IGFBP3 impedes aggressive growth of pediatric liver cancer and is epigenetically silenced in vascular invasive and metastatic tumors

<p>Abstract</p> <p>Background</p> <p>Hepatoblastoma (HB) is an embryonal liver neoplasm of early childhood with a poor prognosis for patients with distant metastases and vascular invasion. We and others have previously shown that the overexpression of <it>insulin-like growth factor 2 </it>(<it>IGF2</it>), loss of imprinting at the <it>IGF2</it>/<it>H19 </it>locus, and amplification of <it>pleomorphic adenoma gene 1 </it>(<it>PLAG1</it>) are common features in HB, suggesting a critical role of the IGF axis in hepatoblastomagenesis. In this study, we investigated the role of the insulin-like growth factor binding protein 3 (IGFBP3), a known competitor of the IGF axis, in pediatric liver cancers.</p> <p>Results</p> <p>The <it>IGFBP3 </it>gene was highly expressed in normal pediatric livers but was heavily downregulated in four HB cell lines and the majority of HB primary tumors (26/36). Detailed methylation analysis of CpG sites in the <it>IGFBP3 </it>promoter region by bisulfite sequencing revealed a high degree of DNA methylation, which is causatively associated with the suppression of <it>IGFBP3 </it>in HB cell lines. Consequently, the treatment of HB cell lines with 5-aza-2'-deoxycytidine resulted in DNA demethylation and reactivation of the epigenetically silenced <it>IGFBP3 </it>expression. Interestingly, <it>IGFBP3 </it>promoter methylation predominantly occurred in metastatic HB with vascular invasion. Restoring <it>IGFBP3 </it>expression in HB cells resulted in reduced colony formation, migration, and invasion.</p> <p>Conclusion</p> <p>This study provides the first direct evidence that the reactivation of <it>IGFBP3 </it>decreases aggressive properties of pediatric liver cancer cells and that <it>IGFBP3 </it>promoter methylation might be used as an indicator for vessel-invasive tumor growth in HB patients.</p

Induction of apoptosis in embryonal tumors

In Tumoren des Kindesalters findet sich oft eine erhöhte Expression von anti-apoptotischen Molekülen und eine übermäßige Aktivierung von embryonalen Signalwegen wie dem Hedgehog-Signalweg. In dieser Arbeit konnten der Apoptose-Induktor Betulinsäure und der Hedgehog-Inhibitor Cyclopamin als stark anti-tumorigen wirksam in Hepatoblastom- und Rhabdomyosarkom-Zelllinien identifiziert werden. Beide Wirkstoffe beeinflussten sowohl das Apoptoseverhalten als auch den Hedgehog-Signalweg der Zellen günstig. Betulinsäure erwies sich zusätzlich in einem Xenograft-Mausmodell als wirksam. Daher könnten beide Substanzen in Zukunft von großem Interesse bei der Therapie von embryonalen Tumoren sein.Childhood tumors frequently show a higher activity of anti-apoptotic molecules and of embryonal signalling pathways like the hedgehog signalling pathway. Here we demonstrated the anti-tumorigenic activity of betulinic acid, an inducer of apoptosis, and of cyclopamine, an inhibitor of the hedgehog pathway in hepatoblastoma and rhabdomyosarcoma cell lines. Each substance was able to induce apoptosis and to inhibit the hedgehog signalling in these cells. In addition, betulinic acid was effective in a xenograft mouse model. Therefore, these compounds might be of high interest for the treatment of embryonal tumors in the future

The genomic landscape of hepatoblastoma and their progenies with HCC-like features.

Hepatoblastoma (HB) is the most common childhood liver cancer and occasionally presents with histological and clinical features reminiscent of hepatocellular carcinoma (HCC). Identification of molecular mechanisms that drive the neoplastic continuation towards more aggressive HCC phenotypes may help to guide the new stage of targeted therapies.We performed comprehensive studies on genetic and chromosomal alterations as well as candidate gene function and their clinical relevance.Whole-exome sequencing identified HB as a genetically very simple tumour (2.9 mutations per tumour) with recurrent mutations in ß-catenin (CTNNB1) (12/15 cases) and the transcription factor NFE2L2 (2/15 cases). Their HCC-like progenies share the common CTNNB1 mutation, but additionally exhibit a significantly increased mutation number and chromosomal instability due to deletions of the genome guardians RAD17 and TP53, accompanied by telomerase reverse-transcriptase (TERT) promoter mutations. Targeted genotyping of 33 primary tumours and cell lines revealed CTNNB1, NFE2L2, and TERT mutations in 72.5%, 9.8%, and 5.9% of cases, respectively. All NFE2L2 mutations affected residues of the NFE2L2 protein that are recognized by the KEAP1/CUL3 complex for proteasomal degradation. Consequently, cells transfected with mutant NFE2L2 were insensitive to KEAP1-mediated downregulation of NFE2L2 signalling. Clinically, overexpression of the NFE2L2 target gene NQO1 in tumours was significantly associated with metastasis, vascular invasion, the adverse prognostic C2 gene signature, as well as poor outcome.Our study demonstrates the importance of CTNNB1 mutations and NFE2L2-KEAP1 pathway activation in HB development and defines loss of genomic stability and TERT promoter mutations as prominent characteristics of aggressive HB with HCC features

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

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/beta-catenin signaling pathway, which is a key regulator of liver progenitor cells in embryonic development. The tumors demonstrate a high rate of beta-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/beta-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 beta-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/beta-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