The Mechanism And Role Of DNMT3a In Activating LINE-1 Through Non-promoter Pathway In Breast Cancer

Breast cancer is the most common(17.1%of all female cancers)cancer in Chinese women.However,drug resistance is one of the major obstacles to chemotherapy success.Long interspersed nuclear element-1(LINE-1)is the only known active autonomous transposon in humans currently.Its abnormal activation in breast cancer will promote cell’s genomic instability.And the genomic instability is not only closely related to the occurrence and the promotion of malignant progression of tumors,but also one of the important factor for the development of drug resistance in breast cancer.Therefore,exploring the causes of abnormal activation of LINE-1 has important practical significance for exploring the development of drug resistance in breast cancer.The methylation of LINE-1 promoter is an important inhibiting mechanism for LINE-1 expression.However our previous research found that the expression of LINE-1 was significantly increased when breast cancer cells treated with paclitaxel(PTX),but meanwhile the methylation of LINE-1 promoter had not significant change.Due to the two modes of "promoter pathway" and "non-promoter pathway" of DNMT3 a activity,our study aims to explore whether DNMT3 a can activate LINE-1 through a "non-promoter pathway" in breast cancer cell lines.Our results show that DNMT3a could bind within the LINE-1 gene body,enhances some spread CpG points methylation and actives LINE-1’s transcription in MDA-MB-231 and MCF-7 breast cancer cells.In addition,we also founded that DNMT3a can activate LINE-1 by enriching on the LINE-1 gene body in the MDA-MB-231 breast cancer cell in response to low concentrations of PTXFinally,we further supported our results with Kaplan-Meier database clinical prognostic analysis,showing that high expression of DNMT3a protein is significantly associated with poor prognosis(lower overall survival and recurrence-free survival.)in patients whom undergoing drug chemotherapy.This study initially explores a new model of LINE-1’s activation,proves the increasing of methylation of LINE-1 gene body mediated by DNMT3a is an important mechanism of abnormal activation of LINE-1,and It also provides some valuable clues for exploring the mechanism of drug resistance.