The O-fucosyltransferase O-fut1 is an extracellular component that is essential for the constitutive endocytic trafficking of Notch in Drosophila.
Notch is a transmembrane receptor that mediates the cell-cell interactions necessary for many cell-fate decisions. Endocytic trafficking of Notch plays important roles in the activation and downregulation of this receptor. A Drosophila O-FucT-1 homolog, encoded by O-fut1, catalyzes the O-fucosylation of Notch, a modification essential for Notch signaling and ligand binding. It was recently proposed that O-fut1 acts as a chaperon for Notch in the endoplasmic reticulum and is required for Notch to exit the endoplasmic reticulum. Here, we report that O-fut1 has additional functions in the endocytic transportation of Notch. O-fut1 was indispensable for the constitutive transportation of Notch from the plasma membrane to the early endosome, which we show was independent of the O-fucosyltransferase activity of O-fut1. We also found that O-fut1 promoted the turnover of Notch, which consequently downregulated Notch signaling. O-fut1 formed a stable complex with the extracellular domain of Notch. In addition, O-fut1 protein added to conditioned medium and endocytosed was sufficient to rescue normal Notch transportation to the early endosome in O-fut1 knockdown cells. Thus, an extracellular interaction between Notch and O-fut1 is essential for the normal endocytic transportation of Notch. We propose that O-fut1 is the first example, except for ligands, of a molecule that is required extracellularly for receptor transportation by endocytosis.
Sasamura
Takeshi
T
Precursory Research for Embryonic Science and Technology (PRESTO Science and Technology Agency, 4-1-8 Honcho Kawaguchi, Saitama, Japan.
Ishikawa
Hiroyuki O
HO
Sasaki
Nobuo
N
Higashi
Syunsuke
S
Kanai
Maiko
M
Nakao
Shiho
S
Ayukawa
Tomonori
T
Aigaki
Toshiro
T
Noda
Katsuhisa
K
Miyoshi
Eiji
E
Taniguchi
Naoyuki
N
Matsuno
Kenji
K
D000818:Animals; D015153:Blotting, Western; D002478:Cells, Cultured; D004330:Drosophila / Q000378:metabolism / Q000502:physiology*; D029721:Drosophila Proteins / Q000378:metabolism*; D016326:Extracellular Matrix Proteins / Q000378:metabolism*; D005647:Fucosyltransferases / Q000378:metabolism*; D005786:Gene Expression Regulation; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D021381:Protein Transport / Q000502:physiology; D051880:Receptors, Notch / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology*
D029721:Drosophila Proteins; D016326:Extracellular Matrix Proteins; C497759:N protein, Drosophila; D051880:Receptors, Notch; D005647:Fucosyltransferases; C471275:O-fucosyltransferase 1, Drosophila