Cowan C A, Henkemeyer M
Center for Developmental Biology and Kent Waldrep Foundation Center for Basic Research on Nerve Growth and Regeneration, University of Texas Southwestern Medical Center, Dallas 75390-9133, USA.
Nature. 2001 Sep 13;413(6852):174-9. doi: 10.1038/35093123.
Bidirectional signals mediated by membrane-anchored ephrins and Eph receptor tyrosine kinases have important functions in cell-cell recognition events, including those that occur during axon pathfinding and hindbrain segmentation. The reverse signal that is transduced into B-ephrin-expressing cells is thought to involve tyrosine phosphorylation of the signal's short, conserved carboxy-terminal cytoplasmic domain. The Src-homology-2 (SH2) domain proteins that associate with activated tyrosine-phosphorylated B-subclass ephrins have not been identified, nor has a defined cellular response to reverse signals been described. Here we show that the SH2/SH3 domain adaptor protein Grb4 binds to the cytoplasmic domain of B ephrins in a phosphotyrosine-dependent manner. In response to B-ephrin reverse signalling, cells increase FAK catalytic activity, redistribute paxillin, lose focal adhesions, round up, and disassemble F-actin-containing stress fibres. These cellular responses can be blocked in a dominant-negative fashion by expression of the isolated Grb4 SH2 domain. The Grb4 SH3 domains bind a unique set of other proteins that are implicated in cytoskeletal regulation, including the Cbl-associated protein (CAP/ponsin), the Abl-interacting protein-1 (Abi-1), dynamin, PAK1, hnRNPK and axin. These data provide a biochemical pathway whereby cytoskeletal regulators are recruited to Eph-ephrin bidirectional signalling complexes.
由膜锚定的ephrin和Eph受体酪氨酸激酶介导的双向信号在细胞间识别事件中具有重要功能，包括轴突导向和后脑分割过程中发生的那些事件。被转导到表达B-ephrin的细胞中的反向信号被认为涉及该信号短的、保守的羧基末端胞质结构域的酪氨酸磷酸化。与活化的酪氨酸磷酸化的B亚类ephrin相关的Src同源2（SH2）结构域蛋白尚未被鉴定，对反向信号的明确细胞反应也未被描述。在这里，我们表明SH2/SH3结构域衔接蛋白Grb4以磷酸酪氨酸依赖性方式与B-ephrin的胞质结构域结合。响应B-ephrin反向信号，细胞增加FAK催化活性，重新分布桩蛋白，失去粘着斑，变圆，并分解含F-肌动蛋白的应力纤维。这些细胞反应可以通过表达分离的Grb4 SH2结构域以显性负性方式被阻断。Grb4 SH3结构域结合一组独特的其他与细胞骨架调节有关的蛋白，包括Cbl相关蛋白（CAP/ponin）、Abl相互作用蛋白-1（Abi-1）、发动蛋白、PAK1、hnRNPK和轴蛋白。这些数据提供了一条生化途径，通过该途径细胞骨架调节因子被招募到Eph-ephrin双向信号复合物中。
