C-C Chemokine receptor type7 (CCR7), plays an important role in chemotactic and metastatic responses in various cancers, including breast cancer. In this study, we demonstrated that microRNA Let-7a down-regulates CCR7 expression and directly influences the migration and invasion of breast cancer cells.

We detected the expressions of CCR7, its ligand CCL21, and Let-7a in breast cancer cell lines and in breast cancer patient tissues. We used synthetic Let-7a oligo-nucleotides and inhibitor of Let-7a and transfection into respective MDA-MB-231 and MCF-7 breast cancer cells and performed the cell proliferation, cell migration and invasion assays. For the confirmed that 3-UTR of CCR7 is a direct target of Let-7a by employing luciferase assay for the reporter gene expressing Let-7a binding sites of CCR7 3-UTR. We also established in vivo invasion animal model using transparent zebrafish embryos to detect the effect of Let-7a on in vivo system.

First, we determined the over-expression of CCR7 in both and higher expression of CCL21 in malignant tissues than in their normal counterparts in breast cancer patients. We also detected the reverse-correlation in expression of CCR7 and Let-7a in breast cancer cell lines and breast cancer patient tissues. Synthetic Let-7a decreased breast cancer cell proliferation, migration and invasion as well as CCR7 protein expression in MDA-MB 231 cells. Inhibitor of Let-7a reversed these Let-7a effects on breast cancer cells in MCF-7 cells. It was confirmed that 3-UTR of CCR7 is a direct target of Let-7a by employing luciferase assay for the reporter gene expressing Let-7a binding sites of CCR7 3-UTR. Interestingly, we analyzed the in vivo invasion, which MDA-MB231 cells after synthetic Let-7a oligo-nucleotides transfection could not invade into the vessels in zebrafish embryos.

These results suggest that targeting of CCL21-CCR7 signaling is a valid approach for breast cancer therapy and Let-7a directly binds the 3-UTR of CCR7 and blocks its protein expression, thereby suppressing migration and invasion of human breast cancer cells. Furthermore, this study underscores the therapeutic potential of Let-7a as an anti-tumor and anti-metastatic manager in breast cancer patients.

The complete article is available as a provisional PDF. The fully formatted PDF and HTML versions are in production.