Regulation of protein turnover by recombinant human insulin-like growth factor-I in L6 myotube cultures.
Muscle cell culture experiments were conducted to determine the relative regulatory effects of insulin-like growth factors (IGF) on protein turnover. The effects of recombinant (rc) human IGF-I, ovine somatomedin (oSm/oIGF-I), and insulin on rates of protein labeling and degradation in L6 myotube cultures were evaluated. Myotube cultures were treated with growth factors following a 4-h serum-free incubation period. Protein labeling was measured by determining the rate of [3H] leucine incorporation into cell protein. Protein degradation was measured by a pulse-chase procedure using [3H] leucine. The apparent half maximal stimulation of protein labeling (12%, 8%, 7%) occurred at approximately .1 nM rcIGF-I, 1 nM oSm/oIGF-I and 15 nM insulin, respectively. The apparent half maximal inhibition of proteolysis (18%, 15% and 11%) occurred at .4 nM rcIGF-I, .6 nM oSm/oIGF-I and 4 nM insulin, respectively. The magnitude of the response for protein labeling and degradation was greatest for rcIGF-I. The results provide additional evidence that IGFs play a primary role in regulating protein turnover in muscle.
Roeder
R A
RA
Department of Animal Science, University of Idaho, Moscow.
Hossner
K L
KL
Sasser
R G
RG
Gunn
J M
JM
D002478:Cells, Cultured; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D024510:Muscle Development; D009132:Muscles / Q000187:drug effects*; D011506:Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000494:pharmacology; D013002:Somatomedins / Q000494:pharmacology*
D007328:Insulin; D011506:Proteins; D011994:Recombinant Proteins; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I