Hu G, Zhang S, Vidal M, Baer J L, Xu T, Fearon E R
Division of Molecular Medicine and Genetics, University of Michigan Medical Center, Ann Arbor, Michigan 48109-0638 USA.
Genes Dev. 1997 Oct 15;11(20):2701-14. doi: 10.1101/gad.11.20.2701.
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.
结直肠癌缺失基因（DCC）被推测作为轴突和细胞导向因子netrin-1的跨膜受体发挥作用。我们在此报告，DCC胞质结构域与果蝇无七基因（sina）的哺乳动物同源基因以及果蝇Sina所编码的蛋白质相结合。Sina在R7光感受器发育中起关键作用，并且与其哺乳动物同源基因（称为Siahs）具有超过85%的氨基酸同一性，但Sina/Siah蛋白质的功能尚未明确。因此，我们试图进一步表征它们与DCC的相互作用。免疫荧光研究表明，Sina/Siah蛋白质主要定位于细胞质中并与DCC相关联。发现DCC被泛素化，并且Sina/Siah蛋白质调节其表达。蛋白酶体抑制剂阻断了Sina/Siah对DCC的作用，并且Sina/Siah蛋白质与泛素结合酶（Ubc）相互作用。一种缺乏氨基末端Ubc结合序列的突变Siah蛋白质与DCC结合，但并未使其降解。通过对在眼中异位表达DCC和Sina的转基因果蝇品系的研究，证实了Sina/Siah与DCC在体内的相互作用。综上所述，这些数据表明Sina/Siah蛋白质通过泛素-蛋白酶体途径调节DCC以及可能的其他蛋白质。
