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The Wnt/β-catenin signaling pathway plays a key role in development and carcinogenesis. Although some target genes of this signaling have been identified in various tissues and neoplasms, the comprehensive understanding of the target genes and their roles in the development of human cancer, including hepatoma and colorectal cancer remain to be fully elucidated. In this study, we searched for genes regulated by the Wnt signaling in liver cancer using HuH-7 hepatoma cells. A comparison of the expression profiles between cells expressing an active form of mutant β-catenin and cells expressing enhanced green fluorescent protein (EGFP) identified seven genes upregulated by the mutant β-catenin gene (CTNNB1). Among the seven genes, we focused in this study on ODAM, odontogenic, ameloblast associated, as a novel target gene. Interestingly, its expression was frequently upregulated in hepatocellular carcinoma, colorectal adenocarcinoma, and hepatoblastoma. We additionally identified a distant enhancer region that was associated with the β-catenin/TCF7L2 complex.Further analyses revealed that ODAM plays an important role in the regulation of the cell cycle, DNA synthesis, and cell proliferation. These data may be useful for clarification of the main molecular mechanism(s) underlying these cancers.

Background Abnormal activation of Wnt/β‐catenin signaling is associated with various aspects of cancer development. This study explored the roles of novel target genes of the Wnt/β‐catenin signaling pathway in cancer cells. Methods Using the haploid chronic myelogenous leukemia cell line HAP1, RNA sequencing (RNA‐seq) was performed to identify genes whose expression was increased by APC disruption and reversed by β‐catenin knockdown (KD). The regulatory mechanism and function of one of the candidate genes was investigated in colorectal cancer (CRC) cells. Results In total, 64 candidate genes whose expression was regulated by Wnt/β‐catenin signaling were identified. Of these candidate genes, the expression levels of six were reduced by β‐catenin KD in HCT116 CRC cells in our previous microarray. One of these genes was Visinin‐like 1 (VSNL1), which belongs to the neuronal calcium‐sensor gene family. The expression of VSNL1 was regulated by the β‐catenin/TCF7L2 complex via two TCF7L2‐binding elements in intron 1. VSNL1 KD‐induced apoptosis in VSNL1‐positive CRC cells. Additionally, forced expression of wild‐type VSNL1, but not a myristoylation, Ca2+‐binding, or dimerization‐defective mutant, suppressed the apoptosis induced by camptothecin and doxorubicin in VSNL1‐negative CRC cells. Conclusion Our findings suggest that VSNL1, a novel target gene of the Wnt/β‐catenin signaling pathway, is associated with apoptosis resistance in CRC cells.

Aberrant activation of the Wnt/β-catenin signaling pathway plays a crucial role in the development and progression of colorectal cancer. Previously, we identified a set of candidate genes that were regulated by this signaling pathway, and the present study focused on motile sperm domain containing 1 (MOSPD1). Immunohistochemical staining revealed that the expression of MOSPD1 was elevated in tumor cells from colorectal cancer tissues compared with in non-tumor cells. Using ChIP-seq data and the JASPAR database, the regulatory region(s) in the MOSPD1 gene as a target of the Wnt/β-catenin signaling pathway were searched, and a region containing three putative TCF-binding motifs in the 3'-flanking region was identified. Additional analyses using reporter assay and ChIP-quantitative PCR suggested that this region harbors enhancer activity through an interaction with transcription factor 7 like 2 (TCF7L2) and β-catenin. In addition, chromatin conformation capture assay revealed that the 3'-flanking region interacts with the MOSPD1 promoter. These data suggested that MOSPD1 was regulated by the β-catenin/TCF7L2 complex through the enhancer element located in the 3'-flanking region. These findings may be helpful for future studies regarding the precise regulatory mechanisms of MOSPD1.

APC (APC regulator of WNT signaling pathway) is not only a gene responsible for familial adenomatous polyposis (FAP), a hereditary disease characterized by hundreds or thousands adenomatous polyps in the colon, but also plays a crucial role in sporadic human cancers. Although most of FAP cases are caused by germline mutations in the coding region of APC, deletions or point mutations in the promoter regions are involved in a limited number of cases. Previously, we reported an FAP case with a large deletion of approximately 10 kb encompassing APC promoter 1B and exon1B of the APC gene. Since precise regulatory mechanism(s) of the transcription of APC remains to be clarified, we searched in this study the regulatory domain(s) in the deleted region. First, we performed cap analysis of gene expression (CAGE) analysis, and compared the amount of APC-1A and APC-1B transcripts in the peripheral blood cells of the patient with that of healthy volunteers. As a result, we found that the deletion decreased the amount of APC-1B to 39% - 45% in the patient compared to the healthy controls, and that it did not change the amount of APC-1A in the patient. In addition, an allele-specific expression analysis by deep cDNA sequencing revealed that the amount of APC transcripts from the mutated APC allele is reduced to 11.2% by the deletion in the patient, suggesting that the deletion resulted in the marked decrease of the transcription of the affected allele and that the remaining expression of deleted allele may be driven by other regulatory region(s) such as promoter 1A. Consistently, CAGE analysis demonstrated that APC-1B transcripts are more abundantly expressed than APC-1A transcripts in all tissues tested except for the brain, suggesting that promoter 1B plays a crucial role in the expression of APC transcription. Analysis of promoter 1B by reporter assay identified a critical region for the transcriptional activation between -117 bp and -49 bp of promoter 1B. These data will contribute to the better understanding of regulatory mechanisms of APC transcription and the evaluation of genetic variants located in promoter 1B. Citation Format: Saya Nakagawa, Kiyoshi Yamaguchi, Kimiko Saito, Kiyoko Takane, Tsuneo Ikenoue, Yoichi Furukawa. Analysis of APC-1B promoter region responsible for familial adenomatous polyposis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2316.