The CDK inhibitor p27 enhances neural differentiation in pluripotent NTERA2 human EC cells, but does not permit differentiation of 2102Ep nullipotent human EC cells

The Subtype Identity of Testicular Cancer Cells Determines Their Immunostimulatory Activity in a Coculture Model

Testicular germ cell cancer (TGCC) is subdivided into several subtypes. While seminomatous germ cell tumors (SGCT) are characterized by an intensive infiltration of immune cells which constitute a pro-inflammatory tumor micromilieu (TME), immune cells in non-seminomatous germ cell tumors (NSGCT) are differently composed and less abundant. Previously, we have shown that the seminomatous cell line TCam-2 promotes T cell and monocyte activation in a coculture model, resulting in mutual interactions between both cell types. Here we set out to compare this feature of TCam-2 cells with the non-seminomatous cell line NTERA-2. Peripheral blood T cells or monocytes cocultured with NTERA-2 cells failed to secrete relevant amounts of pro-inflammatory cytokines, and significantly downregulated the expression of genes encoding activation markers and effector molecules. In contrast, immune cells cocultured with TCam-2 cells produced IL-2, IL-6 and TNFα, and strongly upregulated the expression of multiple pro-inflammatory genes. Furthermore, the expression of genes involved in proliferation, stemness and subtype specification remained unaltered in NTERA-2 cells during coculture with T cells or monocytes, indicating the absence of mutual interactions. Collectively, our findings uncover fundamental differences between SGCT and NSGCT in their capability to generate a pro-inflammatory TME, which possibly impacts the clinical features and prognosis of both TGCC subtypes.

The cyclin-dependent kinase inhibitor p27Kip1 interacts with the aryl hydrocarbon receptor and negatively regulates its transcriptional activity

p27^Kip1 functions to coordinate cell cycle progression through the inhibition of cyclin-dependent kinase (CDK) complexes. p27^Kip1 also exerts distinct activities beyond CDK-inhibition, including functioning as a transcriptional regulator. The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor with diverse biological roles. The regulatory inputs that control AhR-mediated transcriptional responses are an active area of investigation. AhR was previously established as a direct regulator of p27^Kip1 transcription. Here, we report the physical interaction of AhR and p27^Kip1 and show that p27^Kip1 expression negatively regulates AhR-mediated transcription. p27^Kip1 knockout cells display increased AhR nuclear localisation and significantly higher expression of AhR target genes. This work thus identifies new regulatory cross-talk between p27^Kip1 and AhR.

Investigation the effects of vitreous humor on proliferation and dedifferentiation of differentiated NTERA2 cells

Mammals have a limited capacity to regenerate their tissues and organs. One of the mechanisms associated with natural regeneration is dedifferentiation. Several small molecules such as vitamin C and growth factors could improve reprogramming efficiency. In this study, the NTERA2-D1 (NT2) cells were induced towards differentiation (NT2-RA) with 10-5 M retinoic acid (RA) for three days and then subjected to various amounts of vitreous humor (VH). Results show that the growth rate of these cells was reduced, while this rate was partly restored upon treatment with VH (NT2-RA-VH). Cell cycle analysis with PI method also showed that the numbers of cells at the S phase of the cell cycle in these cells were increased. The levels of SSEA3 and TRA-1-81 antigens in NT2-RA were dropped but they increased in NT2- RA-VH to a level similar to the NT2 cells. The level of SSEA1 had an opposite pattern. Expression of OCT4 gene dropped after RA treatment, but it was recovered in NT2-RA-VH cells. In conclusion, we suggest VH as a potent mixture for improving the cellular reprogramming leading to dedifferentiation.

SSEA3 and Sialyl Lewis a Glycan Expression Is Controlled by B3GALT5 LTR through Lamin A-NFYA and SIRT1-STAT3 Signaling in Human ES Cells

B3GALT5 is involved in the synthesis of embryonic stem (ES) cell marker glycan, stage-specific embryonic antigen-3 (SSEA3). This gene has three native promoters and an integrated retroviral long terminal repeat (LTR) promoter. We found that B3GALT5-LTR is expressed at high levels in human ES cells. B3GALT5-LTR is also involved in the synthesis of the cancer-associated glycan, sialyl Lewis a. Sialyl Lewis a is expressed in ES cells and its expression decreases upon differentiation. Retinoic acid induced differentiation of ES cells, decreased the short form of NFYA (NFYAs), increased phosphorylation of STAT3, and decreased B3GALT5-LTR expression. NFYAs activated, and constitutively-active STAT3 (STAT3C) repressed B3GALT5-LTR promoter. The NFYAs and STAT3C effects were eliminated when their binding sites were deleted. Retinoic acid decreased the binding of NFYA to B3GALT5-LTR promoter and increased phospho-STAT3 binding. Lamin A repressed NFYAs and SSEA3 expression. SSEA3 repression mediated by a SIRT1 inhibitor was reversed by a STAT3 inhibitor. Repression of SSEA3 and sialyl Lewis a synthesis mediated by retinoic acid was partially reversed by lamin A short interfering RNA (siRNA) and a STAT3 inhibitor. In conclusion, B3GALT5-LTR is regulated by lamin A-NFYA and SIRT1-STAT3 signaling that regulates SSEA3 and sialyl Lewis a synthesis in ES cells, and sialyl Lewis a is also a ES cell marker.

Dedifferentiation Effects of Rabbit Regenerating Tissue on Partially Differentiated Cells

Cell Stemness can be achieved by various reprogramming techniques namely, somatic cell nuclear transfer, cell fusion, cell extracts, and introduction of transcription factors from which induced pluripotent stem cells (iPSCs) are obtained. iPSCs are valuable cell sources for drug screening and human disease modeling. Alternatives to virus-based introduction of transcription factors include application of DNA-free methods and introduction of chemically defined culturing conditions. However, the possibility of tumor development is still a hurdle. By taking advantage of NTERA-2 cells, a human embryonal carcinoma cell line, we obtained partially differentiated cells and examined the dedifferentiation capacity of regenerative tissue from rabbit ears. Results indicated that treatment of partially differentiated NTERA-2 cells with the regenerating tissue-conditioned medium (CM) induced expression of key pluripotency markers as examined by real-time polymerase chain reaction, flow cytometry, and immunocytochemistry techniques. In this study, it is reported for the first time that the CM obtained from rabbit regenerating tissue contains dedifferentiation factors, taking cells back to the pluripotency. This system could be a simple and efficient way to reprogram the differentiated cells and generate iPSCs for clinical applications as this system is not accompanied by any viral vector, and reprograms the cells within 10 days of treatment. The results may convince the genomic experts to study the unknown signaling pathways involved in the dedifferentiation by regenerating tissue-CM to authenticate the reprogramming model.

p27(Kip1) signaling: Transcriptional and post-translational regulation

p27(Kip1) is an inhibitor of a broad spectrum of cyclin-dependent kinases (CDKs), and the loss of a single p27(Kip1) allele is thereby sufficient to increase tumor incidence via CDK-mediated cell cycle entry. As such, down-regulation of p27(Kip1) protein levels, in particular nuclear expressed p27(Kip1), is implicated in both disease progression and poor prognosis in a variety of cancers. p27(Kip1) expression is positively regulated by the transcription factor MENIN, and inhibited by oncogenic transcription factors MYC and PIM. However, regulation of p27(Kip1) protein expression and function is predominantly through post-translational modifications that alter both the cellular localization and the extent of E3 ubiquitin ligase-mediated degradation. Phosphorylation of p27(Kip1) at Thr(187) and Ser(10) is a prerequisite for its degradation via the E3 ubiquitin ligases SKP2 (nuclear) and KPC (cytoplasmic), respectively. Additionally, Ser(10) phosphorylated p27(Kip1) is predominantly localized in the cytoplasm due to the nuclear export protein CRM1. Another E3 ubiquitin ligase, PIRH2, degrades p27(Kip1) in both the cytoplasm and nucleus independent of phosphorylation state. As such, inhibition of cell cycle entry and progression in a variety of cancers may be achieved with therapies designed to correct p27(Kip1) localization and/or block its degradation.

BMP Inhibition in Seminomas Initiates Acquisition of Pluripotency via NODAL Signaling Resulting in Reprogramming to an Embryonal Carcinoma

Type II germ cell cancers (GCC) can be subdivided into seminomas and non-seminomas. Seminomas are similar to carcinoma in situ (CIS) cells, the common precursor of type II GCCs, with regard to epigenetics and expression, while embryonal carcinomas (EC) are totipotent and differentiate into teratomas, yolk-sac tumors and choriocarcinomas. GCCs can present as seminomas with a non-seminoma component, raising the question if a CIS gives rise to seminomas and ECs at the same time or whether seminomas can be reprogrammed to ECs. In this study, we utilized the seminoma cell line TCam-2 that acquires an EC-like status after xenografting into the murine flank as a model for a seminoma to EC transition and screened for factors initiating and driving this process. Analysis of expression and DNA methylation dynamics during transition of TCam-2 revealed that many pluripotency- and reprogramming-associated genes were upregulated while seminoma-markers were downregulated. Changes in expression level of 53 genes inversely correlated to changes in DNA methylation. Interestingly, after xenotransplantation 6 genes (GDF3, NODAL, DNMT3B, DPPA3, GAL, AK3L1) were rapidly induced, followed by demethylation of their genomic loci, suggesting that these 6 genes are poised for expression driving the reprogramming. We demonstrate that inhibition of BMP signaling is the initial event in reprogramming, resulting in activation of the pluripotency-associated genes and NODAL signaling. We propose that reprogramming of seminomas to ECs is a multi-step process. Initially, the microenvironment causes inhibition of BMP signaling, leading to induction of NODAL signaling. During a maturation phase, a fast acting NODAL loop stimulates its own activity and temporarily inhibits BMP signaling. During the stabilization phase, a slow acting NODAL loop, involving WNTs re-establishes BMP signaling and the pluripotency circuitry. In parallel, DNMT3B-driven de novo methylation silences seminoma-associated genes and epigenetically fixes the EC state.

Differentiation-defective phenotypes revealed by large-scale analyses of human pluripotent stem cells

We examined the gene expression and DNA methylation of 49 human induced pluripotent stem cells (hiPSCs) and 10 human embryonic stem cells and found overlapped variations in gene expression and DNA methylation in the two types of human pluripotent stem cell lines. Comparisons of the in vitro neural differentiation of 40 hiPSCs and 10 human embryonic stem cells showed that seven hiPSC clones retained a significant number of undifferentiated cells even after neural differentiation culture and formed teratoma when transplanted into mouse brains. These differentiation-defective hiPSC clones were marked by higher expression levels of several genes, including those expressed from long terminal repeats of specific human endogenous retroviruses. These data demonstrated a subset of hiPSC lines that have aberrant gene expression and defective potential in neural differentiation, which need to be identified and eliminated before applications in regenerative medicine.

Qualitative modeling identifies IL-11 as a novel regulator in maintaining self-renewal in human pluripotent stem cells

Pluripotency in human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) is regulated by three transcription factors—OCT3/4, SOX2, and NANOG. To fully exploit the therapeutic potential of these cells it is essential to have a good mechanistic understanding of the maintenance of self-renewal and pluripotency. In this study, we demonstrate a powerful systems biology approach in which we first expand literature-based network encompassing the core regulators of pluripotency by assessing the behavior of genes targeted by perturbation experiments. We focused our attention on highly regulated genes encoding cell surface and secreted proteins as these can be more easily manipulated by the use of inhibitors or recombinant proteins. Qualitative modeling based on combining boolean networks and in silico perturbation experiments were employed to identify novel pluripotency-regulating genes. We validated Interleukin-11 (IL-11) and demonstrate that this cytokine is a novel pluripotency-associated factor capable of supporting self-renewal in the absence of exogenously added bFGF in culture. To date, the various protocols for hESCs maintenance require supplementation with bFGF to activate the Activin/Nodal branch of the TGFβ signaling pathway. Additional evidence supporting our findings is that IL-11 belongs to the same protein family as LIF, which is known to be necessary for maintaining pluripotency in mouse but not in human ESCs. These cytokines operate through the same gp130 receptor which interacts with Janus kinases. Our finding might explain why mESCs are in a more naïve cell state compared to hESCs and how to convert primed hESCs back to the naïve state. Taken together, our integrative modeling approach has identified novel genes as putative candidates to be incorporated into the expansion of the current gene regulatory network responsible for inducing and maintaining pluripotency.

p27(Kip1) directly represses Sox2 during embryonic stem cell differentiation

The mechanisms responsible for the transcriptional silencing of pluripotency genes in differentiated cells are poorly understood. We have observed that cells lacking the tumor suppressor p27 can be reprogrammed into induced pluripotent stem cells (iPSCs) in the absence of ectopic Sox2. Interestingly, cells and tissues from p27 null mice, including brain, lung, and retina, present an elevated basal expression of Sox2, suggesting that p27 contributes to the repression of Sox2. Furthermore, p27 null iPSCs fail to fully repress Sox2 upon differentiation. Mechanistically, we have found that upon differentiation p27 associates to the SRR2 enhancer of the Sox2 gene together with a p130-E2F4-SIN3A repressive complex. Finally, Sox2 haploinsufficiency genetically rescues some of the phenotypes characteristic of p27 null mice, including gigantism, pituitary hyperplasia, pituitary tumors, and retinal defects. Collectively, these results demonstrate an unprecedented connection between p27 and Sox2 relevant for reprogramming and cancer and for understanding human pathologies associated with p27 germline mutations.

ADAM23 knockdown promotes neuronal differentiation of P19 embryonal carcinoma cells by up-regulating P27KIP1 expression

ADAM23 (a disintegrin and metalloprotease 23), a member of brain MDC (macrophage-derived chemokine) family, is important for the development of CNS (central nervous system). P19 mouse embryonal carcinoma cells can differentiate into neurons when cultured in aggregates and induced with RA (retinoic acid). We have found that under conditions without RA induction, knocking down ADAM23 with RNAi (RNA interference) promoted neuronal differentiation, and similarly recombinant GST (glutathione transferase)-ADAM23-DIS protein inhibited neuronal differentiation of P19/ADAM23KD (P19/ADAM23-knockdown) cells. In P19/ADAM23KD, there were more cells arrested in G1 phase than normal P19 cells, due to the up-regulation of P57KIP2 and P27KIP1 expression. P27KIP1 was up-regulated during the differentiation process of both P19/ADAM23KD cells without RA induction, and P19 cells with RA induction. Transient overexpression of P27KIP1 in P19 cells also promoted neuronal differentiation of P19 cells. The findings indicate that ADAM23 suppresses neuronal differentiation through its disintegrin domain, and Adam23 KD up-regulates P27KIP1 in P19/ADAM23KD cells, one reason that P19/ADAM23KD cells can differentiate into neurons without RA induction.

Transcription factors Sp1 and p73 control the expression of the proapoptotic protein NOXA in the response of testicular embryonal carcinoma cells to cisplatin

Testicular germ cell tumors (TGCTs) are highly responsive to and curable by cisplatin-based chemotherapy even in advanced stages. We have studied the molecular mechanisms involved in the induction of apoptosis in response to cisplatin, and found that proapoptotic Noxa is transcriptionally up-regulated following cisplatin exposure, even in the absence of p53, in NTERA2 cisplatin-sensitive cells but not in 1411HP-resistant cells. Blockade of Noxa reduced the apoptotic response of embryonal carcinoma (EC) NTERA2 cells to cisplatin. A detailed analysis of the Noxa promoter revealed that p73 and Sp1-like factors, Sp1 and KLF6, played key roles in the transcriptional control of this gene. Overexpression of TAp73 induced Noxa whereas the dominant negative isoform ΔNp73, reduced the levels of Noxa after cisplatin exposure in NTERA2 and 2102EP. Interestingly, down-regulation of Sp1 increased Noxa expression in response to cisplatin. However, blockade of KLF6 decreased cisplatin-induced up-regulation of Noxa in EC cell lines. In addition, tissue microarray analyses of TGCTs revealed that expression of Noxa correlates with good clinical prognosis in patients with embryonal carcinoma. Thus, our data show the transcriptional network that regulates Noxa in EC cells, which is key for their apoptotic response to cisplatin-based chemotherapy, and propose Noxa as a predictive factor of therapeutic response.

Bcl2 enhances induced hematopoietic differentiation of murine embryonic stem cells

Bcl2 is a potent antiapoptotic gene that can increase resistance of adult bone marrow hematopoietic progenitor cells to lethal irradiation, and thereby preserve their ability to differentiate. However, the effect of Bcl2 on murine embryonic stem (ES) cells induced to undergo hematopoietic differentiation in the absence of a toxic stress is not known. To test this, murine CCE-ES cells that can be induced to undergo hematopoietic differentiation in a two-step process that results in upregulation of Bcl2 were used. Upregulation of Bcl2 precedes formation of hematopoietic embryoid bodies (EB) and their further differentiation into hematopoietic colony-forming units, when plated as single cells in methylcellulose. ES cells stably expressing a Bcl2 siRNA plasmid to "knock-down" endogenous expression or cells expressing wild-type (WT) Bcl2 or phosphomimetic Bcl2 mutants were examined. ES cells expressing the Bcl2 siRNA or those expressing a dominant-negative, nonphosphorylatable Bcl2 display a strikingly reduced capacity to form hematopoietic EBs and colony-forming units compared to cells expressing WT or phosphomimetic Bcl2 that demonstrate an increased capacity. Bcl2's effect on induced-hematopoietic differentiation of ES cells does not result from either decreased apoptosis or a reduced number of cells. Rather, Bcl2-enhances hematopoietic differentiation of ES cells by upregulating p27, which results in retardation of the cell cycle at G1/G 0. Thus siRNA silencing of p27 reverts Bcl2's enhancement phenotype in a manner similar to that of Bcl2 "silencing" or expression of a nonphosphorylable Bcl2. In addition to Bcl2's well-described antiapoptotic and cell-cycle retardant effect on somatic cells, Bcl2 may also function to enhance induced hematopoietic cell differentiation of murine ES cells. These findings may have potential relevance for expanding hematopoietic stem/progenitor cell numbers from an ES cell source for stem cell transplantation applications.

Constitutive gene expression predisposes morphogen-mediated cell fate responses of NT2/D1 and 27X-1 human embryonal carcinoma cells

Human embryonal carcinoma (EC) cell lines exhibit considerable heterogeneity in their levels of pluripotency. Thus, NT2/D1 cells differentiate into neural lineages upon exposure to all-trans retinoic acid (ATRA) and non-neural epithelial lineages upon exposure to bone morphogenetic protein-2 (BMP-2). In contrast, 27X-1 cells differentiate into extra-embryonic endodermal (ExE) cells upon treatment with either morphogen. To understand the molecular basis for the differential responses of the two cell lines, we performed gene expression profiling at the undifferentiated EC cell line state to identify constitutive differences in gene expression. NT2/D1 cells preferentially expressed transcripts associated with neurectodermal development, whereas 27X-1 cells expressed high levels of transcripts associated with mesendodermal characteristics. We then determined temporal expression profiles of 27X-1 cells during ExE differentiation upon treatment with ATRA and BMP-2 and compared the data with changes in gene expression observed during BMP-2- and ATRA-induced differentiation of NT2/D1 cells. ATRA and BMP-2 induced distinct sets of transcription factors and phenotypic markers in the two EC cell lines, underlying distinct lineage choices. Although 27X-1 differentiation yielded comprehensive gene expression profiles of parietal endodermal lineages, we were able to use the combined analysis of 27X-1 data with data derived from yolk sac tumors for the identification of transcripts associated with visceral endoderm formation. Our results demonstrate constitutive differences in the levels of pluripotency between NT2/D1 and 27X-1 cells that correlate with lineage potential. This study also demonstrates that EC cells can serve as robust models to investigate early lineage choices during both embryonic and extra-embryonic human development.

RNA interference–mediated cyclooxygenase-2 inhibition prevents prostate cancer cell growth and induces differentiation: modulation of neuronal protein synaptophysin, cyclin D1, and androgen receptor

Cyclooxygenase-2 (COX-2) plays an important role in tumor development and progression. Inconsistent reports on the expression of COX-2 in early versus advanced prostate cancer raised the question on whether COX-2 inhibition affects prostate carcinogenesis. Evidence from recent studies indicates that prostate carcinogenesis depends on the altered expression of several factors including androgen receptor signaling, proinflammatory, and cell cycle regulatory genes. Very often, the outcome of androgen ablation treatment is not effective and, eventually, the cancer becomes androgen independent followed by activation of several survival genes and transcription factors. Most importantly, the extent of the influence of COX-2 on the regulation of the androgen receptor, cyclin D1, and other factors involved in cancer growth is not known. Using RNA interference-mediated COX-2 inhibition in metastatic prostate cancer cells, this study has shown that the silencing of COX-2 at the mRNA level can induce cell growth arrest and down-regulate androgen receptor and cyclin D1. We have further shown for the first time that COX-2 knockdown prostate cancer cells depict morphologic changes associated with enhanced expression of differentiation markers, particularly the neuronal protein synaptophysin along with activation of p21((Waf1/Cip1)) and p27((Kip1)). In summary, our findings determined the role of COX-2 in prostate carcinogenesis and its control on COX-2-independent targets. Second, abrogation of COX-2 and activation of synaptophysin provide evidence for the control of COX-2 on the expression of a neuronal protein. Finally, our findings provide evidence of COX-2-independent targets promoting cell growth arrest and differentiation in cells lacking COX-2 expression at the mRNA level.