Mechanism Of MiR-23a～24-2～27a Cluster Promotes Mammary Carcinoma Cell Invasion And Metastasis

microRNAs (miRNAs) are small noncoding RNAs that regulate the translation of protein coding genes by repressing translation of protein coding mRNA or enhancing mRNA degradation. They are predicted to modulate the expression levels of at least one-third of all human protein coding genes. Current target-prediction computer programs predict that one specific miRNA may target tens to hundreds of genes. Thus, expect that miRNAs play important roles in coordinating many cellular processes. Deregulation of miRNAs has been reported to modulate normal cell growth and differentiation, potentially leading to a variety of disorders including cancer. Thus, the identification of miRNAs that are associated with pathology provides new approaches for understanding disease processes.The miR-23a-24-2-27a cluster is a miRNA cluster, existing intergenically in the vertebrate genome. Members of the cluster are involved in cell cycle control and differentiation, in various cell types. The cluster has also been suggested to play a role in promoting apoptosis by both caspase-dependent and caspase-independent pathways. However, the mechanisms of miR-23a-24-2-27a cluster regulation in cancer progression remains poorly understood. Only a few target genes for the miR-23a-24-2-27a cluster have thus far been identified.Sprouty2(SPRY2), an inhibitor of the Ras/MAPK pathway, is one of four highly conserved family members of Sprouty signal modulatory proteins. SPRY2is recognized to be deregulated in various types of cancers, such as breast, liver and prostate cancer, amongst others. SPRY2might be an important modulator of pathways central to cancer progression, including cell growth, migration and invasion.Using real-time PCR, we detected the expression levels of members of the miR-23a-24-2-27a cluster in clinical specimen of mammary carcinoma and found that the expression levels of members of the miR-23a-24-2-27a cluster were significantly higher in mammary carcinoma with lymph node metastasis compared with that from patients without lymph node metastasis or normal tissue. Next, applying the strategy of vitro and vivo, as well as experimental methods of transwell assay, tail vein injection into nude mice, we observed that the miR-23a-24-2-27a cluster promoted mammary carcinoma cell migration/invasion, moreover, hepatic metastasis. Following, we further described the mechanism by which the miR-23a-24-2-27a cluster contributed to mammary carcinoma cell migration and invasion. By using of luciferase reporter assay, real-time PCR and Western blot, we found the target and signaling pathway of the miR-23a-24-2-27a cluster. We further validate the transcription factor of the miR-23a-24-2-27a cluster. We found c-MYC promoted the transcription and expression of miR-23a-24-2-27a cluster. Finally, we found that treatment with EGF increased the expression of miR-23a-24-2-27a cluster partly by c-MYC. We demonstrated epidermal growth factor (EGF) induced the expression of c-MYC, which increased the expression of mature miR-23a, miR-24-2and miR-27a, subsequently decreased the expression of the target gene, SPRY2, and promoted cell migration/invasion and hepatic metastasis through activation of p44/42MAPK.In summary, we therefore suggest a novel link between epidermal growth factor and the miR-23a-24-2-27a cluster via the regulation of c-MYC, providing the potential for the miR-23a-24-2-27a cluster to be used as biomarker in the diagnosis and/or treatment of breast cancer.