Adenosine 3',5'-cyclic monophosphate (cAMP)-dependent inhibition of IL-5 from human T lymphocytes is not mediated by the cAMP-dependent protein kinase A.
IL-5 is implicated in the pathogenesis of asthma and is predominantly released from T lymphocytes of the Th2 phenotype. In anti-CD3 plus anti-CD28-stimulated PBMC, albuterol, isoproterenol, rolipram, PGE2, forskolin, cholera toxin, and the cAMP analog, 8-bromoadenosine cAMP (8-Br-cAMP) all inhibited the release of IL-5 and lymphocyte proliferation. Although all of the above compounds share the ability to increase intracellular cAMP levels and activate protein kinase (PK) A, the PKA inhibitor H-89 failed to ablate the inhibition of IL-5 production mediated by 8-Br-cAMP, rolipram, forskolin, or PGE2. Similarly, H-89 had no effect on the cAMP-mediated inhibition of lymphocyte proliferation. Significantly, these observations occurred at a concentration of H-89 (3 microM) that inhibited both PKA activity and CREB phosphorylation in intact cells. Additional studies showed that the PKA inhibitors H-8, 8-(4-chlorophenylthio) adenosine-3',5'-cyclic monophosphorothioate Rp isomer, and a myristolated PKA inhibitor peptide also failed to block the 8-Br-cAMP-mediated inhibition of IL-5 release from PBMC. Likewise, a role for PKG was considered unlikely because both activators and inhibitors of this enzyme had no effect on IL-5 release. Western blotting identified Rap1, a downstream target of the cAMP-binding proteins, exchange protein directly activated by cAMP/cAMP-guanine nucleotide exchange factors 1 and 2, in PBMC. However, Rap1 activation assays revealed that this pathway is also unlikely to be involved in the cAMP-mediated inhibition of IL-5. Taken together, these results indicate that cAMP-elevating agents inhibit IL-5 release from PBMC by a novel cAMP-dependent mechanism that does not involve the activation of PKA.
Staples
K J
KJ
Department of Thoracic Medicine, National Heart and Lung Institute, Imperial College School of Medicine, London, United Kingdom.
Bergmann
M
M
Tomita
K
K
Houslay
M D
MD
McPhee
I
I
Barnes
P J
PJ
Giembycz
M A
MA
Newton
R
R
D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000502:physiology*; D017362:Cyclic AMP Response Element-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020662:Guanine Nucleotide Exchange Factors / Q000494:pharmacology; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D015848:Interleukin-5 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D007546:Isoquinolines / Q000494:pharmacology; D008213:Lymphocyte Activation / Q000187:drug effects; D010766:Phosphorylation / Q000187:drug effects; D020889:Rolipram / Q000494:pharmacology; D013449:Sulfonamides; D013601:T-Lymphocytes / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology* / Q000378:metabolism; D020827:rap1 GTP-Binding Proteins / Q000378:metabolism
D017362:Cyclic AMP Response Element-Binding Protein; D004791:Enzyme Inhibitors; D020662:Guanine Nucleotide Exchange Factors; D007166:Immunosuppressive Agents; D015848:Interleukin-5; D007546:Isoquinolines; C116122:RAPGEF3 protein, human; D013449:Sulfonamides; D005576:Colforsin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D002772:Cholera Toxin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020827:rap1 GTP-Binding Proteins; D020889:Rolipram; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide