A Genetic Approach to Identification of Genes Involved in Cellular Senescence and Immortalization
2000 new Scholar Award in aging
One major advance in the study of mammalian aging was the discovery made by Hayflick in the 1960's. He observed that normal human cells had a finite lifespan in vitro and could execute only a limited number of cell divisions. Beyond this limit, cells undergo an irreversible growth arrest known as replicative senescence, or M1 (mortality-1). It was further demonstrated that the lifespan of normal cells in vitro was proportional to the longevity of the organism in vivo. Thus, cellular senescence may reflect the aging process of an organism.
The onset of senescence can also be activated prematurely by oncogenic stimulus, such as the oncogenic form of Ras. Therefore, oncogenic transformation requires immortalizing genetic changes that overcome both replicative senescence and premature senescence elicited by oncogenes.
So far, little is known about the molecular mechanisms underlying replicative senescence and oncogene-mediated premature senescence, or how these control points are bypassed in transformed cells. We have developed a novel retrovirus-based expressional cloning system (the MaRX system), which enables large scale, high throughput phenotypic screening in cultured mammalian cells, even when the desired phenotype has a high background. I propose to use the MaRX system to systematically search for genes that can regulate replicative senescence and premature senescence induced by activated Ras. Through these studies, we hope to gain insights into the molecular pathways leading to immortalization and tumorigenesis in normal human cells.