Activation of LKB1-Akt pathway independent of phosphoinositide 3-kinase plays a critical role in the proliferation of hepatocellular carcinoma from nonalcoholic steatohepatitis

Deciphering the roles of neddylation modification in hepatocellular carcinoma: Molecular mechanisms and targeted therapeutics

Hepatocellular carcinoma (HCC) is the most prevalent type of malignant liver tumor with high morbidity and mortality and severely threatens human health and life quality. Thus, it is of great significance to investigate the molecular mechanism underlying the pathogenesis of HCC and seek biomarkers for early diagnosis. Neddylation, one of the most conserved post-translational modification types in eukaryotes, plays vital roles in the progression of HCC. During the process of neddylation, NEDD8 is covalently conjugated to its substrate proteins, thereby modulating multiple necessary biological processes. Currently, increasing evidence shows that the aberrant activation of neddylation is positively correlated with the occurrence and development of tumors and the poor clinical prognosis of HCC patients. Based on the current investigations, neddylation modification has been reported to target both the cullins and non-cullin substrates and subsequently affect HCC progression, including the virus infection, malignant transformation, tumor cell proliferation, migration and invasion ability, and tumor microenvironment. Therefore, inhibitors targeting the neddylation cascade have been developed and entered clinical trials, indicating satisfactory anti-HCC treatment effects. This review aims to summarize the latest progress in the molecular mechanism of pathologically aberrant neddylation in HCC, as well as the advances of neddylation-targeted inhibitors as potential drugs for HCC treatment.

UBA protein family: An emerging set of E1 ubiquitin ligases in cancer-A review

The Ubiquitin A (UBA) protein family contains seven members that protect themselves or their interacting proteins from proteasome degradation. The UBA protein family regulates cell proliferation, cell cycle, invasion, migration, apoptosis, autophagy, tissue differentiation, and immune response. With the deepening of research, the UBA protein family has been found to be abnormally expressed in a variety of tumor diseases, and the clarification of its relationship with tumor diseases can be used as a molecular therapeutic target and have an important role in the prognosis of tumors. In this paper, we review the structure, biological process, target therapy, and biomarkers of the UBA protein family to provide new ideas for the diagnosis and treatment of tumors.

Fructose-induced progression of steatohepatitis involves disrupting aldolase B-AMPK signaling in methionine adenosyltransferase 1A deficient mice

OBJECTIVE

Aldolases (ALDO) are sensors that regulate AMPK via binding to fructose 1,6-biphosphate (FBP), an intermediate of glucose and fructose metabolism. Fructose consumption is linked to metabolic dysfunction-associated steatotic liver disease (MASLD) progression but whether ALDO-AMPK signaling is involved is unknown. Methionine adenosyltransferase alpha 1 (Mat1a) knockout (KO) mice have low hepatic S-adenosylmethionine (SAMe) level and spontaneously develop steatohepatitis. ALDOB methylation has not been reported and here we investigated whether SAMe level regulates ALDOB and ALDOB-AMPK signaling and whether fructose feeding accelerates MASLD progression by disrupting ALDOB-AMPK signaling.

METHODS

Mass spectrometry identified ALDOB methylation sites and recombinant in vitro approaches assessed how methylation at those sites affects ALDOB oligomerization and activity. Primary hepatocytes cultured with high/low glucose and/or fructose and wild type (WT) and Mat1a KO mice fed with a high-fructose diet examined AMPK-ALDOB signaling and MASLD progression.

RESULTS

In Mat1a KO livers ALDOB R173 is hypomethylated while ALDOB activity is enhanced. Recombinant ALDOB is methylated at R173 and R304 by protein arginine methyltransferase 1. Low hepatic SAMe level results in hypomethylated ALDOB, which favors the tetrameric form that has higher enzymatic activity, and higher capacity to signal to activate AMPK. Fructose, independently of glucose levels, inhibited AMPK activity and induced lipid accumulation in hepatocytes. Mat1a KO mice have hyperactivated AMPK and fructose feeding inhibits it, enhancing the accumulation of fat in the liver and the progression of MASLD.

CONCLUSION

Hepatic SAMe levels regulate ALDOB oligomeric state and enzymatic activity impacting on AMPK signaling and fructose-induced MASLD progression.

S-Adenosylmethionine: A Multifaceted Regulator in Cancer Pathogenesis and Therapy

S-adenosylmethionine (SAMe) is a key methyl donor that plays a critical role in a variety of cellular processes, such as DNA, RNA and protein methylation, essential for maintaining genomic stability, regulating gene expression and maintaining cellular homeostasis. The involvement of SAMe in cancer pathogenesis is multifaceted, as through its multiple cellular functions, it can influence tumor initiation, progression and therapeutic resistance. In addition, the connection of SAMe with polyamine synthesis and oxidative stress management further underscores its importance in cancer biology. Recent studies have highlighted the potential of SAMe as a biomarker for cancer diagnosis and prognosis. Furthermore, the therapeutic implications of SAMe are promising, with evidence suggesting that SAMe supplementation or modulation could improve the efficacy of existing cancer treatments by restoring proper methylation patterns and mitigating oxidative damage and protect against damage induced by chemotherapeutic drugs. Moreover, targeting methionine cycle enzymes to both regulate SAMe availability and SAMe-independent regulatory effects, particularly in methionine-dependent cancers such as colorectal and lung cancer, presents a promising therapeutic approach. Additionally, exploring epitranscriptomic regulations, such as m6A modifications, and their interaction with non-coding RNAs could enhance our understanding of tumor progression and resistance mechanisms. Precision medicine approaches integrating patient subtyping and combination therapies with chemotherapeutics, such as decitabine or doxorubicin, together with SAMe, can enhance chemosensitivity and modulate epigenomics, showing promising results that may improve treatment outcomes. This review comprehensively examines the various roles of SAMe in cancer pathogenesis, its potential as a diagnostic and prognostic marker, and its emerging therapeutic applications. While SAMe modulation holds significant promise, challenges such as bioavailability, patient stratification and context-dependent effects must be addressed before clinical implementation. In addition, better validation of the obtained results into specific cancer animal models would also help to bridge the gap between research and clinical practice.

Peroxisome proliferator-activated receptors: Key regulators of tumor progression and growth

One of the main causes of death on the globe is cancer. Peroxisome-proliferator-activated receptors (PPARs) are nuclear hormone receptors, including PPARα, PPARδ and PPARγ, which are important in regulating cancer cell proliferation, survival, apoptosis, and tumor growth. Activation of PPARs by endogenous or synthetic compounds regulates tumor progression in various tissues. Although each PPAR isotype suppresses or promotes tumor development depending on the specific tissues or ligands, the mechanism is still unclear. PPARs are receiving interest as possible therapeutic targets for a number of disorders. Numerous clinical studies are being conducted on PPARs as possible therapeutic targets for cancer. Therefore, this review will focus on the existing and future uses of PPARs agonists and antagonists in treating malignancies. PubMed, Science Direct, and Scopus databases were searched regarding the effect of PPARs on various types of cancers until the end of May 2023. The results of the review articles showed the therapeutic influence of PPARs on a wide range of cancer on in vitro, in vivo and clinical studies. However, further experimental and clinical studies are needed to be conducted on the influence of PPARs on various cancers.

Ubiquitin-Specific Proteases (USPs) and Metabolic Disorders

Ubiquitination and deubiquitination are reversible processes that modify the characteristics of target proteins, including stability, intracellular localization, and enzymatic activity. Ubiquitin-specific proteases (USPs) constitute the largest deubiquitinating enzyme family. To date, accumulating evidence indicates that several USPs positively and negatively affect metabolic diseases. USP22 in pancreatic β-cells, USP2 in adipose tissue macrophages, USP9X, 20, and 33 in myocytes, USP4, 7, 10, and 18 in hepatocytes, and USP2 in hypothalamus improve hyperglycemia, whereas USP19 in adipocytes, USP21 in myocytes, and USP2, 14, and 20 in hepatocytes promote hyperglycemia. In contrast, USP1, 5, 9X, 14, 15, 22, 36, and 48 modulate the progression of diabetic nephropathy, neuropathy, and/or retinopathy. USP4, 10, and 18 in hepatocytes ameliorates non-alcoholic fatty liver disease (NAFLD), while hepatic USP2, 11, 14, 19, and 20 exacerbate it. The roles of USP7 and 22 in hepatic disorders are controversial. USP9X, 14, 17, and 20 in vascular cells are postulated to be determinants of atherosclerosis. Moreover, mutations in the Usp8 and Usp48 loci in pituitary tumors cause Cushing syndrome. This review summarizes the current knowledge about the modulatory roles of USPs in energy metabolic disorders.

The beneficial impact of metabolic dysfunction-associated fatty liver disease on lenvatinib treatment in patients with non-viral hepatocellular carcinoma

AIM

Lenvatinib is used to treat advanced hepatocellular carcinoma (HCC). Metabolic dysfunction-associated fatty liver disease (MAFLD) is becoming a major etiology of HCC. We aimed to evaluate the impact of MAFLD on the efficacy of lenvatinib.

METHODS

We enrolled 320 patients with HCC who were treated with lenvatinib. All patients were classified into the MAFLD (n = 155) and non-MAFLD (n = 165) groups. Independent factors for overall survival (OS) were analyzed. In the stratification analysis, HCC was categorized as non-viral (n = 115) or viral HCC (n = 205).

RESULTS

The OS rate was significantly higher in the MAFLD group than in the non-MAFLD group (median 21.1 vs. 15.1 months, p = 0.002). Multivariate analysis demonstrated that, in addition to albumin-bilirubin grade and Barcelona Clinic Liver Cancer stage, MAFLD was identified as an independent factor for OS (HR 0.722, 95% CI 0.539-0.966, p = 0.028). In the stratification analysis, the OS rate was significantly higher in the MAFLD group than in the non-MAFLD group among patients with non-viral HCC (median 21.1 vs. 15.1 months, p = 0.002), but not in patients with viral HCC. Furthermore, MAFLD was an independent negative risk factor for OS in patients with non-viral HCC (HR 0.506, 95% CI 0.297-0.864, P < 0.01). However, MAFLD was not an independent factor for OS in patients with viral HCC.

CONCLUSIONS

MAFLD was a beneficial factor for survival in patients with HCC treated with lenvatinib. Moreover, the better OS of the MAFLD group was more pronounced in patients with non-viral HCC. Lenvatinib may be a suitable agent for patients with non-viral HCC and MAFLD.

Hyperphosphorylation of hepatic proteome characterizes nonalcoholic fatty liver disease in S-adenosylmethionine deficiency

Methionine adenosyltransferase 1a (MAT1A) is responsible for hepatic S-adenosyl-L-methionine (SAMe) biosynthesis. Mat1a ^-/- mice have hepatic SAMe depletion, develop nonalcoholic steatohepatitis (NASH) which is reversed with SAMe administration. We examined temporal alterations in the proteome/phosphoproteome in pre-disease and NASH Mat1a ^-/- mice, effects of SAMe administration, and compared to human nonalcoholic fatty liver disease (NAFLD). Mitochondrial and peroxisomal lipid metabolism proteins were altered in pre-disease mice and persisted in NASH Mat1a ^-/- mice, which exhibited more progressive alterations in cytoplasmic ribosomes, ER, and nuclear proteins. A common mechanism found in both pre-disease and NASH livers was a hyperphosphorylation signature consistent with casein kinase 2α (CK2α) and AKT1 activation, which was normalized by SAMe administration. This was mimicked in human NAFLD with a metabolomic signature (M-subtype) resembling Mat1a ^-/- mice. In conclusion, we have identified a common proteome/phosphoproteome signature between Mat1a ^-/- mice and human NAFLD M-subtype that may have pathophysiological and therapeutic implications.

Genetic Predisposition to Hepatocellular Carcinoma

Liver preneoplastic and neoplastic lesions of the genetically susceptible F344 and resistant BN rats cluster, respectively, with human HCC with better (HCCB) and poorer prognosis (HCCP); therefore, they represent a valid model to study the molecular alterations determining the genetic predisposition to HCC and the response to therapy. The ubiquitin-mediated proteolysis of ERK-inhibitor DUSP1, which characterizes HCC progression, favors the unrestrained ERK activity. DUSP1 represents a valuable prognostic marker, and ERK, CKS1, or SKP2 are potential therapeutic targets for human HCC. In DN (dysplastic nodule) and HCC of F344 rats and human HCCP, DUSP1 downregulation and ERK1/2 overexpression sustain SKP2-CKS1 activity through FOXM1, the expression of which is associated with a susceptible phenotype. SAM-methyl-transferase reactions and SAM/SAH ratio are regulated by GNMT. In addition, GNMT binds to CYP1A, PARP1, and NFKB and PREX2 gene promoters. MYBL2 upregulation deregulates cell cycle and induces the progression of premalignant and malignant liver. During HCC progression, the MYBL2 transcription factor positively correlates with cells proliferation and microvessel density, while it is negatively correlated to apoptosis. Hierarchical supervised analysis, regarding 6132 genes common to human and rat liver, showed a gene expression pattern common to normal liver of both strains and BN nodules, and a second pattern is observed in F344 nodules and HCC of both strains. Comparative genetics studies showed that DNs of BN rats cluster with human HCCB, while F344 DNs and HCCs cluster with HCCP.

Hu Antigen R (HuR) Protein Structure, Function and Regulation in Hepatobiliary Tumors

Hu antigen R (HuR) is a 36-kDa ubiquitous member of the ELAV/Hu family of RNA-binding proteins (RBPs), which plays an important role as a post-transcriptional regulator of specific RNAs under physiological and pathological conditions, including cancer. Herein, we review HuR protein structure, function, and its regulation, as well as its implications in the pathogenesis, progression, and treatment of hepatobiliary cancers. In particular, we focus on hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA), tumors where the increased cytoplasmic localization of HuR and activity are proposed, as valuable diagnostic and prognostic markers. An overview of the main regulatory axes involving HuR, which are associated with cell proliferation, invasion, metastasis, apoptosis, and autophagy in HCC, is provided. These include the transcriptional, post-transcriptional, and post-translational modulators of HuR function, in addition to HuR target transcripts. Finally, whereas studies addressing the relevance of targeting HuR in CCA are limited, in the past few years, HuR has emerged as a potential therapeutic target in HCC. In fact, the therapeutic efficacy of some pharmacological inhibitors of HuR has been evaluated, in early experimental models of HCC. We, further, discuss the major findings and future perspectives of therapeutic approaches that specifically block HuR interactions, either with post-translational modifiers or cognate transcripts in hepatobiliary cancers.

Angelica gigas NAKAI and Its Active Compound, Decursin, Inhibit Cellular Injury as an Antioxidant by the Regulation of AMP-Activated Protein Kinase and YAP Signaling

Natural products and medicinal herbs have been used to treat various human diseases by regulating cellular functions and metabolic pathways. Angelica gigas NAKAI (AG) helps regulate pathological processes in some medical fields, including gastroenterology, gynecology, and neuropsychiatry. Although some papers have reported its diverse indications, the effects of AG against arachidonic acid (AA)+ iron and carbon tetrachloride (CCl₄) have not been reported. In HepG2 cells, AA+ iron induced cellular apoptosis and mitochondrial damage, as assessed by mitochondrial membrane permeability (MMP) and the expression of apoptosis-related proteins. On the other hand, AG markedly inhibited these detrimental phenomena and reactive oxygen species (ROS) production induced by AA+ iron. AG activated the liver kinase B1 (LKB1)-dependent AMP-activated protein kinase (AMPK), which affected oxidative stress in the cells. Moreover, AG also regulated the expression of yes-associated protein (YAP) signaling as mediated by the AMPK pathways. In mice, an oral treatment of AG protected against liver toxicity induced by CCl₄, as indicated by the plasma and histochemical parameters. Among the compounds in AG, decursin had antioxidant activity and affected the AMPK pathway. In conclusion, AG has antioxidant effects in vivo and in vitro, indicating that natural products such as AG could be potential candidate for the nutraceuticals to treat various disorders by regulating mitochondrial dysfunction and cellular metabolic pathways.

S-Adenosylmethionine: From the Discovery of Its Inhibition of Tumorigenesis to Its Use as a Therapeutic Agent

Alterations of methionine cycle in steatohepatitis, cirrhosis, and hepatocellular carcinoma induce MAT1A decrease and MAT2A increase expressions with the consequent decrease of S-adenosyl-L-methionine (SAM). This causes non-alcoholic fatty liver disease (NAFLD). SAM administration antagonizes pathological conditions, including galactosamine, acetaminophen, and ethanol intoxications, characterized by decreased intracellular SAM. Positive therapeutic effects of SAM/vitamin E or SAM/ursodeoxycholic acid in animal models with NAFLD and intrahepatic cholestasis were not confirmed in humans. In in vitro experiments, SAM and betaine potentiate PegIFN-alpha-2a/2b plus ribavirin antiviral effects. SAM plus betaine improves early viral kinetics and increases interferon-stimulated gene expression in patients with viral hepatitis non-responders to pegIFNα/ribavirin. SAM prevents hepatic cirrhosis, induced by CCl4, inhibits experimental tumors growth and is proapoptotic for hepatocellular carcinoma and MCF-7 breast cancer cells. SAM plus Decitabine arrest cancer growth and potentiate doxorubicin effects on breast, head, and neck cancers. Furthermore, SAM enhances the antitumor effect of gemcitabine against pancreatic cancer cells, inhibits growth of human prostate cancer PC-3, colorectal cancer, and osteosarcoma LM-7 and MG-63 cell lines; increases genomic stability of SW480 cells. SAM reduces colorectal cancer progression and inhibits the proliferation of preneoplastic rat liver cells in vivo. The discrepancy between positive results of SAM treatment of experimental tumors and modest effects against human disease may depend on more advanced human disease stage at moment of diagnosis.

Genetics, Immunity and Nutrition Boost the Switching from NASH to HCC

Nonalcoholic fatty liver disease (NAFLD) is the leading contributor to the global burden of chronic liver diseases. The phenotypic umbrella of NAFLD spans from simple and reversible steatosis to nonalcoholic steatohepatitis (NASH), which may worsen into cirrhosis and hepatocellular carcinoma (HCC). Notwithstanding, HCC may develop also in the absence of advanced fibrosis, causing a delayed time in diagnosis as a consequence of the lack of HCC screening in these patients. The precise event cascade that may precipitate NASH into HCC is intricate and it entails diverse triggers, encompassing exaggerated immune response, endoplasmic reticulum (ER) and oxidative stress, organelle derangement and DNA aberrancies. All these events may be accelerated by both genetic and environmental factors. On one side, common and rare inherited variations that affect hepatic lipid remodeling, immune microenvironment and cell survival may boost the switching from steatohepatitis to liver cancer, on the other, diet-induced dysbiosis as well as nutritional and behavioral habits may furtherly precipitate tumor onset. Therefore, dietary and lifestyle interventions aimed to restore patients' health contribute to counteract NASH progression towards HCC. Even more, the combination of therapeutic strategies with dietary advice may maximize benefits, with the pursuit to improve liver function and prolong survival.

No Tumor Suppressor Role for LKB1 in Prostate Cancer

To elucidate the pathogenesis of prostate diseases, following in silico analysis, the LKB1 gene was selected for further investigation. The LKB1 gene has been associated with poor prognosis and is frequently mutated in different types of cancers. In this study, 50 benign prostatic hyperplasia (BPH) and 57 prostate cancer (PCa) tissues, including matched normal tissue for the patients, were analyzed by qRT-PCR and DNA sequencing for LKB1 expression and the mutation profile, respectively. Expression of LKB1 was increased in 60.7% of the PCa tissues compared with noncancerous tissue samples (p ≤ 0.001). However, LKB1 expression was lower when compared with normal tissues in BPH (p = 0.920). Four coding sequence alterations were detected in BPH. Three silent mutations were located in codons 9, 32, and 275 and a missense mutation was observed in codon 384. Six alterations were identified in the intronic regions of the LKB1 gene in both PCa and BPH. Five mutations were observed in both patient groups. A new alteration in intron 6 was observed in a patient with PCa. The LKB1 gene may be associated with benign transformations rather than the tumors in prostate pathogenesis when its expression and mutation status are considered. However, the mechanism of LKB1 in PCa needs further studies.

HuR Protein in Hepatocellular Carcinoma: Implications in Development, Prognosis and Treatment

Hu-antigen R (HuR) is a post-transcriptional regulator that belongs to the embryonic lethal abnormal vision Drosophila-like family (ELAV). HuR regulates the stability, translation, subcellular localization, and degradation of several target mRNAs, which are implicated in carcinogenesis and could affect therapeutic options. HuR protein is consistently highly expressed in hepatocellular carcinoma (HCC) compared to the adjacent normal liver tissue and is involved in the post-transcriptional regulation of various genes implicated in liver malignant transformation. Additionally, HuR protein seems to be a putative prognosticator in HCC, predicting worse survival. This review summarizes the recent evidence regarding the role of HuR in primary liver tumors, as presented in clinical studies, in vitro experiments and in vivo animal models. In conclusion, our review supports the consistent role of HuR protein in the development, prognosis, and treatment of HCC. Additional studies are expected to expand current information and exploit its putative employment as a future candidate for more personalized treatment in these tumors.

Naa20, the catalytic subunit of NatB complex, contributes to hepatocellular carcinoma by regulating the LKB1-AMPK-mTOR axis

N-α-acetyltransferase 20 (Naa20), which is a catalytic subunit of the N-terminal acetyltransferase B (NatB) complex, has recently been reported to be implicated in hepatocellular carcinoma (HCC) progression and autophagy, but the underlying mechanism remains unclear. Here, we report that based on bioinformatic analysis of Gene Expression Omnibus and The Cancer Genome Atlas data sets, Naa20 expression is much higher in HCC tumors than in normal tissues, promoting oncogenic properties in HCC cells. Mechanistically, Naa20 inhibits the activity of AMP-activated protein kinase (AMPK) to promote the mammalian target of rapamycin signaling pathway, which contributes to cell proliferation, as well as autophagy, through its N-terminal acetyltransferase (NAT) activity. We further show that liver kinase B1 (LKB1), a major regulator of AMPK activity, can be N-terminally acetylated by NatB in vitro, but also probably by NatB and/or other members of the NAT family in vivo, which may have a negative effect on AMPK activity through downregulation of LKB1 phosphorylation at S428. Indeed, p-LKB1 (S428) and p-AMPK levels are enhanced in Naa20-deficient cells, as well as in cells expressing the nonacetylated LKB1-MPE mutant; moreover, importantly, LKB1 deficiency reverses the molecular and cellular events driven by Naa20 knockdown. Taken together, our findings suggest that N-terminal acetylation of LKB1 by Naa20 may inhibit the LKB1-AMPK signaling pathway, which contributes to tumorigenesis and autophagy in HCC.

Reciprocal Regulation Between Forkhead Box M1/NF-κB and Methionine Adenosyltransferase 1A Drives Liver Cancer

BACKGROUND AND AIMS

Forkhead box M1 (FOXM1) and nuclear factor kappa B (NF-ĸB) are oncogenic drivers in liver cancer that positively regulate each other. We showed that methionine adenosyltransferase 1A (MAT1A) is a tumor suppressor in the liver and inhibits NF-ĸB activity. Here, we examined the interplay between FOXM1/NF-κB and MAT1A in liver cancer.

APPROACH AND RESULTS

We examined gene and protein expression, effects on promoter activities and binding of proteins to promoter regions, as well as effects of FOXM1 inhibitors T0901317 (T0) and forkhead domain inhibitory-6 (FDI-6) in vitro and in xenograft and syngeneic models of liver cancer. We found, in both hepatocellular carcinoma and cholangiocarcinoma, that an induction in FOXM1 and NF-κB expression is accompanied by a fall in MATα1 (protein encoded by MAT1A). The Cancer Genome Atlas data set confirmed the inverse correlation between FOXM1 and MAT1A. Interestingly, FOXM1 directly interacts with MATα1 and they negatively regulate each other. In contrast, FOXM1 positively regulates p50 and p65 expression through MATα1, given that the effect is lost in its absence. FOXM1, MATα1, and NF-κB all bind to the FOX binding sites in the FOXM1 and MAT1A promoters. However, binding of FOXM1 and NF-κB repressed MAT1A promoter activity, but activated the FOXM1 promoter. In contrast, binding of MATα1 repressed the FOXM1 promoter. MATα1 also binds and represses the NF-κB element in the presence of p65 or p50. Inhibiting FOXM1 with either T0 or FDI-6 inhibited liver cancer cell growth in vitro and in vivo. However, inhibiting FOXM1 had minimal effects in liver cancer cells that do not express MAT1A.

CONCLUSIONS

We have found a crosstalk between FOXM1/NF-κB and MAT1A. Up-regulation in FOXM1 lowers MAT1A, but raises NF-κB, expression, and this is a feed-forward loop that enhances tumorigenesis.

mRNA Post-Transcriptional Regulation by AU-Rich Element-Binding Proteins in Liver Inflammation and Cancer

AU-rich element-binding proteins (AUBPs) represent important post-transcriptional regulators of gene expression. AUBPs can bind to the AU-rich elements present in the 3'-UTR of more than 8% of all mRNAs and are thereby able to control the stability and/or translation of numerous target mRNAs. The regulation of the stability and the translation of mRNA transcripts by AUBPs are highly complex processes that occur through multiple mechanisms depending on the cell type and the cellular context. While AUBPs have been shown to be involved in inflammatory processes and the development of various cancers, their important role and function in the development of chronic metabolic and inflammatory fatty liver diseases (FLDs), as well as in the progression of these disorders toward cancers such as hepatocellular carcinoma (HCC), has recently started to emerge. Alterations of either the expression or activity of AUBPs are indeed significantly associated with FLDs and HCC, and accumulating evidence indicates that several AUBPs are deeply involved in a significant number of cellular processes governing hepatic metabolic disorders, inflammation, fibrosis, and carcinogenesis. Herein, we discuss our current knowledge of the roles and functions of AUBPs in liver diseases and cancer. The relevance of AUBPs as potential biomarkers for different stages of FLD and HCC, or as therapeutic targets for these diseases, are also highlighted.

PINE: An Automation Tool to Extract and Visualize Protein-Centric Functional Networks

Recent surges in mass spectrometry-based proteomics studies demand a concurrent rise in speedy and optimized data processing tools and pipelines. Although several stand-alone bioinformatics tools exist that provide protein-protein interaction (PPI) data, we developed Protein Interaction Network Extractor (PINE) as a fully automated, user-friendly, graphical user interface application for visualization and exploration of global proteome and post-translational modification (PTM) based networks. PINE also supports overlaying differential expression, statistical significance thresholds, and PTM sites on functionally enriched visualization networks to gain insights into proteome-wide regulatory mechanisms and PTM-mediated networks. To illustrate the relevance of the tool, we explore the total proteome and its PTM-associated relationships in two different nonalcoholic steatohepatitis (NASH) mouse models to demonstrate different context-specific case studies. The strength of this tool relies in its ability to (1) perform accurate protein identifier mapping to resolve ambiguity, (2) retrieve interaction data from multiple publicly available PPI databases, and (3) assimilate these complex networks into functionally enriched pathways, ontology categories, and terms. Ultimately, PINE can be used as an extremely powerful tool for novel hypothesis generation to understand underlying disease mechanisms.

The role of MDM2-p53 axis dysfunction in the hepatocellular carcinoma transformation

Liver cancer is the second most frequent cause of cancer-related death globally. The main histological subtype is hepatocellular carcinoma (HCC), which is derived from hepatocytes. According to the epidemiologic studies, the most important risk factors of HCC are chronic viral infections (HBV, HCV, and HIV) and metabolic disease (metabolic syndrome). Interestingly, these carcinogenic factors that contributed to HCC are associated with MDM2-p53 axis dysfunction, which presented with inactivation of p53 and overactivation of MDM2 (a transcriptional target and negative regulator of p53). Mechanically, the homeostasis of MDM2-p53 feedback loop plays an important role in controlling the initiation and progression of HCC, which has been found to be dysregulated in HCC tissues. To maintain long-term survival in hepatocytes, hepatitis viruses have lots of ways to destroy the defense strategies of hepatocytes by inducing TP53 mutation and silencing, promoting MDM2 overexpression, accelerating p53 degradation, and stabilizing MDM2. As a result, genetic instability, chronic ER stress, oxidative stress, energy metabolism switch, and abnormalities in antitumor genes can be induced, all of which might promote hepatocytes' transformation into hepatoma cells. In addition, abnormal proliferative hepatocytes and precancerous cells cannot be killed, because of hepatitis viruses-mediated exhaustion of Kupffer cells and hepatic stellate cells (HSCs) and CD4+T cells by disrupting their MDM2-p53 axis. Moreover, inefficiency of hepatic immune response can be further aggravated when hepatitis viruses co-infected with HIV. Unlike with chronic viral infections, MDM2-p53 axis might play a dual role in glucolipid metabolism of hepatocytes, which presented with enhancing glucolipid catabolism, but promoting hepatocyte injury at the early and late stages of glucolipid metabolism disorder. Oxidative stress, fatty degeneration, and abnormal cell growth can be detected in hepatocytes that were suffering from glucolipid metabolism disorder, and all of which could contribute to HCC initiation. In this review, we focus on the current studies of the MDM2-p53 axis in HCC, and specifically discuss the impact of MDM2-p53 axis dysfunction by viral infection and metabolic disease in the transformation of normal hepatocytes into hepatoma cells. We also discuss the therapeutic avenues and potential targets that are being developed to normalize the MDM2-p53 axis in HCC.

The malignancy of liver cancer cells is increased by IL-4/ERK/AKT signaling axis activity triggered by irradiated endothelial cells

The malignant traits involved in tumor relapse, metastasis and the expansion of cancer stem-like cells are acquired via the epithelial-mesenchymal transition (EMT) process in the tumor microenvironment. In addition, the tumor microenvironment strongly supports the survival and growth of malignant tumor cells and further contributes to the reduced efficacy of anticancer therapy. Ionizing radiation can influence the tumor microenvironment, because it alters the biological functions of endothelial cells composing tumor vascular systems. However, to date, studies on the pivotal role of these endothelial cells in mediating the malignancy of cancer cells in the irradiated tumor microenvironment are rare. We previously evaluated the effects of irradiated endothelial cells on the malignant traits of human liver cancer cells and reported that endothelial cells irradiated with 2 Gy reinforce the malignant properties of these cancer cells. In this study, we investigated the signaling mechanisms underlying these events. We revealed that the increased expression level of IL-4 in endothelial cells irradiated with 2 Gy eventually led to enhanced migration and invasion of cancer cells and further expansion of cancer stem-like cells. In addition, this increased level of IL-4 activated the ERK and AKT signaling pathways to reinforce these events in cancer cells. Taken together, our data indicate that ionizing radiation may indirectly modulate malignancy by affecting endothelial cells in the tumor microenvironment. Importantly, these indirect effects on malignancy are thought to offer valuable clues or targets for overcoming the tumor recurrence after radiotherapy.

Hepatocellular carcinoma in the context of non-alcoholic steatohepatitis (NASH): recent advances in the pathogenic mechanisms

Hepatocellular carcinoma (HCC) is the most common type of liver cancer. HCC is particularly aggressive and is one of the leading causes of cancer mortality. In recent decades, the epidemiological landscape of HCC has undergone significant changes. While chronic viral hepatitis and excessive alcohol consumption have long been identified as the main risk factors for HCC, non-alcoholic steatohepatitis (NASH), paralleling the worldwide epidemic of obesity and type 2 diabetes, has become a growing cause of HCC in the US and Europe. Here, we review the recent advances in epidemiological, genetic, epigenetic and pathogenic mechanisms as well as experimental mouse models that have improved the understanding of NASH progression toward HCC. We also discuss the clinical management of patients with NASH-related HCC and possible therapeutic approaches.

Human antigen R: A potential therapeutic target for liver diseases

Human antigen R (HuR), also known as HuA and embryonic lethal abnormal vision-like 1 (ELAVL1), is a ubiquitously expressed RNA binding protein and functions as an RNA regulator and mediates the expression of various proteins by diverse post-transcriptional mechanisms. HuR has been well characterized in the inflammatory responses and in the development of various cancers. The importance of HuR-mediated roles in cell signaling, inflammation, fibrogenesis and cancer development in the liver has attracted a great deal of attention. However, there is still a substantial gap between the current understanding of the potential roles of HuR in the progression of liver disease and whether HuR can be targeted for the treatment of liver diseases. In this review, we introduce the function and mechanistic characterization of HuR, and then focus on the physiopathological roles of HuR in the development of different liver diseases, including hepatic inflammation, alcoholic liver diseases, non-alcoholic fatty liver diseases, viral hepatitis, liver fibrosis and liver cancers. We also summarize existing approaches targeting HuR function. In conclusion, although characterizing the liver-specific HuR function and demonstrating the multi-level regulative networks of HuR in the liver are still required, emerging evidence supports the notion that HuR represents a potential therapeutic target for the treatment of chronic liver diseases.

Methionine adenosyltransferases in liver cancer

Methionine adenosyltransferases (MATs) are essential enzymes for life as they produce S-adenosylmethionine (SAMe), the biological methyl donor required for a plethora of reactions within the cell. Mammalian systems express two genes, MAT1A and MAT2A, which encode for MATα1 and MATα2, the catalytic subunits of the MAT isoenzymes, respectively. A third gene MAT2B, encodes a regulatory subunit known as MATβ which controls the activity of MATα2. MAT1A, which is mainly expressed in hepatocytes, maintains the differentiated state of these cells, whilst MAT2A and MAT2B are expressed in extrahepatic tissues as well as non-parenchymal cells of the liver (e.g., hepatic stellate and Kupffer cells). The biosynthesis of SAMe is impaired in patients with chronic liver disease and liver cancer due to decreased expression and inactivation of MATα1. A switch from MAT1A to MAT2A/MAT2B occurs in multiple liver diseases and during liver growth and dedifferentiation, but this change in the expression pattern of MATs results in reduced hepatic SAMe level. Decades of study have utilized the Mat1a-knockout (KO) mouse that spontaneously develops non-alcoholic steatohepatitis (NASH) and hepatocellular carcinoma (HCC) to elucidate a variety of mechanisms by which MAT proteins dysregulation contributes to liver carcinogenesis. An increasing volume of work indicates that MATs have SAMe-independent functions, distinct interactomes and multiple subcellular localizations. Here we aim to provide an overview of MAT biology including genes, isoenzymes and their regulation to provide the context for understanding consequences of their dysregulation. We will highlight recent breakthroughs in the field and underscore the importance of MAT’s in liver tumorigenesis as well as their potential as targets for cancer therapy.

Expression tendency and prognostic value of TCF21 in hepatocellular carcinoma

BACKGROUND

Transcription factor 21 (TCF21) is identified as a tumor suppressor in a variety of human tumors. The purpose of the study was to examine its expression tendency and prognostic value in hepatocellular carcinoma (HCC).

METHODS

Relative expression of TCF21 mRNA in tissue samples from HCC patients and healthy volunteers were detected through quantitative real-time polymerase chain reaction (qRT-PCR) while its protein level was examined via immunohistochemistry analysis. Chi-square test was adopted to assess the association of TCF21 expression with the clinicopathological characteristic of the patients. Then Kaplan-Meier analysis was employed to analyze the function of TCF21 expression on overall survival among HCC patients.

RESULTS

Both the mRNA and protein levels of TCF21 were significantly reduced in HCC tissue samples compared with healthy controls (p < .05). Also, its expression was obviously affected by the classification of tissue pathology, metastasis, T stage, N stage and pathological grading. According to Kaplan-Meier analysis, patients with higher expression of TCF21 experienced dramatically longer overall survival time than those with lower expression (log rank test, p < .001).

CONCLUSIONS

TCF21 expression was decreased in HCC patients and it could act as a prognostic marker.

Alterations of Methionine Metabolism as Potential Targets for the Prevention and Therapy of Hepatocellular Carcinoma

Several researchers have analyzed the alterations of the methionine cycle associated with liver disease to clarify the pathogenesis of human hepatocellular carcinoma (HCC) and improve the preventive and the therapeutic approaches to this tumor. Different alterations of the methionine cycle leading to a decrease of S-adenosylmethionine (SAM) occur in hepatitis, liver steatosis, liver cirrhosis, and HCC. The reproduction of these changes in MAT1A-KO mice, prone to develop hepatitis and HCC, demonstrates the pathogenetic role of MAT1A gene under-regulation associated with up-regulation of the MAT2A gene (MAT1A:MAT2A switch), encoding the SAM synthesizing enzymes, methyladenosyltransferase I/III (MATI/III) and methyladenosyltransferase II (MATII), respectively. This leads to a rise of MATII, inhibited by the reaction product, with a consequent decrease of SAM synthesis. Attempts to increase the SAM pool by injecting exogenous SAM have beneficial effects in experimental alcoholic and non-alcoholic steatohepatitis and hepatocarcinogenesis. Mechanisms involved in hepatocarcinogenesis inhibition by SAM include: (1) antioxidative effects due to inhibition of nitric oxide (NO•) production, a rise in reduced glutathione (GSH) synthesis, stabilization of the DNA repair protein Apurinic/Apyrimidinic Endonuclease 1 (APEX1); (2) inhibition of c-myc, H-ras, and K-ras expression, prevention of NF-kB activation, and induction of overexpression of the oncosuppressor PP2A gene; (3) an increase in expression of the ERK inhibitor DUSP1; (4) inhibition of PI3K/AKT expression and down-regulation of C/EBPα and UCA1 gene transcripts; (5) blocking LKB1/AMPK activation; (6) DNA and protein methylation. Different clinical trials have documented curative effects of SAM in alcoholic liver disease. Furthermore, SAM enhances the IFN-α antiviral activity and protects against hepatic ischemia-reperfusion injury during hepatectomy in HCC patients with chronic hepatitis B virus (HBV) infection. However, although SAM prevents experimental tumors, it is not curative against already established experimental and human HCCs. The recent observation that the inhibition of MAT2A and MAT2B expression by miRNAs leads to a rise of endogenous SAM and strong inhibition of cancer cell growth could open new perspectives to the treatment of HCC.

Post-translational modifiers of liver kinase B1/serine/threonine kinase 11 in hepatocellular carcinoma

Liver kinase B1 (LKB1) also referred to as serine/threonine kinase 11 (STK11) encodes a 50 kDa evolutionary conserved serine/threonine kinase that is ubiquitously expressed in adult and fetal tissues. LKB1 is a master kinase known to phosphorylate and activate several kinases including AMP-activated protein kinase, a crucial cellular energy sensor. LKB1 shows pleiotropic activity playing diverse roles in multiple processes, including cell polarity and other processes relevant in cancer pathology, such as energy metabolism, proliferation and apoptosis. In spite of the fact that LKB1 is often considered a tumor suppressor in a wide variety of organs, in the last years, several studies have shown that LKB1 is unexpectedly high in hepatocellular carcinoma (HCC), the most common type of primary liver cancer. Post-translational modifications of LKB1 are potentially relevant in HCC. Herein, we provide a comprehensive revision of post-translational modifications of LKB1 in HCC and how they modulate LKB1 function by different mechanisms such as regulation of its activity, localization or stability. Overall, the signature post-translational modifications of LKB1 in HCC appear to play an important role in the rather unique role of LKB1 as an oncogenic driver in liver cancer and may provide an alternative valuable therapeutic approach to regulate LKB1 expression and/or activity in HCC.

Point your SmartPhone at the code above. If you have a QR code reader the video abstract will appear. Or use:

https://youtu.be/YCfD3s4OVcQ

SUMOylation regulates LKB1 localization and its oncogenic activity in liver cancer

BACKGROUND

Even though liver kinase B1 (LKB1) is usually described as a tumor suppressor in a wide variety of tissues, it has been shown that LKB1 aberrant expression is associated with bad prognosis in Hepatocellular Carcinoma (HCC).

METHODS

Herein we have overexpressed LKB1 in human hepatoma cells and by using histidine pull-down assay we have investigated the role of the hypoxia-related post-translational modification of Small Ubiquitin-related Modifier (SUMO)ylation in the regulation of LKB1 oncogenic role. Molecular modelling between LKB1 and its interactors, involved in regulation of LKB1 nucleocytoplasmic shuttling and LKB1 activity, was performed. Finally, high affinity SUMO binding entities-based technology were used to validate our findings in a pre-clinical mouse model and in clinical HCC.

FINDINGS

We found that in human hepatoma cells under hypoxic stress, LKB1 overexpression increases cell viability and aggressiveness in association with changes in LKB1 cellular localization. Moreover, by using site-directed mutagenesis, we have shown that LKB1 is SUMOylated by SUMO-2 at Lys178 hampering LKB1 nucleocytoplasmic shuttling and fueling hepatoma cell growth. Molecular modelling of SUMO modified LKB1 further confirmed steric impedance between SUMOylated LKB1 and the STe20-Related ADaptor cofactor (STRADα), involved in LKB1 export from the nucleus. Finally, we provide evidence that endogenous LKB1 is modified by SUMO in pre-clinical mouse models of HCC and clinical HCC, where LKB1 SUMOylation is higher in fast growing tumors.

INTERPRETATION

Overall, SUMO-2 modification of LKB1 at Lys178 mediates LKB1 cellular localization and its oncogenic role in liver cancer. FUND: This work was supported by grants from NIH (US Department of Health and Human services)-R01AR001576-11A1 (J.M.M and M.L.M-C.), Gobierno Vasco-Departamento de Salud 2013111114 (to M.L.M.-C), ELKARTEK 2016, Departamento de Industria del Gobierno Vasco (to M.L.M.-C), MINECO: SAF2017-87301-R and SAF2014-52097-R integrado en el Plan Estatal de Investigación Cientifica y Técnica y Innovación 2013-2016 cofinanciado con Fondos FEDER (to M.L.M.-C and J.M.M., respectively), BFU2015-71017/BMC MINECO/FEDER, EU (to A.D.Q. and I.D.M.), BIOEF (Basque Foundation for Innovation and Health Research): EITB Maratoia BIO15/CA/014; Instituto de Salud Carlos III:PIE14/00031, integrado en el Plan Estatal de Investigación Cientifica y Técnica y Innovacion 2013-2016 cofinanciado con Fondos FEDER (to M.L.M.-C and J.M.M), Asociación Española contra el Cáncer (T.C.D, P·F-T and M.L.M-C), Daniel Alagille award from EASL (to T.C.D), Fundación Científica de la Asociación Española Contra el Cancer (AECC Scientific Foundation) Rare Tumor Calls 2017 (to M.L.M and M.A), La Caixa Foundation Program (to M.L.M), Programma di Ricerca Regione-Università 2007-2009 and 2011-2012, Regione Emilia-Romagna (to E.V.), Ramón Areces Foundation and the Andalusian Government (BIO-198) (A.D.Q. and I.D.M.), ayudas para apoyar grupos de investigación del sistema Universitario Vasco IT971-16 (P.A.), MINECO:SAF2015-64352-R (P.A.), Institut National du Cancer, FRANCE, INCa grant PLBIO16-251 (M.S.R.), MINECO - BFU2016-76872-R to (E.B.). Work produced with the support of a 2017 Leonardo Grant for Researchers and Cultural Creators, BBVA Foundation (M.V-R). Finally, Ciberehd_ISCIII_MINECO is funded by the Instituto de Salud Carlos III. We thank MINECO for the Severo Ochoa Excellence Accreditation to CIC bioGUNE (SEV-2016-0644). Funding sources had no involvement in study design; in the collection, analysis, and interpretation of data; in the writing of the report; and in the decision to submit the paper for publication.

Upregulation of liver kinase B1 predicts poor prognosis in hepatocellular carcinoma

The majority of studies report that liver kinase B1 (LKB1) acts as a tumor suppressor by inhibiting cell proliferation and metastasis. The present study investigated the expression pattern of LKB1 in 2 cohorts of paired hepatocellular carcinoma (HCC) and analogous non-cancerous tissues (ANT). The results indicated that LKB1 was upregulated in HCC vs. ANT tissues, and that high expression of LKB1 was associated with a higher number of tumor foci, larger tumor size, poorer tumor differentiation, Edmondson-Steiner grade, Barcelona Clinic Liver Cancer grade and tumor-node-metastasis stage. Furthermore, high LKB1 expression was associated with poor overall survival (OS), shorter disease-free survival and early recurrence. Univariate and multivariate analyses demonstrated that high LKB1 expression may serve as an independent prognostic marker for OS, but not for recurrence. In addition, knockdown of LKB1 expression in HCC cell lines inhibited cell proliferation and subcutaneous tumor growth by promoting cell apoptosis. Therefore, the findings of the present study suggest a protooncogenic role of LKB1 in HCC.

Production of Elastin-Derived Peptides Contributes to the Development of Nonalcoholic Steatohepatitis

Affecting more than 30% of the Western population, nonalcoholic fatty liver disease (NAFLD) is the most common liver disease and can lead to multiple complications, including nonalcoholic steatohepatitis (NASH), cancer, hypertension, and atherosclerosis. Insulin resistance and obesity are described as potential causes of NAFLD. However, we surmised that factors such as extracellular matrix remodeling of large blood vessels, skin, or lungs may also participate in the progression of liver diseases. We studied the effects of elastin-derived peptides (EDPs), biomarkers of aging, on NAFLD progression. We evaluated the consequences of EDP accumulation in mice and of elastin receptor complex (ERC) activation on lipid storage in hepatocytes, inflammation, and fibrosis development. The accumulation of EDPs induces hepatic lipogenesis (i.e., SREBP1c and ACC), inflammation (i.e., Kupffer cells, IL-1β, and TGF-β), and fibrosis (collagen and elastin expression). These effects are induced by inhibition of the LKB1-AMPK pathway by ERC activation. In addition, pharmacological inhibitors of EDPs demonstrate that this EDP-driven lipogenesis and fibrosis relies on engagement of the ERC. Our data reveal a major role of EDPs in the development of NASH, and they provide new clues for understanding the relationship between NAFLD and vascular aging.

Neddylation, a novel paradigm in liver cancer

Liver cancer is the sixth most prevailing cancer worldwide. Hepatocellular carcinoma (HCC), the most common form of primary liver cancer, has a rather heterogeneous pathogenesis making it highly refractive to current therapeutic approaches. Hence, HCC patients have a poor and gloomy prognosis making liver cancer the second leading cause of global cancer-related deaths. On this basis, a more global mechanism, such as post-translational modifications (PTMs) of proteins, may provide a valuable therapeutic approach for HCC clinical management by simultaneously regulating multiple disrupted signaling pathways. In the last years, the ubiquitin-like molecule NEDD8 (Neural precursor cell-expressed developmentally downregulated-8) conjugation pathway, neddylation, was shown to be aberrant in HCC patients with a significant positive correlation found among global levels of neddylation and poorer prognosis. Even though the best-established role for NEDD8 is the activation of ubiquitin E3 ligase family of cullin-RING ligases, the putative role for other NEDD8 substrates has been explored in recent years leading to the identification of novel neddylation targets in HCC. Importantly, treatment with the small pharmacological inhibitor Pevonedistat (MLN4924) (Millennium Pharmaceuticals, Takeda Pharmaceutical), currently in clinical trials for the treatment of some types of leukemias and other advanced solid tumors, was shown to suppress the outgrowth of hepatoma cells and liver cancer in pre-clinical mouse models. Overall, considering that the neddylation inhibitor Pevonedistat was well-tolerated and displayed a significant antitumor effect in pre-clinical models, combinatory pharmacological treatment based on Pevonedistat are highly recommended to enter clinical trials targeting advanced HCC.

Deregulation of methionine metabolism as determinant of progression and prognosis of hepatocellular carcinoma

The under-regulation of liver-specific MAT1A gene codifying for S-adenosylmethionine (SAM) synthesizing isozymes MATI/III, and the up-regulation of widely expressed MAT2A, MATII isozyme occurs in hepatocellular carcinoma (HCC). MATα1:MATα2 switch strongly contributes to the fall in SAM liver content both in rodent and human liver carcinogenesis. SAM administration to carcinogen-treated animals inhibits hepatocarcinogenesis. The opposite occurs in Mat1a-KO mice, in which chronic SAM deficiency is followed by HCC development. This review focuses upon the changes, induced by the MATα1:MATα2 switch, involved in HCC development. In association with MATα1:MATα2 switch there occurs, in HCC, global DNA hypomethylation, decline of DNA repair, genomic instability, and deregulation of different signaling pathways such as overexpression of c-MYC (avian myelocytomatosis viral oncogene homolog), increase of polyamine (PA) synthesis and RAS/ERK (Harvey murine sarcoma virus oncogene homolog/extracellular signal-regulated kinase), IKK/NF-kB (I-k kinase beta/nuclear factor kB), PI3K/AKT, and LKB1/AMPK axes. Furthermore, a decrease in MATα1 expression and SAM level induces HCC cell proliferation and survival. SAM treatment in vivo and enforced MATα1 overexpression or MATα2 inhibition, in cultured HCC cells, prevent these changes. A negative correlation of MATα1:MATα2 and MATI/III:MATII ratios with cell proliferation and genomic instability and a positive correlation with apoptosis and global DNA methylation are present in human HCC. Altogether, these data suggest that the decrease of SAM level and the deregulation of MATs are potential therapeutic targets for HCC.

Methionine adenosyltransferases in cancers: Mechanisms of dysregulation and implications for therapy

Methionine adenosyltransferase genes encode enzymes responsible for the biosynthesis of S-adenosylmethionine, the principal biological methyl donor and precursor of polyamines and glutathione. Mammalian cells express three genes - MAT1A, MAT2A, and MAT2B - with distinct expression and functions. MAT1A is mainly expressed in the liver and maintains the differentiated states of both hepatocytes and bile duct epithelial cells. Conversely, MAT2A and MAT2B are widely distributed in non-parenchymal cells of the liver and extrahepatic tissues. Increasing evidence suggests that methionine adenosyltransferases play significant roles in the development of cancers. Liver cancers, namely hepatocellular carcinoma and cholangiocarcinoma, involve dysregulation of all three methionine adenosyltransferase genes. MAT1A reduction is associated with increased oxidative stress, progenitor cell expansion, genomic instability, and other mechanisms implicated in tumorigenesis. MAT2A/MAT2B induction confers growth and survival advantage to cancerous cells, enhancing tumor migration. Highlighted examples from colon, gastric, breast, pancreas and prostate cancer studies further underscore methionine adenosyltransferase genes' role beyond the liver in cancer development. In this subset of extra-hepatic cancers, MAT2A and MAT2B are induced via different regulatory mechanisms. Understanding the role of methionine adenosyltransferase genes in tumorigenesis helps identify attributes of these genes that may serve as valuable targets for therapy. While S-adenosylmethionine, and its metabolite, methylthioadenosine, have been largely explored as therapeutic interventions, targets aimed at regulation of MAT gene expression and methionine adenosyltransferase protein-protein interactions are now surfacing as potential effective strategies for treatment and chemoprevention of cancers. Impact statement This review examines the role of methionine adenosyltransferases (MATs) in human cancer development, with a particular focus on liver cancers in which all three MAT genes are implicated in tumorigenesis. An overview of MAT genes, isoenzymes and their regulation provide context for understanding consequences of dysregulation. Highlighting examples from liver, colon, gastric, breast, pancreas and prostate cancers underscore the importance of understanding MAT's tumorigenic role in identifying future targets for cancer therapy.

Methionine adenosyltransferases in liver health and diseases

Methionine adenosyltransferases (MATs) are essential for cell survival because they catalyze the biosynthesis of the biological methyl donor S-adenosylmethionine (SAMe) from methionine and adenosine triphosphate (ATP). Mammalian cells express two genes, MAT1A and MAT2A, which encode two MAT catalytic subunits, α1 and α2, respectively. The α1 subunit organizes into dimers (MATIII) or tetramers (MATI). The α2 subunit is found in the MATII isoform. A third gene MAT2B, encodes a regulatory subunit β, that regulates the activity of MATII by lowering the inhibition constant (K_i) for SAMe and the Michaelis constant (K_m) for methionine. MAT1A expressed mainly in hepatocytes maintains the differentiated state of these cells whereas MAT2A and MAT2B are expressed in non-parenchymal cells of the liver (hepatic stellate cells [HSCs] and Kupffer cells) and extrahepatic tissues. A switch from the liver-specific MAT1A to MAT2A has been observed during conditions of active liver growth and de-differentiation. Liver injury, fibrosis, and cancer are associated with MAT1A silencing and MAT2A/MAT2B induction. Even though both MAT1A and MAT2A are involved in SAMe biosynthesis, they exhibit distinct molecular interactions in liver cells. This review provides an update on MAT genes and their roles in liver pathologies.

Prohibitin 1 suppresses liver cancer tumorigenesis in mice and human hepatocellular and cholangiocarcinoma cells

Prohibitin 1 (PHB1) is best known as a mitochondrial chaperone, and its role in cancer is conflicting. Mice lacking methionine adenosyltransferase α1 (MATα1) have lower PHB1 expression, and we reported that c-MYC interacts directly with both proteins. Furthermore, c-MYC and MATα1 exert opposing effects on liver cancer growth, prompting us to examine the interplay between PHB1, MATα1, and c-MYC and PHB1's role in liver tumorigenesis. We found that PHB1 is highly expressed in normal hepatocytes and bile duct epithelial cells and down-regulated in most human hepatocellular carcinoma (HCC) and cholangiocarcinoma (CCA). In HCC and CCA cells, PHB1 expression correlates inversely with growth. PHB1 and MAT1A positively regulate each other's expression, whereas PHB1 negatively regulates the expression of c-MYC, MAFG, and c-MAF. Both PHB1 and MATα1 heterodimerize with MAX, bind to the E-box element, and repress E-box promoter activity. PHB1 promoter contains a repressive E-box element and is occupied mainly by MAX, MNT, and MATα1 in nonmalignant cholangiocytes and noncancerous tissues that switched to c-MYC, c-MAF, and MAFG in cancer cells and human HCC/CCA. All 8-month-old liver-specific Phb1 knockout mice developed HCC, and one developed CCA. Five-month-old Phb1 heterozygotes, but not Phb1 flox mice, developed aberrant bile duct proliferation; and one developed CCA 3.5 months after left and median bile duct ligation. Phb1 heterozygotes had a more profound fall in the expression of glutathione synthetic enzymes and higher hepatic oxidative stress following left and median bile duct ligation.

CONCLUSION

We have identified that PHB1, down-regulated in most human HCC and CCA, heterodimerizes with MAX to repress the E-box and positively regulates MAT1A while suppressing c-MYC, MAFG, and c-MAF expression; in mice, reduced PHB1 expression predisposes to the development of cholestasis-induced CCA. (Hepatology 2017;65:1249-1266).

Gastrin activates autophagy and increases migration and survival of gastric adenocarcinoma cells

BACKGROUND

The peptide hormone gastrin exerts a growth-promoting effect in both normal and malignant gastrointestinal tissue. Gastrin mediates its effect via the cholecystokinin 2 receptor (CCKBR/CCK2R). Although a substantial part of the gastric adenocarcinomas express gastrin and CCKBR, the role of gastrin in tumor development is not completely understood. Autophagy has been implicated in mechanisms governing cytoprotection, tumor growth, and contributes to chemoresistance. This study explores the role of autophagy in response to gastrin in gastric adenocarcinoma cell lines.

METHODS

Immunoblotting, survival assays and the xCELLigence system were used to study gastrin induced autophagy. Chemical inhibitors of autophagy were utilized to assess the role of this process in the regulation of cellular responses induced by gastrin. Further, knockdown studies using siRNA and immunoblotting were performed to explore the signaling pathways that activate autophagy in response to gastrin treatment.

RESULTS

We demonstrate that gastrin increases the expression of the autophagy markers MAP1LC3B-II and SQSTM1 in gastric adenocarcinoma cells. Gastrin induces autophagy via activation of the STK11-PRKAA2-ULK1 and that this signaling pathway is involved in increased migration and cell survival. Furthermore, gastrin mediated increase in survival of cells treated with cisplatin is partially dependent on induced autophagy.

CONCLUSION

This study reveals a novel role of gastrin in the regulation of autophagy. It also opens up new avenues in the treatment of gastric cancer by targeting CCKBR mediated signaling and/or autophagy in combination with conventional cytostatic drugs.

A Transcriptional Signature Identifies LKB1 Functional Status as a Novel Determinant of MEK Sensitivity in Lung Adenocarcinoma

LKB1 is a commonly mutated tumor suppressor in non-small cell lung cancer that exerts complex effects on signal transduction and transcriptional regulation. To better understand the downstream impact of loss of functional LKB1, we developed a transcriptional fingerprint assay representing this phenotype. This assay was predictive of LKB1 functional loss in cell lines and clinical specimens, even those without detected sequence alterations in the gene. In silico screening of drug sensitivity data identified putative LKB1-selective drug candidates, revealing novel associations not apparent from analysis of LKB1 mutations alone. Among the candidates, MEK inhibitors showed robust association with signature expression in both training and testing datasets independent of RAS/RAF mutations. This susceptibility phenotype is directly altered by RNA interference-mediated LKB1 knockdown or by LKB1 re-expression into mutant cell lines and is readily observed in vivo using a xenograft model. MEK sensitivity is dependent on LKB1-induced changes in AKT and FOXO3 activation, consistent with genomic and proteomic analyses of LKB1-deficient lung adenocarcinomas. Our findings implicate the MEK pathway as a potential therapeutic target for LKB1-deficient cancers and define a practical NanoString biomarker to identify functional LKB1 loss. Cancer Res; 77(1); 153-63. ©2016 AACR.

Prohibitin 1 Regulates the H19-Igf2 Axis and Proliferation in Hepatocytes

Prohibitin 1 (PHB1) is a mitochondrial chaperone that regulates cell growth. Phb1 knock-out mice exhibit liver injury and hepatocellular carcinoma (HCC). Phb1 knock-out livers show induction of tumor growth-associated genes, H19 and insulin-like growth factor 2 (Igf2). These genes are controlled by the imprinting control region (ICR) containing CCCTC-binding transcription factor (CTCF)-binding sites. Because Phb1 knock-out mice exhibited induction of H19 and Igf2, we hypothesized that PHB1-mediated regulation of the H19-Igf2 axis might control cell proliferation in normal hepatocytes. H19 and Igf2 were induced (8-20-fold) in 3-week-old Phb1 knock-out livers, in Phb1 siRNA-treated AML12 hepatocytes (2-fold), and HCC cell lines when compared with control. Phb1 knockdown lowered CTCF protein in AML12 by ∼30% when compared with control. CTCF overexpression lowered basal H19 and Igf2 expression by 30% and suppressed Phb1 knockdown-mediated induction of these genes. CTCF and PHB1 co-immunoprecipitated and co-localized on the ICR element, and Phb1 knockdown lowered CTCF ICR binding activity. The results suggest that PHB1 and CTCF cooperation may control the H19-Igf2 axis. Human HCC tissues with high levels of H19 and IGF2 exhibited a 40-50% reduction in PHB1 and CTCF expression and their ICR binding activity. Silencing Phb1 or overexpressing H19 in the mouse HCC cell line, SAMe-D, induced cell growth. Blocking H19 induction prevented Phb1 knockdown-mediated growth, whereas H19 overexpression had the reverse effect. Interestingly H19 silencing induced PHB1 expression. Taken together, our results demonstrate that the H19-Igf2 axis is negatively regulated by CTCF-PHB1 cooperation and that H19 is involved in modulating the growth-suppressive effect of PHB1 in the liver.

The possible role of liver kinase B1 in hydroquinone-induced toxicity of murine fetal liver and bone marrow hematopoietic stem cells

Epidemiological studies suggest that the increasing incidence of childhood leukemia may be due to maternal exposure to benzene, which is a known human carcinogen; however, the mechanisms involved remain unknown. Liver Kinase B1 (LKB1) acts as a regulator of cellular energy metabolism and functions to regulate hematopoietic stem cell (HSC) homeostasis. We hypothesize that LKB1 contributes to the deregulation of fetal or bone hematopoiesis caused by the benzene metabolite hydroquinone (HQ). To evaluate this hypothesis, we compared the effects of HQ on murine fetal liver hematopoietic stem cells (FL-HSCs) and bone marrow hematopoietic stem cells (BM-HSCs). FL-HSCs and BM-HSCs were isolated and enriched by a magnetic cell sorting system and exposed to various concentrations of HQ (0, 1.25, 2.5, 5, 10, 20, and 40 μM) for 24 h. We found that the inhibition of differentiation and growth, as well as the apoptosis rate of FL-HSCs, induced by HQ were consistent with the changes in BM-HSCs. Furthermore, G1 cell cycle arrest was observed in BM-HSCs and FL-HSCs in response to HQ. Importantly, FL-HSCs were more sensitive than BM-HSCs after exposure to HQ. The highest induction of LKB1 and adenosine monophosphate-activated protein kinase (AMPK) was observed with a much lower concentration of HQ in FL-HSCs than in BM-HSCs. LKB1 may play a critical role in apoptosis and cell cycle arrest of HQ-treated HSCs. This research has developed innovative ideas concerning benzene-induced hematopoietic toxicity or embryotoxicity, which can provide a new experimental evidence for preventing childhood leukemia. © 2014 Wiley Periodicals, Inc. Environ Toxicol 31: 830-841, 2016.

Investigation of long noncoding RNAs expression profile as potential serum biomarkers in patients with hepatocellular carcinoma

There is an increasing interest in using long noncoding RNAs (lncRNAs) as biomarkers in cancer. Predictive biomarkers in hepatocellular carcinoma (HCC) have great benefit in the choice of therapeutic modality for HCC. The aim of this study is to assess lncRNA-urothelial carcinoma associated-1 (lncRNA-UCA1) and WD repeat containing, antisense to TP53 (WRAP53) expression as novel noninvasive biomarkers for diagnosis of HCC in sera of HCC patients compared with chronic hepatitis C virus (HCV) patients and healthy volunteers and to analyze their relationship with respect to the clinicopathologic features. We retrieved HCC characteristic lncRNAs, lncRNA-UCA1 and lncRNA-WRAP53, based on the microarray signature profiling (released by LncRNADisease database). Quantitative reverse-transcriptase polymerase chain reaction assay (RT-qPCR) was then used to evaluate the expression of selected lncRNAs in the serum of 160 participants. Furthermore, in 20 of 82 HCC cases involved in the study, we examined the expression of lncRNA-UCA1 and lncRNA-WRAP53 in 20 HCC tissues and adjacent nontumor tissues and analyzed its correlation with the serum level of these lncRNAs. The prognostic significance of the investigated parameters in HCC patients was explored. We found that lncRNA-UCA1 and lncRNA-WRAP53 were significantly higher in sera of HCC than those with chronic HCV infection or healthy volunteers. Our data suggested that the increased expression of UCA1 and WRAP53 was associated with advanced clinical parameters in HCC. Of note, tissue levels of the chosen lncRNAs strongly correlate with their sera level. The combination of both lncRNAs with serum alpha fetoprotein resulted in improved sensitivity to 100%. The median follow-up period was 21.5 months. LncRNA-WRAP53 was significant independent prognostic markers in relapse-free survival. LncRNA-UCA1 and lncRNA-WRAP53 upregulation may serve as novel serum biomarkers for HCC diagnosis and prognosis.

Stabilization of LKB1 and Akt by neddylation regulates energy metabolism in liver cancer

The current view of cancer progression highlights that cancer cells must undergo through a post-translational regulation and metabolic reprogramming to progress in an unfriendly environment. In here, the importance of neddylation modification in liver cancer was investigated. We found that hepatic neddylation was specifically enriched in liver cancer patients with bad prognosis. In addition, the treatment with the neddylation inhibitor MLN4924 in Phb1-KO mice, an animal model of hepatocellular carcinoma showing elevated neddylation, reverted the malignant phenotype. Tumor cell death in vivo translating into liver tumor regression was associated with augmented phosphatidylcholine synthesis by the PEMT pathway, known as a liver-specific tumor suppressor, and restored mitochondrial function and TCA cycle flux. Otherwise, in protumoral hepatocytes, neddylation inhibition resulted in metabolic reprogramming rendering a decrease in oxidative phosphorylation and concomitant tumor cell apoptosis. Moreover, Akt and LKB1, hallmarks of proliferative metabolism, were altered in liver cancer being new targets of neddylation. Importantly, we show that neddylation-induced metabolic reprogramming and apoptosis were dependent on LKB1 and Akt stabilization. Overall, our results implicate neddylation/signaling/metabolism, partly mediated by LKB1 and Akt, in the development of liver cancer, paving the way for novel therapeutic approaches targeting neddylation in hepatocellular carcinoma.

Numb downregulation suppresses cell growth and is associated with a poor prognosis of human hepatocellular carcinoma

Numb, an endocytic adaptor, is a known cell fate determinant that participates in asymmetric cell division. The present study aimed to explore the potential roles of Numb in hepatocarcinogenesis. Numb expression was investigated in hepatocellular carcinomas (HCC) with reverse transcription‑quantitative polymerase chain reaction and immunohistochemical examination; its association with the prognosis of HCC patients was analyzed. In addition, the effects of Numb deletion on proliferation of HCC cells and its relevant molecules were evaluated in Huh7 and HepG2 cells. Numb overexpression was observed in 62% of adjacent non‑tumor tissues and 46% of tumor tissues. Overexpression of Numb in HCC was associated with histological grade, portal vein invasion and the number of tumors (P=0.001, 0.022 and 0.034 respectively). Multivariate analysis revealed that Numb expression was an independent prognostic indicator of HCC patients. Methylation of the Numb promoter contributed to hepatocarcinogenesis. In vitro assays demonstrated that Numb silencing resulted in inhibition of cell proliferation, induction of apoptosis, downregulation of cyclin‑dependent protein kinase 4 (CDK4) and S‑phase kinase‑associated protein 2 (SKP2), and upregulation of Bcl‑2 homologous antagonist/killer (BAK) and cyclin‑dependent kinase inhibitor 1 (p21). The present study suggests that downregulation of Numb inhibits colony formation and cell proliferation, induces apoptosis of HCC cells and independently predicts the poor prognosis of HCC patients. Thus, Numb has a potential role in the development and progression of HCC.

NEDDylation in liver cancer: The regulation of the RNA binding protein Hu antigen R

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third leading cause of cancer death. The current view of cancer progression and malignancy supports the notion that cancer cells must undergo through a post-translational modification (PTM) regulation and a metabolic switch or reprogramming in order to progress in an unfriendly environment. NEDDylation is a post-translational modification of the proteins involved in several processes such as cell growth, viability and development. A ground-breaking knowledge on a new critical aspect of HCC research has been to identify that NEDDylation plays a role in HCC by regulating the liver oncogenic driver Hu antigen R (HuR). HuR is a RNA-binding protein that stabilizes target mRNAs involved in cell dedifferentiation, proliferation, and survival, all well-established hallmarks of cancer. And importantly, HuR levels were found to be highly representative in liver and colon cancer. These findings open a completely new area of research, exploring the impact that NEDDylation plays in liver diseases and paving the way for novel therapeutical approaches.

HuR Suppresses Fas Expression and Correlates with Patient Outcome in Liver Cancer

Hepatocellular carcinomas (HCC) show resistance to chemotherapy and have blunt response to apoptotic stimuli. HCC cell lines express low levels of the Fas death receptor and are resistant to FasL stimulation, whereas immortalized hepatocytes are sensitive. The variable Fas transcript levels and consistently low Fas protein in HCC cells suggest posttranscriptional regulation of Fas expression. The 3'-untranslated region (UTR) of Fas mRNA was found to interact with the ribonucleoprotein Human Antigen R (HuR) to block mRNA translation. Silencing of HuR in HCC cells increased the levels of cell surface Fas and sensitized HCC cells to FasL. Two AU-rich domains within the 3'-UTR of Fas mRNA were identified as putative HuR-binding sites and were found to mediate the translational regulation in reporter assay. Hydrodynamic transfection of HuR plasmid into mice induced downregulation of Fas expression in livers and established functional resistance to the killing effects of Fas agonist. Human HCC tumor tissues showed significantly higher overall and cytoplasmic HuR staining compared with normal liver tissues, and the high HuR staining score correlated with worse survival of patients with early-stage HCC. Combined, the protumorigenic ribonucleoprotein HuR blocks the translation of Fas mRNA and effectively prevents Fas-mediated apoptosis in HCC, suggesting that targeting HuR would sensitize cells to apoptotic stimuli and reverse tumorigenic properties.

IMPLICATIONS

Demonstrating how death receptor signaling pathways are altered during progression of HCC will enable the development of better methods to restore this potent apoptosis mechanism.

LKB1 Loss induces characteristic patterns of gene expression in human tumors associated with NRF2 activation and attenuation of PI3K-AKT

Introduction:

Inactivation of serine/threonine kinase 11 (STK11 or LKB1) is common in lung cancer, and understanding the pathways and phenotypes altered as a consequence will aid the development of targeted therapeutic strategies. Gene and protein expressions in a murine model of v-Ki-ras2 Kirsten rat sarcoma viral oncogene homolog (Kras)-mutant lung cancer have been studied to gain insight into the biology of these tumors. However, the molecular consequences of LKB1 loss in human lung cancer have not been fully characterized.

Methods:

We studied gene expression profiles associated with LKB1 loss in resected lung adenocarcinomas, non–small-cell lung cancer cell lines, and murine tumors. The biological significance of dysregulated genes was interpreted using gene set enrichment and transcription factor analyses and also by integration with somatic mutations and proteomic data.

Results:

Loss of LKB1 is associated with consistent gene expression changes in resected human lung cancers and cell lines that differ substantially from the mouse model. Our analysis implicates novel biological features associated with LKB1 loss, including altered mitochondrial metabolism, activation of the nuclear respiratory factor 2 (NRF2) transcription factor by kelch-like ECH-associated protein 1 (KEAP1) mutations, and attenuation of the phosphatidylinositiol 3-kinase and v-akt murine thymoma viral oncogene homolog (PI3K/AKT) pathway. Furthermore, we derived a 16-gene classifier that accurately predicts LKB1 mutations and loss by nonmutational mechanisms. In vitro, transduction of LKB1 into LKB1-mutant cell lines results in attenuation of this signature.

Conclusion:

Loss of LKB1 defines a subset of lung adenocarcinomas associated with characteristic molecular phenotypes and distinctive gene expression features. Studying these effects may improve our understanding of the biology of these tumors and lead to the identification of targeted treatment strategies.

Ubiquitin profiling in liver using a transgenic mouse with biotinylated ubiquitin

Ubiquitination is behind most cellular processes, with ubiquitin substrates being regulated variously according to the number of covalently conjugated ubiquitin molecules and type of chain formed. Here we report the first mammalian system for ubiquitin proteomics allowing direct validation of the MS-identified proteins. We created a transgenic mouse expressing biotinylated ubiquitin and demonstrate its use for the isolation of ubiquitinated proteins from liver and other tissues. The specificity and strength of the biotin-avidin interaction allow very stringent washes, so only proteins conjugated to ubiquitin are isolated. In contrast with recently available antibody-based approaches, our strategy allows direct validation by immunoblotting, therefore revealing the type of ubiquitin chains (mono or poly) formed in vivo. We also identify the conjugating E2 enzymes that are ubiquitin-loaded in the mouse tissue. Furthermore, our strategy allows the identification of candidate cysteine-ubiquitinated proteins, providing a strategy to identify those on a proteomic scale. The novel in vivo system described here allows broad access to tissue-specific ubiquitomes and can be combined with established mouse disease models to investigate ubiquitin-dependent therapeutical approaches.

p27 Is a critical prognostic biomarker in non-alcoholic steatohepatitis-related hepatocellular carcinoma

Non-alcoholic steatohepatitis (NASH) is a recently identified chronic liver disease, which progresses to liver cirrhosis and hepatocellular carcinoma (HCC). As the number of patients studied to date has been limited, clinically useful prognostic biomarkers of NASH-related HCC have not been available. In this study, we investigated the status of a cell-cycle regulator, p27, in NASH-related HCC. p27 has been regarded as a prognostic factor in various types of cancer patients. A total of 22 cases with NASH-related HCC were analyzed for p27 protein expression, and phosphorylation at threonine 157 (T157) and serine 10 (S10) by immunohistochemical analysis. The correlation of p27 with tumor characteristics, disease-free survival (DFS), and overall survival was analyzed. p27 expression was decreased in 13 HCCs (59%), and was significantly correlated with enlarged tumor size (p = 0.01) and increased cell proliferation (p < 0.01). Phospho-p27 at T157 and S10 was detected in four (18%) and seven (32%) cases, respectively, and patients positive for phospho-p27 (S10) showed reduced DFS (hazard ratio 7.623, p = 0.016) by univariate analysis. Further studies with more patients are required to verify the usefulness of p27 as a biomarker for predicting tumor recurrence in NASH patients.

Pleiotropic effects of methionine adenosyltransferases deregulation as determinants of liver cancer progression and prognosis

Downregulation of liver-specific MAT1A gene, encoding S-adenosylmethionine (SAM) synthesizing isozymes MATI/III, and upregulation of widely expressed MAT2A, encoding MATII isozyme, known as MAT1A:MAT2A switch, occurs in hepatocellular carcinoma (HCC). Being inhibited by its reaction product, MATII isoform upregulation cannot compensate for MATI/III decrease. Therefore, MAT1A:MAT2A switch contributes to decrease in SAM level in rodent and human hepatocarcinogenesis. SAM administration to carcinogen-treated rats prevents hepatocarcinogenesis, whereas MAT1A-KO mice, characterized by chronic SAM deficiency, exhibit macrovesicular steatosis, mononuclear cell infiltration in periportal areas, and HCC development. This review focuses upon the pleiotropic changes, induced by MAT1A/MAT2A switch, associated with HCC development. Epigenetic control of MATs expression occurs at transcriptional and post-transcriptional levels. In HCC cells, MAT1A/MAT2A switch is associated with global DNA hypomethylation, decrease in DNA repair, genomic instability, and signaling deregulation including c-MYC overexpression, rise in polyamine synthesis, upregulation of RAS/ERK, IKK/NF-kB, PI3K/AKT, and LKB1/AMPK axis. Furthermore, decrease in MAT1A expression and SAM levels results in increased HCC cell proliferation, cell survival, and microvascularization. All of these changes are reversed by SAM treatment in vivo or forced MAT1A overexpression or MAT2A inhibition in cultured HCC cells. In human HCC, MAT1A:MAT2A and MATI/III:MATII ratios correlate negatively with cell proliferation and genomic instability, and positively with apoptosis and global DNA methylation. This suggests that SAM decrease and MATs deregulation represent potential therapeutic targets for HCC. Finally, MATI/III:MATII ratio strongly predicts patients' survival length suggesting that MAT1A:MAT2A expression ratio is a putative prognostic marker for human HCC.

Progression of liver oncogenesis in the double transgenic mice c-myc/TGF α is not enhanced by cyclooxygenase-2 expression

Cyclooxygenase-2 (COX-2) has been associated with cell growth regulation, tissue remodeling and carcinogenesis. Overexpression of COX-2 in hepatocytes constitutes an ideal condition to evaluate the role of prostaglandins (PGs) in liver pathogenesis. The effect of COX-2-dependent PGs in genetic hepatocarcinogenesis has been investigated in triple c-myc/transforming growth factor α (TGF-α) transgenic mice that express human COX-2 in hepatocytes on a B6CBAxCD1xB6DBA2 background. Analysis of the contribution of COX-2-dependent PGs to the development of hepatocarcinogenesis, evaluated in this model, suggested a minor role of COX-2-dependent prostaglandins to liver oncogenesis as indicated by liver histopathology, morphometric analysis and specific markers of tumor progression. This allows concluding that COX-2 is insufficient for modifying the hepatocarcinogenesis course mediated by c-myc/TGF-α.

The mTOR pathway in hepatic malignancies

The mechanistic/mammalian target of rapamycin (mTOR) pathway plays a critical role in cellular metabolism, growth, and proliferation and has been evaluated as a target for therapy in various malignancies. The mTOR pathway is a major tumor-initiating pathway in hepatocellular carcinoma, with up-regulation seen in up to 50% of tumors. Metformin, which represses mTOR signaling by activating adenosine monophosphate-activated protein kinase, has been shown to decrease liver carcinogenesis in population studies. mTOR inhibitors such as everolimus have been evaluated as adjunctive chemotherapy with some success, although efficacy has been limited by the lack of complete mTOR pathway inhibition. The active site mTOR inhibitors hold greater promise, given that they offer complete mTOR suppression. There is also evidence of mTOR pathway activation in cholangiocarcinoma, although its biological significance in initiating and promoting tumor progression remains ambiguous. This review provides an overview of the complex biochemistry behind the mTOR pathway and its role in carcinogenesis, especially as it pertains to hepatic malignancies.