title: Osteopontin signals through calcium and nuclear factor of activated T cells (NFAT) in osteoclasts: a novel RGD-dependent pathway promoting cell survival.
abstract: Osteopontin (OPN), an integrin-binding extracellular matrix glycoprotein, enhances osteoclast activity; however, its mechanisms of action are elusive. The Ca(2+)-dependent transcription factor NFATc1 is essential for osteoclast differentiation. We assessed the effects of OPN on NFATc1, which translocates to nuclei upon activation. Osteoclasts from neonatal rabbits and rats were plated on coverslips, uncoated or coated with OPN or bovine albumin. OPN enhanced the proportion of osteoclasts exhibiting nuclear NFATc1. An RGD-containing, integrin-blocking peptide prevented the translocation of NFATc1 induced by OPN. Moreover, mutant OPN lacking RGD failed to induce translocation of NFATc1. Thus, activation of NFATc1 is dependent on integrin binding through RGD. Using fluorescence imaging, OPN was found to increase the proportion of osteoclasts exhibiting transient elevations in cytosolic Ca(2+) (oscillations). OPN also enhanced osteoclast survival. The intracellular Ca(2+) chelator 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA) suppressed Ca(2+) oscillations and inhibited increases in NFATc1 translocation and survival induced by OPN. Furthermore, a specific, cell-permeable peptide inhibitor of NFAT activation blocked the effects of OPN on NFATc1 translocation and osteoclast survival. This is the first demonstration that OPN activates NFATc1 and enhances osteoclast survival through a Ca(2+)-NFAT-dependent pathway. Increased NFATc1 activity and enhanced osteoclast survival may account for the stimulatory effects of OPN on osteoclast function in vivo.
authors.affiliation: Department of Physiology and Pharmacology, Schulich School of Medicine and Dentistry, The University of Western Ontario, London N6A5C1, Canada.
authors.forename: Natsuko
authors.initials: N
authors.lastname: Tanabe
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Wheal
authors.forename: Jiyun
authors.initials: J
authors.lastname: Kwon
authors.forename: Hong H
authors.initials: HH
authors.lastname: Chen
authors.forename: Ryan P P
authors.initials: RP
authors.lastname: Shugg
authors.forename: Stephen M
authors.initials: SM
authors.lastname: Sims
authors.forename: Harvey A
authors.initials: HA
authors.lastname: Goldberg
authors.forename: S Jeffrey
authors.initials: SJ
authors.lastname: Dixon
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000502:physiology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling / Q000187:drug effects* / Q000502:physiology; D002417:Cattle; D002467:Cell Nucleus / Q000378:metabolism*; D002470:Cell Survival / Q000187:drug effects / Q000502:physiology; D002478:Cells, Cultured; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D050778:NFATC Transcription Factors / Q000276:immunology*; D009842:Oligopeptides / Q000378:metabolism / Q000494:pharmacology*; D010010:Osteoclasts / Q000166:cytology / Q000378:metabolism*; D053495:Osteopontin / Q000378:metabolism / Q000494:pharmacology*; D011817:Rabbits; D051381:Rats
chemical_list: D002614:Chelating Agents; D050778:NFATC Transcription Factors; D009842:Oligopeptides; C506897:Spp1 protein, rat; D053495:Osteopontin; D004533:Egtazic Acid; C047981:arginyl-glycyl-aspartic acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium