Human breast-cancer cells stimulate the fusion, migration and resorptive activity of osteoclasts in bone explants.
A central event in bone resorption is the recruitment of osteoclasts to future resorption sites. Breast-cancer cells invariably metastasise to the skeleton and induce extensive bone destruction by osteoclasts. However, our understanding of the mechanisms by which cancer cells interact with osteoclasts remains unclear. Consequently, we compared the effects of conditioned medium (CM) from 2 human breast-cancer cell lines, MB-MDA-231 and MCF-7, with those of a normal human breast epithelial cell line, HME, on osteoclastic fusion, resorptive activity and migration from the periosteum to the developing marrow cavity of fetal mouse metatarsals in culture. Osteoclastic resorptive activity was assessed by pre-labelling 17-day-old fetal metatarsal explants with 45Ca, whilst fusion and migration were monitored by histomorphometry and osteoclasts were identified by their tartrate-resistant acid phosphatase activity. CM from TPA-stimulated breast-cancer cell lines produced a significant increase in osteoclastic resorptive activity, whilst the normal breast cell line produced a minimal increase. The breast-cancer cell lines also stimulated osteoclastic fusion and migration in the metatarsal explants, but the normal breast cell line was without effect. The stimulatory effect of CM from MDA-MB-231 cells on osteoclastic fusion, but not migration, was partially inhibited by preventing prostaglandin and leukotriene synthesis by cells within the bone explants. In contrast, a synthetic matrix metalloproteinase (MMP) inhibitor, but not a cysteine proteinase inhibitor, prevented the migration of osteoclasts to the calcified centre of the metatarsal explants in response to CM from MDA-MB-231 cells. MDA-MB-231 cells also induced an increase in the expression of MMP-9 by migrating osteoclasts. Fractionation of the TPA-stimulated breast cancer cell CM established that the resorptive activity was associated with factors of m.w. >3 kDa. We determined by immuno-assay that human breast-cancer cells secrete parathyroid hormone-related protein (PTH-rP), tumour necrosis factor-alpha (TNF-alpha) and interleukins (ILs) 6 and 11. Neutralizing experiments with human antibodies to these cytokines established that PTH-rP and TNF-alpha production by MDA-MB-231 cells were responsible for mediating their effects on osteoclastic migration and ultimately bone resorption in the metatarsal explants.
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Bone Biology Unit, Department of Orthodontics and Paediatric Dentistry, Guy's, King's and St. Thomas' School of Medicine and Dentistry, Guy's Hospital, London, United Kingdom.
Morgan
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HM
Meikle
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Hill
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PA
D000818:Animals; D001862:Bone Resorption; D001842:Bone and Bones / Q000166:cytology* / Q000378:metabolism; D001940:Breast / Q000166:cytology; D001943:Breast Neoplasms / Q000378:metabolism*; D002459:Cell Fusion; D002460:Cell Line; D002465:Cell Movement; D017077:Culture Media, Conditioned / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D017403:In Situ Hybridization; D007375:Interleukin-1 / Q000096:biosynthesis; D017370:Interleukin-11 / Q000096:biosynthesis; D015850:Interleukin-6 / Q000096:biosynthesis; D015289:Leukotrienes / Q000096:biosynthesis; D020780:Matrix Metalloproteinase 9 / Q000096:biosynthesis; D061965:Matrix Metalloproteinase Inhibitors; D008682:Metatarsal Bones / Q000196:embryology / Q000378:metabolism; D051379:Mice; D009362:Neoplasm Metastasis; D009924:Organ Culture Techniques; D010010:Osteoclasts / Q000166:cytology* / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein; D011453:Prostaglandins / Q000096:biosynthesis; D011506:Proteins / Q000378:metabolism; D013997:Time Factors; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000096:biosynthesis / Q000378:metabolism; D014462:Ultrafiltration
D017077:Culture Media, Conditioned; D015853:Cysteine Proteinase Inhibitors; D007375:Interleukin-1; D017370:Interleukin-11; D015850:Interleukin-6; D015289:Leukotrienes; D061965:Matrix Metalloproteinase Inhibitors; C470121:PTHLH protein, human; D044162:Parathyroid Hormone-Related Protein; D011453:Prostaglandins; D011506:Proteins; D014409:Tumor Necrosis Factor-alpha; D020780:Matrix Metalloproteinase 9