Cutting Edge: Induced Loss of Rasgrp1 in Peripheral CD4+ T Cells of Conditional Rasgrp1-Deficient Mice Reveals an Essential Role for Rasgrp1 in TCR/CD28-Induced Ras-MAPK Signaling.

Ras guanine nucleotide-releasing protein 1 (Rasgrp1) is a Ras guanine nucleotide exchange factor that participates in the activation of the Ras-ERK signaling pathway in developing T cells and is required for efficient thymic T cell positive selection. However, the role of Rasgrp1 in mature peripheral T cells has not been definitively addressed, in part because peripheral T cells from constitutive Rasgrp1-deficient mice show an abnormal activated phenotype. In this study, we generated an inducible Rasgrp1-deficient mouse model to allow acute disruption of Rasgrp1 in peripheral CD4+ T cells in the context of normal T cell development. TCR/CD28-mediated activation of Ras-ERK signaling was blocked in Rasgrp1-deficient peripheral CD4+ T cells. Furthermore, Rasgrp1-deficient CD4+ T cells were unable to synthesize IL-2 and the high-affinity IL-2R and were unable to proliferate in response to TCR/CD28 stimulation. These findings highlight an essential function for Rasgrp1 for TCR/CD28-induced Ras-ERK activation in peripheral CD4+ T cells.