Objectives: Macrophage inflammatory protein-1alpha (MIP-1alpha), an osteoclast (OCL) stimulatory factor produced by primary multiple myeloma (MM) cells, increases bone destruction and tumor burden in murine models of MM. Several chemokine receptors (CCR1, CCR5, and CCR9) mediate the effects of MIP-1alpha. In this study, we determined which of these mediates the effects of MIP-1alpha on human OCL formation and myeloma cells.
Methods: We employed RT-PCR analysis, neutralizing antibodies to CCR1 and CCR5 as well as a CCR1-specific antagonist and OCL formation assays to identify the MIP-1alpha receptors involved in MIP-1alpha's effects on myeloma cells and OCL formation.
Results: RT-PCR analysis demonstrated that both CCR1 and CCR5 were expressed by highly purified human OCL precursors, myeloma cell lines, and purified marrow plasma cells from MM patients. Neutralizing antibodies to CCR1 or CCR5 inhibited MIP-1alpha-induced OCL formation. Furthermore, monocyte chemotactic protein-3 (MCP-3), which binds CCR1 but not CCR5 and the CCR1-specific antagonist, BX471, markedly inhibited OCL formation stimulated with MIP-1alpha. Anti-CCR1, anti-CCR5, or BX471 also inhibited the upregulation of beta1 integrin mRNA in myeloma cells induced by MIP-1alpha, as well as the adherence of myeloma cells to stromal cells and IL-6 production by stromal cells in response to myeloma cells.
Conclusion: These data demonstrate that MIP-1alpha utilizes either CCR1 or CCR5 for its effects on OCL formation and myeloma cells, and that blocking either CCR1 or CCR5 inhibits OCL formation and myeloma cell adhesion to stromal cells.