9-cis and all-trans retinoic acid induce a similar phenotype in human teratocarcinoma cells

Abstract. Prior work has shown that all-trans retinoic acid (t-RA) treatment of the human teratocarcinoma (TC) cell line NTERA-2 clone D1 (abbreviated NT2/D1) induces a neuronal phenotype and other cell lineages. This study sought to explore the potential of 9-cis retinoic acid (9-cis RA) as a differentiation-inducing agent of this multipotent cell. Findings reported here show that 9-cis RA induced a phenotype similar to t-RA treatment of NT2/D1 cells. This similarity extended to their effects on the nuclear receptors retinoic acid receptor-β (RAR-β) and retinoid X receptor-α (RXR-α). Both retinoids prominently augmented RAR-β expression and transactivated a reporter plasmid containing putative RAR response elements (RAREs) with direct repeats separated by five nucleotides (DR5). Both retinoids had no appreciable effect on RXR-α expression and both minimally transactivated a reporter plasmid containing putative RXR response elements (RXREs) with direct repeats separated by one nucleotide (DR1). These studies suggest that 9-cis RA and t-RA activate common events during retinoid-mediated NT2/D1 differentiation. This hypothesis was supported by the finding that NT2/D1 cells rendered refractory to t-RA (NTZ/D1-R1) were also resistant to 9-cis RA. To discover alterations that could confer retinoid-refractoriness, retinoid receptor expression was examined in NT2/D1-R1 cells. In contrast to NT2/D1, the NT2/D1-R1 cell was found to have reduced RXR-α expression at the level of total cellular RNA. These studies establish the effectiveness of 9-cis RA as a differentiation agent of human TC cells and demonstrate that retinoids with different nuclear receptor affinities can induce similar phenotypes in NT2/D1 cells. In addition, the findings in the retinoid resistant NT2/Dl-R1 cell implicate a role for specific retinoid receptors in this human TC differentiation program.     

9-cis and all-trans retinoic acid induce a similar phenotype in human teratocarcinoma cells

Abstract. Prior work has shown that all-trans retinoic acid (t-RA) treatment of the human teratocarcinoma (TC) cell line NTERA-2 clone D1 (abbreviated NT2/D1) induces a neuronal phenotype and other cell lineages. This study sought to explore the potential of 9-cis retinoic acid (9-cis RA) as a differentiation-inducing agent of this multipotent cell. Findings reported here show that 9-cis RA induced a phenotype similar to t-RA treatment of NT2/D1 cells. This similarity extended to their effects on the nuclear receptors retinoic acid receptor-β (RAR-β) and retinoid X receptor-α (RXR-α). Both retinoids prominently augmented RAR-β expression and transactivated a reporter plasmid containing putative RAR response elements (RAREs) with direct repeats separated by five nucleotides (DR5). Both retinoids had no appreciable effect on RXR-α expression and both minimally transactivated a reporter plasmid containing putative RXR response elements (RXREs) with direct repeats separated by one nucleotide (DR1). These studies suggest that 9-cis RA and t-RA activate common events during retinoid-mediated NT2/D1 differentiation. This hypothesis was supported by the finding that NT2/D1 cells rendered refractory to t-RA (NT2/D1-R1) were also resistant to 9-cis RA. To discover alterations that could confer retinoid-refractoriness, retinoid receptor expression was examined in NT2/D1-R1 cells. In contrast to NT2/D1, the NT2/D1-R1 cell was found to have reduced RXR-α expression at the level of total cellular RNA. These studies establish the effectiveness of 9-cis RA as a differentiation agent of human TC cells and demonstrate that retinoids with different nuclear receptor affinities can induce similar phenotypes in NT2/D1 cells. In addition, the findings in the retinoid resistant NT2/D1-R1 cell implicate a role for specific retinoid receptors in this human TC differentiation program.     

Retinoic acid induces neuronal differentiation of embryonal carcinoma cells by reducing proteasome-dependent proteolysis of the cyclin-dependent inhibitor p27.

Retinoic acid (RA) treatment of embryonal carcinoma cell line NTERA-2 clone D1 (NT2/D1) induces growth arrest and terminal differentiation along the neuronal pathway. In the present study, we provide a functional link between RA and p27 function in the control of neuronal differentiation in NT2/D1 cells. We report that RA enhances p27 expression, which results in increased association with cyclin E/cyclin-dependent kinase 2 complexes and suppression of their activity; however, antisense clones, which have greatly reduced RA-dependent p27 inducibility (NT2-p27AS), continue to synthesize DNA and are unable to differentiate properly in response to RA as determined by lack of neurite outgrowth and by the failure to modify surface antigens. As to the mechanism involved in RA-dependent p27 upregulation, our data support the concept that RA reduces p27 protein degradation through the ubiquitin/proteasome-dependent pathway. Taken together, these findings demonstrate that in embryonal carcinoma cells, p27 expression is required for growth arrest and proper neuronal differentiation.     

Bone morphogenetic proteins (BMPs) induce epithelial differentiation of NT2D1 human embryonal carcinoma cells

Human embryonal carcinoma (EC) cells represent the stem cells of testicular germ cell tumours (TGCTs) and are morphologically, antigenically and functionally related to the stem cells of early mammalian embryos. Despite the large capacity for differentiation displayed by TGCT stem cells, little is known of the factors controlling their developmental potency. We have analyzed the differentiation elicited in NT2D1 human embryonal carcinoma (EC) cells by Bone Morphogenetic Proteins (BMPs) and compared it with that elicited by retinoic acid (RA). We have found that while RA induced expression of neuronal, endodermal and epithelial markers in NT2D1 human EC cells, treatment with BMPs resulted in a predominantly epithelial phenotype. We also provide evidence to suggest that at least some of the effects elicited by RA in human EC cells might be mediated through RA-induced expression of BMP-7. Thus BMPs may play an important role in specifying the type of differentiation arising from human multipotent stem cells. The manipulation of BMP signalling in human embryonic multipotent stem cells may therefore prove a useful approach in attempts to generate specific differentiated cell types in vitro, and loss of the malignant and/or transformed phenotype.     

Dickkopf‐3 alters the morphological response to retinoic acid during neuronal differentiation of human embryonal carcinoma cells

Dickkopf‐3 (Dkk‐3) and Dkkl‐1 (Soggy) are secreted proteins of poorly understood function that are highly expressed in subsets of neurons in the brain. To explore their potential roles during neuronal development, we examined their expression in Ntera‐2 (NT2) human embryonal carcinoma cells, which differentiate into neurons upon treatment with retinoic acid (RA). RA treatment increased the mRNA and protein levels of Dkk‐3 but not of Dkkl‐1. Ectopic expression of both Dkk‐3 and Dkkl‐1 induced apoptosis in NT2 cells. Gene silencing of Dkk‐3 did not affect NT2 cell growth or differentiation but altered their response to RA in suspension cultures. RA treatment of NT2 cells cultured in suspension resulted in morphological changes that led to cell attachment and flattening out of cell aggregates. Although there were no significant differences in the expression levels of cell adhesion molecules in control and Dkk‐3‐silenced cells, this morphological response was not observed in Dkk‐3‐silenced cells. These findings suggest that Dkk‐3 plays a role in the regulation of cell interactions during RA‐induced neuronal differentiation. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 74: 1243–1254, 2014     

DNA binding, protein interaction and differential expression of the human germ cell nuclear factor.

The mouse germ cell nuclear factor (mGCNF) is an orphan nuclear receptor implicated in diverse biological processes, including gametogenesis, embryonic development and embryonal carcinoma cell differentiation. We have examined the binding and regulation of the human orthologue, hGCNF, expressed in the teratocarcinoma-derived cell line NTera-2/clone D1 (NT2/D1). Binding of GCNF to the direct repeat of the sequence -AGGTCA- (DR-0) is conserved in mammalia. The formation of interspecies dimers of the in vitro synthesized proteins suggests that cellular GCNF binding is mediated by homodimers. Both the mouse and the human protein bind in concert with cellular factors to DNA. Treatment of NT2/D1 cells with all-trans retinoic acid (atRA) is accompanied first by an up-regulation followed later by a down-regulation of hGCNF and its mRNA. Temporary up-regulation in NT2/D1 cells after treatment with atRA suggests that hGCNF is important for human neural determination and differentiation.     

14-3-3 protein family members have a regulatory role in retinoic acid-mediated induction of cytokeratins in F9 cells

We have found that the expression of five 14-3-3 protein isoforms is induced during the retinoic acid (RA)-mediated differentiation of mouse embryonal carcinoma F9 cells. The induced expression of the 14-3-3 proteins is presumed to have a role in enhancing the mitogen-activated protein kinase (MAPK) activity during RA-mediated F9 cell differentiation, because using genetically engineered budding yeast we showed that these isoforms enhanced the signaling in the MAPK cascade mainly through the interaction with Raf-1. Then we assessed the role of increased MAPK activity in F9 cell differentiation by interfering with signaling in the MAPK cascade in F9 cells. The exogenous expression of dominant-negative MEK1 efficiently abrogated RA-mediated induction of the cytokeratins EndoA and EndoC in the F9 cells. These results suggest that the 14-3-3 proteins play a role in the efficient induction of the cytokeratins during F9 cell differentiation through their signal enhancing activity in the MAPK cascade.     

Cyclophilin A is required for retinoic acid-induced neuronal differentiation in p19 cells

Stable transfectants with expression of small interfering RNA for targeting cyclophilin A (CypA) in p19 cells lose their potential for retinoic acid (RA)-induced neuronal differentiation but not Me(2)SO-induced mesodermal differentiation. This difference suggests that CypA is specifically required for the RA-induced neuronal pathway. In addition to the loss of RA-induced RA receptor beta expression and retinoic acid response element (RARE)-binding activity, a dramatic reduction in RA-induced RARE-mediated luciferase activity in the CypA knockdown cell line suggests that CypA affects RARE-mediated regulation of gene expression. Silent mutation of target sequences confirms the specificity of RNA interference in p19 embryonal carcinoma cells. Collectively, our data reveal that a novel function of CypA is required in the processing of RA-induced neuronal differentiation in p19 embryonal carcinoma cells.     

Antisense inhibition of BCL-2 expression induces retinoic acid-mediated cell death during differentiation of human NT2N neurons

Changes in expression of the proto-oncogene Bcl-2 are well known in the developing brain, with a high expression level in young post-mitotic neurons that are beginning the outgrowth of processes. The physiological significance of the Bcl-2 up-regulation in these neurons is not fully understood. We used a differentiation model for human CNS neurons to study the expression and function of Bcl-2. NT2/D1 human neuronal precursor cells differentiated into a neuronal phenotype in the presence of 10 microM retinoic acid for 3-5 weeks. This concentration of retinoic acid was not toxic to undifferentiated NT2/D1 cells but was sufficient to up-regulate the BCL-2 protein in 6 days. The BCL-2 levels increased further after 3 weeks, i.e. when the cells started to show neuronal morphology. Inhibition of the accumulation of endogenous BCL-2 with vectors expressing the antisense mRNA of Bcl-2 caused extensive apoptosis after 3 weeks of the retinoic acid treatment. The loss of neuron-like cells from differentiating cultures indicated that the dead cells were those committed to neuronal differentiation. Death was related to the presence of retinoic acid since withdrawal of retinoic acid after 16 days of treatment dramatically increased cell surviving. The ability of BCL-2 to prevent retinoic acid-induced cell death was also confirmed in undifferentiated NT2/D1 cells that were transfected with a vector containing Bcl-2 cDNA in sense orientation and exposed to toxic doses (40-80 microM) of retinoic acid. Furthermore, down-regulation of BCL-2 levels by an antisense oligonucleotide in neuronally differentiated NT2/D1 cells increased their susceptibility to retinoic acid-induced apoptosis. These results indicate that one function of the up-regulation of endogenous BCL-2 during neuronal differentiation is to regulate the sensitivity of young post-mitotic neurons to retinoic acid-mediated apoptosis.     

Identification and characterization of novel human endogenous retroviral sequences prefentially expressed in undifferentiated embryonal carcinoma cells.

A novel endogenous retroviral sequence (ERV-9) has been isolated from a human embryonal carcinoma cDNA library by hybridization to a probe containing a recently described human repetitive element. DNA sequence analysis of the 4kb cDNA insert (pHE.1) revealed the presence of ORFs potentially coding for putative retrovirus-related gag, pol and env proteins. Northern blot and RNase protection experiments showed that RNA homologous to the pHE.1 insert is detected only in embryonal carcinoma cells as a 8 kb mRNA, and its expression is negatively regulated during retinoic acid induced differentiation of the human teratocarcinoma cell line NT2/D1. Using a pol specific probe we have isolated a genomic locus containing the ERV-9 sequences. Characterization by restriction enzyme analysis and DNA sequencing allowed us to define LTR-like sequences, that are composed by a complex array of subrepetitive elements. In addition we show that ERV-9 LTR sequences are capable to drive expression of linked CAT gene in a cell specific manner as LTR promoter activity has been detected only in NT2/D1 cells.     

Isolation of differentially expressed human cDNA clones: similarities between mouse and human embryonal carcinoma cell differentiation

The study of early human development is of great importance but has been limited by the lack of suitable reagents. Recently, however, the human embryonal carcinoma (EC) cell line NT2D1 has been isolated. This cell line will differentiate upon exposure to retinoic acid (RA). A cDNA library was constructed from poly(A)+ RNA derived from NT2D1 cells treated with 10(-5) M-RA for 7 days (delta NT2D1 cells). By differential cDNA screening, it was found that 1.12% of delta NT2D1 cDNA recombinants screened detected an increase in signal with 32P-cDNAs derived from delta NT2D1 as compared with NT2D1. To compare RA-induced differentiation of mouse and human EC cells, the delta NT2D1 cDNA library was rescreened with 32P-cDNAs derived from the mouse EC cell line F9 and the result compared with 32P-cDNA derived from F9 differentiated to parietalendoderm (F9PE)-like cells and visceral-endoderm (F9VE)-like cells. Approximately 1.2% of the delta NT2D1 cDNA recombinants detected a differential increase in signal following differentiation of mouse EC cells to F9VE and/or F9PE. Of these homologous regulated sequences, 0.3% were common to both mouse and human EC cell RA-induced differentiation. Five different cDNA clones were isolated that detect a marked increase (5- to 75-fold) in mRNA abundance following RA-induced differentiation of NT2D1. Of these five clones, three detect homologous mRNAs which also increase in abundance following differentiation of the mouse EC cell line F9 to PE- and/or VE-like cells; the other two clones do not detect sequences in the mouse mRNAs tested. One clone shows homology to SPARC, a gene known to be regulated during mouse embryonic development. While another clone, SO5A, has a limited range of expression, being detected in F9VE and in a human parietal-endoderm-like cell, but not in F9PE and a human visceral-endoderm-like cell. This work shows that there are both similarities and differences in mouse and human EC cell differentiation, and these cDNA clones provide some of the first reagents for studying the molecular biology of human development.     

Immature human NT2 cells grafted into mouse brain differentiate into neuronal and glial cell types

NT2 cells are a transfectable human embryonal carcinoma cell line, that can be differentiated into postmitotic neuron-like cells (NT2N cells), and transplanted into rodent brains. Differentiation requires a 5-week-long treatment with retinoic acid prior to transplantation. Here, we show that this step can be omitted, and that undifferentiated NT2 cells migrate over long distances and differentiate into both neuron- and oligodendrocyte-like cell types upon grafting into brains of immunocompetent newborn mice. Grafted cells can be traced by fluorogold, with no evidence for tumor formation. Our approach provides an experimental model system which allows the immunohistological and biochemical study of neuronal and glial differentiation of human cells in vivo, and which may be suitable as an in vivo model for pharmacological studies.