title: Human osteoblasts are resistant to Apo2L/TRAIL-mediated apoptosis.
abstract: Apo2 ligand (Apo2L/TRAIL) is a member of the tumor necrosis factor (TNF) cytokine family. Apo2L/TRAIL can selectively induce programmed cell death in transformed cells, although its wide tissue distribution suggests potential physiological roles. We have investigated the expression, in human osteoblast-like cells (NHBC), of Apo2L/TRAIL and the known Apo2L/TRAIL death receptors, DR4 and DR5, and the Apo2L/TRAIL decoy receptors, DcR-1, DcR-2, and osteoprotegerin (OPG). NHBC expressed abundant mRNA corresponding to each of these molecular species. Immunofluorescence staining demonstrated that Apo2L/TRAIL protein was abundant within the cytoplasm of NHBC and OPG was strongly expressed at the cell surface. DR5 and DcR-2 were present in the cell membrane and cytoplasm and DcR-1 was confined to the nucleus. DR4 staining was weak. Neither Apo2L/TRAIL alone, nor in combination with chemotherapeutic agents of clinical relevance to treatment of osteogenic sarcoma, induced cell death in NHBC, as assessed morphologically and by activation of caspase-3. In contrast, the human osteogenic sarcoma cell lines, BTK-143 and G-292, were sensitive to exogenous Apo2L/TRAIL alone, and to the combined effect of Apo2L/TRAIL/cisplatin and Apo2L/TRAIL/doxorubicin treatments, respectively. In NHBC, we observed strong associations between the levels of mRNA corresponding to the pro-apoptotic molecules, Apo2L/TRAIL, DR4, and DR5, and those corresponding to pro-survival molecules, DcR-1, DcR-2, OPG, and FLIP, suggesting that the balance between pro-survival and pro-apoptotic molecules is a mechanism by which NHBC can resist Apo2L/TRAIL-mediated apoptosis. In contrast, osteogenic sarcoma cells had low or absent levels of DcR-1 and DcR-2. These results provide a foundation to explore the role of Apo2L/TRAIL in osteoblast physiology. In addition, they predict that therapeutic use of recombinant Apo2L/TRAIL, in combination with chemotherapeutic agents to treat skeletal malignancies, would have limited toxic effects on normal osteoblastic cells.
authors.affiliation: Department of Orthopaedics and Trauma, Adelaide University and Royal Adelaide Hospital, Adelaide, SA, Australia.
authors.forename: G J
authors.initials: GJ
authors.lastname: Atkins
authors.forename: S
authors.initials: S
authors.lastname: Bouralexis
authors.forename: A
authors.initials: A
authors.lastname: Evdokiou
authors.forename: S
authors.initials: S
authors.lastname: Hay
authors.forename: A
authors.initials: A
authors.lastname: Labrinidis
authors.forename: A C W
authors.initials: AC
authors.lastname: Zannettino
authors.forename: D R
authors.initials: DR
authors.lastname: Haynes
authors.forename: D M
authors.initials: DM
authors.lastname: Findlay
mesh_terms: D000328:Adult; D017209:Apoptosis / Q000502:physiology*; D051017:Apoptosis Regulatory Proteins; D001483:Base Sequence; D016022:Case-Control Studies; D017931:DNA Primers; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D005455:Fluorescent Antibody Technique; D006801:Humans; D008562:Membrane Glycoproteins / Q000235:genetics / Q000502:physiology*; D010003:Osteoarthritis / Q000473:pathology; D010006:Osteoblasts / Q000166:cytology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D053221:TNF-Related Apoptosis-Inducing Ligand; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000502:physiology*
chemical_list: D051017:Apoptosis Regulatory Proteins; D017931:DNA Primers; D008562:Membrane Glycoproteins; D012333:RNA, Messenger; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha