The Expression Of MicroRNA-597 In Breast Cancer And Its Regulation Mechanism

BackgroundsBreast cancer is one of the most malignant cancers worldwide among women.Despite both basic scientists and clinical researchers had done many investigations on breast cancer,the prognosis remains unfavorable.Micro RNAs(miRNAs)are 20-25-nt-long highly conserved non-coding RNAs that bind to sequences within the 3' untranslated region(3' UTR)of m RNAs and post-transcriptionally regulate the expression of target genes.Recent studies have revealed that micro RNAs are involved in a broad range of biological processes through their regulation of complex signal transduction pathways.More than 50% of human miRNAs are located at fragile sites and genomic regions involved in cancers and can lead to the dysregulation of oncogenes and tumor suppressors.There is only one study on miR-597 in pediatric patients with immune thrombocytopenic purpura,but there have been no study on the function of miR-597 in breast cancer.Fos-related antigen 2(FOSL2),also name FRA-2,belongs to the AP-1 transcription factor family which includes the various isoforms of Fos and Jun.Some studies have indicated that FOSL2 exerts a specific function in bone development and appears to associate with diverse physiological and pathological processes,such as photoperiodic regulation,fibrosis,and even in cancer.More recently,FOSL2 has been documented as a key determinant of cellular plasticity during CD4 T cell differentiation.Several previous studies have indicated that FOSL2 plays a key role in the regulation in some pathway,such as TGF-? pathway,for example,FOSL2 induce TGF-? expression as a transcriptional regulator in cardiac fibroblasts.In human breast cancer,FOSL2 expression has been reported to enhance invasive properties,but there have been little studies on the other function of FOSL2 in breast cancer.ObjectivesTo analyze miR-597 expression in breast cancer,specifically its effects on cell proliferation,migration and invasion,and to explore the mechanism of this process.Methods1.Real-time quantitative PCR was used to detect the expression level of miR-597 in the selected 38 cases of pathologically confirmed pair-matched tumors and adjacent non-tumor esophageal tissue samples as well as cell lines MDA-MB-231 and SK-BR-3.2.The proliferation ability in vitro was detected by MTT assay,Ed U assay and cell cycle assay while the migration and invasion ability was measured by wound healing assay and transwell invasion assay respectively after instantaneously transfected with miR-597-mimic.3.Bioinformatics methods were used to predict the targets of miR-597.The real-time quantitative PCR,the dual-luciferase reporter assay and Western Blot were used for identification.The knockdown assay and rescue assay were used for further confirmation.4.The immunohistochemistry and real-time quantitative PCR were used to study the correlation of FOSL2 and miR-597.Results1.As compared with adjacency non-tumor tissues,the expression level of miR-597 in breast cancer tissue is down-regulated,so were in the esophageal cancer cell lines MDA-MB-231 and SK-BR-3.2.Compared to control,the proliferation of miR-597 overexpressing MDA-MB-231 and SK-BR-3 cells was obviously inhibited in vitro,so were migration and invasion.3.FOSL2 is the putative candidate target gene of miR-597.4.The expression of FOSL2 was negatively correlated with that of miR-597 in breast cancer tissues.ConclusionmiR-597 possibly played a role as anti-oncogene in the developing process of breast cancer.It remarkably inhibited the proliferation,migration and invasion of SK-BR-3 and MDA-MB-231 cell lines by inhibiting the expression of FOSL2 through targeting its 3'UTR.