miRNAs from Zebrafish Embryo Extracts Inhibit Breast Cancer Invasiveness and Migration by Modulating miR-218-5p/PI3K Pathway.

Herein, we demonstrate that soluble factors extracted from the distinct phases of the development of zebrafish embryos (ZFEs) exhibit a specific miRNA profile. We removed proteins and concentrated miRNAs in different phase-related samples, which we investigated further. We observed that ZFEs modulate miRNA expression in both normal and cancerous breast cells, significantly inhibiting the invasiveness and motility of triple-negative breast cancer cells. Namely, ZFEs reactivate the synthesis of miR-218-5p in cancerous cells, leading to the downregulation of PI3K, which consequently alters the distribution of phosphoinositides (such as PIP2/PIP3). Moreover, the silencing of miR-218-5p abolished the ZFE effects. Restoring a proper PIP2/PIP3 ratio is crucial for promoting the regression of the malignant phenotype. Phenotypic reversion follows the extensive cytoskeleton rearrangement and the re-emergence of E-cadherin/β-catenin complexes. In addition, ZFEs antagonize the Epithelial Mesenchymal Transition (EMT) by modulating several pathways, including the TCTP-p53 axis. Overall, these results show that embryo extracts enriched with fish miRNAs reactivate endogenous miR-218-5p in cancerous cells, which in turn downregulates critical pathways involved in tumor progression and metastasis.