Negative feedback loop in the Bim-caspase-3 axis regulating apoptosis and activity of osteoclasts.
Proapoptotic Bcl-2 family member Bim plays an essential role in the osteoclast apoptosis and is degraded through ubiquitin/proteasome pathways in a caspase-3-dependent manner. This negative feedback loop in the Bim-caspase-3 axis is important for regulating the survival and activity of osteoclasts.


BACKGROUND
Bim is a member of the proapoptotic Bcl-2 family and regulates the mitochondrial apoptosis pathway. Bim expression is post-translationally regulated in osteoclasts (OCs) through ubiquitin/proteasome pathways, and Bim is critical for their survival and activity.


METHODS
Time-course of change in the expression of Bim in the course of OC apoptosis was examined, and the effect of various proteinase inhibitors on the degradation of Bim was analyzed. The role of caspase-3 and caspase-7 on Bim degradation was studied using RNA interference technique and caspase-3(-/-) mice.


RESULTS
Bim was degraded after caspase-3 activation, which was suppressed by a caspase inhibitor and a proteasome inhibitor. Bim degradation was suppressed by gene knockdown of caspase-3 or in caspase-3(-/-) OCs but not by caspase-7 knockdown. OCs generated from caspase-3(-/-) bone marrow cells exhibited a shorter life span and higher bone-resorbing activity than normal OCs. Association of Bim with E3 ubiquitin ligase c-Cbl was suppressed by gene knockdown of caspase-3 or in caspase-3(-/-) OCs. Actin ring formation and cathepsin K expression were promoted in caspase-3(-/-) OCs.


CONCLUSIONS
Caspase-3 negatively regulates Bim expression by stimulating its degradation through ubiquitin/proteasome pathways, thus creating a negative feedback loop in the Bim-caspase axis.
Wakeyama
Hidetoshi
H
Department of Orthopaedic Surgery, Faculty of Medicine, The University of Tokyo, Tokyo, Japan.
Akiyama
Toru
T
Takahashi
Katsuhiko
K
Amano
Hitoshi
H
Kadono
Yuho
Y
Nakamura
Masaki
M
Oshima
Yasushi
Y
Itabe
Hiroyuki
H
Nakayama
Keiichi I
KI
Nakayama
Keiko
K
Nakamura
Kozo
K
Tanaka
Sakae
S
D000818:Animals; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D053148:Caspase 3 / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D053179:Caspase 7 / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D015536:Down-Regulation; D004789:Enzyme Activation; D025461:Feedback, Physiological; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D010010:Osteoclasts / Q000166:cytology* / Q000201:enzymology / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism*; D050721:Proto-Oncogene Proteins c-cbl / Q000378:metabolism
D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D050721:Proto-Oncogene Proteins c-cbl; D053148:Caspase 3; D053179:Caspase 7