The IGF-I and mTOR signaling pathways are intimately involved in human cancers. These signaling pathways are also highly conserved evolutionally. We have used C. elegans, a genetically amenable system, to identify novel genes involved in these pathways. In C. elegans, loss-of-function mutations in the genes encoding DAF-2 (the insulin/IGF-I-receptor like molecule) and AGE-1 (the PI 3-kinase homolog), respectively, lead to dramatic increase of resistance towards ROS (reactive-oxygen species) and enhancement of animal lifespan. Consistently, null mutations in the daf-18 gene, which encodes the C. elegans homolog of PTEN tumor suppressor, cause sensitivity towards ROS and shorten animal lifespan. We have carried out functional genomic screens using RNAi to identify novel genes involved in regulation of ROS resistance and animal lifespan. In our primary screen, we screened for RNAi clones that could confer resistance towards paraquat, a ROS generating agent. The positive clones were then screen for ability to extend animal lifespan (secondary screen). To this date, we have screened one-third of the C. elegans genome to completion and identified 84 genes that are positive in these two sequential assays. Most of the genes identified are novel for their function in regulation of ROS resistance and animal lifespan. By genetic interaction tests, we have found that 29 of these genes potentially encode novel regulators of the DAF-2/insulin-receptor like signaling pathway. Our subsequent biochemical studies in mammalian cells have confirmed that some of their human homologs indeed function in the IGF-I (insulin-like growth factor I) signaling pathway. In addition, we have identified several genes that encode proteins likely function in the TOR (target-of-rapamycin) signaling pathway. Studying the functions of these genes may help to elucidate the mechanisms by which the TOR pathway is activated by a variety of stimuli. Our studies illustrate the power of functional genomic approach in identifying novel players in these important signaling pathways. These new molecules may serve as targets for developing anti-cancer chemotherapies.
- American Association for Cancer Research