In bone metastasis miR-34a-5p absence inversely correlates with Met expression, while Met oncogene is unaffected by miR-34a-5p in non-metastatic and metastatic breast carcinomas

The highlight of the molecular basis and therapeutic targets of the bone-metastatic process requires the identification of biomarkers of metastasis colonization. Here, we studied miR-34a-5p expression, and Met-receptor expression and localization in bone metastases from ductal breast carcinomas, and in ductal carcinomas without history of metastasis (20 cases). miR-34a-5p was elevated in non-metastatic breast carcinoma, intermediate in the adjacent tissue and practically absent in bone metastases, opposite to pair-matched carcinoma. Met-receptor biomarker was highly expressed and inversely correlated with miR-34a-5p using the same set of bone-metastasis tissues. The miR-34a-5p silencing might depend on aberrant-epigenetic mechanisms of plastic-bone metastases, since in 1833 cells under methyltransferase blockade miR-34a-5p augmented. In fact, 1833 cells showed very low endogenous miR-34a-5p, in respect to parental MDA-MB231 breast carcinoma cells, and the restoration of miR-34a-5p with the mimic reduced Met and invasiveness. Notably, hepatocyte growth factor (HGF)-dependent Met stabilization was observed in bone-metastatic 1833 cells, consistent with Met co-distribution with the ligand HGF at plasma membrane and at nuclear levels in bone metastases. Met-protein level was higher in non-metastatic (low grade) than in metastatic (high grade) breast carcinomas, notwithstanding miR-34a-5p-elevated expression in both the specimens. Thus, mostly in non-metastatic carcinomas the elevated miR-34a-5p unaffected Met, important for invasive/mesenchymal phenotype, while possibly targeting some stemness biomarkers related to metastatic phenotype. In personalized therapies against bone metastasis, we suggest miR-34a-5p as a suitable target of epigenetic reprogramming leading to the accumulation of miR-34a-5p and the down-regulation of Met-tyrosine kinase, a key player of the bone-metastatic process.