GM-CSF and IL-2 share common control mechanisms in response to costimulatory signals in T cells.
Antigen complexed with major histocompatibility complex class I or II molecules on the surface of antigen presenting cells interacts with the T cell receptor (TCR) on the surface of T cells and initiates an activation cascade. So called costimulatory signals, mediated by other cell surface interactions or soluble cytokines produced by antigen presenting cells, are also required for complete T cell activation. High levels of cytokine gene expression in T cells also required both TCR and costimulatory signals. The granulocyte-macrophage colony-stimulating factor requires sequences in the promoter as well as a powerful enhancer located 3kb upstream to respond to TCR-like signals. These promoter and enhancer regions are mainly activated by the transcription factor nuclear factor of activated T cells (NFAT). The activation of NFAT by TCR signals has been well described for interleukin-2 (IL-2) and IL-4 gene transcription in T cells. Costimulatory signals, such as activation of the CD28 cell surface molecule on T cells, lead to activation through a distinct region of the granulocyte-macrophage colony-stimulating factor (GM-CSF) promoter. This region is termed the CK-1 or CD28RE and appears to bind specific members of the NF-kappa B family of transcription factors. Human T leukemia virus type 1 (HTLV-1) infects T cells and can lead to increase GM-CSF expression. We have found that the HTLV-1 transactivator protein, tax, acts as a costimulatory signal for GM-CSF and IL-2 gene transcription, in that it can cooperate with TCR signals to mediate high level gene expression. Tax activates the GM-CSF promoter through the CK-1/CD28RE region and also activates nuclear factor-kappa B binding to this region. However, other transcription factors or coactivators of NF-kappa B are required for tax activation but these remain to be identified. The CK-1/CD28RE of GM-CSF shows a high degree of similarity to the IL-2 CD28RE and the IL-3 gene also contains a related region. This observation, together with the fact that both GM-CSF and IL-2 respond to TCR signals via NFAT, implies a high degree of conservation in the regulation of cytokine gene expression in T cells.
Shannon
M F
MF
Division of Human Immunology, Hanson Centre for Cancer Research, Institute of Medical and Veterinary Science, Adelaide, South Australia.
Himes
S R
SR
Coles
L S
LS
D001483:Base Sequence; D001665:Binding Sites; D018106:CD28 Antigens / Q000502:physiology; D004268:DNA-Binding Proteins / Q000502:physiology; D005786:Gene Expression Regulation; D016356:Gene Products, tax / Q000502:physiology; D016178:Granulocyte-Macrophage Colony-Stimulating Factor / Q000502:physiology*; D006801:Humans; D066298:In Vitro Techniques; D007376:Interleukin-2 / Q000235:genetics / Q000502:physiology*; D007377:Interleukin-3 / Q000235:genetics; D008213:Lymphocyte Activation; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000502:physiology; D011401:Promoter Regions, Genetic; D013601:T-Lymphocytes / Q000502:physiology*
D018106:CD28 Antigens; D004268:DNA-Binding Proteins; D016356:Gene Products, tax; D007376:Interleukin-2; D007377:Interleukin-3; D016328:NF-kappa B; D016178:Granulocyte-Macrophage Colony-Stimulating Factor