title: The pool of preactivated Lck in the initiation of T-cell signaling: a critical re-evaluation of the Lck standby model.
abstract: The initiation of T-cell receptor (TCR) signaling, based on the cobinding of TCR and CD4-Lck heterodimer to a peptide-major histocompatibility complex II on antigen presenting cells, represents a classical model of T-cell signaling. What is less clear however, is the mechanism which translates TCR engagement to the phosphorylation of immunoreceptor tyrosine-based activation motifs on CD3 chains and how this event is coupled to the delivery of Lck function. Recently proposed 'standby model of Lck' posits that resting T-cells contain an abundant pool of constitutively active Lck (pY394(Lck)) required for TCR triggering, and this amount, upon TCR engagement, remains constant. Here, we show that although maintenance of the limited pool of pY394(Lck) is necessary for the generation of TCR proximal signals in a time-restricted fashion, the total amount of this pool, ~2%, is much smaller than previously reported (~40%). We provide evidence that this dramatic discrepancy in the content of pY394(Lck)is likely the consequence of spontaneous phosphorylation of Lck that occurred after cell solubilization. Additional discrepancies can be accounted for by the sensitivity of different pY394(Lck)-specific antibodies and the type of detergents used. These data suggest that reagents and conditions used for the quantification of signaling parameters must be carefully validated and interpreted. Thus, the limited size of pY394(Lck) pool in primary T-cells invites a discussion regarding the adjustment of the quantitative parameters of the standby model of Lck and reevaluation of the mechanism by which this pool contributes to the generation of proximal TCR signaling.
authors.affiliation: 1] Laboratory of Immunobiology, Institute of Molecular Genetics AS CR, Prague, Czech Republic [2] Department of Cell Biology, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
authors.forename: Ondřej
authors.initials: O
authors.lastname: Ballek
authors.affiliation: 1] Laboratory of Immunobiology, Institute of Molecular Genetics AS CR, Prague, Czech Republic [2] Department of Cell Biology, Faculty of Science, Charles University in Prague, Prague, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Valečka
authors.affiliation: Laboratory of Immunobiology, Institute of Molecular Genetics AS CR, Prague, Czech Republic.
authors.forename: Jasper
authors.initials: J
authors.lastname: Manning
authors.affiliation: Laboratory of Immunobiology, Institute of Molecular Genetics AS CR, Prague, Czech Republic.
authors.forename: Dominik
authors.initials: D
authors.lastname: Filipp
mesh_terms: D000818:Animals; D016477:Artifacts; D016227:Benzoquinones / Q000494:pharmacology; D002458:Cell Fractionation / Q000379:methods*; D006801:Humans; D019169:Jurkat Cells; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D017493:Leukocyte Common Antigens / Q000235:genetics / Q000378:metabolism; D008213:Lymphocyte Activation; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D010766:Phosphorylation / Q000187:drug effects; D011948:Receptors, Antigen, T-Cell / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013601:T-Lymphocytes / Q000276:immunology*; D051746:ZAP-70 Protein-Tyrosine Kinase / Q000378:metabolism
chemical_list: D016227:Benzoquinones; D047029:Lactams, Macrocyclic; D011948:Receptors, Antigen, T-Cell; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D051746:ZAP-70 Protein-Tyrosine Kinase; D017493:Leukocyte Common Antigens; C516770:Ptprc protein, mouse; C001277:geldanamycin