Effect of insulin upon protein degradation in cultured human myocytes.
BACKGROUND
The anabolic effects of insulin are well recognized but the mechanism by which insulin decreases muscle protein degradation in human is unclear. However, in a variety of catabolic conditions it is believed to be changes in the activity of the ATP-dependent ubiquitin proteolytic pathway that are responsible for changes in protein degradation in skeletal muscle. The aim of this study was to test the hypothesis that insulin regulates the ATP-dependent ubiquitin proteolytic pathway in human muscle.


METHODS
The effects of insulin and acidosis on protein degradation were measured in human myocytes using L-[14C]phenylalanine. The effect of insulin on the activity of the ATP-dependent ubiquitin pathway was assessed from the mRNA expression of ubiquitin and the ubiquitin-conjugating enzyme E214k in human myocytes.


CONCLUSIONS
Coincubation of human myocytes with 100 nM of insulin was associated with a significant reduction in protein degradation. Metabolic acidosis is known to increase skeletal muscle protein degradation rates, and in our experiments protein degradation at a pH of 7.0 was significantly higher than pH 7.35. Eight-hour exposure to 100 nM of insulin resulted in a significant reduction in the expression of E214k but no change in the expression of ubiquitin.


CONCLUSIONS
In human muscle we have demonstrated regulation by insulin of the ATP-dependent ubiquitin pathway at the level of ubiquitin conjugation.
D002478:Cells, Cultured; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007328:Insulin / Q000494:pharmacology*; D018485:Muscle Fibers, Skeletal / Q000187:drug effects* / Q000378:metabolism; D009124:Muscle Proteins / Q000187:drug effects* / Q000378:metabolism; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D044763:Ubiquitin-Conjugating Enzymes / Q000378:metabolism
D007328:Insulin; D009124:Muscle Proteins; D012333:RNA, Messenger; D025801:Ubiquitin; D044763:Ubiquitin-Conjugating Enzymes