Triptolide promotes senescence of prostate cancer cells through induction of histone methylation and heterochromatin formation

Abstract

Background: Triptolide is a medicinal herb-derived diterpene triepoxide with potent anti-tumor activity against a wide range of tumors. The anti-tumor mechanism of this small molecule has been correlated mainly with its ability to inhibit and inactivate subunits of RNA polymerase II, thereby suppressing global gene transcription. Epigenetic imbalance including histone methylation are well known to play important role in Prostate cancer (PCa) onset and progression. The goal of this study was to investigate whether Triptolide performs its anti-PCa activities by reshaping the histone methylation landscape in PCa cells.Methods: Triptolide-treated PCa cell lines were analyzed by RT-qPCR and western blotting to measure the expression of histone methylases; demethylases and associated histone marks. Detection of senescence was done using Senescence Associated β-Galactosidase Staining. Apoptosis and cell cycle analysis were performed by flow cytometry. Senescence –associated heterochromatine foci were detected by Immunofluorescence. Chromatin Immunoprecipitation associated to qPCR (CHIP-qPCR) was used to measure the accumulation of histone marks on the promoters of target genes.Cell viability was assessed using the CCK-8 assay. Results: We found that Triptolide enhances H3K27me3 level by down-regulating JMJD3 and UTX. Triptolide also enhances H3K9me3 level through up-regulation of SUV39H1. Furthermore, Triptolide up-regulates the expression of HP1α. These events promote heterochromatin formation and deposition on the promoters of E2F1-target genes, which correlates with suppression of gene transcription, decreased cell viability and induction of a senescence-like phenotype in PCa cells. Conclusions: Our results indicate that Triptolide performs its anti-tumor effects including PCa cell senescence at least partially through increasing the levels of repressive histone H3 methylation and formation of repressive chromatin state in PCa cells. Our study suggests Triptolide is a potential epigenetic anti-PCa drug