The Functional Study Of MiR-502 By Targeting Set8 In Breast Cancer

Purpose: Breast cancer is the most common neoplasm among female.Environmental exposure,individual genetic susceptibility and epigenetic alteration are playing a vital part in the pathogenesis of breast cancer.micro RNAs(miRNA)can regulate more than 30% of human genes,as an important epigenetic regulator it can be oncogenes or tumor suppressors.Our previous study based on a large population firstly found that 3’-untranslated regions(UTRs)region of SET8 had been assumed as a potential binding site of miR-502,rs16917496 was in this region and associated with early onset of breast cancer,indicating that SET8 might be regulated by miR-502.Currently,the possible link may exist between miR-502 and SET8 as well as clinical significance of these two molecules in breast cancer are unclear.In this study,we studied the interaction between miR-502 and SET8,the function of miR-502-SET8 in breast cancer as well as the clinical significance of them.Support the pursuit of miR-502 as a potential treatment target for breast cancer.Method: 279 female patients in this study were diagnosed and histologically confirmed primary breast cancer at Tianjin Medical University Cancer Institute and Hospital.The clinicopathological characteristics of each participant were obtained by epidemiology survery or extracted from medical records.All patients were followed-up after surgery through clinical visit and regular telephone contract.Real-time quantitative PCR was used to exam the relative expression of miR-502 and SET8 in 279 breast cancer tumors.Among 279 breast cancer patients,60 breast cancer tumors have adjacent normal tissues.Western bloting assay detected the protein expression of SET8.The relationship between the expression of miR-502,SET8 and clinicopathological characteristics was analyzed by Chi-square test.Survival analysis(including overall survival and disease-free survival)was analyzed by Kaplan-Meier method.The results from Luciferase reporter assay and two expression detection experiments were used to analyze whether SET8 is the direct target gene of miR-502.Cell proliferation,cell cycle,migration and invasion assays were used to analyse the function of miR-502/SET8 in breast cancer.All experiments should be repeated no less than three times,and P-values less than 0.05 were regarded as statistically significant.Result: 1、The relative expression of miR-502 was significantly downregulated in breast cancer tissues than adjacent non-tumor tissues(P<0.0042).In breast cancer tissues the m RNA expression and protein expression of SET8 was higher in breast cancer tissues than adjacent non-tumor tissues(P<0.0001 and P=0.0531).In breast cancer tissues the expression of miR-502 negatively correlated with that of SET8(Pearson r=-0.19,P=0.0014).The RNA expression of miR-502 was significantly associated diagnosed age,menopausal status and the expression of proliferating cell nuclear antigen(PCNA)(P=0.027,0.042,0.020 respectively).The cases with low expression of miR-502 had poorer OS and DFS compared with those with low expression while non-significant was(Log-rank test P=0.298 and 0.741,respectively).In addition,the m RNA expression of SET8 was associated with Estrogen Receptor(ER)status and the expression of PCNA(P=0.025 and 0.015 respectively).The cases with high expression of SET8 had poorer overall survival(OS)and disease-free survival(DFS)than low expression of SET8(Log-rank test P=0.049 and 0.0017,respectively).2、Luciferase reporter assay showed that miR-502 can directly target SET8.This result also validated by Real-time RT-PCR and western blot assay separately.we found that miR-502 can directly target SET8,negatively regulate the expression of SET8.By targeting SET8,miR-502 can cause breast cancer cell cycle arrest in S phase,suppress the proliferation,migration,invasion as well as the process of Epithelial-Mesenchymal Transition(EMT)of breast cance cells.Conclusion: miR-502 as well as SET8 are assiciated with development and prognosis of breast cancer.By targeting SET8,miR-502 can cause breast cancer cell cycle arrest in S phase,suppress the proliferation,migration,invasion as well as the process pf Epithelial-Mesenchymal Transition(EMT)of breast cance cells.These results support the presumption that miR-502 could be a potential therapeutic target for breast cancer.