Function And Mechanism Of Breast Cancer Secreted MiR-199b In Cancer Cell Brain Metastasis

Background:Breast cancer is the most common malignancy in women.Now,the metastasis of distant organs is the leading cause of death in breast cancer patients.The most common distant metastatic organs of breast cancer are the lungs,bones and brain.Among them,breast cancer-brain metastasis is a poor therapeutic effect,which brings a huge challenge for the clinical treatment of breast cancer.Breast cancer-brain metastasis involves multiple complex biological processes.The molecular mechanism of brain metastasis in breast cancer is not fully understood right now.Therefore,further revealing the molecular mechanism of breast cancer-brain metastasis provides important clinical significance for the early diagnosis and treatment of breast cancer-brain metastasis.Malignant tumors can reprogram distant organs through secreted exosomes before metastasis,thereby developing the microenvironment of distant organs into an environment conducive to tumor cell growth.The phenomenon of "cross-talk" between this tumor cell and the pre-metastatic niche is currently considered to be one of the important reasons for the distant metastasis of malignant tumor.This study is based on the assumption that breast cancer cells can be metabolically reprogrammed by exosomes to transform the brain tissue into an environment conducive to cancer cell growth.It was found that miR-199 b secreted by breast cancer cells is positive related to brain metastasis of breast cancer,and the expression level of miR199 b in serum samples of patients with breast cancer brain metastasis is significantly increased.Next,the mechanism of breast cancer-brain metastasis was revealed by in vitro,in vivo experiments and metabolomics analysis.The results suggest that miR-199 b secreted by breast cancer can support breast cancer cells by intercepting the nutrients of neuron-glial cells.This study reveals a new mechanism of breast cancer-brain metastasis from the perspective of tumor cell-brain tissue metabolic microenvironment,and provides a new idea for the early diagnosis and treatment of breast cancer-brain metastasis.Methods:Firstly,the serum samples of breast cancer brain metastases,bone metastases and patients with different stages were collected,and microRNAs related to brain metastasis,miR199 b,were analyzed by deep sequencing.The expression levels of miR199 b in intracellular and exosomes of common breast cancer cell lines,breast cancer brain metastasis cell lines and breast cancer bone metastasis cell lines were compared with normal epithelial cells of breast cancer.The difference in intracellular and exosomal expression levels of miR-199 b in normal mammary epithelial cells and different types of breast cancer cell lines was examined.Then we analyzed the genes targeted by miR-199 b through "TargetScan" and "microRNA.org",and we are intrested in the nutrient transporters of brain cells.Next,in vitro,through double luciferase assay,Western bot assay and mRNA analysis,these nutrient transporters were identified as target genes regulated by miR-199 b.Through the detection of nutrient uptake by brain cells and the metabolic analysis of conditioned medium,we tested whether miR-199 b can affect the up take of nutrients by neuron-glial cells.Through different animal models and metabolomics analysis,it is verified whether miR-199 b can promote brain metastasis in breast cancer and the effect of miR-199 b on brain microenvironment metabolism.Results:Through deep sequencing of patient serum samples,we found that circulating expression of miR-199 b was specificity positively correlated with breast-brain metastasis.Further in vitro experiments showed that miR-199 b secreted by breast cancer cells can be absorbed by neuron-glial cells and affect the expression of nutrient transporters on the cell surface,and also affects some nutrients up take.Animal models and metabolomics analysis have shown that breast cancer secretion of miR-199 b can promote breast cancer-brain metastasis by regulating the metabolic microenvironment of brain.Conclustion:These results suggest that miR-199 b secreted by breast cancer is positively related to breast cancer-brain metastasis and is expected to be a serum marker for predicting breast cancer-brain metastasis.Breast cancer secreted miR-199 b can locate in brain tissue through the circulatory system and is taken up by neuron-glial cells into neuro-glial cells which can intercept its nutrients.This leads to the accumulation of these nutrients in the brain tissue microenvironment,thus providing a favorable growth environment for brain metastasis cells of breast cancer.