Qin Hanjuan, Percival-Smith Anthony, Li Chengjun, Jia Christina Y H, Gloor Greg, Li Shawn S-C
Department of Biochemistry and Biology, University of Western Ontario, London, Ontario N6A 5C1, Canada.
J Biol Chem. 2004 Mar 19;279(12):11304-12. doi: 10.1074/jbc.M311733200. Epub 2003 Dec 11.
Numb, an evolutionarily conserved cell fate-determining factor, plays a pivotal role in the development of Drosophila and vertebrate nervous systems. Despite lacking a transmembrane segment, Numb is associated with the cell membrane during the asymmetric cell division of Drosophila neural precursor cells and is selectively partitioned to one of the two progeny cells from a binary cell division. Numb contains an N-terminal phosphotyrosine-binding (PTB) domain that is essential for both the asymmetric localization and the fate specification function of Numb. We report here the isolation and characterization of a novel PTB domain-binding protein, NIP (Numb-interacting protein). NIP is a multipass transmembrane protein that contains two PTB domain-binding, NXXF motifs required for the interaction with Numb. In dividing Drosophila neuroblasts, NIP is colocalized to the cell membrane with Numb in a basal cortical crescent. Expression of NIP in Cos-7 cells recruited Numb from the cytosol to the plasma membrane. This recruitment of Numb to membrane by NIP was dependent on the presence of at least one NXXF site. In Drosophila Schneider 2 cells, NIP and Numb were colocalized at the plasma membrane. Inhibition of NIP expression by RNA interference released Numb to the cytosol. These results suggest that a direct protein-protein interaction between NIP and Numb is necessary and sufficient for the recruitment of Numb to the plasma membrane. Recruitment of Numb to a basal cortical crescent in a dividing neuroblast is essential for Numb to function as an intrinsic cell fate determinant.
Numb是一种在进化上保守的细胞命运决定因子，在果蝇和脊椎动物神经系统的发育中起关键作用。尽管缺乏跨膜结构域，但在果蝇神经前体细胞的不对称细胞分裂过程中，Numb与细胞膜相关联，并在二元细胞分裂中被选择性地分配到两个子细胞之一中。Numb包含一个N端磷酸酪氨酸结合（PTB）结构域，该结构域对于Numb的不对称定位和命运决定功能均至关重要。我们在此报告了一种新型PTB结构域结合蛋白NIP（Numb相互作用蛋白）的分离和鉴定。NIP是一种多次跨膜蛋白，含有两个与Numb相互作用所需的PTB结构域结合基序NXXF。在分裂的果蝇神经母细胞中，NIP与Numb在基底皮质新月区共定位于细胞膜。NIP在Cos-7细胞中的表达将Numb从细胞质募集到质膜。NIP将Numb募集到膜上这一过程依赖于至少一个NXXF位点的存在。在果蝇Schneider 2细胞中，NIP和Numb共定位于质膜。通过RNA干扰抑制NIP表达会使Numb释放到细胞质中。这些结果表明，NIP和Numb之间直接的蛋白质-蛋白质相互作用对于将Numb募集到质膜是必要且充分的。将Numb募集到分裂的神经母细胞的基底皮质新月区对于Numb作为内在细胞命运决定因子发挥功能至关重要。
