Downregulation of exosomal miR-7-5p promotes breast cancer migration and invasion by targeting RYK and participating in the atypical WNT signalling pathway

BACKGROUNDCurrent studies show that exosomal miRNAs become an important factor in cancer metastasis. Among the many miRNA studies, miR-7-5p has not been thoroughly investigated in breast cancer metastasis. METHODSBioinformatic screening was performed using extant data from the GEO database, and miR-7-5p expression levels in breast cancer cell lines and exosomes were further examined using real-time quantitative PCR (qRT-PCR). The extracted exosomes were characterised by transmission electron microscopy (TEM), particle size analysis and marker protein determination. Cell migration and invasion were then examined using wound healing assays and Transwell assays, respectively. Correlation between miR-7-5p and receptor-like tyrosine kinase (RYK) was analysed by luciferase reporter. The effect of miR-7-5p against RYK-related downstream factors was verified using western blot assays. RESULTSIn this study, we found that the expression of miR-7-5p was significantly different in exosomes secreted from breast cancer cell lines with different high and low invasiveness. Further experiments revealed that miR-7-5p has an important role in inhibiting the migration and invasion of breast cancer. In terms of mechanism of action, miR-7-5p was found to target the RYK, leading to its reduced expression, which in turn caused a reduction in the phosphorylation level of the downstream factor JNK. Reduced levels of phosphorylated JNK factors lead to reduced levels of phosphorylation of c-Jun protein, which in turn leads to increased expression of EMT transcription factors, thereby inhibiting the epithelial-mesenchymal transition (EMT) process to suppress the invasion of breast cancer. CONCLUSIONThus, we demonstrated that exosomes loaded with high levels of miR-7-5p emitted from less aggressive breast cancers can participate in the atypical WNT pathway by targeting the RYK gene and thus inhibit breast cancer metastasis.