Human myeloma cells promote the recruitment of osteoblast precursors: Mediation by interleukin-6 and soluble interleukin-6 receptor

Multiple myeloma is associated with the development of osteolytic bone dise ase characterized by a disruption to normal bone resorption and bone format ion. Although studies have shown that myeloma cells produce factors that pr omote bone resorption little data are available examining the mechanism of decreased bone formation or the factors that mediate this effect. In the pr esent study we describe a novel in vitro coculture system in which to inves tigate the effect of myeloma cells on osteoblast recruitment and differenti ation. Under appropriate conditions mesenchymal stem cells were shown to di fferentiate into colonies of cells, a proportion of which show characterist ics of osteoblasts, in that they express alkaline phosphatase activity and stain positively for collagen and calcium. The addition of the human myelom a cells JJN-3, RPMI-8226, or NCI-H929 to these cultures stimulated a signif icant increase in the total number of colonies (p < 0.005) and the proporti on of osteoblastic colonies (p < 0.005). Media conditioned by these cells a lso were able to promote the formation of both total and osteoblastic colon ies (p < 0.005). The addition of an antibody against the interleukin-6 rece ptor (1L-6R) blocked myeloma cell and myeloma cell-conditioned media induce d osteoblast recruitment (p < 0.01). Furthermore, media conditioned by myel oma cells incubated with phorbol ester, which promotes IL-6R shedding, or a metalloproteinase inhibitor, which inhibits IL-6R shedding, were able to s timulate (p < 0.005) and inhibit osteoblast recruitment (p < 0.005), respec tively. In addition, soluble IL-6R (sIL-6R) and IL-6 together, but not alon e, were able to promote osteoblastic colony formation (p < 0.01). Taken tog ether these data show that myeloma cells promote osteoblast recruitment by release of sIL-6R from myeloma cells.