Increased Small Ubiquitin-like Modifier-Activating Enzyme SAE1 Promotes Hepatocellular Carcinoma by Enhancing mTOR SUMOylation.

SUMOylation, one of the most important posttranslational modifications of proteins, plays an essential role in various biological processes; however, enzymes that control SUMOylation in hepatocellular carcinoma (HCC) are still unclear. Comprehensive exploration of the expression and clinical significance of SUMO enzymes in HCC would be of great value. Here, we obtained the gene expression profile of each small ubiquitin-like modifier (SUMO) protein and the corresponding clinical information from The Cancer Genome Atlas. We found that all SUMO enzymes were significantly increased in HCC tissues compared with that in adjacent nontumorous tissues. We identified a 6-gene prognostic signature, including SAE1, PIAS2, PIAS3, SENP3, SENP5, and UBC9, that could effectively predict the overall survival in patients with HCC. Specifically, SAE1 was the most valuable prognostic indicator. In 282 clinical samples, we found that SAE1 was closely related to the clinicopathologic parameters and prognosis of patients with HCC. In vitro and in vivo studies showed that SAE1 knockdown inhibits the proliferation, migration, and invasion of HCC cells. Mechanistically, we confirmed that SAE1 plays a role in driving HCC progression, which is largely dependent on the SUMOylation of mTOR signaling. In conclusion, our study revealed that the expression of SUMO enzymes, especially SAE1, is highly associated with HCC development and acts as a promising prognostic predictor.

HDAC3 Controls Liver Homeostasis More by Facilitating Deoxyribonucleic Acid Damage Repair than by Regulating Transcription in Hepatocytes.

By controlling DNA damage repair and regulating gene transcription, the critical epigenetic regulator histone deacetylase 3 (HDAC3) plays pivotal roles in liver cancer and liver regeneration; however, the role of HDAC3 in liver homeostasis has not been fully elucidated. In this study, we found that HDAC3-deficient livers developed a defective morphology and metabolism with an increasing degree of DNA damage in the hepatocytes along the portal-central axis of the lobule. Most strikingly, in the Alb-CreERT:Hdac3-/- mice, it was demonstrated that HDAC3 ablation did not impair liver homeostasis in terms of histologic characteristics, function, proliferation, or gene profiles prior to the profound accumulation of DNA damage. Next, we identified that the hepatocytes in the portal area, which carried less DNA damage than those in the central area, repopulated the hepatic lobule by active regeneration and movement toward the center. As a result, the liver became more viable after each surgery. Furthermore, in vivo tracing of keratin-19-expressing hepatic progenitor cells, which lacked HDAC3, showed that the hepatic progenitor cells gave rise to newly generated periportal hepatocytes. In hepatocellular carcinoma, HDAC3 deficiency impaired DNA damage response and enhanced radiotherapy sensitivity in vitro and in vivo. Taken together, we demonstrated that HDAC3 deficiency interferes with liver homeostasis, which is more dependent on the accumulation of DNA damage in hepatocytes than on transcriptional dysregulation. Our findings support the hypothesis that selective HDAC3 inhibition has the potential to augment the effect of chemoradiotherapy aimed at inducing DNA damage in cancer therapy.

Hepatocyte-specific HDAC3 ablation promotes hepatocellular carcinoma in females by suppressing Foxa1/2.

BACKGROUND: Hepatocellular carcinoma (HCC), the most common primary liver cancer, prevails mainly in males and has long been attributed to androgens and higher circumstantial levels of interleukin-6 (IL-6) produced by resident hepatic macrophages. METHODS: Constitutively hepatocyte-specific histone deacetylase 3 (HDAC3)-deficient (HDAC3LCKO) mice and constitutively hepatocyte-specific HDAC3 knockout and systemic IL-6 simultaneously ablated (HDAC3LCKO& IL-6-/-) mice were used in our study to explore the causes of sex differences in HCC. Additionally, we performed human HCC tissues with an IHC score. Correlation analysis and linear regression plots were constructed to reveal the association between HDAC3 and its candidate genes. To further elucidate that HDAC3 controls the expression of Foxa1/2, we knocked down HDAC3 in HUH7 liver cancer cells. RESULTS: We observed a contrary sex disparity, with an earlier onset and higher incidence of HCC in female mice when HDAC3 was selectively ablated in the liver. Loss of HDAC3 led to constant liver injury and the spontaneous development of HCC. Unlike the significant elevation of IL-6 in male mice at a very early age, female mice exhibit stable IL-6 levels, and IL-6 ablation did not eliminate the sex disparity in hepatocarcinogenesis in HDAC3-deficient mice. Oestrogen often protects the liver when combined with oestrogen receptor alpha (ERα); however, ovariectomy in HDAC3-ablated female mice significantly delayed tumourigenesis. The oestrogen-ERα axis can also play a role in tumour promotion in the absence of Foxa1 and Foxa2 in the receptor complex. Loss of HDAC3 profoundly reduced the expression of both Foxa1 and Foxa2 and impaired the binding between Foxa1/2 and ERα. Furthermore, a more frequent HDAC3 decrease accompanied by the simultaneous Foxa1/2 decline was found in female HCC compared to that in male HCC. CONCLUSION: In summary, we reported that loss of HDAC3 reduces Foxa1/2 and thus promotes HCC development in females in an oestrogen-dependent manner.

Brahma-Related Gene 1 Inhibition Prevents Liver Fibrosis and Cholangiocarcinoma by Attenuating Progenitor Expansion.

BACKGROUND AND AIMS: Intrahepatic cholangiocarcinoma (iCCA) is closely correlated with hepatic progenitor cell (HPC) expansion and liver fibrosis. Brahma-related gene 1 (Brg1), an enzymatic subunit of the switch/sucrose nonfermentable complex that is critical in stem cell maintenance and tumor promotion, is prominently up-regulated in both HPCs and iCCA; however, its role in this correlation remains undefined. APPROACH AND RESULTS: A retrospective cohort study indicated that high Brg1 expression suggests poor prognosis in patients with iCCA. In chronically injured livers induced by a 0.1% 3,5-diethoxycarbonyl-1,4-dihydrocollidine diet or bile duct ligation surgery, HPCs were dramatically activated, as indicated by their enhanced expression of Brg1 and a subset of stem cell markers; however, Brg1 ablation in HPCs strongly suppressed HPC expansion and liver fibrosis. Furthermore, in a chemically induced iCCA model, inhibition of Brg1 by a specific inhibitor or inducible gene ablation markedly improved histology and suppressed iCCA growth. Mechanistically, in addition to transcriptionally promoting both Wnt receptor genes and target genes, Brg1 was found to bind to the ß-catenin/transcription factor 4 transcription complex, suggesting a possible approach for regulation of Wnt/ß-catenin signaling. CONCLUSIONS: We have demonstrated the function of Brg1 in promoting HPC expansion, liver cirrhosis, and, ultimately, iCCA development in chronically injured livers, which is largely dependent on Wnt/ß-catenin signaling. Our data suggest that therapies targeting Brg1-expressing HPCs are promising for the treatment of liver cirrhosis and iCCA.

Enhanced SMARCD1, a subunit of the SWI/SNF complex, promotes liver cancer growth through the mTOR pathway.

The chromatin remodeling complex SWI/SNF regulates the accessibility of target genes to transcription factors and plays a critical role in the tumorigenesis of hepatocellular carcinoma (HCC). The SWI/SNF complex is assembled from approximately 15 subunits, and most of these subunits have distinct roles and are often aberrantly expressed in HCC. A comprehensive exploration of the expression and clinical significance of these subunits would be of great value. In the present study, we obtained the gene expression profile of each SWI/SNF subunit and the corresponding clinical information from The Cancer Genome Atlas (TCGA). We found that 14 out of the 15 SWI/SNF subunits were significantly increased in HCC tissues compared with paired normal liver tissues, and 11 subunits were significantly associated with overall survival (OS). We identified a four-gene prognostic signature including actin-like 6A (ACTL6A), AT-rich interaction domain 1A (ARID1A), SWI/SNF related, matrix associated, actin dependent regulator of chromatin subfamily C member 1 (SMARCC1) and SWI/SNF related, matrix associated, actin dependent regulator of chromatin, subfamily D, member 1 (SMARCD1) that could effectively predict OS in HCC patients. Among the genes, SMARCD1 has the most prognostic value. We further conducted in vitro and in vivo experiments and revealed that SMARCD1 promotes liver cancer growth by activating the mTOR signaling pathway. In conclusion, our study has revealed that the expression of SWI/SNF complex subunits, especially SMARCD1, is highly associated with HCC development and acts as a promising prognostic predictor.

Glutamine synthetase-negative hepatocellular carcinoma has better prognosis and response to sorafenib treatment after hepatectomy.

BACKGROUND: Glutamine synthetase (GS) and arginase 1 (Arg1) are widely used pathological markers that discriminate hepatocellular carcinoma (HCC) from intrahepatic cholangiocarcinoma; however, their clinical significance in HCC remains unclear. METHODS: We retrospectively analyzed 431 HCC patients: 251 received hepatectomy alone, and the other 180 received sorafenib as adjuvant treatment after hepatectomy. Expression of GS and Arg1 in tumor specimens was evaluated using immunostaining. mRNA sequencing and immunostaining to detect progenitor markers (cytokeratin 19 [CK19] and epithelial cell adhesion molecule [EpCAM]) and mutant TP53 were also conducted. RESULTS: Up to 72.4% (312/431) of HCC tumors were GS positive (GS+). Of the patients receiving hepatectomy alone, GS negative (GS-) patients had significantly better overall survival (OS) and recurrence-free survival (RFS) than GS+ patients; negative expression of Arg1, which is exclusively expressed in GS- hepatocytes in the healthy liver, had a negative effect on prognosis. Of the patients with a high risk of recurrence who received additional sorafenib treatment, GS- patients tended to have better RFS than GS+ patients, regardless of the expression status of Arg1. GS+ HCC tumors exhibit many features of the established proliferation molecular stratification subtype, including poor differentiation, high alpha-fetoprotein levels, increased progenitor tumor cells, TP53 mutation, and upregulation of multiple tumor-related signaling pathways. CONCLUSIONS: GS- HCC patients have a better prognosis and are more likely to benefit from sorafenib treatment after hepatectomy. Immunostaining of GS may provide a simple and applicable approach for HCC molecular stratification to predict prognosis and guide targeted therapy.

Mettl14-Mediated m6A Modification Facilitates Liver Regeneration by Maintaining Endoplasmic Reticulum Homeostasis.

BACKGROUND & AIMS: N6-methyladenosine (m6A), the most prevalent and dynamic posttranscriptional methylation modification of mammalian mRNA, is involved in various biological processes, but its role in liver regeneration has not been characterized. METHODS: We first conducted transcriptome-wide m6A mRNA sequencing and characterized the expression pattern of m6A in regenerating mouse liver. Next, we generated hepatocyte-specific Mettl3- or Mettl14-deficient mice and investigated their role in liver regeneration. A series of biochemical experiments in vitro and in vivo was further performed to investigate potential mechanisms. RESULTS: We identified an overwhelming proportion of m6A-modified genes with initially up-regulated and subsequently down-regulated m6A levels as liver regeneration progressed. Loss of Mettl14 but not of Mettl3 resulted in markedly disrupted liver regeneration, and Mettl14-ablated hepatocytes were arrested in the G1 phase of the cell cycle. Most strikingly, the Mettl14-ablated regenerating liver exhibited extensive parenchymal necrosis. mRNA transcripts, such as Hsp90b1, Erp29, Stt3a, P4hb, and Lman1, encoding proteins involved in polypeptide processing and the endoplasmic reticulum (ER) stress response, were m6A-hypomethylated, and their mRNA and protein levels were subsequently decreased, resulting in unresolved ER stress, hepatocyte death, and inhibited proliferation. CONCLUSIONS: We demonstrate the essential role of Mettl14 in facilitating liver regeneration by modulating polypeptide-processing proteins in the ER in an m6A-dependent manner.

Loss of Numb promotes hepatic progenitor expansion and intrahepatic cholangiocarcinoma by enhancing Notch signaling.

Numb, a stem cell fate determinant, acts as a tumor suppressor and is closely related to a wide variety of malignancies. Intrahepatic cholangiocarcinoma (iCCA) originates from hepatic progenitors (HPCs); however, the role of Numb in HPC malignant transformation and iCCA development is still unclear. A retrospective cohort study indicated that Numb was frequently decreased in tumor tissues and suggests poor prognosis in iCCA patients. Consistently, in a chemically induced iCCA mouse model, Numb was downregulated in tumor cells compared to normal cholangiocytes. In diet-induced chronic liver injury mouse models, Numb ablation significantly promoted histological impairment, HPC expansion, and tumorigenesis. Similarly, Numb silencing in cultured iCCA cells enhanced cell spheroid growth, invasion, metastasis, and the expression of stem cell markers. Mechanistically, Numb was found to bind to the Notch intracellular domain (NICD), and Numb ablation promoted Notch signaling; this effect was reversed when Notch signaling was blocked by γ-secretase inhibitor treatment. Our results suggested that loss of Numb plays an important role in promoting HPC expansion, HPC malignant transformation, and, ultimately, iCCA development in chronically injured livers. Therapies targeting suppressed Numb are promising for the treatment of iCCA.

Exosomes derived from human umbilical cord mesenchymal stem cells ameliorate IL-6-induced acute liver injury through miR-455-3p.

BACKGROUND: Using a toxin-induced nonhuman primate model of acute liver failure (ALF), we previously reported that peripheral infusion of human umbilical cord mesenchymal stem cells (hUC-MSCs) strongly suppresses the activation of circulating monocytes and interleukin-6 (IL-6) production, thereby disrupting the development of a cytokine storm and improving the prognosis of monkeys. MSCs are considered to play a therapeutic role under different stresses by adaptively producing specific factors, prompting us to investigate the factors that hUC-MSCs produce in response to high serum levels of IL-6, which plays a critical role in initiating and accelerating ALF. METHODS: We stimulated hUC-MSCs with IL-6, and the hUC-MSC-derived exosomes were deeply sequenced. The miRNAs in the exosomes that have potential to suppress IL-6-associated signaling pathway were screened, and the role of one of the most possible miRNAs was tested in the mouse model of inflammatory liver injury. RESULT: We determined that miR-455-3p, which is secreted through exosomes and potentially targets PI3K signaling, was highly produced by hUC-MSCs with IL-6 stimulation. The miR-455-3p-enriched exosomes could inhibit the activation and cytokine production of macrophages challenged with lipopolysaccharide (LPS) both in vivo and in vitro. In a chemical liver injury mouse model, enforced expression of miR-455-3p could attenuate macrophage infiltration and local liver damage and reduce the serum levels of inflammatory factors, thereby improving liver histology and systemic disorder. CONCLUSIONS: miR-455-3p-enriched exosomes derived from hUC-MSCs are a promising therapy for acute inflammatory liver injury.