title: RasGRP1, but not RasGRP3, is required for efficient thymic β-selection and ERK activation downstream of CXCR4.
abstract: T cell development is a highly dynamic process that is driven by interactions between developing thymocytes and the thymic microenvironment. Upon entering the thymus, the earliest thymic progenitors, called CD4(-)CD8(-) 'double negative' (DN) thymocytes, pass through a checkpoint termed "β-selection" before maturing into CD4(+)CD8(+) 'double positive' (DP) thymocytes. β-selection is an important developmental checkpoint during thymopoiesis where developing DN thymocytes that successfully express the pre-T cell receptor (TCR) undergo extensive proliferation and differentiation towards the DP stage. Signals transduced through the pre-TCR, chemokine receptor CXCR4 and Notch are thought to drive β-selection. Additionally, it has long been known that ERK is activated during β-selection; however the pathways regulating ERK activation remain unknown. Here, we performed a detailed analysis of the β-selection events in mice lacking RasGRP1, RasGRP3 and RasGRP1 and 3. We report that RasGRP1 KO and RasGRP1/3 DKO deficient thymi show a partial developmental block at the early DN3 stage of development. Furthermore, DN3 thymocytes from RasGRP1 and RasGRP1/3 double knock-out thymi show significantly reduced proliferation, despite expression of the TCRβ chain. As a result of impaired β-selection, the pool of TCRβ(+) DN4 is significantly diminished, resulting in inefficient DN to DP development. Also, we report that RasGRP1 is required for ERK activation downstream of CXCR4 signaling, which we hypothesize represents a potential mechanism of RasGRP1 regulation of β-selection. Our results demonstrate that RasGRP1 is an important regulator of proliferation and differentiation at the β-selection checkpoint and functions downstream of CXCR4 to activate the Ras/MAPK pathway.
authors: Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada.
authors: Dominic P
authors: DP
authors: Golec
authors: Nancy A
authors: NA
authors: Dower
authors: James C
authors: JC
authors: Stone
authors: Troy A
authors: TA
authors: Baldwin
mesh_terms: D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation; D005260:Female; D055786:Gene Knockout Techniques; D020662:Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000276:immunology*; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D019718:Receptors, CXCR4 / Q000276:immunology*; D013601:T-Lymphocytes / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D013950:Thymus Gland / Q000166:cytology* / Q000276:immunology / Q000378:metabolism; D020663:ras Guanine Nucleotide Exchange Factors / Q000235:genetics / Q000276:immunology*
chemical_list: D020662:Guanine Nucleotide Exchange Factors; C526545:RasGRP3 protein, mouse; C112278:Rasgrp1 protein, mouse; D019718:Receptors, CXCR4; D020663:ras Guanine Nucleotide Exchange Factors