Downregulation of SFRP1 is a protumorigenic event in hepatoblastoma and correlates with beta-catenin mutations

Abstract

Background Hepatoblastoma (HB) and pediatric hepatocellular carcinoma (HCC) are the most common malignant liver tumors in childhood. Both tumor types exhibit genetic and epigenetic alterations in the WNT/β-catenin signaling pathway, which is a key regulator of liver progenitor cells in embryonic development. The tumors demonstrate a high rate of β-catenin mutations and gene expression changes of several WNT antagonists. However, the role of the WNT inhibitory factor secreted frizzled-related protein 1 (SFRP1) has not been addressed in pediatric liver cancer so far. Results In our study, we investigated the gene expression level, DNA methylation status and functional relevance of SFRP1 in HB cell lines and in pediatric liver tumor patient samples. SFRP1 was downregulated due to DNA promoter methylation in all tested HB cell lines. Overexpression of SFRP1 in HB cell lines diminished tumor cell proliferation, colony formation and migration potential. In addition, the SFRP1-expressing HB cell lines showed reduced WNT/β-catenin signaling pathway activity and decreased expression of WNT target genes. To evaluate the utility of SFRP1 as a biomarker in pediatric liver cancer, we determined the gene expression level and DNA methylation status of SFRP1 in 45 pediatric liver tumor patient samples. The correlation analysis of different clinical parameters and tumor characteristics revealed a significant correlation of reduced SFRP1 expression with the presence of mutant β-catenin. The methylation status of SFRP1 was furthermore associated to a pediatric liver tumor type with HCC-like characteristics, TERT mutations and an older age at diagnosis. Conclusion Altogether, our data demonstrate that the epigenetic suppression of the WNT/β-catenin antagonist SFRP1 has an important impact on the malignant behavior of HB cells. Although SFRP1 methylation is a common event in HCC-like pediatric liver tumors, its potential as a prognostic or diagnostic biomarker needs to be further investigated.

Genetic and epigenetic basis of hepatoblastoma diversity

“…Sanger sequencing of CTNNB1 exon 3 and TERT promoter. To detect a large deletion including exon 3 of the CTNNB1 gene, genomic DNA samples derived from each tumor and the corresponding noncancerous tissues were amplified by PCR using a primer pair specific for exon 2 (5′-AAAATCCAGCGTGGACAAT GG-3′) and exon 4 (5′-TGTGGCAAGTTCTGCATCATC-3′) and analyzed using gel electrophoresis 61 . The breakpoint of exon3 deletions and point mutations in exon 3 was identified by capillary DNA sequencer ABI 3100 (Thermo Fisher Scientific).…”

Epigenetics in hepatoblastoma

“…The secreted frizzled-related protein 1 (SFRP1) is another known antagonist of the Wnt pathway, which directly binds to WNT proteins or the frizzled receptor, and is commonly downregulated in several cancers such as colorectal cancer, bladder cancer, non-small cell lung cancer, gastric cancer, and HCC [89] . The major mechanism driving the downregulation of SFRP1 in these tumors is the hypermethylation of its promoter [90][91][92][93][94] , which also occurs in HB tissues and cell lines [95] . Consistently, overexpression of SFRP1 hampers the Wnt/β-catenin pathway in human HB cell lines, resulting in inhibition of tumor cell growth, colony formation, and migration, whereas SFRP1 knockdown stimulates tumor cell growth [95,96] .…”

<p>Hypoxic Non-Small-Cell Lung Cancer Cell-Secreted Exosomal microRNA-582-3p Drives Cancer Cell Malignant Phenotypes by Targeting Secreted Frizzled-Related Protein 1</p>

“…31 The downregulation of SFRP1 was discovered in hepatoblastoma and its overexpression diminished the proliferation and migration of hepatoblastoma cells. 32 In addition, in a skin carcinogenesis model, SFRP1 knockout mice showed early tumor initiation and increased tumorigenic potential of cancer stem cells. Moreover, the downregulation of SFRP1 was correlated with poor survival in patients with epithelial cancers, suggesting the involvement of SFRP1 in tumorigenesis.…”