Glucocorticoids abate p70(S6k) and eIF4E function in L6 skeletal myoblasts

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Abstract

The catabolic properties of glucocorticoid hormones are largely attributable to dual regulation of protein degradation and synthesis. With regard to the latter, glucocorticoids modulate the translational machinery, namely that component functional in translation initiation. This investigation revealed that in L6 myoblasts, dexamethasone, a synthetic glucocorticoid, deactivated the ribosomal protein S6 kinase (p70(S6k)) within 4 h, as evidenced by diminished phosphorylation of its physiological substrate, the 40S ribosomal protein S6. This deactivation correlated with dephosphorylation of p70(S6k) at Thr389, whereas phosphorylation of Ser411 was unaffected. Furthermore, glucocorticoid administration induced dephosphorylation of the cap-dependent translational repressor, eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1), thereby facilitating conjunction of the inhibitor and eIF4E. The mechanism of action is reminiscent of classical transcriptional regulation by steroid hormone receptors in that these effects were preceded by a temporal lag and were sensitive to inhibitors of glucocorticoid receptor function as well as transcriptional and translational inhibition. Okadaic acid and calyculin A corrected the dexamethasone-induced dephosphorylation of p70(S6k) and 4E-BP1, implicating a PP1- and/or PP2A-like protein phosphatase(s) in the observed phenomena. Hence, glucocorticolds attenuate distal constituents of the phosphatidylinositol-3 kinase signaling pathway and thereby encumber the protein synthetic apparatus.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume279
Issue number1 42-1
StatePublished - Aug 19 2000

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Eukaryotic Initiation Factor-4E
Skeletal Myoblasts
70-kDa Ribosomal Protein S6 Kinases
Glucocorticoids
Dexamethasone
Carrier Proteins
Ribosomal Protein S6
Phosphorylation
Phosphatidylinositol 3-Kinase
Hormones
Ribosomal Protein S6 Kinases
Okadaic Acid
Steroid Receptors
Myoblasts
Phosphoprotein Phosphatases
Glucocorticoid Receptors
Proteolysis
Proteins

All Science Journal Classification (ASJC) codes

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)

Cite this

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title = "Glucocorticoids abate p70(S6k) and eIF4E function in L6 skeletal myoblasts",
abstract = "The catabolic properties of glucocorticoid hormones are largely attributable to dual regulation of protein degradation and synthesis. With regard to the latter, glucocorticoids modulate the translational machinery, namely that component functional in translation initiation. This investigation revealed that in L6 myoblasts, dexamethasone, a synthetic glucocorticoid, deactivated the ribosomal protein S6 kinase (p70(S6k)) within 4 h, as evidenced by diminished phosphorylation of its physiological substrate, the 40S ribosomal protein S6. This deactivation correlated with dephosphorylation of p70(S6k) at Thr389, whereas phosphorylation of Ser411 was unaffected. Furthermore, glucocorticoid administration induced dephosphorylation of the cap-dependent translational repressor, eukaryotic initiation factor 4E (eIF4E) binding protein 1 (4E-BP1), thereby facilitating conjunction of the inhibitor and eIF4E. The mechanism of action is reminiscent of classical transcriptional regulation by steroid hormone receptors in that these effects were preceded by a temporal lag and were sensitive to inhibitors of glucocorticoid receptor function as well as transcriptional and translational inhibition. Okadaic acid and calyculin A corrected the dexamethasone-induced dephosphorylation of p70(S6k) and 4E-BP1, implicating a PP1- and/or PP2A-like protein phosphatase(s) in the observed phenomena. Hence, glucocorticolds attenuate distal constituents of the phosphatidylinositol-3 kinase signaling pathway and thereby encumber the protein synthetic apparatus.",
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