title: Interaction of CED-6/GULP, an adapter protein involved in engulfment of apoptotic cells with CED-1 and CD91/low density lipoprotein receptor-related protein (LRP).
abstract: The prompt clearance of cells undergoing apoptosis is critical during embryonic development, normal tissue turnover, as well as inflammation and autoimmunity. The molecular details of the engulfment of apoptotic cells are not fully understood. ced-6 and its human homologue gulp, encode an adapter protein, whose function in engulfment is highly evolutionarily conserved; however, the upstream and downstream components of CED-6 mediated signaling are not known. Recently, ced-1 has been shown to encode a transmembrane protein on phagocytic cells, with two functional sequence motifs in its cytoplasmic tail that are important for engulfment. In this study, using a combination of biochemical approaches and yeast two-hybrid analysis, we present evidence for a physical interaction between GULP/CED-6 and one of the two motifs (NPXY motif) in the cytoplasmic tail of CED-1. The phosphotyrosine binding domain of GULP was necessary and sufficient for this interaction. Since the precise mammalian homologue of CED-1 is not known, we undertook a database search for human proteins that contain the motifs shown to be important for CED-1 function and identified CD91/LRP (low density lipoprotein receptor-related protein) as one candidate. Interestingly, recent studies have also identified CD91/LRP as a receptor involved in the phagocytosis of apoptotic cells in mammals. The GULP phosphotyrosine binding domain was able to specifically interact with one specific NPXY motif in the CD91 cytoplasmic tail. During these studies we have also identified the mouse GULP sequence. These studies suggest a physical link between CED-1 or CD91/LRP and the adapter protein CED-6/GULP during engulfment of apoptotic cells and further elucidate the pathway suggested by the genetic studies.
authors.affiliation: Beirne Carter Center for Immunology Research and the Department of Microbiology, University of Virginia, Charlottesville, Virginia 22908, USA.
authors.forename: Hua Poo
authors.initials: HP
authors.lastname: Su
authors.forename: Kumiko
authors.initials: K
authors.lastname: Nakada-Tsukui
authors.forename: Annie-Carole
authors.initials: AC
authors.lastname: Tosello-Trampont
authors.forename: Yonghe
authors.initials: Y
authors.lastname: Li
authors.forename: Guojun
authors.initials: G
authors.lastname: Bu
authors.forename: Peter M
authors.initials: PM
authors.lastname: Henson
authors.forename: Kodimangalam S
authors.initials: KS
authors.lastname: Ravichandran
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D019556:COS Cells; D029742:Caenorhabditis elegans Proteins; D003593:Cytoplasm / Q000378:metabolism; D016208:Databases, Factual; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D026503:Low Density Lipoprotein Receptor-Related Protein-1 / Q000378:metabolism*; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry; D010750:Phosphoproteins / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics* / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D020798:Two-Hybrid System Techniques
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C112888:CED-6 protein, C elegans; D029742:Caenorhabditis elegans Proteins; C454119:GULP1 protein, human; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008565:Membrane Proteins; D010455:Peptides; D010750:Phosphoproteins; D011506:Proteins; C422043:ced-1 protein, C elegans; D005982:Glutathione Transferase