EphB receptors trigger Akt activation and suppress Fas receptor-induced apoptosis in malignant T lymphocytes

Treatment of hematopoietic malignancies often requires allogeneic bone marrow transplantation, and the subsequent graft-versus-leukemia response is crucial for the elimination of malignant cells. Cytotoxic T lymphocytes and NK cells responsible for the immunoelimination express Fas ligand and strongly rely on the induction of Fas receptor-mediated apoptosis for their action. Although cancer cells are removed successfully by graft-versus-leukemia reactions in myeloid malignancies, their efficiency is low in T cell leukemias. This may be partially because of the ability of malignant T cells to escape apoptosis. Our work shows that Eph family receptor EphB3 is consistently expressed by malignant T lymphocytes, most frequently in combination with EphB6, and that stimulation with their common ligands, ephrin-B1 and ephrin-B2, strongly suppresses Fas-induced apoptosis in these cells. This effect is associated with Akt activation and with the inhibition of the Fas receptor-initiated caspase proteolytic cascade. Akt proved to be crucial for the prosurvival response, because inhibition of Akt, but not of other molecules central to T cell biology, including Src kinases, MEK1 and MEK2, blocked the antiapoptotic effect. Overall, this demonstrates a new role for EphB receptors in the protection of malignant T cells from Fas-induced apoptosis through Akt engagement and prevention of caspase activation. Because Fas-triggered apoptosis is actively involved in the graft-versus-leukemia response and cytotoxic T cells express ephrin-Bs, our observations suggest that EphB receptors are likely to support immunoevasivenes of T cell malignancies and may represent promising targets for therapies, aiming to enhance immunoelimination of cancerous T cells.     

Unusual T cell populations in adult murine bone marrow. Prevalence of CD3+CD4-CD8- and alpha beta TCR+NK1.1+ cells

The T cell populations present in normal murine bone marrow have not been previously analyzed in detail, mainly because of their relative rarity. In order to permit such analyses, bone marrow T cells were enriched by depleting Mac1-positive cells, which constitute 65 to 90% of bone marrow cells (BMC), and then studied by two-color flow cytometry. Analysis of the remaining cells revealed that the T cell profile of adult murine bone marrow is markedly different from that of other lymphoid organs. A very high proportion of bone marrow CD3+ cells (approximately one-third) are CD4-CD8-. CD3+CD4-CD8- cells are much more concentrated among BMC T cells than among thymocytes or splenic T cells, suggesting that bone marrow may be either a site of extrathymic TCR gene rearrangement, or a major site to which such cells home from the thymus. The expression of NK1.1 was also evaluated on Mac1-depleted BMC populations. Surprisingly, up to 39% of alpha beta TCR+ BMC were found to express NK1.1. Most alpha beta TCR+NK1.1+ BMC also expressed CD4 or CD8. NK1.1+ alpha beta TCR+ cells represented a much greater proportion of BMC T cells than of other lymphoid (splenocyte or thymocyte) T cell populations. Mac1-depleted BMC of nude mice contained very few cells with this phenotype. These results are consistent with the hypothesis that NK1.1+ alpha beta TCR+ cells are generated primarily in the thymus of normal animals and migrate preferentially to bone marrow, where they may function as regulatory elements in hematopoiesis.     

Tumor refractoriness to anti-VEGF treatment is mediated by CD11b+Gr1+ myeloid cells

Vascular endothelial growth factor (VEGF) is an essential regulator of normal and abnormal blood vessel growth. A monoclonal antibody (mAb) that targets VEGF suppresses tumor growth in murine cancer models and human patients. We investigated cellular and molecular events that mediate refractoriness of tumors to anti-angiogenic therapy. Inherent anti-VEGF refractoriness is associated with infiltration of the tumor tissue by CD11b+Gr1+ myeloid cells. Recruitment of these myeloid cells is also sufficient to confer refractoriness. Combining anti-VEGF treatment with a mAb that targets myeloid cells inhibits growth of refractory tumors more effectively than anti-VEGF alone. Gene expression analysis in CD11b+Gr1+ cells isolated from the bone marrow of mice bearing refractory tumors reveals higher expression of a distinct set of genes known to be implicated in active mobilization and recruitment of myeloid cells. These findings indicate that, in our models, refractoriness to anti-VEGF treatment is determined by the ability of tumors to prime and recruit CD11b+Gr1+ cells.     

Fas-negative osteosarcoma tumor cells are selected during metastasis to the lungs: the role of the Fas pathway in the metastatic process of osteosarcoma

Low expression of Fas by different tumors including osteosarcoma, correlates with poor prognosis. We found that osteosarcoma lung metastases from patients expressed negligible amounts of Fas, but primary tumors often expressed high Fas levels. The reason for this discrepancy is unknown. We hypothesized that because FasL is constitutively expressed in the lungs, Fas-positive (Fas(+)) tumor cells entering the lungs would bind with FasL and die from Fas-induced apoptosis, resulting in the "selection" of Fas-negative (Fas(-)) cells, which would eventually form metastases. To test this hypothesis, we injected K7 osteosarcoma cells, which express functional Fas in vitro, into mice and confirmed that its bone tumors were Fas(+), but lung metastases were Fas(-). Next, to inhibit Fas signaling without affecting Fas expression, we transfected these cells with a FADD-dominant negative (FDN) plasmid and developed K7/FDN cells. Metastases formed by K7/FDN cells contained Fas(+) tumor cells. Moreover, K7/FDN cells were retained in the lungs longer and formed more lung metastases than K7 cells. In addition, the incidence of lung metastases in FasL-deficient mice injected with K7 cells was higher than that in wild-type mice. Metastases from FasL-deficient mice but not from wild-type mice contained Fas(+) tumor cells. Based on that, we conclude that Fas(-) osteosarcoma cells are selected during lung metastases formation and that inhibition of Fas signaling in tumors or lack of FasL in the host environment allows the proliferation of Fas(+) osteosarcoma cells in the lungs and promotes metastases growth. Therefore, Fas may be considered as a new therapeutic target for osteosarcoma treatment.     

Role of T-lymphocytes in the mechanisms of hemopoiesis-inducing microenvironment activation in inflammation]

On the model of acute infectious peritonitis in mice, the inflammation was shown to accompany pronounced activation of bone marrow haemopoiesis. The increased number of committed precursor cells of erythro- and granulomonocytopoiesis, morphologically differentiated elements and enhancing colony-stimulating and erythropoietic activities of GIM cells origin were shown as well. Thy 1.2+ cells, migrating to bone marrow, were shown to play an important role in hemopoiesis stimulation inflammation. These stimulate the processes of myeloid precursor proliferation directly (by means of lymphokines) and in cooperation with monocytes-macrophages of GIM.     

Effect of graft-versus-host disease (GVHD) on host hematopoietic progenitor cells is mediated by Fas-Fas ligand interactions but this does not explain the effect of GVHD on donor cells.

The acute graft-versus-host disease (GVHD) generated in BDF1 mice by the injection of spleen cells from the C57BL/6 parental strain induces a direct cell-mediated attack on host lymphohematopoietic populations, resulting in the reconstitution of the host with donor hematopoietic stem cells. We examined the effect of GVHD on the donor and host hematopoiesis in parental-induced acute GVHD. The bone marrow was hypoplastic and the number of hematopoietic progenitor cells significantly decreased at 4 weeks after GVHD induction. However, extramedullary splenic hematopoiesis was present and the number of hematopoietic progenitor cells in the spleen significantly increased at this time. Fas expression on the host spleen cells and bone marrow cells significantly increased during weeks 2 to 8 of GVHD. Host cell incubation with anti-Fas Ab induced apoptosis, and the number of hematopoietic progenitor cells decreased during these weeks. A significant correlation between the augmented Fas expression on host bone marrow cells and the decreased number of host bone marrow cells by acute GVHD was observed. Furthermore, the injection of Fas ligand (FasL)-deficient B6/gld spleen cells failed to affect host bone marrow cells. Although Fas expression on repopulating donor cells also increased, Fas-induced apoptosis by the repopulating donor cells was not remarkable until 12 weeks, when more than 90% of the cells were donor cells. The number of hematopoietic progenitor cells in the bone marrow and the spleen by the repopulating donor cells, however, decreased over an extended time during acute GVHD. This suggests that Fas-FasL interactions may regulate suppression of host hematopoietic cells but not of donor hematopoietic cells. Hematopoietic dysfunctions caused by the reconstituted donor cells are independent to Fas-FasL interactions and persisted for a long time during parental-induced acute GVHD.     

The inhibitor of growth protein 5 (ING5) depends on INCA1 as a co-factor for its antiproliferative effects

The proteins of the Inhibitor of Growth (ING) family are involved in multiple cellular functions such as cell cycle regulation, apoptosis, and chromatin remodeling. For ING5, its actual role in growth suppression and the necessary partners are not known. In a yeast-two-hybrid approach with human bone marrow derived cDNA, we identified ING5 as well as several other proteins as interaction partners of Inhibitor of cyclin A1 (INCA1) that we previously characterized as a novel interaction partner of cyclin A1/CDK2. ING5 expression in leukemic AML blasts was severely reduced compared to normal bone marrow. In line, ING5 inhibited bone marrow colony formation upon retroviral transduction. However, Inca1(-/-) bone marrow colony formation was not suppressed by ING5. In murine embryonic fibroblast (MEF) cells from Inca1(+/+) and Inca1(-/-) mice, overexpression of ING5 suppressed cell proliferation only in the presence of INCA1, while ING5 had no effect in Inca1(-/-) MEFs. ING5 overexpression induced a delay in S-phase progression, which required INCA1. Finally, ING5 overexpression enhanced Fas-induced apoptosis in Inca1(+/+) MEFs, while Inca1(-/-) MEFs were protected from Fas antibody-induced apoptosis. Taken together, these results indicate that ING5 is a growth suppressor with suppressed expression in AML whose functions depend on its interaction with INCA1.     

Bone marrow derived cells in tumor angiogenesis and growth: are they the good,the bad or the evil?

Increasing evidence implicates an important role for a variety of bone marrow derived cells (BMDCs) in tumor angiogenesis and metastatic tumor growth. These cells are derived either from the hematopoietic or mesenchymal cell lineage, and they are distinguished, in part, by the expression of the panhematopoietic marker ‐ CD45. Some of these cell populations can colonize tumors perivascularily, and appear to promote angiogenesis and tumor cell proliferation by paracraine mechanisms, whereas others can contribute “directly” to the growth of tumor vessel capillaries or metastases. In this review we focus in particular on the role of hemangiocytes or recruited bone marrow derived circulating cells (RBCCs) in neovascularization, the contribution of VEGFR1+ hematopoietic stem cells and endothelial precursor cells in metastasis, and the involvement of myeloid derived suppressor CD11b+/Gr‐1+ cells in the resistance of tumors to certain antiangiogenic drugs, e.g., VEGF blocking antibodies.     

IL-10 protects mouse intestinal epithelial cells from Fas-induced apoptosis via modulating Fas expression and altering caspase-8 and FLIP expression

We have previously shown that the absence of Fas/Fas ligand significantly reduced tissue damage and intestinal epithelial cell (IEC) apoptosis in an in vivo model of T cell-mediated enteropathy. This enteropathy was more severe in IL-10-deficient mice, and this was associated with increased serum levels of IFN-gamma and TNF-alpha and an increase in Fas expression on IECs. In this study, we investigated the potential of IL-10 to directly influence Fas expression and Fas-induced IEC apoptosis. Mouse intestinal epithelial cell lines MODE-K and IEC4.1 were cultured with IFN-gamma, TNF-alpha, or anti-Fas monoclonal antibody (mAb) in the presence or absence of IL-10. Fas expression and apoptosis were determined by FACScan analysis of phycoerythrin-anti-Fas mAb staining and annexin V staining, respectively. Treatment with a combination of IFN-gamma and TNF-alpha induced significant apoptosis. Anti-Fas mAb alone did not induce much apoptosis unless cells were pretreated with IFN-gamma and TNF-alpha. These IECs constitutively expressed low levels of Fas, which significantly increased by preincubation of the cells with IFN-gamma and TNF-alpha. Treatment with cytokine or cytokine plus anti-Fas mAb increased apoptosis, which correlated with a decreased Fas-associated death domain IL-1-converting enzyme-like inhibitory protein (FLIP) level, increased caspase-8 activity, and subsequently increased caspase-3 activity. IL-10 diminished both cytokine- and anti-Fas mAb-induced apoptosis, and this was correlated with decreased cytokine-induced Fas expression, increased FLIP, and decreased caspase-8 and caspase-3 activity. In conclusion, IL-10 modulated cytokine induction of Fas expression on IEC cell lines and regulated IEC susceptibility to TNF-alpha, IFN-gamma, and Fas-mediated apoptosis. These findings suggest that IL-10 directly modulates IEC responses to T cell-mediated apoptotic signals.     

The death-inducing signalling complex is recruited to lipid rafts in Fas-induced apoptosis

Membrane microdomains known as lipid rafts have been shown recently to be involved in Fas signalling and apoptosis in T and B cell lines. Here, we have investigated further the role of lipid rafts in Fas-induced apoptosis in non-transformed human CD4 T cells. We show that Fas-induced apoptosis in CD4 T cells was inhibited by the lipid raft disrupter methyl-beta-cyclodextrin. When lipid rafts were isolated from control and Fas ligand treated cells, we found that a small proportion of Fas was present in the raft fraction in untreated cells and that this was greatly increased upon Fas ligation. The other components of the Death Inducing Signalling Complex (DISC), FADD, and procaspase 8, were also present at higher levels in the raft fraction isolated from Fas ligand treated cells. We conclude that formation of the DISC occurs in lipid rafts and that these membrane microdomains are required for efficient Fas signalling and apoptosis.     

Induction of histiocytic sarcoma in mouse skeletal muscle

Myeloid sarcomas are extramedullary accumulations of immature myeloid cells that may present with or without evidence of pathologic involvement of the bone marrow or peripheral blood, and often coincide with or precede a diagnosis of acute myeloid leukemia (AML). A dearth of experimental models has hampered the study of myeloid sarcomas and led us to establish a new system in which tumor induction can be evaluated in an easily accessible non-hematopoietic tissue compartment. Using ex-vivo transduction of oncogenic Kras(G12V) into p16/p19(-/-) bone marrow cells, we generated transplantable leukemia-initiating cells that rapidly induced tumor formation in the skeletal muscle of immunocompromised NOD.SCID mice. In this model, murine histiocytic sarcomas, equivalent to human myeloid sarcomas, emerged at the injection site 30-50 days after cell implantation and consisted of tightly packed monotypic cells that were CD48+, CD47+ and Mac1+, with low or absent expression of other hematopoietic lineage markers. Tumor cells also infiltrated the bone marrow, spleen and other non-hematopoietic organs of tumor-bearing animals, leading to systemic illness (leukemia) within two weeks of tumor detection. P16/p19(-/-); Kras(G12V) myeloid sarcomas were multi-clonal, with dominant clones selected during secondary transplantation. The systemic leukemic phenotypes exhibited by histiocytic sarcoma-bearing mice were nearly identical to those of animals in which leukemia was introduced by intravenous transplantation of the same donor cells. Moreover, murine histiocytic sarcoma could be similarly induced by intramuscular injection of MLL-AF9 leukemia cells. This study establishes a novel, transplantable model of murine histiocytic/myeloid sarcoma that recapitulates the natural progression of these malignancies to systemic disease and indicates a cell autonomous leukemogenic mechanism.     

Fas-Mediated apoptosis is inhibited by TSH and iodine in moderate concentrations in primary human thyrocytes in vitro.

Programmed cell death (apoptosis) can be found in normal thyroid tissue and in various diseases affecting the thyroid gland. The Fas/Fas ligand (FasL) system is involved in the induction of apoptosis in human thyrocytes. Cross-linking the Fas receptor with its own ligand or with an antibody capable of oligomerizing with the receptor induces programmed cell death. We investigated the role of Fas-induced apoptosis in primary human thyrocytes in vitro. Cell cultures of normal human thyrocytes were prepared from specimens obtained during surgery for uninodular goiter. Apoptosis was induced by incubation of the cells with a monoclonal IgM anti-Fas antibody. The presence of apoptosis was determined by FACS analysis of FITC-labelled annexin V binding combined with dye exclusion of propidium iodide. We found a significant rate of Fas-induced apoptosis in normal thyrocytes after activation with a monoclonal anti-Fas antibody. TSH was able to inhibit Fas-mediated apoptosis in a dose-dependent manner. This effect was more pronounced when thyrocytes were incubated in the presence of interferon-gamma. Low concentrations of iodine were able to inhibit apoptosis, while high concentrations of iodine increased the rate of Fas-induced apoptosis. Our results show that Fas-mediated apoptosis is inducible in normal human thyrocytes in vitro and is influenced by TSH and iodine. The Fas/FasL system may play an important role in the regulation of cell number within the thyroid gland, and may be involved in the processes leading to goiter in iodine deficiency.     

Enhanced expression of Fas-associated death domain-like IL-1-converting enzyme (FLICE)-inhibitory protein induces resistance to Fas-mediated apoptosis in activated mast cells

Mast cells play a critical role in host immune responses and are implicated in the pathogenesis of allergic inflammation. Though mouse mast cell line MC/9 expresses cell surface Fas Ag and is sensitive to Fas-induced apoptosis, activated MC/9 cells are resistant to Fas-induced cell death by cross-linking of FcepsilonRI or FcgammaR. Fas-associated death domain-like IL-1-converting enzyme (FLICE)-inhibitory protein (FLIP), a caspase-8 inhibitor that lacks the cysteine domain, is one of the negative regulators of receptor-mediated apoptosis. In this report, we show that activation of mast cells by cross-linking of FcepsilonRI or FcgammaR can induce enhanced expression of FLIP and consequently a resistance to Fas-induced apoptosis, although the expression level of Fas Ag is not changed. Addition of antisense oligonucleotide for FLIP prevents resistance to Fas-induced apoptosis of activated mast cells, suggesting that endogenous FLIP inhibits Fas-mediated apoptosis in activated mast cells. Thus, the enhanced expression of FLIP in activated mast cells contributes to the resistance to Fas-induced apoptosis, which may result in the development and prolongation of allergic inflammation.     

Poly(I:C) induce bone marrow precursor cells into myeloid-derived suppressor cells

Dendritic cells (DC) and myeloid-derived suppressor cells (MDSC) are important cells involved in immune response. DC can be generated from mouse bone marrow (BM) in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and IL-4. Recent studies have revealed that combined treatment of bone marrow MDSC with LPS plus IFN-γ inhibited the DC development but enhanced MDSC functions, such as NO release and T cell suppression. In our study, bone marrow precursor cells cultures in GM-CSF and IL-4 were treated with poly(I:C) through the culture, Gr1(+)CD11b(+) cells with MDSC functions, such as NO release and T cell suppression were accumulated in the culture system. Then the similar phenomenon was observed in the vesicular stomatitis virus infection in vivo. In conclusion, we demonstrated that the bone marrow precursor cells in the presence of GM-CSF and IL-4 can differentiate into MDSC, which is dependent on the dynamic of interaction with poly(I:C).     

Differential control of autoantibodies and lymphoproliferation by Fas ligand expression on CD4+ and CD8+ T cells in vivo.

We have previously shown that the gld autoimmune syndrome is suppressed in lethally irradiated gld mice reconstituted with a mixture of normal and gld bone marrow (BM). Furthermore, in vivo depletion of normal Thy-1+ cells restores lymphoproliferation and autoantibody production in such chimeras, suggesting that T cells bearing Fas ligand are responsible for correcting the gld defect. In this study, mixed-BM chimeras lacking either normal CD4+ (B6CD4KO-B6gld) or normal CD8+ T cells (B6CD8KO-B6gld) were generated to determine the contribution of the normal T cell subsets to disease suppression. Lymphoproliferation was completely suppressed in B6CD4KO-B6gld chimeras but only modestly in B6CD8KO-B6gld chimeras. On the other hand, both types of mixed-BM chimeras had incomplete effects on the suppression of serum autoantibodies when compared with B6gld reconstituted with isologous BM. These results suggest that both T cell subsets provide Fas ligand to suppress immune cells responsible for autoantibody production; however, CD8+ T cells are mainly responsible for preventing lymphoproliferation.     

Inhibition of histone deacetylase activity enhances Fas receptor-mediated apoptosis in leukemic lymphoblasts

We recently reported that butyrate, an inhibitor of histone deacetylases, is capable of inducing Fas-independent apoptosis in the acute lymphoblastic leukemia cell line CCRF-CEM. Here we demonstrate that butyrate enhances Fas-induced apoptosis in this cell line. The application of different histone deacetylase inhibitors revealed that tetra-acetylated histone H4 is associated with the amplifying effect of butyrate on Fas-induced cell death. FasL, Fas, FADD, RIP, caspase-8, caspase-3, Bid, FLIP(S+L), FLASH and FAP-1, proteins known to act within the Fas-apoptosis cascade, showed no changes in their expression levels in cells treated with butyrate compared with untreated cells. Analyses of Fas-oligomerization and Western blotting as well as enzyme activity assays of caspase-2, caspase-3 and caspase-8 suggest that butyrate enhances Fas-induced apoptosis downstream of Fas but upstream of caspase-8 activation. In immunoprecipitation experiments a 37 kD butyrate-regulated protein was detected which specifically interacts with caspase-8.     

Hypermethylation of the gene promoter and enhancer region can regulate Fas expression and sensitivity in colon carcinoma

Expression of the cell surface receptor Fas is frequently lost or decreased during tumor progression in human colon carcinomas. The methylation status of a 583 bp CpG-rich region within the Fas promoter (-575 to +8) containing 28 CpG sites was determined in human colon carcinoma cell lines. In Caco(2) (no Fas expression), 82-93% of CpG sites were methylated, whereas none were methylated in GC(3)/c1 (high Fas expression). In RKO (intermediate level of Fas), a single CpG site, located at -548, was 100% methylated. The inhibitor of methylation, 5-aza-2'-deoxycytidine (5-azadC), upregulated Fas expression in four of eight cell lines, and sensitized RKO cells to recombinant FasL-induced apoptosis. The p53-binding region in the first intron of the Fas gene was partially methylated in Caco(2), and 5-azadC potentiated Ad-wtp53-induced upregulation of Fas expression. Methylation-specific PCR of the first intron detected partial methylation in four out of 10 colon carcinoma tumor samples in vivo. The data suggest that DNA hypermethylation is one mechanism that contributes to the downregulation of Fas expression and subsequent loss of sensitivity to Fas-induced apoptosis in colon carcinoma cells.