The Mechanism of CD47-Dependent Killing of T Cells: Heterotrimeric Gi-Dependent Inhibition of Protein Kinase A

• Published in: The Journal of immunology (1950) 2003-04, Vol.170 (7), p.3544-3553
• Main Authors: Manna, Partha Pratim, Frazier, William A
• Format: Article
• Language: English
• Subjects: Antibodies, Monoclonal - pharmacology; Antigens, CD - immunology; Antigens, CD - physiology; Apoptosis - immunology; Carrier Proteins - agonists; Carrier Proteins - antagonists & inhibitors; Carrier Proteins - immunology; Carrier Proteins - physiology; CD47 Antigen; Cyclic AMP - biosynthesis; Cyclic AMP - physiology; Cyclic AMP-Dependent Protein Kinases - antagonists & inhibitors; Cyclic AMP-Dependent Protein Kinases - physiology; DNA Fragmentation; GTP-Binding Protein alpha Subunits, Gi-Go - physiology; Humans; Intracellular Membranes - physiology; Intracellular Signaling Peptides and Proteins; Jurkat Cells; Membrane Potentials - physiology; Mitochondria - physiology; Oligopeptides - pharmacology; Permeability; Pertussis Toxin - pharmacology; Protein Subunits - physiology; T-Lymphocyte Subsets - cytology; T-Lymphocyte Subsets - enzymology; T-Lymphocyte Subsets - immunology; Thrombospondin 1 - pharmacology
• ISSN: 0022-1767; 1550-6606
• DOI: 10.4049/jimmunol.170.7.3544

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.