Final Activity Report Summary - DNA DAMAGE - RNAi (Identification and characterization of novel genes involved in DNA damage- response pathways in humans) In the scientific project described here, I identified microRNA genes (miRNAs, miRs) that are potent promoters of human cancers. miRNA genes encode short RNAs that are widely expressed in multi-cellular organisms. They suppress the expression of protein coding-genes, which encode messenger RNAs (mRNAs) that bear fully or partially complementary sequences to that of the miRNAs. Typically, hundreds of potential protein coding target genes are predicted for each miRNA. While approximately 450 human miRNA genes were found so far, the function of only a handful of them has been determined. We recently performed a functional genetic screen for miRNAs that mediate bypass of cellular senescence, induced by the activation of cancer promoting genes (oncogenes). (Senescence is a cancer defence mechanism, which leads to proliferation arrest and eventually cell death.) We discovered that miR-372 and miR-373 can induce the tumourigenic transformation of primary (non-cancerous) human cells, and described their involvement in the development of testicular germ cell tumours. Our experiments demonstrated the power of miRNAs to change cellular fate, and exemplified the potential of miRNA-genetic screens to identify cancer relevant genes.In order to identify and characterise miRNAs that are potential oncogenes, I performed a large-scale assay, in which I introduced into primary cells each of the known human miRNA genes, and examined their capacity to promote the tumourigenic transformation of these cells. I performed experiments to identify relevant target genes to the miRNAs identified in the screen, using target-predicting software and different experimental approaches that can select for possible target mRNA-candidates. Furthermore, I examined cellular pathways that were affected by these miRNAs, in order to uncover their mechanism of action in promoting human cancer.With the identification of hundreds of miRNAs in the human genome that can potentially target thousands of protein coding genes, only a few of which with a known function, it becomes clear that systematic searches for miRNA functions should be performed. In my research I carried out genetic screens to identify and characterise miRNAs with the capacity to induce transformation of primary human cells. I believe that these experiments will enable us to identify miRNAs with cancer relevant functions and uncover their relevant target genes and their mechanism of action. The results of this research may contribute to the development of better diagnostic tools and to a better understanding of the efficiency of cancer therapy. In the future, these miRNAs might be used for designing better cancer therapeutics, due to their unique molecular properties (i.e. their small size and molecular specificity).
