Protease-activated receptor-2 mediates proliferative responses in skeletalmyoblasts

Protease-activated receptor-2 (PAR-2) is a G protein-coupled receptor that is cleaved by proteases within the N terminus, exposing a new tethered liga nd that binds and activates the receptor. Activators of PAR-2 include tryps in and mast cell tryptase, Skeletal myoblasts are known to express PAR-1, a thrombin receptor. The current study was undertaken to determine whether m yoblasts express PAR-2, Primary neonatal rat and mouse skeletal myoblast cu ltures were shown to express PAR-2 in polymerase chain reaction and immunoc ytochemical studies, Expression of PAR-2 was also demonstrated by immunohis tochemistry in developing mouse skeletal muscle in vivo. Trypsin or a synth etic peptide corresponding to the rat PAR-2 tethered ligand caused a dose-d ependent elevation in intracellular calcium in cultured rat myoblasts, with an EC50 of 13 nM or 56 muM, respectively. Studies aimed at identifying the function of PAR-2 in myoblasts demonstrated no effect of the receptor-acti vating peptide on survival or fusion in serum-deprived myoblasts, The PAR-2 -activating peptide did, however, stimulate proliferation of serum-deprived myoblasts, These results demonstrate that skeletal muscle cells express PA R-2, activation of which leads to stimulation of myoblast proliferation.