State Key Laboratory of Genetic Engineering, Institute of Genetics, School of Life Sciences, Fudan University, 200433 Shanghai, People's Republic of China.
Mol Biol Rep. 2010 Jun;37(5):2431-7. doi: 10.1007/s11033-009-9754-5. Epub 2009 Aug 23.
LNX (Ligand of Numb-protein X) was originally isolated as a binding partner to the cell-fate Determinant Numb during development, and then identified to act as a RING finger-type E3 ubiquitin ligase for the ubiquitylation and degradation of Numb. LNX contains 4 PDZ domains which are proved to play a central role in organizing diverse cell signaling assemblies. A yeast two-hybrid screening was used to identify LNX as a potential binding partner for RhoC. RhoC, a member of the Ras family of small GTPases, promotes reorganization of the actin cytoskeleton and regulation of cell shape, attachment, and motility. The interaction between LNX and RhoC in mammalian cells was identified by co-immunoprecipitation assays, and the efficient binding required the first PDZ domain of LNX. LNX and RhoC were further colocalized with each other in mammalian cells, in which RhoC changed its sublocalization from cytoplasm to nucleus when co-transferred with LNX. Furthermore, co-expression of RhoC reduced the transcriptional activity of AP-1, which was up-regulated by over-expression of LNX alone. These results suggest that LNX and RhoC might be part of a larger protein complex that would have important functions in signaling transduction about regulating the transcriptional activities of AP-1.
LNX（神经嵴衍生转化蛋白 X 配体）最初是作为发育过程中细胞命运决定因子 Numb 的结合伴侣被分离出来的，后来被鉴定为一种 RING 指型 E3 泛素连接酶，可导致 Numb 的泛素化和降解。LNX 包含 4 个 PDZ 结构域，这些结构域被证明在组织多种细胞信号组装中发挥着核心作用。利用酵母双杂交筛选技术，鉴定出 LNX 是 RhoC 的一个潜在结合伴侣。RhoC 是 Ras 家族小 GTP 酶的成员，可促进肌动蛋白细胞骨架的重排和细胞形状、黏附以及运动的调节。通过免疫共沉淀实验鉴定了哺乳动物细胞中 LNX 和 RhoC 之间的相互作用，并且高效结合需要 LNX 的第一个 PDZ 结构域。在哺乳动物细胞中，LNX 和 RhoC 进一步共定位，其中 RhoC 当其与 LNX 共转染时，其亚细胞定位从细胞质改变为细胞核。此外，RhoC 的共表达降低了 LNX 单独过表达时上调的 AP-1 的转录活性。这些结果表明，LNX 和 RhoC 可能是更大的蛋白质复合物的一部分，该复合物在调节 AP-1 的转录活性的信号转导中具有重要功能。
