Ectopic B-Raf Expression Enhances Extracellular Signal-regulated Kinase (ERK) Signaling in T Cells and Prevents Antigen-presenting Cell-induced Anergy

• Published in: The Journal of biological chemistry 2003-09, Vol.278 (38), p.35940-35949
• Main Authors: Dillon, Tara J., Karpitski, Vladamir, Wetzel, Scott A., Parker, David C., Shaw, Andréy S., Stork, Philip J.S.
• Format: Article
• Language: English
• Subjects: Animals; Antigen-Presenting Cells - metabolism; Antigens, CD - biosynthesis; Antigens, Differentiation, T-Lymphocyte - biosynthesis; B-Raf protein; Blotting, Western; Cell Division; Cell Nucleus - metabolism; DNA-Binding Proteins; Dose-Response Relationship, Drug; Enzyme Activation; ets-Domain Protein Elk-1; Fibroblasts - metabolism; Flow Cytometry; histocompatibility antigen H-2; Humans; Jurkat Cells; Lectins, C-Type; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mitogen-Activated Protein Kinases - metabolism; Models, Biological; Peptides - chemistry; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins B-raf; Proto-Oncogene Proteins c-raf - biosynthesis; Proto-Oncogene Proteins c-raf - metabolism; rap1 GTP-Binding Proteins - metabolism; Receptors, Antigen, T-Cell - metabolism; Signal Transduction; T-Lymphocytes - cytology; T-Lymphocytes - enzymology; T-Lymphocytes - metabolism; Tissue Distribution; Transcription Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M301506200

T cells that receive stimulation through the T cell receptor (TCR) in the absence of costimulation become anergic and are refractory to subsequent costimulation. This unresponsiveness is associated with the constitutive activation of the small G protein, Rap1, and the lack of Ras-dependent activation of ERK. Recent studies suggest that Rap1 can activate the MAP kinase kinase kinase B-Raf that is either endogenously or ectopically expressed. Peripheral T cells generally do not express B-Raf; therefore, to test the hypothesis that ectopic expression of B-Raf could permit Rap1 to activate ERK signaling, we generated transgenic mice expressing B-Raf within peripheral T cells. This converted Rap1 into an activator of ERK, to enhance ERK activation and proliferation following TCR engagement in the absence of costimulation. When T cells were incubated with engineered APCs presenting antigen on I-Ek and expressing low levels of B7, they became anergic, displayed constitutive activation of Rap1, and were deficient in Ras and ERK activation. However, when incubated with the same APCs, T cells expressing the B-Raf transgene proliferated upon restimulation and displayed elevated ERK activation. Thus B-Raf expression and enhanced ERK activation is sufficient to prevent anergy in a model of APC-induced T cell anergy. However, studies using anti-TCR antibody-induced anergy showed that the ability of ERKs to reverse T cell anergy is dependent on the anergic model utilized.