title: A molecular framework for two-step T cell signaling: Lck Src homology 3 mutations discriminate distinctly regulated lipid raft reorganization events.
abstract: Costimulation by CD28 or lipid-raft-associated CD48 potentiate TCR-induced signals, cytoskeletal reorganization, and IL-2 production. We and others have proposed that costimulators function to construct a raft-based platform(s) especially suited for TCR engagement and sustained and processive signal transduction. Here, we characterize TCR/CD48 and TCR/CD28 costimulation in T cells expressing Lck Src homology 3 (SH3) mutants. We demonstrate that Lck SH3 functions after initiation of TCR-induced tyrosine phosphorylation and concentration of transducers within rafts, to regulate the costimulation-dependent migration of rafts to the TCR contact site. Expression of kinase-active/SH3-impaired Lck mutants disrupts costimulation-dependent raft recruitment, sustained TCR protein tyrosine phosphorylation, and IL-2 production. However, TCR-induced apoptosis, shown only to require "partial" TCR signals, is unaffected by expression of kinase-active/SH3-impaired Lck mutants. Therefore, two distinctly regulated raft reorganization events are required for processive and sustained "complete" TCR signal transduction and T cell activation. Together with recent characterization of CD28 and CD48 costimulatory activities, these findings provide a molecular framework for two signal models of T cell activation.
authors.affiliation: Department of Microbiology, Immunology, and Molecular Genetics and The Molecular Biology Institute, University of California School of Medicine, Los Angeles, CA 90095, USA.
authors.forename: V P
authors.initials: VP
authors.lastname: Patel
authors.forename: M
authors.initials: M
authors.lastname: Moran
authors.forename: T A
authors.initials: TA
authors.lastname: Low
authors.forename: M C
authors.initials: MC
authors.lastname: Miceli
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000502:physiology; D017209:Apoptosis / Q000235:genetics / Q000276:immunology; D018106:CD28 Antigens / Q000502:physiology; D000071178:CD48 Antigen; D004789:Enzyme Activation / Q000235:genetics / Q000276:immunology; D006825:Hybridomas; D007376:Interleukin-2 / Q000096:biosynthesis; D008024:Ligands; D008213:Lymphocyte Activation / Q000235:genetics; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000235:genetics* / Q000378:metabolism; D021962:Membrane Microdomains / Q000378:metabolism* / Q000502:physiology; D051379:Mice; D016297:Mutagenesis, Site-Directed; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding / Q000235:genetics / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics* / Q000276:immunology*; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D018909:src Homology Domains / Q000235:genetics* / Q000276:immunology* / Q000502:physiology
chemical_list: D015703:Antigens, CD; D018106:CD28 Antigens; D000071178:CD48 Antigen; C000604066:Cd48 protein, mouse; D007376:Interleukin-2; D008024:Ligands; D010750:Phosphoproteins; D011948:Receptors, Antigen, T-Cell; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)