Inhibition of T lymphocyte activation by cAMP is associated with down-regulation of two parallel mitogen-activated protein kinase pathways, the extracellular signal-related kinase and c-Jun N-terminal kinase.
The induction of T cell proliferation requires signals from the TCR and a co-receptor molecule, such as CD28, that activate parallel and partially cross-reactive signaling pathways. These pathways are disrupted by agonists that utilize adenylate cyclase and cAMP-dependent protein kinase A (PKA). We found that the adenylate cyclase activator, forskolin, inhibits anti-CD3-induced shift in Lck electrophoretic mobility, suggesting an intervention at the TCR-coupled phosphoinositide turnover that precedes the activation of PKC. The shift of Lck following direct PKC activation by 12-O-tetradecanoyl phorbol 13-acetate, which bypasses early receptor-triggered biochemical events, is insensitive to forskolin. Nevertheless, forskolin also inhibits PKC downstream events, such as c-jun expression, which is critical for the activation process of T cells. To further analyze potential cross points between positively and negatively regulating signaling pathways in T cells, we tested the effects of activators of the adenylate cyclase or PKA on two parallel mitogen-activated protein kinase signaling pathways mediated by extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase. Using a PKC-specific inhibitor, GF109203X, or PKC-depleted T cells, we found that a large part of the anti-CD3-induced ERK activation is PKC dependent. Both PKC-dependent and -independent activation of ERK were sensitive to inhibition by forskolin or a cell-permeable cAMP analogue, dbcAMP. Furthermore, the effect of 12-O-tetradecanoyl phorbol 13-acetate and ionomycin, which synergized to fully activate c-Jun N-terminal kinase, was also sensitive to inhibition by forskolin. Our results suggest that PKA inhibits T cell activation by interfering with multiple events along the two signaling pathways operating downstream of the TCR and the CD28 co-receptor molecules.
Tamir
A
A
Department of Microbiology and Immunology, Faculty of Health Sciences, Ben Gurion University of the Negev, Beer Sheva, Israel.
Granot
Y
Y
Isakov
N
N
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066246:ErbB Receptors / Q000737:chemistry; D006801:Humans; D007211:Indoles / Q000494:pharmacology; D007527:Isoenzymes / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases; D015459:Leukemia-Lymphoma, Adult T-Cell / Q000473:pathology; D008213:Lymphocyte Activation / Q000187:drug effects*; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D016399:Lymphoma, T-Cell / Q000473:pathology; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D008934:Mitogens / Q000494:pharmacology*; D008969:Molecular Sequence Data; D016853:Muromonab-CD3 / Q000494:pharmacology; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000502:physiology*; D011499:Protein Processing, Post-Translational / Q000187:drug effects*; D011518:Proto-Oncogene Proteins / Q000502:physiology; D016755:Proto-Oncogene Proteins c-jun / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013601:T-Lymphocytes / Q000187:drug effects* / Q000276:immunology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004791:Enzyme Inhibitors; D007211:Indoles; D007527:Isoenzymes; D008301:Maleimides; D008934:Mitogens; D016853:Muromonab-CD3; D009419:Nerve Tissue Proteins; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D016755:Proto-Oncogene Proteins c-jun; D005576:Colforsin; D003994:Bucladesine; D000242:Cyclic AMP; D066246:ErbB Receptors; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases; D000262:Adenylyl Cyclases; C070515:bisindolylmaleimide I; D013755:Tetradecanoylphorbol Acetate