Reference+
Martin, N. P., Marron Fernandez de Velasco, E., Mizuno, F., Scappini, E. L., Gloss, B., Erxleben, C., Williams, J. G., Stapleton, H. M., Gentile, S., & Armstrong, D. L. (2014). A Rapid Cytoplasmic Mechanism for PI3 Kinase Regulation by the Nuclear Thyroid Hormone Receptor, TRβ, and Genetic Evidence for Its Role in the Maturation of Mouse Hippocampal Synapses In Vivo. Endocrinology, 155(9), 3713–3724. https://doi.org/10.1210/en.2013-2058
Info
FirstAuthor:: Martin, Negin P.
Author:: Marron Fernandez de Velasco, Ezequiel
Author:: Mizuno, Fengxia
Author:: Scappini, Erica L.
Author:: Gloss, Bernd
Author:: Erxleben, Christian
Author:: Williams, Jason G.
Author:: Stapleton, Heather M.
Author:: Gentile, Saverio
Author:: Armstrong, David L.
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Title:: A Rapid Cytoplasmic Mechanism for PI3 Kinase Regulation by the Nuclear Thyroid Hormone Receptor, TRβ, and Genetic Evidence for Its Role in the Maturation of Mouse Hippocampal Synapses In Vivo
Year:: 2014
Citekey:: MartinEtAl_2014_RapidCytoplasmicMechanism
itemType:: journalArticle
Journal:: Endocrinology
Volume:: 155
Issue:: 9
Pages:: 3713-3724
DOI:: 10.1210/en.2013-2058
Link
Abstract
Several rapid physiological effects of thyroid hormone on mammalian cells in vitro have been shown to be mediated by the phosphatidylinositol 3-kinase (PI3K), but the molecular mechanism of PI3K regulation by nuclear zinc finger receptor proteins for thyroid hormone and its relevance to brain development in vivo have not been elucidated. Here we show that, in the absence of hormone, the thyroid hormone receptor TRβ forms a cytoplasmic complex with the p85 subunit of PI3K and the Src family tyrosine kinase, Lyn, which depends on two canonical phosphotyrosine motifs in the second zinc finger of TRβ that are not conserved in TRα. When hormone is added, TRβ dissociates and moves to the nucleus, and phosphatidylinositol (3, 4, 5)-trisphosphate production goes up rapidly. Mutating either tyrosine to a phenylalanine prevents rapid signaling through PI3K but does not prevent the hormone-dependent transcription of genes with a thyroid hormone response element. When the rapid signaling mechanism was blocked chronically throughout development in mice by a targeted point mutation in both alleles of Thrb, circulating hormone levels, TRβ expression, and direct gene regulation by TRβ in the pituitary and liver were all unaffected. However, the mutation significantly impaired maturation and plasticity of the Schaffer collateral synapses on CA1 pyramidal neurons in the postnatal hippocampus. Thus, phosphotyrosine-dependent association of TRβ with PI3K provides a potential mechanism for integrating regulation of development and metabolism by thyroid hormone and receptor tyrosine kinases.
Blue: Important conclusions
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in the absence of hormone, the thyroid hormone receptor TR forms a cytoplasmic complex with the p85 subunit of PI3K and the Src family tyrosine kinase, Lyn, which depends on two canonical phosphotyrosine motifs in the second zinc finger of TR that are not conserved in TR .
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Mutating either tyrosine to a phenylalanine prevents rapid signaling through PI3K but does not prevent the hormone-dependent transcription of genes with a thyroid hormone response element.
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the mutation significantly impaired maturation and plasticity of the Schaffer collateral synapses on CA1 pyramidal neurons in the postnatal hippocampus.
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identify a specific molecular mechanism for rapid PI3K activation by TR , which involves a cytoplasmic complex of TR , the p85 regulatory subunit of PI3K, and the Src family kinase, Lyn.
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Complex formation involves two canonical, but previously unidentified, phosphotyrosine motifs in the second, DNA-binding zincfinger domain of TR that are not conserved in most other nuclear receptors or even in most nonmammalian orthologs of TR .
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when TR signaling through PI3K was blocked throughout development, the maturation and plasticity of the Schaffer collateral synapses from CA3 to CA1 pyramidal neurons in the postnatal mouse hippocampus was impaired dramatically
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fold for the p85 regulatory subunit of PI3K and the Src kinase Lyn. Binding of the thyroid hormone results in the dissociation of the complex, which allows PI3K activity to increase and TR to move to the nucleus, in which it regulates transcription.
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We also show that the association between TR and the p85 regulatory subunit of PI3K, which we reported previously (24), depends on the canonical SH2 binding motif in TR ,
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We also identified a Src-family protein tyrosine kinase, Lyn, as part of the TR -PI3K complex in CHO cells, and showed that mutating the canonical Lyn binding motif in TR , KYEGK, blocked thyroid hormone signaling through PI3K, even though it did not prevent association between TR and p85.
Yellow: Interesting
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we investigated how T3-depleted serum might promote both TR retention in the cytoplasm and PI3K stimulation by thyroid hormone.
- cómo de realista es que no haya nada de T3 en un tejido. No sé cómo de fisiológico es esto.
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TR , but not TR , has a canonical SH2 recognition sequence, YVGM, at the end of the second zinc finger loop (Figure 4A), which could be phosphorylated by tyrosine kinases that are activated by the growth factors in serum. Src kinase activity has been shown to be required for T3 signaling through PI3K in alveolar epithelial cells (12), and TR has been reported to be phosphorylated on tyrosine
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The Lyn tyrosine kinase is a well-known activator of the PI3K pathway (35, 36). Integrin receptors stimulate Src kinases through a KYEGK motif (37), and TR 1 contains a KYEGK motif at Y147 nearby YVGM
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blocking the binding of TR to p85 by mutating Y171 might eliminate any dominant-negative effect of the mutant, in much the same way that receptor knockdown proved much less deleterious to the organism than hormone withdrawal
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novel mouse line (TR 147F; see Materials and Methods) with a targeted mutation knocked into the Thrb gene (Figure 6A) to substitute phenylalanine for tyrosine at residue 147 of TR 1, which prevents Lyn binding to the mutant receptor
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we observed dramatic impairments in synaptic strength and plasticity in acutely isolated slices of hippocampi from postnatal day 12–18 TR 147F mice
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thyroid hormone has been shown to stimulate PI3K activity in the hippocampus
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TR acts as a cytoplasmic, phosphotyrosine-dependent scaf
Green: Agree with the paper
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the increase in FRET elicited by 100 nM T3 involved T3 binding to a canonical receptor protein and activation of PI3K. F
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in the absence of hormone, immunoprecipitation of TR 1, but not TR , pulls down native p85
- p85 es la subunidad reguladora de PI3K
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pharmacological inhibition of Src family kinases with 200 nM SU6656 in our CHO cells reduced PIP3 production by thyroid hormone
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observed a TR 1 association with Lyn
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in CHO cells the TR receptor for thyroid hormone binds both the p85 subunit of the PI3K and the Lyn protein kinase through distinct, canonical phosphotyrosine motifs
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The specificity that we have observed between TR and signaling through PI3K is also consistent with reports that selective TR agonists are highly effective stimulators of metabolism (48), which is also regulated by PI3K
Red: Disagree with the paper
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On the other hand, our results do categorically rule out a role for other thyroid hormone receptors in this particular aspect of synaptic maturation in the mouse hippocampus, such as TR or integrins that have also been reported to signal through PI3K.