Suppression of <scp>mTOR</scp> Signaling by <scp>miR</scp> ‐302/367 Cluster in Breast Cancer Cells

The mTOR signaling pathway is central in regulating key cellular functions, including cell cycle progression, protein synthesis, and glucose metabolism. Dysregulation of this pathway is a hallmark of many cancers. We previously demonstrated the multimodal tumor suppressive effects of the miR-302/367 cluster. In this investigation, we explored the effects of exogenous overexpression of the miR-302/367 cluster on mTOR signaling in malignant cells and assessed its direct targeting of pathway components. Bioinformatic analyses revealed PIK3CB, RRAGD, FNIP1, and FNIP2 as potential targets of miR-302/367 involved in mTOR regulation. Dual-luciferase reporter assays validated the direct interaction between the miR-302/367 cluster with PIK3CB, RRAGD, and FNIP1. Transfection of SK-BR-3 and MDA-MB-231 breast cancer cell lines with a vector expressing miR-302/367 resulted in the downregulation of these three genes at the transcript level. Furthermore, the protein levels of FNIP1, RRAGD, and PIK3CB were also diminished in both cell lines. Additionally, cell proliferation was inhibited, and profiling of gene and protein expression indicated a downregulation of several other components of the mTOR pathway, suggesting a broad inhibitory effect of miR-302/367 on mTOR signaling. These results reveal a novel molecular mechanism by which the miR-302/367 cluster may exert tumor-suppressive effects by modulating mTOR pathway activity at multiple levels in breast cancer cells, thereby suggesting its potential relevance for future therapeutic investigation in cancer treatment.