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MEF2 transcription factors are key regulators of sprouting angiogenesis.

ABSTRACT: Angiogenesis, the fundamental process by which new blood vessels form from existing ones, depends on precise spatial and temporal gene expression within specific compartments of the endothelium. However, the molecular links between proangiogenic signals and downstream gene expression remain unclear. During sprouting angiogenesis, the specification of endothelial cells into the tip cells that lead new blood vessel sprouts is coordinated by vascular endothelial growth factor A (VEGFA) and Delta-like ligand 4 (Dll4)/Notch signaling and requires high levels of Notch ligand DLL4. Here, we identify MEF2 transcription factors as crucial regulators of sprouting angiogenesis directly downstream from VEGFA. Through the characterization of a Dll4 enhancer directing expression to endothelial cells at the angiogenic front, we found that MEF2 factors directly transcriptionally activate the expression of Dll4 and many other key genes up-regulated during sprouting angiogenesis in both physiological and tumor vascularization. Unlike ETS-mediated regulation, MEF2-binding motifs are not ubiquitous to all endothelial gene enhancers and promoters but are instead overrepresented around genes associated with sprouting angiogenesis. MEF2 target gene activation is directly linked to VEGFA-induced release of repressive histone deacetylases and concurrent recruitment of the histone acetyltransferase EP300 to MEF2 target gene regulatory elements, thus establishing MEF2 factors as the transcriptional effectors of VEGFA signaling during angiogenesis.

SUBMITTER: Sacilotto N

PROVIDER: S-EPMC5110996 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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MEF2 transcription factors are key regulators of sprouting angiogenesis.

Sacilotto Natalia N Chouliaras Kira M KM Nikitenko Leonid L LL Lu Yao Wei YW Fritzsche Martin M Wallace Marsha D MD Nornes Svanhild S García-Moreno Fernando F Payne Sophie S Bridges Esther E Liu Ke K Biggs Daniel D Ratnayaka Indrika I Herbert Shane P SP Molnár Zoltán Z Harris Adrian L AL Davies Benjamin B Bond Gareth L GL Bou-Gharios George G Schwarz John J JJ De Val Sarah S

Genes & development 20161001 20

Angiogenesis, the fundamental process by which new blood vessels form from existing ones, depends on precise spatial and temporal gene expression within specific compartments of the endothelium. However, the molecular links between proangiogenic signals and downstream gene expression remain unclear. During sprouting angiogenesis, the specification of endothelial cells into the tip cells that lead new blood vessel sprouts is coordinated by vascular endothelial growth factor A (VEGFA) and Delta-li ...[more]

PMID: 27898394

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Project description:The Nuclear Factor I (NFI) family of transcription factors (TFs) plays key roles in cellular differentiation, proliferation, and homeostasis. As such, NFI family members engage in large number of interactions with other proteins and the chromatin. However, despite their well-established significance, the NFIs interactomes, their dynamics, and their functions have not been comprehensively examined. Here, we employed complementary omics-level techniques, i.e. interactomics (affinity purification mass spectrometry (AP-MS) and proximity-dependent biotinylation (BioID)), and chromatin immunoprecipitation sequencing (ChIP-Seq), to obtain a comprehensive view of the NFI proteins and their interactions. Our analyses included all four main NFI family members, and a less studied short isoform of NFIB (NFIB4), which lacks the DNA binding domain. We observed that, despite exhibiting some redundancy, each family member had unique high-confidence interactors and target genes, highlighting distinct roles within the transcriptional regulatory networks. The study revealed that NFIs interact with a large number of other TFs to co-regulate a broad range of regulatory networks and cellular processes. Notably, time-dependent proximity-labeling unveiled a highly dynamic nature of NFI protein-protein interaction networks and hinted at temporal modulation of NFI interactions. Furthermore, gene ontology (GO) enrichment analysis of NFI interactome and targetome revealed the involvement of NFIs in transcriptional regulation, chromatin organization, and cellular signaling pathways, and pathways related with cancer. Additionally, we observed that NFIB4 engages with proteins associated with mRNA regulation, which suggests that NFIs have roles beyond traditional DNA binding and transcriptional modulation. We propose that NFIs serve as pioneering TFs, playing critical roles in regulating other TFs and influencing a wide range of cellular processes. These insights into NFI protein-protein interactions and their dynamic, context-dependent nature provide a deeper understanding of gene regulation mechanisms and hint at the role of NFIs as master regulators.

Project description:UnlabelledExpression of the osteocyte-derived bone formation inhibitor sclerostin in adult bone requires a distant enhancer. We show that MEF2 transcription factors control this enhancer and mediate inhibition of sclerostin expression by PTH.IntroductionSclerostin encoded by the SOST gene is a key regulator of bone formation. Lack of SOST expression is the cause for the progressive bone overgrowth disorders sclerosteosis and Van Buchem disease. We have previously identified a distant enhancer within the 52-kb Van Buchem disease deletion downstream of the SOST gene that is essential for its expression in adult bone. Furthermore, we and others have reported that SOST expression is suppressed by PTH. The aim of this study was to identify transcription factors involved in SOST bone enhancer activity and mediating PTH responsiveness.Materials and methodsRegulation of the SOST enhancer and promoter was studied by luciferase reporter gene assays. Transcription factor binding sites were mapped by footprint analysis and functional mutation analyses using transient transfections of osteoblast-like UMR-106 cells that exhibit endogenous SOST expression. Specific transcription factor binding was predicted by sequence analysis and shown by gel retardation assays and antibody-induced supershifts. Expression of myocyte enhancer factors 2 (MEF2) was detected by in situ hybridization, quantitative RT-PCR (qPCR), and immunohistochemistry. The role of MEF2s in SOST expression was assessed by reporter gene assays and siRNA-mediated RNA knockdown.ResultsPTH completely suppressed the transcriptional activity of the SOST bone enhancer but did not affect the SOST promoter. A MEF2 response element was identified in the bone enhancer. It was essential for transcriptional activation, bound MEF2 transcription factors, and mediated PTH responsiveness. Expression of MEF2s in bone was shown by qPCR, in situ hybridization, and immunohistochemistry. MEF2s and sclerostin co-localized in osteocytes. Enhancer activity was stimulated by MEF2C overexpression and inhibited by co-expression of a dominant negative MEF2C mutant. Finally, siRNA-mediated knockdown of MEF2A, C, and D suppressed endogenous SOST expression in UMR-106 osteoblast-like cells.ConclusionsThese data strongly suggest that SOST expression in osteocytes of adult bone and its inhibition by PTH is mediated by MEF2A, C, and D transcription factors controlling the SOST bone enhancer. Hence, MEF2s are implicated in the regulation of adult bone mass.

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MEF2 transcription factors are key regulators of sprouting angiogenesis.

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MEF2 transcription factors are key regulators of sprouting angiogenesis.

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