Abstract
BackgroundSomatic mutations are involved in hepatocellular carcinoma (HCC) progression, but the genetic mechanism associated to hepatocarcinogenesis remains poorly understood. We report that Eyes absent homolog 2 (EYA2) suppresses the HCC progression, while EYA2(A510E) mutation identified by exome sequencing attenuates the tumor-inhibiting effect of EYA2.MethodsWhole-exome sequencing was performed on six pairs of human HCC primary tumors and matched adjacent tissues. Focusing on EYA2, expression level of EYA2 in human HCC samples was evaluated by quantitative real-time PCR, western blot and immunohistochemistry. Loss- and gain-of-function studies, hepatocyte-specific deletion of EYA2 (Eya2−/−) in mice and RNA sequencing analysis were used to explore the functional effect and mechanism of EYA2 on HCC cell growth and metastasis. EYA2 methylation status was evaluated using Sequenom MassARRAY and publicly available data analysis.ResultsA new somatic mutation p.Ala510Glu of EYA2 was identified in HCC tissues. The expression of EYA2 was down-regulated in HCC and associated with tumor size (P = 0.001), Barcelona Clinic Liver Cancer stage (P = 0.016) and tumor differentiation (P = 0.048). High level of EYA2 was correlated with a favorable prognosis in HCC patients (P = 0.003). Results from loss-of-function and gain-of-function experiments suggested that knockdown of EYA2 enhanced, while overexpression of EYA2 attenuated, the proliferation, clone formation, invasion, and migration of HCC cells in vitro. Delivery of EYA2 gene had a therapeutic effect on inhibition of orthotopic liver tumor in nude mice. However, EYA2(A510E) mutation led to protein degradation by unfolded protein response, thus weakening the inhibitory function of EYA2. Hepatocyte-specific deletion of EYA2 in mice dramatically promoted diethylnitrosamine-induced HCC development. EYA2 was also down-regulated in HCC by aberrant CpG methylation. Mechanically, EYA2 combined with DACH1 to transcriptionally regulate SOCS3 expression, thus suppressing the progression of HCC via SOCS3-mediated blockade of the JAK/STAT signaling pathway.ConclusionsIn our study, we identified and validated EYA2 as a tumor suppressor gene in HCC, providing a new insight into HCC pathogenesis.
Highlights
The progression in understanding the molecular basis of hepatocarcinogenesis has attributed to genetic and epigenetic analyses of oncogenes and tumor-suppressor genes [1]
Eyes absent homolog 2 (EYA2) somatic mutations in hepatocellular carcinoma (HCC) are identified by exome sequencing analysis The genomic DNA obtained from six pairs of HCC primary tumors and matched adjacent tissues was analyzed by whole-exome sequencing
A three-caller bioinformatics pipeline, previously designed by our laboratory [10], was conducted to identify the somatic variants (SNVs and indels) by comparing variants identified in the HCC and the tumor exome datasets, against dbSNP and germline variants which were presented in the matched adjacent samples
Summary
The progression in understanding the molecular basis of hepatocarcinogenesis has attributed to genetic and epigenetic analyses of oncogenes and tumor-suppressor genes [1]. The genesis of cancer can be triggered by loss-of-function mutations in tumor suppressor genes and gain-of-function mutations in proto-oncogenes [2]. Despite the improvements in the knowledge of the characteristic of this type of tumor, the pathogenesis of HCC is still unclear, and specific targeted drugs are still lacking. The discovery of additional genes potentially regulating HCC might provide important suggestions in the development of new drugs and clinical treatments. Somatic mutations are involved in hepatocellular carcinoma (HCC) progression, but the genetic mechanism associated to hepatocarcinogenesis remains poorly understood. We report that Eyes absent homolog 2 (EYA2) suppresses the HCC progression, while EYA2(A510E) mutation identified by exome sequencing attenuates the tumor-inhibiting effect of EYA2
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