Notch ligand activity is modulated by glycosphingolipid membrane composition in Drosophila melanogaster.
Endocytosis of the transmembrane ligands Delta (Dl) and Serrate (Ser) is required for the proper activation of Notch receptors. The E3 ubiquitin ligases Mindbomb1 (Mib1) and Neuralized (Neur) regulate the ubiquitination of Dl and Ser and thereby promote both ligand endocytosis and Notch receptor activation. In this study, we identify the alpha1,4-N-acetylgalactosaminyltransferase-1 (alpha4GT1) gene as a gain of function suppressor of Mib1 inhibition. Expression of alpha4GT1 suppressed the signaling and endocytosis defects of Dl and Ser resulting from the inhibition of mib1 and/or neur activity. Genetic and biochemical evidence indicate that alpha4GT1 plays a regulatory but nonessential function in Notch signaling via the synthesis of a specific glycosphingolipid (GSL), N5, produced by alpha4GT1. Furthermore, we show that the extracellular domain of Ser interacts with GSLs in vitro via a conserved GSL-binding motif, raising the possibility that direct GSL-protein interactions modulate the endocytosis of Notch ligands. Together, our data indicate that specific GSLs modulate the signaling activity of Notch ligands.
Hamel
Sophie
S
Institut Pasteur, Centre National de la Recherche Scientifique URA2578, 75724 Paris, Cedex 15, France.
Fantini
Jacques
J
Schweisguth
François
F
D000595:Amino Acid Sequence; D000818:Animals; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism*; D017124:Conserved Sequence; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology* / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D004705:Endocytosis; D005799:Genes, Dominant / Q000235:genetics; D017344:Genes, Insect / Q000235:genetics; D016153:Genes, Suppressor; D006028:Glycosphingolipids / Q000096:biosynthesis / Q000378:metabolism*; D016695:Glycosyltransferases / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins / Q000737:chemistry / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D000072100:Jagged-1 Protein; D008024:Ligands; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D021381:Protein Transport; D051880:Receptors, Notch / Q000378:metabolism*; D000072099:Serrate-Jagged Proteins; D014921:Wings, Animal / Q000033:anatomy & histology
D002135:Calcium-Binding Proteins; D029721:Drosophila Proteins; D006028:Glycosphingolipids; D036341:Intercellular Signaling Peptides and Proteins; D047908:Intracellular Signaling Peptides and Proteins; D000072100:Jagged-1 Protein; D008024:Ligands; D008565:Membrane Proteins; D051880:Receptors, Notch; C000606278:Ser protein, Drosophila; D000072099:Serrate-Jagged Proteins; C064045:delta protein; D016695:Glycosyltransferases; C544529:alpha4GT1 protein, Drosophila