Cholera toxin beta subunit induces the differentiation of human medulloblastoma cell line DEV in a neuronal pathway

Function of ID1 protein in human cord blood-derived neural stem-like cells

The effect of dominant-negative regulator of basic helix-loop-helix (bHLH) transcription factors, an ID1 protein, on growth and differentiation of neural stem-like cell line derived from human umbilical cord blood (HUCB-NSC) was investigated. This nontransformed, mesodermal germ layer-originated line contains high levels of ID1 protein, whose intercellular distribution reflects HUCB-NSC differentiation status. Whereas cells remained undifferentiated and self-renewing in serum-free (SF) cultures, ID1 protein, although highly expressed, did not attain cell nuclei and was localized mainly in cytoplasm. In long-term-expanded cultures of partially committed (primed) HUCB-NSC grown in a low serum concentration (LS cultures) ID1 protein became translocated toward cell nuclei. Further neuronal differentiation of the cells, either spontaneous in the presence of serum or induced by neuromorphogens (dBcAMP, RA), resulted in almost complete depletion of ID1 mRNA and protein. Accordingly, HUCB-NSC transfectants overexpressing the ID1 gene were significantly inhibited in their differentiation. Notably, only neuronal and not glial development was affected after ID1 overexpression. A similar gain-of-function effect of ID1 transfection was observed in human NSC-like line (DEV) of medullobastoma origin, which is constitutively devoid of ID1 expression. Thus, our results on HUCB-NSC confirm further its neural-specific behavior and the crucial role of ID1 protein as a potent negative regulator of neural stem cell differentiation, pointing out that this protein distribution between cytoplasmic and nuclear cell compartments can be one of the most important steps in differentiation signal transduction.

Differential MAP kinases activation during semaphorin3A-induced repulsion or apoptosis of neural progenitor cells

Semaphorins are multifunctional factors implicated in various developmental processes. Little is known about the intracellular pathways ensuring appropriate signal transduction that encode the diverse functions observed. In this study, we investigated whether mitogen-activated protein kinases (MAPK), which are key elements of signal transduction in eukaryotic cells, were activated during semaphorin 3A (Sema3A)-induced repulsion or apoptosis of neural progenitor cells. We found that selective recruitment of the ERK1/2 pathway occurred during Sema3A-induced neural progenitor cell repulsion, whereas p38 MAPK activation was necessary for induction of apoptosis. Moreover, we provide evidence for the involvement of vascular endothelial growth factor receptor 1 (VEGFR1) in the activation of ERK1/2. Additional experiments performed with native cerebellar progenitors confirmed such a selective recruitment of MAPK during Sema3A-dependent migration or apoptosis. Altogether, our results suggest a model to explain how a single factor can exert different functions for a given cell type by the selective recruitment of intracellular pathways.

Human medulloblastoma cell line DEV is a potent tool to screen for factors influencing differentiation of neural stem cells

The aim of our study was to investigate whether a human neural cell line could be used as a reliable screening tool to examine the functional conservation, in humans, of transcription factors involved in neuronal or glial specification in other species. Gain-of-function experiments were performed on DEV cells, a cell line derived from a human medulloblastoma. Genes encoding nine different transcription factors were tested for their influence on the process of specification of human DEV cells towards a neuronal or glial fate. In a first series of experiments, DEV cells were transfected with murine genes encoding transcription factors known to be involved in the neuronal differentiation cascade. Neurogenins-1, -2, and -3; Mash-1; and NeuroD increased the differentiation of DEV cells towards a neuronal phenotype by a factor of 2-3.5. In a second series of experiments, we tested transcription factors involved in invertebrate glial specification. In the embryonic Drosophila CNS, the development of most glial cells depends on the master regulatory gene glial cell missing (gcm). Expression of gcm in DEV cells induced a twofold increase of astrocytic and a sixfold increase of oligodendroglial cell types. Interestingly, expression of tramtrack69, which is required in all Drosophila glial cells, resulted in a fourfold increase of only the oligodendrocyte phenotype. Expression of the related tramtrack88 protein, which is not expressed in the fly glia, or the C. elegans lin26 protein showed no effect. These results show that the Drosophila transcription factor genes tested can conserve their function upon transfection into the human DEV cells, qualifying this cell line as a screening tool to analyze the mechanisms of neuronal and glial specification.

Semaphorin 3A-vascular endothelial growth factor-165 balance mediates migration and apoptosis of neural progenitor cells by the recruitment of shared receptor

The dynamic and coordinated interaction between cells and their microenvironment controls cell migration, proliferation, and apoptosis, mediated by different cell surface molecules. We have studied the response of a neuroectodermal progenitor cell line, Dev, to a guidance molecule, semaphorin 3A (Sema3A), described previously as a repellent-collapsing signal for axons, and we have shown that Sema3A acts as a repellent guidance cue for migrating progenitor cells and, on prolonged application, induces apoptosis. Both repulsion and induction of cell death are mediated by neuropilin-1, the ligand-binding component of the Sema3A receptor. The vascular endothelial growth factor, VEGF165, antagonizes Sema3A-induced apoptosis and promotes cell survival, migration, and proliferation. Surprisingly, repulsion by Sema3A also depends on expression of VEGFR1, a VEGF165 receptor, expressed in Dev cells. Moreover, we found that these repulsive effects of Sema3A require tyrosine kinase activity, which can be attributed to VEGFR1. These results indicate that the balance between guidance molecules and angiogenic factors can modulate the migration, apoptosis (or survival), and proliferation of neural progenitor cells through shared receptors.

Chemosensitivity in childhood brain tumours in vitro: evidence of differential sensitivity to lomustine (CCNU) and vincristine

The aim of this study was to examine the range of sensitivity of a panel of short-term cultures derived from different types of malignant childhood brain tumours including medulloblastoma, ependymoma and glioblastoma multiforme to three cytotoxic drugs, lomustine (CCNU), vincristine (VCR) and procarbazine (PCB). Sensitivity was assessed using a modification of the dimethylthiazolyl-2,5-diphenyl tetrazolium bromide (MTT) assay. Short-term cell lines derived from ependymomas were considerably more resistant to VCR than other types of childhood brain tumours, while cultures derived from supratentorial primitive neuroectodermal tumour (PNET) displayed marked sensitivity to both lomustine and VCR. Cultures from ependymomas, medulloblastoma and astrocytic gliomas had similar sensitivity to lomustine and PCB as cultures derived from adult malignant astrocytoma.

Soluble factors, including TNF alpha, secreted by human T cells are both cytotoxic and cytostatic for medulloblastoma cells

We studied the effect of the treatment of a medulloblastoma cell line by human T cells derived soluble factors. Medulloblastoma is one of the more common aggressive solid neoplasms in children for which there is no adequate therapy. Cell lines established from such tumours may be helpful to test the effect of various molecules on cell proliferation. Previous studies have suggested that T cell-derived factors may be toxic for the medulloblastoma cell line Dev. Cytokines were thought to mediate this effect. In this paper, we described changes in morphology, survival and cell cycle induced in Dev cells cocultured with human T cell lines chronically infected with a retrovirus (HTLV-I) and known to secrete high level of cytokines TNF alpha, IL1alpha and IL6. Such cocultures resulted in the death of a part of Dev cells and in decreased proliferation of surviving cells, associated with morphological changes and increase in vimentin expression. Treatment with conditioned medium from infected Dev cells, containing virus induced cytokines, triggered the same effect. Reduction of these effects by TNF alpha deprivation of conditioned medium suggested that this cytokine may be implicated. Direct treatment of Dev cells with recombinant cytokines indicated that TNF alpha, but not IL1 or IL6, is associated with Dev cell alterations. TNF alpha was shown to induce the death of Dev cells by an apoptotic pathway. Furthermore, TNF alpha had a bimodal effect on the cell cycle of surviving Dev cells. These differential effects of such cytokines on medulloblastoma cells could be therefore of interest for immunotherapy of these tumours.

Retroviral vectors for the expression of two genes in human multipotent neural precursors and their differentiated neuronal and glial progeny

Retroviral vectors allow stable integration of exogenous DNA into genomic DNA and therefore gene transmission to progeny. Multipotent neural precursors and immortal cell lines prepared from them have been demonstrated to integrate into either adult or developing brain in a nontumorigenic, functional manner, without interfering with normal neurobiological processes. These cells thus appear to provide a Trojan horse ideally adapted to directing the expression of transgenes appropriately in a host brain. Here we investigated and optimized the transduction capacity of MuLV-based retroviral vectors in which internal ribosomal entry segments (IRESs) drive coexpression of two heterologous gene products from a single bicistronic mRNA in a human multipotent neural precursor cell line, "Dev," which was prepared from a medulloblastoma. For this, two vectors containing two different combinations of three viral IRESs were used and the capacity of different pseudotyped vectors to permit an efficient and stable transduction of Dev cells was compared. Our data show that (1) the best recombinant vectors for Dev cell transduction are those pseudotyped with the 10A1 MuLV envelope (40% of transduction) and (2) the initial coexpression of neo and plap, observed in transduced undifferentiated Dev cells, is maintained in differentiated Dev cells with a neuronal or glial phenotype. Therefore, these double-IRES vectors may provide an efficient means of transducing the coexpression of two proteins in undifferentiated human neural precursors that is maintained in their differentiated progeny. These data suggest that the double-IRES strategy is well adapted to potential therapeutic situations when coexpression of two different transgenes may be required in the same cell.