Raf-1 provides a dominant but not exclusive signal for the induction of CD69 expression on T cells.
Stimulation of the T cell antigen receptor (TCR) induces a number of intracellular signaling pathways which lead to the transcription of a variety of new genes. Of the newly synthesized proteins, the earliest to be detected on the cell surface is the type II integral membrane protein CD69. Cross-linking of this activation antigen induces signaling events related to T cell activation. The proto-oncogene product Ras has been reported to up-regulate CD69. However, which of the potential effectors of Ras induces the expression of CD69 has remained unclear. Using transient transfection, we have shown a constitutively active form of the serine/threonine kinase Raf-1 to be sufficient to induce CD69 expression in human Jurkat T cells. Raf-1 was further shown to be necessary for PMA-induced CD69 expression, since transfection of a dominant inhibitory form of Raf-1 blocked the up-regulation of CD69 by PMA. In addition, studies with the calcium ionophore ionomycin identified a previously uncharacterized pathway regulating the expression of CD69 in T cells. Elevation of intracellular calcium induced the expression of CD69 in both Jurkat cells and peripheral blood T cells. This effect was sensitive to the immunosuppressive drug cyclosporin A, indicating that calcium-induced CD69 expression is mediated by the protein phosphatase calcineurin. Taken together, these results define Raf-1 as the major signaling mediator of CD69 expression in T cells and suggest that multiple mechanisms exist to regulate the level of CD69 expression following TCR stimulation.
Taylor-Fishwick
D A
DA
Signal Transduction Branch, Naval Medical Research Institute, Bethesda, MD 20889, USA.
Siegel
J N
JN
D015703:Antigens, CD / Q000096:biosynthesis* / Q000187:drug effects*; D000945:Antigens, Differentiation, T-Lymphocyte / Q000096:biosynthesis* / Q000187:drug effects*; D016572:Cyclosporine / Q000494:pharmacology; D004306:Dose-Response Relationship, Immunologic; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology; D015759:Ionomycin / Q000494:pharmacology; D007476:Ionophores / Q000494:pharmacology; D037181:Lectins, C-Type; D008223:Lymphoma; D008934:Mitogens / Q000494:pharmacology; D017346:Protein Serine-Threonine Kinases / Q000494:pharmacology*; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000494:pharmacology*; D019908:Proto-Oncogene Proteins c-raf; D015398:Signal Transduction / Q000187:drug effects*; D013601:T-Lymphocytes / Q000187:drug effects / Q000276:immunology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects; D000099192:CD69 Antigens
D015703:Antigens, CD; D000945:Antigens, Differentiation, T-Lymphocyte; D016572:Cyclosporine; D007166:Immunosuppressive Agents; D015759:Ionomycin; D007476:Ionophores; D037181:Lectins, C-Type; D008934:Mitogens; D017346:Protein Serine-Threonine Kinases; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D019908:Proto-Oncogene Proteins c-raf; D013755:Tetradecanoylphorbol Acetate; D000099192:CD69 Antigens; C000715470:MAS1 protein, human