GABP factors bind to a distal interleukin 2 (IL-2) enhancer and contribute to c-Raf-mediated increase in IL-2 induction

Mol Cell Biol. 1997 Aug;17(8):4381-9. doi: 10.1128/MCB.17.8.4381.

Abstract

Triggering of the T-cell receptor-CD3 complex activates two major signal cascades in T lymphocytes, (i) Ca2+-dependent signal cascades and (ii) protein kinase cascades. Both signal cascades contribute to the induction of the interleukin 2 (IL-2) gene during T-cell activation. Prominent protein kinase cascades are those that activate mitogen-activated protein (MAP) kinases. We show here that c-Raf, which is at the helm of the classic MAP-Erk cascade, contributes to IL-2 induction through a distal enhancer element spanning the nucleotides from positions -502 to -413 in front of the transcriptional start site of the IL-2 gene. Induction of this distal IL-2 enhancer differs from induction of the proximal IL-2 promoter-enhancer, since it is induced by phorbol esters alone and independent from Ca2+ signals. In DNA-protein binding studies, we detected the binding of transcription factors GABP alpha and -beta to a dyad symmetry element (DSE) of the distal enhancer, which is formed by palindromic binding sites of Ets-like factors. Introduction of point mutations suppressing GABP binding to the DSE interfered with the induction of the distal enhancer and the entire IL-2 promoter-enhancer, while overexpression of both GABP factors enhanced the IL-2 promoter-enhancer induction. Overexpression of BXB, a constitutive active version of c-Raf, and of further members of the Ras-Raf-Erk signal cascade exerted an increase of GABP-mediated promoter-enhancer induction. In conjunction with previously published data on c-Raf-induced phosphorylation of GABP factors (E. Flory, A. Hoffmeyer, U. Smola, U. R. Rapp, and J. T. Bruder, J. Virol. 70:2260-2268, 1996), these results indicate a contribution of GABP factors to the Raf-mediated enhancement of IL-2 induction during T-cell activation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Cloning, Molecular
  • Cyclosporine / pharmacology
  • DNA / genetics
  • DNA / metabolism
  • DNA-Binding Proteins / metabolism*
  • Enhancer Elements, Genetic / genetics*
  • GA-Binding Protein Transcription Factor
  • Gene Expression Regulation / genetics*
  • Humans
  • Interleukin-2 / genetics*
  • Ionomycin / pharmacology
  • Ionophores / pharmacology
  • Jurkat Cells
  • Point Mutation
  • Protein Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-raf
  • Signal Transduction / genetics
  • T-Lymphocytes
  • Tetradecanoylphorbol Acetate / pharmacology
  • Transcription Factors / metabolism*

Substances

  • DNA-Binding Proteins
  • GA-Binding Protein Transcription Factor
  • Interleukin-2
  • Ionophores
  • Proto-Oncogene Proteins
  • Transcription Factors
  • Ionomycin
  • Cyclosporine
  • DNA
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-raf
  • Tetradecanoylphorbol Acetate