CHINESE-HAMSTER OVARY CELLS EXPRESSING ALPHA(4)BETA(1) INTEGRIN STIMULATE OSTEOCLAST FORMATION IN-VITRO

It is reported that Chinese hamster ovary cells transfected with human alpha(4) cDNA (alpha(4)CHOs) and expressing functional alpha(4)beta(1 ) integrin developed bone metasasis in nude mice. To clarify the role of alpha(4)beta(1) integrin in bone metastasis, in terms of tumor-medi ated bone destruction, we examined whether alpha(4)CHOs stimulate oste oclast formation in cocultures with mouse bone marrow cells, The numbe r of osteoclast-like cells identified as tartrate-resistant acid phosp hatase positive multinucleated cells (TRAP(+) MNCs) formed hom bone ma rrow cells increased with the increasing number of alpha(4)CHOs cocult ured, The effects of 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) and pr ostaglandin E-2 (PGE(2)) on TRAP(+) MNC formation were enhanced in coc ultures with alpha(4)CHOs. TRAP(+) MNCs induced by alpha(4)CHOs posses sed calcitonin receptors and resorbed calcified tissues. In cocultures , alpha(4)CHOs and bone marrow stromal cells were in contact with each other and bone marrow stromal cells expressed vascular cell adhesion molecule-1 (VCAM-1), which is one of the ligands for alpha(4)beta(1) i ntegrin, TRAP(+) MNC formation was not stimulated in cocultures where direct contact between alpha(4)CHOs and bone marrow cells was inhibite d by membrane filters. alpha(4)CHOs do not support TRAP(S) MNC formati on in cocultures with spleen cells but do support TRAP(+) mononuclear cell and MNC formation from spleen cells in the presence of osteoblast ic cells. Cultured media from alpha(4)CHOs, bone marrow cells, and coc ultures of alpha(4)CHOs and bone marrow cells did not stimulate TRAP() MNC formation or enhance the effects of 1,25(OH)(2)D-3 and PGE, in b one marrow cultures. The concentrations of PGE, and interleukin-6 (IL- 6) in cultured media were not different between the cultures of bone m arrow cells and the cocultures of bone marrow cells and alpha(4)CHOs. Anti-human cu, and anti-mouse VCAM-1 antibodies inhibited TRAP(+) MNC formation induced by alpha(4)CHOs. These results indicate that alpha(4 )CHOs stimulated TRAP(+) MNC formation through direct cell-to-cell int eraction between alpha(4)beta(1) and VCAM-1, It is suggested that in a ddition to various soluble factors regulating osteoclast formation, ce ll-to-cell interaction between tumor cells and bone marrow cells is im portant for inducing osteoclasts at the site of bone metastasis and le ading to bone destruction.