Spatial characterisation of β-catenin-mutated hepatocellular adenoma subtypes by proteomic profiling of the tumour rim

Background & Aims

Hepatocellular adenomas (HCAs) are rare, benign, liver tumours classified at the clinicopathological, genetic, and proteomic levels. The β-catenin-activated (b-HCA) subtypes harbour several mutation types in the β-catenin gene (CTNNB1) associated with different risks of malignant transformation or bleeding. Glutamine synthetase is a surrogate marker of β-catenin pathway activation associated with the risk of malignant transformation. Recently, we revealed an overexpression of glutamine synthetase in the rims of exon 3 S45-mutated b-HCA and exon 7/8-mutated b-HCA compared with the rest of the tumour. A difference in vascularisation was found in this rim shown by diffuse CD34 staining only at the tumour centre. Here, we aimed to characterise this tumour heterogeneity to better understand its physiopathological involvement.

Methods

Using mass spectrometry imaging, genetic, and proteomic analyses combined with laser capture microdissection, we compared the tumour centre with the tumour rim and with adjacent non-tumoural tissue.

Results

The tumour rim harboured the same mutation as the tumour centre, meaning both parts belong to the same tumour. Mass spectrometry imaging showed different spectral profiles between the rim and the tumour centre. Proteomic profiling revealed the significant differential expression of 40 proteins at the rim compared with the tumour centre. The majority of these proteins were associated with metabolism, with an expression profile comparable with a normal perivenous hepatocyte expression profile.

Conclusions

The difference in phenotype between the tumour centres and tumour rims of exon 3 S45-mutated b-HCA and exon 7/8-mutated b-HCA does not depend on CTNNB1 mutational status. In a context of sinusoidal arterial pathology, tumour heterogeneity at the rim harbours perivenous characteristics and could be caused by a functional peripheral venous drainage.

Impact and implications

Tumour heterogeneity was revealed in β-catenin-mutated hepatocellular adenomas (b-HCAs) via the differential expression of glutamine synthase at tumour rims. The combination of several spatial approaches (mass spectrometry imaging, genetic, and proteomic analyses) after laser capture microdissection allowed identification of a potential role for peripheral venous drainage underlying this difference. Through this study, we were able to illustrate that beyond a mutational context, many factors can downstream regulate gene expression and contribute to different clinicopathological phenotypes. We believe that the combinations of spatial analyses that we used could be inspiring for all researchers wanting to access heterogeneity information of liver tumours.

Unclassified hepatocellular adenoma with beta-catenin mutation: a case report

Background

Hepatocellular adenoma (HCA) subtypes are considered as risk factors for malignant transformation; thus, an accurate diagnosis is important. We report a case of resected HCA previously diagnosed as unclassified HCA using immunohistochemistry, subsequently discovered to harbor a mutation in exon 3 of the beta (β)-catenin gene using deoxyribonucleic acid (DNA) sequencing.

Case presentation

The patient was a 26-year-old woman who was referred to our hospital because of a 150-mm tumor in the right lobe of the liver. Considering the possibility of malignancy, we performed right lobe hepatectomy. Based on the histopathological and immunohistochemical findings, the tumor was diagnosed as an unclassified HCA. Next, we performed sequencing of DNA isolated from the tumor and identified a mutation in exon 3 of β-catenin, suggesting that the tumor contained an activating mutation of the β-catenin gene.

Conclusion

β-Catenin mutations in HCA cannot be detected by immunohistochemistry alone, and molecular analysis is required to accurately diagnose and evaluate its prognosis.

E-cadherin expression increases cell proliferation by regulating energy metabolism through nuclear factor-κB in AGS cells

β-Catenin is a central player in Wnt signaling, and activation of Wnt signaling is associated with cancer development. E-cadherin in complex with β-catenin mediates cell-cell adhesion, which suppresses β-catenin-dependent Wnt signaling. Recently, a tumor-suppressive role for E-cadherin has been reconsidered, as re-expression of E-cadherin was reported to enhance the metastatic potential of malignant tumors. To explore the role of E-cadherin, we established an E-cadherin-expressing cell line, EC96, from AGS cells that featured undetectable E-cadherin expression and a high level of Wnt signaling. In EC96 cells, E-cadherin re-expression enhanced cell proliferation, although Wnt signaling activity was reduced. Subsequent analysis revealed that nuclear factor-κB (NF-κB) activation and consequent c-myc expression might be involved in E-cadherin expression-mediated cell proliferation. To facilitate rapid proliferation, EC96 cells enhance glucose uptake and produce ATP using both mitochondria oxidative phosphorylation and glycolysis, whereas AGS cells use these mechanisms less efficiently. These events appeared to be mediated by NF-κB activation. Therefore, E-cadherin re-expression and subsequent induction of NF-κB signaling likely enhance energy production and cell proliferation.