Nerve growth factor inhibits Na+/H+ exchange and HCO3 - absorption through parallel phosphatidylinositol 3-kinase-mTOR and ERK pathways in thick ascending limb

David Good, Thampi George, Bruns Watts

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22 Citations (Scopus)

Abstract

In the medullary thick ascending limb, inhibiting the basolateral NHE1 Na+/H+ exchanger with nerve growth factor (NGF) induces actin cytoskeleton remodeling that secondarily inhibits apical NHE3 and transepithelial HCO3 - absorption. The inhibition by NGF is mediated 50% through activation of extracellular signal-regulated kinase (ERK). Here we examined the signaling pathway responsible for the remainder of the NGF-induced inhibition. Inhibition of HCO3 - absorption was reduced 45% by the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 and 50% by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), a downstream effector of PI3K. The combination of a PI3K inhibitor plus rapamycin did not cause a further reduction in the inhibition by NGF. In contrast, the combination of a PI3K inhibitor plus the MEK/ ERK inhibitor U0126 completely eliminated inhibition by NGF. Rapamycin decreased NGF-induced inhibition of basolateral NHE1 by 45%. NGF induced a 2-fold increase in phosphorylation of Akt, a PI3K target linked to mTOR activation, and a 2.2-fold increase in the activity of p70 S6 kinase, a downstream effector of mTOR. p70 S6 kinase activation was blocked by wortmannin and rapamycin, consistent with PI3K, mTOR, and p70 S6 kinase in a linear pathway. Rapamycin-sensitive inhibition of NHE1 by NGF was associated with an increased level of phosphorylated mTOR in the basolateral membrane domain. These findings indicate that NGF inhibits HCO3 - absorption in the medullary thick ascending limb through the parallel activation of PI3K-mTOR and ERK signaling pathways, which converge to inhibit NHE1. The results identify a role for mTOR in the regulation of Na+/H+ exchange activity and implicate NHE1 as a possible downstream effector contributing to mTOR's effects on cell growth, proliferation, survival, and tumorigenesis.

Original languageEnglish (US)
Pages (from-to)26602-26611
Number of pages10
JournalJournal of Biological Chemistry
Volume283
Issue number39
DOIs
StatePublished - Sep 26 2008

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Phosphatidylinositol 3-Kinase
Extracellular Signal-Regulated MAP Kinases
Nerve Growth Factor
Sirolimus
Extremities
70-kDa Ribosomal Protein S6 Kinases
Chemical activation
Sodium-Hydrogen Antiporter
Phosphorylation
2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one
Mitogen-Activated Protein Kinase Kinases
Cell growth
Actin Cytoskeleton
Actins

ASJC Scopus subject areas

  • Biochemistry
  • Cell Biology
  • Molecular Biology

Cite this

@article{2756b67e9c784908989570330175a784,
title = "Nerve growth factor inhibits Na+/H+ exchange and HCO3 - absorption through parallel phosphatidylinositol 3-kinase-mTOR and ERK pathways in thick ascending limb",
abstract = "In the medullary thick ascending limb, inhibiting the basolateral NHE1 Na+/H+ exchanger with nerve growth factor (NGF) induces actin cytoskeleton remodeling that secondarily inhibits apical NHE3 and transepithelial HCO3 - absorption. The inhibition by NGF is mediated 50{\%} through activation of extracellular signal-regulated kinase (ERK). Here we examined the signaling pathway responsible for the remainder of the NGF-induced inhibition. Inhibition of HCO3 - absorption was reduced 45{\%} by the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 and 50{\%} by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), a downstream effector of PI3K. The combination of a PI3K inhibitor plus rapamycin did not cause a further reduction in the inhibition by NGF. In contrast, the combination of a PI3K inhibitor plus the MEK/ ERK inhibitor U0126 completely eliminated inhibition by NGF. Rapamycin decreased NGF-induced inhibition of basolateral NHE1 by 45{\%}. NGF induced a 2-fold increase in phosphorylation of Akt, a PI3K target linked to mTOR activation, and a 2.2-fold increase in the activity of p70 S6 kinase, a downstream effector of mTOR. p70 S6 kinase activation was blocked by wortmannin and rapamycin, consistent with PI3K, mTOR, and p70 S6 kinase in a linear pathway. Rapamycin-sensitive inhibition of NHE1 by NGF was associated with an increased level of phosphorylated mTOR in the basolateral membrane domain. These findings indicate that NGF inhibits HCO3 - absorption in the medullary thick ascending limb through the parallel activation of PI3K-mTOR and ERK signaling pathways, which converge to inhibit NHE1. The results identify a role for mTOR in the regulation of Na+/H+ exchange activity and implicate NHE1 as a possible downstream effector contributing to mTOR's effects on cell growth, proliferation, survival, and tumorigenesis.",
author = "David Good and Thampi George and Bruns Watts",
year = "2008",
month = "9",
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pages = "26602--26611",
journal = "Journal of Biological Chemistry",
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publisher = "American Society for Biochemistry and Molecular Biology Inc.",
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T1 - Nerve growth factor inhibits Na+/H+ exchange and HCO3 - absorption through parallel phosphatidylinositol 3-kinase-mTOR and ERK pathways in thick ascending limb

AU - Good, David

AU - George, Thampi

AU - Watts, Bruns

PY - 2008/9/26

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N2 - In the medullary thick ascending limb, inhibiting the basolateral NHE1 Na+/H+ exchanger with nerve growth factor (NGF) induces actin cytoskeleton remodeling that secondarily inhibits apical NHE3 and transepithelial HCO3 - absorption. The inhibition by NGF is mediated 50% through activation of extracellular signal-regulated kinase (ERK). Here we examined the signaling pathway responsible for the remainder of the NGF-induced inhibition. Inhibition of HCO3 - absorption was reduced 45% by the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 and 50% by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), a downstream effector of PI3K. The combination of a PI3K inhibitor plus rapamycin did not cause a further reduction in the inhibition by NGF. In contrast, the combination of a PI3K inhibitor plus the MEK/ ERK inhibitor U0126 completely eliminated inhibition by NGF. Rapamycin decreased NGF-induced inhibition of basolateral NHE1 by 45%. NGF induced a 2-fold increase in phosphorylation of Akt, a PI3K target linked to mTOR activation, and a 2.2-fold increase in the activity of p70 S6 kinase, a downstream effector of mTOR. p70 S6 kinase activation was blocked by wortmannin and rapamycin, consistent with PI3K, mTOR, and p70 S6 kinase in a linear pathway. Rapamycin-sensitive inhibition of NHE1 by NGF was associated with an increased level of phosphorylated mTOR in the basolateral membrane domain. These findings indicate that NGF inhibits HCO3 - absorption in the medullary thick ascending limb through the parallel activation of PI3K-mTOR and ERK signaling pathways, which converge to inhibit NHE1. The results identify a role for mTOR in the regulation of Na+/H+ exchange activity and implicate NHE1 as a possible downstream effector contributing to mTOR's effects on cell growth, proliferation, survival, and tumorigenesis.

AB - In the medullary thick ascending limb, inhibiting the basolateral NHE1 Na+/H+ exchanger with nerve growth factor (NGF) induces actin cytoskeleton remodeling that secondarily inhibits apical NHE3 and transepithelial HCO3 - absorption. The inhibition by NGF is mediated 50% through activation of extracellular signal-regulated kinase (ERK). Here we examined the signaling pathway responsible for the remainder of the NGF-induced inhibition. Inhibition of HCO3 - absorption was reduced 45% by the phosphatidylinositol 3-kinase (PI3K) inhibitors wortmannin or LY294002 and 50% by rapamycin, a specific inhibitor of mammalian target of rapamycin (mTOR), a downstream effector of PI3K. The combination of a PI3K inhibitor plus rapamycin did not cause a further reduction in the inhibition by NGF. In contrast, the combination of a PI3K inhibitor plus the MEK/ ERK inhibitor U0126 completely eliminated inhibition by NGF. Rapamycin decreased NGF-induced inhibition of basolateral NHE1 by 45%. NGF induced a 2-fold increase in phosphorylation of Akt, a PI3K target linked to mTOR activation, and a 2.2-fold increase in the activity of p70 S6 kinase, a downstream effector of mTOR. p70 S6 kinase activation was blocked by wortmannin and rapamycin, consistent with PI3K, mTOR, and p70 S6 kinase in a linear pathway. Rapamycin-sensitive inhibition of NHE1 by NGF was associated with an increased level of phosphorylated mTOR in the basolateral membrane domain. These findings indicate that NGF inhibits HCO3 - absorption in the medullary thick ascending limb through the parallel activation of PI3K-mTOR and ERK signaling pathways, which converge to inhibit NHE1. The results identify a role for mTOR in the regulation of Na+/H+ exchange activity and implicate NHE1 as a possible downstream effector contributing to mTOR's effects on cell growth, proliferation, survival, and tumorigenesis.

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