title: Ephrin-A1 induces c-Cbl phosphorylation and EphA receptor down-regulation in T cells.
abstract: Eph receptor tyrosine kinases are expressed by T lineage cells, and stimulation with their ligands, the ephrins, has recently been shown to modulate T cell behavior. We show that ephrin-A1 stimulation of Jurkat T cells induces tyrosine phosphorylation of EphA3 receptors and cytoplasmic proteins, including the c-cbl proto-oncogene. Cbl phosphorylation was also observed in peripheral blood T cells. In contrast, stimulation of Jurkat cells with the EphB receptor ligand ephrin-B1 does not cause Cbl phosphorylation. EphA activation also induced Cbl association with Crk-L and Crk-II adapters, but not the related Grb2 protein. Induction of Cbl phosphorylation upon EphA activation appeared to be dependent upon Src family kinase activity, as Cbl phosphorylation was selectively abrogated by the Src family inhibitor 4-amino-5(4-chlorophenyl-7-(tert-butyl)pyrazolo[3,4-d]pyrimidine, while EphA phosphorylation was unimpaired. Ephrin-A1 stimulation of Jurkat cells was also found to cause down-regulation of endogenous EphA3 receptors from the cell surface and their degradation. In accordance with the role of Cbl as a negative regulator of receptor tyrosine kinases, overexpression of wild-type Cbl, but not its 70-Z mutant, was found to down-regulate EphA receptor expression. Receptor down-regulation could also be inhibited by blockage of Src family kinase activity. Our findings show that EphA receptors can actively signal in T cells, and that Cbl performs multiple roles in this signaling pathway, functioning to transduce signals from the receptors as well as regulating activated EphA receptor expression.
authors.affiliation: Immunology and Allergy, Department of Pediatrics, Research Institute, Hospital for Sick Children, and University of Toronto, Toronto, Canada.
authors.forename: Nigel
authors.initials: N
authors.lastname: Sharfe
authors.forename: Andrew
authors.initials: A
authors.lastname: Freywald
authors.forename: Ana
authors.initials: A
authors.lastname: Toro
authors.forename: Chaim M
authors.initials: CM
authors.lastname: Roifman
mesh_terms: D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism / Q000502:physiology; D015536:Down-Regulation / Q000276:immunology; D004789:Enzyme Activation / Q000187:drug effects; D036382:Ephrin-A1 / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D019169:Jurkat Cells; D010766:Phosphorylation / Q000187:drug effects; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D050721:Proto-Oncogene Proteins c-cbl; D011743:Pyrimidines / Q000494:pharmacology; D036121:Receptor, EphA3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D036122:Receptor, EphA4 / Q000037:antagonists & inhibitors / Q000235:genetics; D036081:Receptors, Eph Family / Q000037:antagonists & inhibitors* / Q000096:biosynthesis / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D016176:T-Lymphocyte Subsets / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D014162:Transfection; D014443:Tyrosine / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases; D019061:src-Family Kinases / Q000037:antagonists & inhibitors
chemical_list: C412373:AG 1879; D036382:Ephrin-A1; C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D011518:Proto-Oncogene Proteins; D011743:Pyrimidines; D014443:Tyrosine; D050721:Proto-Oncogene Proteins c-cbl; D044767:Ubiquitin-Protein Ligases; D036121:Receptor, EphA3; D036122:Receptor, EphA4; D036081:Receptors, Eph Family; D019061:src-Family Kinases; C067419:CBL protein, human