Transforming growth factor-β and its receptor are differentially regulated in human embryonal carcinoma cells

The human embryonal carcinoma cell lines Tera-2 clone 13 and NTera-2 clone D1 can be induced by retinoic acid to differentiate in vitro into neuroectodermal derivatives. The undifferentiated cells are rapidly proliferating and tumorigenic, whereas retinoic-acid-treated cells possess a decreased growth rate, lose their transformed phenotype and show a finite lifespan. Differentiation is accompanied by a marked increase in the levels of mRNA for TGF-beta 1 and TGF-beta 2 and the production of TGF-beta activity. Just like murine embryonal carcinoma cells the growth of Tera-2 clone 13 cells is not affected by the addition of either TGF-beta 1 or TGF-beta 2 to the culture medium. In contrast to published data on murine embryonal carcinoma cells, Tera-2 clone 13 and NTera-2 clone D1 cells bind TGF-beta 1 with high affinity, which is due to the presence of type-III TGF-beta receptors. Furthermore, and again in contrast to murine embryonal carcinoma cells, treatment of the human embryonal carcinoma cells with retinoic acid causes a nearly complete loss of TGF-beta 1 binding sites. These results are discussed in the light of similarities and differences in the regulation of growth and differentiation of human and murine embryonal carcinoma cell lines.     

Neurotransmitter receptor expression and activity during neuronal differentiation of embryonal carcinoma and stem cells: from basic research towards clinical applications

Abstract.  Embryonal carcinoma and embryonic stem cells have served as models to understand basic aspects of neuronal differentiation and are promising candidates for regenerative medicine. Besides being well characterized regarding the capability of embryonal carcinoma and embryonic stem cells to be precursors of different tissues, the molecular mechanisms controlling neuronal differentiation are hardly understood. Neuropeptide and neurotransmitter receptors are expressed at early stages of differentiation prior to synaptogenesis, triggering transient changes in calcium concentration and inducing neurone-specific gene expression. In vitro neuronal differentiation of embryonal carcinoma and embryonic stem cells closely resembles early neuronal development in vivo . Murine P19 EC cells are a well-characterized model for in vitro differentiation, which upon treatment with retinoic acid differentiate into neurones. Expression and activity of various receptor proteins is regulated during their differentiation. Stimulation of kinin-B2, endothelin-B, muscarinic acetylcholine, and N-methyl-D-aspartate receptors results in transient increases of intracellular free calcium concentration [Ca²⁺]_i in P19 cells undergoing neuronal differentiation, whereas embryonal cells do not respond or show a smaller change in [Ca²⁺]_i than differentiating cells. Receptor inhibition, as studied with the example of the kinin-B2 receptor, aborts neuronal maturation of P19 cells, demonstrating the crucial importance of B2 receptors during the differentiation process. Future success in obtaining desired neuronal phenotypes from pluripotent cells in vitro may offer new therapeutic perspectives for curing genetic and acquired dysfunctions of the developing and adult nervous system.     

Cardiomyocyte-like cells differentiated in vitro from embryonic carcinoma cells P19 are characterized by functional expression of adrenoceptors and Ca2+ channels

Summary P19 embryonal carcinoma cells were differentiated via embryolike aggregates (embryoid bodies) into spontaneously beating myocytes. During the whole process of differentiation the functional expression of cardiac-specific receptors and ionic channels was characterized by measuring the chronotropic reactivity, action potentials, and ionic currents in response to various cardioactive drugs. Positive chronotropic effects obtained at different maximal effective concentrations of adrenoceptor-mediated agonists indicated differential adrenoceptor expression during the in vitro development of cardiomyocyte-like cells. No cardiac-specific response was obtained with the muscarinic cholinoceptor agonist carbachol. Single beating cells were enzymatically isolated and investigated by the patch-clamp technique. Pacemaker action potentials similar to those of embryonal cardiomyocytes exhibited amplitudes ranging from 50 to 85 mV. The action potentials were synchronous to the mechanical contractions and, comparable to the chronotropic effects, were modulated by BayK 8644, isradipine, and adrenaline. The functional expression of L-type Ca²⁺ channels was demonstrated by the Ca²⁺ channel blockers isradipine, nisoldipine, gallopamil, and diltiazem causing negative chronotropic responses, as well as by the Ca²⁺ channel activator BayK 8644 causing positive chronotropic responses. These effects gradually increased with time of differentiation. The expression of L-type Ca²⁺ channels and of nicotinic acetylcholine receptors was confirmed in voltage-clamp experiments. The study demonstrates that P19 embryonal carcinoma cells can be induced to differentiate into cardiomyocyte-like cells comparable to embryonal and neonatal heart cells lacking the muscarinic cholinoceptor response only.     

Fibroblast growth factor complexed to the cytotoxin saporin is growth inhibitory but not cytotoxic for embryonal carcinoma cells

Fibroblast growth factors (FGFs) have been implicated in a number of proliferative lesions, including malignant tumor growth and vascularization. As a result, cytotoxic agents that target cell surface FGF receptors are currently under investigation. Previous reports have shown that conjugation of basic FGF with the ribosome inactivator, saporin, results in a potent cytotoxin specific for cells bearing high-affinity FGF receptors. In this report, we have used this FGF receptor-dependent cytotoxin to study receptor interactions at the surface of embryonal carcinoma cells, which express low numbers of high-affinity FGF receptors. The growth of three embryonal carcinoma cell lines and one embryonic stem cell line was shown to be inhibited by bFGF-saporin, suggesting that these cells are able to bind and internalize FGF through high-affinity FGF receptors. In addition, we determined that the responses of these cells to bFGF-saporin are qualitatively different than the responses of CHO-KI cells, which also exhibit low numbers of high-affinity FGF receptors. Specifically, pretreatment with bFGF-saporin reduces the cloning efficiency of CHO-KI cells 8- to 10-fold, whereas bFGF-saporin has little or no effect on the cloning efficiency of embryonal carcinoma cells. This finding suggests that bFGF-saporin is cytotoxic for CHO-KI cells, but not for embryonal carcinoma cells. Thus, our findings argue strongly that other factors, in addition to high-affinity FGF receptor number, are important in determining sensitivity of cells of bFGF-saporin.     

Correlation of receptors for growth factors on mouse embryonal carcinoma cells with growth in serum-free, hormone-supplemented medium

High affinity receptors for insulin, transferrin, epidermal growth factor (EGF) and a multiplication-stimulating activity (MSA) have been identified and partially characterized on a mouse embryonal carcinoma cell line, OTT-6050, using various ¹²⁵I-ligands. With the exception of MSA receptors which bound both MSA and insulin, the receptors for EGF, insulin and transferrin exhibited specificity of binding for their respective ligands. There is a correlation between the saturation of these receptors and the concentration of growth factors necessary for optimal growth of OTT-6050 cells in serum-free medium supplemented with insulin (or MSA), transferrin, EGF, fibroblast growth factor (FGF) and Pedersen fetuin on culture surfaces treated with polylysine or various types of collagen. Cells cultured in this medium exhibit growth rates equivalent to that observed with cells maintained in medium containing 5% fetal calf serum (FCS). These results suggest that relatively undifferentiated mouse embryonal carcinoma cells or endoderm cells possess receptors for various growth factors and that their presence on these cells is correlated with the ability of these cells to mitogenically respond to these growth factors.     

Changes in S1P1 and S1P2 expression during embryonal development and primitive endoderm differentiation of F9 cells

Sphingosine 1-phosphate (S1P) is a ligand for S1P family receptors (S1P(1)-S1P(5)). Of these receptors, S1P(1), S1P(2), and S1P(3) are ubiquitously expressed in adult mice, while S1P(4) and S1P(5) are tissue specific. However, little is known of their expression during embryonal development. We performed Northern blot analyses in mouse embryonal tissue and found that such expression is developmentally regulated. We also examined the expression of these receptors during primitive endoderm (PrE) differentiation of mouse F9 embryonal carcinoma (EC) cells, a well-known in vitro endoderm differentiation system. S1P(2) mRNA was abundantly expressed in F9 EC cells, but little S1P(1) and no S1P(3), S1P(4), or S1P(5) mRNA was detectable. However, S1P(1) mRNA expression was induced during EC-to-PrE differentiation. Studies using small interference RNA of S1P(1) indicated that increased S1P(1) expression is required for PrE differentiation. Thus, S1P(1) may play an important function in PrE differentiation that is not substituted for by S1P(2).     

Two distinct sequence elements mediate retroviral gene expression in embryonal carcinoma cells.

Moloney murine leukemia virus (M-MuLV) and M-MuLV-derived retroviral vectors are not expressed in early mouse embryos or in embryonal carcinoma cells. M-MuLV-derived mutants or M-MuLV-related variants which transduce the neomycin phosphotransferase gene can, however, induce drug resistance in embryonal carcinoma cells with high efficiency. In this study we investigated the sequences critical for retroviral gene expression in two different embryonal carcinoma cell lines, F9 and PCC4. We show that two synergistically acting sequence elements mediate expression in embryonal carcinoma cells. One of these is located within the U3 region of the viral long terminal repeat, and the second one is in the 5' untranslated region of the retrovirus. The latter element, characterized by a single point mutation, affects the level of stable RNA in infected cells, suggesting a regulatory mechanism similar to that of human immunodeficiency virus in human T cells.     

Inhibition of soluble yeast mitochondria ATPase by ethidium-bromide.

Surface galactosyl residues of alive embryonal carcinoma cells were tritium-labeled by the galactose oxidase NaB(3H)4 method. The labeled glycopeptides isolated from Pronase digests of the cells, were found to be similar to those prepared from endogeneously labeled embryonal carcinoma cells. They consisted mostly of high molecular weight material, and contained receptors for peanut agglutinin. It is concluded that at least a fraction of the high molecular weight glycopeptides characteristic of early embryonic cells, is displayed on the cell suface.     

Basigin, a new, broadly distributed member of the immunoglobulin superfamily, has strong homology with both the immunoglobulin V domain and the beta-chain of major histocompatibility complex class II antigen

Lotus tetragonolobus agglutinin (LTA) binds preferentially to early embryonic cells in the mouse. The affinity-purified antibody raised against LTA receptors from embryonal carcinoma cells were used to screen a lambda gt11 expression library of F9 embryonal carcinoma cells, resulting in detection of a cDNA clone specifying a new glycoprotein termed "basigin." The glycoprotein has been suggested to be a transmembrane one, and was found to be a new member of the immunoglobulin (Ig) superfamily. The molecular weight of basigin was largely in the range between 43,000 and 66,000, while that of the peptide portion with a putative signal sequence was inferred to be about 30,000. Significant levels of basigin mRNA were detected not only in embryonal carcinoma cells, but also in mouse embryos at 9-15 days of gestation and in various organs of the adult mouse. The Ig-like domain of basigin is unique, since it has strong homology to both the beta-chain of major histocompatibility class II antigen and the Ig V domain. The number of amino acids between the two conserved cysteine residues is intermediate between those of the Ig V and C domains. Therefore, basigin is an interesting protein in connection with the molecular evolution of the superfamily.     

Clonal lines of teratocarcinoma cells in vitro: Differentiation and cytogenetic characteristics

Clonal lines of embryonal carcinoma cells have been established in culture from four independently-derived transplantable teratocarcinomas of mice: three from strain C3H and one from strain 129/Sv. Cells from all lines retain the capacity to differentiate into a variety of tissue types both in tumors formed following the injection of cells into syngeneic animals and in vitro under appropriate culture conditions. Analysis of their G-banded chromosomes indicated that the four lines have near-diploid but not absolutely normal karyo-types. The same chromosomal abnormalities were often present in more than one line. Tetraploid embryonal carcinoma cells made by Colcemid or cytochalasin B treatment were also pluripotential in spite of chromosomal instability. Hybrid cells were readily obtained between diploid or tetraploid embryonal carcinoma cells and mouse 3T3 fibroblasts. Hybrid cells failed to differentiate and were contact inhibited like the 3T3 parent.     

Developmentally regulated cell surface structures on mouse and human embryonal carcinoma cell lines

Three monoclonal antibodies 5.1.H, 8.7.D and 13.7.A raised against semi-purified Tera 1 membrane fractions recognize distinct onco-foetal antigens which are developmentally regulated on cells such as Tera 2 clone 13 and appear to be restricted in their expression to undifferentiated ectoblastic cells and certain organized cystic structures mimicking the foetal intestine. These antigens, absent from normal adult tissues, differ markedly from glycosidic stage-specific antigens such as 75.12 which, while functioning as embryonal carcinoma differentiation markers, are also expressed on certain adult tissues. No evidence for a role of fucosyltransferases in regulating either 75.12 or SSEA-1 antigen expression on embryonal carcinoma cells or for the presence of lectin-like structures recognizing these antigens on such cells was found.     

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.     

A cell surface glycoprotein involved in the compaction of embryonal carcinoma cells and cleavage stage embryos

Fab fragments of rabbit anti-embryonal carcinoma cells IgG dramatically perturb cell-cell interactions between embryonal carcinoma cells and between early mouse embryo blastomeres. These antibodies prevent compaction of preimplantation embryos (or trigger their decompaction) and have similar effects on embryonal carcinoma cells. They probably act through the masking of specific molecules (Fab targets) involved in the mechanisms of recognition between cells during compaction. Fab target molecules have been extracted from embryonal carcinoma cell membranes and purified using their property to inhibit the effects mediated by anti-embryonal carcinoma Fab. The solubilization of the Fab targets could be achieved using both detergent extraction and trypsin treatment of membranes. In the latter case, a glycoprotein of 84,000 daltons could be purified which has all the properties expected from the Fab target and accounts for most of the Fab-inhibiting activity of embryonal carcinoma cell membranes.     

Expression of embryonic and MHC antigens in heterokaryons of murine embryonal carcinoma and human melanoma cells

Mouse embryonal carcinoma cells were fused with human melanoma cells or with cytoplasts of these cells. The expression of embryonic and major histocompatibility complex (MHC) antigens was studied in single heterokaryons and cybrids in the population after fusion. Recognition of heterokaryons by differential staining of mouse and human nuclei was combined with indirect immunofluorescent staining of specific membrane antigens. Complete suppression of embryonic antigen expression was found in heterokaryons within 2 days after fusion. Cybrids, formed by fusion of embryonal carcinoma cells with melanoma cytoplasts, showed a transient decrease in the expression of embryonic antigens. The expression of human MHC antigens, both class I (HLA-A, B, C) and class II (HLA-DR), was only slightly influenced in heterokaryons. No activation of mouse MHC antigens was found. The results indicate that melanoma cells contain trans-acting factors exerting a negative control on the expression of embryonic antigens. In contrast the continued expression of human MHC antigens in heterokaryons suggests that embryonal carcinoma cells either are devoid of or contain only a very limited amount of trans-acting factors controlling the expression of MHC antigens.     

Retinoic acid-induced neural differentiation of embryonal carcinoma cells.

We have previously shown that the P19 line of embryonal carcinoma cells develops into neurons, astroglia, and fibroblasts after aggregation and exposure to retinoic acid. The neurons were initially identified by their morphology and by the presence of neurofilaments within their cytoplasm. We have more fully documented the neuronal nature of these cells by showing that their cell surfaces display tetanus toxin receptors, a neuronal cell marker, and that choline acetyl-transferase and acetyl cholinesterase activities appear coordinately in neuron-containing cultures. Several days before the appearance of neurons, there is a marked decrease in the amount of an embryonal carcinoma surface antigen, and at the same time there is a substantial decrease in the volumes of individual cells. Various retinoids were able to induce the development of neurons in cultures of aggregated P19 cells, but it did not appear that polyamine metabolism was involved in the effect. We have isolated a mutant clone which does not differentiate in the presence of any of the drugs which are normally effective in inducing differentiation of P19 cells. This mutant and others may help to elucidate the chain of events triggered by retinoic acid and other differentiation-inducing drugs.