Mammalian homologs of seven in absentia regulate DCC via the ubiquitin-proteasome pathway.
DCC (deleted in colorectal cancer) 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 Drosophila lines 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.
Hu
G
G
Division of Molecular Medicine and Genetics, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0638 USA.
Zhang
S
S
Vidal
M
M
Baer
J L
JL
Xu
T
T
Fearon
E R
ER
D000818:Animals; D030801:Animals, Genetically Modified; D016466:CHO Cells; D019556:COS Cells; D015815:Cell Adhesion Molecules / Q000096:biosynthesis / Q000378:metabolism*; D002460:Cell Line; D006224:Cricetinae; D000075389:DCC Receptor; D004330:Drosophila; D015723:Gene Library; D016163:Genes, DCC; D005909:Glioblastoma / Q000235:genetics; D006801:Humans; D008322:Mammals; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D012441:Saccharomyces cerevisiae; D014162:Transfection; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins
D015815:Cell Adhesion Molecules; D000075389:DCC Receptor; C501909:DCC protein, human; D009687:Nuclear Proteins; D011956:Receptors, Cell Surface; D011993:Recombinant Fusion Proteins; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D000098563:Seven in Absentia Proteins