Unoccupied alpha(v)beta3 integrin regulates osteoclast apoptosis by transmitting a positive death signal.
Cell/matrix detachment is a general inducer of programmed cell death, an event mediated by loss of integrin/ligand association. Because alpha(v)beta3 is the major integrin expressed by the osteoclast, we asked whether its occupancy promotes survival of the resorptive cell. Thus, we generated wild-type preosteoclasts and placed them on selective matrix proteins. Consistent with the posture that alpha(v)beta3 occupancy promotes survival, preosteoclasts plated on native collagen, a matrix not recognized by the integrin, undergo apoptosis 4-fold faster than those on the alpha(v)beta3 ligand, vitronectin. To further explore the role of alpha(v)beta3 in osteoclast apoptosis, wild-type and beta3-/- preosteoclasts were suspended and apoptosis determined, with time. Beta3-/- preosteoclasts, in suspension, undergo a rate of apoptosis only 40-60% of that of their wild-type counterparts, indicating that unoccupied alpha(v)beta3 transmits a positive death signal that we find regulated by caspase-8. Attesting to specificity of the unoccupied integrin-transmitted death signal, apoptosis in the absence of alpha(v)beta3 is mediated by capsase-9. We have shown that the resorptive defect of beta3-/- osteoclasts is rescued by wild-type beta3 cDNA but not by one bearing a S752P mutation. To determine whether the same holds true regarding osteoclast apoptosis, we constructed lentivirus vectors encoding green fluorescent protein, wild-type beta3, or beta3S752P. Once again, native beta3-/- preosteoclasts were protected against apoptosis. Similar to its effect on bone resorption, transduced wild-type beta3 normalizes the apoptotic rate of beta3-/- preosteoclasts. Unexpectedly, however, beta3S752P transductants also die at a rate indistinguishable from wild type. Thus, unoccupied alpha(v)beta3 integrin regulates osteoclast apoptosis via a component of the integrin that is different than that regulating resorption.
Zhao
Haibo
H
Department of Pathology and Immunology, Washington University School of Medicine, Campus Box 8118, 660 South Euclid Avenue, St. Louis, Missouri 63110, USA.
Ross
F Patrick
FP
Teitelbaum
Steven L
SL
D000818:Animals; D017209:Apoptosis; D015153:Blotting, Western; D001854:Bone Marrow Cells / Q000166:cytology*; D053181:Caspase 8; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000378:metabolism; D005434:Flow Cytometry; D005822:Genetic Vectors; D049452:Green Fluorescent Proteins / Q000378:metabolism; D047468:Immunoprecipitation; D039302:Integrin alphaVbeta3 / Q000737:chemistry* / Q000502:physiology*; D016023:Integrins / Q000378:metabolism; D016086:Lentivirus / Q000235:genetics; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009154:Mutation; D010006:Osteoblasts / Q000378:metabolism; D010010:Osteoclasts / Q000378:metabolism / Q000473:pathology*; D012190:Retroviridae / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors; D019096:Vitronectin / Q000737:chemistry
D018076:DNA, Complementary; D039302:Integrin alphaVbeta3; D016023:Integrins; D019096:Vitronectin; D049452:Green Fluorescent Proteins; C505526:Casp8 protein, mouse; D053181:Caspase 8; D020169:Caspases