Project description:MLL-AF4 is a hallmark genomic aberration which arises prenatally in high-risk infant acute lymphoblastic leukemia (ALL). In human embryonic stem cells (hESCs), MLL-AF4 skewed hemato-endothelial specification but was not sufficient for transformation. Additional cooperating genetic insults seem required for MLL-AF4-mediated leukemogenesis. FLT3 is highly expressed in MLL-AF4+ ALL through activating mutations (FLT3-TKD or FLT3-ITD) or increased transcriptional expression, being therefore considered a potential cooperating event in MLL-AF4+ ALL. Here, we explored the developmental impact of FLT3 activation on its own or in cooperation with MLL-AF4 in the hematopoietic fate of hESCs. FLT3 activation did not impact specification of CD45-CD31+ hemogenic precursors but significantly enhanced the formation of CD45+CD34+ and CD45+ blood cells and blood progenitors with clonogenic potential. Importantly, FLT3 activation through FLT3 mutations or FLT3-WT overexpression completely abrogated hematopoietic differentiation from MLL-AF4-expressing hESCs, indicating that FLT3 activation cooperates with MLL-AF4 to inhibit human embryonic hematopoiesis. Cell cycle/apoptosis analyses suggest that FLT3 activation directly impacts hESC specification rather than selective proliferation/survival of hESC-emerging hematopoietic derivatives. Transcriptional profiling supported the limited impact of FLT3 activation on hESC specification towards CD45-hemogenic precursors and the enhanced hematopoiesis upon FLT3 activation, and inhibited hematopoiesis upon MLL-AF4 expression in FLT3-activated hESCs which was associated to large transcriptional changes and regulation of master early hematopoietic genes. Also, although FLT3 activation and MLL-AF4 cooperate to inhibit embryonic hematopoiesis the underlying molecular/genetic mechanisms differ depending on how FLT3 activation is achieved. Finally, FLT3 activation did not cooperate with MLL-AF4 to immortalize/transform hESC-derived hematopoietic cells. 18 samples were analyzed. CD45- hemogenic precursors EV, 2 biological rep CD45- hemogenic precursors FLT3-TKD, 2 biological rep CD45- hemogenic precursors FLT3-WT, 2 biological rep CD45- hemogenic precursors FLT3-TKD/MLLAF4, 2 biological rep CD45- hemogenic precursors FLT3-WT/MLLAF4, 2 biological rep CD45+ blood cells EV, 1 biological rep CD45+ blood cells FLT3-TKD, 2 biological rep CD45+ blood cells FLT3-WT, 2 biological rep CD45+ blood cells FLT3-TKD/MLLAF4, 2 biological rep CD45+ blood cells FLT3-WT/MLLAF4, 1 biological rep

Project description:Rationale: The mechanistic foundation of vascular maturation is still largely unknown. Several human pathologies are characterized by deregulated angiogenesis and unstable blood vessels. Solid tumours, for instance, get their nourishment from newly formed structurally abnormal vessels which present wide and irregular inter-endothelial junctions. Expression and clustering of the main endothelial-specific adherens junction protein, vascular endothelial (VE)-cadherin (VEC), upregulate genes with key roles in endothelial differentiation and stability. Objective: We aim at understanding the molecular mechanisms through which VEC triggers the expression of a set of genes involved in endothelial differentiation and vascular stabilization. Methods and Results: We compared a VEC-null cell line with the same line reconstituted with VEC wild type cDNA. VEC expression and clustering upregulated endothelial-specific genes with key roles in vascular stabilization including claudin-5, Vascular Endothelial-Protein Tyrosine Phosphatase (VE-PTP) and von Willebrand factor (vWf). Mechanistically VEC exerts this effect by inhibiting Polycomb protein activity on the specific gene promoters. This is achieved by preventing nuclear translocation of FoxO1 and β-catenin, which contribute to Polycomb repressive complex-2 (PRC2) binding to promoter regions of claudin-5, VE-PTP and vWf. VE-cadherin/β-catenin complex also sequesters a core subunit of PRC2 (Ezh2) at the cell membrane, preventing its nuclear translocation. Inhibition of Ezh2/VE-cadherin association increases Ezh2 recruitment to claudin-5, VE-PTP and vWf promoters, causing gene downregulation. RNAseq comparison of VEC-null and VEC-positive cells suggested a more general role of VE-cadherin in activating endothelial genes and triggering a vascular stability-related gene expression program. In pathological angiogenesis of human ovarian carcinomas, reduced VEC expression paralleled decreased levels of Claudin-5 and VE-PTP. Conclusions: These data extend the knowledge of Polycomb-mediated regulation of gene expression to endothelial cell differentiation and vessel maturation. The identified mechanism opens novel therapeutic opportunities to modulate endothelial gene expression and induce vascular normalization through pharmacological inhibition of the Polycomb-mediated repression system. Keywords: Polycomb, endothelial cells, VE-cadherin, vessel maturation, vascular biology, vascular permeability, cell signalling, epigenetics, gene regulation. Downloaded from http://circres.ahajour Conclusions: These data extend the knowledge of Polycomb-mediated regulation of gene expression to endothelial cell differentiation and vessel maturation. The identified mechanism opens novel therapeutic opportunities to modulate endothelial gene expression and induce vascular normalization through pharmacological inhibition of the Polycomb-mediated repression system

Project description:Human embryonic stem cells (hESCs) are a powerful tool for modeling regenerative therapy. To search for the genes that promote hematopoietic development from human pluripotent stem cell, we overexpressed a list of hematopoietic regulator genes in human pluripotent stem cell-derived CD34+CD43- endothelial cells (ECs) enriched in hemogenic endothelium. Among genes tested, only SOX17, a gene encoding a transcription factor of the SOX family, promoted cell growth and supported expansion of CD34+CD43+CD45-/low cells expressing a hemogenic endothelial maker VE-cadherin. SOX17 was highly expressed in CD34+CD43- ECs but at a low level in CD34+CD43+CD45- pre-hematopoietic progenitor cells (pre-HPCs) and CD34+CD43+CD45+ HPCs. SOX17-overexpressing cells formed sphere-like colonies and generated few hematopoietic progenies. However, they retained hemogenic potential and gave rise to hematopoietic progenies upon inactivation of SOX17. Global gene expression analyses revealed that the CD34+CD43+CD45-/low cells expanded upon overexpression of SOX17 are hemogenic endothelium-like cells developmentally placed between ECs and pre-HPCs. Of interest, SOX17 also reprogrammed both pre-HPCs and HPCs into hemogenic endothelium-like cells. Genome-wide mapping of SOX17 revealed that SOX17 directly activates transcription of key regulator genes for vasculogenesis, hematopoiesis, and erythrocyte differentiation. Depletion of SOX17 in CD34+CD43- ECs severely compromised their hemogenic activity. These findings suggest that SOX17 plays a critical role in priming hemogenic potential in ECs, thereby regulates hematopoietic development from hESCs. This SuperSeries is composed of the SubSeries listed below. ChIP on chip analysis was carried out using the Mouse Promoter ChIP-on-chip Microarray Set (G4490A, Agilent, Palo Alto, Calif., USA). MEFs were subjected to ChIP assay using a Ring1B antibody. Purified immunoprecipitated and input DNA was subjected to T7 RNA polymerase-based amplification. Labeling, hybridization and washing were carried out according to the Agilent mammalian ChIP-on-chip protocol (ver.9.0). Scanned images were quantified with Agilent Feature Extraction software under standard conditions. Human ES cells were differentiated for 6 days in EBs, then CD34+CD43-CD45- endothelial cells were isolated, plated onto OP9 cells, and transduced with the 4OH-tamoxifen (4OHT)-inducible 3M-CM-^WFLAG-tagged Sox17-ERT retrovirus. The cells were seeded on OP9 stromal cells and cultured in the presence of 4OH-tamoxifen. At day 27 of the co-culture with OP9 cells, CD34+CD43+CD45low hemogenic endothelium-like cells overexpressing Sox17-ERT were collected by CD34 magnetic-activated cell sorting (MACS) and subjected to a ChIP-chip analysis. ChIP on chip analysis was carried out using the Mouse Promoter ChIP-on-chip Microarray Set (G4490A, Agilent, Palo Alto, Calif., USA). MEFs were subjected to ChIP assay using a Ring1B antibody. Purified immunoprecipitated and input DNA was subjected to T7 RNA polymerase-based amplification. Labeling, hybridization and washing were carried out according to the Agilent mammalian ChIP-on-chip protocol (ver.9.0). Scanned images were quantified with Agilent Feature Extraction software under standard conditions. Human ES cells were differentiated for 6 days in EBs, then CD34+CD43-CD45- endothelial cells were isolated, plated onto OP9 cells, and transduced with the 4OH-tamoxifen (4OHT)-inducible 3M-CM-^WFLAG-tagged Sox17-ERT retrovirus. The cells were seeded on OP9 stromal cells and cultured in the presence of 4OH-tamoxifen. At day 27 of the co-culture with OP9 cells, CD34+CD43+CD45low hemogenic endothelium-like cells overexpressing Sox17-ERT were collected by CD34 magnetic-activated cell sorting (MACS) and subjected to a ChIP-chip analysis.

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