Posters

Aim: The Mitogen-Activated Protein Kinase (MAPK) pathway and the AKT pathway regulate cell growth, survival and migration through the transduction of signals from the cell surface to the nucleus. Both signaling pathways are deregulated in many human cancers and in the majority of melanomas. Single point mutations in N-RAS, a membrane-bound GTPase leads to the activation of both pathways. The aim of our research project was to elucidate the impact of N-RAS activation on melanocyte growth and survival. Methods: We utilized normal primary human melanocytes and applied a highly efficient third generation lentiviral transduction system that allowed ectopic expression of the melanoma-associated NRAS Q61K oncogene. Results: Oncogenic N-RASQ61K ectopically expressed in primary melanocytes induced a proliferation arrest that was associated with accumulation of the cyclin dependent kinase inhibitors p16, p14ARF, p53 and p21 and the concomitant activation of pRb. In addition, NRAS Q61K promoted a robust DNA damage response that included the accumulation of DNA damage foci, p53 phosphorylation and activation of a DNA damage signalling kinase, CHK2. Furthermore human melanocytes expressing N-RASQ61K were positive for several markers of senescence, including increased cellular size, senescence-associated b-galactosidase and the formation of DAPI-stainable, senescence-associated heterochromatic foci. Conclusions: Here we show that oncogenic N-RAS, which plays a pivotal role in cell transformation, triggers a senescence-type growth arrest in primary human melanocytes.1 page(s