The Role Of PRMT5 In The Prognosis Of Breast Cancer Patients

Background: Breast cancer is the most common malignant tumors among female patients worldwide,it is also the second cause of fatality in female malignant tumors.There are many factors that affect the prognosis of breast cancer patients,including tumor histological type,hormone receptor status,age,pregnancy and breastfeeding.Recent studies have considered some oncogenes and their expression products as new factors in the development of breast cancer.Protein arginine methyltransferase 5(PRMT5)is a member of the protein arginine methyltransferase family,existing universally in the cytoplasm and nucleus.It can covalently modify histone and non-histone proteins and maintain numerous cellular regulatory networks.Besides,it was reported to be an oncoprotein that participates in tumor progression through both epigenetic silencing and organelle biogenesis.However,research on the biological role and clinical significance of PRMT5 in breast carcinoma was limited.The aim of this study was to investigate the expression of PRMT5 in breast cancer and to explore its role in the prognosis of breast cancer,and to confirm the biological role of PRMT5 in breast cancer cells by in vitro experiments.Objective: To investigate the expression of PRMT5 in breast cancer and to explore its role in the development and prognosis of breast cancer.Methods:1.The expression of PRMT5 in breast cancer specimens(1)Western-blot was used to detect the protein expression of PRMT5 in primary breast cancer,metastatic breast cancer and normal breast tissue.(2)Immunohistochemical staining was performed to detect the expression of PRMT5 and Ki-67 in different breast cancer tissues in breast cancer microarrays and the expression of the two was semi-quantitatively analyzed.2.The correlation of PRMT5 expression and breast cancer patients’ prognosis We analyzed the relationship between breast cancer patients’ PRMT5 mRNA expression levels and patient survival rates in TCGA database.3.The mechanisms of PRMT5 affecting the prognosis of breast cancer patients(1)We constructed PRMT5 overexpression and knockdown human breast cancer MDA-MB-231 cell lines,western-blot was performed to identify PRMT5 protein levels in transfected cells.(2)MTT,flow cytometry,and western-blot were performed to verify the proliferative ability,cell cycle progression,cell apoptosis,and the expression of apoptosis-related protein in post-transfected cells to detect the effect of PRMT5 on the biological function of human breast cancer MDA-MB-231 cells.Results:1.We found that the protein level of PRMT5 in normal breast tissues was significantly lower than that in primary and metastatic breast cancer tissues both in fresh breast cancer tissue and breast cancer tissue arrays.Immunohistochemical staining showed that in breast cancer tissues Ki-67 was positively correlated with PRMT5 expression.The expression of PRMT5 in group with high Ki-67 expression was higher than that group with low Ki-67 expression.2.We analyzed the primary breast cancer and normal specimens in TCGA database and found that PRMT5 mRNA level in normal specimens was significantly lower than that in primary breast cancer patients.The relapse free survival(RFS)in breast cancer patients with high PRMT5 expression was significant lower than those patients with low PRMT5 expression.In HER-2 positive breast cancer and TNBC,PRMT5 expression was negatively correlated with overall survival(OS).Besides,there was no significant corrrelation between PRMT5 expression and Luminal type breast cancer survival.3.MTT assay showed that the growth rate of MDA-MB-231-PRMT5 cells was significantly faster than that of the control group from Day 4,while the growth rate of MDA-MB-231-shPRMT5 cells was slowed down on the fourth day.Flow cytometry showed that the number of S phase cells increased and the number of G2 phase cells decreased after PRMT5 overexpression.No significant changes were observed in cell apoptosis in MDA-MB-231-PRMT5 cells compared with negative control cells.After PRMT5 knockdown,the number of S phase cells decreased,the number of G1 phase cells increased.At the same time,cell apoptosis rate increased,the expression of cleaved caspase 3 and PARP increased,and the expression of Bcl-2 decreased.Moreover,the expression of p-ERK in MDA-MB-231-shPRMT5 cells was lower than that in control cells.Conclusions: PRMT5 is highly expressed in breast cancer patients,and the prognosis of PRMT5 overexpressed patients is poor.PRMT5 can regulate the proliferation,apoptosis and cell cycle progression of breast cancer cells,and then participate in the development of breast cancer.