Regulation of calpain and calpastatin in differentiating myoblasts: mRNA levels, protein synthesis and stability

S. Barnoy, L. Supino-Rosin, N. S. Kosower*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Calpain (Ca2+-dependent intracellular protease)-induced proteolysis has been considered to play a role in myoblast fusion to myotubes. We found previously that calpastatin (the endogenous inhibitor of calpain) diminishes transiently during myoblast differentiation. To gain information about the regulation of calpain and calpastatin in differentiating myoblasts, we evaluated the stability and synthesis of calpain and calpastatin, and measured their mRNA levels in L8 myoblasts. We show here that μ-calpain and m-calpain are stable, long-lived proteins in both dividing and differentiating L8 myoblasts. Calpain is synthesized in differentiating myoblasts, and calpain mRNA levels do not change during differentiation. In contrast, calpastatin (though also a long-lived protein in myoblasts), is less stable in differentiating myoblasts than in the dividing cells, and its synthesis is inhibited upon initiation of differentiation. Inhibition of calpastatin is followed by a diminution in calpastatin mRNA levels. A similar calpastin mRNA diminution is observed upon drug-induced inhibition of protein translation. On the other hand, transforming growth factor β (which inhibits differentiation) allows calpastatin is regulated mainly at the level of translation and that an inhibition of calplastin synthesis leads to the decrease in its mRNA stability. The existing calpastatin then diminishes, resulting in decreased calplastin activity in the fusing myoblasts, allowing calpain activation and protein degration required for fushion.

Original languageEnglish
Pages (from-to)413-420
Number of pages8
JournalBiochemical Journal
Issue number2
StatePublished - 15 Oct 2000


  • Ca-dependent protease
  • Cell fusion
  • Protease inhibitor


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