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

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).

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.

Conclusions: NOS2 is associated with Ezh2-mediated H3K27me3 in HUVEC. This might contribute to an epigenetic suppression of iNOS inducibility in human endothelial cells.