circHMCU Promotes Proliferation and Metastasis of Breast Cancer by Sponging the let-7 Family

Circular RNA (circRNA), as a kind of novel identified non-coding RNA, has become the focus of attention for its vital physiological and pathological roles. However, the function and mechanism of circRNAs in the regulation of cancer progression are largely unknown. In the present study we found a circRNA termed circHMCU whose expression was associated with poor prognosis. It was upregulated in cell lines with high metastatic potential compared with its parental cell line and in breast cancer tissues compared with normal tissues. In vitro results proved that circHMCU could significantly promote proliferation, migration, and invasion abilities of breast cancer cells via affecting the G(1) phase cell cycle checkpoint and the epithelial-mesenchymal transition (EMT) pathway. Further in vivo studies showed that overexpression of circHMCU contributed to rapid proliferation and lung metastasis of breast cancer. For determination of the mechanisms, bioinformatics analysis revealed two complementary sequences within circHMCU for let-7 microRNAs, which was validated by a luciferase reporter assay. Finally, let-7 microRNAs could rescue the functions of circHMCU in breast cancer via suppressing the expression of MCY, HMGA2, and CCND1. Taken together, our findings demonstrated that circHMCU exerted oncogenic functions in breast cancer and could be a used as a novel biomarker in the diagnosis and prognosis of breast cancer.