Glucocorticoids inhibit precursor incorporation into protein in splenic lymphocytes by stimulating protein degradation and expanding intracellular amino acid pools

Richard G. MacDonald, John A. Cidlowski

Research output: Contribution to journalArticle

12 Citations (Scopus)

Abstract

In the presence of tracer concentrations of extracellular leucine (5 μM), treatment of rat splenic lymphocyte suspensions in vitro with 1 μM dexamethasone for 2.5-4 h caused a 30-35% inhibition of [3H]leucine incorporation into protein. As the extracellular leucine concentration was raised to 5 mM, this inhibition was progressively reduced to 0-12%. This phenomenon correlated with a marked dependence on extracellular leucine concentration of the dexamethasone-dependent enlargement of free intracellular leucine pools in splenic lymphocytes: a 123% increase in pool size with tracer extracellular leucine; a 10% increase with 5 mM leucine. Varying extracellular leucine had no effect on: (1) nuclear [3H]dexamethasone binding by the cells; (2) the concentration of dexamethasone needed for half-maximal inhibition of [3H]leucine incorporation; (3) the time course of onset and maximal expression of the hormonal inhibition of [3H]leucine incorporation; or (4) the magnitude of dexamethasone-dependent inhibition of [3H]uridine incorporation into RNA by these cells. There was no detectable effect of dexamethasone on uptake and retention of [3H]leucine by the cells, regardless of the extracellular leucine concentration. Treatment of splenic lymphocytes for 4 h in vitro with 1 μM dexamethasone caused a small shift of ribosomes from larger aggregate polysomes to smaller forms. Thus, glucocorticoid-induced inhibition of amino acid incorporation in splenic lymphocytes is a multicomponent response, of which an actual decrease in protein synthesis is only a small part. Enlargement of free intracellular amino acid pools, probably resulting from increased protein degradation, is the major contributing factor to the hormonal inhibition of amino acid incorporation.

Original languageEnglish (US)
Pages (from-to)236-247
Number of pages12
JournalBBA - General Subjects
Volume717
Issue number2
DOIs
StatePublished - Aug 6 1982

Fingerprint

Lymphocytes
Leucine
Glucocorticoids
Proteolysis
Amino Acids
Degradation
Dexamethasone
Proteins
Polyribosomes
Uridine
Ribosomes
Rats
Suspensions
RNA

Keywords

  • (Spleen lymphocyte)
  • Amino acid incorporation
  • Amino acid pool
  • Glucocorticoid
  • Protein degradation

ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology

Cite this

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title = "Glucocorticoids inhibit precursor incorporation into protein in splenic lymphocytes by stimulating protein degradation and expanding intracellular amino acid pools",
abstract = "In the presence of tracer concentrations of extracellular leucine (5 μM), treatment of rat splenic lymphocyte suspensions in vitro with 1 μM dexamethasone for 2.5-4 h caused a 30-35{\%} inhibition of [3H]leucine incorporation into protein. As the extracellular leucine concentration was raised to 5 mM, this inhibition was progressively reduced to 0-12{\%}. This phenomenon correlated with a marked dependence on extracellular leucine concentration of the dexamethasone-dependent enlargement of free intracellular leucine pools in splenic lymphocytes: a 123{\%} increase in pool size with tracer extracellular leucine; a 10{\%} increase with 5 mM leucine. Varying extracellular leucine had no effect on: (1) nuclear [3H]dexamethasone binding by the cells; (2) the concentration of dexamethasone needed for half-maximal inhibition of [3H]leucine incorporation; (3) the time course of onset and maximal expression of the hormonal inhibition of [3H]leucine incorporation; or (4) the magnitude of dexamethasone-dependent inhibition of [3H]uridine incorporation into RNA by these cells. There was no detectable effect of dexamethasone on uptake and retention of [3H]leucine by the cells, regardless of the extracellular leucine concentration. Treatment of splenic lymphocytes for 4 h in vitro with 1 μM dexamethasone caused a small shift of ribosomes from larger aggregate polysomes to smaller forms. Thus, glucocorticoid-induced inhibition of amino acid incorporation in splenic lymphocytes is a multicomponent response, of which an actual decrease in protein synthesis is only a small part. Enlargement of free intracellular amino acid pools, probably resulting from increased protein degradation, is the major contributing factor to the hormonal inhibition of amino acid incorporation.",
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AU - Cidlowski, John A.

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N2 - In the presence of tracer concentrations of extracellular leucine (5 μM), treatment of rat splenic lymphocyte suspensions in vitro with 1 μM dexamethasone for 2.5-4 h caused a 30-35% inhibition of [3H]leucine incorporation into protein. As the extracellular leucine concentration was raised to 5 mM, this inhibition was progressively reduced to 0-12%. This phenomenon correlated with a marked dependence on extracellular leucine concentration of the dexamethasone-dependent enlargement of free intracellular leucine pools in splenic lymphocytes: a 123% increase in pool size with tracer extracellular leucine; a 10% increase with 5 mM leucine. Varying extracellular leucine had no effect on: (1) nuclear [3H]dexamethasone binding by the cells; (2) the concentration of dexamethasone needed for half-maximal inhibition of [3H]leucine incorporation; (3) the time course of onset and maximal expression of the hormonal inhibition of [3H]leucine incorporation; or (4) the magnitude of dexamethasone-dependent inhibition of [3H]uridine incorporation into RNA by these cells. There was no detectable effect of dexamethasone on uptake and retention of [3H]leucine by the cells, regardless of the extracellular leucine concentration. Treatment of splenic lymphocytes for 4 h in vitro with 1 μM dexamethasone caused a small shift of ribosomes from larger aggregate polysomes to smaller forms. Thus, glucocorticoid-induced inhibition of amino acid incorporation in splenic lymphocytes is a multicomponent response, of which an actual decrease in protein synthesis is only a small part. Enlargement of free intracellular amino acid pools, probably resulting from increased protein degradation, is the major contributing factor to the hormonal inhibition of amino acid incorporation.

AB - In the presence of tracer concentrations of extracellular leucine (5 μM), treatment of rat splenic lymphocyte suspensions in vitro with 1 μM dexamethasone for 2.5-4 h caused a 30-35% inhibition of [3H]leucine incorporation into protein. As the extracellular leucine concentration was raised to 5 mM, this inhibition was progressively reduced to 0-12%. This phenomenon correlated with a marked dependence on extracellular leucine concentration of the dexamethasone-dependent enlargement of free intracellular leucine pools in splenic lymphocytes: a 123% increase in pool size with tracer extracellular leucine; a 10% increase with 5 mM leucine. Varying extracellular leucine had no effect on: (1) nuclear [3H]dexamethasone binding by the cells; (2) the concentration of dexamethasone needed for half-maximal inhibition of [3H]leucine incorporation; (3) the time course of onset and maximal expression of the hormonal inhibition of [3H]leucine incorporation; or (4) the magnitude of dexamethasone-dependent inhibition of [3H]uridine incorporation into RNA by these cells. There was no detectable effect of dexamethasone on uptake and retention of [3H]leucine by the cells, regardless of the extracellular leucine concentration. Treatment of splenic lymphocytes for 4 h in vitro with 1 μM dexamethasone caused a small shift of ribosomes from larger aggregate polysomes to smaller forms. Thus, glucocorticoid-induced inhibition of amino acid incorporation in splenic lymphocytes is a multicomponent response, of which an actual decrease in protein synthesis is only a small part. Enlargement of free intracellular amino acid pools, probably resulting from increased protein degradation, is the major contributing factor to the hormonal inhibition of amino acid incorporation.

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