title: Evidence of reciprocal regulation between the high extracellular calcium and RANKL signal transduction pathways in RAW cell derived osteoclasts.
abstract: During bone resorption, osteoclasts are exposed to high Ca2+ concentrations (up to 40 mM). The role of high extracellular Ca2+ in receptor activator of NF-kappaB ligand (RANKL)-mediated osteoclast survival and their functional interrelationship is unclear. In this study, we show that RANKL enhances osteoclast tolerance to high extracellular Ca2+ by protecting the cell from cell death in a dose dependent manner. We have provided evidence that RANKL does this by attenuating high extracellular Ca2+-induced Ca2+ elevations. Moreover, we have found that high extracellular Ca2+-induced cell death was partially inhibited by a caspase-3 inhibitor, suggesting caspase-3-mediated apoptosis is involved. Conversely, using reporter gene assays and Western blot analysis, we have demonstrated that high extracellular Ca2+ desensitizes the RANKL-induced activation of NF-kappaB and c-Jun N-terminal kinase (JNK), and inhibits constitutive and RANKL-stimulated ERK phosphorylation, indicating a negative feed-back mechanism via specific RANKL signaling pathways. Taken together, this study provides evidence for a reciprocal regulation between high extracellular Ca2+ and RANKL signaling in RAW cell derived osteoclasts. Our data imply a cross talk mechanism of extracellular Ca2+ on osteoclast survival through the regulation of RANKL.
authors.affiliation: Molecular Orthopaedic Laboratory, School of Surgery and Pathology, University of Western Australia, Nedlands WA, Australia. jiakexu@cyllene.uwa.edu.au
authors.forename: Jiake
authors.initials: J
authors.lastname: Xu
authors.forename: Cathy
authors.initials: C
authors.lastname: Wang
authors.forename: Renzhi
authors.initials: R
authors.lastname: Han
authors.forename: Nathan
authors.initials: N
authors.lastname: Pavlos
authors.forename: Tony
authors.initials: T
authors.lastname: Phan
authors.forename: James H
authors.initials: JH
authors.lastname: Steer
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Bakker
authors.forename: David A
authors.initials: DA
authors.lastname: Joyce
authors.forename: Ming H
authors.initials: MH
authors.lastname: Zheng
mesh_terms: D000818:Animals; D002118:Calcium / Q000008:administration & dosage / Q000378:metabolism* / Q000494:pharmacology; D002352:Carrier Proteins / Q000378:metabolism* / Q000494:pharmacology; D016923:Cell Death / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D045604:Extracellular Fluid / Q000378:metabolism*; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000378:metabolism* / Q000494:pharmacology; D016328:NF-kappa B / Q000378:metabolism; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D053245:RANK Ligand; D011994:Recombinant Proteins / Q000494:pharmacology; D015398:Signal Transduction
chemical_list: D002352:Carrier Proteins; D008562:Membrane Glycoproteins; D016328:NF-kappa B; D053245:RANK Ligand; D011994:Recombinant Proteins; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D002118:Calcium