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Autocatalytic Inactivation of Lysosomal Cathepsins Is Associated with Inhibition of Protein Breakdown by Insulin-Like Growth Factor-1 (IGF-1) in Myotubes

Authors
Journal
Biochemical and Biophysical Research Communications
0006-291X
Publisher
Elsevier
Publication Date
Volume
208
Issue
1
Identifiers
DOI: 10.1006/bbrc.1995.1345
Disciplines
  • Biology

Abstract

Abstract 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 β, an intrinsic inhibitor for cathepsins, was influenced. The addition of E-64, L-3-carboxy-trans-2,3-epoxypropionyl-leucylamide-(4-guanidino) 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.

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