title: Dual role of Cbl links critical events in BCR endocytosis.
abstract: Receptor endocytosis down-regulates ligand-induced signaling in a timely manner and depends on cytoskeletal remodeling. In B lymphocytes, internalization of B cell receptors (BCRs) is also critical to antigen presentation. However, the mechanisms underlying BCR endocytosis are not fully understood. Similarly, the molecular mechanisms linking endocytosis to cytoskeletal remodeling remain poorly defined. We used flow cytometry, pull-down assays, immunochemistry and fluorescence microscopy to investigate BCR internalization in the DT40 B cell line. We demonstrate that ablation of Cbl impacts BCR endocytosis and the underlying cytoskeletal dynamics. Specifically, we demonstrate that ligand-induced endocytosis is impaired in Cbl-/- cells and that the ubiquitin ligase activity is required for Cbl to promote endocytosis. We also show that phosphorylation of CrkII, activation of Rac downstream of CrkII and BCR capping require Cbl. Furthermore, we show that the association of Cbl and CrkII requires phosphorylation of Cbl, but not its ubiquitin ligase activity. Our data indicate that Cbl promotes BCR endocytosis and attenuates ligand-induced signaling by virtue of its ability to orchestrate receptor ubiquitylation and cytoskeletal dynamics.
authors.affiliation: Wistar Institute and Ludwig Institute for Cancer Research, 3601 Spruce Street, Philadelphia, PA 19104-4268, USA. mjacob@wistar.org
authors.forename: Michele
authors.initials: M
authors.lastname: Jacob
authors.forename: Leslie
authors.initials: L
authors.lastname: Todd
authors.forename: Maame F
authors.initials: MF
authors.lastname: Sampson
authors.forename: Ellen
authors.initials: E
authors.lastname: Puré
mesh_terms: D000199:Actins / Q000378:metabolism; D000818:Animals; D000906:Antibodies / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D002645:Chickens; D003599:Cytoskeleton / Q000276:immunology; D015536:Down-Regulation / Q000276:immunology; D004705:Endocytosis / Q000276:immunology*; D006801:Humans; D008024:Ligands; D010766:Phosphorylation; D017434:Protein Structure, Tertiary / Q000502:physiology; D050721:Proto-Oncogene Proteins c-cbl / Q000172:deficiency / Q000502:physiology*; D050737:Proto-Oncogene Proteins c-crk / Q000378:metabolism; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D015398:Signal Transduction / Q000276:immunology; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D020744:rac GTP-Binding Proteins / Q000378:metabolism
chemical_list: D000199:Actins; D000906:Antibodies; D008024:Ligands; D050737:Proto-Oncogene Proteins c-crk; D011947:Receptors, Antigen, B-Cell; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D020744:rac GTP-Binding Proteins