Role of melatonin in the modulation of miR-148b and miR-210 in triple-negative breast cell line

Breast cancer has high rates of incidence and mortality, and it is the most common cancer among women. MicroRNAs (miRNAs) are small molecules of non-coding mRNA that play a key role in gene regulation. Recent studies have shown that miRNAs are directly involved in the initiation and progression of various tumor types, including breast cancer. Several miRNAs have been described as promoters or suppressors of metastasis and may be associated with tumor growth and metastasis. Exogenous administration of melatonin, a hormone secreted by the pineal gland, has been shown several oncostatics effects on different types of cancers. Herein, we investigated if the antimetastatic effects of melatonin were coordinated by miRNAs involved in tumor progression. The expression of 384 miRNAs was measured using Taqman Low-density Array (TLDA) cards. Considering the cut-off we imposed (fold change >1.5 and (fold change >1.5 and<0.5) were evidenced the modulation of 17 miRNAs (11 up and 6 down). Among all miRNAs modulated, the selected miR-210 and miR-148b were further confirmed by qRT-PCR and tested for functional investigations. First, we engineered cells for miR-210 or miR-148b overexpression or depletion (stable or transient), then we evaluated the effect of melatonin on c-Myc protein expression and migration. Melatonin reduced c-Myc expression and migration in cell depleted or not for miR-148b. However no effect on c-Myc or migration was observed for cells depleted for miR-148b when compared with control cells. c-Myc and migration were reduced in cells treated with melatonin or expressing anti-miR-210 (depleted). In summary, our results suggest that, even if melatonin alters miRNA expression, the modulations of the miRNAs we studied, miR-210 and miR-148b, are not essential for melatonin inhibition of cell migration and c-Myc expression. One of the hypotheses is that c-Myc is not a target of these miRNAs in MDA-MB-231 cells, and it is believed that melatonin effects on miRNAs could be just “epiphenomenon” due to general Dicer/Drosha deregulations. Nevertheless, melatonin remains a powerful molecule for metastatic traits inhibition, which modulates a set of protein-coding genes, such as c-Myc. However, a direct link between expression modulations of certain proteins or miRNAs and melatonin effects has still to be established. (AU)