Abstract A57: Dual role of the histone methyltransferase PR-SET7/SETD8 in the local regulation of Pol II promoter-proximal pausing

Abstract

Abstract Tumor suppressor gene silencing in cancers is often achieved through epigenetic mechanisms which involve the hypermethylation of promoter-associated CpG islands and a local shift from permissive to repressive histone modifications. Recently, we showed that epigenetic silencing of the tumor suppressor gene TMS1/ASC in human breast cancer cells is accompanied by a local shift from histone H4 lysine 16 acetylation (H4K16Ac) to H4 lysine 20 trimethylation (H4K20me3). H4K16Ac and H4K20me3 were found to play antagonistic roles in the regulation of RNA polymerase II promoter-proximal pausing, a critical post-initiation regulatory step that controls the rate of release of initiated Pol II into productive elongation and ultimately transcriptional output. We found that H4K16Ac, mediated by the histone acetyltransferase hMOF and acting in the MSL complex, facilitates the release of paused Pol II by promoting the recruitment of the BRD4/pTEFb complex whereas the local deposition of H4K20me3, mediated by the histone methyltransferase SUV420H2, enforces the pause and promotes gene repression by inhibiting the recruitment of MSL and subsequent H4K16Ac. However, how the local balance between hMOF-mediated H4K16Ac and SUV420H2-mediated H4K20me3 is achieved and converge to regulate Pol II pausing remains unclear. Here, we demonstrate that the histone methyltransferase PR-SET7/SETD8, which monomethylates histone H4 lysine 20 (H4K20me1), controls both H4K16Ac and H4K20me3, and as a result, regulates Pol II pausing and release. Specifically, we show that PR-SET7 and/or H4K20me1 is necessary for the local recruitment of the MSL complex, subsequent H4K16Ac and release from pausing. Although dispensable for SUV420H2 recruitment, PR-SET7 is required for SUV420H2-mediated H4K20me3, playing a role in enforcing Pol II pausing and subsequent epigenetic gene silencing. Whereas depletion of SUV420H2 is sufficient to deplete H4K20me3 and relieve H4K20me3-mediated Pol II pausing, pausing is maintained in the absence of PR-SET7 and local H4K20me1 due to a failure to recruit the MSL complex. These findings highlight the requirement for PR-SET7 and H4K20me1 in establishing both the H4K16Ac and H4K20me3 marks and points to its dual role in the regulation of Pol II pausing dynamics. Furthermore, our data suggests that the reversible repression imposed by the local conversion of H4K20me1 to H4K20me3 is a critical intermediate step in the epigenetic silencing of tumor suppressor genes in cancers. Citation Format: Priya Kapoor, Paula M. Vertino. Dual role of the histone methyltransferase PR-SET7/SETD8 in the local regulation of Pol II promoter-proximal pausing. [abstract]. In: Proceedings of the AACR Special Conference on Chromatin and Epigenetics in Cancer; Jun 19-22, 2013; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2013;73(13 Suppl):Abstract nr A57.