Activation of NF-kappa B Signaling Promotes Growth of Prostate Cancer Cells in Bone

Julie A Sterling,James R Edwards,David J Degraff,Robert J Matusik,Renjie Jin,Changki Lee,Serk In Park

doi:10.1371/journal.pone.0060983

Abstract

Patients with advanced prostate cancer almost invariably develop osseous metastasis. Although many studies indicate that the activation of NF-κB signaling appears to be correlated with advanced cancer and promotes tumor metastasis by influencing tumor cell migration and angiogenesis, the influence of altered NF-κB signaling in prostate cancer cells within boney metastatic lesions is not clearly understood. While C4-2B and PC3 prostate cancer cells grow well in the bone, LNCaP cells are difficult to grow in murine bone following intraskeletal injection. Our studies show that when compared to LNCaP, NF-κB activity is significantly higher in C4-2B and PC3, and that the activation of NF-κB signaling in prostate cancer cells resulted in the increased expression of the osteoclast inducing genes PTHrP and RANKL. Further, conditioned medium derived from NF-κB activated LNCaP cells induce osteoclast differentiation. In addition, inactivation of NF-κB signaling in prostate cancer cells inhibited tumor formation in the bone, both in the osteolytic PC3 and osteoblastic/osteoclastic mixed C4-2B cells; while the activation of NF-κB signaling in LNCaP cells promoted tumor establishment and proliferation in the bone. The activation of NF-κB in LNCaP cells resulted in the formation of an osteoblastic/osteoclastic mixed tumor with increased osteoclasts surrounding the new formed bone, similar to metastases commonly seen in patients with prostate cancer. These results indicate that osteoclastic reaction is required even in the osteoblastic cancer cells and the activation of NF-κB signaling in prostate cancer cells increases osteoclastogenesis by up-regulating osteoclastogenic genes, thereby contributing to bone metastatic formation.

Highlights

Almost all patients with advanced prostate cancer (PCa) develop osseus metastasis
The activation of NF-kB signaling was confirmed using the NGL reporter, an NF-kB reporter plasmid which has an NF-kB responsive element coupled to a Green Fluorescent Protein (GFP)/ Luciferase reporter [35] (Fig. 1A). qRT-PCR analysis showed that Receptor Activator of NF-kB Ligand (RANKL) and Parathyroid hormonerelated protein (PTHrP) expression are significantly increased in NFkB activated LNCaP cells, compared to empty vector control cells (Fig. 1B and 1C)
RANKL and PTHrP are known as key factors of osteoclastogenesis in the bone, and they play a key role in the bone metastasis of many cancers [15,42,43,44,45]

Summary

Introduction

Almost all patients with advanced prostate cancer (PCa) develop osseus metastasis. The development of tumor growth in the bone is the most critical complication of advanced PCa, frequently resulting in significant morbidity and mortality [1]. Unlike other types of cancer, an initial metastatic deposit of PCa cells is almost strictly limited to bone and is often the only site of distal spread even in late stages of disease [2]. Once prostate tumor cells enter the skeleton, a destructive cycle of gross skeletal damage and tumor growth occurs, at which point curative therapy is no longer possible and palliative treatment becomes the only option. Understanding the mechanism by which the PCa cells thrive within the bone environment and developing effective method(s) to prevent or treat PCa bone metastasis is critical to increase the survival rate of advanced PCa patients

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Conclusion