GABP factors bind to a distal interleukin 2 (IL-2) enhancer and contribute to c-Raf-mediated increase in IL-2 induction.
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.
Avots
A
A
Department of Molecular Pathology, Institute of Pathology, University of Würzburg, Germany.
Hoffmeyer
A
A
Flory
E
E
Cimanis
A
A
Rapp
U R
UR
Serfling
E
E
D003001:Cloning, Molecular; D016572:Cyclosporine / Q000494:pharmacology; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004742:Enhancer Elements, Genetic / Q000235:genetics*; D051268:GA-Binding Protein Transcription Factor; D005786:Gene Expression Regulation / Q000235:genetics*; D006801:Humans; D007376:Interleukin-2 / Q000235:genetics*; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D019169:Jurkat Cells; D017354:Point Mutation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction / Q000235:genetics; D013601:T-Lymphocytes; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism*
D004268:DNA-Binding Proteins; D051268:GA-Binding Protein Transcription Factor; D007376:Interleukin-2; D007476:Ionophores; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D015759:Ionomycin; D016572:Cyclosporine; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D013755:Tetradecanoylphorbol Acetate