Barnes H, Larsen B, Tyers M, van Der Geer P
Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California 92093-0359, USA.
J Biol Chem. 2001 Jun 1;276(22):19119-25. doi: 10.1074/jbc.M011437200. Epub 2001 Mar 20.
v-Src transforms fibroblasts in vitro and causes tumor formation in the animal by tyrosine phosphorylation of critical cellular substrates. Exactly how v-Src interacts with these substrates remains unknown. One of its substrates, the adaptor protein Shc, is thought to play a crucial role during cellular transformation by v-Src by linking v-Src to Ras. We used Shc proteins with mutations in either the phosphotyrosine binding (PTB) or Src homology 2 domain to determine that phosphorylation of Shc in v-Src-expressing cells depends on the presence of a functional PTB domain. We purified a 100-kDa Shc PTB-binding protein from Src-transformed cells that was identified as the beta chain of the low density lipoprotein receptor-related protein LRP1. LRP1 acts as an import receptor for a variety of proteins and is involved in clearance of the beta-amyloid precursor protein. This study shows that LRP1 is tyrosine-phosphorylated in v-Src-transformed cells and that tyrosine-phosphorylated LRP1 binds in vivo and in vitro to Shc. The association between Shc and LRP1 may provide a mechanism for recruitment of Shc to the plasma membrane where it is phosphorylated by v-Src. It is at the membrane that Shc is thought to be involved in Ras activation. These observations further suggest that LRP1 could function as a signaling receptor and may provide new avenues to investigate its possible role during embryonal development and the onset of Alzheimer's disease.
v-Src 在体外可使成纤维细胞发生转化，并通过关键细胞底物的酪氨酸磷酸化在动物体内引发肿瘤形成。v-Src 究竟如何与这些底物相互作用仍不清楚。其底物之一，衔接蛋白 Shc，被认为在 v-Src 介导的细胞转化过程中通过将 v-Src 与 Ras 相连而发挥关键作用。我们使用了在磷酸酪氨酸结合（PTB）结构域或 Src 同源 2 结构域发生突变的 Shc 蛋白，以确定在表达 v-Src 的细胞中 Shc 的磷酸化依赖于功能性 PTB 结构域的存在。我们从 Src 转化的细胞中纯化出一种 100 kDa 的 Shc PTB 结合蛋白，它被鉴定为低密度脂蛋白受体相关蛋白 LRP1 的β链。LRP1 作为多种蛋白质的导入受体，参与β-淀粉样前体蛋白的清除。这项研究表明，LRP1 在 v-Src 转化的细胞中发生酪氨酸磷酸化，并且酪氨酸磷酸化的 LRP1 在体内和体外都能与 Shc 结合。Shc 与 LRP1 之间的关联可能为 Shc 募集到质膜提供一种机制，在质膜上 Shc 被 v-Src 磷酸化。正是在膜上，Shc 被认为参与 Ras 激活。这些观察结果进一步表明，LRP1 可能作为一种信号受体发挥作用，并可能为研究其在胚胎发育和阿尔茨海默病发病过程中的潜在作用提供新途径。
