Dissociation between the translocation and the activation of Akt in fMLP-stimulated human neutrophils--effect of prostaglandin E2.
PGE(2) and other cAMP-elevating agents are known to down-regulate most functions stimulated by fMLP in human polymorphonuclear neutrophils. We reported previously that the inhibitory potential of PGE(2) resides in its capacity to suppress fMLP-stimulated PI-3Kgamma activation via the PGE(2) receptor EP(2) and hence, to decrease phosphatidylinositol 3,4,5-triphosphate [PI(3,4,5)P(3)] formation. Akt activity is stimulated by fMLP through phosphorylation on threonine 308 (Thr308) and serine 473 (Ser473) by 3-phosphoinositide-dependent kinase 1 (PDK1) and MAPK-AP kinase (APK)-APK-2 (MAPKAPK-2), respectively, in a PI-3K-dependent manner. Despite the suppression of fMLP-induced PI-3Kgamma activation observed in the presence of PGE(2), we show that Akt is fully phosphorylated on Thr308 and Ser473. However, fMLP-induced Akt translocation is decreased markedly in this context. PGE(2) does not affect the phosphorylation of MAPKAPK-2 but decreases the translocation of PDK1 induced by fMLP. Other cAMP-elevating agents such as adenosine (Ado) similarly block the fMLP-induced PI-3Kgamma activation process but do not inhibit Akt phosphorylation. However, Akt activity stimulated by fMLP is down-regulated slightly by agonists that elevate cAMP levels. Whereas protein kinase A is not involved in the maintenance of Akt phosphorylation, it is required for the inhibition of Akt translocation by PGE(2). Moreover, inhibition of fMLP-stimulated PI-3Kdelta activity by the selective inhibitor IC87114 only partially affects the late phase of Akt phosphorylation in the presence of PGE(2). Taken together, these results suggest that cAMP-elevating agents, such as PGE(2) or Ado, are able to induce an alternative mechanism of Akt activation by fMLP in which the translocation of Akt to PI(3,4,5)P(3)-enriched membranes is not required prior to its phosphorylation.
Burelout
Chantal
C
Centre de Recherche en Rhumatologie-Immunologie, Centre de Recherche du CHUL, 2705 Boul. Laurier, Room T1-49, Sainte-Foy, Québec, Canada G1V 4G2.
Naccache
Paul H
PH
Bourgoin
Sylvain G
SG
D064413:3-Phosphoinositide-Dependent Protein Kinases; D058544:Class Ib Phosphatidylinositol 3-Kinase; D000242:Cyclic AMP / Q000378:metabolism; D015232:Dinoprostone / Q000494:pharmacology / Q000502:physiology*; D004789:Enzyme Activation; D006801:Humans; D066298:In Vitro Techniques; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D007546:Isoquinolines / Q000494:pharmacology; D020935:MAP Kinase Signaling System / Q000187:drug effects / Q000502:physiology; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013449:Sulfonamides / Q000494:pharmacology
D064413:3-Phosphoinositide-Dependent Protein Kinases; D058544:Class Ib Phosphatidylinositol 3-Kinase; D000242:Cyclic AMP; D015232:Dinoprostone; D007527:Isoenzymes; D007546:Isoquinolines; D009240:N-Formylmethionine Leucyl-Phenylalanine; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D013449:Sulfonamides; C546760:PIK3CG protein, human; C578562:PDPK1 protein, human; C063509:N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide