title: The EphB6 receptor inhibits JNK activation in T lymphocytes and modulates T cell receptor-mediated responses.
abstract: EphB6 is the most recently identified member of the Eph receptor tyrosine kinase family. EphB6 is primarily expressed in thymocytes and a subpopulation of T cells, suggesting that it may be involved in regulation of T lymphocyte differentiation and functions. We show here that overexpression of EphB6 in Jurkat T cells and stimulation with the EphB6 ligand, ephrin-B1, results in the selective inhibition of TCR-mediated activation of JNK but not the MAPK pathway. EphB6 appears to suppress the JNK pathway by preventing T cell receptor (TCR)-induced activation of the small GTPase Rac1, a critical event in initiating the JNK cascade. Furthermore, EphB6 blocked anti-CD3-induced secretion of IL-2 and CD25 expression in a ligand-dependent manner. Dominant negative EphB6 suppressed the inhibitory activity of the endogenous receptor and enhanced anti-CD3-induced JNK activation, CD25 expression, and IL-2 secretion, confirming the requirement for EphB6-specific signaling. Activation of the JNK pathway and the establishment of an IL-2/IL-2R autocrine loop have been shown to play a role in the negative selection of CD4(+)CD8(+) self-reacting thymocytes. In agreement, stimulation of murine thymocytes with ephrin-B1 not only blocked anti-CD3-induced CD25 up-regulation and IL-2 production, but also inhibited TCR-mediated apoptosis. Thus, EphB6 may play an important role in regulating thymocyte differentiation and modulating responses of mature T cells.
authors.affiliation: Division of Immunology and Allergy, Department of Pediatrics, Infection, Immunity, Injury, and Repair Program, Research Institute, The Hospital for Sick Children and the University of Toronto, Ontario M5G 1X8, Canada.
authors.forename: Andrew
authors.initials: A
authors.lastname: Freywald
authors.forename: Nigel
authors.initials: N
authors.lastname: Sharfe
authors.forename: Cher
authors.initials: C
authors.lastname: Rashotte
authors.forename: Thomas
authors.initials: T
authors.lastname: Grunberger
authors.forename: Chaim M
authors.initials: CM
authors.lastname: Roifman
mesh_terms: D004789:Enzyme Activation; D006801:Humans; D007376:Interleukin-2 / Q000096:biosynthesis; D048031:JNK Mitogen-Activated Protein Kinases; D019169:Jurkat Cells; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism / Q000502:physiology; D036261:Receptor, EphB6 / Q000502:physiology*; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D015375:Receptors, Interleukin-2 / Q000096:biosynthesis; D013601:T-Lymphocytes / Q000201:enzymology* / Q000502:physiology
chemical_list: D007376:Interleukin-2; D036261:Receptor, EphB6; D011948:Receptors, Antigen, T-Cell; D015375:Receptors, Interleukin-2; D048031:JNK Mitogen-Activated Protein Kinases; D020928:Mitogen-Activated Protein Kinases