β2-Adrenoceptor (β2-AR) agonists promote muscle growth,and are widely used in production livestock.The aim of this study was to elucidate some effects of the selective β2-adrenoceptor agonist clenbuterol (CLB) on myoblast proliferation.We found that CLB induces cell cycle arrest in C2C 12 myoblasts.This effect is partly due to the enhanced stability of p27,rather than the increased gene transcription via cAMP response element-bindingprotein (CREB).Specifically,CLB treatment enhanced the accumulation of p27 in the nucleus while depleting it from the cytosol via a mechanism that requires β2-AR.Surprisingly,p27 accumulation was not reversed by the protein kinase A (PKA) inhibitor H-89,but interestingly,was alleviated by the knockdown of β-arrestin 2.Thus,our work provides a basis for β2-AR agonists inhibit myoblasts proliferation through signaling via β2-AR,β-arrestin 2,and p27.