Nspc1 regulates the key pluripotent Oct4–Nanog–Sox2 axis in P19 embryonal carcinoma cells via directly activating Oct4

[PCGF1 is highly expressed in rectal adenocarcinoma and silencing PCGF1 inhibits proliferation of rectal adenocarcinoma cells in vitro]

OBJECTIVE

To investigate the expression of PCGF1 in rectal adenocarcinoma (READ) and the effect of PCGF1 silencing on proliferation READ cells in vitro.

METHODS

The UALCAN and ENCORI online databases were used to analyze the expression level of PCGF1 in READ tissues and normal tissues and its association with the clinicopathological parameters and survival outcomes of patients with READ. The expression levels of PCGF1 were detected in two READ cell lines and a normal rectal epithelial cell line (HcoEpiC cells) using qPCR and Western blotting. Lentiviral vectors were used to construct PCGF1-overexpressing and PCGF1-silenced cell lines, and the proliferative activity of the cells was assessed using CCK-8 assay. The effect of PCGF1 silencing on tumor proliferation in vivo was also evaluated by observing tumorigenicity of the cells in nude mice.

RESULTS

PCGF1 was highly expressed in READ tissue (P < 0.001), and its expression levels was correlated with READ stage, differentiation and lymph node metastasis (P < 0.001). A high PCGF1 expression level was associated with a poor survival outcome of READ patients (P < 0.05). In SW837 and SW1463 cells, PCGF1 silencing significantly lowered the proliferative activity of the cells both in vitro (P < 0.05) and in nude mice (P < 0.01).

CONCLUSION

PCGF1 is highly expressed in READ tissue and may potentially serve as a prognostic biomarker as well as a therapeutic target for READ.

PCGF1 promotes epigenetic activation of stemness markers and colorectal cancer stem cell enrichment

Colorectal cancer (CRC) stem cells are resistant to cancer therapy and are therefore responsible for tumour progression after conventional therapy fails. However, the molecular mechanisms underlying the maintenance of stemness are poorly understood. In this study, we identified PCGF1 as a crucial epigenetic regulator that sustains the stem cell-like phenotype of CRC. PCGF1 expression was increased in CRC and was significantly correlated with cancer progression and poor prognosis in CRC patients. PCGF1 knockdown inhibited CRC stem cell proliferation and CRC stem cell enrichment. Importantly, PCGF1 silencing impaired tumour growth in vivo. Mechanistically, PCGF1 bound to the promoters of CRC stem cell markers and activated their transcription by increasing the H3K4 histone trimethylation (H3K4me3) marks and decreasing the H3K27 histone trimethylation (H3K27me3) marks on their promoters by increasing expression of the H3K4me3 methyltransferase KMT2A and the H3K27me3 demethylase KDM6A. Our findings suggest that PCGF1 is a potential therapeutic target for CRC treatment.

Oct4-Mediated Inhibition of Lsd1 Activity Promotes the Active and Primed State of Pluripotency Enhancers

An aberrant increase in pluripotency gene (PpG) expression due to enhancer reactivation could induce stemness and enhance the tumorigenicity of cancer stem cells. Silencing of PpG enhancers (PpGe) during embryonic stem cell differentiation involves Lsd1-mediated H3K4me1 demethylation and DNA methylation. Here, we observed retention of H3K4me1 and DNA hypomethylation at PpGe associated with a partial repression of PpGs in F9 embryonal carcinoma cells (ECCs) post-differentiation. H3K4me1 demethylation in F9 ECCs could not be rescued by Lsd1 overexpression. Given our observation that H3K4me1 demethylation is accompanied by strong Oct4 repression in P19 ECCs, we tested if Oct4 interaction with Lsd1 affects its catalytic activity. Our data show a dose-dependent inhibition of Lsd1 activity by Oct4 and retention of H3K4me1 at PpGe in Oct4-overexpressing P19 ECCs. These data suggest that Lsd1-Oct4 interaction in cancer stem cells could establish a "primed" enhancer state that is susceptible to reactivation, leading to aberrant PpG expression.

Pcgf1 Regulates Early Neural Tube Development Through Histone Methylation in Zebrafish

The neural induction constitutes the initial step in the generation of the neural tube. Pcgf1, as one of six Pcgf paralogs, is a maternally expressed gene, but its role and mechanism in early neural induction during neural tube development have not yet been explored. In this study, we found that zebrafish embryos exhibited a small head and reduced or even absence of telencephalon after inhibiting the expression of Pcgf1. Moreover, the neural induction process of zebrafish embryos was abnormally activated, and the subsequent NSC self-renewal was inhibited after injecting the Pcgf1 MO. The results of in vitro also showed that knockdown of Pcgf1 increased the expression levels of the neural markers Pax6, Pou3f1, and Zfp521, but decreased the expression levels of the pluripotent markers Oct4, Hes1, and Nanog, which further confirmed that Pcgf1 was indispensable for maintaining the pluripotency of P19 cells. To gain a better understanding of the role of Pcgf1 in early development, we analyzed mRNA profiles from Pcgf1-deficient P19 cells using RNA-seq. We found that the differentially expressed genes were enriched in many functional categories, which related to the development phenotype, and knockdown of Pcgf1 increased the expression of histone demethylases. Finally, our results showed that Pcgf1 loss-of-function decreased the levels of transcriptional repression mark H3K27me3 at the promoters of Ngn1 and Otx2, and the levels of transcriptional activation mark H3K4me3 at the promoters of Pou5f3 and Nanog. Together, our findings reveal that Pcgf1 might function as both a facilitator for pluripotent maintenance and a repressor for neural induction.

Repression of PCGF1 Decreases the Proliferation of Glioblastoma Cells in Association with Inactivation of c-Myc Signaling Pathway

Purpose

Glioblastoma (GBM) is the most common primary brain tumor with a poor therapeutic outcome. Polycomb group factor 1 (PCGF1), a member of the PcG (Polycomb group) family, is highly expressed in the developing nervous system of mice. However, the function and the mechanism of PCGF1 in GBM proliferation still remain unclear.

Methods

Knockdown of PCGF1 was performed in U87 GBM cell by shRNA strategy via lentivirus vector. MTT assay, colony formation assays, and flow cytometry were used to measure the properties of cell proliferation and cell cycle distribution, respectively. GeneChip analysis was performed to identify the downstream effector molecules. Rescue assay was constructed to verify the screening results.

Results

We first found that knockdown of PCGF1 led to the inhibition of U87 cells proliferation and decreased colony formation ability. The data from GeneChip expression profiling and Ingenuity Pathway Analysis (IPA) indicated that many of the altered gene cells are associated with the cell proliferation control pathways. We have further confirmed the suppression of AKT/GSK3β/c-Myc/cyclinD1 expressions by Western blotting analysis. The over-expression of c-Myc could partly restore the attenuated proliferation ability caused by knockdown of PCGF1.

Conclusion

All the above evidences suggested that PCGF1 might be closely associated with tumorigenesis and progression of glioblastoma (GBM), in which process the oncoprotein c-Myc may participate. PCGF1 could thus be a potential therapeutic target for the treatment of glioblastoma (GBM).

lncRNAs combine and crosstalk with NSPc1 in ATRA-induced differentiation of U87 glioma cells

Nervous system polycomb 1 (NSPc1) is a member of the polycomb group (PcG) family of proteins and has been demonstrated to maintain the differentiation and pluripotency of stem cells. Long non-coding RNAs (lncRNAs) have been demonstrated to be involved in the control of pluripotency and differentiation in embryonic and pluripotent cells. In the present study, the expression levels of NSPc1 were associated with the malignant potential of various glioma cell lines. Additionally, lncRNAs were differentially expressed in glioblastoma cell lines. Following induced differentiation of U87 glioblastoma cells with all-trans retinoic acid, the expression levels of NSPc1 decreased initially, reaching its lowest point on day 6, but then subsequently increased until day 10. The expression of lncRNA candidates decreased in the cell differentiation stage. Additionally, the expression of metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), sex-determining region of the Y chromosome-box 2 overlapping transcript (SOX2OT) and antisense non-coding RNA in the INK4 locus (ANRIL) was significantly altered relative to the expression levels of NSPc1. RNA immunoprecipitation (RIP) assays demonstrated that MALAT1, SOX2OT and ANRIL bind to NSPc1 in U87 glioblastoma cells and the enrichment of ANRIL in anti-NSPc1 antibody group was associated with the expression levels of NSPc1 during U87 cell differentiation. Small interfering RNA mediated downregulation of NSPc1 expression with MALAT1, SOX2OT and ANRIL, inhibited the proliferation, and promoted apoptosis in U87 cells. The results of the present study demonstrate that MALAT1, SOX2OT and ANRIL combine and crosstalk with NSPc1 in U87 cells to affect proliferation and apoptosis.

The Fine Tuning of Drp1-Dependent Mitochondrial Remodeling and Autophagy Controls Neuronal Differentiation

Mitochondria play a critical role in neuronal function and neurodegenerative disorders, including Alzheimer’s, Parkinson’s and Huntington diseases and amyotrophic lateral sclerosis, that show mitochondrial dysfunctions associated with excessive fission and increased levels of the fission protein dynamin-related protein 1 (Drp1). Our data demonstrate that Drp1 regulates the transcriptional program induced by retinoic acid (RA), leading to neuronal differentiation. When Drp1 was overexpressed, mitochondria underwent remodeling but failed to elongate and this enhanced autophagy and apoptosis. When Drp1 was blocked during differentiation by overexpressing the dominant negative form or was silenced, mitochondria maintained the same elongated shape, without remodeling and this increased cell death. The enhanced apoptosis, observed with both fragmented or elongated mitochondria, was associated with increased induction of unfolded protein response (UPR) and ER-associated degradation (ERAD) processes that finally affect neuronal differentiation. These findings suggest that physiological fission and mitochondrial remodeling, associated with early autophagy induction are essential for neuronal differentiation. We thus reveal the importance of mitochondrial changes to generate viable neurons and highlight that, rather than multiple parallel events, mitochondrial changes, autophagy and apoptosis proceed in a stepwise fashion during neuronal differentiation affecting the nuclear transcriptional program.

Networks of Transcription Factors for Oct4 Expression in Mice

The present review aimed to assess the networks of transcription factors regulating the Oct4 expression in mice. Through a comprehensive analysis of the binding sites and the interrelationships of the transcription factors of Oct4, it is found that transcription factors of Oct4 form three regulating complexes centered by Oct4-Sox2, Nanog, and Lrh1. They bind on CR4, CR2, and CR1 regions of Oct4 promoter/enhancer, respectively, to activate Oct4 transcription synergistically. This article also discusses the mechanisms of fine-tuning the Oct4 expression. These findings have important implications in the field of stem cell and developmental biology.

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.

The variant Polycomb Repressor Complex 1 component PCGF1 interacts with a pluripotency sub-network that includes DPPA4, a regulator of embryogenesis

PCGF1 encodes one of six human Polycomb RING finger homologs that are linked to transcriptional repression and developmental gene regulation. Individual PCGF proteins define discrete Polycomb Repressor Complex 1 (PRC1) multi-protein complexes with diverse subunit composition whose functions are incompletely understood. PCGF1 is a component of a variant PRC1 complex that also contains the BCL6 co-repressor BCOR and the histone demethylase KDM2B. To further investigate the role of PCGF1, we mapped the physical interactions of the protein under endogenous conditions in a cell model of neuronal differentiation. Using stringent statistical cut-offs, 83 highly enriched interacting proteins were identified, including all previously reported members of the variant PRC1 complex containing PCGF1, as well as proteins linked to diverse cellular pathways such as chromatin and cell cycle regulation. Notably, a sub-network of proteins associated with the establishment and maintenance of pluripotency (NANOG, OCT4, PATZ1, and the developmental regulator DPPA4) were found to independently interact with PCGF1 in a subsequent round of physical interaction mapping experiments. Furthermore, knockdown of PCGF1 results in reduced expression of DPPA4 and other subunits of the variant PRC1 complex at both mRNA and protein levels. Thus, PCGF1 represents a physical and functional link between Polycomb function and pluripotency.

A cell-free system toward deciphering the post-translational modification barcodes of Oct4 in different cellular contexts

The octamer-binding transcription factor 4 (Oct4) is essential for maintaining the self-renewal and pluripotency of embryonic stem cells (ESCs). Post-translational modifications (PTMs) of Oct4 critically control its structure, function and intracellular localization. However, determination of Oct4 PTM profiles has largely been restricted by the quantity and purity of the Oct4 protein samples required for mass spectrometric analyses. In this study, by incubating the Escherichia coli-derived His-tagged Oct4 proteins with the whole cell lysates of a variety of human cells followed by retrieving the reacted Oct4 proteins with the Ni-NTA beads, we developed a labor- and cost-effective in vitro PTM method that allowed for mass spectrometric determination of the phosphorylation profiles of Oct4 proteins exposed to various cell-free systems. A number of Oct4 phosphorylation sites that were commonly present in all the cell-free systems or specifically present in a particular cellular context were identified, indicating that Oct4 is controlled by both common and distinct PTM regulatory pathways. Our work provided a proof-of-concept that such a cell-free system-based in vitro PTM approach can be applied to systematically map out the physiologically-relevant PTM sites in Oct4 proteins, which opened up an avenue to fully decipher the Oct4 PTM barcodes in various cellular contexts.