RESUMO
Sos-1 and Sos-2 are ubiquitously expressed Ras-guanine exchange factors involved in Erk-MAP kinase pathway activation. Using mice lacking genes encoding Sos-1 and Sos-2, we evaluated the role of these proteins in peripheral T-cell signaling and function. Our results confirmed that TCR-mediated Erk activation in peripheral CD4(+) T cells does not depend on Sos-1 and Sos-2, although IL-2-mediated Erk activation does. Unexpectedly, however, we show an increase in AKT phosphorylation in Sos-1/2dKO CD4(+) T cells upon TCR and IL-2 stimulation. Activation of AKT was likely a consequence of increased recruitment of PI3K to Grb2 upon TCR and/or IL-2 stimulation in Sos-1/2dKO CD4(+) T cells. The increased activity of the PI3K/AKT pathway led to downregulation of the surface receptor CD62L in Sos-1/2dKO T cells and a subsequent impairment in T-cell migration.
Assuntos
Linfócitos T CD4-Positivos/imunologia , Movimento Celular/imunologia , Fosfatidilinositol 3-Quinases/imunologia , Proteína SOS1/imunologia , Transdução de Sinais/imunologia , Proteínas Son Of Sevenless/imunologia , Animais , Movimento Celular/genética , Ativação Enzimática/genética , Ativação Enzimática/imunologia , Proteína Adaptadora GRB2/genética , Proteína Adaptadora GRB2/imunologia , Interleucina-2/genética , Interleucina-2/imunologia , Selectina L/genética , Selectina L/imunologia , Camundongos , Camundongos Knockout , Fosfatidilinositol 3-Quinases/genética , Fosforilação/genética , Fosforilação/imunologia , Proteínas Proto-Oncogênicas c-akt/genética , Proteínas Proto-Oncogênicas c-akt/imunologia , Receptores de Antígenos de Linfócitos T/genética , Receptores de Antígenos de Linfócitos T/imunologia , Proteína SOS1/genética , Transdução de Sinais/genética , Proteínas Son Of Sevenless/genéticaRESUMO
The duration and/or the magnitude of Ras-Erk activation are known to be crucial for cell-fate decisions. In T cells, sustained Erk activation correlates with differentiation/proliferation, whereas transient Erk activation parallels with unresponsiveness/apoptosis. The mechanism by which Son of sevenless (Sos) proteins and Ras guanyl-releasing protein 1 (RasGRP1) contribute to dynamics of Erk activation in mature T cells is not yet known. Here, we have assessed this issue using stimuli inducing either transient or sustained TCR signaling and RNA interference mediated suppression of Sos1, Sos2, and RasGRP1 expression in primary human T cells. We found that transient Erk activation depends on RasGRP1 but not on Sos. Conversely, sustained Erk signaling and T-cell activation depend on both Sos1 and RasGRP1. In summary, our data show for the first time that the two guanine nucleotide exchange factors expressed in T cells are differentially involved in the regulation of the duration of Erk phosphorylation and T-cell activation.
Assuntos
MAP Quinases Reguladas por Sinal Extracelular/imunologia , Ativação Linfocitária/fisiologia , Sistema de Sinalização das MAP Quinases/fisiologia , Receptores de Antígenos de Linfócitos T/imunologia , Proteína SOS1/imunologia , Linfócitos T/imunologia , Proteínas de Ligação a DNA/biossíntese , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/imunologia , Ativação Enzimática/fisiologia , MAP Quinases Reguladas por Sinal Extracelular/biossíntese , MAP Quinases Reguladas por Sinal Extracelular/genética , Feminino , Regulação da Expressão Gênica/fisiologia , Fatores de Troca do Nucleotídeo Guanina/biossíntese , Fatores de Troca do Nucleotídeo Guanina/genética , Fatores de Troca do Nucleotídeo Guanina/imunologia , Humanos , Masculino , Fosforilação/fisiologia , Receptores de Antígenos de Linfócitos T/genética , Receptores de Antígenos de Linfócitos T/metabolismo , Proteína SOS1/genética , Proteína SOS1/metabolismo , Proteínas Son Of Sevenless/genética , Proteínas Son Of Sevenless/imunologia , Proteínas Son Of Sevenless/metabolismo , Linfócitos T/citologia , Linfócitos T/metabolismoRESUMO
Activation of the small G protein Ras is required for thymocyte differentiation. In thymocytes, Ras is activated by the Ras guanine exchange factors (RasGEFs) Sos1, Sos2, and RasGRP1. We report the development of a floxed allele of sos1 to assess the role of Sos1 during thymocyte development. Sos1 was required for pre-T-cell receptor (pre-TCR)- but not TCR-stimulated developmental signals. Sos1 deletion led to a partial block at the DN-to-DP transition. Sos1-deficient thymocytes showed reduced pre-TCR-stimulated proliferation, differentiation, and ERK phosphorylation. In contrast, TCR-stimulated positive selection, and negative selection under strong stimulatory conditions, remained intact in Sos1-deficient mice. Comparison of RasGEF expression at different developmental stages showed that relative to Sos2 and RasGRP1, Sos1 is most abundant in DN thymocytes, but least abundant in DP thymocytes. These data reveal that Sos1 is uniquely positioned to affect signal transduction early in thymocyte development.
Assuntos
Proteína SOS1/imunologia , Linfócitos T/imunologia , Animais , Diferenciação Celular/imunologia , Proliferação de Células , Feminino , Marcação de Genes , Fatores de Troca do Nucleotídeo Guanina/imunologia , Masculino , Camundongos , Camundongos Knockout , Modelos Imunológicos , Receptores de Antígenos de Linfócitos T/metabolismo , Proteína SOS1/deficiência , Proteína SOS1/genética , Transdução de Sinais/imunologia , Proteínas Son Of Sevenless/imunologia , Linfócitos T/citologiaRESUMO
RasGRP1 and Sos are two Ras-guanyl-nucleotide exchange factors that link TCR signal transduction to Ras and MAPK activation. Recent studies demonstrate positive selection of developing thymocytes is crucially dependent on RasGRP1, whereas negative selection of autoreactive thymocytes appears to be RasGRP1 independent. However, the role of RasGRP1 in T regulatory (Treg) cell development and function is unknown. In this study, we characterized the development and function of CD4(+)CD25(+)Foxp3(+) and CD8(+)CD44(high)CD122(+) Treg lineages in RasGRP1(-/-) mice. Despite impaired CD4 Treg cell development in the thymus, the periphery of RasGRP1(-/-) mice contained significantly increased frequencies of CD4(+)Foxp3(+) Treg cells that possessed a more activated cell surface phenotype. Furthermore, on a per cell basis, CD4(+)Foxp3(+) Treg cells from mutant mice are more suppressive than their wild-type counterparts. Our data also suggest that the lymphopenic environment in the mutant mice plays a dominant role of favored peripheral development of CD4 Treg cells. These studies suggest that whereas RasGRP1 is crucial for the intrathymic development of CD4 Treg cells, it is not required for their peripheral expansion and function. By contrast to CD4(+)CD25(+)Foxp3(+) T cells, intrathymic development of CD8(+)CD44(high)CD122(+) Treg cells is unaffected by the RasGRP1(-/-) mutation. Moreover, RasGRP1(-/-) mice contained greater numbers of CD8(+)CD44(high)CD122(+) T cells in the spleen, relative to wild-type mice. Activated CD8 Treg cells from RasGRP1(-/-) mice retained their ability to synthesize IL-10 and suppress the proliferation of wild-type CD8(+)CD122(-) T cells, albeit at a much lower efficiency than wild-type CD8 Treg cells.
