Autocatalytic inactivation of lysosomal cathepsins is associated with inhibition of protein breakdown by insulin-like growth factor-1 (IGF-1) in myotubes.
Protein breakdown was monitored in C2C12 myotubes as the rate of release of radioactivity after prelabeling cell protein with [3H] tyrosine. IGF-1 (13 nM) and insulin (100 nM) prolonged the half-life of long-lived proteins. Enzymatic activities of cathepsins B and B+L were inhibited by the addition of IGF-1 or insulin. Immunoblotting of cathepsins B and L revealed extensive degradation of heavy chain forms by IGF-1. However, neither expression of cathepsins B and L genes nor expression of cystatin beta, an intrinsic inhibitor for cathepsins, was influenced. The addition of E-64, L-3-carboxy-trans-2,3-epoxypropionyl-leucylamide-(4-guanidin o) butane, a inhibitor of cathepsins B and L, increased protein contents of heavy chains of cathepsins B and L in the IGF-1 treated cells. Inhibition of protein breakdown by IGF-1 is mediated by autocatalytic inactivation of lysosomal cathepsins B and L.
Tsujinaka
T
T
Department of Surgery II, Osaka University Medical School, Japan.
Ebisui
C
C
Fujita
J
J
Morimoto
T
T
Ogawa
A
A
Ishidoh
K
K
Kominami
E
E
Yano
M
M
Shiozaki
H
H
Monden
M
M
D000704:Analysis of Variance; D000818:Animals; D015152:Blotting, Northern; D002401:Cathepsin B / Q000096:biosynthesis; D056668:Cathepsin L; D002403:Cathepsins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D002460:Cell Line; D015891:Cystatins / Q000096:biosynthesis; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D010450:Endopeptidases; D015870:Gene Expression / Q000187:drug effects*; D006207:Half-Life; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D007930:Leucine / Q000031:analogs & derivatives / Q000494:pharmacology; D008247:Lysosomes / Q000201:enzymology*; D051379:Mice; D018482:Muscle, Skeletal; D014176:Protein Biosynthesis; D011506:Proteins / Q000378:metabolism*; D012313:RNA / Q000096:biosynthesis / Q000378:metabolism; D051381:Rats
D015891:Cystatins; D015853:Cysteine Proteinase Inhibitors; D007328:Insulin; D011506:Proteins; D012313:RNA; D007334:Insulin-Like Growth Factor I; D002403:Cathepsins; D010450:Endopeptidases; D003546:Cysteine Endopeptidases; D002401:Cathepsin B; D056668:Cathepsin L; C534278:Ctsl protein, mouse; C534280:Ctsl protein, rat; D007930:Leucine; C024974:E 64