A role for EZH2 in silencing of IFN-gamma inducible MHC2TA transcription in uveal melanoma

• Published in: Journal of Immunology 2007-10, Vol.179 (8), p.5317-5325
• Main Authors: Holling, Tjadine M, Bergevoet, Marloes W T, Wilson, Louis, Van Eggermond, Marja C J A, Schooten, Erik, Steenbergen, Renske D M, Snijders, Peter J F, Jager, Martine J, Van den Elsen, Peter J
• Format: Article
• Language: English
• Subjects: Base Sequence; Cell Line, Tumor; DNA-Binding Proteins - physiology; Enhancer of Zeste Homolog 2 Protein; Gene Expression Regulation, Neoplastic - immunology; Gene Silencing - immunology; Histocompatibility Antigens Class II - biosynthesis; Histocompatibility Antigens Class II - genetics; Humans; Interferon-gamma - physiology; Melanoma - genetics; Melanoma - immunology; Melanoma - metabolism; Molecular Sequence Data; Nuclear Proteins - antagonists & inhibitors; Nuclear Proteins - biosynthesis; Nuclear Proteins - genetics; Polycomb Repressive Complex 2; Promoter Regions, Genetic - immunology; RNA Interference - immunology; Trans-Activators - antagonists & inhibitors; Trans-Activators - biosynthesis; Trans-Activators - genetics; Transcription Factors - physiology; Transcription, Genetic - immunology; Uveal Neoplasms - genetics; Uveal Neoplasms - immunology; Uveal Neoplasms - metabolism
• ISSN: 0022-1767; 1550-6606; 1365-2567
• DOI: 10.4049/jimmunol.179.8.5317

We investigated the contribution of epigenetic mechanisms in MHC2TA transcriptional silencing in uveal melanoma. Although no correlation was observed between impaired CIITA transcript levels after IFN-gamma induction and DNA methylation of MHC2TA promoter IV (CIITA-PIV), an association was found with high levels of trimethylated histone H3-lysine 27 (3Me-K27-H3) in CIITA-PIV chromatin. The 3Me-K27-H3 modification correlated with a strong reduction in RNA polymerase II-recruitment to CIITA-PIV. Interestingly, we observed that none of these epigenetic modifications affected recruitment of activating transcription factors to this promoter. Subsequently, we demonstrated the presence of the histone methyltransferase EZH2 in CIITA-PIV chromatin, which is known to be a component of the Polycomb repressive complex 2 and able to triple methylate histone H3-lysine 27. RNA interference-mediated down-regulation of EZH2 expression resulted in an increase in CIITA transcript levels after IFN-gamma induction. Our data therefore reveal that EZH2 contributes to silencing of IFN-gamma-inducible transcription of MHC2TA in uveal melanoma cells.