Breast cancer increases osteoclastogenesis by secreting M-CSF and upregulating RANKL in stromal cells

Background. Breast cancer metastasis to bone causes resorption of the miner alized matrix by osteoclasts. Macrophage colony stimulating factor (M-CSF) and receptor activator of the NF-kappaB ligand (RANKL) are produced by stro mal cells and are essential for osteoclast formation. The human breast canc er cell line, MDA-MB-231, reliably forms bone metastases in a murine model and stimulates osteoclast formation in culture. We hypothesized that NMA-MB -231 stimulates osteoclast formation through secretion of M-CSF and/or RANK L. Materials and methods. We cocultured MDA-MB-231 and a bone marrow derived c ell line, UAMS-33, and evaluated the expression of M-CSF and RANKL mRNA. Os teoclast formation was assessed using these cells added to hematopoietic ce ll cultures. Results. MDA-MB-231 exhibited constitutive expression of M-CSF mRNA. As exp ected, addition of recombinant M-CSF (30 ng/ml) and RANKL (30 ng/ml) to hem atopoietic osteoclast precursors supported osteoclast formation, while the addition of soluble RANKL alone or MDA-231 without added RANKL did not. Not ably, coculture of MDA-231 with hematopoietic cells and added soluble RANKL stimulated significant osteoclast formation, indicating that MDA-231 serve d as an effective source for M-CSF. MDA-231 did not express RANKL. However, when cocultured with the murine bone marrow stromal cell line UAMS-33, RAN KL expression was significantly increased in the latter cells. MDA-231 also stimulated osteoclast formation in coculture with UAMS-33 and hematopoieti c cells. Conclusions. We conclude that MDA-MB-231 increases osteoclast formation by secreting adequate amounts of M-CSF protein and enhancing the expression of RANKL by stromal support cells. The ability to stimulate osteoclasts may e xplain the ability to metastasize to bone. (C) 2001 Academic Press.