Archipelago regulates Cyclin E in Drosophila and is mutated in human cancer cell lines. K.H. Moberg 1, D.W. Bell 1,2, D.C.R. Wahrer 1,2, D.A. Haber 1,2, I.K. Hariharan 1. 1) MGH Cancer Center, Massachusetts General Hosp, Charlestown, MA; 2) Center for Cancer Risk Analysis, Massachusetts General Hosp, Charlestown MA.
Exit from the cell cycle requires downregulation of the activity of G1 cyclin-cdk complexes. This down-regulation is accomplished at two levels: by the induction of cdk inhibitors like dacapo, and by a concurrent decrease in the levels of the G1/S regulator Cyclin E. Using an eyelessFLP system, we have isolated alleles of a novel Drosophila gene called archipelago based upon their overproliferative phenotype. We find that archipelago is required to down-regulate Cyclin E protein levels both in cells exiting the cell cycle, and in actively dividing cells. archipelago was cloned and found to encode an F-box/WD family member. F-box/WD proteins recruit substrates to E3-type ubiquitin-ligase complexes by direct binding via the WD-repeat domain. The mutations recovered in our screen fall within the archipelago WD-repeat domain, and disrupt the ability of the protein to bind Cyclin E protein in vitro. Consistent with Cyclin E hyperactivity, archipelago mutant cells show evidence of accelerated progression through G1/S and defects in cell cycle exit. These data directly implicate the Archipelago protein in developmental control of G1/S progression via it's role in Cyclin E proteolysis. Based upon these findings, we have characterized a highly conserved human homolog, hAgo, and found mutations in four cancer cell lines, including three derived from ovarian tumors. Finally, it is likely that archipelago regulates targets in addition to Cyclin E. We have therefore begun to investigate the role of archipelago in the proteolytic control of other developmental signaling pathways.