PTHrP‐induced MCP‐1 production by human bone marrow endothelial cells and osteoblasts promotes osteoclast differentiation and prostate cancer cell proliferation and invasion in vitro

Abstract

Prostate cancer (PCa) preferentially metastasizes to bone resulting in osteoblastic lesions with underlying osteolytic activities. The mechanisms through which PCa cells promote osteolytic activities and subsequent osteoblastic bone formation remain poorly understood. Parathyroid hormone-related protein (PTHrP), produced by bone cells and PCa, binds to receptors on osteoblasts and stimulates bone formation and resorption. We have previously reported that MCP-1 acts as a paracrine and autocrine factor for PCa progression. However, the role of PTHrP in regulating MCP-1 expression in bone microenvironment, specifically by human bone marrow endothelial cells (HBME) and osteoblasts (hFOB), as well as by PCa cells, has not been studied. Accordingly, we first determined the effect of PTHrP on MCP-1 expression by bone cells and PCa cells. PTHrP induced both MCP-1 protein and mRNA expression by HBME and hFOB cells, but not by PCa LNCaP and PC3 cells. To further determine the mechanisms of PTHrP-induced MCP-1 transcription, analysis of the MCP-1 promoter was performed. MCP-1 promoter activity was induced by PTHrP. Both C/EBPb and NF-jB binding elements are required for PTHrP-induced MCP-1 transcription. Finally, when a constitutively-active PTH receptor construct was transfected into HBME and hFOB cells, MCP-1 production was increased. The conditioned media collected from these cells induced osteoclast differentiation and PC3 proliferation and invasion in vitro. These inductions were partially inhibited by MCP-1 neutralizing antibody. We conclude that PTHrP-induced MCP-1 production by HBME and hFOB cells promotes osteoclast differentiation in vitro and such induction may play a critical role in PCa development in the bone microenvironment. ' 2007 Wiley-Liss, Inc.Key words: PTHrP; MCP-1; human bone marrow endothelial cell; prostate cancer; metastasis Bone is the most common site of prostate cancer (PCa) metastasis with skeletal metastases occurring in up to 90% of patients dying from PCa.1,2 Histological studies have revealed that bone metastatic lesions are a heterogeneous mixture of osteoblastic and osteolytic lesions, although they are most often radiographically characterized as predominately osteoblastic responses.3-6 Many reports have showed that osteoblastic metastases form on trabecular bone at the sites of previous osteoclastic resorption, and that such resorption may be required for subsequent osteoblastic bone formation.2,6 Thus, bone destruction appears to be an early stage in the development of PCa bone metastasis. However, the mechanisms through which PCa cells promote bone resorption and subsequent osteoblastic bone formation remain poorly understood.PCa metastasis develops in the skeleton through crosstalk between tumor cells and bone microenvironment. The bone microenvironment, which consists of the extracellular matrix, stromal cells, osteoblasts, osteoclasts, endothelial cells, adipocytes and hematopoietic cell lineages, produces multiple factors which can enhance the growth of PCa cells and promote tumo...

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