MiR-204-5p/Six1 feedback loop promotes epithelial-mesenchymal transition in breast cancer

Epithelial-mesenchymal transition (EMT) is a vital process in epithelial cancer invasion and metastasis. The induction of EMT by Six1 has been described as a common mode of cancer progression, which could promote breast cancer migration and invasion. In the study, we found that miR-204-5p could suppress the migration and invasion of breast cancer cell lines. Since overexpression of Six1 promote EMT, we identified a mechanism by which miR-204-5p inhibited the EMT by downregulating the Six1, which was mediated by a conserved miR-204-5p seed-matching sequence in the 3'-UTR of Six1 mRNA. We also identified that upregulation of Six1 could downregulate miR-204-5p expression, affecting the migration and invasion of breast cancer cell lines. In conclusion, the frequent upregulation of Six1 and/or downregulation of miR-204-5p in breast cancer may shift the equilibrium of these reciprocal regulations and lock breast cancer cells in the mesenchymal state.