Human Myeloma Cells Promote the Recruitment of Osteoblast Precursors: Mediation by Interleukin-6 and Soluble Interleukin-6 Receptor

Abstract

Multiple myeloma is associated with the development of osteolytic bone disease characterized by a disruption to normal bone resorption and bone formation. Although studies have shown that myeloma cells produce factors that promote bone resorption little data are available examining the mechanism of decreased bone formation or the factors that mediate this effect. In the present study we describe a novel in vitro coculture system in which to investigate the effect of myeloma cells on osteoblast recruitment and differentiation. Under appropriate conditions mesenchymal stem cells were shown to differentiate into colonies of cells, a proportion of which show characteristics of osteoblasts, in that they express alkaline phosphatase activity and stain positively for collagen and calcium. The addition of the human myeloma cells JJN-3, RPMI-8226, or NCI-H929 to these cultures stimulated a significant increase in the total number of colonies (p < 0.005) and the proportion of osteoblastic colonies (p < 0.005). Media conditioned by these cells also were able to promote the formation of both total and osteoblastic colonies (p < 0.005). The addition of an antibody against the interleukin-6 receptor (IL-6R) blocked myeloma cell and myeloma cell-conditioned media induced osteoblast recruitment (p < 0.01). Furthermore, media conditioned by myeloma cells incubated with phorbol ester, which promotes IL-6R shedding, or a metalloproteinase inhibitor, which inhibits IL-6R shedding, were able to stimulate (p < 0.005) and inhibit osteoblast recruitment (p < 0.005), respectively. In addition, soluble IL-6R (sIL-6R) and IL-6 together, but not alone, were able to promote osteoblastic colony formation (p < 0.01). Taken

Myeloma cells block RUNX2/CBFA1 activity in human bone marrow osteoblast progenitors and inhibit osteoblast formation and differentiation

“…5 In contrast with our evidence and histomorphometric results, previously published data have shown that HMCLs promote the recruitment of osteoblast precursors, increasing the number of osteoblastic colonies in vitro. 28 The opposite results obtained by these authors could be explained by their different experimental system, which includes murine BM cultures and a lower percentage of HMCL-conditioned media (10%) compared with our system.…”

Inactivation of NF-κB Involved in Osteoblast Development through Interleukin-6

“…IL-6 has two receptors (IL-6R); a membrane-bound form (22) and a soluble form (23). Both bind IL-6 and associate with gp130 (24,25) to promote recruitment and differentiation of osteoblast precursors (26,27). Recent study of conditioned medium from myeloma cells revealed that the IL-6/soluble IL-6R complex induces osteoblast recruitment and colony formation in bone marrow cells (27).…”

“…Both bind IL-6 and associate with gp130 (24,25) to promote recruitment and differentiation of osteoblast precursors (26,27). Recent study of conditioned medium from myeloma cells revealed that the IL-6/soluble IL-6R complex induces osteoblast recruitment and colony formation in bone marrow cells (27). Another study showed that IL-6-type cytokines affect osteoblast differentiation; i.e., IL-6 increases ALP activity and decreases secretion of osteocalcin (28,29).…”

Role of osteoblast suppression in multiple myeloma

“…Although there is an increase in osteoblast recruitment, the activity of individual osteoblasts appears to be reduced. Karadag et al [2000] employed an in vitro method to allow MSCs to differentiate into osteoblasts. Co-culture of the MSCs with myeloma cell lines caused an increase in the number of osteoblast colonies; the researchers subsequently identified IL-6 and soluble IL-6 receptor as being critical in this process.…”