title: Jedi-1 and MEGF10 signal engulfment of apoptotic neurons through the tyrosine kinase Syk.
abstract: During the development of the peripheral nervous system there is extensive apoptosis, and these neuronal corpses need to be cleared to prevent an inflammatory response. Recently, Jedi-1 and MEGF10, both expressed in glial precursor cells, were identified in mouse as having an essential role in this phagocytosis (Wu et al., 2009); however, the mechanisms by which they promote engulfment remained unknown. Both Jedi-1 and MEGF10 are homologous to the Drosophila melanogaster receptor Draper, which mediates engulfment through activation of the tyrosine kinase Shark. Here, we identify Syk, the mammalian homolog of Shark, as a signal transducer for both Jedi-1 and MEGF10. Syk interacted with each receptor independently through the immunoreceptor tyrosine-based activation motifs (ITAMs) in their intracellular domains. The interaction was enhanced by phosphorylation of the tyrosines in the ITAMs by Src family kinases (SFKs). Jedi association with Syk and activation of the kinase was also induced by exposure to dead cells. Expression of either Jedi-1 or MEGF10 in HeLa cells facilitated engulfment of carboxylated microspheres to a similar extent, and there was no additive effect when they were coexpressed. Mutation of the ITAM tyrosines of Jedi-1 and MEGF10 prevented engulfment. The SFK inhibitor PP2 or a selective Syk inhibitor (BAY 61-3606) also blocked engulfment. Similarly, in cocultures of glial precursors and dying sensory neurons from embryonic mice, addition of PP2 or knock down of endogenous Syk decreased the phagocytosis of apoptotic neurons. These results indicate that both Jedi-1 and MEGF10 can mediate phagocytosis independently through the recruitment of Syk.
authors.affiliation: Department of Biochemistry, the Vanderbilt Brain Institute, and the Kennedy Center for Human Development, Vanderbilt University School of Medicine, Nashville, Tennessee 37232, USA.
authors.forename: Jami L
authors.initials: JL
authors.lastname: Scheib
authors.forename: Chelsea S
authors.initials: CS
authors.lastname: Sullivan
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Carter
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000378:metabolism; D002452:Cell Count; D002478:Cells, Cultured; D018920:Coculture Techniques; D004622:Embryo, Mammalian; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005727:Ganglia, Spinal / Q000166:cytology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D047468:Immunoprecipitation; D061625:Immunoreceptor Tyrosine-Based Activation Motif / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D019751:Intramolecular Transferases / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D017628:Microglia; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D009474:Neurons; D009536:Niacinamide / Q000031:analogs & derivatives / Q000494:pharmacology; D010587:Phagocytosis / Q000187:drug effects / Q000235:genetics; D010766:Phosphorylation / Q000187:drug effects / Q000235:genetics; D011505:Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics*; D019311:Staurosporine / Q000494:pharmacology; D000072377:Syk Kinase; D014162:Transfection
chemical_list: C477642:2-(7-(3,4-dimethoxyphenyl)imidazo(1,2-c)pyrimidin-5-ylamino)nicotinamide; D029681:Arabidopsis Proteins; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; C522125:Jedi protein, mouse; C525222:Megf10 protein, mouse; D008565:Membrane Proteins; D011743:Pyrimidines; D034741:RNA, Small Interfering; D049452:Green Fluorescent Proteins; D009536:Niacinamide; D011505:Protein-Tyrosine Kinases; C000606896:SYK protein, human; D000072377:Syk Kinase; C000606897:Syk protein, mouse; D019751:Intramolecular Transferases; C568454:marneral synthase, Arabidopsis; D019311:Staurosporine