Also, IL-2-activated NK cells were shown to utilize membrane-bound Apo-2L in mediating lysis of Jurkat cells. Furthermore, Apo-2L-induced apoptosis of Jurkat cells was more rapid than FasL-induced apoptosis, indicating an important and distinct role for Apo-2L in apoptotic cell destruction. In conclusion, we report that NK cells express Apo-2L and that IL-2 activated CD3(-)NK cells utilize the Apo-2L pathway in mediating target cell lysis.

c-E10 is a caspase-recruiting domain-containing protein that interacts with components of death receptors signaling pathway and activates nuclear factor-kappaB

Members of the tumor necrosis factor receptor superfamily induce apoptosis via interaction with FADD and regulate cell growth and differentiation through TRADD and TRAFs molecules. While screening for molecules involved in the regulation of death receptor signaling, we identified a novel protein, c-E10. c-E10 contains an amino-terminal caspase-recruiting domain (CARD) and shares a sequence homologous with E10, a viral CARD-containing protein that binds to c-E10. In transfection experiments c-E10 oligomerizes, binds to the cytoplasmic portion of TRAIL receptor 1 (DR4) and coprecipitates with TRADD. Expression of c-E10 under the control of a doxycycline-dependent transcriptional transactivator results in NF-kappaB activation, which is inhibited by dominant negative forms of TRAF2 and NIK kinase. Thus, our results suggest that c-E10 is an adapter protein that activates NF-kappaB through a molecular pathway involved in death receptor signaling.

Safety and antitumor activity of recombinant soluble Apo2 ligand

TNF and Fas ligand induce apoptosis in tumor cells; however, their severe toxicity toward normal tissues hampers their application to cancer therapy. Apo2 ligand (Apo2L, or TRAIL) is a related molecule that triggers tumor cell apoptosis. Apo2L mRNA is expressed in many tissues, suggesting that the ligand may be nontoxic to normal cells. To investigate Apo2L's therapeutic potential, we generated in bacteria a potently active soluble version of the native human protein. Several normal cell types were resistant in vitro to apoptosis induction by Apo2L. Repeated intravenous injections of Apo2L in nonhuman primates did not cause detectable toxicity to tissues and organs examined. Apo2L exerted cytostatic or cytotoxic effects in vitro on 32 of 39 cell lines from colon, lung, breast, kidney, brain, and skin cancer. Treatment of athymic mice with Apo2L shortly after tumor xenograft injection markedly reduced tumor incidence. Apo2L treatment of mice bearing solid tumors induced tumor cell apoptosis, suppressed tumor progression, and improved survival. Apo2L cooperated synergistically with the chemotherapeutic drugs 5-fluorouracil or CPT-11, causing substantial tumor regression or complete tumor ablation. Thus, Apo2L may have potent anticancer activity without significant toxicity toward normal tissues.

Mature T lymphocyte apoptosis--immune regulation in a dynamic and unpredictable antigenic environment

Apoptosis of mature T lymphocytes preserves peripheral homeostasis and tolerance by countering the profound changes in the number and types of T cells stimulated by diverse antigens. T cell apoptosis occurs in at least two major forms: antigen-driven and lymphokine withdrawal. These forms of death are controlled in response to local levels of IL-2 and antigen in a feedback mechanism termed propriocidal regulation. Active antigen-driven death is mediated by the expression of death cytokines such as FasL and TNF. These death cytokines engage specific receptors that assemble caspase-activating protein complexes. These signaling complexes tightly regulate cell death but are vulnerable to inherited defects. Passive lymphokine withdrawal death may result from the cytoplasmic activation of caspases that is regulated by mitochondria and the Bcl-2 protein. The human disease, Autoimmune Lymphoproliferative Syndrome (ALPS) is due to dominant-interfering mutations in the Fas/APO-1/CD95 receptor and other components of the death pathway. The study of ALPS patients reveals the necessity of apoptosis for preventing autoimmunity and allows the genetic investigation of apoptosis in humans. Immunological, cellular, and molecular evidence indicates that throughout the life of a T cell, apoptosis may be evoked in excessive, harmful, or useless clonotypes to preserve a healthy and balanced immune system.

GUDC inhibits cytochrome c release from human cholangiocyte mitochondria

Although ursodeoxycholic acid (UDC) is considered effective treatment for primary biliary cirrhosis (PBC), its mechanism of action is unclear. We tested the hypothesis that UDC is taken up by cholangiocytes and inhibits caspase 3-dependent apoptosis. We used the human cholangiocyte cell line (H69) and assessed it for expression and function of an apical sodium-dependent bile acid transporter (ASBT) by RT-PCR and uptake of tritiated taurocholic acid. We experimentally induced apoptosis in H69 cells using beauvericin (BV) and determined caspase 3 activation using a fluorogenic substrate and mitochondrial cytochrome c release (CC) into the cytosol by immunoblot analysis. We found that a functional ASBT is expressed by H69 cells as demonstrated by RT-PCR and bile acid uptake studies. Exposure of H69 cells to BV induced apoptosis in 39.4 +/- 1.3% of cells at 2 h (0.23 +/- 0.2% in controls). In contrast, when H69 cells were preincubated with GUDC (50 mM) for 24 h and then exposed to BV, apoptosis was inhibited by 23% (P < 0.03). In cholangiocytes pretreated with GUDC for 24 h and those treated with BV for 2 h, caspase 3-like activity was reduced by 79% and mitochondrial CC release was inhibited. In summary, the human cholangiocyte cell line H69 possesses a functional bile acid transporter, and GUDC decreases BV-induced apoptosis and inhibits activity of caspase 3 protease by blocking CC release from mitochondria. These preliminary results are consistent with our hypothesis that the beneficial effect of UDC on PBC may involve decreased apoptosis after GUDC uptake by cholangiocytes.

Sensitization of AIDS-Kaposi’s Sarcoma Cells to Apo-2 Ligand-Induced Apoptosis by Actinomycin D

Kaposi’s sarcoma (KS) is the most frequent malignancy associated with HIV infection (AIDS-KS), a complication that leads to high mortality and morbidity. AIDS-KS cells are resistant to killing by chemotherapeutic drugs/NK cells and Fas-induced apoptosis, suggesting that the acquisition of antiapoptotic characteristics by AIDS-KS cells may contribute to their prolonged survival. Apo-2 ligand (Apo-2L)/TNF-related apoptosis-inducing ligand, a new member of the TNF family, has been identified as an apoptosis-inducing molecule. In this study we examined the sensitivity of 10 different AIDS-KS isolates to Apo-2L-mediated cytotoxicity. AIDS-KS cells were relatively resistant to Apo-2L; however, Apo-2L and actinomycin D (Act D) used in combination synergistically potentiated the induction of cell death in nine of the 10 isolates. Apo-2L induced apoptosis in &gt;80% of AIDS-KS cells pretreated with Act D. The caspase inhibitors, zIETD-fmk and zDEVD-fmk, inhibited apoptosis in AIDS-KS by sApo-2L, suggesting that caspase 3-like and caspase 8 or 10 activities are essential for Apo-2L-mediated apoptosis. Act D treatment of AIDS-KS cells markedly and selectively down-regulated Bcl-xL expression, while the expressions of decoy receptors 1 and 2, Bax, cellular FLICE (Fas-associated death domain protein-like IL-1-converting enzyme) inhibitory protein, FADD (Fas-associated death domain protein), procaspase 8, and p53 were not affected. These findings suggest the possible involvement of Bcl-xL in Act D-induced sensitization of AIDS-KS cells to Apo-2L-mediated apoptosis. Furthermore, Act D did not sensitize PBMC or fibroblast cells to Apo-2L. Thus, Apo-2L and Act D used in combination may be of therapeutic value in the treatment of AIDS-KS.

Cytotoxicity and induction of proinflammatory cytokines from human monocytes exposed to fine (PM2.5) and coarse particles (PM10-2.5) in outdoor and indoor air

Increased incidence of mortality and morbidity due to cardiopulmonary complications has been found to associate with elevated levels of particulate air pollution (particulate matter with an aerodynamic diameter < 10 microm, PM10 and <2.5 microm, PM2. 5). Lung injury and an imbalance of inflammatory mediators are proposed causative mechanisms, while the toxic constituents may be acidity, transition metals, organic, and biogenic materials. To compare the ability of inhalable fine particles (PM2.5), and coarse particles (PM10-2.5) to cause cell injury and cytokine production in monocytes, dichotomous Andersen samplers were used to collect size-fractionated PM10 for in vitro testing of the particle extracts. Particles from both outdoor and indoor air were collected onto Teflon filters, on nine separate occasions. Each filter was water extracted and each extract assessed for ability to cause cell death, as well as interleukin (IL)-6 and IL-8 production in human monocytes. Significant toxicity and cytokine production was induced by outdoor PM10-2.5, but not by outdoor PM2.5 or the particles collected indoors. Outdoor PM10-2.5 induced 20 times the amounts of IL-6 and IL-8 than the fine particles. Cytotoxicity was inhibited by deferoxamine, a chelator of transition metals, while cytokine production was not. On the other hand, lipopolysaccharide binding protein (LBP) completely inhibited cytokine induction by PM10-2.5, suggesting that gram-negative bacteria and/or endotoxins are components of PM10-2.5. The effective proinflammatory effects of endotoxin on macrophages may upset lung homeostasis while metals-induced cytotoxicity/necrosis may set up inflammation independent of macrophage-derived cytokines.

Tumoricidal activity of tumor necrosis factor-related apoptosis-inducing ligand in vivo

To evaluate the utility of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) as a cancer therapeutic, we created leucine zipper (LZ) forms of human (hu) and murine (mu) TRAIL to promote and stabilize the formation of trimers. Both were biologically active, inducing apoptosis of both human and murine target cells in vitro with similar specific activities. In contrast to the fulminant hepatotoxicity of LZ-huCD95L in vivo, administration of either LZ-huTRAIL or LZ-muTRAIL did not seem toxic to normal tissues of mice. Finally, repeated treatments with LZ-huTRAIL actively suppressed growth of the TRAIL-sensitive human mammary adenocarcinoma cell line MDA-231 in CB.17 (SCID) mice, and histologic examination of tumors from SCID mice treated with LZ-huTRAIL demonstrated clear areas of apoptotic necrosis within 9-12 hours of injection.