Functions And Molecular Mechanisms Of BRD4/JMJD6 In Estrogen Receptor α-dependent Super Enhancer And Its Target Gene Activation

Aberrant levels of estrogen(17β-estradiol,E2)induce the abnormal activation of estrogen target genes,which is an important cause leading to estrogen receptor alpha(ERa)-positive breast cancer.However,the molecular mechanisms of the transcriptional activation of estrogen target genes have not been fully elucidated.Although super enhancer(SE)plays a pivotal role in gene transcriptional regulation as an epigenetic regulatory element,the molecular mechanisms of super enhancer in such regulation in ERa-positive breast cancer are still not fully understood.We focused on studying how super enhancers at the genome in ERα-positive breast cancer cells recruit epigenetic regulators and cofactors to cooperate with estrogen receptors for activation,which further leads to transcriptional activation of cognate coding genes associated with breast carcinogenesis.In the current study,we studied the recruitment of bromodomain containing 4(BRD4)and JmjC domain-containing protein 6(JMJD6)to ERa-bound super enhancers from the perspective of bioinformatics analysis of high-throughput sequencing data,which are key steps of E2/ERa-induced super enhancer activation and cognate target gene transcription.The binding of BRD4 and JMJD6 to ERa-bound super enhancers is required for RNA polymerase Ⅱ(Pol Ⅱ)recruitment and production of enhancer RNAs(eRNAs)on super enhancers,resulting in transcriptional activation of E2-target genes associated with super enhancers.JMJD6 was found to physically interact with mediator complex subunit 12(MED 12)in the Mediator complex to regulate its recruitment.Surprisingly,JMJD6 is necessary for MED 12 to interact with coactivator associated arginine methyltransferase 1(CARM1),which methylates MED 12 at multiple arginine sites and regulates its chromatin binding.Consistent with the critical roles they play in transcriptional activation,BRD4 and JMJD6 are required for E2/ERα-induced breast cancer cell growth and tumorigenesis.Our data have uncovered several critical regulators of E2/ERα-induced super enhancers,genes associated with super enhancers and breast cancer cell growth,providing several promising therapeutic targets for ERa-positive breast cancers.