Human chorionic gonadotropin beta (HCGbeta) down-regulates E-cadherin and promotes human prostate carcinoma cell migration and invasion

BACKGROUND: Membrane-associated human chorionic gonadotropin beta (HCGbeta) is correlated with a poor prognosis in localized prostate adenocarcinoma. The relationship between HCGbeta and metastasis, however, is unclear. METHODS: To shed some light on the issue, two stable prostate carcinoma cell lines overexpressing HCGbeta, designated DU145 HCGbeta and PC3 HCGbeta, were created and compared with empty vector stably transfected DU145 and PC3 cells (control cells). RESULTS: HCGbeta expression resulted in a change in morphology; the cells were more elongated and had multiple pseudopodia, while the control cells were more rounded. This change in morphology was duplicated by incubating control cells in conditioned medium from the DU145 HCGbeta or PC3 HCGbeta cells, or by adding purified HCGbeta to control medium. The DU145 HCGbeta and PC3 HCGbeta cells were also less adherent than the controls, as assessed by the ease with which trypsin-EDTA could remove them from culture plates. Reduced adherence could be duplicated by incubation of control cells with either conditioned medium or purified HCGbeta. Western blot analysis showed that DU145 HCGbeta and PC3 HCGbeta cells expressed less E-cadherin than control cells and that a change of medium increased expression of E-cadherin. Addition of conditioned medium, or purified HCGbeta, to control cells down-regulated E-cadherin. Cell migration and invasion assays showed that DU145 HCGbeta and PC3 HCGbeta cells were more migratory and invasive than controls and that treatment of control cells with either conditioned medium or purified HCGbeta increased their migratory/invasive capacity. CONCLUSION: The data indicate that HCGbeta is directly responsible for changes in prostate carcinoma cells associated with an increased metastatic phenotype.     

TGFβ‐induced epithelial‐to‐mesenchymal transition in prostate cancer cells is mediated via TRPM7 expression

Growth factors, such as the transforming growth factor beta (TGFβ), play an important role in promoting metastasis of prostate cancer, thus understanding how TGFβ could induce prostate cancer cell migration may enable us to develop targeted strategies for treatment of advanced metastatic prostate cancer. To more clearly define the mechanism(s) involved in prostate cancer cell migration, we undertook a series of studies utilizing non‐malignant prostate epithelial cells RWPE1 and prostate cancer DU145 and PC3 cells. Our studies show that increased cell migration was observed in prostate cancer cells, which was mediated through epithelial‐to‐mesenchymal transition (EMT). Importantly, addition of Mg²⁺, but not Ca²⁺, increased cell migration. Furthermore, TRPM7 expression, which functions as an Mg²⁺ influx channel, was also increased in prostate cancer cells. Inhibition of TRPM7 currents by 2‐APB, significantly blocked cell migration in both DU145 and PC3 cells. Addition of growth factor TGFβ showed a further increase in cell migration, which was again blocked by the addition of 2‐APB. Importantly, TGFβ addition also significantly increased TRPM7 expression and function, and silencing of TRPM7 negated TGFβ‐induced cell migration along with a decrease in EMT markers showing loss of cell adhesion. Furthermore, resveratrol, which decreases prostate cancer cell migration, inhibited TRPM7 expression and function including TGFβ‐induced cell migration and activation of TRPM7 function. Together, these results suggest that Mg²⁺ influx via TRPM7 promotes cell migration by inducing EMT in prostate cancer cells and resveratrol negatively modulates TRPM7 function thereby inhibiting prostate cancer metastasis.     

miRNA-135在调控前列腺癌细胞增殖中的应用及机制

目的 观察miRNA-135在调控激素非依赖性前列腺癌细胞增殖能力中的作用及其机制.方法 利用微小核糖核酸(miRNA)基因芯片检测激素非依赖性前列腺癌和激素依赖性前列腺癌组织中miRNA-135的表达差异.经过体外转染miRNA-135后对DU145和PC3细胞进行MTT检测,了解细胞的增殖情况.利用miRNA-135靶基因预测软件miRwalk和miRanda预测,初筛miRNA-135调控的基因和相关通路.结果 miRNA基因芯片结果显示,激素依赖性前列腺癌组织中miRNA-135的表达量高于激素非依赖性前列腺癌组织(P﹤0.05);miR-NA-135可以抑制DU145和PC3细胞的生长,尤其在第48 h和第72 h以后(P﹤0.05);转染miRNA-135后,前列腺癌细胞株DU145和PC3中STAT6的表达水平较转染NC的细胞株明显下调.结论 miRNA-135能够抑制激素非依赖性前列腺细胞DU145和PC3的增殖能力,有望成为前列腺癌治疗的新靶标.     

Analysis of cabazitaxel‐resistant mechanism in human castration‐resistant prostate cancer

Cabazitaxel (CBZ) is approved for docetaxel‐resistant castration‐resistant prostate cancer (CRPC). However, efficacy of CBZ for CRPC is limited and there are no effective treatments for CBZ‐resistant CRPC. In order to investigate the CBZ‐resistant mechanism, the establishment of a CBZ‐resistant cell line is urgently needed. We established CBZ‐resistant CRPC cell lines DU145CR and PC3CR by incubating DU145 and PC3 cells with gradually increasing concentrations of CBZ for approximately 2 years. We analyzed the gene expression profiles and cell cycle changes using microarray and flow cytometry. Pathway analysis revealed DU145CR cells had enhanced gene clusters of cell division and mitotic nuclear division. Enhancement of ERK signaling was detected in DU145CR cells. DU145CR cells had resistance to G₂/M arrest induced by CBZ through ERK signaling activation. The MEK inhibitor PD184352 significantly inhibited cell proliferation of DU145CR. In contrast to DU145CR, PC3CR cells had enhancement of PI3K/AKT signaling. The PI3K/mTOR inhibitor NVP‐BEZ 235 had a significant antitumor effect in PC3CR cells. Cabazitaxel ‐resistant CRPC cells established in our laboratory had enhancement of cell cycle progression signals and resistance to G₂/M arrest induced by CBZ. Enhancement of ERK signaling or PI3K/AKT signaling were detected in the cell lines, so ERK or PI3K/AKT could be therapeutic targets for CBZ‐resistant CRPC.     

Transient receptor potential melastatin 4 channel contributes to migration of androgen-insensitive prostate cancer cells

Impaired Ca²⁺ signaling in prostate cancer contributes to several cancer hallmarks, such as enhanced proliferation and migration and a decreased ability to induce apoptosis. Na⁺ influx via transient receptor potential melastatin 4 channel (TRPM4) can reduce store-operated Ca²⁺ entry (SOCE) by decreasing the driving force for Ca²⁺. In patients with prostate cancer, gene expression of TRPM4 is elevated. Recently, TRPM4 was identified as a cancer driver gene in androgen-insensitive prostate cancer.We investigated TRPM4 protein expression in cancer tissue samples from 20 patients with prostate cancer. We found elevated TRPM4 protein levels in prostatic intraepithelial neoplasia (PIN) and prostate cancer tissue compared to healthy tissue. In primary human prostate epithelial cells (hPEC) from healthy tissue and in the androgen-insensitive prostate cancer cell lines DU145 and PC3, TRPM4 mediated large Na⁺ currents. We demonstrated significantly increased SOCE after siRNA targeting of TRPM4 in hPEC and DU145 cells. In addition, knockdown of TRPM4 reduced migration but not proliferation of DU145 and PC3 cells. Taken together, our data identify TRPM4 as a regulator of SOCE in hPEC and DU145 cells, demonstrate a role for TRPM4 in cancer cell migration and suggest that TRPM4 is a promising potential therapeutic target.     

Thapsigargin resistance in human prostate cancer cells

BACKGROUND: Thapsigargin (TG) is a potent inhibitor of sarcoplasmic/endoplasmic reticulum Ca2+ ATPases (SERCAs). TG-based prodrugs are being developed for the treatment of prostate cancer (PC). To develop optimal TG-based therapeutics it is important to understand the mechanisms of resistance to TG that may potentially occur in cancer cells. METHODS: DU145/TG and PC3/TG cells were derived from human PC DU145 and PC3 cells, respectively, by incremental exposure to TG. Growth assays, Western blot analyses, cDNA microarrays, semiquantitative and real-time polymerase chain reaction (PCR), Northern blot analyses, and immunohistochemistry were used to study these cells. RESULTS: DU145/TG cells are 1100-fold and PC3/TG cells are 1350-fold resistant to TG. Although expression of both SERCA and p-glycoprotein can mediate TG resistance in hamster cells, neither is modulated in DU145/TG cells. In contrast, in PC3/TG cells, SERCA, and not p-glycoprotein, is significantly overexpressed but cannot by itself account for the 1350-fold resistance to TG in these cells. Several genes not previously identified to be altered by TG selection are modulated in DU145/TG and PC3/TG cells. Furthermore, the spectrum of genes modulated in DU145/TG cells are distinct from that in PC3/TG cells, even though both cells are of prostate origin and share the same TG-resistant phenotype. CONCLUSIONS: PC cells can adapt to SERCA inhibition by TG. However, they demonstrate cell type-specific plasticity with respect to gene expression upon TG selection. Further, previously not described mechanisms of resistance appear to be recruited in the TG-resistant PC cells, which provide a novel model to study mechanisms of resistance and adaptation in PC on TG-mediated dysregulation of Ca2+ homeostasis.     

Indole-3-carbinol inhibits prostate cancer cell migration via degradation of beta-catenin

We determined whether indole-3-carbinol (I3C) could affect DU145 human prostate carcinoma cell migration to prevent the development and progression of prostate cancer. Although previous studies have shown anticancer properties of I3C in various cancer cell lines, it has not been determined how I3C regulates epidermal growth factor (EGF)-induced migration and related signaling pathways. DU145 cells were treated with I3C (100 microM) in the absence or presence of EGF (10 ng/ml). Our results showed that I3C significantly inhibited DU145 cell migration with and without EGF stimulation. It has been reported that the beta-catenin signaling pathway controls androgen receptor (AR)-mediated prostate cancer progression, which plays a key role in the metastasis of prostate cancer. Western blot analysis demonstrated that I3C led to the phosphorylation of beta-catenin and subsequent degradation of beta-catenin in the absence and presence of EGF. In contrast, I3C did not have any effect on the expression of beta-catenin mRNA. From these results, we suggest that I3C inhibits EGF (dependent or independent)-induced DU145 cell migration through beta-catenin degradation.     

Differential expression of cell surface molecules in prostate cancer cells

The expression of 119 cell surface molecules was catalogued for three prostate cancer cell lines, LNCaP, PC3, and DU145, all of which were established from metastases. Many of these molecules are common to all three cell lines, whereas some are differentially expressed. More prostate basal epithelial cell-specific than luminal epithelial cell-specific molecules are detected, especially in DU145 and PC3 cells. The cancer cells also express molecules that are not normally associated with prostate epithelial cells. As a population, expression of these molecules appears to be heterogeneous. This heterogeneity may be an inherent property of the population.     

Apoptotic signaling in bufalin‐ and cinobufagin‐treated androgen‐dependent and ‐independent human prostate cancer cells

Prostate cancer has its highest incidence in the USA and is becoming a major concern in Asian countries. Bufadienolides are extracts of toxic glands from toads and are used as anticancer agents, mainly on leukemia cells. In the present study, the antiproliferative and apoptotic mechanisms of bufalin and cinobufagin on prostate cancer cells were investigated. Proliferation of LNCaP, DU145, and PC3 cells was measured by 3‐(4,5‐dimethylthiazol‐2‐yle)‐2,5‐diphenyltetrazolium bromide assay and the doubling time (tD) was calculated. Bufalin and cinobufagin caused changes in the tD of three prostate cancer cell lines, which were more significant than that of human mesangial cells. In addition, bufadienolides induced prostate cancer cell apoptosis more significantly than that in breast epithelial cell lines. After treatment, the caspase‐3 activity and protein expression of caspase‐3, ‐8, and ‐9 were elevated. The expression of other apoptotic modulators, including mitochondrial Bax and cytosolic cytochrome c, were also increased. However, expression of p53 was only enhanced in LNCaP cells. Downregulation of p53 by antisense TP53 restored the cell viability suppressed by bufalienolides. Furthermore, the increased expression of Fas was more significant in DU145 and PC3 cells with mutant p53 than in LNCaP cells. Transfection of Fas small interfering RNA restored cell viability in the bufadienolide‐treated cells. These results suggest that bufalin and cinobufagin suppress cell proliferation and cause apoptosis in prostate cancer cells via a sequence of apoptotic modulators, including Bax, cytochrome c, and caspases. The upstream mediators might be p53 and Fas in androgen‐dependent LNCaP cells and Fas in androgen‐independent DU145 and PC3 cells. (Cancer Sci 2008; 99: 2467–2476)     

Versican accumulation in human prostatic fibroblast cultures is enhanced by prostate cancer cell-derived transforming growth factor beta1

We have previously demonstrated that peritumoral stromal matrix derived from prostate cancer patients who relapse after radical surgery contains elevated levels of versican. The purpose of this study was to determine whether prostate cancer cells control stromal cell secretion of versican. Serum-free conditioned medium from three prostate adenocarcinoma cell lines, LNCaP, PC3, and DU145, was added to cultures of fibroblasts established from prostatic tissue of patients with benign prostatic hyperplasia, and the medium was harvested at 24, 48, and 72 h. Immunoblotting with an antiversican core protein antibody revealed that prostatic fibroblast medium harvested at 72 h contained increased levels of versican after treatment with either LNCaP-, PC3- or DU145-conditioned medium (2.5-, 4.5-, and 5-fold, respectively) compared with control cultures. This increase in versican in the culture medium was not observed after coincubation with transforming growth factor beta1-neutralizing antisera. The results of this study suggest that prostate tumor cells induce host stromal cells to secrete increased versican levels via a paracrine mechanism mediated by transforming growth factor beta1.     

Resveratrol activates autophagic cell death in prostate cancer cells via downregulation of STIM1 and the mTOR pathway

Resveratrol (RSV), a natural polyphenol, has been suggested to induce cell cycle arrest and activate apoptosis‐mediated cell death in several cancer cells, including prostate cancer. However, several molecular mechanisms have been proposed on its chemopreventive action, the precise mechanisms by which RSV exerts its anti‐proliferative effect in androgen‐independent prostate cancer cells remain questionable. In the present study, we show that RSV activates autophagic cell death in PC3 and DU145 cells, which was dependent on stromal interaction molecule 1 (STIM1) expression. RSV treatment decreases STIM1 expression in a time‐dependent manner and attenuates STIM1 association with TRPC1 and Orai1. Furthermore, RSV treatment also decreases ER calcium storage and store operated calcium entry (SOCE), which induces endoplasmic reticulum (ER) stress, thereby, activating AMPK and inhibiting the AKT/mTOR pathway. Similarly, inhibition of SOCE by SKF‐96365 decreases the survival and proliferation of PC3 and DU145 cells and inhibits AKT/mTOR pathway and induces autophagic cell death. Importantly, SOCE inhibition and subsequent autophagic cell death caused by RSV was reversed by STIM1 overexpression. STIM1 overexpression restored SOCE, prevents the loss of mTOR phosphorylation and decreased the expression of CHOP and LC3A in PC3 cells. Taken together, for the first time, our results revealed that RSV induces autophagy‐mediated cell death in PC3 and DU145 cells through regulation of SOCE mechanisms, including downregulating STIM1 expression and trigger ER stress by depleting ER calcium pool. © 2015 The Authors. Molecular Carcinogenesis, published by Wiley Periodicals, Inc.     

CCL2 induces resistance to the antiproliferative effect of cabazitaxel in prostate cancer cells

Understanding the mechanism of chemoresistance and disease progression in patients with prostate cancer is important for developing novel treatment strategies. In particular, developing resistance to cabazitaxel is a major challenge in patients with docetaxel‐resistant and castration‐resistant prostate cancer (CRPC) because cabazitaxel is often administered as a last resort. However, the mechanism by which cabazitaxel resistance develops is still unclear. C‐C motif chemokine ligands (CCL) were shown to contribute to the castration resistance of prostate cancer cells via an autocrine mechanism. Therefore, we focused on CCL as key factors of chemoresistance in prostate cancer cells. We previously established a cabazitaxel‐resistant cell line, DU145‐TxR/CxR, from a previously established paclitaxel‐resistant cell line, DU145‐TxR. cDNA microarray analysis revealed that the expression of CCL2 was upregulated in both DU145‐TxR and DU145‐TxR/CxR cells compared with DU145 cells. The secreted CCL2 protein level in DU145‐TxR and DU145‐TxR/CxR cells was also higher than in parental DU145 cells. The stimulation of DU145 cells with CCL2 increased the proliferation rate under treatments with cabazitaxel, and a CCR2 (a specific receptor of CCL2) antagonist suppressed the proliferation of DU145‐TxR and DU145‐TxR/CxR cells under treatments of cabazitaxel. The CCL2‐CCR2 axis decreased apoptosis through the inhibition of caspase‐3 and poly(ADP‐ribose) polymerase (PARP). CCL2 is apparently a key contributor to cabazitaxel resistance in prostate cancer cells. Inhibition of the CCL2‐CCR2 axis may be a potential therapeutic strategy against chemoresistant CRPC in combination with cabazitaxel.     

Effect of CKBM on prostate cancer cell growth in vitro and in vivo

Prostate carcinoma and metastasis are common among male subjects worldwide. CKBM is a drug product targeting prostate cancer in multiple ways. Prostate cancer cell lines PC3 and DU145 were treated with CKBM. The effect of CKBM on the cell's viability, cell cycle, adhesive and invasive properties and its growth in an animal model were assessed. Results indicated that CKBM inhibited PC3 and DU145 cell growth in vitro at IC(50 )values 3.923 and 4.697% respectively, and it brought about cell cycle arrest at G2/M phase. CKBM also attenuated DU145 cells to invade and adhere to extracellular matrices including Matrigel, laminin, fibronectin and collagen IV. Moreover, PC3 tumor xenograft growth was inhibited by over 60% after 28-day of 0.2, 0.4 or 0.8 ml/day CKBM treatment. The present study indicates that CKBM is effective against prostate cancer cell growth in vitro and in vivo. Further studies are required to elucidate its mechanism of action.     

HER3 is required for the maintenance of neuregulin‐dependent and ‐independent attributes of malignant progression in prostate cancer cells

HER3 (ERBB3) is a catalytically inactive pseudokinase of the HER receptor tyrosine kinase family, frequently overexpressed in prostate and other cancers. Aberrant expression and mutations of 2 other members of the family, EGFR and HER2, are key carcinogenic events in several types of tumors, and both are well‐ validated therapeutic targets. In this study, we show that HER3 is required to maintain the motile and invasive phenotypes of prostate (DU‐145) and breast (MCF‐7) cancer cells in response to the HER3 ligand neuregulin‐1 (NRG‐1), epidermal growth factor (EGF) and fetal bovine serum. Although MCF‐7 breast cancer cells appeared to require HER3 as part of an autocrine response induced by EGF and FBS, the response of DU‐145 prostate cancer cells to these stimuli, while requiring HER3, did not appear to involve autocrine stimulation of the receptor. DU‐145 cells required the expression of HER3 for efficient clonogenicity in vitro in standard growth medium and for tumorigenicity in immunodeficient mice. These observations suggest that prostate cancer cells derived from tumors that overexpress HER3 are dependent on its expression for the maintenance of major attributes of neoplastic aggressiveness, with or without cognate ligand stimulation. © 2009 UICC     

The synthetic retinoid ST1926 attenuates prostate cancer growth and potentially targets prostate cancer stem‐like cells

Retinoids are vitamin A derivatives that regulate crucial biological processes such as cellular proliferation, apoptosis, and differentiation. The use of natural retinoids in cancer therapy is limited due to their toxicity and the acquired resistance by cancer cells. Therefore, synthetic retinoids were developed, such as the atypical adamantyl retinoid ST1926 that provides enhanced bioavailability and reduced toxicity. We have assessed the in vitro and in vivo antitumor properties and mechanism of action of ST1926 in targeting cancer stem‐like cells population of human prostate cancer (PCa) cell lines, DU145 and PC3, and mouse PCa cell lines, PLum‐AD and PLum‐AI. We demonstrated that ST1926 substantially reduced proliferation of PCa cells and induced cell cycle arrest, p53‐independent apoptosis, and early DNA damage. It also decreased migration and invasion of PCa cells and significantly reduced prostate spheres formation ability in vitro denoting sufficient eradication of the self‐renewal ability of the highly androgen‐resistant cancer stem cells. Importantly, ST1926 potently inhibited PCa tumor growth and progression in vivo. Our results highlight the potential of ST1926 in PCa therapy and warrant its clinical development.     

Bauhinia purprea agglutinin‐modified liposomes for human prostate cancer treatment

Bauhinia purprea agglutinin (BPA) is a well‐known lectin that recognizes galactosyl glycoproteins and glycolipids. In the present study, we firstly found that BPA bound to human prostate cancer specimens but not to normal prostate ones. Therefore, we sought to develop BPA‐PEG‐modified liposomes (BPA‐PEG‐LP) encapsulating anticancer drugs for the treatment of prostate cancer. We examined the tumor targetability of BPA‐PEG‐LP with human prostate cancer DU145 cells, and observed that fluorescently labeled BPA‐PEG‐LP dominantly associated with the cells via the interaction between liposome‐surface BPA and cell‐surface galactosyl molecules. We also observed that BPA‐PEG‐LP accumulated in the prostate cancer tissue after the i.v. injection to DU145 solid cancer‐bearing mice, and strongly bound to the cancer cells. In a therapeutic study, DU145 solid cancer‐bearing mice were i.v. injected thrice with BPA‐PEG‐LP encapsulating doxorubicin (BPA‐PEG‐LPDOX, 2 mg/kg/day as the DOX dosage) or PEG‐modified liposomes encapsulating DOX (PEG‐LPDOX). As a result, BPA‐PEG‐LPDOX significantly suppressed the growth of the DU145 cancer cells, whereas PEG‐LPDOX at the same dosage as DOX showed little anti‐cancer effect. The present study suggested that BPA‐PEG‐LP could be a useful drug carrier for the treatment of human prostate cancers.     

Radiosensitivity of human prostate cancer and malignant melanoma cell lines

The relative radioresponsiveness of human prostate cancer compared to malignant melanoma is well known. The effects of beta-estradiol or testosterone on the X-irradiation survival of several human cell lines were studied, including: human prostate carcinoma cell lines PC3 and DU145 and human malignant melanoma cell lines A375 and A875. Lines PC3 and DU145 demonstrated 55-61 fmol per 10(6) cells of androgen receptor with no detectable estrogen or progesterone receptor. Cells were irradiated at 120 cGy/min dose rate. There was no detectable toxicity of up to 10(-4) M testosterone or beta-estradiol on PC3 or DU145 cells in the absence of X-irradiation. At plating efficiencies from 11-13%, and plating densities of 1 x 10(4) cells per 60 cm2 flask, cell lines PC3 and DU145 demonstrated a Do of 108.5 +/- 6.5, n 2.1 +/- 0.7 cGy, and Do of 143.5 +/- 1.5 cGy, n 2.4 +/- 0.5, respectively. The addition of testosterone or beta-estradiol at 10(-4) to 10(-10) M prior to or after, X-irradiation did not alter radiosensitivity. At the same dose rate of 120 cGy/min, malignant melanoma cell lines A375 and A875 had a Do of 125 +/- 2.5 cGy, n 1.56 +/- 0.8 SF2 0.65 +/- 0.03 and line A875 demonstrated a Do of 129 +/- 4.5 cGy, n 1.58 +/- 0.4 SF2 0.55 +/- 0.04, respectively. The radiosensitivity of melanoma cell lines did not decrease at low dose rate 5 cGy/min. Thus, the in vitro radiosensitivity of androgen receptor positive prostate cancer cell lines is not necessarily altered by the presence of androgen before or after irradiation. The data support the concept that all malignant melanoma cell lines do not show a broad-shouldered cell survival curve in vitro and intrinsic cellular radioresistance.     

Prostate cancer mediates osteoclastogenesis through two different pathways

The present study was undertaken to test the effects of prostate cancer cell lines (LNCaP, DU145, PC3, and MDA PCa 2b) on osteoclastogenesis. Crude conditioned medium (CM) from all four prostate cancer cell lines enhanced expression of the mRNA for receptor activator of NF-kappaB ligand (RANKL) in a mouse osteoblast cell line, MC3T3-E1; however, CM had no effect on expression of osteoprotegerin (OPG) mRNA. Coculture of MC3T3-E1 with prostate cancer cells yielded similar results. The number of mature osteoclasts induced by soluble RANKL increased significantly when osteoclast precursor cells were cultured with CM from LNCaP and DU145 cells. CM from LNCaP and DU145 cells also induced maturation from precursor in the absence of soluble RANKL, and this effect was not blocked by OPG. Addition of CM from DU145 cells increased expression of MMP-9 mRNA by osteoclast precursors. Our findings indicate that prostate cancer mediates osteoclastogenesis through induction of RANKL expression by osteoblasts and through direct actions on osteoclast precursors mediated by some factors other than RANKL.