title: Identification of tubby and tubby-like protein 1 as eat-me signals by phage display.
abstract: Phagocytosis is an important process for the removal of apoptotic cells or cellular debris. Eat-me signals control the initiation of phagocytosis and hold the key for in-depth understanding of its molecular mechanisms. However, because of difficulties to identify unknown eat-me signals, only a limited number of them have been identified and characterized. Using a newly developed functional cloning strategy of open reading frame (ORF) phage display, we identified nine putative eat-me signals, including tubby-like protein 1 (Tulp1). This further led to the elucidation of tubby as the second eat-me signal in the same protein family. Both proteins stimulated phagocytosis of retinal pigment epithelium (RPE) cells and macrophages. Tubby-conjugated fluorescent microbeads facilitated RPE phagocytosis. Tubby and Tulp1, but not other family members, enhanced the uptake of membrane vesicles by RPE cells in synergy. Retinal membrane vesicles of Tubby mice and Tulp1(-/-) mice showed reduced activities for RPE phagocytosis, which were compensated by purified tubby and Tulp1, respectively. These data reveal a novel activity of tubby and Tulp1, and demonstrate that unbiased identification of eat-me signals by the broadly applicable strategy of ORF phage display can provide detailed insights into phagocyte biology.
authors.affiliation: Bascom Palmer Eye Institute, Department of Ophthalmology, University of Miami Miller School of Medicine, 1638 NW 10th Avenue, Miami, FL 33136, USA.
authors.forename: Nora B
authors.initials: NB
authors.lastname: Caberoy
authors.forename: Dony
authors.initials: D
authors.lastname: Maiguel
authors.forename: Youngbae
authors.initials: Y
authors.lastname: Kim
authors.forename: Wei
authors.initials: W
authors.lastname: Li
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002460:Cell Line; D045744:Cell Line, Tumor; D021961:Cell Membrane Structures / Q000378:metabolism; D003001:Cloning, Molecular; D005136:Eye Proteins / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D008264:Macrophages / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008863:Microspheres; D020125:Mutation, Missense / Q000502:physiology; D019151:Peptide Library; D010586:Phagocytes / Q000502:physiology; D010587:Phagocytosis / Q000502:physiology*; D011485:Protein Binding / Q000502:physiology; D011506:Proteins / Q000502:physiology*; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D055213:Retinal Pigment Epithelium / Q000166:cytology / Q000502:physiology; D017384:Sequence Deletion / Q000502:physiology; D013552:Swine; D014162:Transfection
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D005136:Eye Proteins; D019151:Peptide Library; D011506:Proteins; D011993:Recombinant Fusion Proteins; C508878:TUB protein, human; C105443:TULP1 protein, human; C098988:Tub protein, mouse; C491353:Tulp1 protein, mouse