Digital Signaling and Hysteresis Characterize Ras Activation in Lymphoid Cells

Das, Jayajit; Ho, Mary; Zikherman, Julie; Govern, Christopher C.; Yang, Ming; Weiss, Arthur; Chakraborty, Arup K.; Roose, Jeroen P.

doi:10.1016/j.cell.2008.11.051

Cited by 376 publications

(554 citation statements)

References 40 publications

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“…Candidates for such downstream signaling modules include the MAPK pathway (34), especially feedback to upstream signaling through cytoplasmic phospholipase 2 (cpla2). cpla2 is absent in mature lymphocytes, and this may be why our recent results show that feedback regulation of SOS underlies a digital response in mature T cells (27). Although cpla2 is present in thymocytes (35), the unimodal ERK response to PMA stimulation seen in our experiments (Fig.…”

Section: Discussioncontrasting

confidence: 48%

“…At later time points, a bimodal pattern of signaling is predicted as a second population of cells exhibiting much higher levels of active Ras emerges; that is, thymocytes are ''on'' or ''off.'' Bimodality is the consequence of positive feedback regulation of SOS resulting in a bifurcation, whereby a single stable solution transforms into two stable solutions and an unstable solution when stimulus exceeds a threshold value (27). Positive feedback is one of the biological motifs that are known to show bistability and switch-like responses (28).…”

Section: A Sharp Increase In Ras Activation Beyond a Threshold Ligandmentioning

confidence: 99%

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Origin of the sharp boundary that discriminates positive and negative selection of thymocytes

Prasad¹,

Zikherman

Das³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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T lymphocytes play a key role in adaptive immunity and are activated by interactions of their T cell receptors (TCR) with peptides (p) derived from antigenic proteins bound to MHC gene products. The repertoire of T lymphocytes available in peripheral organs is tuned in the thymus. Immature T lymphocytes (thymocytes) interact with diverse endogenous peptides bound to MHC in the thymus. TCR expressed on thymocytes must bind weakly to endogenous pMHC (positive selection) but must not bind too strongly to them (negative selection) to emerge from the thymus. Negatively selecting pMHC ligands bind TCR with a binding affinity that exceeds a sharply defined (digital) threshold. In contrast, there is no sharp threshold separating positively selecting ligands from those that bind too weakly to elicit a response. We describe results of computer simulations and experiments, which suggest that the contrast between the characters of the positive and negative selection thresholds originates in differences in the way in which Ras proteins are activated by ligands of varying potency. The molecular mechanism suggested by our studies generates hypotheses for how genetic aberrations may dampen the digital negative selection response, with concomitant escape of autoimmune T lymphocytes from the thymus.positive feedback ͉ Ras activation ͉ signal transduction ͉ T cell antigen receptor ͉ thymic development

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Section: Discussioncontrasting

confidence: 48%

Section: A Sharp Increase In Ras Activation Beyond a Threshold Ligandmentioning

confidence: 99%

Origin of the sharp boundary that discriminates positive and negative selection of thymocytes

Prasad¹,

Zikherman

Das³

et al. 2009

Proc. Natl. Acad. Sci. U.S.A.

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“…However, we failed to detect any increased phosphorylation of more TCR-proximal signaling proteins, such as Lck, ZAP-70, and LAT, which suggests that stimulation with low concentrations of antibodies could not fully recapitulate what was previously observed when the TCR was engaged by tetramers bound to low-affinity antigens in the absence of costimulation. The molecular events that meditate ERK activation can be driven by hysteretic regulatory effects, and it is therefore assumed that minor changes in TCR-proximal signals can have a major effect on ERK activity (37,38). It is therefore possible that TCR cross-linking with low concentrations of antibodies might not be sensitive enough to detect effects on early regulators of TCR signaling, but could still reveal the consequences on downstream proteins, such as ERK, that exhibit a digital mode of activation.…”

Section: Discussionmentioning

confidence: 99%

Themis1 enhances T cell receptor signaling during thymocyte development by promoting Vav1 activity and Grb2 stability

et al. 2016

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The T cell signaling protein Themis1 is essential for the positive and negative selection of thymocytes in the thymus. Although the developmental defect that results from the loss of Themis1 suggests that it enhances T cell receptor (TCR) signaling, Themis1 also recruits Src homology 2 domain-containing phosphatase-1 (SHP-1) to the vicinity of TCR signaling complexes, suggesting that it has an inhibitory role in TCR signaling. We used TCR signaling reporter mice and quantitative proteomics to explore the role of Themis1 in developing T cells. We found that Themis1 acted mostly as a positive regulator of TCR signaling in vivo when receptors were activated by positively selecting ligands. Proteomic analysis of the Themis1 interactome identified SHP-1, the TCR-associated adaptor protein Grb2, and the guanine nucleotide exchange factor Vav1 as the principal interacting partners of Themis1 in isolated mouse thymocytes. Analysis of TCR signaling in Themis1-deficient and Themis1-overexpressing mouse thymocytes demonstrated that Themis1 promoted Vav1 activity both in vitro and in vivo. The reduced activity of Vav1 and the impaired T cell development in Themis1 −/− mice were due in part to increased degradation of Grb2, which suggests that Themis1 is required to maintain the steady-state abundance of Grb2 in thymocytes. Together, these data suggest that Themis1 acts as a positive regulator of TCR signaling in developing T cells, and identify a mechanism by which Themis1 regulates thymic selection.

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“…These findings have led to an assumption that Grb2 may be responsible for TCR-induced Ras-Erk kinase activation in T cells (9). A recent study further shows that Sos regulates Ras activation in an "on or off" manner possibly via Grb2, whereas Ras-GRP may gradually tune Ras activity in cultured T cells, suggesting that Ras activation can be "digital or analog" (24). However, our experiments demonstrate that the Grb2 −/− (T) mutation does not affect the activation of Ras-Erks, but does affect the activation of JNK and p38 kinases in thymocytes.…”

Section: Discussionmentioning

confidence: 99%

Grb2 functions at the top of the T-cell antigen receptor–induced tyrosine kinase cascade to control thymic selection

Jang

Zhang

Chiang

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Grb2 is an adaptor molecule that mediates Ras-MAPK activation induced by various receptors. Here we show that conditional ablation of Grb2 in thymocytes severely impairs both thymic positive and negative selections. Strikingly, the mutation attenuates T-cell antigen receptor (TCR) proximal signaling, including tyrosine phosphorylation of multiple signaling proteins and Ca 2+ influx. The defective TCR signaling can be attributed to a marked impairment in Lck activation. Ectopic expression of a mutant Grb2 composed of the central SH2 and the C-terminal SH3 domains in Grb2 −/− thymocytes fully restores thymocyte development. Thus, Grb2 plays a pivotal role in both thymic positive and negative selection. It amplifies TCR signaling at the top end of the tyrosine phosphorylation cascade via a scaffolding function.T lymphopoiesis is a sequential developmental process regulated by multiple environmental signals. The final outcome is the generation of different lineages of T cells with a diverse antigen receptor repertoire (1-4). Diversification of the T-cell antigen receptor (TCR) is initially generated through successive rearrangements of the V-(D)-J genes in CD4 and CD8 doublenegative (DN) T precursors. Successful rearrangement of the TCR β gene allows DN T cells to express pre-TCR and to develop into CD4 and CD8 double-positive (DP) cells, at which stage the TCR repertoire is further shaped by thymic selection. Cells expressing a TCR with too strong or too weak an affinity/avidity for MHC-peptide complexes will die via apoptosis, the processes termed negative selection or neglect. In contrast, cells bearing a TCR with moderate avidity toward MHC-peptide complexes will survive the selection (positive selection) and become mature CD4 + or CD8 + single positive (SP) thymocytes (5-8).The importance of TCR signaling in thymic positive and negative selection has been demonstrated in a variety of experimental models. However, it remains to be determined precisely how TCR signaling is initiated and propagated intracellularly during thymic selection. The first step in initiating the TCR signaling cascade is thought to be the phosphorylation of tyrosine residues in immunoreceptor tyrosine-based activation motifs (ITAMs) of the CD3ζ chain by the Src family tyrosine kinase Lck (9-11). Phosphorylated ITAMs of the CD3ζ chain then recruit tyrosine kinase Zap70 to the TCR complexes, where it can be activated by autophosphorylation. Upon activation, Zap70 phosphorylates the membrane anchor protein linker for activation of T cells (LAT), which in turn assembles signaling complexes containing multisignaling molecules, including Grb2, SLP-76, Vav, Gads, PLCγ-1, and Itk. The coordination between these signaling components in the complexes determines multiple downstream cellular responses, including Ca 2+ mobilization, cytoskeleton reorganization, and activation of nuclear transcription factors, which eventually define various T-cell development programs (9, 12-14).Grb2 is a positive regulator of Ras signaling downstream of many growth fa...

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Digital Signaling and Hysteresis Characterize Ras Activation in Lymphoid Cells

Cited by 376 publications

References 40 publications

Origin of the sharp boundary that discriminates positive and negative selection of thymocytes

Origin of the sharp boundary that discriminates positive and negative selection of thymocytes

Themis1 enhances T cell receptor signaling during thymocyte development by promoting Vav1 activity and Grb2 stability

Grb2 functions at the top of the T-cell antigen receptor–induced tyrosine kinase cascade to control thymic selection

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