OncologyDickkopf-1 (DKK1) promotes invasion and metastasis of hepatocellular carcinoma
Introduction
Hepatocellular carcinoma (HCC) is one of the most common and aggressive cancers, ranking as the third leading cause of cancer death worldwide [1]. The disease is most prevalent in parts of Africa and Asia, but its incidence in the Western world is showing an alarming rise [2]. Due to advances in surgical techniques and perioperative management, hepatic resection has evolved into a safe procedure with low operative mortality, less than 2% in large liver surgery centres [3], [4]. However, the long-term survival of patients with HCC after hepatic resection remains unsatisfactory, mainly because of the high incidence of recurrence and metastasis [5].
Abundant evidence has shown that recurrence and metastasis of HCC is a multistep process that involves complex biological and pathological events [6]. Despite extensive clinical as well as basic research efforts, the molecular mechanisms that contribute to the metastasis of HCC are poorly understood. Therefore, there is clearly an urgent need to identify novel metastatic factors as a promising approach to define novel targets for therapeutic strategies.
In our institute, HCC was phenotypically divided into three categories: solitary large hepatocellular carcinoma (SLHCC, diameter > 5 cm, and one node), nodular hepatocellular carcinoma (NHCC, node number ≥ 2) and small hepatocellular carcinoma (SHCC, diameter ≤ 5 cm) [4]. Our clinical observations implied different invasive and metastatic abilities between SLHCC and NHCC. Using cDNA microarray to profile gene expression patterns in SLHCC and NHCC, we previously found that Dickkopf-1 (Dkk1) was significantly elevated in NHCC tissues with high metastatic potential compared to SLHCC, suggesting that DKK1 may be involved in the regulation of HCC invasion and metastasis [7].
DKK1, a secreted protein, is a known negative regulator of the Wnt signalling pathway, which plays an important role in a variety of cellular processes, including proliferation, differentiation, survival, apoptosis and cell motility [8], [9]. DKK1 was frequently found to be overexpressed in patients with Wilms tumour, hepatoblastoma, multiple myeloma and breast cancer, indicating a potential oncogenic role of DKK1 in carcinogenesis [10], [11], [12]. Yu et al. found that DKK1 overexpression correlated with beta-catenin cytoplasmic/nuclear accumulation in clinical HCC samples and that high DKK1 expression predicted unfavourable prognoses in HCC patients. These findings suggest that DKK1 is a novel prognostic predictor for HCC patients [13].
However, the mechanism of how DKK1 contributes to the invasion and metastasis of HCC is unclear. Therefore, we carried out the present study to investigate the clinical significance, biological function and molecular mechanism of DKK1 in the invasion and metastasis of HCC.
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Patients and tissue specimens
In the present study, specimens of HCC tissue and paracarcinomatous liver tissue (PCLT) were obtained for immunohistochemistry analysis from 120 HCC patients who underwent hepatectomy procedures from November 2001 to December 2004 at the Department of Surgery of Xiangya Hospital of Central South University (CSU). These patients included 104 males and 16 females with a median age of 45.0 years (range: 18–71 years). Among these 120 cases of HCC, fresh specimens of HCC without vascular invasion
The expression of DKK1 in hepatocellular carcinoma tissues
The protein expression levels of DKK1 were detected in 120 paired HCC tissues and PCLTs by using immunohistochemical staining (Fig. 1). The results revealed a cytoplasmic distribution of DKK1. The DKK1 protein was detected in 52 of 120 HCC tissues and in 24 of 120 PCLTs. The positive expression rate of DKK1 was significantly higher in HCC tissues than that in PCLTs (43.3% vs. 20%; P < 0.001). The eight specimens of normal liver tissue all stained negatively.
The relationship of DKK1 expression in hepatocellular carcinoma with the clinicopathologic characteristics and prognosis of patients
As shown in Table 1, the
Discussion
DKK1 functions as negative regulator of the canonical Wnt pathway [17]. Specifically, Wnt binds to the frizzled receptor (Fz) and the low-density lipoprotein receptor-related protein-5/6 (LRP5/6), resulting in beta-catenin accumulation and migration to the nucleus, which further interacts with the transcription factor TCF triggering signals important for proliferation [18]. DKK1 binds to LRP5/6 and blocks interaction with Wnt, resulting in beta-catenin degradation and retardation of
Grant support
National Natural Science Foundation of China (No. 30700364).
Conflicts of interest
The authors report no conflicts of interest.
Acknowledgement
The authors thank Dr. Zhong-Shu Yan for his help with English improvement and critical review of this manuscript.
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