Increased levels of FoxA1 transcription factor in pluripotent P19 embryonal carcinoma cells stimulate neural differentiation

FOXA1 and FOXA2: the regulatory mechanisms and therapeutic implications in cancer

FOXA1 (Forkhead Box A1) and FOXA2 (Forkhead Box A2) serve as pioneering transcription factors that build gene expression capacity and play a central role in biological processes, including organogenesis and differentiation, glycolipid metabolism, proliferation, migration and invasion, and drug resistance. Notably, FOXA1 and FOXA2 may exert antagonistic, synergistic, or complementary effects in the aforementioned biological processes. This article focuses on the molecular mechanisms and clinical relevance of FOXA1 and FOXA2 in steroid hormone-induced malignancies and highlights potential strategies for targeting FOXA1 and FOXA2 for cancer therapy. Furthermore, the article describes the prospect of targeting upstream regulators of FOXA1/FOXA2 to regulate its expression for cancer therapy because of the drug untargetability of FOXA1/FOXA2.

Suppressor of Fused Regulation of Hedgehog Signaling is Required for Proper Astrocyte Differentiation

Hedgehog signaling is essential for vertebrate development; however, less is known about the negative regulators that influence this pathway. Using the mouse P19 embryonal carcinoma cell model, suppressor of fused (SUFU), a negative regulator of the Hedgehog (Hh) pathway, was investigated during retinoic acid (RA)-induced neural differentiation. We found Hh signaling increased activity in the early phase of differentiation, but was reduced during terminal differentiation of neurons and astrocytes. This early increase in pathway activity was required for neural differentiation; however, it alone was not sufficient to induce neural lineages. SUFU, which regulates signaling at the level of Gli, remained relatively unchanged during differentiation, but its loss through CRISPR-Cas9 gene editing resulted in ectopic expression of Hh target genes. Interestingly, these SUFU-deficient cells were unable to differentiate toward neural lineages without RA, and when directed toward these lineages, they showed delayed and decreased astrocyte differentiation; neuron differentiation was unaffected. Ectopic activation of Hh target genes in SUFU-deficient cells remained throughout RA-induced differentiation and this was accompanied by the loss of Gli3, despite the presence of the Gli3 message. Thus, the study indicates the proper timing and proportion of astrocyte differentiation requires SUFU, likely acting through Gli3, to reduce Hh signaling during late-stage differentiation.

N6-Methyladenosine detected in RNA of testicular germ cell tumors is controlled by METTL3, ALKBH5, YTHDC1/F1/F2, and HNRNPC as writers, erasers, and readers

BACKGROUND

Type II testicular germ cell tumors (GCTs) arise from a common precursor lesion (germ cell neoplasia in situ) and are stratified into seminomas and non-seminomas, which differ considerably in morphology, gene expression, and epigenetic landscape. The N6-methyladenosine (6mA) epigenetic modification is the most abundant modification in mRNA and is also detectable in eukaryotic DNA. The functional role of 6mA is not fully understood, but 6mA residues may influence transcription by affecting splicing, miRNA processing, and mRNA stability. Additionally, the methyl group of 6mA destabilizes Watson-Crick base-pairing affecting RNA structure and protein binding.

OBJECTIVES

Here, we analyzed the presence of the 6mA epigenetic modification in germ cells and GCT tissues and cell lines.

MATERIALS AND METHODS

We screened for the presence of 6mA in DNA and RNA by immunohistochemistry, mass spectrometry or ELISA-based quantification assays. Additionally, expression of 6mA writer-, eraser- and reader-factors was analyzed by microarrays, qRT-PCR, western blotting and screening of public databases.

RESULTS

We demonstrate that 6mA is detectable in RNA, but not DNA, of GCT cell lines and tissues, fibroblasts, and Sertoli cells as well as germ cells of different developmental stages. Based on expression analyses, our results suggest METTL3, ALKBH5, YTHDC1, YTHDF1, YTHDF2 and HNRNPC as main writers, erasers, and readers of the 6mA modification in GCTs.

DISCUSSION

Owing to the lack of 6mA in DNA of GCTs, a functional role in regulating DNA transcription can be excluded. Interestingly, expression levels of 6mA regulators are comparable between tumor and normal tissues/cells, suggesting a similar mechanism of 6mA regulation in RNA. Finally, we demonstrate that 6mA levels in RNA increase upon differentiation of GCT cell lines, suggesting a role of 6mA in cell fate decisions.

CONCLUSION

In summary, our data provide the starting point for further experiments deciphering the role of 6mA in the RNA of GCTs.

FOXA1 reprograms the TGF-β-stimulated transcriptional program from a metastasis promoter to a tumor suppressor in nasopharyngeal carcinoma

Nasopharyngeal carcinoma (NPC) is a unique subtype of head and neck squamous carcinoma that is notorious for its high metastatic potential. In this study, we reported that FOXA1 protein was decreased in NPC cells. Loss of FOXA1 is associated with lymph node metastasis and poor prognosis. Silencing FOXA1 in NP69 and C666-1 NPC cells accelerated cell proliferation and migration, while re-expression of FOXA1 has opposite effects. Microarray and RNA-seq analysis revealed that re-expression of FOXA1 in NPC cells reprogrammed the TGF-β-stimulated transcription program, which is characterized by promotion of TGF-β-inducible tumor-suppressive targets but repression of TGF-β-inducible oncogenes expression in NPC cells, leading to restoration of NPC cell sensitivity to TGF-β's growth-inhibitory effect. BAMBI, a TGF-β responsive tumor suppressor, was induced by FOXA1 in NPC cells. FOXA1 binding on the BAMBI gene facilitated SMAD2/3 binding to the BAMBI promoter via increasing BAMBI associated H3K4me1 and H3K27ac modification. Enforced expression of BAMBI in NPC cells suppressed cell proliferation and invasiveness. Our data suggested that FOXA1 is a master factor in controlling the TGF-β-stimulated transcriptome and a regulator of TGF-β biological functions in NPC oncogenesis.

Hypoxia downregulates the angiogenesis in human placenta via Notch1 signaling pathway

Placentation, which is critical for maternal-fetal exchange of nutrients and gases, is a complicated process comprising stepwise vasculogenesis and angiogenesis. Hypoxia caused by impaired trophoblast invasion may cause various angiogenic abnormalities in human placenta. The Notch1 signaling pathway plays an important role in the regulation of angiogenesis. The angiogenesis of human umbilical vein endothelial cells (HUVECs) under normal/hypoxic conditions and the mRNA/protein level of Notch1/Dell4/Jagged1 were investigated in this study. The effects of DAPT/JAG-1 on the migration of HUVECs were also assessed by cell wound healing assay, so as to discover the possible role of notch1 signaling pathway in the angiogenesis of human placenta. The results showed that angiogenic ability of HUVECs was seriously reduced under hypoxic conditions. The mRNA and protein levels of Notch1/Dell4/Jagged1 were decreased in the hypoxic group compared to the control one. In addition, the migration capability of HUVECs was significantly obstructed when treated with DAPT and under hopoxic condition, but promoted when treated with JAG-1. The above results demonstrate that hypoxia downregulates the angiogenesis in human placenta via Notch1 signaling pathway.

Co‑expression of Axin and APC gene fragments inhibits colorectal cancer cell growth via regulation of the Wnt signaling pathway

Adenomatous polyposis coli (APC) and Axin interactions serve an important role in colorectal cancer (CRC) pathogenesis. The aim of the present study was to assess the combined effects of Axin and APC co-expression in CRC cells, and to determine the underlying mechanisms involved. SW480 cells were divided into the following groups: Untransfected (SW480 group), transfected with pEGFP-N₃plus pCS2-MT (SW480/vector-vector), transfected with pEGFP-N₃-APC5 (SW480/APC5), and transfected with pEGFP-N₃-APC5 pluspCS2-MT-Axin (SW480/APC5-Axin). APC5 and Axin mRNA levels were determined by reverse transcription-polymerase chain reaction. MTT assays and flow cytometry analysis were performed to assess cell growth and cell cycle distribution, respectively. Quantitative PCR and western blot analyses were conducted to evaluate the mRNA and protein levels, respectively, of Wnt signaling effectors, including β-catenin, c-myc and survivin. Successful transfection of SW480 cells was determined with APC and APC-Axin plasmids as indicated by the green fluorescence signals. Notably, SW480/APC5 cell growth was inhibited by 40.33%, and cells co-expressing APC5 and Axin demonstrated 61.27% inhibition of cell growth compared with SW480 control cells. The results demonstrate that APC5 may induce G1/S arrest in SW480 cells, and Axin may enhance cell growth arrest induced by APC5. The mRNA and protein levels of β-catenin, c-myc and survivin were significantly reduced in SW480/APC-Axin cells when compared with the SW480/APC group. In conclusion, co-expression of APC5 and Axin genes significantly downregulated Wnt signaling in human SW480 CRC cells and inhibited cell growth, when compared with cells transfected with APC5 alone. These results may provide experimental evidence to support combined gene therapy in CRC.

E167K polymorphism of TM6SF2 gene affects cell cycle of hepatocellular carcinoma cell HEPA 1-6

BACKGROUND

Some studties reported that the polymorphism of TM6SF2 gene E167K affects the occurrence and the progression of hepatocytes carcinoma (hepatocellular, HCC). In oeder to investigate the effects of the polymorphism of TM6SF2 gene E167K in the pathogenesis of HCC, we explored its influence on the cell cycle in hepatocellular carcinoma cell HEPA1-6.

METHODS

HEPA 1-6 cells which could respectively overexpress TM6SF2 wild type and E167K variant were cultured and HEPA 1-6 cells with zero load plasmids were used as matched control. Flow cytometry was used to detect the cell cycles of these 3 type of HEPA 1-6 cells. Realtime fluores-cence quantitative PCR and western blot were used to analyzed the expression of regulatory factors (Cyclin D1、p53、P16、P27、P21 and Rb) of cell cycle. T-test was used in statistical analysis.

RESULTS

Cell cycle phase distribution was presented by the proportion of cells in each phases (%). Compared with the control group, the cell cycle phase distribution (G₁ phase 57.36 ± 0.21%, G₂/M phase 25.61 ± 0.36%,S phases 19.31 ± 0.25%) had no differences in wild type group (G₁ phase 57.63 ± 0.28%, G₂/M phase 25.77 ± 0.51%, S phases 19.54 ± 0.25%; P < 0.05). Between variant type group and wild type group,G₁ phase was significantly decreased (variant type group G₁ phase 36.26 ± 0.31%, P < 0.05),S phase and G₂/M phase were increased(variant type group S phase 28.41 ± 0.31%, P < 0.05;G₂/M phase 35.23 ± 0.14%, P < 0.05), respectively. Compared with control group,the relative expression of CyclinD1、P53 and Rb mRNA in variant type group was significantly upregulated (2.03 ± 0.01 VS 1.04 ± 0.06, 1.88 ± 0.05 VS 1.37 ± 0.03, 1.29 ± 0.06 VS 1.15 ± 0.03, P < 0.05) and P27 mRNA in variant type group was significantly downregulated (0.56 ± 0.02 VS 0.85 ± 0.05, P < 0.05). Compared with wild type group, the relative expression of CyclinD1、P53 and Rb mRNA in variant type group was significantly upregulated (wild type group 1.00 ± 0.00, 1.48 ± 0.09, 1.18 ± 0.01, P < 0.05) and P27 mRNA in variant type group was significantly downregulated (variant type group 0.82 ± 0.05,P < 0.05). There was no statistical significance between wild type group and control group (P > 0.05). P16 and P21 expression showed no statistical sigtfificance in any of these three groups (P > 0.05).

CONCLUSION

E167K polymorphism of TM6SF2 gene affects cell cycles of HEPA1-6 cells via up-regulating CyclinD1、P53 and Rb and down-regulating P27.

Cytosine modifications modulate the chromatin architecture of transcriptional enhancers

Epigenetic mechanisms are believed to play key roles in the establishment of cell-specific transcription programs. Accordingly, the modified bases 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) have been observed in DNA of genomic regulatory regions such as enhancers, and oxidation of 5mC into 5hmC by Ten-eleven translocation (TET) proteins correlates with enhancer activation. However, the functional relationship between cytosine modifications and the chromatin architecture of enhancers remains elusive. To gain insights into their function, 5mC and 5hmC levels were perturbed by inhibiting DNA methyltransferases and TETs during differentiation of mouse embryonal carcinoma cells into neural progenitors, and chromatin characteristics of enhancers bound by the pioneer transcription factors FOXA1, MEIS1, and PBX1 were interrogated. In a large fraction of the tested enhancers, inhibition of DNA methylation was associated with a significant increase in monomethylation of H3K4, a characteristic mark of enhancer priming. In addition, at some specific enhancers, 5mC oxidation by TETs facilitated chromatin opening, a process that may stabilize MEIS1 binding to these genomic regions.

An Intronic cis-Regulatory Element Is Crucial for the Alpha Tubulin Pl-Tuba1a Gene Activation in the Ciliary Band and Animal Pole Neurogenic Domains during Sea Urchin Development

In sea urchin development, structures derived from neurogenic territory control the swimming and feeding responses of the pluteus as well as the process of metamorphosis. We have previously isolated an alpha tubulin family member of Paracentrotus lividus (Pl-Tuba1a, formerly known as Pl-Talpha2) that is specifically expressed in the ciliary band and animal pole neurogenic domains of the sea urchin embryo. In order to identify cis-regulatory elements controlling its spatio-temporal expression, we conducted gene transfer experiments, transgene deletions and site specific mutagenesis. Thus, a genomic region of about 2.6 Kb of Pl-Tuba1a, containing four Interspecifically Conserved Regions (ICRs), was identified as responsible for proper gene expression. An enhancer role was ascribed to ICR1 and ICR2, while ICR3 exerted a pivotal role in basal expression, restricting Tuba1a expression to the proper territories of the embryo. Additionally, the mutation of the forkhead box consensus sequence binding site in ICR3 prevented Pl-Tuba1a expression.

Reconstructed cell fate-regulatory programs in stem cells reveal hierarchies and key factors of neurogenesis

Cell lineages, which shape the body architecture and specify cell functions, derive from the integration of a plethora of cell intrinsic and extrinsic signals. These signals trigger a multiplicity of decisions at several levels to modulate the activity of dynamic gene regulatory networks (GRNs), which ensure both general and cell-specific functions within a given lineage, thereby establishing cell fates. Significant knowledge about these events and the involved key drivers comes from homogeneous cell differentiation models. Even a single chemical trigger, such as the morphogen all-trans retinoic acid (RA), can induce the complex network of gene-regulatory decisions that matures a stem/precursor cell to a particular step within a given lineage. Here we have dissected the GRNs involved in the RA-induced neuronal or endodermal cell fate specification by integrating dynamic RXRA binding, chromatin accessibility, epigenetic promoter epigenetic status, and the transcriptional activity inferred from RNA polymerase II mapping and transcription profiling. Our data reveal how RA induces a network of transcription factors (TFs), which direct the temporal organization of cognate GRNs, thereby driving neuronal/endodermal cell fate specification. Modeling signal transduction propagation using the reconstructed GRNs indicated critical TFs for neuronal cell fate specification, which were confirmed by CRISPR/Cas9-mediated genome editing. Overall, this study demonstrates that a systems view of cell fate specification combined with computational signal transduction models provides the necessary insight in cellular plasticity for cell fate engineering. The present integrated approach can be used to monitor the in vitro capacity of (engineered) cells/tissues to establish cell lineages for regenerative medicine.

Foxa1 contributes to the repression of Nanog expression by recruiting Grg3 during the differentiation of pluripotent P19 embryonal carcinoma cells

Transcription factor Foxa1 plays a critical role during neural differentiation and is induced immediately after retinoic acid (RA)-initiated differentiation of pluripotent P19 embryonal carcinoma cells, correlated with the downregulated expression of pluripotency-related genes such as Nanog. To study whether Foxa1 participates in the repression of pluripotency factors, we expressed Foxa1 ectopically in P19 cells and identified that Nanog was repressed directly by Foxa1. We confirmed that Foxa1 was able to interact with Grg3, which is a transcriptional corepressor that expresses in P19 cells as well as during RA-induced P19 cell differentiation. Knockdown of Foxa1 or Grg3 delayed the downregulation of Nanog expression during RA-induced P19 cell differentiation. Furthermore, we found that Foxa1 recruited Grg3 to the Nanog promoter -2kb upstream region and switched the promoter to an inactive chromatin status represented by typical modifications in histone H3. Together, our results suggested a critical involvement of Foxa1 in the negative regulation of Nanog expression during the differentiation of pluripotent stem cells.

Foxm1 mediates LIF/Stat3-dependent self-renewal in mouse embryonic stem cells and is essential for the generation of induced pluripotent stem cells

Activation of signal transducer and activator of transcription 3 (Stat3) by leukemia inhibitory factor (LIF) is required for maintaining self-renewal and pluripotency of mouse embryonic stem cells (mESCs). Here, we have confirmed transcription factor Forkhead Box m1 (Foxm1) as a LIF/Stat3 downstream target that mediates LIF/Stat3-dependent mESC self-renewal. The expression of Foxm1 relies on LIF signaling and is stimulated by Stat3 directly in mESCs. The knockdown of Foxm1 results in the loss of mESC pluripotency in the presence of LIF, and the overexpression of Foxm1 alone maintains mESC pluripotency in the absence of LIF and feeder layers, indicating that Foxm1 is a mediator of LIF/Stat3-dependent maintenance of pluripotency in mESCs. Furthermore, the inhibition of Foxm1 expression prevents the reprogramming of mouse embryonic fibroblasts to induced pluripotent stem cells (iPSCs), suggesting that Foxm1 is essential for the reprogramming of somatic cells into iPSCs. Our results reveal an essential function of Foxm1 in the LIF/Stat3-mediated mESC self-renewal and the generation of iPSCs.

Adenovirus-mediated RNA interference targeting FOXM1 transcription factor suppresses cell proliferation and tumor growth of nasopharyngeal carcinoma

BACKGROUND

The Forkhead Box M1 (FOXM1) transcription factor, which regulates the expression of genes essential for cell proliferation and transformation, is implicated in tumorigenesis and tumor progression. FOXM1 has attracted much attention as a potential target for the prevention and/or therapeutic intervention in human carcinomas.

METHODS

The levels of FOXM1 expression in clinical tissue specimens and cell lines of human malignant nasopharyngeal carcinoma (NPC) were measured. Knockdown of FOXM1 expression was performed by small interfering RNA in NPC cells. An adenovirus vector (named AdFOXM1shRNA) was constructed to express a short hairpin RNA specific to FOXM1. The efficacy of AdFOXM1shRNA for tumor gene therapy in NPC cells and an in vivo NPC grafting model was assessed.

RESULTS

A strong expression of FOXM1 was observed in clinical tissue specimens and cell lines of human NPC. Knockdown of FOXM1 expression by FOXM1 specific small interfering RNA diminished the NPC cell proliferation. The infection of AdFOXM1shRNA in NPC cells resulted in the knockdown of FOXM1 mRNA and protein levels, correlated with the reduction of proliferation and anchorage-independent growth of the cancer cells. The growth of NPC tumors was significantly suppressed when inoculated mice were injected with AdFOXM1shRNA in the tumor.

CONCLUSIONS

Together, our results suggest that FOXM1 is a potential therapeutic target for NPC and AdFOXM1shRNA may be an additional gene therapeutic intervention to be evaluated in future treatment strategies for patients with NPC.

Inhibition of FOXM1 transcription factor suppresses cell proliferation and tumor growth of breast cancer

The forkhead box M1 (FOXM1) transcription factor regulates the expression of genes essential for cell proliferation and transformation and is implicated in tumorigenesis and tumor progression. FOXM1 has been considered as a potential target for the prevention and/or therapeutic intervention in human carcinomas. In this study, we observed a strong expression of FOXM1 in clinical tissue specimens and cell lines of human breast cancer and a correlation between FOXM1 levels and the proliferation ability in the tested MCF-7, MDA-MB-231 and ZR-75-30 cells. By using an adenovirus vector (named AdFOXM1shRNA) that expresses a short hairpin RNA (shRNA) to downregulate FOXM1 expression specifically, we found that the knockdown of FOXM1 expression diminished the proliferation and anchorage-independent growth of the breast cancer cells. The FOXM1 silencing in ZR-75-30 cells dramatically prevented the tumorigenicity of the AdFOXM1shRNA-treated cells in vitro and in vivo. Furthermore, the efficacy of AdFOXM1shRNA for tumor gene therapy was assessed with the breast cancer xenograft mouse model and the tumor growth was significantly suppressed when inoculated mice were injected with AdFOXM1shRNA in the tumors. Together, our results suggest that FOXM1 is a potential therapeutic target for breast cancer and AdFOXM1shRNA may be an additional gene therapeutic intervention for breast cancer treatment.

MicroRNAs up-regulated by CagA of Helicobacter pylori induce intestinal metaplasia of gastric epithelial cells

CagA of Helicobacter pylori is a bacterium-derived oncogenic protein closely associated with the development of gastric cancers. MicroRNAs (miRNAs) are a class of widespread non-coding RNAs, many of which are involved in cell growth, cell differentiation and tumorigenesis. The relationship between CagA protein and miRNAs is unclear. Using mammalian miRNA profile microarrays, we found that miRNA-584 and miRNA-1290 expression was up-regulated in CagA-transformed cells, miRNA-1290 was up-regulated in an Erk1/2-dependent manner, and miRNA-584 was activated by NF-κB. miRNA-584 sustained Erk1/2 activities through inhibition of PPP2a activities, and miRNA-1290 activated NF-κB by knockdown of NKRF. Foxa1 was revealed to be an important target of miRNA-584 and miRNA-1290. Knockdown of Foxa1 promoted the epithelial-mesenchymal transition significantly. Overexpression of miRNA-584 and miRNA-1290 induced intestinal metaplasia of gastric epithelial cells in knock-in mice. These results indicate that miRNA-584 and miRNA-1290 interfere with cell differentiation and remodel the tissues. Thus, the miRNA pathway is a new pathogenic mechanism of CagA.

Multiple modes of chromatin remodeling by Forkhead box proteins

Forkhead box (FOX) proteins represent a large family of transcriptional regulators unified by their DNA binding domain (DBD) known as a 'forkhead' or 'winged helix' domain. Over 40 FOX genes have been identified in the mammalian genome. FOX proteins share significant sequence similarities in the DBD which allow them to bind to a consensus DNA response element. However, their modes of action are quite diverse as they regulate gene expression by acting as pioneer factors, transcription factors, or both. This review focuses on the mechanisms of chromatin remodeling with an emphasis on three sub-classes-FOXA, FOXO, and FOXP members. FOXA proteins serve as pioneer factors to open up local chromatin structure and thereby increase accessibility of chromatin to factors regulating transcription. FOXP proteins, in contrast, function as classic transcription factors to recruit a variety of chromatin modifying enzymes to regulate gene expression. FOXO proteins represent a hybrid subclass having dual roles as pioneering factors and transcription factors. A subset of FOX proteins interacts with condensed mitotic chromatin and may function as 'bookmarking' agents to maintain transcriptional competence at specific genomic sites. The overall diversity in chromatin remodeling function by FOX proteins is related to unique structural motifs present within the DBD flanking regions that govern selective interactions with core histones and/or chromatin coregulatory proteins. This article is part of a Special Issue entitled: Chromatin in time and space.

Stable expression of FoxA1 promotes pluripotent P19 embryonal carcinoma cells to be neural stem-like cells

FoxA1 belongs to the fork head/winged-helix transcription factor family and participates in stimulating neuronal differentiation of pluripotent stem cells at early stages. To explore the biological roles of FoxA1 during this process, the stable expression of a GFP-FoxA1 fusion protein was established in P19 pluripotent embryonal carcinoma cells. Although they still express pluripotency-related transcription factors such as Oct4, Nanog, and Sox2, the generated P19 GFPFoxA1 cells exhibited a decreased activity of alkaline phosphatase and an increased expression of SSEA-3 compared with P19 cells. Elevated levels of nestin expression and prominin-1+ populations were observed in P19 GFPFoxA1 cells, implicating that the stable expression of FoxA1 promoted P19 cells to gain partial characteristics of neural stem cells. Furthermore, the promoter of nestin was confirmed to be bound and activated by FoxA1 directly. The expression of neuron-specific marker tubulin betaIII also existed in P19 GFPFoxA1 cells. P19 GFPFoxA1 cells showed an earlier onset of differentiation during RA-induced neuronal differentiation, evidenced by a more rapid change on the Nanog decrease and the tubulin betaIII increase. Thus, overexpression of FoxA1 alone may promote pluripotent P19 cells to become neural stem-like cells.

Epigenetic switch involved in activation of pioneer factor FOXA1-dependent enhancers

Transcription factors (TFs) bind specifically to discrete regions of mammalian genomes called cis-regulatory elements. Among those are enhancers, which play key roles in regulation of gene expression during development and differentiation. Despite the recognized central regulatory role exerted by chromatin in control of TF functions, much remains to be learned regarding the chromatin structure of enhancers and how it is established. Here, we have analyzed on a genomic-scale enhancers that recruit FOXA1, a pioneer transcription factor that triggers transcriptional competency of these cis-regulatory sites. Importantly, we found that FOXA1 binds to genomic regions showing local DNA hypomethylation and that its cell-type-specific recruitment to chromatin is linked to differential DNA methylation levels of its binding sites. Using neural differentiation as a model, we showed that induction of FOXA1 expression and its subsequent recruitment to enhancers is associated with DNA demethylation. Concomitantly, histone H3 lysine 4 methylation is induced at these enhancers. These epigenetic changes may both stabilize FOXA1 binding and allow for subsequent recruitment of transcriptional regulatory effectors. Interestingly, when cloned into reporter constructs, FOXA1-dependent enhancers were able to recapitulate their cell type specificity. However, their activities were inhibited by DNA methylation. Hence, these enhancers are intrinsic cell-type-specific regulatory regions of which activities have to be potentiated by FOXA1 through induction of an epigenetic switch that includes notably DNA demethylation.

Foxm1 transcription factor is required for maintenance of pluripotency of P19 embryonal carcinoma cells

Transcription factor Foxm1 plays a critical role during embryonic development and its expression is repressed during retinoic acid (RA)-induced differentiation of pluripotent P19 embryonal carcinoma cells at the early stage, correlated with downregulation of expression of pluripotency markers. To study whether Foxm1 participates in the maintenance of pluripotency of stem cells, we knock down Foxm1 expression in P19 cells and identify that Oct4 are regulated directly by Foxm1. Knockdown of Foxm1 also results in spontaneous differentiation of P19 cells to mesodermal derivatives, such as muscle and adipose tissues. Maintaining Foxm1 expression prevents the downregulation of pluripotency-related transcription factors such as Oct4 and Nanog during P19 cell differentiation. Furthermore, overexpression of FOXM1 alone in RA-differentiated P19 cells (4 days) or human newborn fibroblasts restarts the expression of pluripotent genes Oct4, Nanog and Sox2. Together, our results suggest a critical involvement of Foxm1 in maintenance of stem cell pluripotency.