title: RasGRP1 transmits prodifferentiation TCR signaling that is crucial for CD4 T cell development.
abstract: TCR signaling plays a governing role in both the survival and differentiation of bipotent double-positive thymocytes into the CD4(+) and CD8(+) single-positive T cell lineages. A central mediator of this developmental program is the small GTPase Ras, emitting cytoplasmic signals through downstream MAPK pathways and eventually affecting gene expression. TCR signal transduction orchestrates the activation of Ras by integrating at least two Ras-guanyl nucleotide exchange factors, RasGRP1 and Sos. In this study, we have characterized the relationship between RasGRP1 function and its potential roles in promoting ERK activity, cell survival, maturation, and lineage commitment. Investigations on RasGRP1(-/-) mice expressing a transgenic (Tg) MHC class II-restricted TCR revealed that the development of CD4 T cells expressing this Tg TCR is completely dependent on RasGRP1. Unexpectedly, a small number of functional CD8 single-positive thymocytes expressing the Tg MHC class II-restricted TCR exists in mutant mice. In addition, RasGRP1(-/-) double-positive thymocytes exhibit marked deficits in TCR-stimulated up-regulation of the positive selection marker CD69 and the antiapoptotic protein Bcl-2, whereas CD5 induction is unaffected. To evaluate the role of RasGRP1 in providing cellular survival signaling, we enforced Bcl-2 expression in RasGRP1(-/-) thymocytes. These studies demonstrate that RasGRP1 function cannot be fully complemented by Tg Bcl-2 expression. Therefore, we propose that RasGRP1 transmits differentiation signaling critically required for CD4 T cell development.
authors.affiliation: Department of Microbiology and Immunology, University of British Columbia, Vancouver, British Columbia, Canada.
authors.forename: John J
authors.initials: JJ
authors.lastname: Priatel
authors.forename: Xiaoxi
authors.initials: X
authors.lastname: Chen
authors.forename: Salim
authors.initials: S
authors.lastname: Dhanji
authors.forename: Ninan
authors.initials: N
authors.lastname: Abraham
authors.forename: Hung-Sia
authors.initials: HS
authors.lastname: Teh
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000166:cytology* / Q000201:enzymology / Q000276:immunology / Q000378:metabolism*; D018414:CD8-Positive T-Lymphocytes / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics / Q000276:immunology*; D002470:Cell Survival / Q000235:genetics / Q000276:immunology; D020662:Guanine Nucleotide Exchange Factors / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D000949:Histocompatibility Antigens Class II / Q000502:physiology; D020935:MAP Kinase Signaling System / Q000235:genetics / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008822:Mice, Transgenic; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000096:biosynthesis; D011948:Receptors, Antigen, T-Cell / Q000037:antagonists & inhibitors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D013602:T-Lymphocytes, Cytotoxic / Q000166:cytology / Q000276:immunology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology / Q000201:enzymology / Q000276:immunology; D018631:ras Proteins / Q000235:genetics / Q000502:physiology*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; D000949:Histocompatibility Antigens Class II; D019253:Proto-Oncogene Proteins c-bcl-2; C112278:Rasgrp1 protein, mouse; D011948:Receptors, Antigen, T-Cell; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D018631:ras Proteins