title: The mechanism of CD47-dependent killing of T cells: heterotrimeric Gi-dependent inhibition of protein kinase A.
abstract: CD47 has been implicated in both positive and negative regulation of T cells as well as in T cell death. To clarify the role of CD47 in T cell function, we have studied the mechanism of T cell death in response to CD47 ligands, including mAb 1F7, thrombospondin-1, and a CD47 agonist peptide derived from it. CD47(-/-) Jurkat T cells (JINB8) were resistant to killing by all three ligands, indicating the essential role of CD47. Primary human T cells were also killed by CD47 ligands, but only after activation with anti-CD3. CD47-mediated cell death occurred without active caspases, DNA fragmentation, or Bcl-2 degradation. Pretreatment of Jurkat and primary T cells with pertussis toxin (PTX) prevented CD47-mediated death, indicating the involvement of G((i)alpha). Pretreatment of T cells with 8-bromo cAMP, forskolin, or 3-isobutyl-1-methylxanthine prevented the CD47-mediated apoptosis, and 1F7 dramatically reduced intracellular cAMP levels, an effect reversed with PTX. H89 and protein kinase A (PKA) inhibitor peptide, a specific PKA inhibitor, prevented rescue of T cells by PTX, 8-bromo cAMP, and forskolin, indicating a direct role for one or more PKA substrates. Thus, CD47-mediated killing of activated T cells occurs by a novel pathway involving regulation of cAMP levels by heterotrimeric G((i)alpha) with subsequent effects mediated by PKA.
authors.affiliation: Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Partha Pratim
authors.initials: PP
authors.lastname: Manna
authors.forename: William A
authors.initials: WA
authors.lastname: Frazier
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology; D015703:Antigens, CD / Q000276:immunology / Q000502:physiology*; D017209:Apoptosis / Q000276:immunology*; D051928:CD47 Antigen; D002352:Carrier Proteins / Q000819:agonists / Q000037:antagonists & inhibitors / Q000276:immunology / Q000502:physiology*; D000242:Cyclic AMP / Q000096:biosynthesis / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors* / Q000502:physiology*; D053938:DNA Fragmentation; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology*; D006801:Humans; D007425:Intracellular Membranes / Q000502:physiology; D047908:Intracellular Signaling Peptides and Proteins; D019169:Jurkat Cells; D008564:Membrane Potentials / Q000502:physiology; D008928:Mitochondria / Q000502:physiology; D009842:Oligopeptides / Q000494:pharmacology; D010539:Permeability; D037342:Pertussis Toxin / Q000494:pharmacology; D021122:Protein Subunits / Q000502:physiology; D016176:T-Lymphocyte Subsets / Q000166:cytology* / Q000201:enzymology / Q000276:immunology*; D019700:Thrombospondin 1 / Q000494:pharmacology
chemical_list: C120273:4N1K peptide; D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D051928:CD47 Antigen; C497894:CD47 protein, human; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009842:Oligopeptides; D021122:Protein Subunits; D019700:Thrombospondin 1; C015482:protein kinase modulator; D000242:Cyclic AMP; D037342:Pertussis Toxin; D017868:Cyclic AMP-Dependent Protein Kinases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go