Bache Kristi G, Raiborg Camilla, Mehlum Anja, Madshus Inger Helene, Stenmark Harald
Department of Biochemistry, Institute for Cancer Research, the Norwegian Radium Hospital, Montebello, Oslo, Norway.
Eur J Biochem. 2002 Aug;269(16):3881-7. doi: 10.1046/j.1432-1033.2002.03046.x.
The hepatocyte growth factor-regulated tyrosine kinase substrate Hrs is an early endosomal protein that is thought to play a regulatory role in the trafficking of growth factor/receptor complexes through early endosomes. Stimulation of cells with epidermal growth factor (EGF) rapidly leads to phosphorylation of Hrs, raising the question whether the receptor tyrosine kinase phosphorylates Hrs directly. Here, we present evidence that a downstream kinase, rather than the active receptor kinase is responsible. We show that the nonreceptor tyrosine kinase Src is able to phosphorylate Hrs in vitro and in vivo, but that Hrs is nevertheless phosphorylated in Src-, Yes- and Fyn-negative cells. Moreover, we show that only 10-20% of Hrs is phosphorylated following EGF stimulation, and that phosphorylation occurs at multiple tyrosines located in different parts of Hrs. These results suggest that Hrs is a substrate for several kinases downstream of the EGF receptor.
肝细胞生长因子调节的酪氨酸激酶底物Hrs是一种早期内体蛋白，被认为在生长因子/受体复合物通过早期内体的转运过程中发挥调节作用。用表皮生长因子（EGF）刺激细胞会迅速导致Hrs磷酸化，这就引发了一个问题，即受体酪氨酸激酶是否直接使Hrs磷酸化。在这里，我们提供证据表明，是一种下游激酶而非活性受体激酶对此负责。我们发现非受体酪氨酸激酶Src能够在体外和体内使Hrs磷酸化，但在Src、Yes和Fyn缺失的细胞中Hrs仍会被磷酸化。此外，我们表明在EGF刺激后只有10% - 20%的Hrs被磷酸化，并且磷酸化发生在位于Hrs不同部位的多个酪氨酸上。这些结果表明Hrs是EGF受体下游几种激酶的底物。
