The abnormal expression of several
microRNAs has a causal role in
tumorigenesis with either
antineoplastic or oncogenic functions. Here we demonstrated that miR-126 and miR-126* play a
tumor suppressor role in human
melanoma through the direct or indirect repression of several key oncogenic molecules. The expression levels of miR-126&126* were elevated in normal melanocytes and primary
melanoma cell lines, whereas they markedly declined in metastatic cells. Indeed, the restored expression of miR-126&126* in two advanced
melanoma cell lines was accompanied by a significant reduction of proliferation, invasion and chemotaxis in vitro as well as of growth and dissemination in vivo. In accordance, the reverse functional effects were obtained by knocking down miR-126&126* by transfecting antisense LNA
oligonucleotides in
melanoma cells. Looking for the effectors of these
antineoplastic functions, we identified ADAM9 and MMP7, two
metalloproteases playing a pivotal role in
melanoma progression, as direct targets of miR-126&126*. In addition, as ADAM9 and MMP7 share a role in the proteolytic cleavage of the
HB-EGF precursor, we looked for the effectiveness of this regulatory pathway in
melanoma, confirming the decrease of
HB-EGF activation as a consequence of miR-126&126*-dependent downmodulation of ADAM9 and MMP7. Finally, gene profile analyses showed that miR-126&126* reexpression was sufficient to inactivate other key signaling pathways involved in the oncogenic transformation, as PI3K/AKT and MAPK, and to restore melanogenesis, as indicated by KIT/MITF/TYR induction. In view of this miR-126&126* wide-ranging action, we believe that the replacement of these
microRNAs might be considered a promising therapeutic approach.