RasGRF2, a Guanosine Nucleotide Exchange Factor for Ras GTPases, Participates in T-Cell Signaling Responses

Abstract

The Ras pathway is critical for the development and function of T lymphocytes. The stimulation of this GTPase in T cells occurs primarily through the Vav1- and phospholipase C-γ1-dependent activation of RasGRP1, a diacylglycerol-responsive Ras GDP/GTP exchange factor. Here, we show that a second exchange factor, RasGRF2, also participates in T-cell signaling. RasGRF2 is expressed in T cells, translocates to immune synapses, activates Ras, and stimulates the transcriptional factor NF-AT (nuclear factor of activated T cells) through Ras- and phospholipase C-γ1-dependent routes. T-cell receptor-, Vav1-, and Ca²⁺-elicited pathways synergize with RasGRF2 for NF-AT stimulation. The analysis of RasGRF2-deficient mice indicates that this protein is required for the induction of bona fide NF-AT targets such as the cytokines tumor necrosis factor alpha and interleukin 2, while it plays minor roles in Ras activation itself. The comparison of lymphocytes from Vav1^−/−, Rasgrf2^−/−, and Vav1^−/−; Rasgrf2^−/− mice demonstrates that the RasGRF2 pathway cooperates with the Vav1/RasGRP1 route in the blasting transformation and proliferation of mature T cells. These results identify RasGRF2 as an additional component of the signaling machinery involved in T-cell receptor- and NF-AT-mediated immune responses.

X.R.B.'s work is supported by grants from the U.S. National Cancer Institute/NIH (5R01-CA73735-10), the Spanish Ministry of Education and Science (MES) (SAF2006-01789), the Castilla-León Autonomous Government (SA053A05), and the Red Temática de Investigación Cooperativa en Cáncer (RTICC) (RD06/0020/0001), Fondo de Investigaciones Sanitarias (FIS), Carlos III Institute, Spanish Ministry of Health. E.S. is supported by grants from the MES (GEN2003-20239-C062) and FIS (PI061274, RD06/0020/0000). S.R. has been partially supported by the NCI/NIH and the MES Juan de la Cierva program. All Spanish funding is cosponsored by the European Union FEDER program.

We thank B. Alarcón and P. Delgado for their initial help for setting up the immune synapse experiments, J. Almeida and A. Orfao for help in the T-cell stimulation and flow cytometry experiments, V. Tybulewicz for his generous gift of vav1^−/− mice, J. Tamame and M. T. Blázquez for technical assistance, and M. J. Caloca for comments on the manuscript.

We declare no conflicts of interest related to this work.