Search

CTNNB1 mutations activating s-catenin are frequent somatic events in hepatocellular carcinoma (HCC) and adenoma (HCA), particularly associated with a risk of malignant transformation. We aimed to understand the relationship between CTNNB1 mutation types, tumor phenotype, and level of s-catenin activation in the malignant transformation. To this purpose, CTNNB1 mutation spectrum was analyzed in 220 HCAs, 373 HCCs, and 17 borderline HCA/HCC lesions. s-catenin activation level was assessed in tumors by quantitative reverse-transcriptase polymerase chain reaction and immunohistochemistry (IHC), in cellulo by TOP-Flash assay. Overall, s-catenin activity was higher in malignant mutated tumors, compared to adenomas, and this was related to different spectrum of CTNNB1 mutations in HCCs and HCAs. In benign tumors, we defined three levels of s-catenin activation related to specific mutations: (1) S45, K335, and N387 mutations led to weak activation; (2) T41 mutations were related to moderate activity; and (3) highly active mutations included exon 3 deletions and amino acid substitutions within the s-TRCP binding site (D32-S37). Accordingly, in vitro, K335I and N387K mutants showed a lower activity than S33C. Tumors with highly active mutations demonstrated strong/homogeneous glutamine synthase (GS) staining and were associated with malignancy. In contrast, weak mutants demonstrated heterogeneous pattern of GS staining and were more frequent in HCAs except for the S45 mutants identified similarly in 20% of mutated HCAs and HCCs; however, in most of the HCCs, the weak S45 mutant alleles were duplicated, resulting in a final high s-catenin activity. Conclusion: In conclusion, high s-catenin activity driven by specific CTNNB1 mutations and S45 allele duplication is associated with malignant transformation. Consequently, HCAs with S45 and all high/moderate mutants should be identified with precise IHC criteria or mutation screening. (Hepatology 2016)

SummaryHepatocellular adenomas (HCA) are benign liver tumors predominantly developed in women using oral contraceptives. Here, exome sequencing identified recurrent somatic FRK mutations that induce constitutive kinase activity, STAT3 activation, and cell proliferation sensitive to Src inhibitors. We also found uncommon recurrent mutations activating JAK1, gp130, or β-catenin. Chromosome copy number and methylation profiling revealed patterns that correlated with specific gene mutations and tumor phenotypes. Finally, integrative analysis of HCAs transformed to hepatocellular carcinoma revealed β-catenin mutation as an early alteration and TERT promoter mutations as associated with the last step of the adenoma-carcinoma transition. In conclusion, we identified the genomic diversity in benign hepatocyte proliferation, several therapeutic targets, and the key genomic determinants of the adenoma-carcinoma transformation sequence.

Background: Hepatocellular carcinomas (HCC) are related to various etiologies including alcohol intake, obesity, hemochromatosis, hepatitis B and hepatitis C virus infection. Additional risk factors remain to be identified particularly in HCC developed without cirrhosis. We identified a fragment of Adeno-Associated Virus type 2 (AAV2, a defective DNA virus considered as non-pathogenic) inserted in an HCC genome and this result prompted us to screen a large series of HCC samples. Methods: We screened 150 HCC and matched non-tumor liver samples for AAV2 sequences using PCR and next generation sequencing. Expression of the genes targeted by viral integration was quantified and the functional consequences of AAV2 integration within TERT promoter was analyzed in 3 HCC cell lines using luciferase assay Results: Among the 150 tumors, we identified 7 cases (5%) with a clonal AAV2 insertion whereas no clonal insertion was found in the corresponding non-tumor liver tissues. In the first HCC tumor, we identified a 208 base pairs insertion of an AAV2 fragment within the TERT (coding for the telomerase reverse transcriptase) promoter. In HCC cell lines, we demonstrated that this AAV2 insertion resulted in an increased TERT promoter activity. We next identified 6 additional clonal somatic integrations of AAV2, all occurred within known cancer driver genes, CCNA2 (4 cases), CCNE1 or TNFSF10 leading to over-expression of the targeted gene without generating chimeric viral-endogeneous functional fusion transcripts. In CCNA2 (coding for cyclin A2), the four integration sites were identified within intron 2 and AAV2 insertion ranged from 219 to 1,975bp occurring in both orientations. In CCNE1 (coding for cyclin E1), we identified a 368bp AAV2 integration within intron 4. In the remaining case, AAV2 integration occurred in the 3′ UTR of TNSFS10 (coding for the receptor TRAIL), 244 bp after the stop codon. In 6 out of the 7 tumors, the inserted AAV2 included the 3′inverse tandem region. Strikingly, almost all the tumors were developed on non-fibrotic liver (6 out of 7 cases, P Conclusion: Infection by AAV2, that is very frequent the general population (around 30 to 60% of individuals), is involved in the pathogenesis of rare human HCC by recurrent somatic integration in cancer driver genes challenging its safety as a vector for gene therapy. Citation Format: Shalini Datta, Jean-Charles Nault, Andrea Franconi, Sandrine Imbeaud, Maxime Mallet, Gabrielle Couchy, Eric Letouze, Camilla Pilati, Benjamin Verret, Jean-Frédéric Blanc, Charles Balabaud, Julien Calderaro, Alexis Laurent, Mélanie Letexier, Paulette Bioulac-Sage, Fabien Calvo, Jessica Zucman-Rossi. Adeno-associated virus 2 (AAV2) induces recurrent insertional mutagenesis in human hepatocellular carcinomas. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 919. doi:10.1158/1538-7445.AM2015-919