Regulation of the Nanog gene by both positive and negative cis-regulatory elements in embryonal carcinoma cells and embryonic stem cells

Mechanisms Regulating Stemness and Differentiation in Embryonal Carcinoma Cells

Just over ten years have passed since the seminal Takahashi-Yamanaka paper, and while most attention nowadays is on induced, embryonic, and cancer stem cells, much of the pioneering work arose from studies with embryonal carcinoma cells (ECCs) derived from teratocarcinomas. This original work was broad in scope, but eventually led the way for us to focus on the components involved in the gene regulation of stemness and differentiation. As the name implies, ECCs are malignant in nature, yet maintain the ability to differentiate into the 3 germ layers and extraembryonic tissues, as well as behave normally when reintroduced into a healthy blastocyst. Retinoic acid signaling has been thoroughly interrogated in ECCs, especially in the F9 and P19 murine cell models, and while we have touched on this aspect, this review purposely highlights how some key transcription factors regulate pluripotency and cell stemness prior to this signaling. Another major focus is on the epigenetic regulation of ECCs and stem cells, and, towards that end, this review closes on what we see as a new frontier in combating aging and human disease, namely, how cellular metabolism shapes the epigenetic landscape and hence the pluripotency of all stem cells.

AP-1 Gene Expression Levels May Be Correlated with Changes in Gene Expression of Some Stemness Factors in Colon Carcinomas

The AP-1 transcription factor is a heterodimer protein that regulates gene expression in response to a variety of extrinsic stimuli through signal transduction. It is involved in processes including differentiation, proliferation, and apoptosis. Among the genes it regulates are transcription factors that contribute to the stemness phenotype. Cancer stem cells have the ability to self-renew and initiate differentiation into heterogenic cancer cells, which may cause metastasis and relapses. In the present study, we evaluated the effect of AP-1 complexes, as well as the C-FOS and C-JUN genes, in relation to NANOG, OCT3/4, and SOX2 transcription factors. All assays were undertaken with colon cancer stem cells. Knockdown experiments with siRNA were performed for each individual gene as well as their combination. Changes in gene expression were calculated with quantitative polymerase chain reaction experiments, while the effect on cell cycle distribution and apoptosis was studied by flow cytometry. The results differed depending on the percentage of repression, as well as the gene that was suppressed. In all cases, the number of apoptotic cells was increased. These findings indicate that AP-1 may have a crucial role in the maintenance of cancer stem cells.

Identification and characterization of a nanog homolog in Japanese flounder (Paralichthys olivaceus)

The homeodomain-containing transcription factor nanog plays a key role in maintaining the pluripotency and self-renewal of embryonic stem cells in mammals. Stem cells offered as a significant and effective tool for generation of transgenic animals and preservation of genetic resources. The molecular genetic organization and expression of nanog gene in marine fish have not been reported yet. In this study, we isolated and characterized the flounder nanog gene as a first step towards understanding the mechanism of the plurpotency of fish stem cells and develop a potential molecular marker to identify the stem cells in vivo and in vitro. Phylogenetic, gene structure and chromosome synteny analysis provided the evidence that Po-nanog is homologous to the mammalian nanog gene. Protein sequence comparison showed that flounder Nanog shared low similarity with other vertebrate orthologs except for a conserved homeodomain. Quantitative RT-PCR analysis showed that flounder nanog was maternally expressed, and the transcripts were present from the one-cell stage to the neurula stage with the peaking at blastula stage. Whole mount in situ hybridization analyses demonstrated that the transcripts were present in all blastomeres of the early embryo. Tissue distribution analysis indicated that nanog was detectable only in gonads. Further, the expression was significantly high in ovary than in testis. In situ hybridization revealed that the transcripts were located in the cytoplasm of the oogonia and oocytes in ovary, only in the spermatogonia but no spermatocytes or spermatids in testis. The promoter region was also analyzed to have several basal core promoter elements and transcription factor binding sites. All these results suggest that Po-Nanog may have a conservative function between teleosts and mammals.

Zfp281 mediates Nanog autorepression through recruitment of the NuRD complex and inhibits somatic cell reprogramming

The homeodomain transcription factor Nanog plays an important role in embryonic stem cell (ESC) self-renewal and is essential for acquiring ground-state pluripotency during reprogramming. Understanding how Nanog is transcriptionally regulated is important for further dissecting mechanisms of ESC pluripotency and somatic cell reprogramming. Here, we report that Nanog is subjected to a negative autoregulatory mechanism, i.e., autorepression, in ESCs, and that such autorepression requires the coordinated action of the Nanog partner and transcriptional repressor Zfp281. Mechanistically, Zfp281 recruits the NuRD repressor complex onto the Nanog locus and maintains its integrity to mediate Nanog autorepression and, functionally, Zfp281-mediated Nanog autorepression presents a roadblock to efficient somatic cell reprogramming. Our results identify a unique transcriptional regulatory mode of Nanog gene expression and shed light into the mechanistic understanding of Nanog function in pluripotency and reprogramming.

RNA interference-mediated silencing of NANOG reduces cell proliferation and induces G0/G1 cell cycle arrest in breast cancer cells

Since the processes of normal embryogenesis and neoplasia share many of similar pathways, tumor development has been interpreted as an abnormal form of organogenesis. NANOG is a homeodomain-containing transcription factor that functions to maintain self-renewal and proliferation of embryonic stem cells (ESCs). Aberrant expression of NANOG has been observed in many types of human malignancies. However, its potential implication in tumorigenesis has not been fully clarified. In this study, we have employed small interference RNA (RNAi) technology to silence endogenous NANOG expression in breast cancer cells and successfully selected three independent clones with stably inhibited NANOG expression of MCF-7 cells. Functional analysis revealed that down-regulation of NANOG reduced cell proliferation, colony formation and migration ability of MCF-7 cells. Consistently, proliferation of breast cancer MDA-MB-231 cells was also significantly inhibited after the knockdown of NANOG expression. Interestingly, we found that the expression levels of cyclinD1 and c-myc were markedly down-regulated and the cell cycle were blocked at the G0/G1 phases after the knockdown of NANOG, while the expression of cyclinE and signal transducers and activators of transcription3 (STAT3) remained unaffected. In addition, the expression of NANOG and cyclinD1 can be rescued after the transfection of pcDNA3.1 (-)-NANOG expression vector into the three clones. Finally, our chromatin immunoprecipitation (ChIP) experiment showed that NANOG protein can bind to the promoter region of cyclinD1 and regulate cells cycle. Taken together, our findings may not only establish a molecular basis for the role of NANOG in modulating cell cycle progression of breast cancer cells but also suggest a potential target for the treatment of at least some subtypes of breast cancer.

Expression of the stem cell marker, Nanog, in human endometrial adenocarcinoma

The embryonic stem cell self-renewal gene, Nanog, has been shown to be expressed in several tumor types and to regulate tumor development. The aim of this study was to carry out a detailed analysis of Nanog expression in human endometrial adenocarcinoma (EAC). Immunohistochemical analysis and reverse transcription-polymerase chain reaction were used to characterize Nanog, Sox2, and Oct4 expression in tissue arrays containing EAC, benign endometrium samples, and tumorosphere cells. Tumorosphere formation of EAC-derived cells in the stem cell culture medium was also analyzed. Nanog expression was then analyzed in secondary tumors initiated by the injection of tumorospheres or tumorosphere-derived differentiated cells into 15 female nude mice. Apoptosis and cell proliferation were detected in the fluorescence-activated cell sorter and 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide experiments, respectively. The Nanog protein was expressed in a majority of EAC samples (45 of 55, 81.8%), but not in benign endometrium samples (0 of 26, 0.0%). Oct4 and Sox2 were also commonly expressed in EAC samples (42 of 55, 76.4% and 39 of 55, 70.9%, respectively). Subsets of cancer cells from all EAC samples (15 of 15, 100%) exhibited the capacity to form Nanog-positive tumorospheres. The tumorospheres also expressed Nanog, Oct4, and Sox2 mRNA and showed a higher proliferation potential than differentiated cells. All 15 mice that were injected with tumorosphere cell-formed tumors, whereas only 3 of 15 mice injected with differentiated cells derived from tumorospheres developed tumors. All secondary xenograft tumors still expressed Nanog protein and Nanog, Oct4, and Sox2 mRNA, and had higher proliferation and lower apostosis than did differentiated cells. Overexpression of Nanog in EACs suggests that Nanog may represent a potential therapeutic target for EAC. In addition, Nanog may be useful as a biomarker in an immunohistochemical panel to differentiate between EAC and benign endometrial tissues. The expression of Nanog in tumorospheres may be indicative of the presence of a population of endometrial cancer stem cells, and its expression in xenograft tumors suggests that Nanog may also be associated with tumor metastasis.