CEBPB Enhances Plantinum Resistance Of Ovarian Cancer By Reprogramming H3K79 Methylation

Objective: The chemoresistance of tumor cells has been the main course of poor prognosis and high mortality in ovarian cancer.Epigenetics has played a critical role in regulating the malignant phenotype.The main purpose of this study was to find out whether there were specific key factors to regulate multiple drug resistance genes and their potential drug resistance mechanisms.Moreover,we tried to find out whether we could target the key regulators of epigenetics to reverse the chemoresistance of tumor cells.Methods: In order to explore the epigenetic reprogramming of HG-SOC,we performed the genome-scale analysis of the histone methylation patterns with six different histone methylation sites.Before the ChIP-seq and RNA-seq,magnetic separation of tumor epithelial cells and preparation of pooled samples from 20 normal fallopian tube samples and 20 HG-SOC have been performed.In order to identify potential key regulators of histone methylation,we tried to find out if these regulators were correlated with patient prognosis using clinical database and clinical sample information.Various drug resistance experiments in vitro and in vivo have been done to identify if these regulators promoted cisplatin resistance.Integrated bioinformatic analysis with ChIP-seq and RNA-seq have been performed to find out whether these regulators reprogrammed histone methylation to regulate multiple functionally associated genes.Phospho-antibody array and other drug resistance related experiments were performed to identify how CEBPB regulated the malignant phenotype.Results: The differentially expressed genes resulting from the six histone methylation sites were analyzed between serous ovarian cancer and normal control tissue.35 upstream regulatory factors which could modulate the histone methylation were revealed with motif analysis of differentially methylated chromatin.Moreover,CEBPB was highly correlated with H3K79 methylation.Further clinical analysis and bioinformatic analysis confirmed that CEBPB with high expression was associated with cisplatin resistance of tumor cells and poor prognosis.Mechanically CEBPB interacted with DOT1 L and enhanced the DNA binding activity of DOT1 L to regulate the methylation of H3K79.Moreover,CEBPB was mediated by DOT1 L to promote cisplatin resistance of tumor cells.Inhibition or shRNA of CEBPB or DOT1 L which could reduce their expression can reverse the cisplatin resistance of tumor cells.Conclusions: We identified a new path that specific TFs could control multiple functionally related genes by epigenetic reprogramming.As a cofactor of DOT1 L,CEBPB collocated with it to target genes and maintained an open chromatin state of many drug resistance genes.TFs such as CEBPB could modify the chromatin state through the interaction with epigenetic enzymes such as DOT1 L.Our study provides a possibility for developing therapeutic agents targeting CEBPB or the interaction of CEBPB-DOT1 L,and it plays an important role in identifying chromatin-modifying transcriptional factors in cancer.