ABSTRACT
BACKGROUND: Prostate cancer (PCa) has a propensity to metastasize to bone. Tumor cells replace bone marrow and can elicit an osteoblastic, osteolytic, or mixed bone response. Our objective was to elucidate the mechanisms and key factors involved in promoting osteoclastogenesis in PCa bone metastasis. METHODS: We cultured osteoblast-like MC3T3-E1 cells with conditioned medium (CM) from PC-3 and C4-2B cells. MC3T3-E1 mineralization decreased in the presence of PC-3 CM, whereas C4-2B CM had no effect on mineralization. Using oligo arrays and validating by real-time PCR, we observed a decrease in the expression of mineralization-associated genes in MC3T3-E1 cells grown in the presence of PC-3 CM. In addition, PC-3 CM induced the expression of osteoclastogenesis-associated genes IGFBP-5, IL-6, MCP-1, and RANKL while decreasing OPG expression in MC3T3-E1 cells. Furthermore, CM from MC3T3-E1 cells cultured in the presence of PC-3 CM, in association with soluble RANKL, increased osteoclastogenesis in RAW 264.7 cells. Investigation of PCa metastases and xenografts by immunohistochemistry revealed that the osteoclastic factor IL-6 was expressed in the majority of PCa bone metastases and to a lesser extent in PCa soft tissue metastases. In vitro it was determined that soluble IL-6R (sIL-6R) was necessary for IL-6 to inhibit mineralization in MC3T3-E1 cells. RESULTS: PC-3 cells inhibit osteoblast activity and induce osteoblasts to produce osteoclastic factors that promote osteoclastogenesis, and one of these factors, IL-6, is highly expressed in PCa bone metastases. CONCLUSIONS: IL-6 may have an important role in promoting osteoclastogenesis in PCa bone metastasis through its' interaction with sIL-6R.
Subject(s)
Bone Neoplasms/metabolism , Osteoblasts/metabolism , Osteoclasts/metabolism , Osteolysis/metabolism , Prostatic Neoplasms/metabolism , Animals , Bone Neoplasms/secondary , Calcification, Physiologic/drug effects , Calcification, Physiologic/genetics , Cell Line, Tumor , Culture Media, Conditioned/pharmacology , Fluorescent Antibody Technique, Direct , Gene Expression/drug effects , Gene Expression Profiling , Humans , Macrophages/drug effects , Macrophages/metabolism , Macrophages/pathology , Male , Mice , Mice, SCID , Oligonucleotide Array Sequence Analysis , Osteoblasts/pathology , Osteoclasts/pathology , Prostatic Neoplasms/pathology , Tibia/metabolism , Tibia/pathology , Tissue Array Analysis , Xenograft Model Antitumor AssaysABSTRACT
OBJECTIVES: To examine estrogen receptor-beta (ERbeta) expression in prostate cancer (CaP) metastases, thereby providing a basis for conducting estrogen therapy studies in patients with metastatic CaP. Advanced androgen-independent CaP is a serious health problem with no effective treatment at present. Estrogens have been reported to inhibit the growth of CaP cells in androgen-free environments. Recent reports have shown that the prostatic epithelium and primary CaP cells express ERbeta, with decreased expression of ERbeta accompanying CaP progression. It has been proposed that ERbeta may play a role in the growth regulation of prostate cells. The targeting of ERs by selective ER modulators might be an effective method of treating advanced CaP. METHODS: The anti-ERbeta antibody GC17 was used in immunohistochemistry to characterize the expression of ERbeta in CaP metastasis specimens (n = 60) obtained from 20 patients who had died of CaP. Statistical analyses were performed to evaluate the association of ERbeta expression with clinical parameters, including prostate-specific antigen levels, radiotherapy, and estrogen exposure. RESULTS: Nuclear ERbeta staining was detected in all bone CaP metastases (33 of 33) and nonosseous CaP metastases (27 of 27). However, a large variability in the percentage of immunoreactive cells (5% to 100%) was found among patients, as well as among individual patient samples. A statistically significant negative association between nuclear ERbeta staining and estrogen exposure (P = 0.05) was detected. CONCLUSIONS: Our data have shown that ERbeta is expressed in CaP metastases, validating the initiation of studies to evaluate selective ER modulators for treatment of advanced CaP.
