Neuronal Differentiation Of NT2 Cells Research Articles

Neuronal Differentiation of NT2 Cells in Monolayer and Spheroid Cultures

Metabolism and differentiation of cultured cells are influenced by changes in cellular morphology. In this study, we investigated the differences in cell proliferation and neuronal differentiation of NT2 cells in monolayer (2D) and spheroid (3D) cultures. In the monolayer culture, the cells adhered and extended on a tissue culture plate. For the spheroid culture, we fabricated a microwell chip comprising 195 circular microwells (600 ìm in diameter) on a cutture plate, and the surface was modified with polyethylene glycol to promote spheroid formation. The cells were aggregated in each microwell and formed spheroids within 24 hours of culture, and the spheroid morphology was maintained thoughout the culture period. Although the cell proliferation ability in monolayer culture was higher than that in spheroid culture, the neuronal differentiation ability of NT2 spheroid culture was higher than that in monolayer culture. Furthermore, the neuronal differentiation of NT2 spheroids was dramatically enhanced by retinoic acid treatment. These results indicate that NT2 cell properties are influenced by differences in cell morphologies, and that spheroid culture is a promising technique to induce neuronal differentiation.

Transcription of the Human Sodium Channel SCN1A Gene Is Repressed by a Scaffolding Protein RACK1

Voltage-gated sodium channel α subunit type I (Nav1.1, encoded by SCN1A gene) plays a critical role in the initiation of action potential in the central nervous system. Downregulated expression of SCN1A is believed to be associated with epilepsy. Here, we found that the SCN1A promoter (P1c), located at the 5' untranslated exon 1c, drove the reporter gene expression in human NT2 cells, and a region between nt +53 and +62 downstream of the P1c promoter repressed the promoter activity. Further analyses showed that a scaffolding protein RACK1 (receptor for activated C kinase 1) was involved in binding to this silencer. Knockdown of RACK1 expression in NT2 cells deprived the repressive role of the silencer on the P1c promoter and increased SCN1A transcription, suggesting the potential involvement of RACK1 in negatively regulating SCN1A transcription via interaction with the silencer. Furthermore, we demonstrated that the binding of the protein complex including RACK1 to the SCN1A promoter motif was decreased in neuron-like differentiation of the NT2 cells induced by retinoic acid and resulted in the upregulation of SCN1A transcription. Taken together, this study reports a novel role of RACK1 in regulating SCN1A expression that participates in retinoic acid-induced neuronal differentiation of NT2 cells.

Divergent Modulation of Neuronal Differentiation by Caspase-2 and -9

Human Ntera2/cl.D1 (NT2) cells treated with retinoic acid (RA) differentiate towards a well characterized neuronal phenotype sharing many features with human fetal neurons. In view of the emerging role of caspases in murine stem cell/neural precursor differentiation, caspases activity was evaluated during RA differentiation. Caspase-2, -3 and -9 activity was transiently and selectively increased in differentiating and non-apoptotic NT2-cells. SiRNA-mediated selective silencing of either caspase-2 (si-Casp2) or -9 (si-Casp9) was implemented in order to dissect the role of distinct caspases. The RA-induced expression of neuronal markers, i.e. neural cell adhesion molecule (NCAM), microtubule associated protein-2 (MAP2) and tyrosine hydroxylase (TH) mRNAs and proteins, was decreased in si-Casp9, but markedly increased in si-Casp2 cells. During RA-induced NT2 differentiation, the class III histone deacetylase Sirt1, a putative caspase substrate implicated in the regulation of the proneural bHLH MASH1 gene expression, was cleaved to a ∼100 kDa fragment. Sirt1 cleavage was markedly reduced in si-Casp9 cells, even though caspase-3 was normally activated, but was not affected (still cleaved) in si-Casp2 cells, despite a marked reduction of caspase-3 activity. The expression of MASH1 mRNA was higher and occurred earlier in si-Casp2 cells, while was reduced at early time points during differentiation in si-Casp9 cells. Thus, caspase-2 and -9 may perform opposite functions during RA-induced NT2 neuronal differentiation. While caspase-9 activation is relevant for proper neuronal differentiation, likely through the fine tuning of Sirt1 function, caspase-2 activation appears to hinder the RA-induced neuronal differentiation of NT2 cells.

Nucleoside Drugs Induce Cellular Differentiation by Caspase-Dependent Degradation of Stem Cell Factors

BackgroundStem cell characteristics are an important feature of human cancer cells and play a major role in the therapy resistance of tumours. Strategies to target cancer stem cells are thus of major importance for cancer therapy. Differentiation therapy by nucleoside drugs represents an attractive approach for the elimination of cancer stem cells. However, even if it is generally assumed that the activity of these drugs is mediated by their ability to modulate epigenetic pathways, their precise mode of action remains to be established. We therefore analysed the potential of three nucleoside analogues to induce differentiation of the embryonic cancer stem cell line NTERA 2 D1 and compared their effect to the natural ligand retinoic acid.Methodology/Principal FindingsAll nucleoside analogues analyzed, but not retinoic acid, triggered proteolytic degradation of the Polycomb group protein EZH2. Two of them, 3-Deazaneplanocin A (DZNep) and 2′-deoxy-5-azacytidine (decitabine), also induced a decrease in global DNA methylation. Nevertheless, only decitabine and 1β-arabinofuranosylcytosine (cytarabine) effectively triggered neuronal differentiation of NT2 cells. We show that drug-induced differentiation, in contrast to retinoic acid induction, is caused by caspase activation, which mediates depletion of the stem cell factors NANOG and OCT4. Consistent with this observation, protein degradation and differentiation could be counteracted by co-treatment with caspase inhibitors or by depletion of CASPASE-3 and CASPASE-7 through dsRNA interference. In agreement with this, OCT4 was found to be a direct in-vitro-target of CASPASE-7.Conclusions/SignificanceWe show that drug-induced differentiation is not a consequence of pharmacologic epigenetic modulation, but is induced by the degradation of stem-cell-specific proteins by caspases. Our results thus uncover a novel pathway that induces differentiation of embryonic cancer stem cells and is triggered by the established anticancer drugs cytarabine and decitabine. These findings suggest new approaches for directly targeting the stem cell fraction of human tumours.

Retraction: Hes1 is a target of microRNA-23 during retinoic-acid-induced neuronal differentiation of NT2 cells.

Nature 423, 838–842 (2003). In this article, the messenger RNA that is identified to be a target of microRNA-23 (miR-23) is from the gene termed human ‘homolog of ES1’ (HES1), accession number Y07572, and not from the gene encoding the transcriptional repressor ‘Hairy enhancer of split’ HES1 (accession number NM_00524) as stated in our paper.

Functional analysis of microRNAs during the retinoic acid-induced neuronal differentiation of human NT2 cells.

MicroRNAs (miRNAs) are phylogenetically widespread small RNAs in animals and plants. These small RNAs can regulate a gene expression at a translational level and play roles during the development of C. elegans, D. melanogaster and plants. Although more than two hundred miRNAs have been found in mammals, the target mRNAs of miRNAs is unknown. Recently, we identified Hes1, bHLH transcriptional repressor, as a target of miR-23 in NT2 cells. In this study, we further investigate that the expression of Hes1 is regulated by miR-23 during the retinoic acid (RA)-induced neural differentiation of NT2 cells. Reduction in the level of miR-23 by siRNAs resulted in the accumulation of Hes1 in differentiated NT2 cells. Moreover, a reduction in the level of miR-23 by siRNA-miR-23 affected the RA-induced neural differentiation of NT2 cells. Thus, our results indicate that miR-23 has a critical role in the RA-induced neuronal differentiation of NT2 cells.

Hes1 is a target of microRNA-23 during retinoic-acid-induced neuronal differentiation of NT2 cells.

MicroRNAs (miRNAs) are phylogenetically widespread small RNAs of 18-25 nucleotides in length, and are found in animals and plants. These small RNAs can regulate gene expression at a translational level through interactions with their target messenger RNAs, and they have a role in the development of Caenorhabditis elegans and plants. Although more than two hundred miRNAs have been found in mammals, their mRNA targets remain to be identified. Here, we demonstrate that the expression of Hes1, basic helix-loop-helix transcriptional repressor, is regulated by miRNA-23 (miR-23) in NT2 cells. miR-23 is almost complementary to part of the coding region, just upstream of the termination codon, of Hes1 mRNA. Reduction in the level of miR-23 by small interfering RNAs resulted in the accumulation of Hes1, and hindered the retinoic-acid-induced neuronal differentiation of NT2 cells. Thus, our results indicate that miR-23 regulates the expression of Hes1 at the post-transcriptional level, and participates in retinoic-acid-induced neuronal differentiation of NT2 cells.

Molecular cloning and characterization of WNT14B, a novel member of the WNT gene family.

WNT14B was cloned and characterized in this study. WNT14B encoded 357-amino acid WNT family protein with the signal peptide and an N-linked glycosylation site. WNT14B was most homologous to WNT14 (61.4% total amino acid identity). WNT15 cDNA fragment previously isolated by another group corresponds to a part of ORF of the WNT14B cDNA (codon 216-335). Exon-intron boundaries were conserved between WNT14B and WNT14 genes. WNT14B and WNT3 genes were clustered in the human chromosome 17q21 region in head to head manner. Intergenic region between WNT14B and WNT3 genes was about 33 kb in size. The 6.6-kb WNT14B mRNA was moderately expressed in fetal kidney and adult kidney. Although WNT14B mRNA was not detected in fetal brain and adult brain by northern blot analyses, WNT14B mRNA was detected in brain, especially in occipital lobe, by RNA dot blot analysis. Among 48 human cancer cell lines derived from various tissues, WNT14B was expressed in a teratocarcinoma cell line NT2 with the potential to differentiate into neuronal cells. WNT14B mRNA was significantly up-regulated by all-trans retinoic acid in NT2 cells. These results strongly suggest that WNT14B might be implicated in the early process of neuronal differentiation of NT2 cells induced by retinoic acid.

Increased expression of Galpha(q/11) and of phospholipase-Cbeta1/4 in differentiated human NT2-N neurons: enhancement of phosphoinositide hydrolysis.

The CNS is enriched in phosphoinositide-specific phospholipase C (PLC) and in the G proteins linked to its activation. Although the regional distributions of these signaling components within the brain have been determined, neither their cell type-specific localizations (i.e., neuronal versus glial) nor the functional significance of their high expression has been definitively established. In this study, we have examined the expression of phosphoinositide signaling proteins in human NT2-N cells, a well characterized model system for CNS neurons. Retinoic acid-mediated differentiation of NT2 precursor cells to the neuronal phenotype resulted in five- to 15-fold increases in the expression of PLC-beta1, PLC-beta4, and Galpha(q/11) (the prime G protein activator of these isozymes). In contrast, the expression of PLC-beta3 and PLC-gamma1 was markedly reduced following neuronal differentiation. Similar alterations in cell morphology and in the expression of PLC-beta1, PLC-beta3, and Galpha(q/11) expression were observed when NT2 cells were differentiated with berberine, a compound structurally unrelated to retinoic acid. NT2-N neurons exhibited a significantly higher rate of phosphoinositide hydrolysis than NT2 precursor cells in response to direct activation of either G proteins or PLC. These results indicate that neuronal differentiation of NT2 cells is associated with dramatic changes in the expression of proteins of the phosphoinositide signaling system and that, accordingly, differentiated NT2-N neurons possess an increased ability to hydrolyze inositol lipids.

Production of human CNS neurons from embryonal carcinoma cells using a cell aggregation method.

When treated with retinoic acid (RA), a human embryonal carcinoma (EC) cell line, NTera2 cl.D/1 (NT2), differentiates into several morphologically distinct cell types, which include terminally differentiated postmitotic central nervous system (CNS) neurons. Accumulating evidence has demonstrated the significant potential of NT2 cells in studies related to cancer therapy and neurodegenerative diseases. However, preparation of enriched NT2 neurons often requires a lengthy period (ca. five weeks) and depends largely on tedious techniques similar to those used for primary neuronal cultures. Here, we report a rapid protocol for the preparation of these human CNS neurons. Using the method of cell aggregation, enriched NT2 neurons can be obtained in approximately two weeks. We also demonstrated that cell aggregation reduced the time normally required for the induction of neuronal differentiation, as revealed by the early expression of neuronal markers. The period of RA treatment could also be reduced if NT2 cells were maintained as aggregates for a sufficient period of time. Taken together, our findings demonstrated that cell aggregation promoted RA-induced neuronal differentiation of NT2 cells and provided a rapid protocol for the efficient production of NT2 neurons. The ability to produce large quantities of human CNS neurons should facilitate future use of these neurons for basic research and applications in cell therapy.