cAMP-dependent protein kinase (PKA) inhibits T cell activation by phosphorylating ser-43 of raf-1 in the MAPK/ERK pathway

Cell Signal. 2000 Aug;12(8):557-63. doi: 10.1016/s0898-6568(00)00097-8.


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.

MeSH terms

  • Cyclic AMP / analogs & derivatives
  • Cyclic AMP / pharmacology
  • Cyclic AMP-Dependent Protein Kinases / physiology*
  • Humans
  • Jurkat Cells
  • Lymphocyte Activation*
  • MAP Kinase Signaling System* / drug effects
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Phosphorylation
  • Phosphoserine / metabolism*
  • Point Mutation
  • Proto-Oncogene Proteins c-raf / genetics
  • Proto-Oncogene Proteins c-raf / metabolism*
  • T-Lymphocytes / drug effects
  • T-Lymphocytes / enzymology*
  • T-Lymphocytes / immunology


  • Phosphoserine
  • Cyclic AMP
  • Proto-Oncogene Proteins c-raf
  • Cyclic AMP-Dependent Protein Kinases
  • Mitogen-Activated Protein Kinase 1