Loss of caspase-8 expression in neuroblastoma is related to malignancy and resistance to TRAIL-induced apoptosis.

UNLABELLED: Background and Procedures NB-derived cell lines were tested for their sensitivity to apoptosis induced by the tumor-selective apoptotic ligand TRAIL. Noninvasive S-type cell lines are highly sensitive to TRAIL, whereas invasive N-type cell lines are resistant. RESULTS: Although both S- and N-type cell lines express TRAIL-R2, FADD, and caspases-3 and -10, only S-type cells express caspase-8. Reduced levels of caspase-8 protein were also observed in a stage IV NB tumor when compared to a ganglioneuroma. The caspase-8 gene is not deleted in either N-type NB cell lines or high-stage tumors, and expression can be induced by demethylation. CONCLUSIONS: Therefore, caspase-8 expression is silenced in malignant NB, which correlates to tumor severity and resistance to TRAIL-induced apoptosis.

MYCN-related suppression of functional CD44 expression enhances tumorigenic properties of human neuroblastoma cells.

Highly malignant neuroblastoma tumors with MYCN amplification have been shown to downregulate the expression of the CD44 adhesion receptor. We have previously shown that MYCN amplified neuroblastoma cell lines either lack CD44 expression or express a nonfunctional, nonhyaluronic acid-binding CD44 receptor. By analysis of cells with manipulated expression of either CD44 or MYCN, we demonstrate that transfection of cells with a CD44 full-length cDNA construct produced a functional receptor in single copy MYCN cells and a nonfunctional CD44 receptor in MYCN amplified cells, similar to the CD44 receptor expressed by cells with enforced MYCN. Analysis of the in vivo growth properties of the transfectants revealed that the restoration of a functional CD44 receptor in nonamplified cells resulted in the suppression of in vivo cell growth, therefore linking the MYCN-related lack of hyaluronic acid-binding function of CD44 to the highly tumorigenic properties of a subset of neuroblastoma cells.

Loss of caspase-8 expression in highly malignant human neuroblastoma cells correlates with resistance to tumor necrosis factor-related apoptosis-inducing ligand-induced apoptosis.

Human neuroblastoma (NB) is a highly heterogeneous childhood cancer that is aggressively malignant or can undergo spontaneous regression that may involve apoptosis. NB-derived cell lines were tested for their sensitivity to apoptosis induced by the tumor-selective ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). Noninvasive S-type cell lines (NB cell lines of substrate adherent phenotype) are highly sensitive to TRAIL, whereas invasive N-type cell lines (NB cell lines of neuronal phenotype) are resistant. Whereas both S- and N-type cell lines express TRAIL-R2, FADD, and caspase-3 and -10, only S-type cells express caspase-8. Reduced levels of caspase-8 protein were also observed in a malignant stage IV NB tumor when compared with a benign ganglioneuroma. The caspase-8 gene is not deleted in either N-type NB cell lines or high-stage NB tumors. Caspase-8 expression can be induced by demethylation with 5-aza-2'deoxycytidine, which enhances sensitivity to TRAIL. Therefore, caspase-8 expression is silenced in malignant NB, which correlates to tumor severity and resistance to TRAIL-induced apoptosis.

Absence of functional CD44 hyaluronan receptor on human NMYC-amplified neuroblastoma cells.

CD44 represents a heterogeneous group of surface glycoproteins, involved in cell-cell and cell-matrix interactions. CD44 is the major receptor for hyaluronate (HA), a component of cell matrices, and most of CD44 known functions are attributed to its ability to recognize HA. We have recently shown that although a majority of human neuroblastomas (NBs), a childhood cancer, express high levels of CD44H, high stages and tumors with amplification of the NMYC proto-oncogene fail to express CD44. Lack of CD44 expression is strongly associated with the presence of NMYC amplification and has been further shown to represent a new feature for predicting risk of disease progression and dissemination. In the present study, we have investigated the role of CD44 expressed by NB cell lines and the possible relationship among the presence of NMYC amplification, functional expression of CD44 receptor, and tumorigenic properties of NB cells. A panel of cell lines with variable NMYC amplification and/or overexpression, as well as clonal and stable NMYC-transfected NB cells, were analyzed for CD44 expression and ability to bind HA. Our results confirmed previous observations that in NB cell lines lack of CD44 is not always related to the presence of NMYC amplification, with a number of cell lines or transfectants with both CD44 expression and NMYC amplification. However, the ability of the CD44 receptor to bind immobilized hyaluronan was restricted to CD44H+ cell lines without NMYC amplification (SH-EP and ACN). The HA-binding function was CD44 dependent and could be specifically blocked by an anti-CD44 antibody. No induction of functional HA binding was obtained with NMYC-amplified cell lines or NMYC transfectants, despite an induced increase of CD44 expression upon differentiation or after tentative activation of the receptor with phorbol esters. Inhibition of N-linked glycosylation with tunicamycin resulted in decreased HA binding of cells bearing an active CD44 receptor. We conclude that NMYC-amplified NB cell lines either do not express CD44 at all or express a nonfunctional receptor, whereas nonamplified cells constitutively express an active receptor. The lack of functional HA binding in NB cells might be partly due to incomplete N-glycosylation. The involvement of NMYC in the regulation of N-linked glycosylation can be suspected.

Expression of stem cell factor and its receptor by human neuroblastoma cells and tumors.

Bone marrow (BM) is a frequent site of metastasis in children with neuroblastoma (NB). Nonhematopoietic cell lines of the same neuroectodermal origin produce both stem cell factor (SCF) and its receptor, the product of the c-kit protooncogene (c-kit). Because recombinant SCF is likely to be soon clinically tested to accelerate BM recovery after high-dose chemotherapy, a treatment administered to children with disseminated NB, we addressed the question of whether SCF/c-kit complex could play a role in the proliferation and metastasis of NB cells. Northern blot analysis showed SCF mRNA transcripts in 7 of 8 (88%) NB cell lines and c-kit in 1 (13%). Neither c-kit nor SCF could be detected by Western blotting in cell extracts or by surface immunofluorescence and flow cytometry. Soluble SCF protein was detected by enzyme immunoassay at low concentrations in the cell supernatants in the same 7 NB cell lines. Treatment of 4 NB cell lines by SCF +/- cytokines relevant to BM physiology did not induce c-kit antigenic expression or modulate 3H-thymidine uptake. Likewise, the latter was not changed by incubating the cells with anti-c-kit neutralizing antibodies. Immunohistochemical analysis showed weak diffuse or focal staining for SCF and c-kit in few primary or metastatic tumor samples, only once simultaneously. We conclude that NB cell lines usually produce low levels of soluble SCF but do not express c-kit and that both proteins are rarely detected in NB tumors. The SCF/c-kit complex appears to be unlikely to stimulate NB growth or metastasis; thus, recombinant SCF could be safely administered to children with NB.