Inhibition of T cell activation by cyclic adenosine 5'-monophosphate requires lipid raft targeting of protein kinase A type I by the A-kinase anchoring protein ezrin.
(1/23)
cAMP negatively regulates T cell immune responses by activation of type I protein kinase A (PKA), which in turn phosphorylates and activates C-terminal Src kinase (Csk) in T cell lipid rafts. Using yeast two-hybrid screening, far-Western blot, immunoprecipitation and immunofluorescense analyses, and small interfering RNA-mediated knockdown, we identified Ezrin as the A-kinase anchoring protein that targets PKA type I to lipid rafts. Furthermore, Ezrin brings PKA in proximity to its downstream substrate Csk in lipid rafts by forming a multiprotein complex consisting of PKA/Ezrin/Ezrin-binding protein 50, Csk, and Csk-binding protein/phosphoprotein associated with glycosphingolipid-enriched microdomains. The complex is initially present in immunological synapses when T cells contact APCs and subsequently exits to the distal pole. Introduction of an anchoring disruptor peptide (Ht31) into T cells competes with Ezrin binding to PKA and thereby releases the cAMP/PKA type I-mediated inhibition of T cell proliferation. Finally, small interfering RNA-mediated knockdown of Ezrin abrogates cAMP regulation of IL-2. We propose that Ezrin is essential in the assembly of the cAMP-mediated regulatory pathway that modulates T cell immune responses. (+info)
Prostaglandin E2 inhibits tumor necrosis factor-alpha RNA through PKA type I.
(2/23)
Tumor necrosis factor-alpha (TNF-alpha) is a cytokine that may contribute to the pathogenesis of septic shock, rheumatoid arthritis, cancer, and diabetes. Prostaglandins endogenously produced by macrophages act in an autocrine fashion to limit TNF-alpha production. We investigated the timing and signaling pathway of prostaglandin-mediated inhibition of TNF-alpha production in Raw 264.7 and J774 macrophages. TNF-alpha mRNA levels were rapidly modulated by PGE(2) or carbaprostacylin. PGE(2) or carbaprostacyclin prevented and rapidly terminated on-going TNF-alpha gene transcription within 15 min of prostaglandin treatment. Selective activation of PKA type I, but not PKA type II or Epac, with chemical analogs of cAMP was sufficient to inhibit LPS-induced TNF-alpha mRNA levels. The mechanisms by which prostaglandins limit TNF-alpha mRNA levels may underlie endogenous regulatory mechanisms that limit inflammation, and may have important implications for understanding chronic inflammatory disease pathogenesis. (+info)
Protein kinase A RI-alpha predicts for prostate cancer outcome: analysis of radiation therapy oncology group trial 86-10.
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