Dapper Homolog 1 Is a Novel Tumor Suppressor in Gastric Cancer through Inhibiting the Nuclear Factor-κB Signaling Pathway

Shiyan Wang,Ning Zhang,Ka Fai To,Qian Tao,Wei Kang,Joanna H M Tong,Lili Li,Xiaoxing Li,Jun Yu,Joseph J Y Sung,Minnie Y Y Go

doi:10.2119/molmed.2012.00243

Abstract

Dapper homolog 1 (DACT1) is a disheveled partner in the planar cell polarity pathway. By using genome-wide promoter methylation screening, dapper homolog 1 (DACT1) was found to be frequently methylated in gastric cancer. We aim to clarify its epigenetic inactivation, biological function and clinical implication in gastric cancer. We demonstrated that DACT1 was silenced in 7 of 10 gastric cancer cell lines and in primary gastric cancers. Transcriptional gene silence of DACT1 was mainly regulated by promoter hypermethylation. Ectopic expression of DACT1 in silenced gastric cancer cell lines (AGS, BGC823 and MGC803) by stable transfection suppressed colony formation (P < 0.001), induced cell apoptosis (P < 0.01) and retarded tumorigenesis in nude mice (P < 0.001). The tumor suppressive effect of DACT1 was further confirmed by loss of DACT1 function experiment. The proapoptotic and antiproliferative effect by DACT1 was associated with inhibition of nuclear factor (NF)-κB activation and its downstream factors, including B-cell CLL/lymphoma-2, Bcl-X, interleukin-8 and tumor necrosis factor-α. Moreover, promoter methylation of DACT1 was detected in 29.3% (60/205) of primary gastric tumors. DACT1 methylation was significantly associated with tumor metastasis (P < 0.05), invasion (P < 0.05) and advanced tumor stage (P < 0.0005). These findings provided insight into the role of DACT1 as a novel functional tumor suppressor in gastric cancer through inhibiting NF-κB signaling pathway. Promoter methylation of DACT1 is associated with tumor aggressiveness.

Highlights

Gastric cancer is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide [1]
The bisulfite genomic sequencing (BGS) results were consistent with the results of methylationspecific PCR (MSP), in which dense methylation was found in methylated cell lines (AGS, MKN45 and Kato III), but not in unmethylated MKN28 and normal gastric tissues (Figure 1D)
To test whether methylation directly mediates DACT1 silencing, we treated three silenced cell lines (MKN28, AGS and Kato III) with demethylation agent 5-Aza. This treatment reduced DACT1 promoter methylation level and restored DACT1 expression in AGS and Kato III cell lines (Figure 1E), inferring transcriptional gene silence of DACT1 was mediated by promoter methylation in GC cells

Summary

Introduction

Gastric cancer is one of the most common malignancies and remains the second leading cause of cancer-related death worldwide [1]. The mechanism leading to gastric cancer development remains elusive. Hypermethylation of CpG island in the promoter region of tumor suppressor gene is associated with transcriptional gene silence and contributes to the development and progression of gastric carcinogenesis [2,3,4]. We used a novel approach by genome-wide promoter methylation analysis to identify hypermethylation silenced genes in tumors and identified dapper homolog 1. (DACT1) as a potential tumor suppressor gene frequently silenced by methylation in gastric cancer [5]. As a critical branch of noncanonical WNT signaling, PCP pathway is activated by the binding of noncanonical Wnt proteins to transmembrane receptors (Frizzled), which leads to the recruitment of cytoplasmic Dishevelled (Dvl) to the plasma membrane. Dvl converts upstream PCP signaling into specific downstream programs, leading to cytoskeleton reorganization in cell movement and polarity [9]. Upstream PCP components include transmembrane Frizzled, Vang-like (Vangl) and cytoplasmic Dvl and Prickle, which control the downstream PCP executors

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