A tight control of Rif1 by Oct4 and Smad3 is critical for mouse embryonic stem cell stability

PRAMEL7 and CUL2 decrease NuRD stability to establish ground-state pluripotency

Pluripotency is established in E4.5 preimplantation epiblast. Embryonic stem cells (ESCs) represent the immortalization of pluripotency, however, their gene expression signature only partially resembles that of developmental ground-state. Induced PRAMEL7 expression, a protein highly expressed in the ICM but lowly expressed in ESCs, reprograms developmentally advanced ESC+serum into ground-state pluripotency by inducing a gene expression signature close to developmental ground-state. However, how PRAMEL7 reprograms gene expression remains elusive. Here we show that PRAMEL7 associates with Cullin2 (CUL2) and this interaction is required to establish ground-state gene expression. PRAMEL7 recruits CUL2 to chromatin and targets regulators of repressive chromatin, including the NuRD complex, for proteasomal degradation. PRAMEL7 antagonizes NuRD-mediated repression of genes implicated in pluripotency by decreasing NuRD stability and promoter association in a CUL2-dependent manner. Our data link proteasome degradation pathways to ground-state gene expression, offering insights to generate in vitro models to reproduce the in vivo ground-state pluripotency.

Tyrosine phosphorylation-mediated YAP1-TFAP2A interactions coordinate transcription and trastuzumab resistance in HER2+ breast cancer

Trastuzumab resistance in HER2+ breast cancer (BC) is the major reason leading to poor prognosis of BC patients. Oncogenic gene overexpression or aberrant activation of tyrosine kinase SRC is identified to be the key modulator of trastuzumab response. However, the detailed regulatory mechanisms underlying SRC activation-associated trastuzumab resistance remain poorly understood. In the present study, we discover that SRC-mediated YAP1 tyrosine phosphorylation facilitates its interaction with transcription factor AP-2 alpha (activating enhancer binding protein 2 alpha, TFAP2A), which in turn promotes YAP1/TEAD-TFAP2A (YTT) complex-associated transcriptional outputs, thereby conferring trastuzumab resistance in HER2+ BC. Inhibition of SRC kinase activity or disruption of YTT complex sensitizes cells to trastuzumab treatment in vitro and in vivo. Additionally, we also identify YTT complex co-occupies the regulatory regions of a series of genes related to trastuzumab resistance and directly regulates their transcriptions, including EGFR, HER2, H19 and CTGF. Moreover, YTT-mediated transcriptional regulation is coordinated by SRC kinase activity. Taken together, our study reveals that SRC-mediated YTT complex formation and transcriptions are responsible for multiple mechanisms associated with trastuzumab resistance. Therefore, targeting HER2 signaling in combination with the inhibition of YTT-associated transcriptional outputs could serve as the treatment strategy to overcome trastuzumab resistance caused by SRC activation.

A NR2E1-interacting peptide of LSD1 inhibits the proliferation of brain tumour initiating cells

OBJECTIVES

Elimination of brain tumour initiating cells (BTICs) is important for the good prognosis of malignant brain tumour treatment. To develop a novel strategy targeting BTICs, we studied NR2E1(TLX) involved self-renewal mechanism of BTICs and explored the intervention means.

MATERIALS AND METHODS

NR2E1 and its interacting protein-LSD1 in BTICs were studied by gene interference combined with cell growth, tumour sphere formation, co-immunoprecipitation and chromatin immunoprecipitation assays. NR2E1 interacting peptide of LSD1 was identified by Amide Hydrogen/Deuterium Exchange and Mass Spectrometry (HDX-MS) and analysed by in vitro functional assays. The in vivo function of the peptide was examined with intracranial mouse model by transplanting patient-derived BTICs.

RESULTS

We found NR2E1 recruits LSD1, a lysine demethylase, to demethylate mono- and di-methylated histone 3 Lys4 (H3K4me/me2) at the Pten promoter and repress its expression, thereby promoting BTIC proliferation. Using Amide Hydrogen/Deuterium Exchange and Mass Spectrometry (HDX-MS) method, we identified four LSD1 peptides that may interact with NR2E1. One of the peptides, LSD1-197-211 that locates at the LSD1 SWIRM domain, strongly inhibited BTIC proliferation by promoting Pten expression through interfering NR2E1 and LSD1 function. Furthermore, overexpression of this peptide in human BTICs can inhibit intracranial tumour formation.

CONCLUSION

Peptide LSD1-197-211 can repress BTICs by interfering the synergistic function of NR2E1 and LSD1 and may be a promising lead peptide for brain tumour therapy in future.

Single-cell multiomics reveals the complexity of TGFβ signalling to chromatin in iPSC-derived kidney organoids

TGFβ1 plays a regulatory role in the determination of renal cell fate and the progression of renal fibrosis. Here we show an association between SMAD3 and the histone methyltransferase, EZH2, during cell differentiation; ChIP-seq revealed that SMAD3 and EZH2 co-occupy the genome in iPSCs and in iPSC-derived nephron progenitors. Through integration of single cell gene expression and epigenome profiling, we identified de novo ACTA2^+ve/POSTN^+ve myofibroblasts in kidney organoids treated with TGFβ1, characterised by increased SMAD3-dependent cis chromatin accessibility and gene expression associated with fibroblast activation. We have identified fibrosis-associated regulons characterised by enrichment of SMAD3, AP1, the ETS family of transcription factors, and NUAK1, CREB3L1, and RARG, corresponding to enriched motifs at accessible loci identified by scATACseq. Treatment with the EZH2 specific inhibitor GSK343, blocked SMAD3-dependent cis co-accessibility and inhibited myofibroblast activation. This mechanism, through which TGFβ signals directly to chromatin, represents a critical determinant of fibrotic, differentiated states.

iPSCs derived from insulin resistant offspring of type 2 diabetic patients show increased oxidative stress and lactate secretion

Background

The genetic factors associated with insulin resistance (IR) are not well understood. Clinical studies on first-degree relatives of type 2 diabetic (T2D) patients, which have the highest genetic predisposition to T2D, have given insights into the role of IR in T2D pathogenesis. Induced pluripotent stem cells (iPSCs) are excellent tools for disease modeling as they can retain the genetic imprint of the disease. Therefore, in this study, we aimed to investigate the genetic perturbations associated with insulin resistance (IR) in the offspring of T2D parents using patient-specific iPSCs.

Methods

We generated iPSCs from IR individuals (IR-iPSCs) that were offspring of T2D parents as well as from insulin-sensitive (IS-iPSCs) individuals. We then performed transcriptomics to identify key dysregulated gene networks in the IR-iPSCs in comparison to IS-iPSCs and functionally validated them.

Results

Transcriptomics on IR-iPSCs revealed dysregulated gene networks and biological processes indicating that they carry the genetic defects associated with IR that may lead to T2D. The IR-iPSCs had increased lactate secretion and a higher phosphorylation of AKT upon stimulation with insulin. IR-iPSCs have increased cellular oxidative stress indicated by a high production of reactive oxygen species and higher susceptibility to H2O2 -induced apoptosis.

Conclusions

IR-iPSCs generated from offspring of diabetic patients confirm that oxidative stress and increased lactate secretion, associated with IR, are inherited in this population, and may place them at a high risk of T2D. Overall, our IR-iPSC model can be employed for T2D modeling and drug screening studies that target genetic perturbations associated with IR in individuals with a high risk for T2D.

Sarcomatoid Yolk Sac Tumor Harbors Somatic Mutations That Are Otherwise Rare in Testicular Germ Cell Tumors

In testicular germ cell tumors (TGCTs), components with nonspecific sarcomatous features that express keratins and glypican 3 are classified as sarcomatoid yolk sac tumor (SYST). SYST is most frequently seen in metastatic sites after chemotherapy. Like so-called "somatic-type" malignancies arising in TGCTs, SYST is markedly resistant to systemic therapy and has a more aggressive clinical course than conventional types of TGCT. However, the clinicopathologic and molecular features of SYST remain incompletely described. This study evaluated a multi-institutional series of 20 SYSTs using massively parallel sequencing and p53 immunohistochemistry. The histologic and clinical characteristics of the cases were also assessed, including analyses of disease-specific outcomes. DNA sequencing identified somatic mutations in 12/20 cases (60%), including recurrent TP53 and RIF1 mutations (present in 4/20 cases, 20% each). In 3 of the 4 SYST with TP53 mutations, there was molecular evidence of loss of heterozygosity. Immunohistochemistry demonstrated diffuse overexpression of p53 protein in 3/4 (75%) cases with TP53 mutations. The remaining TP53-mutant case demonstrated multifocal overexpression of p53, suggestive of subclonal inactivation of the gene. Overexpression of p53 protein was not seen in any of 15 TP53 wild-type cases evaluated by immunohistochemistry. A subset of 4 cases underwent RNA sequencing (fusion panel), which demonstrated the absence of oncogenic gene fusions. A 2-tiered grading system based on 3 histologic parameters (cellularity, number of mitoses, and necrosis) demonstrated that high-grade SYSTs have a higher risk of disease-specific death compared to low-grade tumors. The risk of disease-specific mortality was also higher in SYSTs with somatic mutations. In conclusion, this study demonstrated that 60% of SYSTs harbor somatic oncogenic mutations that are otherwise rare in TGCTs, and the presence of these mutations is associated with an aggressive clinical course. In addition, the results presented herein suggest that grading SYSTs may be clinically relevant.

Glucose-6-Phosphate Dehydrogenase, Redox Homeostasis and Embryogenesis

Normal embryogenesis requires complex regulation and precision, which depends on multiple mechanistic details. Defective embryogenesis can occur by various mechanisms. Maintaining redox homeostasis is of importance during embryogenesis. NADPH, as produced from the action of glucose-6-phosphate dehydrogenase (G6PD), has an important role in redox homeostasis, serving as a cofactor for glutathione reductase in the recycling of glutathione from oxidized glutathione and for NADPH oxidases and nitric oxide synthases in the generation of reactive oxygen (ROS) and nitrogen species (RNS). Oxidative stress differentially influences cell fate and embryogenesis. While low levels of stress (eustress) by ROS and RNS promote cell growth and differentiation, supra-physiological concentrations of ROS and RNS can lead to cell demise and embryonic lethality. G6PD-deficient cells and organisms have been used as models in embryogenesis for determining the role of redox signaling in regulating cell proliferation, differentiation and migration. Embryogenesis is also modulated by anti-oxidant enzymes, transcription factors, microRNAs, growth factors and signaling pathways, which are dependent on redox regulation. Crosstalk among transcription factors, microRNAs and redox signaling is essential for embryogenesis.

Src-Yap1 signaling axis controls the trophectoderm and epiblast lineage differentiation in mouse embryonic stem cells

The tyrosine kinase Src is highly expressed in embryonic stem cells (ESCs) and ESC-differentiated cells, however, its functional role remains obscured. Here, we constitutivelyexpressed Src in mouse ESCs and found these cells retained comparable levels of the core pluripotent factors, such as Oct4 and Sox2, while promoted the expression of epiblast lineage markers and restrained trophoblast lineage markers compared to the control ESCs. Knockdown of Src in mouse ESCs showed the opposite effect. Directly differentiation of these ESCs to epiblast and trophoblast lineage cells revealed that Src activation dramatically accelerated the production of epiblast-like cells and inhibited the induction of trophoblast-like cells in vitro. Mechanistically, we found Src activation enhanced the Yap1-Tead interaction and their transcriptional output in mouse ESCs through specially upregulating Yap1 tyrosine phosphorylation. Subsequently, we found that overexpression of Yap1 in mouse ESCs phenocopied the differentiation patterns of Src overexpressing cells in vitro. Moreover, inhibition of Src kinase activity by Dasatinib or Yap1/Tead-mediated transcription with Verteporfin reversed the differentiation patterns of Src overexpressing ESCs. Taken together, our results unravel a novel Src-Yap1 regulatory axis during mouse ESC differentiation to trophectoderm and epiblast lineage cells in vitro.

Lin28 Inhibits the Differentiation from Mouse Embryonic Stem Cells to Glial Lineage Cells through Upregulation of Yap1

The RNA-binding protein Lin28 regulates neurogliogenesis in mammals, independently of the let-7 microRNA. However, the detailed regulatory mechanism remains obscured. Here, we established Lin28a or Lin28b overexpression mouse embryonic stem cells (ESCs) and found that these cells expressed similar levels of the core pluripotent factors, such as Oct4 and Sox2, and increased Yap1 but decreased lineage-specific markers compared to the control ESCs. Further differentiation of these ESCs to neuronal and glial lineage cells revealed that Lin28a/b overexpression did not affect the expression of neuronal marker βIII-tubulin, but dramatically inhibited the glial lineage markers, such as Gfap and Mbp. Interestingly, overexpression of Yap1 in mouse ESCs phenocopied Lin28a/b overexpression ESCs by showing defect in glial cell differentiation. Inhibition of Yap1/Tead-mediated transcription with verteporfin partially rescued the differentiation defect of Lin28a/b overexpression ESCs. Mechanistically, we demonstrated that Lin28 can directly bind to Yap1 mRNA, and the induction of Yap1 by Lin28a in mESCs is independent of Let7. Taken together, our results unravel a novel Lin28-Yap1 regulatory axis during mESC to glial lineage cell differentiation, which may shed light on glial cell generation in vitro.

hnRNP-K Targets Open Chromatin in Mouse Embryonic Stem Cells in Concert with Multiple Regulators

The transcription factor Oct4 plays a key regulatory role in the induction and maintenance of cellular pluripotency. In this article, we show that ubiquitous and multifunctional poly(C) DNA/RNA-binding protein hnRNP-K occupies Oct4 (Pou5f1) enhancers in embryonic stem cells (ESCs) but is dispensable for the initiation, maintenance, and downregulation of Oct4 gene expression. Nevertheless, hnRNP-K has an essential cell-autonomous function in ESCs to maintain their proliferation and viability. To better understand mechanisms of hnRNP-K action in ESCs, we have performed ChIP-seq analysis of genome-wide binding of hnRNP-K and identified several thousands of hnRNP-K target sites that are frequently co-occupied by pluripotency-related and common factors (Oct4, TATA-box binding protein, Sox2, Nanog, Otx2, etc.), as well as active histone marks. Furthermore, hnRNP-K localizes exclusively within open chromatin, implying its role in the onset and/or maintenance of this chromatin state. Stem Cells 2019;37:1018-1029.

Single‑cell intratumoral stemness analysis reveals the involvement of cell cycle and DNA damage repair in two different types of esophageal cancer

Intratumoral heterogeneity, particularly the potential cancer stemness of single cancer cells, has not yet been fully elucidated in human esophageal cancer. Single‑cell transcriptome sequencing of two types of esophageal adenocarcinoma (EAC) and two types of esophageal squamous cell carcinoma (ESCC) tissues was performed, and the intratumoral cancer stemness of the types of esophageal cancer were characterized at the single‑cell level in the present study. By comparing the transcriptomic profiles of single cancer cells with high and low stemness in individual patients, it was revealed that the overexpression of cell cycle‑associated genes in EAC cells was highly correlated with stemness, whereas overexpression of genes involved in the signaling pathways of DNA replication and DNA damage repair was significantly correlated with stemness in ESCC. High expression of these stemness‑associated genes was correlated with poor prognosis of patients. Additionally, poly [ADP‑ribose] polymerase(PARP)4 was identified as a novel cancer stemness‑associated gene in ESCC and its association with survival was validated in a cohort of 121 patients with ESCC. These findings have profound potential implications for the use of cell cycle inhibitors in EAC and PARP inhibitors in ESCC, which may provide novel mechanistic insights into the plasticity of esophageal cancer.

Cell cycle and pluripotency: Convergence on octamer‑binding transcription factor 4 (Review)

Embryonic stem cells (ESCs) have unlimited expansion potential and the ability to differentiate into all somatic cell types for regenerative medicine and disease model studies. Octamer-binding transcription factor 4 (OCT4), encoded by the POU domain, class 5, transcription factor 1 gene, is a transcription factor vital for maintaining ESC pluripotency and somatic reprogramming. Many studies have established that the cell cycle of ESCs is featured with an abbreviated G1 phase and a prolonged S phase. Changes in cell cycle dynamics are intimately associated with the state of ESC pluripotency, and manipulating cell-cycle regulators could enable a controlled differentiation of ESCs. The present review focused primarily on the emerging roles of OCT4 in coordinating the cell cycle progression, the maintenance of pluripotency and the glycolytic metabolism in ESCs.

Interaction of Rif1 Protein with G-Quadruplex in Control of Chromosome Transactions

Recent studies on G-quadruplex (G4) revealed crucial and conserved functions of G4 in various biological systems. We recently showed that Rif1, a conserved nuclear factor, binds to G4 present in the intergenic regions and plays a major role in spatiotemporal regulation of DNA replication. Rif1 may tether chromatin fibers through binding to G4, generating specific chromatin domains that dictate the replication timing. G4 and its various binding partners are now implicated in many other chromosome regulations, including transcription, replication initiation, recombination, gene rearrangement, and transposition.

Rif1 and Exo1 regulate the genomic instability following telomere losses

Telomere attrition is linked to cancer, diabetes, cardiovascular disease and aging. This is because telomere losses trigger further genomic modifications, culminating with loss of cell function and malignant transformation. However, factors regulating the transition from cells with short telomeres, to cells with profoundly altered genomes, are little understood. Here, we use budding yeast engineered to lack telomerase and other forms of telomere maintenance, to screen for such factors. We show that initially, different DNA damage checkpoint proteins act together with Exo1 and Mre11 nucleases, to inhibit proliferation of cells undergoing telomere attrition. However, this situation changes when survivors lacking telomeres emerge. Intriguingly, checkpoint pathways become tolerant to loss of telomeres in survivors, yet still alert to new DNA damage. We show that Rif1 is responsible for the checkpoint tolerance and proliferation of these survivors, and that is also important for proliferation of cells with a broken chromosome. In contrast, Exo1 drives extensive genomic modifications in survivors. Thus, the conserved proteins Rif1 and Exo1 are critical for survival and evolution of cells with lost telomeres.