CA2 and breast cancer: Next, treatment of p27−/−(Δ51) cells with calpain inhibitor (Calpain Inh), a competitive inhibitor of the Ca2+-dependent neutral cysteine protease, exhibited an remarkable positive effect on PHLPP2 protein accumulation (Fig. 2h), revealing that protease calpain might participate p27 regulation of PHLPP2 abundance in human BC cells.