Dissociation between the translocation and the activation of Akt in fMLP-stimulated human neutrophils--effect of prostaglandin E2

J Leukoc Biol. 2007 Jun;81(6):1523-34. doi: 10.1189/jlb.0406256. Epub 2007 Mar 5.

Abstract

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3-Phosphoinositide-Dependent Protein Kinases
  • Class Ib Phosphatidylinositol 3-Kinase
  • Cyclic AMP / metabolism
  • Dinoprostone / pharmacology
  • Dinoprostone / physiology*
  • Enzyme Activation
  • Humans
  • In Vitro Techniques
  • Isoenzymes / antagonists & inhibitors
  • Isoenzymes / metabolism
  • Isoquinolines / pharmacology
  • MAP Kinase Signaling System / drug effects
  • MAP Kinase Signaling System / physiology
  • N-Formylmethionine Leucyl-Phenylalanine / pharmacology*
  • Neutrophils / drug effects
  • Neutrophils / physiology*
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphorylation
  • Protein Serine-Threonine Kinases / metabolism
  • Protein Transport
  • Proto-Oncogene Proteins c-akt / antagonists & inhibitors
  • Proto-Oncogene Proteins c-akt / metabolism*
  • Sulfonamides / pharmacology

Substances

  • Isoenzymes
  • Isoquinolines
  • Phosphoinositide-3 Kinase Inhibitors
  • Sulfonamides
  • N-Formylmethionine Leucyl-Phenylalanine
  • Cyclic AMP
  • Class Ib Phosphatidylinositol 3-Kinase
  • PIK3CG protein, human
  • 3-Phosphoinositide-Dependent Protein Kinases
  • PDPK1 protein, human
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Dinoprostone
  • N-(2-(4-bromocinnamylamino)ethyl)-5-isoquinolinesulfonamide