Hepatocyte growth factor (HGF; scatter factor) is a multipotent protein with mitogenic, motogenic, and developmental functions. Upon activation, the HGF-receptor c-Met binds and phosphorylates the multisite docking protein Gab1. Besides binding motifs for phosphatidylinositol 3-kinase and Grb2, Gab 1 contains multiple Tyr-X-X-Pro (YXXP) motifs which, when phosphorylated, are potential binding sites for the adapter proteins c-Crk and Crk-like (CRKL). Stimulation of human embryonic kidney cells (HEK293) with HGF leads to Gab1 association with CRKL. The Gab1-CRKL interaction requires both, the SH2 domain of CRKL and the region containing the YXXP motifs in Gab1. CRKL binds via its first SH3 domain to several downstream signal transducers, including C3G an activator of the small GTPase Rap1. Indeed, Rap1 was rapidly activated after HGF stimulation of HEK293 cells. Rap1 activation through HGF was suppressed through transfection of a truncated C3G protein which only contains the SH3-binding motifs of C3G. Transfection of nonmutated Gab1 led to a strong increase of Rap1.GTP in the absence of HGF. In contrast, transfection of the GabDeltaYXXP mutant abolished the elevation of Rap1.GTP by HGF. A replating assay indicated that HGF decreases the adhesion of HEK293 cells. The results presented here delineate a novel signaling pathway from HGF to the GTPase Rap1 which depends on the interaction of the adapter protein CRKL with the exchange factor C3G and could be linked to cell migration.

中文翻译：

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肝细胞生长因子/分散因子（HGF）通过大对接蛋白Gab1和衔接子CRKL向小GTPase Rap1发出信号。

肝细胞生长因子（HGF；散射因子）是一种具有促有丝分裂，运动发生和发育功能的多能蛋白质。激活后，HGF受体c-Met结合并磷酸化多位点对接蛋白Gab1。除了磷脂酰肌醇3-激酶和Grb2的结合基序外，Gab 1还包含多个Tyr-XX-Pro（YXXP）基序，这些基团在被磷酸化时是衔接蛋白c-Crk和Crk-like（CRKL）的潜在结合位点。用HGF刺激人类胚胎肾细胞（HEK293）导致Gab1与CRKL缔合。Gab1-CRKL相互作用既需要CRKL的SH2结构域，又需要Gab1中包含YXXP基序的区域。CRKL通过其第一个SH3结构域与几个下游信号转导子结合，包括小GTPase Rap1的激活子C3G。的确，HGF刺激HEK293细胞后，Rap1被迅速激活。通过转染截短的C3G蛋白（仅包含C3G的SH3结合基序），抑制了通过HGF激活Rap1。在没有HGF的情况下，未突变的Gab1的转染导致Rap1.GTP的强烈增加。相反，GabDeltaYXXP突变体的转染消除了HGF对Rap1.GTP的升高。重新铺板试验表明，HGF降低了HEK293细胞的粘附力。此处介绍的结果描述了从HGF到GTPase Rap1的新型信号传导途径，这取决于衔接子蛋白CRKL与交换因子C3G的相互作用，并可能与细胞迁移有关。在没有HGF的情况下，未突变的Gab1的转染导致Rap1.GTP的强烈增加。相反，GabDeltaYXXP突变体的转染消除了HGF对Rap1.GTP的升高。重新铺板试验表明，HGF降低了HEK293细胞的粘附力。此处介绍的结果描述了从HGF到GTPase Rap1的新型信号传导途径，这取决于衔接子蛋白CRKL与交换因子C3G的相互作用，并可能与细胞迁移有关。在没有HGF的情况下，未突变的Gab1的转染导致Rap1.GTP的强烈增加。相反，GabDeltaYXXP突变体的转染消除了HGF对Rap1.GTP的升高。重新铺板试验表明，HGF降低了HEK293细胞的粘附力。此处介绍的结果描述了从HGF到GTPase Rap1的新型信号传导途径，这取决于衔接子蛋白CRKL与交换因子C3G的相互作用，并可能与细胞迁移有关。