RasGRP is essential for mouse thymocyte differentiation and TCR signaling

Abstract

The Ras signaling pathway plays a critical role in thymopoiesis and T cell activation, but the mechanism of Ras regulation is controversial. At least one mode of Ras regulation in T cells involves the messenger diacylglycerol (DAG). RasGRP, a Ras activator with a DAG-binding C1 domain, is expressed in T cells and thymocytes. Here we show that thymi of RasGRP-null mutant mice have approximately normal numbers of immature thymocytes but a marked deficiency of mature, single-positive (CD4+CD8- and CD4-CD8+) thymocytes. In Ras signaling and proliferation assays, mutant thymocytes showed a complete lack of response to DAG analogs or T cell receptor (TCR) stimulation by antibodies. Thus, TCR and DAG are linked through RasGRP to Ras signaling.

Duration and Strength of Extracellular Signal-Regulated Kinase Signals Are Altered During Positive Versus Negative Thymocyte Selection

“…Accordingly, positive selection is also attenuated in mice deficient in CD3␦ and biochemical analysis revealed that ERK activation is severely impaired in these mice (11). Recent evidence has also shown that a novel guanine nucleotide exchange factor for Ras, RasGRP, is involved in thymocyte-positive selection (12). These studies along with studies using pharmacological inhibitors of the ERK pathway (13)(14)(15) clearly support the role for ERK during positive selection.…”

Mast Cells in Airway Hyporesponsive C3H/HeJ Mice Express a Unique Isoform of the Signaling Protein Ras Guanine Nucleotide Releasing Protein 4 That Is Unresponsive to Diacylglycerol and Phorbol Esters

“…They also increased their expression of prostaglandin D 2 synthase Ͼ100-fold (22). T cells express RasGRP1, and targeted disruption of this GEF's gene in mice results in a marked deficiency of mature CD4 ϩ /CD8 Ϫ and CD4 Ϫ /CD8 ϩ T cells (23). In a similar manner, it now appears that RasGRP4 regulates the final stages of MC differentiation and maturation, including what protease and lipid mediators MCs produce.…”

“…The 3T3 cell line was examined because this fibroblast line was used in the transfection experiments noted below to evaluate the role of mRasGRP4 in cellular adherence and activation of H-Ras. Finally, the T cell hybridoma was examined because mRasGRP1 was cloned from a T cell hybridoma and because this GEF is essential for T cell development and function in the mouse (23,26).…”

Early endosome localization and activity of RasGEF1b, a toll-like receptor-inducible Ras guanine-nucleotide exchange factor

“…27,33 Some functions for GEFs in the immune system have been described. RasGRP is important to mouse thymocyte differentiation after TCR stimulation, 34 and members of Vav family are essential for response of B lymphocytes to LPS. 35 Numerous studies with tumour cell lines, such as Jurkat cells or EL4 mouse lymphoma cells, indicate that Ras represents an essential link between TCR stimulation and cellular proliferation or cytokine gene induction.…”