ER stress induces anabolic resistance in muscle cells through PKB-induced blockade of mTORC1

Louise Deldicque, Luc Bertrand, Amy Patton, Marc Francaux, Keith Baar

Research output: Contribution to journalArticle

30 Citations (Scopus)

Abstract

Background: Anabolic resistance is the inability to increase protein synthesis in response to an increase in amino acids following a meal. One potential mediator of anabolic resistance is endoplasmic reticulum (ER) stress. The purpose of the present study was to test whether ER stress impairs the response to growth factors and leucine in muscle cells. Methods: Muscle cells were incubated overnight with tunicamycin or thapsigargin to induce ER stress and the activation of the unfolded protein response, mTORC1 activity at baseline and following insulin and amino acids, as well as amino acid transport were determined. Results: ER stress decreased basal phosphorylation of PKB and S6K1 in a dose-dependent manner. In spite of the decrease in basal PKB phosphorylation, insulin (10-50 nM) could still activate both PKB and S6K1. The leucine (2.5-5 mM)-induced phosphorylation of S6K1 on the other hand was repressed by low concentrations of both tunicamycin and thapsigargin. To determine the mechanism underlying this anabolic resistance, several inhibitors of mTORC1 activation were measured. Tunicamycin and thapsigargin did not change the phosphorylation or content of either AMPK or JNK, both increased TRB3 mRNA expression and thapsigargin increased REDD1 mRNA. Tunicamycin and thapsigargin both decreased the basal phosphorylation state of PRAS40. Neither tunicamycin nor thapsigargin prevented phosphorylation of PRAS40 by insulin. However, since PKB is not activated by amino acids, PRAS40 phosphorylation remained low following the addition of leucine. Blocking PKB using a specific inhibitor had the same effect on both PRAS40 and leucine-induced phosphorylation of S6K1. Conclusion: ER stress induces anabolic resistance in muscle cells through a PKB/PRAS40-induced blockade of mTORC1.

Original languageEnglish (US)
Article numbere20993
JournalPLoS One
Volume6
Issue number6
DOIs
StatePublished - 2011

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Phosphorylation
Endoplasmic Reticulum Stress
endoplasmic reticulum
myocytes
Muscle Cells
Thapsigargin
Muscle
tunicamycin
phosphorylation
Tunicamycin
Cells
Leucine
leucine
Amino Acids
amino acids
insulin
Insulin
Chemical activation
unfolded protein response
Unfolded Protein Response

ASJC Scopus subject areas

  • Agricultural and Biological Sciences(all)
  • Biochemistry, Genetics and Molecular Biology(all)
  • Medicine(all)

Cite this

ER stress induces anabolic resistance in muscle cells through PKB-induced blockade of mTORC1. / Deldicque, Louise; Bertrand, Luc; Patton, Amy; Francaux, Marc; Baar, Keith.

In: PLoS One, Vol. 6, No. 6, e20993, 2011.

Research output: Contribution to journalArticle

Deldicque, Louise ; Bertrand, Luc ; Patton, Amy ; Francaux, Marc ; Baar, Keith. / ER stress induces anabolic resistance in muscle cells through PKB-induced blockade of mTORC1. In: PLoS One. 2011 ; Vol. 6, No. 6.
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AB - Background: Anabolic resistance is the inability to increase protein synthesis in response to an increase in amino acids following a meal. One potential mediator of anabolic resistance is endoplasmic reticulum (ER) stress. The purpose of the present study was to test whether ER stress impairs the response to growth factors and leucine in muscle cells. Methods: Muscle cells were incubated overnight with tunicamycin or thapsigargin to induce ER stress and the activation of the unfolded protein response, mTORC1 activity at baseline and following insulin and amino acids, as well as amino acid transport were determined. Results: ER stress decreased basal phosphorylation of PKB and S6K1 in a dose-dependent manner. In spite of the decrease in basal PKB phosphorylation, insulin (10-50 nM) could still activate both PKB and S6K1. The leucine (2.5-5 mM)-induced phosphorylation of S6K1 on the other hand was repressed by low concentrations of both tunicamycin and thapsigargin. To determine the mechanism underlying this anabolic resistance, several inhibitors of mTORC1 activation were measured. Tunicamycin and thapsigargin did not change the phosphorylation or content of either AMPK or JNK, both increased TRB3 mRNA expression and thapsigargin increased REDD1 mRNA. Tunicamycin and thapsigargin both decreased the basal phosphorylation state of PRAS40. Neither tunicamycin nor thapsigargin prevented phosphorylation of PRAS40 by insulin. However, since PKB is not activated by amino acids, PRAS40 phosphorylation remained low following the addition of leucine. Blocking PKB using a specific inhibitor had the same effect on both PRAS40 and leucine-induced phosphorylation of S6K1. Conclusion: ER stress induces anabolic resistance in muscle cells through a PKB/PRAS40-induced blockade of mTORC1.

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