Identification of a human HECT family protein with homology to the Drosophila tumor suppressor gene hyperplastic discs

Use of the differential display technique to isolate progestin-regulated ge nes in T-47D human breast cancer cells led to identification of a novel gen e, EDD, The cDNA sequence contains a 2799 amino acid open reading frame sha ring 40% identity with the predicted 2894 amino acid product of the Drosoph ila melanogaster tumor suppressor gene hyperplastic discs, while the carbox y-terminal 889 amino acids show 96% identity to a rat 100 kDa HECT domain p rotein. EDD mRNA was progestin-induced in T-47D cells and was highly abunda nt in testes and expressed at moderately high le,els in other tissues, sugg esting a broad role for EDD, Anti-EDD antibodies immunoprecipitated an appr oximately 300 kDa protein from T-47D cell lysates, HECT family proteins fun ction as E3 ubiquitin-protein ligases, targeting specific proteins for ubiq uitin-mediated proteolysis. EDD is likely to function as an E3 as irt vitro translated protein hound ubiquitin reversibly through a conserved HECT dom ain cysteine residue. EDD was localized by FISH to chromosome 8q22, a locus disrupted in a variety of cancers. Given the homology between EDD and the hyperplastic discs protein, which is required for control of imaginal disc growth in Drosophila, EDD potentially has a role in regulation of cell prol iferation or differentiation.