The foundational framework of tumors: Gametogenesis, p53, and cancer

The completion-of-tumor hypothesis involved in the dynamic interplay between the initiating oncogenic event and progression is essential to better recognize the foundational framework of tumors. Here we review and extend the gametogenesis-related hypothesis of tumors, because high embryonic/germ cell traits are common in tumors. The century-old gametogenesis-related hypothesis of tumors postulated that tumors arise from displaced/activated trophoblasts, displaced (lost) germ cells, and the reprogramming/reactivation of gametogenic program in somatic cells. Early primordial germ cells (PGCs), embryonic stem (ES) cells, embryonic germ cells (EGCs), and pre-implantation embryos at the stage from two-cell stage to blastocysts originating from fertilization or parthenogenesis have the potential to develop teratomas/teratocarcinomas. In addition, the teratomas/teratocarcinomas/germ cells occur in gonads and extra-gonads. Undoubtedly, the findings provide strong support for the hypothesis. However, it was thought that these tumor types were an exception rather than verification. In fact, there are extensive similarities between somatic tumor types and embryonic/germ cell development, such as antigens, migration, invasion, and immune escape. It was documented that embryonic/germ cell genes play crucial roles in tumor behaviors, e.g. tumor initiation and metastasis. Of note, embryonic/germ cell-like tumor cells at different developmental stages including PGC and oocyte to the early embryo-like stage were identified in diverse tumor types by our group. These embryonic/germ cell-like cancer cells resemble the natural embryonic/germ cells in morphology, gene expression, the capability of teratoma formation, and the ability to undergo the process of oocyte maturation and parthenogenesis. These embryonic/germ cell-like cancer cells are derived from somatic cells and contribute to tumor formation, metastasis, and drug resistance, establishing asexual meiotic embryonic life cycle. p53 inhibits the reactivation of embryonic/germ cell state in somatic cells and oocyte-like cell maturation. Based on earlier and our recent studies, we propose a novel model to complete the gametogenesis-related hypothesis of tumors, which can be applied to certain somatic tumors. That is, tumors tend to establish a somatic asexual meiotic embryonic cycle through the activation of somatic female gametogenesis and parthenogenesis in somatic tumor cells during the tumor progression, thus passing on corresponding embryonic/germ cell traits leading to the malignant behaviors and enhancing the cells' independence. This concept may be instrumental to better understand the nature and evolution of tumors. We rationalize that targeting the key events of somatic pregnancy is likely a better therapeutic strategy for cancer treatment than directly targeting cell mitotic proliferation, especially for those tumors with p53 inactivation.

Impact of Reck expression and promoter activity in neuronal in vitro differentiation

Reck (REversion-inducing Cysteine-rich protein with Kazal motifs) tumor suppressor gene encodes a multifunctional glycoprotein which inhibits the activity of several matrix metalloproteinases (MMPs), and has the ability to modulate the Notch and canonical Wnt pathways. Reck-deficient neuro-progenitor cells undergo precocious differentiation; however, modulation of Reck expression during progression of the neuronal differentiation process is yet to be characterized. In the present study, we demonstrate that Reck expression levels are increased during in vitro neuronal differentiation of PC12 pheochromocytoma cells and P19 murine teratocarcinoma cells and characterize mouse Reck promoter activity during this process. Increased Reck promoter activity was found upon induction of differentiation in PC12 cells, in accordance with its increased mRNA expression levels in mouse in vitro models. Interestingly, Reck overexpression, prior to the beginning of the differentiation protocol, led to diminished efficiency of the neuronal differentiation process. Taken together, our findings suggest that increased Reck expression at early stages of differentiation diminishes the number of neuron-like cells, which are positive for the beta-3 tubulin marker. Our data highlight the importance of Reck expression evaluation to optimize in vitro neuronal differentiation protocols.

A Novel Artificially Humanized Anti-Cripto-1 Antibody Suppressing Cancer Cell Growth

Cripto-1 is a member of the EGF-CFC/FRL1/Cryptic family and is involved in embryonic development and carcinogenesis. We designed a novel anti-Cripto-1 artificial antibody and assessed the recognition to the antigen and the potential to suppress the growth of cancer stem cells. First, single chain antibody clones were isolated by bio-panning with the affinity to recombinant Cripto-1 protein from our original phage-display library. Then, the variable regions of heavy chain VH and light chain VL in each clone were fused to constant regions of heavy chain CH and light chain CL regions respectively. These fused genes were expressed in ExpiCHO-S cells to produce artificial humanized antibodies against Cripto-1. After evaluation of the expression levels, one clone was selected and the anti-Cripto-1 antibody was produced and purified. The purified antibody showed affinity to recombinant Cripto-1 at 1.1 pmol and immunoreactivity to cancer tissues and cell lines. The antibody was available to detect the immunoreactivity in tissue microarrays of malignant tumors as well as in Cripto-1 overexpressing cells. Simultaneously, the antibody exhibited the potential to suppress the growth of human colon cancer derived GEO cells overexpressing Cripto-1 with IC₅₀ at approximately 110 nM. The artificially humanized antibody is proposed to be a good candidate to target cancer cells overexpressing Cripto-1.

TGFβ Family Signaling Pathways in Pluripotent and Teratocarcinoma Stem Cells' Fate Decisions: Balancing Between Self-Renewal, Differentiation, and Cancer

The transforming growth factor-β (TGFβ) family factors induce pleiotropic effects and are involved in the regulation of most normal and pathological cellular processes. The activity of different branches of the TGFβ family signaling pathways and their interplay with other signaling pathways govern the fine regulation of the self-renewal, differentiation onset and specialization of pluripotent stem cells in various cell derivatives. TGFβ family signaling pathways play a pivotal role in balancing basic cellular processes in pluripotent stem cells and their derivatives, although disturbances in their genome integrity induce the rearrangements of signaling pathways and lead to functional impairments and malignant transformation into cancer stem cells. Therefore, the identification of critical nodes and targets in the regulatory cascades of TGFβ family factors and other signaling pathways, and analysis of the rearrangements of the signal regulatory network during stem cell state transitions and interconversions, are key issues for understanding the fundamental mechanisms of both stem cell biology and cancer initiation and progression, as well as for clinical applications. This review summarizes recent advances in our understanding of TGFβ family functions in naїve and primed pluripotent stem cells and discusses how these pathways are involved in perturbations in the signaling network of malignant teratocarcinoma stem cells with impaired differentiation potential.

Tumor-Free Transplantation of Patient-Derived Induced Pluripotent Stem Cell Progeny for Customized Islet Regeneration

Human induced pluripotent stem cells (iPSCs) and derived progeny provide invaluable regenerative platforms, yet their clinical translation has been compromised by their biosafety concern. Here, we assessed the safety of transplanting patient-derived iPSC-generated pancreatic endoderm/progenitor cells. Transplantation of progenitors from iPSCs reprogrammed by lentiviral vectors (LV-iPSCs) led to the formation of invasive teratocarcinoma-like tumors in more than 90% of immunodeficient mice. Moreover, removal of primary tumors from LV-iPSC progeny-transplanted hosts generated secondary and metastatic tumors. Combined transgene-free (TGF) reprogramming and elimination of residual pluripotent cells by enzymatic dissociation ensured tumor-free transplantation, ultimately enabling regeneration of type 1 diabetes-specific human islet structures in vivo. The incidence of tumor formation in TGF-iPSCs was titratable, depending on the oncogenic load, with reintegration of the cMYC expressing vector abolishing tumor-free transplantation. Thus, transgene-free cMYC-independent reprogramming and elimination of residual pluripotent cells are mandatory steps in achieving transplantation of iPSC progeny for customized and safe islet regeneration in vivo.

SIGNIFICANCE

Pluripotent stem cell therapy for diabetes relies on the safety as well as the quality of derived insulin-producing cells. Data from this study highlight prominent tumorigenic risks of induced pluripotent stem cell (iPSC) products, especially when reprogrammed with integrating vectors. Two major underlying mechanisms in iPSC tumorigenicity are residual pluripotent cells and cMYC overload by vector integration. This study also demonstrated that combined transgene-free reprogramming and enzymatic dissociation allows teratoma-free transplantation of iPSC progeny in the mouse model in testing the tumorigenicity of iPSC products. Further safety assessment and improvement in iPSC specification into a mature β cell phenotype would lead to safe islet replacement therapy for diabetes.

Surrounding cells affect the gene expression pattern of human beta-defensins in squamous cell carcinoma in vitro

BACKGROUND/AIM

Defensins are basic peptides involved in non-immune bio-defense mechanisms in a normal epithelium. Human oral squamous cell carcinoma cells (OSCC) also produce human beta-defensins (HBDs), although their exact function is not clear. This study aimed to analyze the variation in gene expression levels of hBDs in co-cultures of OSCC with murine cells.

MATERIALS AND METHODS

Two OSCC cell lines (HSC-3, HSC-4) were co-cultured with mouse embryonic fibroblasts, NIH/3T3 or a mouse chondrogenic cell line derived from teratocarcinoma, ATDC5, for 1.5 days. Expression patterns of the hBD genes were investigated by real-time polymerase chain reaction (RT-PCR).

RESULTS

hBD1 expression increased when co-cultured with NIH/3T3 but decreased when co-cultured with ATDC5. Expression of hBD2 and hBD4 tended to decrease. OSCC cells formed colonies when co-cultured with NIH/3T3 but were scattered when co-cultured with ATDC5.

CONCLUSION

hBDs expression in OSCC is dependent on the type of co-cultured cells and differences in gene expression may be responsible for the morphological differences observed. OSCC may produce HBDs for purposes other than bio-defense by surrounding cells.

[Low expression of activin A in mouse and human embryonic teratocarcinoma cells]

TGFP3 family factors play an important role in regulating the balance of self-renewal and differentiation of mouse and human pluripotent stem and embryonic teratocarcinoma cells. The expression patterns of TGFbeta family signaling ligands and functional roles of these signaling pathways differ significantly in mouse and human embryonic stem cells, but the activity and functional role of these factors in mouse and human embryonic teratocarcinoma cells were not sufficiently investigated. Comparative quantitative real-time PCR analysis of the expression of TGF@[beta] family factors in mouse embryonic stem, embryonic germ, and embryonic teratocarcinoma cells showed that embryonic teratocarcinoma cells express lower ActivinA than pluripotent stem cells but similar levels of factors Nodal, Lefty 1, TGFbeta1, BMP4, and GDF3. In human nullipotent embryonic teratocarcinoma PA-1 cells, most factors of the TGFbeta family (ACTIVINA, NODAL, LEFTY 1, BMP4, and GDF3) are expressed at lower levels than in human embryonic stem cells: Thus, in mouse and human nullipotent teratocarcinoma cells, theexpression of ActivinA is significantly reduced com- pared ivith embryonic stem cells. Presumably, these differences may be associated with changes in the functional activity of the respective signaling pathways and deregulation of proliferative and antiproliferative mechanisms in embryonic teratocarcinoma cells.

Transcriptional regulation of Rex1 (zfp42) in normal prostate epithelial cells and prostate cancer cells

Rex1 (zfp42) was identified by our laboratory because of its reduced expression in F9 teratocarcinoma stem cells after retinoic acid (RA) treatment. The Rex1 (Zfp42) gene is currently widely used as a marker of embryonic stem cells. We compared the transcriptional regulation of the human Rex1 gene in NTera-2 (NT-2) human teratocarcinoma, normal human prostate epithelial cells (PrEC), and prostate cancer cells (PC-3) by promoter/luciferase analyses. Oct4, Sox2, Nanog, and Dax1 transcripts are expressed at higher levels in NT-2 and PrEC cells than in PC-3 cells. Co-transfection analyses showed that YY1 and Rex1 are positive regulators of hRex1 transcription in NT-2 and PrEC cells, whereas Nanog is not. Serial deletion constructs of the hRex1 promoter were created and analyzed, by which we identified a potential negative regulatory site that is located between -1 and -0.4 kb of the hRex1 promoter. We also delineated regions of the hRex1 promoter between -0.4 kb and the TSS that, when mutated, reduced transcriptional activation; these are putative Rex1 binding sites. Mutation of a putative Rex1 binding site in electrophoretic mobility shift assays (EMSA) resulted in reduced protein binding. Taken together, our results indicate that hRex1 binds to the hRex1 promoter region at -298 bp and positively regulates hRex1 transcription, but that this regulation is lost in PC-3 human prostate cancer cells. This lack of positive transcriptional regulation by the hRex1 protein may be responsible for the lack of Rex1 expression in PC-3 prostate cancer cells.

Targeted Vezf1-null mutation impairs vascular structure formation during embryonic stem cell differentiation

OBJECTIVE

Vezf1 encodes an early zinc finger transcription factor that is essential for normal vascular development and functions in a dose-dependent manner. Here, we investigated the role of Vezf1 during processes of endothelial cell differentiation and maturation by studying mutant Vezf1 embryonic stem (ES) cells using the in vitro embryoid body differentiation model and the in vivo teratocarcinoma model.

METHODS AND RESULTS

Vezf1-/- ES cell-derived embryoid bodies failed to form a well-organized vascular network and showed dramatic vascular sprouting defects. Our results indicate that the retinol pathway is an important mediator of Vezf1 function and that loss of Vezf1 results in reduced retinol/vitamin A signaling and aberrant extracellular matrix (ECM) formation. Unexpectedly, we also uncovered defects during in vitro differentiation of Vezf1-/- ES cells along hematopoietic cell lineages. Vezf1-/- ES cell-derived teratocarcinomas were able to spontaneously differentiate into cell types of all 3 germ layers. However, histological and immunohistochemical examination of these tumors showed decreased cell proliferation, delayed differentiation, and large foci of cells with extensive deposition of ECM. Embryoid bodies and teratocarcinomas derived from heterozygous ES cells displayed an intermediate phenotype.

CONCLUSIONS

Together, these results suggest that Vezf1 is involved in early differentiation processes of the vasculature by regulating cell differentiation, proliferation, and ECM distribution and deposition.

[Regulation of in vitro and in vivo differentiation of mouse embryonic stem cells, embryonic germ cells, and teratocarcinoma cells by TGFb family signaling factors]

The activity of specific signaling and transcription factors determines the cell fate in normal development and in tumor transformation. The transcriptional profiles of gene-components of different branches of TGFbeta family signaling pathways were studied in experimental models of initial stages of three-dimensional in vitro differentiation of embryonic stem cells, embryonic germ cells and teratocarcinoma cells and in teratomas and teratocarcinomas developed after their transplantation into immunodeficient Nude mice. Gene profile analysis of studied cell systems have revealed that expression patterns of ActivinA, Nodal, Lefty1, Lefty2, TGF TGFbeta1, BMP4, and GDF were identical in pluripotent stem cells whereas the mRNAs of all examined genes with the exception of Inhibin betaA/ActivinA were detected in the teratocarcinoma cells. These results indicate that differential activity of signaling pathways of the TGFbeta family factors regulates pluripotent state maintenance and pluripotent stem cell differentiation into the progenitors of three germ layers and extraembryonic structures and that normal expression pattern of TGFbeta family factors is rearranged in embryonic teratocarcinoma cells during tumor growth in vitro and in vivo.

ZNF423 is critically required for retinoic acid-induced differentiation and is a marker of neuroblastoma outcome

Retinoids play key roles in differentiation, growth arrest, and apoptosis and are increasingly being used in the clinic for the treatment of a variety of cancers, including neuroblastoma. Here, using a large-scale RNA interference-based genetic screen, we identify ZNF423 (also known as Ebfaz, OAZ, or Zfp423) as a component critically required for retinoic acid (RA)-induced differentiation. ZNF423 associates with the RARalpha/RXRalpha nuclear receptor complex and is essential for transactivation in response to retinoids. Downregulation of ZNF423 expression by RNA interference in neuroblastoma cells results in a growth advantage and resistance to RA-induced differentiation, whereas overexpression of ZNF423 leads to growth inhibition and enhanced differentiation. Finally, we show that low ZNF423 expression is associated with poor disease outcome in neuroblastoma patients.

Dendritic multishell architectures for drug and dye transport

Here we present the efficiency and versatility of newly developed core-multishell nanoparticles (CMS NPs), to encapsulate and transport the antitumor drugs doxorubicin hydrochloride (Dox), methotrexate (Mtx) and sodium ibandronate (Ibn) as well as dye molecules, i.e., a tetrasulfonated indotricarbocyanine (ITCC) and nile red. Structurally, the CMS NPs are composed of hyperbranched poly(ethylene imine) core functionalized by alkyl diacids connected to monomethyl poly(ethylene glycol). In order to evaluate their transport in aqueous media in vitro, we have used and compared SEC, UV, ITC, and NMR techniques. We observed that the CMS NPs were able to spontaneously encapsulate and transport Dox, Mtx and nile red in both organic and aqueous media as determined by SEC and UV-VIS spectroscopy. For the VIS transparent Ibn Isothermal Titration Calorimetric (ITC) experiments show an exothermic interaction with the CMS NPs. The enthalpic stabilization (DeltaH) upon encapsulation was in the order of approximately 7 kcals/mol which indicates stable interaction between Ibn and nanoparticles. A T(1) inversion recovery NMR experiment was carried out for 31P and 1H nuclei of Ibn and an increment of spin-lattice relaxation time for respective nuclei was observed upon encapsulation. CMS NPs were also found to encapsulate ITCC dye with stoichiometry of 6-8 molecules/nanocarrier. For in vivo imaging studies the dye loaded CMS NPs were injected to F9 teratocarcinoma bearing mice and a strong contrast was observed in the tumor tissues compared to free dye after 6 h of administration.

[Growth and differentiation of cell hybrids obtained by fusing mouse PCC4azal teratocarcinoma cells and mouse spleen cells under different in vitro culture conditions]

Cell hybrids obtained by fusing mouse PCC4azal teratocarcinoma cells and spleen cells induced to proliferation and treated with the demethylating agent 5-azacytidine prior to fusion are described. The obtained hybrids demonstrated no expression of T lymphocyte marker genes CD11 and CD45, which indicates possible somatic nucleus reprogramming by factors present in teratocarcinoma cells. Irrespective of culture conditions, cell hybrids demonstrated a relatively stable chromosome number: they lost on average no more than four chromosomes after 30 passages. Culturing in medium containing hypoxanthine, aminopterin, and thymidine (selective conditions) decreased the differentiation capacity of cell hybrids compared to nonselective conditions, which is likely due to the inhibition of their metabolism. For the first time, teratocarcinoma cell hybrid differentiation into cardiomyocytes under the influence of DMSO has been demonstrated in vitro.

Impact of hyperglycemia on early embryo development and embryopathy: in vitro experiments using a mouse model

BACKGROUND

The aim of this study is to model the processes of early embryopathy seen in human pregnancy complicated by maternal hyperglycemia secondary to maternal diabetes using a mouse embryo culture system.

METHODS

Female mice were superovulated and mated in pairs. Two-cell embryos were harvested from the oviducts and cultured in vitro in KSOM medium (synthetic oviductal medium enriched with potassium) supplemented with 0.2, 5.56, 15.56 or 25.56 mM d-glucose. Cell proliferation, differentiation and apoptosis were assessed. Experiments were performed in constant, embryos exposed to a particular concentration of glucose (0.2, 5.56, 15.56 or 25.56 mM) from harvest to either Day 5 post fertilization (pf) or Day 8 pf, and fluctuating, embryos exposed to alternate high 25.56 mM and normal 5.56 mM concentrations of glucose between harvest and Day 5 pf, glycemic culture.

RESULTS

Expected levels of blastocyst formation and hatching were seen at 0.2 and 5.56 mM concentrations of glucose but both were impaired at higher concentrations (chi(2), P < 0.005; P < 0.001). Total cell numbers (P < 0.002) and cell allocation to the inner cell mass (P < 0.01) were reduced, but with no evidence of enhanced apoptosis in the hyperglycemic cultures. Variation in hyperglycemic exposure of the embryos on Days 2, 3 and 4 showed no adverse effects of hyperglycemia up to 24 h, but 48 and 72 h exposures were equally embryopathic (P < 0.01).

CONCLUSIONS

Hyperglycemic exposure for >24 h is toxic to early embryo development. These findings may explain the lower than expected implantation rates and higher than expected rates of congenital abnormality and early pregnancy loss seen in patients with diabetes, particularly those with poor diabetic control.

Efficiency of two different transfection reagents for use with human NTERA2 cells

The teratocarcinoma cell line NTERA2 is recently used in a wide range of researches (from developmental biology to toxicology, for their ability to be induced to neural differentiation. In order to study the genetic potential of these cells, it is needed to use methods for gene silencing and/or mRNA interference, allowing cell viability and further differentiation. To check these features, we simultaneously tested the transfection efficiency of NTERA2, A549 and HeLa cells with Metafectene PRO (Biontex, Germany) and another optimal transfection reagent currently used in our Laboratory, using as a reporter gene the DsRed2 vector (Clontech, Mountain View, CA). Under our culture conditions for NTERA2 and HeLa cells, Metafectene PRO transfection method was found to possess high throughput performance, that allows low concentration rate and low exposure time to excitation light source, thus reducing both toxicity and phototoxicity.

Retinoic acid receptor isotype specificity in F9 teratocarcinoma stem cells results from the differential recruitment of coregulators to retinoic response elements

The retinoic acid receptor (RAR) alpha, beta(2), and gamma isotypes each regulate specific subsets of target genes in F9 teratocarcinoma stem cells. We used chromatin immunoprecipitation assays to monitor the association of RARgamma, retinoic X receptor (RXR) alpha, and coregulators with the RARbeta(2), Hoxa1, and Cyp26A1 retinoic acid response elements (RAREs) in F9 wild type and RARalpha, -beta(2), and -gamma null cells. Additionally we quantitatively monitored expression of the corresponding mRNAs. We demonstrated that the association of RARgamma and/or RXRalpha with a RARE was not sufficient for retinoic acid (RA)-mediated transcription of the corresponding target gene. However, the ability of RARgamma and/or RXRalpha to recruit pCIP (AIB1/ACTR/RAC-3/TRAM-1/SRC-3) and p300 to a RARE did correlate with RA-associated transcription of target mRNAs. Therefore, the specific functions of the RAR isotypes do not manifest at the level of their DNA binding but rather from a differential ability to recruit specific components of the transcriptional machinery. We also demonstrated that RA-mediated displacement of the polycomb group protein SUZ12 from a RARE was inhibited in the absence of RARgamma. Thus, transcriptional components of the RAR signaling pathway are specifically required for displacement of SUZ12 from RAREs during RA-mediated differentiation of F9 cells.

[Sinonasal teratocarcinosarcoma: a clinical, radiologic and pathologic study of 5 cases]

OBJECTIVE

To study the clinical, radiologic and pathologic features, as well as differential diagnosis of teratocarcinosarcoma in nasal cavity and paranasal sinuses.

METHODS

Light microscopic examination and immunohistochemical study was performed in 5 cases of sinonasal teratocarcinosarcoma. The clinical, radiologic and pathologic features were analyzed and the literature was reviewed.

RESULTS

All 5 patients were males and their age ranged from 34 to 43 years (mean age = 39 years). The clinical presentation was nasal obstruction, epistaxis and headache. Physical examination often revealed a polypoid mass with contact bleeding. Computed tomography showed a homogeneous nasal mass with obturation of sinuses. Cystic changes, calcification or ossification was not observed. Histologically, the tumor showed a heterogeneous admixture of components from the 3 germ cell layers, exhibiting various degrees of maturation. Squamous epithelium, smooth muscle cells, chondro-osseous tissue, intestinal or respiratory type epithelium, "fetal-type" clear cells and immature neuroepithelium were commonly seen. Immunohistochemical study demonstrated that the epithelial component expressed cytokeratin and epithelial membrane antigen, while the mesenchymal component variably expressed vimentin, smooth muscle actin and S-100 protein. On the other hand, the neuroepithelial component expressed neuron-specific enolase, synaptophysin and chromogranin, and the primitive component expressed CD99. The initial biopsy diagnosis included capillary hemangioma, olfactory neuroblastoma, craniopharyngioma and malignant mixed tumor. Follow-up information was available in all patients. Two of which had local recurrence and 1 had cervical lymph node metastasis.

CONCLUSIONS

Sinonasal teratocarcinosarcoma is a rare and highly malignant tumor occurring in sinonasal tract. It manifests mainly in adult males and is characterized by a complex admixture of teratomatous and carcinosarcomatous components. "Fetal-type" clear cells, squamous epithelium and immature neuroepithelium represent important histologic characteristics useful in diagnosis.

Nasal teratocarcinosarcoma - a case report

A 79-year-old man noticed nasal obstruction and bleeding caused by a pedunculated tumor in the left nasal cavity. The tumor revealed a malignant neoplasm predominantly composed of immature neuroepithelial cells with rosettes and palisading patterns, rhabdomyoblastic cells with positivity for desmin and cross-striations, and immature mucin-producing glandular cells. Small amounts of mature chondroid tissue and neurofibrillary matrix were also present. Therefore, the tumor was diagnosed as nasal teratocarcinosarcoma.

ER stress induces the expression of Jpk, which inhibits cell cycle progression in F9 teratocarcinoma cell

Jopock (Jpk), a transacting factor associated with the position-specific regulatory element of murine Hoxa-7, has shown to induce cell death in both prokaryotic and eukaryotic cells when introduced and overexpressed. Since Jpk protein harbors a transmembrane domain (TM) and a putative endoplasmic reticulum (ER) -retention signal at the N terminus, a subcellular localization of the protein was analyzed after fusing it into the green fluorescent protein (GFP). Both N-term- (Jpk-EGFP) and C-term-fused Jpk (EGFP-Jpk) showed to be localized in the ER when analyzed under the fluorescence microscope after staining the cells with ER- and Mito-Tracker. Through deletion analysis TM turned out to be important for ER localization of Jpk. When flow cytometric analysis was performed, both cells expressing Jpk-EGFP and EGFP-Jpk led cell cycle arrest and subsequent apoptotic cell death. In order to see whether Jpk is expressed during ER stress-mediated apoptosis, F9 cells were treated with DTT, an ER stress inducer. In the presence of 4 mM of DTT, about 50% of cells died strongly expressing Jpk (sevenfold) as well as Grp78, a molecular chaperone, and CHOP-10, a well-known apoptotic protein. When cells were transfected with both pEGFP-Jpk and pJpk-EGFP, cell cycle progression was interrupted compared to those of control cells. In summary, excess ER stress upregulated the expression of Jpk, which seemed to inhibit the cell cycle progression. These results altogether suggest that Jpk could be a useful cell death-triggering molecule applicable for cancer therapy as well as a useful target molecule for the treatment of certain neurodegenerative diseases caused by ER stress.

Jpk, a novel cell death inducer, regulates the expression of Hoxa7 in F9 teratocarcinoma cells, but not during apoptosis

Hox proteins play critical role in animal pattern formation during embryogenesis. During the study on the regulation of Hox gene expression, a novel gene, Jpk, has been isolated as a putative regulatory factor associating with the upstream regulatory sequence of murine Hoxa7. Since overexpression of Jpk caused cell death in bacteria as well as in eukaryotic cells and Hox has been reported to participate in apoptosis, we tried to analyze the relationship between Jpk and Hoxa7 during apoptosis after confirming the regulatory effect of Jpk on the expression of Hoxa7 in F9 teratocarcinoma cells. For that purpose, an effector (pEGFP-Jpk) and reporter (pGL2-NM307) plasmid containing a luciferase gene under the 307 bp (NM307) of Hoxa7 upstream regulatory sequence was constructed. In the presence of Jpk (effector), luciferase activity was increased and this enhancement was decreased by siRNA against Jpk, suggesting that Jpk is a regulatory factor of Hoxa7. In order to see whether Jpk still regulates the expression of Hoxa7 during apoptosis, F9 cells were transiently transfected with pcDNA-Jpk, and the expression of Jpk, Hoxa7, and CHOP-10 was analyzed using RT-PCR. Hoxa7 and CHOP-10 were not upregulated in the presence of Jpk although Jpk seemed to cause apoptosis, indicating that the regulatory mechanism of Jpk on the expression of Hoxa7 might be different depending on the cell status, that is, an apoptotic or proliferative condition.

Regulation of COX-2 mediated signaling by alpha3 type IV noncollagenous domain in tumor angiogenesis

Human alpha3 chain, a noncollagenous domain of type IV collagen [alpha3(IV)NC1], inhibits angiogenesis and tumor growth. These biologic functions are partly attributed to the binding of alpha3(IV)NC1 to alphaVbeta3 and alpha3beta1 integrins. alpha3(IV)NC1 binds alphaVbeta3 integrin, leading to translation inhibition by inhibiting focal adhesion kinase/phosphatidylinositol 3-kinase/Akt/mTOR/4E-BP1 pathways. In the present study, we evaluated the role of alpha3beta1 and alphaVbeta3 integrins in tube formation and regulation of cyclooxygenase-2 (COX-2) on alpha3(IV)NC1 stimulation. We found that although both integrins were required for the inhibition of tube formation by alpha3(IV)NC1 in endothelial cells, only alpha3beta1 integrin was sufficient to regulate COX-2 in hypoxic endothelial cells. We show that binding of alpha3(IV)NC1 to alpha3beta1 integrin leads to inhibition of COX-2-mediated pro-angiogenic factors, vascular endothelial growth factor, and basic fibroblast growth factor by regulating IkappaBalpha/NFkappaB axis, and is independent of alphaVbeta3 integrin. Furthermore, beta3 integrin-null endothelial cells, when treated with alpha3(IV)NC1, inhibited hypoxia-mediated COX-2 expression, whereas COX-2 inhibition was not observed in alpha3 integrin-null endothelial cells, indicating that regulation of COX-2 by alpha3(IV)NC1 is mediated by integrin alpha3beta1. Our in vitro and in vivo findings demonstrate that alpha3beta1 integrin is critical for alpha3(IV)NC1-mediated inhibition of COX-2-dependent angiogenic signaling and inhibition of tumor progression.

[Comparative analysis of expression of TGFbeta family factors and their receptors in mouse embryonic stem and embryonic teratocarcinoma cells]

Specific factors that determine the cell fate in early embryogenesis are modulated during interaction of signaling pathways to form a unique regulatory network inside the cell, which is essential for differentiation of various cell populations. We carried out a comparative study of expression of the genes of TGFbeta growth factors and their receptors at the initial stages of differentiation of the embryonic stem cells, during formation of spheroids of the embryonic teratocarcinoma cells, and during growth of neoplastic cells in vivo in immunodeficient mice. The patterns of expression of the genes Activin, Nodal, Lefty1, Lefty2, BMP, and TGF1 and their receptors ActRI, ActRII, BMPRI, TGFbeta1R1, and Tdgf proved to be identical. Expression of alpha-fetoprotein and transcription factor Gata4 protein, specific for the primary endoderm, was detected in the embryonic teratocarcinoma cells. In Undifferentiated embryonic stem cells, expression of Gata4 was found at the mRNA level, while expression at the level of proteins appeared only in the primary endoderm cells in the embryoid bodies. The results obtained suggest that despite the existence of similar signaling systems in the embryonic stem and teratocarcinoma cells, the presence of different intracellular specific factors forms radically different regulatory pathways, which determine the program of their differentiation.

Potential Gene Therapy Strategies for Cancer Stem Cells

To be maximally effective, therapy of cancer must be directed against both the resting stem cells and the proliferating cells of the cancer. The cell populations of both normal and cancer tissues consist of resting stem cells, proliferating transit-amplifying cells, terminally differentiating cells and dying (apoptotic) cells. The difference between normal tissue renewal and growth of cancers is that some of the transit-amplifying cells in the cancer population do not mature into terminally differentiating cells, but instead continue to proliferate and do not die (maturation arrest). Because of this the number of cancer cells increase, whereas the cell population of normal tissues remains a relatively constant. Conventional radiation treatment and chemotherapy kill the actively proliferating transit- amplifying cells of the cancer. Differentiation therapy, using specific targeted inhibitors of activation, effectively induces differentiation of the proliferating transit-amplifying cancer cells. However, even if the proliferating cancer cells are completely inhibited or eliminated, the cancer stem cells may restore the transit-amplifying population, so that clinical remission is usually temporary. The hypothesis presented in this paper is that successful cancer therapy must be directed against both the resting stem cells and the proliferating cells of the cancer. This may be possible if specific stem cell signals are inhibited using gene therapy, while at the same time attacking proliferating cells by conventional radiation treatment or chemotherapy. With advances in approaches using specific inhibitory RNA, such combination therapy may now be possible, but critical problems in delivering the inhibitory effect specifically to the cancer stem cells have yet to be worked out.

Extensive post-transcriptional regulation of microRNAs and its implications for cancer

MicroRNAs (miRNAs) are short, noncoding RNAs that post-transcriptionally regulate gene expression. While hundreds of mammalian miRNA genes have been identified, little is known about the pathways that regulate the production of active miRNA species. Here we show that a large fraction of miRNA genes are regulated post-transcriptionally. During early mouse development, many miRNA primary transcripts, including the Let-7 family, are present at high levels but are not processed by the enzyme Drosha. An analysis of gene expression in primary tumors indicates that the widespread down-regulation of miRNAs observed in cancer is due to a failure at the Drosha processing step. These data uncover a novel regulatory step in miRNA function and provide a mechanism for miRNA down-regulation in cancer.

Cytotoxicity of a Novel Fibroblast Growth Factor Receptor Targeted Immunotoxin on a Human Ovarian Teratocarcinoma Cell Line

Basic fibroblast growth factor (bFGF) is an important tumor-associated growth factor that contributes to proliferation and angiogenesis of tumor. The high-affinity receptor for bFGF, fibroblast growth factor receptor (FGFR), is found to be overexpressed in a number of tumor cells. For the purpose of exploring the significance of bFGF/FGFR in tumor-targeted therapy, a recombinant immunotoxin contained the N-terminal 389 residues of diphtheria toxin (DT), and the full length of human bFGF was designed, expressed, and purified. The bioactivity of the product was evaluated by testing the cytotoxicity on PA-1 cells (a human ovarian teratocarcinoma cell line with high-level expression of FGFR) in vitro. The immunotoxin showed a significant cytotoxicity on PA-1 cells (IC(50) 8 - 9 ng/mL), and this effect could be antagonized by equine diphtheria antitoxin (DAT), bFGF, anti-bFGF monoclonal antibody (MAb), and anti- FGFR polyclonal antibody (PAb), respectively. Additionally, Chinese hamster ovary (CHO) cells and Hep-2 cells (a human epidermoid laryngocarcinoma cell line) with low expression of FGFR were tested to be resistant to the immunotoxin. The results indicated that FGFR might be an effective target for tumor therapy, and bFGF-mediated immunotoxin could be a potential candidate in the treatment of cancer.

Polyunsaturated fatty acids mobilize intracellular Ca2+in NT2 human teratocarcinoma cells by causing release of Ca2+from mitochondria

In a variety of disorders, overaccumulation of lipid in nonadipose tissues, including the heart, skeletal muscle, kidney, and liver, is associated with deterioration of normal organ function, and is accompanied by excessive plasma and cellular levels of free fatty acids (FA). Increased concentrations of FA may lead to defects in mitochondrial function found in diverse diseases. One of the most important regulators of mitochondrial function is mitochondrial Ca2+([Ca2+]m), which fluctuates in coordination with intracellular Ca2+([Ca2+]i). Polyunsaturated FA (PUFA) have been shown to cause [Ca2+]imobilization albeit by unknown mechanisms. We have found that PUFA but not monounsaturated or saturated FA cause [Ca2+]imobilization in NT2 human teratocarcinoma cells. Unlike the [Ca2+]iresponse to the muscarinic G protein-coupled receptor agonist carbachol, PUFA-mediated [Ca2+]imobilization in NT2 cells is independent of phospholipase C and inositol-1,4,5-trisphospate (IP3) receptor activation, as well as IP3-sensitive internal Ca2+stores. Furthermore, PUFA-mediated [Ca2+]imobilization is inhibited by the mitochondria uncoupler carboxyl cyanide m-chlorophenylhydrozone. Direct measurements of [Ca2+]mwith X-rhod-1 and45Ca2+indicate that PUFA induce Ca2+efflux from mitochondria. Further studies show that ruthenium red, an inhibitor of the mitochondrial Ca2+uniporter, blocks PUFA-induced Ca2+efflux from mitochondria, whereas inhibitors of the mitochondrial permeability transition pore cyclosporin A and bongkrekic acid have no effect. Thus PUFA-gated Ca2+release from mitochondria, possibly via the Ca2+uniporter, appears to be the underlying mechanism for PUFA-induced [Ca2+]imobilization in NT2 cells.

Activation of classical protein kinase C reduces the expression of human cationic amino acid transporter 3 (hCAT-3) in the plasma membrane

We have previously shown that activation of PKC (protein kinase C) results in internalization of hCAT-1 [human CAT-1 (cationic amino acid transporter 1)] and a decrease in arginine transport [Rotmann, Strand, Martiné and Closs (2004) J. Biol. Chem. 279, 54185-54192]. However, others found increased transport rates for arginine in response to PKC activation, suggesting a differential effect of PKC on different CAT isoforms. Therefore we investigated the effect of PKC on hCAT-3, an isoform expressed in thymus, brain, ovary, uterus and mammary gland. In Xenopus laevis oocytes and human U373MG glioblastoma cells, hCAT-3-mediated L-arginine transport was significantly reduced upon treatment with compounds that activate classical PKC. In contrast, inactive phorbol esters and an activator of novel PKC isoforms had no effect. PKC inhibitors (including the PKCalpha-preferring Ro 31-8280) reduced the inhibitory effect of the PKC-activating compounds. Microscopic analyses revealed a PMA-induced reduction in the cell-surface expression of fusion proteins between hCAT-3 and enhanced green fluorescent protein expressed in X. laevis oocytes and glioblastoma cells. Western-blot analysis of biotinylated surface proteins demonstrated a PMA-induced decrease in hCAT-3 in the plasma membrane, but not in total protein lysates. Pretreatment with a PKC inhibitor also reduced this PMA effect. It is concluded that similar to hCAT-1, hCAT-3 activity is decreased by PKC via reduction of transporter molecules in the plasma membrane. Classical PKC isoforms seem to be responsible for this effect.

Differential Regulation of Intracellular Calcium Oscillations by Mitochondria and Gap Junctions

Fluctuations of intracellular Ca2+ ([Ca2+]i) regulate a variety of cellular functions. The classical Ca2+ transport pathways in the endoplasmic reticulum (ER) and plasma membrane are essential to [Ca2+]i oscillations. Although mitochondria have recently been shown to absorb and release Ca2+ during G protein-coupled receptor (GPCR) activation, the role of mitochondria in [Ca2+]i oscillations remains to be elucidated. Using fluo-3-loaded human teratocarcinoma NT2 cells, we investigated the regulation of [Ca2+]i oscillations by mitochondria. Both the muscarinic GPCR agonist carbachol and the ER Ca2+-adenosine triphosphate inhibitor thapsigargin (Tg) induced [Ca2+]i oscillations in NT2 cells. The [Ca2+]i oscillations induced by carbachol were unsynchronized among individual NT2 cells; in contrast, Tg-induced oscillations were synchronized. Inhibition of mitochondrial functions with either mitochondrial blockers or depletion of mitochondrial DNA eliminated carbachol--but not Tg-induced [Ca2+]i oscillations. Furthermore, carbachol-induced [Ca2+]i oscillations were partially restored to mitochondrial DNA-depleted NT2 cells by introduction of exogenous mitochondria. Treatment of NT2 cells with gap junction blockers prevented Tg-induced but not carbachol-induced [Ca2+]i oscillations. These data suggest that the distinct patterns of [Ca2+]i oscillations induced by GPCR and Tg are differentially modulated by mitochondria and gap junctions.

Gene expression profiling of mouse teratocarcinomas uncovers epigenetic changes associated with the transformation of mouse embryonic stem cells

The molecular mechanisms of the development of teratocarcinomas from stem cells are largely unknown. To determine which genes are associated with the transformation of these cells, we have performed oligonucleotide microarray analysis, using Affymetrix U74A GeneChips, on both cell cultures and tumors in nude mice. We identified 68 genes that significantly differed in expression between the ES cell culture and the teratocarcinoma cell line, SCC-PSA1, and 51 genes with statistically different expression patterns between the ES cell tumors and the teratocarcinomas (P < .00005). We found that there were 20 genes that had common expression patterns in both groups. We also examined the role of the transition from in vitro to in vivo by comparing ES cell culture to ES cell tumor, and teratocarcinoma cell line to teratocarcinomas. We identified 22 genes that were upregulated in the ES cell tumors and 42 that had a decreased expression in the tumor (P < .0001). In comparing SCC-PSA1 to its tumor, we identified 34 upregulated genes and 25 downregulated genes (P < .001). There were only 10 genes in common from these two lists. GenMapp search revealed that several pathways, especially the cell cycle pathway, are actively involved in the induction of teratocarcinomas. Our results indicate that many key development genes may play a key role in the transformation of ES cells into teratocarcinoma cells.

The Detection of Differentiation-inducing Chemicals by using Green Fluorescent Protein Expression in Genetically Engineered Teratocarcinoma Cells

The murine embryonal teratocarcinoma cell line, P19, was genetically manipulated in order to provide preliminary information on compounds that induce differentiation. Without chemical induction, P19 cells remain in an undifferentiated state, but can be induced to differentiate into specific cell types. For example, dimethyl sulphoxide (DMSO) induces cardiac and skeletal muscle differentiation, whereas retinoic acid stimulates neuronal differentiation. P19 cells were transfected with a construct containing a segment of the murineTert (mTert) promoter sequence combined with the green fluorescent protein (GFP) gene, which acts as a reporter gene. mTert expression, the reverse transcriptase component of murine telomerase, is closely linked to telomerase activity and is down-regulated during differentiation. Three retinoids and DMSO induced the differentiation of P19 cells, which was determined by a reduction in mTert_GFP expression, detected by flow cytometry and confocal microscopy as independent methods of detection. A test substance, ethanol, and a control substance, saccharin, did not cause a decrease in mTert_GFP expression. In addition, it could be demonstrated that the mTert_GFP test detects developmentally relevant effects at non-cytotoxic concentrations. The ID50 values derived for the reduction of mTert_GFP expression were lower than the IC50 values detected with the MTT test, by a factor of 21.4 for all-trans retinoic acid, 12.7 for 9-cis retinoic acid, 29.6 for 13-cis retinoic acid, and 8.7 for DMSO. In comparison to the IC50 value for the P19 cell line, a similar IC50 value was obtained with 3T3 cells for ethanol, but there was a 2-fold increase for DMSO. The retinoids were not cytotoxic to 3T3 cells at the concentrations tested. This newly developed test is capable of detecting differentiation-inducing compounds at non-cytotoxic concentrations within 4 days. It offers a method for detecting chemicals with specific toxicological mechanisms, such as the retinoids, which could provide additional information in embryotoxicity testing as different promoters could be employed. Here, we report the use of this novel test system for the successful analysis of DMSO and three retinoids with different in vivo teratogenic potentials.

Sphingolipid-to-glycerophospholipid conversion in SPL-null cells implies the existence of an alternative isozyme

Sphingosine-1-phosphate (S1P) lyase catalyzes the cleavage of the bioactive lipid molecule S1P to phosphoethanolamine and hexadecenal, both of which are utilized as glycerophospholipid precursors. Until now, only one gene, SPL, has been identified as encoding a S1P lyase. In the present study, SPL-null F9 cells were able to convert radiolabeled dihydrosphingosine to glycerophospholipids, albeit at much lower efficiency than parent cells. Lysates prepared from the SPL-null cells exhibited weak but significant dihydrosphingosine-1-phosphate lyase activity in vitro. These results provide evidence of the existence of an alternative S1P lyase.

Resistance mechanisms following cisplatin and oxaliplatin treatment of the human teratocarcinoma cell line 2102EP

BACKGROUND

Oxaliplatin and cisplatin are widely used in cancer chemotherapy, however, their clinical efficiency is often limited by the development of resistance.

MATERIALS AND METHODS

We examined different mechanisms of resistance in the human teratocarcinoma cell line 2102EP following exposure to cisplatin or oxaliplatin. Cells were exposed ten times with IC90-doses of 30 microM cisplatin and 50 microM oxaliplatin, respectively. Different cell clones were tested for expression of resistance using the SRB-assay. Moreover, resistance mechanisms in terms of drug uptake, platinum-adduct formation, GSH metabolism, DNA mismatch repair and p53 protein function were investigated.

RESULTS

Three cisplatin cell clones with significant resistance factors of 2.0 to 2.6 were found. Two oxaliplatin cell clones showed only weak resistance, with resistance factors of 1.6 and 1.7, respectively. In all three cisplatin-exposed cell clones a decreased cellular uptake of cisplatin was found. Furthermore, mechanisms of DNA damage tolerance may also play a role in the development of cisplatin-resistance in these cells. However, only two cell clones showed a decreased level of platinum-DNA-adducts. An increased DNA-repair of platinum-DNA adducts was not seen. In addition, no differences in expression of mismatch-repair proteins MSH2 and MLH1, tumor suppressor protein p53, or glutathione metabolism were found. However, significant resistance mechanisms for the observed oxaliplatin resistance could not be identified, although in one oxaliplatin-exposed cell clone, there was some evidence that a decreased cellular uptake of oxaliplatin may contribute to the observed low level resistance.

CONCLUSIONS

The data add weight to the hypothesis that resistance mechanisms following oxaliplatin exposure may be similar to cisplatin. The precise mechanisms of resistance in the oxaliplatin-resistant cell clones are still not fully understood and current studies are underway to further eluciate this finding.

The Road From Teratocarcinoma to Human Embryonic Stem Cells

In this article, a brief review of the research that began with the study of murine teratomas of the testis and ultimately led to the culture of human embryonic stem cells is discussed. Most of the space will be devoted to the studies in which the author personally took part, and the discussion will also touch upon some of the crucial experiments important for the understanding of this entire research effort.

Modulation of the retinoic acid-induced cell apoptosis and differentiation by the human TR4 orphan nuclear receptor

In our previous studies, the TR4 orphan nuclear receptor (TR4) has been demonstrated to suppress retinoic acid (RA)-induced transactivation via a negative feedback control mechanism and in situ analysis showed that TR4 is extensively expressed in mouse brain, especially in regions where the cells are proliferating. To further study the potential roles of TR4 during cell differentiation, a tetracycline-inducible system with anti-sense TR4 in teratocarcinoma P19 cell lines was generated to analyze the retinoic acid-induced differentiation of these cells. The results indicated that the expression of TR4 reduced by doxycycline anti-sense TR4 would alter the retinoic acid-induced differentiation pathway that results in the changes of cell morphology and cell cycle profile. Unexpectedly, our data further indicated that the RA-induced apoptosis, judging by DNA fragmentation, could also be altered by the induction of anti-sense TR4. Together, these findings provide the first in vivo evidence that an orphan nuclear receptor, such as TR4, may play major roles in the RA-mediated apoptosis or differentiation in P19 cells.

Apoptotic cell death induced by hydrogen peroxide in NT2 parental and mitochondrial DNA depleted cells

Oxidative stress has been implicated in several pathologies associated with degenerative processes. Mitochondria are involved in cell death by necrosis or apoptosis due to a large load of Ca2+, the formation of reactive oxygen species (ROS), mitochondrial depolarization and the release of cytochrome c that initiates the caspase cascade. Nevertheless, the role of mitochondria in cell death processes induced by hydrogen peroxide (H2O2) has not been fully established. In this study, we analyzed the cytotoxic effect of H2O2 on rho+ human teratocarcinoma (NT2) cells and on mitochondria-DNA depleted rho0 NT2 cells, lacking functional mitochondria. The cells were exposed to H2O2 for 24 h and cell viability was dose-dependently decreased in both cell lines upon H2O2 exposure, although cell susceptibility was higher in rho0 NT2 cells. Moreover a decrease in mitochondrial membrane potential (Deltapsi(m)), mitochondrial cytochrome c release, caspases activation and DNA fragmentation were largely induced by H2O2 and occurred in both cell lines. Nevertheless, increased cell toxicity in rho0 cells upon H2O2 exposure was accompanied by a higher activation of the effector caspases-3 and -6. The data support that, in general, no differences were observed in cells containing functional (rho+) or non-functional (rho0) mitochondria upon H2O2-induced apoptotic cell death.

Interference with ubiquitination causes oxidative damage and increased protein nitration: implications for neurodegenerative diseases

Inhibition of the proteasomal pathway for degrading abnormal proteins leads to protein aggregation, increased oxidative damage and increased protein nitration. We now show that interference with polyubiquitination has similar consequences. Expression of a dominant-negative mutant form of ubiquitin (K48R) in NT-2 and SK-N-MC cells caused decreased cell growth rates and increased oxidative damage (protein carbonyls and lipid peroxidation), nitric oxide production and elevated protein nitration. It also rendered cells highly sensitive to 4-hydroxy-2,3-trans-nonenal, a neurotoxic end-product of lipid peroxidation, hydrogen peroxide and deprivation of growth factors. Overexpression of wild-type ubiquitin did not produce these effects. Our data show that interference with the ubiquitin-proteasome pathway at a different point and by a different mechanism can produce many of the common features of human neurodegenerative diseases, such as increased lipid peroxidation, protein oxidation and protein nitration. We suggest that defects in this pathway at multiple points could produce the common features of neurodegenerative diseases, and that more such defects remain to be discovered.

Control of radiosensitivity of F9 mouse teratocarcinoma cells by regulation of histone H2AX gene expression using a tetracycline turn-off system

The mouse histone H2AX has unique COOH-terminal serine residues that are phosphorylated in response to double-strand DNA breaks introduced by ionizing radiation. This suggests that H2AX acts to maintain genomic stability. We constructed a tetracycline (tet)-directed turn-off vector and integrated it into F9 mouse teratocarcinoma cells by homologous recombination. In homozygously recombined cells, expression of the histone H2AX gene was repressed to 0.02% of the expression observed in wild-type cells by the addition of doxycycline, an analog of tet. Sensitivity of cells with repressed H2AX expression to X-irradiation was increased 1.95x, indicating that DNA repair was impaired by repression of H2AX. When we s.c. injected tet-regulated F9 cells into the flanks of mice, tumor growth was slightly suppressed by X-irradiation in H2AX-repressed tumors, whereas without X-irradiation, tumor growth did not differ by H2AX status. Thus, H2AX might be a potential molecular target for sensitizing cancer cells to radiotherapy to minimize required irradiation doses.

Mitochondria dysfunction of Alzheimer's disease cybrids enhances Abeta toxicity

Alzheimer's disease (AD) brain reveals high rates of oxygen consumption and oxidative stress, altered antioxidant defences, increased oxidized polyunsaturated fatty acids, and elevated transition metal ions. Mitochondrial dysfunction in AD is perhaps relevant to these observations, as such may contribute to neurodegenerative cell death through the formation of reactive oxygen species (ROS) and the release of molecules that initiate programmed cell death pathways. In this study, we analyzed the effects of beta-amyloid peptide (Abeta) on human teratocarcinoma (NT2) cells expressing endogenous mitochondrial DNA (mtDNA), mtDNA from AD subjects (AD cybrids), and mtDNA from age-matched control subjects (control cybrids). In addition to finding reduced cytochrome oxidase activity, elevated ROS, and reduced ATP levels in the AD cybrids, when these cell lines were exposed to Abeta 1-40 we observed excessive mitochondrial membrane potential depolarization, increased cytoplasmic cytochrome c, and elevated caspase-3 activity. When exposed to Abeta, events associated with programmed cell death are activated in AD NT2 cybrids to a greater extent than they are in control cybrids or the native NT2 cell line, suggesting a role for mtDNA-derived mitochondrial dysfunction in AD degeneration.

DNA methylation as an epigenetic regulator of neural 5-lipoxygenase expression: evidence in human NT2 and NT2-N cells

Increased expression of 5-lipoxygenase is associated with various neuropathologies and may be related to epigenetic gene regulation. DNA methylation in promoter regions is typically associated with gene silencing. We found that human NT2 cells, which differentiate into neuron-like NT2-N cells, express 5-lipoxygenase and we investigated the relationship between 5-lipoxygenase expression and the methylation state of the 5-lipoxygenase core promoter. We used the demethylating agent 5-aza-2'-deoxycytidine and the histone deacetylase inhibitor valproate to alter DNA methylation and to induce histone modifications. 5-Lipoxygenase expression and DNA methylation were assayed with RT-PCR and bisulfite genomic sequencing, respectively. Neuronal differentiation of proliferating NT2 precursors decreased 5-lipoxygenase expression. 5-Aza-2'-deoxycytidine increased 5-lipoxygenase mRNA levels only in proliferating cells, whereas valproate increased 5-lipoxygenase mRNA levels in a cell cycle-independent manner. In both precursors and differentiated cells, CpG dinucleotides of the promoter were poorly methylated. In precursors, both 5-aza-2'-deoxycytidine and valproate further reduced the number of methylated CpGs. Moreover, we found evidence for cytosine methylation in CpWpG (W=adenine or thymine) and other asymmetrical sequences; CpWpG methylation was reduced by valproate in NT2-N but not in NT2 cells. This is the first report demonstrating that the dynamics of DNA methylation relates to neural 5-lipoxygenase gene expression.

Transcriptional regulation of the murine brca2 gene by CREB/ATF transcription factors

The brca2 gene encodes a nuclear protein which is mainly involved in DNA repair and, when mutated, is responsible for some of the hereditary breast cancers. However, brca2 expression is also deregulated in sporadic breast tumors. In the mouse brca2 gene we had earlier identified a region of 148bp upstream of the transcription start site sufficient to activate its expression. In the present report, we show that the -92 to -40bp region is essential for the transcription of brca2 in murine mammary cells and that this nucleotide sequence contains one putative CREB/ATF consensus site (cAMP responsive element: CRE). We demonstrated that the mutation of this binding site led to a highly significant reduction of the mouse brca2 transcription, and that CREB, CREM, and/or ATF-1 functionally bound to and regulated this promoter. Therefore, the regulation of the promoter of the mouse brca2 gene is driven by this family of transcription factors.

Retinoic acid causes cell growth arrest and an increase in p27 in F9 wild type but not in F9 retinoic acid receptor β2 knockout cells

We have previously shown that an F9 teratocarcinoma retinoic acid receptor beta(2) (RARbeta(2)) knockout cell line exhibits no growth arrest in response to all-trans-retinoic acid (RA), whereas F9 wild type (Wt), F9 RARalpha(-/-), and F9 RARgamma(-/-) cell lines do growth arrest in response to RA. To examine the role of RARbeta(2) in growth inhibition, we analyzed the cell cycle regulatory proteins affected by RA in F9 Wt and F9 RARbeta(2)(-/-) cells. Flow microfluorimetry analyses revealed that RA treatment of F9 Wt cells greatly increased the percentage of cells in the G1/G0 phase of the cell cycle. In contrast, RA did not alter the cell cycle distribution profile of RARbeta(2)(-/-) cells. In F9 Wt cells, cyclin D1, D3, and cyclin E protein levels decreased, while cyclin D2 and p27 levels increased after RA treatment. Compared to the F9 Wt cells, the F9 RARbeta(2)(-/-) cells exhibited lower levels of cyclins D1, D2, D3, and E in the absence of RA, but did not exhibit further changes in the levels of these cell cycle regulators after RA addition. Since RA significantly increased the level of p27 protein (approximately 24-fold) in F9 Wt as compared to the F9 RARbeta(2)(-/-) cells, we chose to study p27 in greater detail. The p27 mRNA level and the rate of p27 protein synthesis were increased in RA-treated F9 Wt cells, but not in F9 RARbeta(2)(-/-) cells. Moreover, RA increased the half-life of p27 protein in F9 Wt cells. Reduced expression of RARbeta(2) is associated with the process of carcinogenesis and RARbeta(2) can mediate the growth arrest induced by RA in a variety of cancer cells. Using both genetic and molecular approaches, we have identified some of the molecular mechanisms, such as the large elevation of p27, through which RARbeta(2) mediates these growth inhibitory effects of RA in F9 cells.

Expression and distribution of c-kit receptor and its ligand in human CNS germ cell tumors: A useful histological marker for the diagnosis of germinoma

We previously reported the expression of protooncogene c-kit in CNS germ cell tumors and suggested that the soluble form of c-kit (s-kit) may represent a specific clinical marker for germinoma-containing tumors. Here we investigated the expression of stem cell factor (SCF), a specific ligand of c-kit, in CNS germ cell tumor samples from 16 patients, using immunohistochemical methods to assay the expression of c-kit and SCF protein. The immunostaining patterns of c-kit and SCF were almost identical. In all germinoma-containing tumors, c-kit and SCF were diffusely expressed on the surface of germinoma cells; lymphocytes and interstitial cells were negatively stained. In immature teratomas, only some mature components, e.g., cartilage and gland, were immunoreactive for c-kit and SCF. Syncytiotrophoblastic giant cells (STGCs) were negative for both SCF and c-kit, suggesting that germinoma cells primarily coexpress SCF and c-kit. The coexpression of c-kit and SCF may be an important immunohistochemical marker for the diagnosis of CNS germinoma, and the SCF/c-kit pathway may be an alternative molecular target for the treatment of human CNS germinomas.

A blockade in Wnt signaling is activated following the differentiation of F9 teratocarcinoma cells

Aberrant activation of the Wnt signaling pathway is a common event in human tumor progression. Wnt signaling has also been implicated in maintaining a variety of adult and embryonic stem cells by imposing a restraint to differentiation. To understand the effect of Wnt signaling on the differentiation of epithelial cells, we used mouse teratocarcinoma F9 cells as a model. The F9 cells can be differentiated into visceral endoderm (VE) resembling absorptive columnar epithelial cells. We performed comparative gene expression analysis on retinoic acid-differentiated and undifferentiated F9 cells and confirmed that markers of VE and intestinal epithelium were induced upon differentiation. The induction of these markers by retinoic acid was reduced in the presence of Wnt, although Wnt alone did not change their expression. This suggests that Wnt signaling inhibited the differentiation of F9 cells by altering gene expression. This inhibition was also reflected in the morphology of the F9 cells as their apical-basal polarity was disrupted by inclusion of Wnt during differentiation. These results support a model in which Wnt modulates the expression of genes required for normal terminal differentiation of the stem cells. However, it follows that progenitor cells must escape from Wnt signaling to attain the differentiated state. Accordingly, we found that differentiated F9 cells no longer responded to Wnt and that a blockade in Wnt signaling occurred upstream of Axin. Consistent with this, Wnt negative regulators, such as Dickkopf-1 and Disabled-2, were induced upon the differentiation of F9 cells. We propose that a similar system to produce Wnt inhibitors regulates homeostasis of certain stem cell compartments in vivo.

Overexpression of PREP-1 in F9 teratocarcinoma cells leads to a functionally relevant increase of PBX-2 by preventing its degradation

To bind DNA and to be retained in the nucleus, PBX proteins must form heterodimeric complexes with members of the MEINOX family. Therefore the balance between PBX and MEINOX must be an important regulatory feature. We show that overexpression of PREP-1 influences the level of PBX-2 protein maintaining the PREP-1-PBX balance. This effect has important functional consequences. F9 teratocarcinoma cells stably transfected with PREP-1 had an increased DNA binding activity to a PREP-PBX-responsive element. Because PREP-1 binds DNA efficiently only when dimerized to PBX, the increased DNA binding activity suggests that the level of PBX might also have increased. Indeed PREP-1-overexpressing cells had a higher level of PBX-2 and PBX-1b proteins. PBX-2 increase did not depend on increased mRNA level or a higher rate of translation but rather because of a protein stabilization process. Indeed, PBX-2 level drastically decreased after 3 h of cycloheximide treatment in control but not in PREP-1-overexpressing cells and the proteasome inhibitor MG132 prevented PBX-2 decay in control cells. Hence, dimerization with PREP-1 appears to decrease proteasomal degradation of PBX-2. Retinoic acid induces differentiation of F9 teratocarcinoma cells with a cascade synthesis of HOX proteins. In PREP-1-overexpressing cells, HOXb1 induction was more sustained (3 days versus 1 day) and the induced level of MEIS-1b, another TALE (three amino acid loop extension) protein involved in embryonal development, was higher. Thus an increase in PREP-1 leads to changes in the fate-determining HOXb1 and has therefore important functional consequences.

Analysis of plausible downstream target genes of Hoxc8 in F9 teratocarcinoma cells. Putative downstream target genes of Hoxc8

Although Hox genes are known to mediate developmental decisions involved in pattern formation during embryogenesis, it is still not well understood what Hox regulates. In order to analyze Hoxc8 downstream target genes, a stable cell line overexpressing Hoxc8 was established using F9 murine teratocarcinoma cells, proteom samples were analyzed by 2-DE, and compared with controls. The protein spots having differences more than 4 fold in intensity were selected, analyzed by MALDI-TOF, and grouped in terms of putative function; cytoskeleton and motility (vimentin, gamma-actin, tropomyosin, and tubulin beta-5 chain); folding, modification and degradation of protein (GRP78, proteasome subunit alpha type 5, 26S proteasome regulatory subunit p27 protein, and PDIR); metabolism (ATP synthase beta subunit, Pgam1, and CAII); transcription/translation factors and general nucleic acid binding proteins (RbAp46, PCNA, eEF-1-beta, and nucleophosmin). Although it may not be significant, 50% of the genes were located on chromosomes 2 and 3, suggesting the possibility of a non-random distribution of Hox downstream genes. Almost 50% of the genes analyzed showed some relation with Hox protein directly or indirectly; i.e., tubulin beta 5, EF-1 beta and PCNA have been reported to contain putative Hox binding regulatory sites and genes like vimentin, pgam1 and nucleophosmin to be regulated by RA, a potent modulator of Hox expression. These results altogether imply that proteom analysis could be a possible tool for the analysis of the potent Hox realizator genes, which provides a new insight into the function of Hox on pattern formation during embryogenesis.

Turning teratocarcinoma cells into neurons: rapid differentiation of NT-2 cells in floating spheres

Cells from the human teratocarcinoma line NTera-2 can be induced to terminally differentiate into postmitotic neurons when treated with retinoic acid. However, this differentiation process is rather time consuming as it takes between 42 and 54 days. Here, we propose a modified differentiation protocol which reduces the time needed for differentiation considerably without compromising the quantity of the neurons obtained. The introduction of a proliferation step as free floating cell spheres cuts the total time needed to obtain high yields of purified NT-2 neurons to about 24-28 days. The cells obtained show neuronal morphology and migrate to form ganglion-like cell conglomerates. Differentiated cells express neuronal polarity markers such as the cytoskeleton associated proteins MAP2 and Tau. Moreover, the generation of neurons in sphere cultures induced immunoreactivity to the ELAV-like neuronal RNA-binding proteins HuC/D, which have been implicated in mechanisms of nerve cell differentiation.

Degenerate suppression PCR identifies the beta2-adrenergic receptor as upregulated by neuronal differentiation

Communication between cells is necessary for the functioning of a multicellular organism. Cells process a large amount of information through G-protein-coupled receptors, and activation of this receptor class has been implicated in neuronal differentiation. In this study, we used a method based on PCR with degenerated primers to identify G-protein-coupled receptors regulated by retinoic acid-induced differentiation of the human teratocarcinoma cell line NTera-2/D1. Subtracted cDNA libraries and control cDNA served as templates in half-sided PCR with a forward degenerate primer based on a conserved sequence from human serotonergic, adrenergic, and dopaminergic receptors and reverse primers on adaptors with long terminal repeats commonly employed in subtractive suppression hybridization. We developed conditions to amplify G-protein-coupled receptors from adaptor-ligated cDNA and found the beta2-adrenergic receptor to be upregulated fourfold. This seems to be physiologically relevant, as it could also be shown in rat primary cortical cultures maturing in vitro. The method presented here makes use of the otherwise unused control cDNA from subtractive suppression hybridization experiments and could be easily adapted to other gene families.

Transient modulation of cytoplasmic and nuclear retinoid receptors expression in differentiating human teratocarcinoma NT2 cells

Human embryonal carcinoma Ntera2/D1 (NT2) cells treated with retinoic acid (RA) differentiate into several cell types including post-mitotic neurons. In this study we asked if RA-induced differentiation alters the expression of RA and retinol (ROL) binding proteins. The regulation of the intracellular carrier proteins for ROL and RA, cellular retinol binding protein I (CRBP-I), and cellular retinoic acid binding protein I and II (CRABP-I, CRABP-II) were studied along with the nuclear RA receptors RARalpha, RARbeta and RARgamma2. PCR analysis of total mRNA from RA-treated cells showed a biphasic early induction of CRBP-I, CRABP-II, and RARgamma2 genes. The immediate early gene Krox-24, a zinc finger transcription factor which is up-regulated during neuronal differentiation, was also induced, but after 1 week of treatment. The induction of CRBP-I protein synthesis in differentiating NT2 cells was confirmed by western blotting and immunofluorescence experiments. Conversely, the synthetic retinoid N-(4-hydroxyphenyl)retinamide, which induces cell death, but not differentiation in different tumour cell types, did not produce the same modulation on gene expression in NT2 cells. These data suggest that the RA-specific induction of CRBP-I and CRABP-II could be an early event in the process leading to neuronal differentiation of NT2 cells.

Sec61alpha synthesis is enhanced during translocation of nascent chains of collagen type IV in F9 teratocarcinoma cells after retinoic acid treatment

Nascent procollagen peptides and other secretory proteins are transported across the endoplasmic reticulum (ER) membrane through a protein-conducting channel called translocon. Sec61alpha, a multispanning membrane translocon protein, has been implicated as being essential for translocation of polypeptide chains into the cisterns of the ER. Sec61alpha forms a protein complex with collagen and Hsp47, an ER-resident heat shock protein that binds specifically to collagen. However, it is not known whether Sec61alpha is ubiquitously produced in collagen-producing F9 teratocarcinoma cells or under heat shock treatment. Furthermore, the production and utilization of Sec61alpha may depend on the stage of cell differentiation. Cultured F9 teratocarcinoma cells are capable of differentiation in response to low concentrations of retinoic acid. This differentiation results in loss of tumorigenicity. Mouse F9 cells were grown in culture medium at 37 degrees C and 43 degrees C (heat shock treatment) treated or not with retinoic acid, and labeled in certain instances with 35S-methionine. Membrane-bound polysomes of procollagen IV were then isolated. Immunoprecipitation and Western blot analysis were performed using polyclonal antibodies against collagen IV, Hsp47 and Sec61alpha. Under retinoic acid-untreated conditions, F9 cells produced undetectable amounts of Sec61alpha. Sec61alpha, Hsp47 and type IV collagen levels were increased after retinoic acid treatment. Heat shock treatment did not alter Sec61alpha levels, suggesting that Sec61alpha production is probably not affected by heat shock. These data indicate that the enhanced production of Sec61alpha in retinoic acid-induced F9 teratocarcinoma cells parallels the increased synthesis of Hsp47 and collagen type IV.