Osteoblast-Derived Factors Induce Androgen-Independent Proliferation and Expression of Prostate-Specific Antigen in Human Prostate Cancer Cells

Abstract

Purpose: Prostate cancer metastasizes to the skeleton to form osteoblastic lesions. Androgen ablation is the current treatment for metastatic prostate cancer. This therapy is palliative, and the disease will return in an androgenindependent form that is preceded by a rising titer of prostate-specific antigen (PSA). Here, we investigated the possibility that human osteoblasts might secrete factors that contribute to the emergence of androgen-independent prostate cancer.Experimental Design: Primary cultures of human osteoblasts were used as a source of conditioned medium (OCM). Proliferation, expression of androgen-regulated genes, and transactivation of the androgen receptor (AR) were monitored in LNCaP human prostate cancer cells in response to OCM using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, Northern blot analysis, and reporter gene constructs. Levels of interleukin-6 (IL-6) present in OCM were measured, and its contribution to proliferation and expression of PSA were investigated by neutralization studies with anti IL-6 antibodies.Results: OCM increased the proliferation and expression of PSA at both the protein and RNA levels in LNCaP cells. Synergistic increases in the activities of PSA (6.1 kb)-and pARR 3 -tk-luciferase reporters were measured in cells cotreated with both OCM and androgen. OCM targeted the NH 2 -terminal domain of the AR. The effect of OCM on transcriptional activity of the AR was inhibited by an antiandrogen. Neutralizing antibodies to IL-6 blocked proliferation and expression of PSA by OCM.Conclusion: Osteoblasts secrete factors, such as IL-6, that cause androgen-independent induction of PSA gene expression and proliferation of prostate cancer cells by a mechanism that partially relies on the AR. Identifying such molecular mechanisms may lead to improved clinical management of metastatic prostate cancer.

Bone Morphogenetic Protein-6 Promotes Osteoblastic Prostate Cancer Bone Metastases through a Dual Mechanism

“…Alternatively, the BMP-induced osteoblastogenesis may make the bone microenvironment favorable for the establishment of prostate cancer metastases, which would account for the predisposition of prostate cancer metastases to bone (53). Osteoblasts produce a variety of factors such as transforming growth factor-h and interleukin-6 that may promote prostate cancer progression (54)(55)(56)(57)(58)(59)(60). Thus, if BMPs promote osteoblastogenesis, Figure 6.…”

Androgen receptor decoy molecules block the growth of prostate cancer

“…LNCaP cells (3 ϫ 10 5 per well) were transiently transfected according to published methods (5). After 24 h, the medium was replaced with serumfree RPMI medium 1640 with R1881, progesterone, estradiol, dexamethasone, FSK, IL-6 (50 ng/ml; R&D Systems, Minneapolis, MN), or conditioned media from primary cultures of osteoblasts (18). Luciferase activities were measured by using the Dual Luciferase Assay System (Promega, Madison, WI) with the aid of a multiplate luminometer (EG&G Berthold, Wildbad, Germany) and normalized to protein concentration.…”

An androgen receptor N-terminal domain antagonist for treating prostate cancer

“…Although these therapies are initially effective in 90% of patients, the disease will inevitably recur as lethal castration-resistant prostate cancer (CRPC). In spite of castrate levels of androgen, development of CRPC is considered to be causally related to continued transactivation of AR by mechanisms that may include amplification or overexpression of AR (3,4), gain-of-function mutations that allow AR to be activated by steroids or antiandrogens (5,6), ligand-independent activation of the AR NTD by interleukin-6 or kinases (7)(8)(9)(10), overexpression of AR coactivators (11)(12)(13)(14), intracrine signaling by increased intratumoral androgens (15), and expression of constitutively active splice variants of AR that lack the C-terminal LBD and are correlated with poor prognosis (16)(17)(18)(19). Patients succumb to metastatic CRPC usually within 2 years of onset.…”