title: cAMP-dependent protein kinase (PKA) inhibits T cell activation by phosphorylating ser-43 of raf-1 in the MAPK/ERK pathway.
abstract: cAMP-dependent protein kinase (PKA) has been suggested to interfere with T-cell activation by inhibiting interleukin (IL-2) receptor alpha-chain (CD25) expression and IL-2 production. The Ras/MAP kinase pathway has been found to be necessary for induction of the IL-2 production. In this study, we have scrutinized the Ras/MAP kinase pathway in Jurkat T-cells to attempt to identify any sites for PKA-mediated regulatory phosphorylations. Here we unambiguously demonstrate that PKA directly inhibits anti-CD3-induced MAP kinase activation. In vitro phosphorylation experiments showed that Raf-1 was extensively phosphorylated by PKA, while ERK2 and MEK were not. Phosphopeptide mapping identified Ser-43 of Raf-1 as the only site phosphorylated by PKA in the Ras/MAPK pathway. Transient transfection experiments demonstrated that mutations of Ser-43 of the Raf-1 kinase were rendered insensitive to cAMP-mediated inhibition.
authors.affiliation: Institute of Immunology, The National Hospital N-0027, Oslo, Norway.
authors.forename: C
authors.initials: C
authors.lastname: Ramstad
authors.forename: V
authors.initials: V
authors.lastname: Sundvold
authors.forename: H K
authors.initials: HK
authors.lastname: Johansen
authors.forename: T
authors.initials: T
authors.lastname: Lea
mesh_terms: D000242:Cyclic AMP / Q000031:analogs & derivatives / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D008213:Lymphocyte Activation; D020935:MAP Kinase Signaling System / Q000187:drug effects; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism*; D017354:Point Mutation; D019908:Proto-Oncogene Proteins c-raf / Q000235:genetics / Q000378:metabolism*; D013601:T-Lymphocytes / Q000187:drug effects / Q000201:enzymology* / Q000276:immunology
chemical_list: D010768:Phosphoserine; D000242:Cyclic AMP; D019908:Proto-Oncogene Proteins c-raf; D017868:Cyclic AMP-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1