TR-FRET Cellular Assays for Interrogating Posttranslational Modifications of Histone H3

Posttranslational modifications such as phosphorylation, acetylation, and methylation play important roles in regulating the structures and functions of histones, which in turn regulate gene expression and DNA repair and replication. Histone-modifying enzymes, such as deacetylases, methyltransferases and demethylases, have been pursued as therapeutic targets for various diseases. However, detection of the activities of these enzymes in high-throughput cell-based formats has remained challenging. The authors have developed high-throughput LanthaScreen cellular assays for Histone H3 site-specific modifications. These assays use cells expressing green fluorescence protein-tagged Histone H3 transiently delivered via BacMam and terbium-labeled anti-Histone H3 modification-specific antibodies. Robust time-resolved Förster resonance energy transfer signals were detected for H3 lysine-9 acetylation and dimethylation (H3K9me2), serine-10 phosphorylation, K4 di- and trimethylation, and K27 trimethylation. Consistent with previous reports, hypoxic stress increased K4 methylation levels, and methyltransferase G9a inhibitor UNC-0638 decreased K9me2 levels significantly, with little effects on other modifications. To demonstrate the utility of this assay platform in screening, the K9 acetylation assay was used to profile the Enzo Epigenetics Library. Twelve known HDAC inhibitors were identified as hits and followed up in a dose-response format. In conclusion, this assay platform enables high-throughput cell-based analysis of diverse types of posttranslational modifications of Histone H3.