CC-chemokine ligand 20/macrophage inflammatory protein-3α and CC-chemokine receptor 6 are overexpressed in myeloma microenvironment related to osteolytic bone lesions

The expression of the chemokine CC-chemokine ligand 20 (CCL20)/macrophage inflammatory protein (MIP)-3 alpha and its receptor CC-chemokine receptor 6 (CCR6) by multiple myeloma (MM) and microenvironment cells and their potential relationship with osteoclast (OC) formation and osteolytic bone lesions in MM patients was investigated in this study. First, we found that MM cells rarely produce CCL20/MIP-3 alpha but up-regulate its production by bone marrow (BM) osteoprogenitor cells and osteoblasts in coculture with the involvement of soluble factors as interleukin-1 beta and tumor necrosis factor alpha. MM cells also stimulate both CCL20/MIP-3 alpha and CCR6 expression by OCs in coculture. Thereafter, we showed that CCL20/MIP-3 alpha significantly increases both the number of multinucleated tartrate-resistant acid phosphatase-positive OCs and receptor activator of nuclear factor-kappa B-positive OC progenitor cells similar to CCL3/MIP-1 alpha. Finally, we found that blocking anti-CCL20/MIP-3 alpha. and anti-CCR6 antibodies significantly inhibits MM-induced OC formation. In vitro data were further expanded in vivo analyzing a total number of 64 MM patients. Significantly higher CCL20/MIP-3 alpha levels were detected in MM patients versus monoclonal gammopathy of uncertain significance (MGUS) subjects and in MM osteolytic patients versus nonosteolytic ones. Moreover, a significant increase of CCL20/MIP-3 alpha-positive osteoblasts in osteolytic MM patients compared with nonosteolytic ones was observed. Interestingly, no significant difference in BM CCL20/MIP-3 alpha expression and level was observed between MGUS and nonosteolytic MM patients. Our data indicate that CCL20/MIP-3 alpha and its receptor CCR6 are up-regulated in the bone microenvironment by MM cells and contribute to OC formation and osteolytic bone lesions in MM patients.