The mechanism of CD47-dependent killing of T cells: heterotrimeric Gi-dependent inhibition of protein kinase A.
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.
Manna
Partha Pratim
PP
Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, MO 63110, USA.
Frazier
William A
WA
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
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