Mammalian homologs of seven in absentia regulate DCC via the ubiquitin–proteasome pathway
- Division of Molecular Medicine and Genetics,1Departments of Internal Medicine, 2Human Genetics, and 3Pathology, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0638 USA; 4 Departments of Pharmacology and 5Genetics, Yale University School of Medicine, New Haven, Connecticut 06536-0812 USA; 6Massachusetts General Hospital Cancer Center, Charlestown, Massachusetts 02129 USA
Abstract
DCC (deleted in colorectalcancer) is postulated to function as transmembrane receptor for the axon and cell guidance factor netrin-1. We report here that the DCC cytoplasmic domain binds to proteins encoded by mammalian homologs of the Drosophila seven in absentia (sina) gene, as well as Drosophila Sina. Sina has a critical role in R7 photoreceptor development and shows upward of 85% amino acid identity with its mammalian homologs (termed Siahs), but the function of the Sina/Siah proteins has not been defined. We sought, therefore, to characterize further their interaction with DCC. Immunofluorescence studies suggested the Sina/Siah proteins localized predominantly in the cytoplasm and in association with DCC. DCC was found to be ubiquitinated and the Sina/Siah proteins regulated its expression. Proteasome inhibitors blocked the effects of Sina/Siah on DCC, and the Sina/Siah proteins interacted with ubiquitin-conjugating enzymes (Ubcs). A mutant Siah protein lacking the amino-terminal Ubc-binding sequences complexed with DCC, but did not degrade it. The in vivo interaction between Sina/Siah and DCC was confirmed through studies of transgenic Drosophilalines in which DCC and Sina were ectopically expressed in the eye. Taken together, the data imply that the Sina/Siah proteins regulate DCC and perhaps other proteins via the ubiquitin–proteasome pathway.
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Footnotes
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↵7 Corresponding author.
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E-MAIL efearon{at}mmg.im.med.umich.edu; FAX (313) 647-7979.
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- Received June 17, 1997.
- Accepted August 21, 1997.
- Cold Spring Harbor Laboratory Press