Upregulation of hsa_circ_0136666 contributes to breast cancer progression by sponging miR‐1299 and targeting CDK6

Circular RNAs (circRNAs) can participate in multiple cancers, including breast cancer. Increasing circRNAs are recognized in various cancers because of the high‐throughput sequencing. However, the potential physiological effect of hsa_circ_0136666 in breast cancer progression is unknown. In our study, the biological role of hsa_circ_0136666 in breast cancer development was studied. It was displayed that hsa_circ_0136666 was greatly increased in breast cancer. In addition, overexpression of hsa_circ_0136666 was able to promote Michigan Cancer Foundation‐7 (MCF7) and BT474 cell proliferation and triggered cell cycle in G2/M phase. microRNA plays critical role in tumor development and they can act as direct targets of circRNAs. miR‐1299 has been implicated as a famous tumor suppressor in many cancers. Here, miR‐1299 was predicted as the target of hsa_circ_0136666. Meanwhile, its Upregulation repressed breast cancer proliferation, migration and invasion capacity, which could be reversed by the increase of hsa_circ_0136666. Furthermore, Cyclin‐dependent kinase 6 (CDK6) was speculated as the downstream target of miR‐1299. In MCF7 and BT474 cells, CDK6 was greatly overexpressed and it was shown that CDK6 contributed a lot to breast cancer progression. Subsequently, it was implied that hsa_circ_0136666 could modulate CDK6 levels positively in vitro. In conclusion, it was revealed that Upregulation of hsa_circ_0136666 promoted breast cancer progression by sponging miR‐1299 and targeting CDK6. We predicted cyclin‐dependent kinase 6 (CDK6) as the target of miR‐1299 using bioinformatics analysis. The association between them was proved in our research and miR‐1299 inhibitors increased the expression of CDK6, and it was exhibited that overexpression of CDK6 was able to induce breast cancer progression and hsa_circ_0136666 modulated its expression positively. Taken these together, our data implied that hsa_circ_0136666/miR‐1299/CDK6 axis was involved in breast cancer and hsa_circ_0136666 might act as a biomarker for breast cancer treatment.