ABSTRACT: Osteoclasts are essential for bone dynamics and calcium homeostasis. Recently, we reported that serum calcium-decreasing factor, caldecrin, which is a secretory-type serine protease isolated from the pancreas, inhibits osteoclast differentiation by suppression of NFATc1 activity regardless of its own protease activity (Hasegawa, H., Kido, S., Tomomura, M., Fujimoto, K., Ohi, M., Kiyomura, M., Kanegae, H., Inaba, A., Sakagami, H., and Tomomura, A. (2010) Serum calcium-decreasing factor, caldecrin, inhibits osteoclast differentiation by suppression of NFATc1 activity. J. Biol. Chem. 285, 25448-25457). Here, we investigated the effects of caldecrin on the function of mature osteoclasts by treatment with receptor activator of NF-κB ligand (RANKL). Caldecrin inhibited the RANKL-stimulated bone
