SIRT7 regulates hepatocellular carcinoma response to therapy by altering the p53-dependent cell death pathway.

BACKGROUND: Optimal therapeutic strategies for hepatocellular carcinoma (HCC) patients are still challenging due to the high recurrence rate after surgical resection and chemotherapy resistance. Growing evidence shows that genetic and epigenetic alterations are involved in HCC progression and resistance to therapy, however the molecular mechanisms underlying resistance to therapy have not been fully understood. METHODS: Expression of SIRT7 in 17 paired paraffin-embedded HCC tissues and adjacent nontumoral liver tissues was examined by immunohistochemistry and Western blot. The mRNA expression of SIRT7 in 20 paired frozen HCC tissues and adjacent nontumoral liver tissues was analyzed by quantitative RT-PCR. The biologic consequences of overexpression and knockdown of SIRT7 in HCC therapy sensitivity were studied in vitro and in vivo. Interaction between SIRT7 and p53 were studied in HCC cell lines. RESULTS: SIRT7 expression was frequently upregulated in clinical HCC samples, and its expression was highly associated with TACE-resistance and poor survival (P = 0.008.) Depletion of SIRT7 from multiple liver cancer cell lines significantly increased doxorubicin toxicity while overexpression of SIRT7 largely abolished doxorubicin induced apoptosis. At the molecular level, we observed that SIRT7 interacts with and induces deacetylation of p53 at lysines 320 and 373. Deacetylated p53 showed significantly less affinity for the NOXA promoter and its transcription. In mouse xenografts, SIRT7 suppression increased doxorubicin induced p53 activation, inhibited tumor growth and induced apoptosis. CONCLUSION: The newly identified SIRT7-p53-NOXA axis partially illustrates the molecular mechanism of HCC resistance to therapy and represents a novel potential therapeutic target for HCC treatment.

Protein arginine methyl transferase 1- and Jumonji C domain-containing protein 6-dependent arginine methylation regulate hepatocyte nuclear factor 4 alpha expression and hepatocyte proliferation in mice.

Alcohol is a well-established risk factor for hepatocellular carcinoma (HCC), but the mechanisms by which it promotes liver cancer are not well understood. Several studies have shown that cellular protein arginine methylation is inhibited by alcohol. Arginine methylation is controlled by the reciprocal activity of protein arginine methyltransferases, primarily protein arginine methyl transferase 1 (PRMT1), and a demethylase Jumonji C domain-containing protein 6 (JMJD6). The aim of this study was to explore the role of arginine methylation changes in alcohol pathogenesis. We found that PRMT1 activity is inhibited in livers of mice fed with alcohol compared to pair-fed mice. Using hepatocyte-specific PRMT1 knockout mice, we identified that loss of PRMT1 results in enhanced hepatocyte proliferation and a 33% increase in liver size. This increased hepatocyte proliferation was associated with reduced expression of hepatocyte nuclear factor 4 alpha (Hnf4α), an important regulator of liver tumorigenesis. We found that PRMT1 regulates Hnf4α expression directly through arginine methylation at the (Hnf4α) promoter. In the absence of PRMT1, JMJD6 can demethylate the Hnf4α promoter and suppress its expression. We were able to restore Hnf4α expression and abolish the increase in hepatocyte proliferation by knockdown of JMJD6 in PRMT1 knockout mice. Knockdown of JMJD6 in alcohol-fed mice similarly increased Hnf4α expression. We then examined whether loss of arginine methylation might play a role in alcohol-associated liver cancers. We examined 25 human HCC specimens and found a strong correlation (R = 0.8; P < 0.01) between arginine methylation levels and Hnf4α expression in these specimens, suggesting that the above mechanism is relevant in patients. CONCLUSION: Taken together, these data suggest that PRMT1 inhibition, such as induced by alcohol, may result in epigenetic changes leading to loss of Hnf4α. This effect may contribute to alcohol's ability to promote liver tumors. (Hepatology 2018;67:1109-1126).

Mechanisms of doxorubicin resistance in hepatocellular carcinoma.

Hepatocellular carcinoma, one of the most common solid tumors worldwide, is poorly responsive to available chemotherapeutic approaches. While systemic chemotherapy is of limited benefit, intra-arterial delivery of doxorubicin to the tumor frequently produces tumor shrinkage. Its utility is limited, in part, by the frequent emergence of doxorubicin resistance. The mechanisms of this resistance include increased expression of multidrug resistance efflux pumps, alterations of the drug target, topoisomerase, and modulation of programmed cell death pathways. Many of these effects result from changes in miRNA expression and are particularly prominent in tumor cells with a stem cell phenotype. This review will summarize the current knowledge on the mechanisms of doxorubicin resistance of hepatocellular carcinoma and the potential for approaches toward therapeutic chemosensitization.

Forkhead box class O transcription factors in liver function and disease.

The forkhead box transcription factor class O (FOXO) family represents a group of transcription factors that is required for a number of stress-related transcriptional programs including antioxidant response, gluconeogenesis, cell cycle control, apoptosis, and autophagy. The liver utilizes several FOXO-dependent pathways to adapt to its routine cycles of feeding and fasting and to respond to the stresses induced by disease. FOXO1 is a direct transcriptional regulator of gluconeogenesis, reciprocally regulated by insulin, and has profound effects on hepatic lipid metabolism. FOXO3 is required for antioxidant responses and autophagy and is altered in hepatitis C infection and fatty liver. Emerging evidence suggests dysregulation of FOXO3 in some hepatocellular carcinomas. FOXOs are notable for the extensive number of functionally significant posttranslational modifications that they undergo. Recent advances in our understanding how FOXOs are regulated are providing a more detailed picture of how specific combinations of posttranslational modifications alter both nuclear translocation as well as transcriptional specificity under different conditions. This review summarizes emerging knowledge of FOXO function in the liver, FOXO changes in liver disease, and the posttranslational modifications responsible for these effects.

Impact of stem cell marker expression on recurrence of TACE-treated hepatocellular carcinoma post liver transplantation.

BACKGROUND: Liver transplantation is the most effective therapy for cirrhosis-associated hepatocellular carcinoma (HCC) but its utility is limited by post-transplant tumor recurrence. Use of the Milan, size-based criteria, has reduced recurrence rate to less than 10% but many patients remain ineligible. Reduction of tumor size with local therapies has been used to "downstage" patients to allow them to qualify for transplantation, but the optimal criteria to predict tumor recurrence in these latter patients has not been established. The existence of a progenitor cell population, sometimes called cancer stem cells (CSCs), has been proposed to be one mechanism accounting for the chemotherapy resistance and recurrence of hepatocellular carcinoma. The aim of this study was to determine if transcatheter arterial chemoemolization (TACE) treated tumors have increased CSC marker expression and whether these markers could be used to predict tumor recurrence. METHODS: Formalin fixed specimens were obtained from 39 HCC liver explants (23 with no treatment and 16 after TACE). Immunohistochemical staining was performed for EpCAM, CD44, CD90, and CD133. Staining for each marker was scored 0-3 by evaluating the number and intensity of positive tumor cells in 5 hpf of tumor in each specimen. RESULTS: TACE treated tumors displayed greater necrosis and fibrosis than non-TACE treated samples but there were no differences in morphology between the viable tumor cells of both groups. In TACE treated specimens, the staining of both EpCAM and CD133 was greater than in non-TACE specimens but CD44 and CD90 were the same. In the TACE group, the presence of high EpCAM staining was associated with tumor recurrence. Four of ten EpCAM high patients recurred while 0 of 6 EpCAM low patients recurred (P = 0.040). None of the other markers predicted recurrence. CONCLUSION: High pre-transplant EpCAM staining predicted HCC recurrence. This suggests that the abundance of tumor cells with a CSC phenotype may be a critical factor in the likelihood of tumor recurrence in patients receiving liver transplantation after TACE.