TAILIEUCHUNG - Báo cáo khoa học: Phosphorylation of Hrs downstream of the epidermal growth factor receptor

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. . | Eur. J. Biochem. 269 3881-3887 2002 FEBS 2002 doi Phosphorylation of Hrs downstream of the epidermal growth factor receptor Kristi G. Bache1 Camilla Raiborg1 Anja Mehlum1 Inger Helene Madshus2 and Harald Stenmark1 1 Department of Biochemistry Institute for Cancer Research the Norwegian Radium Hospital Montebello Oslo Norway institute of Pathology the National Hospital Oslo Norway 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. Keywords endosome membrane trafficking Src tyrosine kinase. The growth factor or cytokine stimulated phosphorylation of macromolecules regulates cellular functions such as adhesion cytoskeletal function membrane trafficking and gene transcription reviewed in 1 . The hepatocyte growth factor regulated tyrosine kinase substrate Hrs is a protein that becomes rapidly phosphorylated upon growth factor and cytokine stimulation 2 3 . It was first shown to be phosphorylated in cells treated with HGF as well as platelet-derived growth factor PDGF and epidermal ịg-owth factor EGF 2 . Later Hrs was also identified as a tyrosine

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