Kenji Hiura

Osteoclasts enhance myeloma cell growth and survival via cell-cell contact: a vicious cycle between bone destruction and myeloma expansion

Multiple myeloma (MM) expands in the bone marrow and causes devastating bone destruction by enhancing osteoclastic bone resorption in its vicinity, suggesting a close interaction between MM cells and osteoclasts (OCs). Here, we show that peripheral blood mononuclear cell-derived OCs enhanced growth and survival of primary MM cells as well as MM cell lines more potently than stromal cells, and that OCs protected MM cells from apoptosis induced by serum depletion or doxorubicin. OCs produced osteopontin (OPN) and interleukin 6 (IL-6), and adhesion of MM cells to OCs increased IL-6 production from OCs. In addition, IL-6 and OPN in combination enhanced MM cell growth and survival. However, the effects of OCs on MM cell growth and survival were only partially suppressed by a simultaneous addition of anti-IL-6 and anti-OPN antibodies and were completely abrogated by inhibition of cellular contact between MM cells and OCs. These results demonstrate that OCs enhance MM cell growth and survival through a cell-cell contact-mediated mechanism that is partially dependent on IL-6 and OPN. It is suggested that interactions of MM cells with OCs augment MM growth and survival and, thereby, form a vicious cycle, leading to extensive bone destruction and MM cell expansion.

Role of Osteopontin in Bone Remodeling Caused by Mechanical Stress

Changes in the number and proportion of osteopontin mRNA (Opn) expressing osteocytes and osteoclasts caused by the mechanical stress applied during experimental tooth movement were examined in the present study. Opn expression was detected in the osteocytes on the pressure side at the early stage, and gradually spread to those on the tension side and also to the osteoblasts and bone‐lining cells in the alveolar bone. Only 3.3% of the osteocytes located on the pressure side expressed Opn in the interradicular septum of control rats; in contrast, the value was increased to 87.5% at 48 h after the initiation of tooth movement. These results indicate that these cells responded to mechanical stress loaded on the bone with expression of the osteopontin gene. Following the increased expression of Opn in these cells, a 17‐fold greater number of osteoclasts compared with the control and numerous resorption pits were observed on the pressure side of the alveolar bone. Injection of arginine‐glycine‐aspartic acid‐serine peptide but not that of arginine‐glycine‐glutamic acid‐serine peptide strongly inhibited the increase in the number of osteoclasts. Furthermore, an in vitro migration assay demonstrated the chemotactic activity of osteopontin (OPN) on the precursor of osteoclasts. Our study strongly suggests that OPN is an important factor triggering bone remodeling caused by mechanical stress.

A simple method to assess osteoclast-mediated bone resorption using unfractionated bone cells

To determine osteoclastic bone resorption we established a simple assay system in which unfractionated cells obtained from femora of 13-day-old mice were cultured on a dentine slice and the number of osteoclasts and their induced pit area on the slices were measured. When the bone cells (1 x 10(5) cells/dentine slice) were cultured in the presence of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] or human parathyroid hormone (hPTH) for 4 days, at which time newly-formed osteoclasts were not detected, the pit area was dose-dependently increased, being a 4.3- or 4.1-fold respective increase over the control at a 10(-8) M concentration of hormones. Chick calcitonin (cCT) inhibited the osteoclastic bone resorption induced by either of these hormones. cCT alone also suppressed the bone resorption by the cells (3 x 10(5) cells/dentine slice). These findings indicate that 1,25(OH)2D3 or hPTH may mainly activate pre-existing osteoclasts, resulting in increased bone resorption, and that cCT may suppress this osteoclastic activity. When 1,25(OH)2D3 or hPTH was added to the cells pre-cultured in factor-free medium for 6 days, at which time pre-existing osteoclasts had almost degenerated, new osteoclasts were formed, resulting in an increase in pit formation. Thus this system is a useful method which could more sensitively evaluate the effects of hormones or factors on osteoclast formation and activation than other previous systems.

ETIDRONATE (EHDP) INHIBITS OSTEOCLASTIC-BONE RESORPTION, PROMOTES APOPTOSIS AND DISRUPTS ACTIN RINGS IN ISOLATE-MATURE OSTEOCLASTS

Abstract. Bisphosphonates, therapeutic reagents against tumoral bone diseases (Pagets disease or osteoporosis), are potent inhibitors of bone resorption. The mechanisms by which they directly act on mature osteoclasts remain unclear. Using a recently developed technique for isolation of highly purified mammalian mature osteoclasts, we demonstrated that etidronate [ethane-1-hydroxy-1,1-diphosphonate (EHDP), 1-hydroxy-1,1-ethylidenebisphosphonate], inhibited directly osteoclastic bone-resorbing activity by pit assay. In addition, EHDP also directly induced apoptosis and disrupted actin rings in osteoclasts. The data support previous data on non-purified osteoclasts and results in vivo.

Existence of parathyroid hormone binding sites on murine hemopoietic blast cells

We demonstrated that 125I-labeled human parathyroid hormone (1-34;8,18-Nle,34-Tyr)[[125I]hPTH(1-34)] bound specifically to hemopoietic blast cells supported by granulocyte-macrophage colony-stimulating factor. Half-maximal inhibition of binding was achieved at concentrations of unlabeled hPTH(1-34) of about 5 x 10(-9)M. Insulin and hPTH(39-68) did not compete for PTH binding sites. Specific binding of hPTH(1-34) was detected in neither macrophages nor multinucleated cells (MNCs). Furthermore, treatment of hemopoietic blast cells with hPTH(1-34) stimulated MNC formation, and the range of concentrations (10(-10)-10(-8)M) over which hPTH(1-34) caused these effects was similar to that which inhibited the binding of [125I]hPTH(1-34). These findings suggest the presence of a PTH receptor on osteoclast precursors and the direct effect of PTH on them, resulting in osteoclast-mediated bone resorption.

Mechanism for bone invasion of oral cancer cells mediated by interleukin-6 in vitro and in vivo

Osteoclastic bone resorption is an important step in bone invasion in several malignancies. Although interleukin (IL)‐6 accelerates osteoclastic bone resorption, it remains unclear whether IL‐6 may be involved in bone invasion of oral cancer.

Vicious cycle between myeloma cell binding to bone marrow stromal cells via VLA-4-VCAM-1 adhesion and macrophage inflammatory protein-1α and MIP-1β production

Multiple myeloma (MM) cell adhesion to stromal cells via very late antigen (VLA)-4 and vascular cell adhesion molecule (VCAM)-1 interaction causes enhanced secretion of osteoclastogenic activity by MM cells. We have reported that MM cell-derived macrophage inflammatory protein (MIP)-1α and MIP-1β are responsible for most of the osteoclastogenic activity in MM. Thus, adhesion-mediated osteoclastogenesis may be caused by enhanced production of MIP-1 via VLA-4–VCAM-1 interaction. The present study was undertaken to clarify whether MM cell-derived MIP-1 plays a role in VLA-4–VCAM-1 adhesion-mediated osteoclastogenesis. Adhesion of MM cells to VCAM-1 upregulated MIP-1α and MIP-1β production from MM cells and enhanced production of osteoclastogenic activity by MM cells. Blockade of MIP-1α and MIP-1β actions not only abrogated elaboration of osteoclastogenic activity, but also suppressed spontaneous MM cell adhesion to VCAM-1. These results demonstrate that MM cell adhesion to VCAM-1 upregulates MIP-1 production by MM cells to cause enhancement of osteoclastogenesis. In addition, the results suggest that the increased production of MIP-1 further enhances MM cell binding to stromal cells via stimulation of VLA-4–VCAM-1 adhesion, forming a “vicious cycle” between MM cell adhesion to stromal cells and MIP-1 production via VLA-4–VCAM-1 interaction.

Expression of RANK is dependent upon differentiation into the macrophage/osteoclast lineage: induction by 1α,25-dihydroxyvitamin D3 and TPA in a human myelomonocytic cell line, HL60

Receptor activator of nuclear factor (RANK) is a member of the tumor necrosis factor receptor superfamily indispensable for osteoclast differentiation. However, little is known about the regulatory mechanism of RANK expression. In the present study, RANK expression during macrophage/osteoclast differentiation was investigated using a human myelomonocytic cell line, HL60, capable of differentiating into mature osteoclasts under appropriate conditions. RANK mRNA expression was barely detectable in growing HL60 cells. We found that treatment with 1alpha,25-dihydroxyvitamin D(3) and TPA resulted in an apparent induction of RANK mRNA and protein in association with differentiation into the macrophage/osteoclast lineage. Induction of RANK was time and dose dependent and lineage specific. Moreover, RANK induction was blocked by an RNA polymerase II inhibitor, suggesting an involvement of a transcriptional mechanism. The induced RANK was functional as it was able to bind RANK ligand and activate NF-kappaB. In the induced HL60 cells expressing both c-Fms and RANK, RANK mRNA expression was further enhanced by RANKL, but not by macrophage colony-stimulating factor. These results suggest a positive feedback regulation of RANK expression by its own intracellular signaling. The in vitro system described here may be a useful model to elucidate the regulatory mechanism of RANK expression and its role in human osteoclastogenesis.

Malignant B-Lymphoid Cells with Bone Lesions Express Receptor Activator of Nuclear Factor-κB Ligand and Vascular Endothelial Growth Factor to Enhance Osteoclastogenesis

Purpose: Receptor activator of nuclear factor-κB ligand (RANKL) is a key mediator of osteoclastogenesis. Because certain types of tumor cells aberrantly express RANKL, and because bone destruction also develops in B-cell lymphomas of bone origin, we investigated RANKL expression and the mechanisms of osteoclastogenesis in B-lymphoid neoplasms. Experimental Design and Results: Immunohistochemistry of bone specimens resected from patients with primary B-cell lymphoma of bone with bone destruction revealed that lymphoma cells express RANKL as well as vascular endothelial cell growth factor (VEGF). The tumor cells isolated from the bone specimens enhanced osteoclastogenesis in vitro. In contrast, B-cell lymphoma infiltrating to the bone marrow without bone destruction did not express RANKL. Both RANKL and VEGF were expressed by a portion of B-lymphoid cell lines, including Daudi and IM-9. These RANKL-expressing tumor cells enhanced osteoclastogenesis from RAW264.7 cells and human monocyte-derived preosteoclasts in the absence of stromal cells/osteoblasts in a RANKL-dependent manner. Furthermore, conditioned media from Daudi cells enhanced transmigration of preosteoclasts that was inhibited by anti-VEGF antibody, suggesting that tumor cell–derived VEGF mediates recruitment of osteoclast precursors. Moreover, cocultures of B-lymphoid cell lines with osteoclasts enhanced the growth of B-lymphoid cells. Conclusions: Some malignant B cells aberrantly express functional RANKL as well as VEGF to enhance osteoclastogenesis. The coexpression of RANKL and VEGF may also contribute to the close cellular interactions with osteoclastic cells, thereby forming a vicious cycle between osteoclastic bone destruction and tumor expansion in bone.

Inhibitory mechanisms of H+‐ATPase inhibitor bafilomycin A1 and carbonic anhydrase II inhibitor acetazolamide on experimental bone resorption

The effects of the vacuolar-type H(+)-ATPase inhibitor bafilomycin A1 (baf.A1) and the carbonic anhydrase II inhibitor acetazolamide (AZ) on bone resorption and procathepsin L secretion of rat osteoclasts were investigated using the bone slice assay method, pit formation test. Baf.A1 completely suppressed osteoclastic bone resorption stimulated by parathyroid hormone (PTH), but did not affect procathepsin L secretion, while AZ suppressed both bone resorption and procathepsin L secretion. These findings suggest that bone resorption by procathepsin L secretion and its processing are regulated by proton production and proton secretion.The effects of the vacuolar‐type H+‐ATPase inhibitor bafilomycin A1 (baf. A1) and the carbonic anhydrase II inhibitor acetazolamide (AZ) on bone resorption and procathepsin L secretion of rat osteoclasts were investigated using the bone slice assay method, pit formation test. Baf. A1 completely suppressed osteoclastic bone resorption stimulated by parathyroid hormone (PTH), but did not affect procathepsin L secretion, while AZ suppressed both bone resorption and procathepsin L secretion. These findings suggest that bone resorption by procathepsin L secretion and its processing are regulated by proton production and proton secretion.