Myc down-regulation induces apoptosis in M14 melanoma cells by increasing p27(kip1) levels

In recent years, increasing evidence indicated the importance of a deregula ted c-myc gene in the melanoma pathogenesis, We have previously demonstrate d that treatment of melanoma cells with c-myc antisense oligodeoxynucleotid es can inhibit cell proliferation and activate apoptosis, To gain insight i nto the mechanisms activated by Myc down-regulation, we have now developed an experimental model that allows modulating Myc protein expression in mela noma cells. This was achieved by originating stable melanoma cell clones ex pressing ecdysone-inducible c-myc antisense RNA. We show that the induction of c-myc antisense RNA in M14 melanoma cells leads to an inhibition of cel l proliferation characterized by accumulation of cells in the G(1) phase of the cell cycle (up to 80%) and activation of apoptosis (50%), These data a re associated with an increase of p27(kipl) levels and a significant reduct ion of the cdk2-associated kinase activity, In addition, we show that an ec topic overexpression of p27(kiPl) in this experimental model can enhance th e apoptotic rate. Our results indicate that down-regulation of Myc protein induces a G(1) arrest and activates apoptosis by increasing p27(kipl) conte nt in melanoma cells, that are known to be defective for the p16-cyclinD/cd k4-pRb G(1) checkpoint. This is particularly relevant for identifying new t herapeutic strategies based on the re-establishment of the apoptotic pathwa ys in cancer cells.