The undifferentiated state of muscle stem (satellite) cells (MuSCs) is maintained by the canonical Notch pathway. Although three bHLH transcriptional factors, Hey1, HeyL and Hes1, are considered to be potential effectors of the Notch pathway exerting anti-myogenic effects, neither HeyL nor Hes1 inhibits myogenic differentiation of myogenic cell lines. Furthermore, whether these factors work redundantly or cooperatively is unknown. Here, we showed cellautonomous functions of Hey1 and HeyL in MuSCs using conditional and genetic null mice. Analysis of cultured MuSCs revealed antimyogenic activity of both HeyL and Hes1. We found that HeyL forms heterodimeric complexes with Hes1 in living cells. Moreover, our ChIP-seq experiments demonstrated that, compared with HeyL alone, the HeyL-Hes1 heterodimer binds with high affinity to specific sites in the chromatin, including the binding sites of Hey1. Finally, analyses of myogenin promoter activity showed that HeyL and Hes1 act synergistically to suppress myogenic differentiation. Collectively, these results suggest that HeyL and Hey1 function redundantly in MuSCs, and that HeyL requires Hes1 for effective DNA binding and biological activity.

Although transcription factors regulating endothelial cell (EC)-specific gene expression have been identified, it is not known how those factors induce EC-specificity. We previously reported that DNA hypomethylation of the proximal promoter elicits EC-specific expression of Roundabout4 (Robo4). However, the mechanisms establishing EC-specific hypomethylation of the Robo4 promoter remain unknown. In this study, we demonstrated that the hypermethylated Robo4 proximal promoter is demethylated as human iPS cells differentiate into endothelial cells. Reporter assays demonstrated that ETV2, an ETS family transcription factor, bound to ETS motifs in the proximal promoter and activated Robo4 expression. Immunoprecipitation demonstrated direct interaction between ETV2 and methylcytosine-converting enzymes TET1 and TET2. Adenoviral expression of ETV2-TET1/TET2 complexes demethylated the Robo4 promoter and induced Robo4 expression in non-ECs. In summary, we propose a novel regulatory model of EC-specific gene expression via promoter demethylation induced by ETV2-TET1/TET2 complexes during endothelial differentiation.

Roundabout4 (Robo4) is an endothelial cell-specific receptor that regulates vascular stability. Recently, Robo4 has been shown to regulate vascular permeability in inflammation. However, the mechanisms regulating the Robo4 gene in the context of inflammation are poorly understood. In this study, we found that intravenous injection of tumor necrosis factor (TNF) α increased Robo4 expression in mouse organs. In vitro analyses showed that TNFα increased Robo4 expression in human primary endothelial cells, but not in cells pretreated with a nuclear factor (NF)-κB inhibitor. Reporter assays using wild-type and mutant Robo4 promoters indicated that TNFα activated the Robo4 promoter and that both the 2753 and 2220 NF-κB motifs were essential for this activation. Electrophoretic mobility shift assays demonstrated that the NF-κB p65-p50 heterodimer bound to these motifs. These findings were further supported by chromatin immunoprecipitation assays in endothelial cells. Taken together, these results indicated that TNFα induced Robo4 expression by facilitating NF-κB p65-p50 heterodimer binding to the 2753 and 2220 motifs in the Robo4 promoter in endothelial cells in the context of inflammation.

Roundabout4 (Robo4) is an endothelial cell-specific protein that stabilizes the vasculature in pathological angiogenesis and inflammation. We previously determined a 3-kb Robo4 promoter and demonstrated the importance of the upstream region for nuclear factor-kappaB (NF-κB)-mediated promoter activation induced by tumor necrosis factor α (TNFα). This region contains unique genomic features, including promoter region-specific DNA hypermethylation and chromatin condensation; however, the function of the region remains poorly understood. In this study, we analyzed the DNA sequences of the region and identified a motif for polycomb repressive complex 2 (PRC2). Chromatin immunoprecipitation assay indicates the binding of the PRC2 component, SUZ12, to the motif. A mutation in the motif decreased DNA methylation in embryonic stem cells and increased Robo4 promoter activity in endothelial cells. An inhibitor for the PRC2 component, EZH2, induced the promoter activity and expression of Robo4 in endothelial cells treated with or without TNFα. Taken together, these results indicate that the PRC2 components maintain DNA hypermethylation and suppress Robo4 expression via the PRC2 binding motif in the upstream promoter.