RasGRP1, but not RasGRP3, is required for efficient thymic β-selection and ERK activation downstream of CXCR4

• Published in: PloS one 2013, Vol.8 (1), p.e53300-e53300
• Main Authors: Golec, Dominic P, Dower, Nancy A, Stone, James C, Baldwin, Troy A
• Format: Article
• Language: English
• Subjects: Animals; Biology; CD4 antigen; CD8 antigen; Cell activation; Cell Line; Cell Proliferation; CXCR4 protein; Developmental stages; Differentiation; Extracellular signal-regulated kinase; Female; Gene expression; Gene Knockout Techniques; Guanine Nucleotide Exchange Factors - genetics; Guanine Nucleotide Exchange Factors - immunology; Immunology; Kinases; Lymphocytes; Male; MAP kinase; MAP Kinase Signaling System; Mice; Mice, Inbred C57BL; ras Guanine Nucleotide Exchange Factors - genetics; ras Guanine Nucleotide Exchange Factors - immunology; Receptors, CXCR4 - immunology; Signal transduction; Signaling; T cell receptors; T-cell receptor; T-Lymphocytes - cytology; T-Lymphocytes - immunology; T-Lymphocytes - metabolism; Thymocytes; Thymopoiesis; Thymus; Thymus Gland - cytology; Thymus Gland - immunology; Thymus Gland - metabolism
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0053300

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.