CHD1L promotes lineage reversion of hepatocellular carcinoma through opening chromatin for key developmental transcription factors.

UNLABELLED: High-grade tumors with poor differentiation usually show phenotypic resemblance to their developmental ancestral cells. Cancer cells that gain lineage precursor cell properties usually hijack developmental signaling pathways to promote tumor malignant progression. However, the molecular mechanisms underlying this process remain unclear. In this study, the chromatin remodeler chromodomain-helicase-DNA-binding-protein 1-like (CHD1L) was found closely associated with liver development and hepatocellular carcinoma (HCC) tumor differentiation. Expression of CHD1L decreased during hepatocyte maturation and increased progressively from well-differentiated HCCs to poorly differentiated HCCs. Chromatin immunoprecipitation followed by high-throughput deep sequencing found that CHD1L could bind to the genomic sequences of genes related to development. Bioinformatics-aided network analysis indicated that CHD1L-binding targets might form networks associated with developmental transcription factor activation and histone modification. Overexpression of CHD1L conferred ancestral precursor-like properties of HCC cells both in vitro and in vivo. Inhibition of CHD1L reversed tumor differentiation and sensitized HCC cells to sorafenib treatment. Mechanism studies revealed that overexpression of CHD1L could maintain an active "open chromatin" configuration at promoter regions of estrogen-related receptor-beta and transcription factor 4, both of which are important regulators of HCC self-renewal and differentiation. In addition, we found a significant correlation of CHD1L with developmental transcriptional factors and lineage differentiation markers in clinical HCC patients. CONCLUSION: Genomic amplification of chromatin remodeler CHD1L might drive dedifferentiation of HCC toward an ancestral lineage through opening chromatin for key developmental transcriptional factors; further inhibition of CHD1L might "downgrade" poorly differentiated HCCs and provide novel therapeutic strategies.

A disrupted RNA editing balance mediated by ADARs (Adenosine DeAminases that act on RNA) in human hepatocellular carcinoma.

OBJECTIVE: Hepatocellular carcinoma (HCC) is a heterogeneous tumour displaying a complex variety of genetic and epigenetic changes. In human cancers, aberrant post-transcriptional modifications, such as alternative splicing and RNA editing, may lead to tumour specific transcriptome diversity. DESIGN: By utilising large scale transcriptome sequencing of three paired HCC clinical specimens and their adjacent non-tumour (NT) tissue counterparts at depth, we discovered an average of 20 007 inferred A to I (adenosine to inosine) RNA editing events in transcripts. The roles of the double stranded RNA specific ADAR (Adenosine DeAminase that act on RNA) family members (ADARs) and the altered gene specific editing patterns were investigated in clinical specimens, cell models and mice. RESULTS: HCC displays a severely disrupted A to I RNA editing balance. ADAR1 and ADAR2 manipulate the A to I imbalance of HCC via their differential expression in HCC compared with NT liver tissues. Patients with ADAR1 overexpression and ADAR2 downregulation in tumours demonstrated an increased risk of liver cirrhosis and postoperative recurrence and had poor prognoses. Due to the differentially expressed ADAR1 and ADAR2 in tumours, the altered gene specific editing activities, which was reflected by the hyper-editing of FLNB (filamin B, ß) and the hypo-editing of COPA (coatomer protein complex, subunit α), are closely associated with HCC pathogenesis. In vitro and in vivo functional assays prove that ADAR1 functions as an oncogene while ADAR2 has tumour suppressive ability in HCC. CONCLUSIONS: These findings highlight the fact that the differentially expressed ADARs in tumours, which are responsible for an A to I editing imbalance, has great prognostic value and diagnostic potential for HCC.

AKR7A3 suppresses tumorigenicity and chemoresistance in hepatocellular carcinoma through attenuation of ERK, c-Jun and NF-κB signaling pathways.

Hepatocellular carcinoma (HCC), which accounts for 85-90% of primary liver cancer, is now the second leading cause of cancer-related mortality worldwide. Here we reported that Aldo-Keto Reductase family 7A isoform 3 (AKR7A3) is frequently down-regulated in HCC, associating with poor overall survival rate, elevated serum α-fetoprotein (AFP) and poor differentiation of HCC. The promoter region of AKR7A3 was detected to be hypermethylated. Loss of heterozygosity (LOH) was also detected in AKR7A3. Functional assays on both AKR7A3 overexpressed and knockdown cells, including foci formation, colony formation in soft agar, migration, invasion and tumor formation in nude mice, demonstrated the strong tumor suppressive functions of AKR7A3. In addition, treatment of chemotherapy drug cisplatin showed that AKR7A3 sensitizes tumor cells to apoptosis. Mechanistically, western blot analysis showed that overexpression of AKR7A3 inhibits the activation of ERK, c-Jun and NF-κB. In summary, we found that AKR7A3 functions as a tumor suppressor gene in HCC through attenuating c-Jun, ERK and NF-κB signaling pathways.

Recoding RNA editing of AZIN1 predisposes to hepatocellular carcinoma.

A better understanding of human hepatocellular carcinoma (HCC) pathogenesis at the molecular level will facilitate the discovery of tumor-initiating events. Transcriptome sequencing revealed that adenosine-to-inosine (A→I) RNA editing of AZIN1 (encoding antizyme inhibitor 1) is increased in HCC specimens. A→I editing of AZIN1 transcripts, specifically regulated by ADAR1 (encoding adenosine deaminase acting on RNA-1), results in a serine-to-glycine substitution at residue 367 of AZIN1, located in ß-strand 15 (ß15) and predicted to cause a conformational change, induced a cytoplasmic-to-nuclear translocation and conferred gain-of-function phenotypes that were manifested by augmented tumor-initiating potential and more aggressive behavior. Compared with wild-type AZIN1 protein, the edited form has a stronger affinity to antizyme, and the resultant higher AZIN1 protein stability promotes cell proliferation through the neutralization of antizyme-mediated degradation of ornithine decarboxylase (ODC) and cyclin D1 (CCND1). Collectively, A→I RNA editing of AZIN1 may be a potential driver in the pathogenesis of human cancers, particularly HCC.