Epigenetic suppression of iNOS expression in human endothelial cells: A potential role of Ezh2-mediated H3K27me3

Abstract Objective Cytokines strongly induce expression of the inducible nitric oxide synthase (iNOS) in rodent but not in human endothelial cells. We recently identified NOS2 as a potential target of the histone methyltransferase enhancer of zeste homolog 2 which mediates trimethylation of histone 3 at lysine 27 (H3K27me3). Methods and results Compared to an unspecific IgG control, chromatin immunoprecipitation using a H3K27me3-specific antibody followed by DNA quantification by PCR showed a strong DNA enrichment — indicating that NOS2 is associated with H3K27me3 in human umbilical vein endothelial cells (HUVEC). siRNA-mediated knock down of Ezh2 diminished NOS2 DNA enrichment — suggesting that the association of NOS2 with H3K27me3 is mediated by Ezh2. Ezh2 knock down, however, was not sufficient to increase iNOS expression after stimulation of HUVEC. Conclusion NOS2 is associated with Ezh2-mediated H3K27me3 in HUVEC. This might contribute to an epigenetic suppression of iNOS inducibility in human endothelial cells.