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T cell receptor-independent basal signaling via Erk and Abl kinases suppresses RAG gene expression.

Roose JP, Diehn M, Tomlinson MG, Lin J, Alizadeh AA, Botstein D, Brown PO, Weiss A - PLoS Biol. (2003)

Bottom Line: This TCR-like pathway results in constitutive low-level activity of Erk and Abl kinases.Inhibition of Abl by the drug STI-571 or inhibition of signaling events upstream of Erk increases RAG-1 expression.Our data suggest that physiologic gene expression programs depend upon tonic activity of signaling pathways independent of receptor ligation.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of California, San Francisco, USA.

ABSTRACT
Signal transduction pathways guided by cellular receptors commonly exhibit low-level constitutive signaling in a continuous, ligand-independent manner. The dynamic equilibrium of positive and negative regulators establishes such a tonic signal. Ligand-independent signaling by the precursors of mature antigen receptors regulates development of B and T lymphocytes. Here we describe a basal signal that controls gene expression profiles in the Jurkat T cell line and mouse thymocytes. Using DNA microarrays and Northern blots to analyze unstimulated cells, we demonstrate that expression of a cluster of genes, including RAG-1 and RAG-2, is repressed by constitutive signals requiring the adapter molecules LAT and SLP-76. This TCR-like pathway results in constitutive low-level activity of Erk and Abl kinases. Inhibition of Abl by the drug STI-571 or inhibition of signaling events upstream of Erk increases RAG-1 expression. Our data suggest that physiologic gene expression programs depend upon tonic activity of signaling pathways independent of receptor ligation.

Show MeSH
Model of the Constitutive Signaling Pathway That Provides a Basal Repression of RAG Gene TranscriptionConstitutive signaling in resting thymoytes and our model Jurkat T cell line represses RAG gene expression. Chemical inhibition of signaling molecules, genetic modifications, or induced expression of genes that resulted in elevated RAG expression are summarized in the gray-shaded boxes. The tonic signal and therefore normal expression of RAG genes rely strongly on signaling through the adapter LAT. The effects of basal phosphorylation of LAT are twofold: (1) recruitment and activation of PLCγ generates low levels of second messengers that signal through calcium and Ras pathways, culminating in Erk kinase activity; and (2) phosphorylation of tyrosine residue 6 of LAT, likely establishing a LAT–PLCγ–Abl complex, is required for low-level kinase activity of Abl. Abl and Erk kinase activities deliver unique repressive signals to control RAG gene expression.
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pbio.0000053-g008: Model of the Constitutive Signaling Pathway That Provides a Basal Repression of RAG Gene TranscriptionConstitutive signaling in resting thymoytes and our model Jurkat T cell line represses RAG gene expression. Chemical inhibition of signaling molecules, genetic modifications, or induced expression of genes that resulted in elevated RAG expression are summarized in the gray-shaded boxes. The tonic signal and therefore normal expression of RAG genes rely strongly on signaling through the adapter LAT. The effects of basal phosphorylation of LAT are twofold: (1) recruitment and activation of PLCγ generates low levels of second messengers that signal through calcium and Ras pathways, culminating in Erk kinase activity; and (2) phosphorylation of tyrosine residue 6 of LAT, likely establishing a LAT–PLCγ–Abl complex, is required for low-level kinase activity of Abl. Abl and Erk kinase activities deliver unique repressive signals to control RAG gene expression.

Mentions: The effects of selective inhibitors, together with the results of our previous experiments with mutant cell lines, point to a tonic signaling pathway that closely resembles a TCR-inducible pathway, with Src family kinase activity as the most upstream component and MAPK as the most downstream component regulating RAG-1 and RAG-2 expression in Jurkat cells (for a model, see Figure 8). The same inhibitors yielded very similar results in two mouse thymocyte cell lines, SCB29 and DPK (data not shown). The SCB29 cell line is derived from a Scid mouse and expresses a pre-TCR (Groettrup et al. 1992). DPK is a CD4+CD8+ thymocyte line expressing a transgene-encoded TCR (Kaye and Ellenberger 1992). Since TCR signaling has been studied in great detail in Jurkat T cells, we proceeded to use this model for our experiments and verified our results in primary thymocytes.


T cell receptor-independent basal signaling via Erk and Abl kinases suppresses RAG gene expression.

Roose JP, Diehn M, Tomlinson MG, Lin J, Alizadeh AA, Botstein D, Brown PO, Weiss A - PLoS Biol. (2003)

Model of the Constitutive Signaling Pathway That Provides a Basal Repression of RAG Gene TranscriptionConstitutive signaling in resting thymoytes and our model Jurkat T cell line represses RAG gene expression. Chemical inhibition of signaling molecules, genetic modifications, or induced expression of genes that resulted in elevated RAG expression are summarized in the gray-shaded boxes. The tonic signal and therefore normal expression of RAG genes rely strongly on signaling through the adapter LAT. The effects of basal phosphorylation of LAT are twofold: (1) recruitment and activation of PLCγ generates low levels of second messengers that signal through calcium and Ras pathways, culminating in Erk kinase activity; and (2) phosphorylation of tyrosine residue 6 of LAT, likely establishing a LAT–PLCγ–Abl complex, is required for low-level kinase activity of Abl. Abl and Erk kinase activities deliver unique repressive signals to control RAG gene expression.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC261890&req=5

pbio.0000053-g008: Model of the Constitutive Signaling Pathway That Provides a Basal Repression of RAG Gene TranscriptionConstitutive signaling in resting thymoytes and our model Jurkat T cell line represses RAG gene expression. Chemical inhibition of signaling molecules, genetic modifications, or induced expression of genes that resulted in elevated RAG expression are summarized in the gray-shaded boxes. The tonic signal and therefore normal expression of RAG genes rely strongly on signaling through the adapter LAT. The effects of basal phosphorylation of LAT are twofold: (1) recruitment and activation of PLCγ generates low levels of second messengers that signal through calcium and Ras pathways, culminating in Erk kinase activity; and (2) phosphorylation of tyrosine residue 6 of LAT, likely establishing a LAT–PLCγ–Abl complex, is required for low-level kinase activity of Abl. Abl and Erk kinase activities deliver unique repressive signals to control RAG gene expression.
Mentions: The effects of selective inhibitors, together with the results of our previous experiments with mutant cell lines, point to a tonic signaling pathway that closely resembles a TCR-inducible pathway, with Src family kinase activity as the most upstream component and MAPK as the most downstream component regulating RAG-1 and RAG-2 expression in Jurkat cells (for a model, see Figure 8). The same inhibitors yielded very similar results in two mouse thymocyte cell lines, SCB29 and DPK (data not shown). The SCB29 cell line is derived from a Scid mouse and expresses a pre-TCR (Groettrup et al. 1992). DPK is a CD4+CD8+ thymocyte line expressing a transgene-encoded TCR (Kaye and Ellenberger 1992). Since TCR signaling has been studied in great detail in Jurkat T cells, we proceeded to use this model for our experiments and verified our results in primary thymocytes.

Bottom Line: This TCR-like pathway results in constitutive low-level activity of Erk and Abl kinases.Inhibition of Abl by the drug STI-571 or inhibition of signaling events upstream of Erk increases RAG-1 expression.Our data suggest that physiologic gene expression programs depend upon tonic activity of signaling pathways independent of receptor ligation.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, University of California, San Francisco, USA.

ABSTRACT
Signal transduction pathways guided by cellular receptors commonly exhibit low-level constitutive signaling in a continuous, ligand-independent manner. The dynamic equilibrium of positive and negative regulators establishes such a tonic signal. Ligand-independent signaling by the precursors of mature antigen receptors regulates development of B and T lymphocytes. Here we describe a basal signal that controls gene expression profiles in the Jurkat T cell line and mouse thymocytes. Using DNA microarrays and Northern blots to analyze unstimulated cells, we demonstrate that expression of a cluster of genes, including RAG-1 and RAG-2, is repressed by constitutive signals requiring the adapter molecules LAT and SLP-76. This TCR-like pathway results in constitutive low-level activity of Erk and Abl kinases. Inhibition of Abl by the drug STI-571 or inhibition of signaling events upstream of Erk increases RAG-1 expression. Our data suggest that physiologic gene expression programs depend upon tonic activity of signaling pathways independent of receptor ligation.

Show MeSH