Hepatoma-derived growth factor: A survival-related protein in prostate oncogenesis and a potential target for vitamin K2

Highlights

• Hepatoma-derived growth factor (HDGF) is overexpressed in both androgen-dependent and androgen-independent prostate cancer.

• Forced overexpression of HDGF promotes cell proliferation of benign prostate epithelial cells.

• Gene silencing of HDGF reduced cell proliferation in human prostate cancer cells.

• HDGF up-regulates the expression of antiapoptotic proteins cyclin E and BCL-2, whereas simultaneously down-regulating Bax expression.

• Targeting HDGF by vitamin k2 inhibited the cell proliferation of HDGF overexpressing prostate cells by inhibiting phospho-AKT and NF-kB expression.

Abstract

Hepatoma-derived growth factor (HDGF) is a heparin-binding growth factor, which has previously been shown to be expressed in a variety of cancers. HDGF overexpression has also previously been correlated with a poor prognosis in several cancers. The significance of HDGF in prostate cancer, however, has not been investigated. Here, we show that HDGF is overexpressed in both androgen-sensitive LNCaP cells and androgen-insensitive DU145, 22RV1, and PC-3 cells. Forced overexpression enhanced cell viability of RWPE-1 cells, whereas HDGF knockdown reduced cell proliferation in human prostate cancer cells. We also show that HDGF may serve as a survival-related protein as ectopic overexpression of HDGF in RWPE cells up-regulated the expression of antiapoptosis proteins cyclin E and BCL-2, whereas simultaneously down-regulating proapoptotic protein BAX. Western blot analysis also showed that HDGF overexpression modulated the activity of phospho-AKT as well as NF-kB, and these results correlated with in vitro migration and invasion assays. We next assessed the therapeutic potential of HDGF inhibition with a HDGF monoclonal antibody and vitamin k₂, showing reduced cell proliferation as well as inhibition of NF-kB expression in HDGF overexpressed RWPE cells treated with a HDGF monoclonal antibody and vitamin K₂. Collectively, our results suggest that HDGF is a relevant protein in prostate oncogenesis and may serve as a potential therapeutic target in prostate cancer.

Introduction

Prostate cancer (PCa) is one the most commonly diagnosed cancers and is currently the second leading cause of cancer-related deaths among men in the United States [1]. Although surgery, androgen ablation and radiation therapy are effective treatments of PCa, cases commonly progress to a hormone independent state. The current standard of treatment in advanced, hormone-refractory PCa is unsatisfactory [2]. Therefore, new modalities of treatment are needed. Deeper understanding of the molecular mechanisms underlying PCa development and progression may lead to the development of novel targeted therapies designed to treat PCa.

Hepatoma-derived growth factor (HDGF) is a heparin-binding growth factor originally identified after being purified from supernatant cultures of human hepatoma cell lines [3]. Previous works have shown HDGF to be a potent mitogen, stimulating the growth of vascular smooth muscle cells, hepatoma cells, and endothelial cells [4], [5], [6]. HDGF has also been shown to be highly expressed in a variety of malignancies, including hepatocellular carcinoma (HCC), gastric cancer, non–small cell lung cancer (NSCLC), pancreatic cancer, and melanoma [7], [8], [9], [10], [11]. Overexpression of HDGF also appears to correlate with a poor prognosis in patients with HCC, lung, and gastric cancers [7], [8], [9]. Although the underlying molecular mechanisms by which HDGF promotes carcinogenesis are not entirely understood, it appears to play a critical role in the development of a variety of malignancies and appears to be involved in a variety of cancer promoting processes, including cancer cell growth, regulation of apoptosis, angiogenesis, and invasion [12], [13], [14], [15], [16]. In preclinical models, therapeutic targeting of HDGF appears to have anticancer properties. Zhao et al. [17] showed that anti-HDGF neutralizing antibodies in combination with bevacizumab and chemotherapy prevented relapse of NSCLC in a heterotransplant model, whereas Kishima et al. [6] showed that antisense oligonucleotides of HDGF suppressed growth of hepatoma cells.

Despite its known role in the development and pathogenesis of other malignancies, little is known about the potential role HDGF may play in the development of PCa. We, therefore, set out to characterize HDGF in the development of PCa as well as its potential anticancer properties by targeted inhibition in PCa cell lines.