title: The molecular machinery for cAMP-dependent immunomodulation in T-cells.
abstract: cAMP inhibits Src-family kinase signalling by PKA (protein kinase A)-mediated phosphorylation and activation of Csk (C-terminal Src kinase). The PKA type I-Csk pathway is assembled and localized in membrane microdomains (lipid rafts) and regulates immune responses activated through the TCR (T-cell receptor). PKA type I is targeted to the TCR-CD3 complex during T-cell activation via an AKAP (A-kinase-anchoring protein) that serves as a scaffold for the cAMP-PKA/Csk pathway in lipid rafts of the plasma membrane during T-cell activation. Displacement of PKA by anchoring disruption peptides prevents cAMP/PKA type I-mediated inhibition of T-cell activation. These findings provide functional evidence that PKA type I regulation of T-cell responses is dependent on AKAP anchoring. Furthermore, we show that upon TCR/CD28 co-ligation, beta-arrestin in complex with PDE4 (phosphodiesterase 4) is recruited to lipid rafts. The CD28-mediated recruitment of PDE4 to lipid rafts potentiates T-cell immune responses and counteracts the local, TCR-induced production of cAMP that produces negative feedback in the absence of a co-receptor stimulus. The specific recruitment of PDE4 thus serves to abrogate the negative feedback by cAMP which is elicited in the absence of a co-receptor stimulus.
authors.affiliation: The Biotechnology Centre of Oslo, University of Oslo, P.O. Box 1125, Blindern, N-0317 Oslo, Norway. kjetil.tasken@biotek.uio.no
authors.forename: K
authors.initials: K
authors.lastname: Taskén
authors.forename: A J
authors.initials: AJ
authors.lastname: Stokka
mesh_terms: D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D000818:Animals; D018106:CD28 Antigens / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4; D006801:Humans; D021962:Membrane Microdomains / Q000276:immunology / Q000378:metabolism; D011948:Receptors, Antigen, T-Cell / Q000276:immunology / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology* / Q000378:metabolism*
chemical_list: D018106:CD28 Antigens; D011948:Receptors, Antigen, T-Cell; D000242:Cyclic AMP; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4