Fas binding to calmodulin regulates apoptosis in osteoclasts.
Promotion of osteoclast apoptosis is one therapeutic approach to osteoporosis. Calmodulin, the major intracellular Ca(2+) receptor, modulates both osteoclastogenesis and bone resorption. The calmodulin antagonist, trifluoperazine, rescues bone loss in ovariectomized mice (Zhang, L., Feng, X., and McDonald, J. M. (2003) Endocrinology 144, 4536-4543). We show here that a 3-h treatment of mouse osteoclasts with either of the calmodulin antagonists, tamoxifen or trifluoperazine, induces osteoclast apoptosis dose-dependently. Tamoxifen, 10 microm, and trifluoperazine, 10 microm, induce 7.3 +/- 1.8-fold and 5.3 +/- 0.9-fold increases in osteoclast apoptosis, respectively. In Jurkat cells, calmodulin binds to Fas, the death receptor, and this binding is regulated during Fas-mediated apoptosis (Ahn, E. Y., Lim, S. T., Cook, W. J., and McDonald, J. M. (2004) J. Biol. Chem. 279, 5661-5666). In osteoclasts, calmodulin also binds Fas. When osteoclasts are treated with 10 microm trifluoperazine, the binding between Fas and calmodulin is dramatically decreased at 15 min and gradually recovers by 60 min. A point mutation of the Fas death domain in the Lpr(-cg) mouse renders Fas inactive. Using glutathione S-transferase fusion proteins, the human Fas cytoplasmic domain is shown to bind calmodulin, whereas a point mutation (V254N) comparable with the Lpr(-cg) mutation in mice has markedly reduced calmodulin binding. Osteoclasts derived from Lpr(-cg) mice have diminished calmodulin/Fas binding and are more sensitive to calmodulin antagonist-induced apoptosis than those from wild-type mice. Both tamoxifen- and trifluoperazine-induced apoptosis are increased 1.6 +/- 0.2-fold in Lpr(-cg)-derived osteoclasts compared with osteoclasts derived from wild-type mice. In summary, calmodulin antagonists induce apoptosis in osteoclasts by a mechanism involving interference with calmodulin binding to Fas. The effects of calmodulin/Fas binding on calmodulin antagonist-induced apoptosis may open a new avenue for therapy for osteoporosis.
Wu
Xiaojun
X
Department of Pathology, University of Alabama at Birmingham, 35294, USA.
Ahn
Eun-Young
EY
McKenna
Margaret A
MA
Yeo
Hyeonju
H
McDonald
Jay M
JM
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D002147:Calmodulin / Q000037:antagonists & inhibitors / Q000502:physiology*; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D008297:Male; D051379:Mice; D010010:Osteoclasts / Q000166:cytology*; D010024:Osteoporosis / Q000188:drug therapy; D013629:Tamoxifen / Q000494:pharmacology; D014268:Trifluoperazine / Q000494:pharmacology; D019014:fas Receptor / Q000502:physiology*
D002147:Calmodulin; D019014:fas Receptor; D013629:Tamoxifen; D014268:Trifluoperazine; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases