The Study On The Mechanism Of Transcription Factors FOXM1 In The Regulation Of Breast Cancer Stem Cells

Breast cancer is a malignant tumor that occurs in mammary epithelial cells.Breast tumor heterogeneity is one of the characteristics of malignant breast cancer.In the development and progression of breast cancer,cells undergo multiple division and proliferation,and there are cell subpopulation with different proliferation rate,metastasis ability,drug sensitivity,vascular viability and prognosis.Breast cancer stem cells are composed of a subset of tumor cells with abnormal stem cell characteristics in the breast tumor,with the same self renewal ability and pluripotency as normal stem cells,and can produce heterogeneous breast cancer.Therefore,it is very important to study the molecular mechanism of the development of breast cancer stem cells.FOXM1 is a transcription factor produced by the FOXM1 gene that recognizes RYAAAYA specific nucleotide sequences and plays an important role in the development of tumors.In tumor cells,the transcription factor FOXM1 is mainly involved in the cell cycle Gl/S phase and G2/M phase transition and M phase of the process,regulating cell cycle and DNA damage repair,promote angiogenesis and cell migration and other physiological processes.This paper focuses on whether FOXM1 is involved in the development of breast cancer stem cells and its possible mechanism in this process.In order to investigate whether FOXM1 was involved in the development of tumor stem cells,we used Flow cytometry analysis to find that ALDHI+ cell subpopulation in breast cancer MDA-MB-436 cells were significantly higher than those in MCF-7 cells,and the expression of FOXM1 in breast cancer MDA-MB-436 cells were significantly higher than those in MCF-7 cells.The expression of FOXM1 in MDA-MB-436 cells and MCF-7 cells was compared with that in MDA-MB-436 mammosphere cells and MCF-7 mammosphere cells and in ALDH1+ cell subpopulation and ALDH1-cell subpopulation respectively,Which established the relationship between the expression level of FOXM1 and the stem cell characteristics of breast cancer cells.To investigate the expression differences of FOXM1 in breast cancer MDA-MB-436 ALDHI+cell subpopulation,ALDH1-cell subpopulation and MDA-MB-436 parental cells,and MDA-MB-436 mammosphere cells,MDA-MB-436 normal cells,We found that FOXM1 was upregulated in the breast cancer stem cell subpopulation.The lentiviral expression system of hFOXM1 and hFOXM1 shRNA was constructed and infected with breast cancer MCF7 cells and MDA-MB-436 cells.It was found that high expression of FOXM1 could promote the enhancement of stem cell characteristics in breast cancer MCF7 cells and the low expression of FOXM1 could decrease stem cell characteristics in breast cancer in MDA-MB-436 cells.In order to study the mechanism of FOXM1 involved in the regulation of tumor stem cells,we constructed the PFOXM1/EGFP lentiviral FOXM1 tracer expression system based on the FOXM1 promoter sequence,and successfully isolated the breast cancer MDA-MB-436-FOXM1Low cell subpopulation by flow sorting MDA-MB-436-FOXM1High cell subpopulation,and found that breast cancer MDA-MB-436-FOXM1High cell subpopulation tem cell characteristics was significantly stronger than the MDA-MB-436-FOXM1Low cell subpopulation.Sequencing by transcriptome assays the transcriptional expression levels difference in the breast cancer MDA-MB-436-FOXM1High cell subpopulation and the MDA-MB-436-FOXM1Low cell subpopulation,The ALDH1A2 gene was found high expression in the MDA-MB-436-FOXM1Highcell subpopulation,and further study found that transcription factor FOXM1 can be directly involved in ALDH1A2 gene expression regulation by directly bind to the ALDH1A2 promoter-555 to-549,-239 to-233 sites.Using the Protein Atlas database,TCGA database and Kaplan-Meier Plotter database analysis,it was found that FOXM1 was highly expressed in clinical breast cancer samples,and FOXM1 expression was correlated with clinical poor prognosis.It was found that high expression of FOXM1 in clinical breast cancer patients promoted the development of breast cancer.The study found that transcription factor FOXM1 promoted the formation of breast cancer stem cells,and inhibition of FOXM1 expression decreased the breast cancer stem cell characteristics.Breast cancer cells have different cell subpopulations include FOXM1 expression levels,and Breast cancer cell subpopulation include FOXM1 overexpression have the characteristics of tumor stem cells.The FOXM1 regulated the formation of breast cancer stem cells by upregulating the expression of ALDH1A2.