Down-regulation of the ubiquitin-proteasome proteolysis system by amino acids and insulin involves the adenosine monophosphate-activated protein kinase and mammalian target of rapamycin pathways in rat hepatocytes.
The purpose of this work was to examine whether changes in dietary protein levels could elicit differential responses of tissue proteolysis and the pathway involved in this response. In rats fed with a high protein diet (55%) for 14 days, the liver was the main organ where adaptations occurred, characterized by an increased protein pool and a strong, meal-induced inhibition of the protein breakdown rate when compared to the normal protein diet (14%). This was associated with a decrease in the key-proteins involved in expression of the ubiquitin-proteasome and autophagy pathway gene and a reduction in the level of hepatic ubiquitinated protein. In hepatocytes, we demonstrated that the increase in amino acid (AA) levels was sufficient to down-regulate the ubiquitin proteasome pathway, but this inhibition was more potent in the presence of insulin. Interestingly, AICAR, an adenosine monophosphate-activated protein kinase (AMPK) activator, reversed the inhibition of protein ubiquination induced by insulin at high AA concentrations. Rapamycin, an mammalian target of rapamycin (mTOR) inhibitor, reversed the inhibition of protein ubiquination induced by a rise in insulin levels with both high and low AA concentrations. Moreover, in both low and high AA concentrations in the presence of insulin, AICAR decreased the mTOR phosphorylation, and in the presence of both AICAR and rapamycin, AICAR reversed the effects of rapamycin. These results demonstrate that the inhibition of AMPK and the activation of mTOR transduction pathways, are required for the down-regulation of protein ubiquitination in response to high amino acid and insulin concentrations.
CNRH-IdF, UMR914 Nutrition Physiology and Ingestive Behavior, AgroParisTech, 16 rue Claude, 75005, Paris, France.
Nattida
N
Chotechuang
Dalila
D
Azzout-Marniche
Cécile
C
Bos
Catherine
C
Chaumontet
Claire
C
Gaudichon
Daniel
D
Tomé
D055372:AMP-Activated Protein Kinases / Q000378:metabolism*; D000596:Amino Acids / Q000494:pharmacology*; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D004044:Dietary Proteins / Q000008:administration & dosage; D015536:Down-Regulation; D020869:Gene Expression Profiling; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D008297:Male; D009929:Organ Size; D010766:Phosphorylation; D019518:Postprandial Period; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D057149:Ubiquitinated Proteins / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects / Q000235:genetics
D000596:Amino Acids; D004044:Dietary Proteins; D007004:Hypoglycemic Agents; D007328:Insulin; D012265:Ribonucleotides; D025801:Ubiquitin; D057149:Ubiquitinated Proteins; D000620:Aminoimidazole Carboxamide; C546845:mTOR protein, rat; D058570:TOR Serine-Threonine Kinases; D055372:AMP-Activated Protein Kinases; D046988:Proteasome Endopeptidase Complex; C031143:AICA ribonucleotide; D020123:Sirolimus