DEVELOPMENTAL CONTROL OF CATHEPSIN-B EXPRESSION IN BOVINE FETAL MUSCLES

Expression of lysosomal cysteine proteinases was studied during fetal calf muscle development. The peptide cleaving activities of cathepsins B and L decreased strongly from 80 to 250 days of fetal age. This dec rease in cathepsin activities occurred similarly in three muscles exhi biting different metabolic and contractile properties in adult animals . Cathepsin B from adult or fetal muscle revealed similar enzymatic pr operties, but presented a five- 60 sixfold lower concentration in adul t muscle as indicated by active-site titration with ,3-epoxypropionyl- leucylamido-(4-guanidino)butane. During fetal growth, decreases in mus cle cathepsin 8 specific activity and active enzyme concentration were associated with a parallel drop of cathepsin B mRNA levels. Bovine ca thepsin B is encoded by two different transcripts resulting from alter native polyadenylation [Mordier, S. B., Bechet, D. M., Roux, M. P., Ob led, A., and Ferrara, M. (1995) Eur. J. Biochem. 229, 35-44]. As revea led by ribonuclease protection assays, the two mRNAs encoding cathepsi n B declined similarly during fetal muscle growth. This study indicate s that lysosomal proteinases in skeletal muscle are under developmenta l control. The decrease of muscle cathepsins during fetal development appears sufficient to account for the low levels of these enzymes in a dult muscles. In fetuses, high activities of lysosomal cysteine protei nases might be important for remodeling muscles during early developme nt. (C) 1996 Academic Press, Inc.