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Hepatocellular Carcinoma (HCC) is the most frequent malignant tumor of the liver, but its prognosis is poor. Histone acetylation is an important epigenetic regulatory mode that modulates chromatin structure and transcriptional status to control gene expression in eukaryotic cells. Generally, histone acetylation and deacetylation processes are controlled by the opposing activities of histone acetyltransferases (HATs) and histone deacetylases (HDACs). Dysregulation of histone modification is reported to drive aberrant transcriptional programmes that facilitate liver cancer onset and progression. Emerging studies have demonstrated that several HDAC inhibitors exert tumor-suppressive properties via activation of various cell death molecular pathways in HCC. However, the complexity involved in the epigenetic transcription modifications and non-epigenetic cellular signaling processes limit their potential clinical applications. This review brings an in-depth view of the oncogenic mechanisms reported to be related to aberrant HCC-associated histone acetylation, which might provide new insights into the effective therapeutic strategies to prevent and treat HCC.

Additional file 1: Supplemental Figure 1. Anthracycline-resistant cell lines HL60/ADR cells, K562/A02 cells and THP/ADR cells showed resistance to doxorubicin. Cell viability was examined after treatment with different doses of doxorubicin for 24 h by CCK-8 assay. (A) HL60, (B) HL60/ADR, (C) K562, (D) K562/A02, (E) THP-1, (F) THP-1/ADR. Supplemental Figure 2. Differential gene and protein expression in K562 and K562/A02. (A) RT-PCR analysis showed differential gene expression in K562 and K562/A02. (B) Western blot analysis shows protein expression of differential gene in K562 and K562/A02. Data represent three independent experiments, results are shown in the format, mean ± S.D. (*P 0.05). Supplemental Figure 3. Chidamide sensitizes anthracycline-resistant cells to anthracycline in vivo. (A) K562 cells (1 × 107 cells) were implanted into NOD/SCID mice. The mice were randomly divided into 4 groups (5 mice in each group). Doxorubicin was injected into the mice at day 5 and day 12 after leukemic cells inoculation. And chidamide was administered 3 times every week from day 6 after leukemic cells inoculation. (B) The volume of each tumor was measured every 3 days. The tumor volume was calculated by the formula (V = 0.5*length*width2). (C) The visual analysis of tumors harvested from mice. (D-E) The measurement of xenograft tumor volume and weight. (F) The mRNA expression levels of HDAC3, AKT, P21 and CDK2 were measured using RT-PCR in tumor sections. Data represent three independent experiments, data are expressed as mean values± S.D. (*P 0.05). Supplemental Figure 4A-I. Chidamide affected the behavior of anthracycline- resistant cells. (A) CCK-8 assays were used to assess the proliferative abilities of K562/A02 cells. The proportion of G0/G1 phase (B) and S phase (C) were measured in response to incubation with chidamide in K562/A02 cells. The proportion of G0/G1 phase (D) and S phase (E) were measured in THP-1/ADR cells. (F-G) represent apoptosis analysis with flow cytometry in K562/A02 cells and (H-I) in THP-1/ADR cells (Annexin V/PI). Data represent three independent experiments, results are shown in the format, mean ± S.D. (*P 0.05). Supplemental Figure 4J-W. K562, HL60 and patient-derived anthracycline-sensitive AML cells are sensitive to chidamide monotherapy, and chidamide sensitizes anthracycline-resistant cells to anthracycline in K562/A02 and THP/ADR cells. CCK-8 assays were used to assess the proliferative abilities of K562 (J), HL60 (K), patient-derived cells (L). (M-N) are representatives of flow cytometry (Annexin V/PI) for detection of apoptosis. The apoptotic rate of cells was measured by flow cytometry in K562 (O) and HL60 cells (P). (Q-R) represent cell cycle analysis with flow cytometry in K562 cells and HL60 cells. The proportion of G0/G1 phase and S phase were measured in response to incubation with chidamide in K562 cells (S) and HL60 cells (T). The cell viability of (U) K562/A02 and (V) THP-1/ADR cells treated by combination therapy were measured with CCK-8 assays. (W) HDAC activity of K562/A02 cells was measured after treated with chidamide. Data represent three independent experiments, results are shown in the format, mean ± S.D. (*P 0.05). Supplemental Figure 5. Molecular mechanisms of chidamide activity in K562/A02 and THP-1/ADR cells. Anthracycline-resistant AML cells were treated with different concentrations of chidamide. Expression levels of HDAC3, AKT, P21 and CDK2 were measured using RT-PCR in K562/A02 cells (A) and THP-1/ADR cells (B). (C) K562/A02 and (D) THP-1/ADR were treated with chidamide and the expression levels of HDAC3, P-AKT, AKT, P21 and CDK2 were measured by Western blot. RT-PCR analysis of HDAC3, AKT, CDK2 and P21 (E) and western blot analysis (F) in K562/ADR cells treated with a combination of chidamide and doxorubicin. The expression of pathway genes was measured by RT-PCR (G) and Western blot (H) in THP-1/ADR cells treated with combination therapy. Data represent three independent experiments, and results are shown in the format, means ± S.D. (*P 0.05). Figure S7. AKT inhibitor reduces cell proliferation, increases cell apoptosis, induces cell cycle arrest at G0/G1 phase, and suppresses the expression of HDAC3, CDK2 and P21. K562/A02 cells were incubated with an AKT inhibitor (MK2206-2HCL). (A) CCK-8 assays were used to assess cell proliferation ability. (B) Flow cytometry was used to analyze cell apoptosis. (C) is a representative of flow cytometry plot for detection of apoptosis. (D-E) Cell cycles of K562/A02 cells were analyzed by flow cytometry after PI staining. (F) is a representative of flow cytometry for cell cycle detection. (G) Expression levels of HDAC3, AKT, P21 and CDK2 were measured by RT-PCR. (H) Expression levels of HDAC3, P-AKT, AKT, P21 and CDK2 were measured by Western blot. GAPDH was used as an internal control. Data represent three independent experiments, results are shown in the format, mean ± S.D. (*P 0.05). Table S1.Comparison of different anthracycline-based chemotherapy regimens.