Deregulation of at least one component of the Ink4/Cyclin D1/retinoblastoma pathway is a common feature of most of human cancers, but the mechanism by which these genes contribute to tumorigenesis is poorly understood. In studies using Drosophila we discovered that Cyclin D/Cdk4 complexes, in addition to their widely appreciated function as promoters of cell cycle progression, also regulate rates of increase in cell mass (growth). CycD/Cdk4 does this via unknown targets, distinct from those in the well-studied pRb/E2F pathway. We are using Drosophila genetics to identify and characterize these novel growth-regulatory targets, which we believe may be important for understanding CycD/Cdk4 function during normal and neoplastic development.
Specific aims of this project comprise: 1) Identification and characterization of growth regulatory targets of CycD/Cdk4 using proven, genome-wide screens for mutations that dominantly suppress overgrowth of the eye caused by ectopic CycD/Cdk4; 2) Identification of CycD/Cdk4 targets by gene expression profiling; 3) development of a Drosophila CycD/Cdk4 kinase assay for characterizing putative targets; 4) Characterizing the Hph/Hif-1/VHL and JAK/STAT pathways as mediators of CycD/Cdk4-driven growth; and 5) Tests to determine whether CycD/Cdk4 effects cellular growth by modulating nutrient import, protein synthesis, protein degradation, or mitochondrial function. This project aims to elucidate how CycD/Cdk4 alters cell physiology to promote growth, and should contribute to molecular paradigms explaining how cell growth and cell division are coupled. It should also allow identification of novel Cyclin D and Ink4 targets in humans, and thus help to reveal how growth of our own cells is controlled during normal and neoplastic development. Some of the identified genes could be useful targets for cancer diagnosis or anti-cancer chemotherapeutics. ? ?
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