Downregulation of BCL2 by miRNAs augments drug-induced apoptosis--a combined computational and experimental approach.

A number of anti-cancer strategies aim to target the mitochondrial apoptotic machinery to induce tumour cell death. Mitochondria play a key role as death amplifiers by releasing apoptogenic factors from the mitochondrial inter-membrane space into the cytosol. BCL2 proteins are known for their ability to regulate both mitochondrial physiology and cell death, and their deregulated expression often renders cancer cells insensitive to apoptosis-inducing anticancer drugs. Recently, a few microRNAs, a novel class of gene regulators, have been demonstrated to regulate expression of some members of the BCL2 family. Here, we have combined computational and experimental approaches to identify miRNAs that can regulate the anti-apoptotic protein BCL2. We report that miR-195, miR-24-2 and miR-365-2 act as negative regulators of BCL2 through direct binding to their respective binding sites in the 3'-UTR of the human BCL2 gene. Ectopic expression of miR-195, miR-24-2 and miR-365-2 individually led to a significant reduction of the levels of BCL2 protein. Additionally, we found that overexpression of these miRNAs induced dissipation of the mitochondrial membrane potential and release of cytochrome c from mitochondria into the cytosol. Furthermore, we demonstrated that overexpression of these miRNAs not only caused an increase in apoptosis but also augmented the apoptotic effect of etoposide in breast cancer MCF7 cells. These data not only show the apoptotic nature of miR-195, miR-24-2 and miR-365-2 but also highlight the therapeutic potential of these miRNAs.