TET1-mediated Gene Body's Transcriptional Regulatory Network And Molecular Mechanism

DNA methylation as a silent epigenetic marker was first proposed in the 1970 s,and the hypermethylation of gene promoters leading to the inactivation of oncogene expression was considered a common feature of most tumors.Tumor cells can be reprogrammed to a more normal state by using DNA demethylating drugs,such as 5-aza-2 '-deoxycytidine(DAC),which have been used clinically in cancer treatment.However,the therapeutic effect of DAC is not ideal.For solid tumors,DAC is significantly less effective than for hematologic diseases.Even in patients with myelodysplastic syndrome,which is used as a first-line treatment,only about 50 percent of patients treated with DAC achieved a clinical response.Studies have shown that only a small number of DAC demethylated genes are activated,and many genes with hypermethylated promoters are still actively expressed,suggesting that the mechanisms controlling gene expression are more complex than we know.Previous studies have identified different transcriptional subtypes of the same gene associated with cancer.However,the mechanism by which these isomers are produced remains unclear.Here,we used RRBS and RNA-seq techniques to find a mismatch between promoter methylation and gene expression.Further studies showed that exon transcription was significantly correlated with methylation levels in the nearby CpG island(CGIs).Based on these results,we hypothesized that it was possible to initiate exon transcription by "putative promoters" in genes,and this was confirmed by dual luciferase reporter expression assay and RNA polymerase microarray.We also demonstrated that promoter-like activity is affected by adjacent CGIs,which are not sensitive to DAC but can be demethylated by the hydroxymethylase TET1.TET1 is involved in DNA demethylation through repeated oxidation of 5-methylcytosine(5mC)to 5-methylmethylcytosine(5hmC),so this activity is associated with cancer progression.The mutation or low expression of TET1 and the decrease of 5hmC in different genomic regions occur not only in hematologic malignancies,but also in solid cancers.However,the understanding of how TET1 and 5hmC affect tumor gene expression is still insufficient.This study is the first to reveal the function of TET1 and components in gene transcriptional regulation.In addition,we revealed a new mechanism by which histone H3K36me3 methylation may affect putative promoter activity.5hmC recruited Me CP2 and CREB1 as co-activators of SETD2 promoter,enhanced their gene expression,and led to increased expression of H3K36me3 in the genome.Our results suggest that putative promoters exist in the genome,and that TET1 can influence the presumed transcriptional activity of promoters through gene body demethylation.With the emergence of a large number of genome sequence data,it is very important to fully understand the transcription initiation process and to characterize and predict the promoter sequence.