Expansion of liver cancer stem cells during aging in methionine adenosyltransferase 1A-deficient mice

β-CATENIN stabilizes HIF2 through lncRNA and inhibits intravenous immunoglobulin immunotherapy

Introduction

Tumor-initiating cells (TICs) are rare, stem-like, and highly malignant. Although intravenous hepatitis B and C immunoglobulins have been used for HBV and HCV neutralization in patients, their tumor-inhibitory effects have not yet been examined. Hepatitis B immunoglobulin (HBIG) therapy is employed to reduce hepatocellular carcinoma (HCC) recurrence in patients after living donor liver transplantations (LDLT).

Hypothesis

We hypothesized that patient-derived intravenous immunoglobulin (IVIG) binding to HCC associated TICs will reduce self-renewal and cell viability driven by β-CATENIN-downstream pathways. β-CATENIN activity protected TICs from IVIG effects.

Methods

The effects of HBIG and HCIG binding to TICs were evaluated for cell viability and self-renewal.

Results

Inhibition of β-CATENIN pathway(s) augmented TIC susceptibility to HBIG- and HCIG-immunotherapy. HBV X protein (HBx) upregulates both β-CATENIN and NANOG expression. The co-expression of constitutively active β-CATENIN with NANOG promotes self-renewal ability and tumor-initiating ability of hepatoblasts. HBIG bound to HBV+ cells led to growth inhibition in a TIC subset that expressed hepatitis B surface antigen. The HBx protein transformed cells through β-CATENIN-inducible lncRNAs EGLN3-AS1 and lnc-β-CatM. Co-expression of constitutively active β-CATENIN with NANOG promoted self-renewal ability of TICs through EGLN3 induction. β-CATENIN-induced lncRNAs stabilized HIF2 to maintain self-renewal of TICs. Targeting of EGLN3-AS1 resulted in destabilization of EZH2-dependent β-CATENIN activity and synergized cell-killing of TICs by HBIG or HCIG immunotherapy.

Discussion

Taken together, WNT and stemness pathways induced HIF2 of TICs via cooperating lncRNAs resulting in resistance to cancer immunotherapy. Therefore, therapeutic use of IVIG may suppress tumor recurrence through inhibition of TICs.

HCV and tumor-initiating stem-like cells

Neoplasms contain tumor-initiating stem-like cells (TICs) that are characterized by increased drug resistance. The incidence of many cancer types have trended downward except for few cancer types, including hepatocellular carcinoma (HCC). Therefore mechanism of HCC development and therapy resistance needs to be understood. These multiple hits by hepatitis C virus (HCV) eventually promotes transformation and TIC genesis, leading to HCC development. This review article describes links between HCV-associated HCC and TICs. This review discusses 1) how HCV promotes genesis of TICs and HCC development; 2) how this process avails itself as a novel therapeutic target for HCC treatment; and 3) ten hall marks of TIC oncogenesis and HCC development as targets for novel therapeutic modalities.

Keep a watchful eye on methionine adenosyltransferases, novel therapeutic opportunities for hepatobiliary and pancreatic tumours

Methionine adenosyltransferases (MATs) synthesize S-adenosylmethionine (SAM) from methionine, which provides methyl groups for DNA, RNA, protein, and lipid methylation. MATs play a critical role in cellular processes, including growth, proliferation, and differentiation, and have been implicated in tumour development and progression. The expression of MATs is altered in hepatobiliary and pancreatic (HBP) cancers, which serves as a rare biomarker for early diagnosis and prognosis prediction of HBP cancers. Independent of SAM depletion in cells, MATs are often dysregulated at the transcriptional, post-transcriptional, and post-translational levels. Dysregulation of MATs is involved in carcinogenesis, chemotherapy resistance, T cell exhaustion, activation of tumour-associated macrophages, cancer stemness, and activation of tumourigenic pathways. Targeting MATs both directly and indirectly is a potential therapeutic strategy. This review summarizes the dysregulations of MATs, their proposed mechanism, diagnostic and prognostic roles, and potential therapeutic effects in context of HBP cancers.

Immunotherapy and Microbiota for Targeting of Liver Tumor-Initiating Stem-like Cells

Cancer contains tumor-initiating stem-like cells (TICs) that are resistant to therapies. Hepatocellular carcinoma (HCC) incidence has increased twice over the past few decades, while the incidence of other cancer types has trended downward globally. Therefore, an understanding of HCC development and therapy resistance mechanisms is needed for this incurable malignancy. This review article describes links between immunotherapies and microbiota in tumor-initiating stem-like cells (TICs), which have stem cell characteristics with self-renewal ability and express pluripotency transcription factors such as NANOG, SOX2, and OCT4. This review discusses (1) how immunotherapies fail and (2) how gut dysbiosis inhibits immunotherapy efficacy. Gut dysbiosis promotes resistance to immunotherapies by breaking gut immune tolerance and activating suppressor immune cells. Unfortunately, this leads to incurable recurrence/metastasis development. Personalized medicine approaches targeting these mechanisms of TIC/metastasis-initiating cells are emerging targets for HCC immunotherapy and microbiota modulation therapy.

KRAB-ZFPs and cancer stem cells identity

Studies on carcinogenesis continue to provide new information about different disease-related processes. Among others, much research has focused on the involvement of cancer stem cells (CSCs) in tumor initiation and progression. Studying the similarities and differences between CSCs and physiological stem cells (SCs) allows for a better understanding of cancer biology. Recently, it was shown that stem cell identity is partially governed by the Krϋppel-associated box domain zinc finger proteins (KRAB-ZFPs), the biggest family of transcription regulators. Several KRAB-ZFP factors exert a known effect in tumor cells, acting as tumor suppressor genes (TSGs) or oncogenes, yet their role in CSCs is still poorly characterized. Here, we review recent studies regarding the influence of KRAB-ZFPs and their cofactor protein TRIM28 on CSCs phenotype, stemness features, migration and invasion potential, metastasis, and expression of parental markers.

Cost-Effective Production of ATP and S-Adenosylmethionine Using Engineered Multidomain Scaffold Proteins

Adenosine triphosphate (ATP) and S-adenosyl-L-methionine (SAM) are important intermediates that are widely present in living organisms. Large-scale preparation and application of ATP or SAM is limited by expensive raw materials. To lower the production costs for ATP/SAM, in this study we used strategies applying engineered multidomain scaffold proteins to synthesize ATP and SAM. An artificial scaffold protein containing CBM3 domain, IM proteins and CL-labeled proteins was assembled to form complex 1 for catalytic reactions to increase ATP production. The ATP synthesis system produced approximately 25 g/L of ATP with approximately 15 g/L of ADP and 5 g/L of AMP using 12.5 g/L of adenosine and 40 g/L of sodium hexametaphosphate reaction at 35 °C and a pH of 8.5 for 6 h. Based on the above ATP synthesis system, two CL-labeled methionine adenosyltransferases (CL9-MAT4 and CL9-MAT5) were applied to construct scaffold protein complex 2 to achieve SAM synthesis. Approximately 25 μg of MAT4 in a reaction system with 0.3 M MgCl2 catalyzed at 20 °C and a pH of 8 catalyzed 0.5 g/L of l-Met to produce approximately 0.9 g/L of SAM. Approximately 25 μg of MAT5 in a reaction system with 0.7 M MgCl2 catalyzed at 35 °C and a pH of 8 catalyzed 0.5 g/L of l-Met to produce approximately 1.2 g/L of SAM. Here, we showed that low-cost substrates can be efficiently converted into high-value additional ATP and SAM via multi-enzyme catalytic reactions by engineered multidomain scaffold proteins.

Molecular subclassification of gastrointestinal cancers based on cancer stem cell traits

Human gastrointestinal malignancies are highly heterogeneous cancers. Clinically, heterogeneity largely contributes to tumor progression and resistance to therapy. Heterogeneity within gastrointestinal cancers is defined by molecular subtypes in genomic and transcriptomic analyses. Cancer stem cells (CSCs) have been demonstrated to be a major source of tumor heterogeneity; therefore, assessing tumor heterogeneity by CSC trait-guided classification of gastrointestinal cancers is essential for the development of effective therapies. CSCs share critical features with embryonic stem cells (ESCs). Molecular investigations have revealed that embryonic genes and developmental signaling pathways regulating the properties of ESCs or cell lineage differentiation are abnormally active and might be oncofetal drivers in certain tumor subtypes. Currently, multiple strategies allow comprehensive identification of tumor subtype-specific oncofetal signatures and evaluation of subtype-specific therapies. In this review, we summarize current knowledge concerning the molecular classification of gastrointestinal malignancies based on CSC features and elucidate their clinical relevance. We also outline strategies for molecular subtype identification and subtype-based therapies. Finally, we explore how clinical implementation of tumor classification by CSC subtype might facilitate the development of more effective personalized therapies for gastrointestinal cancers.

Differential mechanisms of autophagy in cancer stem cells: Emphasizing gastrointestinal cancers

Gastrointestinal (GI) cancers are one of the most common forms of malignancies and still are the most important cause of cancer-related mortality worldwide. Autophagy is a conserved catabolic pathway involving lysosomal degradation and recycling of whole cellular components, which is essential for cellular homeostasis. For instance, it acts as a pivotal intracellular quality control and repair mechanism but also implicated in cell reformation during cell differentiation and development. Indeed, GI cancer stem cells (CSCs) are thought to be responsible for tumour initiation, traditional therapies resistance, metastasis and tumour recurrence. Molecular mechanisms of autophagy in normal vs CSCs gain great interest worldwide. Here, we shed light on the role of autophagy in normal stem cells differentiation for embryonic progression and its role in maintaining the activity and self-renewal capacity of CSCs which offer novel viewpoints on promising cancer therapeutic strategies based on the differential roles of autophagy in CSCs.

Cell fate, metabolic reprogramming and lncRNA of tumor-initiating stem-like cells induced by alcohol

Alcoholism synergizes the development of the hepatocellular carcinoma (HCC) in patients infected with hepatitis B or C virus (HBV or HCV). Tumor-initiating stem-like cells (TICs) are refractory to therapy and have expression of stemness transcription factors. Leaky-gut-derived endotoxin stimulates TLR4-NANOG pathway that skews asymmetric cell division and that metabolically reprograms hepatocytes/liver progenitor cells, leading to self-renewal. TICs isolated from mouse HCC models or human HCCs are tumorigenic and have p53 degradation via phosphorylation of the protective protein NUMB and its dissociation from p53 by the oncofetal protein TBC1D15. Furthermore, dysregulation of lncRNA promotes genesis of TICs, leading to HCC development. This review describes roles of cell fate decision, metabolic reprogramming and lncRNA for TIC genesis and liver oncogenesis. This project was supported by NIH grants 1R01AA018857-01, 5R21AA025470, P50AA11999 (Animal Core, Morphology Core, and Pilot Project Program), R24AA012885 (Non-Parenchymal Liver Cell Core) and pilot project funding (5P30DK048522-13).

Integrin α6 (CD49f), The Microenvironment and Cancer Stem Cells

Cancer is a highly prevalent and potentially terminal disease that affects millions of individuals worldwide. Here, we review the literature exploring the intricacies of stem cells bearing tumorigenic characteristics and collect evidence demonstrating the importance of integrin α6 (ITGA6, also known as CD49f) in cancer stem cell (CSC) activity. ITGA6 is commonly used to identify CSC populations in various tissues and plays an important role sustaining the self-renewal of CSCs by interconnecting them with the tumorigenic microenvironment.

The Emerging Roles of Cancer Stem Cells and Wnt/Beta-Catenin Signaling in Hepatoblastoma

Hepatoblastoma (HB) is the most common form of primary liver malignancy found in pediatric populations. HB is considered to be clonal and arises from hepatoblasts, or embryonic liver progenitor cells. These less differentiated tumor-initiating progenitor cells, or cancer stem cells (CSCs), may contribute to tumor recurrence and resistance to therapies, and have high metastatic abilities. Phenotypic heterogeneity, undesired genetic and epigenetic alterations, and dysregulated signaling pathways provide CSCs with a survival advantage over current therapies. The molecular and cellular basis of HB and the mechanism of CSC induction are not fully understood. The Wnt/beta-catenin pathway is one of the major developmental pathways and is believed to play an important role in the pathogenesis of HB and CSC formation. This review summarizes the cellular and molecular characteristics of HB with a specific emphasis on CSCs and Wnt/beta-catenin signaling.

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.

NANOG-Dependent Metabolic Reprogramming and Symmetric Division in Tumor-Initiating Stem-like Cells

Alcohol abuse synergistically heightens the development of the third most deadliest cancer hepatocellular carcinoma (HCC) in patients infected with hepatitis C virus (HCV). Ectopically expressed TLR4 promotes liver tumorigenesis in alcohol-fed HCV Ns5a or Core transgenic mice. CD133+/CD49f + tumor-initiating stem cell-like cells (TICs) isolated from these models are tumorigenic have p53 degradation via phosphorylation of the protective protein NUMB and its dissociation from p53 by the oncoprotein TBC1D15. Nutrient deprivation reduces overexpressed TBC1D15 in TICs via autophagy-mediated degradation, suggesting a possible role of this oncoprotein in linking metabolic reprogramming and self-renewal.

The Evolving Landscape of Cancer Stem Cells and Ways to Overcome Cancer Heterogeneity

Cancer stem cells (CSCs) with therapeutic resistance and plasticity can be found in various types of tumors and are recognized as attractive targets for treatments. As CSCs are derived from tissue stem or progenitor cells, and/or dedifferentiated mature cells, their signal transduction pathways are critical in the regulation of CSCs; chronic inflammation causes the accumulation of genetic mutations and aberrant epigenetic changes in these cells, potentially leading to the production of CSCs. However, the nature of CSCs appears to be stronger than the treatments of the past. To improve the treatments targeting CSCs, it is important to inhibit several molecules on the signaling cascades in CSCs simultaneously, and to overcome cancer heterogeneity caused by the plasticity. To select suitable target molecules for CSCs, we have to explore the landscape of CSCs from the perspective of cancer stemness and signaling systems, based on the curated databases of cancer-related genes. We have been studying the integration of a broad range of knowledge and experiences from cancer biology, and also from other interdisciplinary basic sciences. In this review, we have introduced the concept of developing novel strategies targeting CSCs.

Prohibitin 1 Acts As a Negative Regulator of Wingless/Integrated-Beta-Catenin Signaling in Murine Liver and Human Liver Cancer Cells

Prohibitin1 (PHB1) is a mitochondrial chaperone with diverse functions that include cell proliferation, apoptosis, and mitochondrial homoeostasis. Liver‐specific Phb1 knockout (KO) mice develop spontaneous injury and hepatocellular carcinoma (HCC). Our previous work demonstrated that PHB1 negatively regulates the H19‐insulin‐like growth factor 2 (IGF2)‐H19‐IGF2 axis signaling pathway and E‐box activity in hepatocytes and HCC cells. Phb1 KO livers exhibited increased expression of multiple wingless/integrated (WNT) target genes compared to control littermates. Therefore, we hypothesized that PHB1 is a negative regulator of WNT‐beta‐catenin signaling in the liver. Analysis of livers from Phb1 KO mice demonstrated an activation of the WNT‐beta‐catenin pathway as determined by phosphorylation of glycogen synthase kinase 3 (GSK3)beta^{serine [Ser]9} and protein kinase B (AKT)^Ser473. Phb1 KO livers showed increased messenger RNA (mRNA) levels of multiple WNT ligands, with Wnt7a (79‐fold), Wnt10a (12‐fold), and Wnt16 (48‐fold) being most highly overexpressed compared to control littermates. Subcellular fractionation of liver cells from Phb1 KO mice indicated that hepatocytes are the main source of WNT ligands. Immunostaining and cellular colocalization analysis of Phb1 KO livers demonstrated expression of WNT7a, WNT10a, and WNT16 in hepatocytes. Chromatin immunoprecipitation revealed increased binding of transcription factor E2F1 (E2F1) to the Wnt10a promoter in Phb1 KO livers and WNT9A in HepG2 cells. PHB1 silencing in HepG2 cells activated WNT signaling, whereas its overexpression caused inactivation of this pathway. PHB1 silencing in HepG2 cells induced the expression of multiple WNT ligands of which WNT9A induction was partly regulated through E2F1. Conclusion: PHB1 acts as a negative regulator of WNT signaling, and its down‐regulation causes the induction of multiple WNT ligands and downstream activation of canonical WNT‐beta‐catenin signaling in murine liver and human HCC cells, in part through E2F1.

Participation of liver stem cells in cholangiocarcinogenesis after aflatoxin B1 exposure of glutathione S-transferase A3 knockout mice

Aflatoxin B1, arguably the most potent human carcinogen, induces liver cancer in humans, rats, trout, ducks, and so on, but adult mice are totally resistant. This resistance is because of a detoxifying enzyme, mouse glutathione S-transferase A3, which binds to and inactivates aflatoxin B1 epoxide, preventing the epoxide from binding to DNA and causing mutations. Glutathione S-transferase A3 or its analog has not been detected in any of the sensitive species, including humans. The generation of a glutathione S-transferase A3 knockout (represented as KO or -/-) mice has allowed us to study the induction of liver cancer in mice by aflatoxin B1. In contrast to the induction of hepatocellular carcinomas in other species, aflatoxin B1 induces cholangiocarcinomas in GSTA3-/- mice. In other species and in knockout mice, the induction of liver cancer is preceded by extensive proliferation of small oval cells, providing additional evidence that oval cells are bipolar stem cells and may give rise to either hepatocellular carcinoma or cholangiocarcinoma depending on the nature of the hepatocarcinogen and the species of animal. The recent development of mouse oval cell lines in our laboratory from aflatoxin B1-treated GSTA3-/- mice should provide a new venue for study of the properties and potential of putative mouse liver stem cells.

Inhibition of CREB binding protein-beta-catenin signaling down regulates CD133 expression and activates PP2A-PTEN signaling in tumor initiating liver cancer cells

Background

The WNT-beta-catenin pathway is known to regulate cellular homeostasis during development and tissue regeneration. Activation of WNT signaling increases the stability of cytoplasmic beta-catenin and enhances its nuclear translocation. Nuclear beta-catenin function is regulated by transcriptional co-factors such as CREB binding protein (CBP) and p300. Hyper-activated WNT-beta-catenin signaling is associated with many cancers. However, its role in inducing stemness to liver cancer cells, its autoregulation and how it regulates tumor suppressor pathways are not well understood. Here we have investigated the role of CBP-beta-catenin signaling on the expression of CD133, a known stem cell antigen and PP2A-PTEN pathway in tumor initiating liver cancer cells.

Methods

Human hepatoblastoma cell line HepG2 and clonally expanded CD133 expressing tumor initiating liver cells (TICs) from premalignant murine liver were used in this study. CBP-beta-catenin inhibitor ICG001 was used to target CBP-beta catenin signaling in liver cancer cells in vitro. Western blotting and real time PCR (qPCR) were used to quantify protein expression/phosphorylation and mRNA levels, respectively. CBP and CD133 gene silencing was performed by siRNA transfection. Fluorescence Activated Cell Sorting (FACS) was performed to quantify CD133 positive cells. Protein Phosphatase (PP2A) activity was measured after PP2AC immunoprecipitation.

Results

CBP inhibitor ICG001 and CBP silencing significantly reduced CD133 expression and anchorage independent growth in HepG2 and murine TICs. CD133 silencing in TICs decreased cell proliferation and expression levels of cell cycle regulatory genes, CyclinD1 and CyclinA2. ICG001 treatment and CBP silencing reduced the levels of phospho^{Ser380/Tyr382/383}PTEN, phospho^Ser473-AKT, Phospho-^Ser552beta-catenin in TICs. ICG001 mediated de-phosphorylation of PTEN in TICs was PP2A dependent and partly prevented by co-treatment with PP2A inhibitor okadaic acid.

Conclusions

CBP-beta-catenin signaling promotes stemness via CD133 induction and cell proliferation in TICs. We found a novel functional link between CBP-beta-catenin and PP2A-PTEN-AKT pathway in liver TICs. Therefore, CBP-beta-catenin-PP2A-PTEN-AKT signaling axis could be a novel therapeutic target to prevent liver tumor initiation and cancer recurrence.

Electronic supplementary material

The online version of this article (10.1186/s12964-018-0222-5) contains supplementary material, which is available to authorized users.

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.

Will a mAb-Based Immunotherapy Directed against Cancer Stem Cells Be Feasible?

The cancer stem cell (CSC) hypothesis suggests that within a tumor, there is a small subpopulation of cells with stem cell properties responsible for tumor maintenance and metastasis generation. This hypothesis also implies that new antitumor drugs, rather than targeting the bulk of the tumor mass, would be more effective if they directly targeted the CSC subpopulation. The CSCs from several types of tumors have been identified with mAbs recognizing surface antigens in these cells; however, antigens specifically or exclusively expressed in the CSC population have not yet been identified. Thus, questioning the possibility of using therapeutic antibodies directed against the CSCs. Here, we review the possibilities of using antibodies directly targeting the CSCs as therapeutic agents in the form of naked antibodies, antibodies conjugated to nanoparticles, or antibody cocktails.

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.

The C-terminus domain of the hepatitis B virus x protein stimulates the proliferation of mouse foetal hepatic progenitor cells, although it is not required for the formation of spheroids

The hepatitis B virus X (HBx) protein is an important factor in hepatitis B virus (HBV)-associated hepatocellular carcinoma (HCC). The C-terminal region of HBx plays a major role in the replication of HBV. Notably, HBx promotes the expansion and tumourigenesis of hepatic progenitor cells (HPCs) in mice. However, it remains unclear as to whether the C-terminal region of HBx is required for the stimulation fo the proliferation of mouse foetal HPCs (FHPCs). In our study, we used EpCAM+, CD133+ and CD49f+ FHPCs, which are bipotential clonogenic cells. These FHPCs transformed into mature hepatocytes and cholangiocytes when cultured under conditions that facilitate differentiation. Compared with the FHPCs grown as monolayers, spherical cell proliferation occurred more rapidly. Furthermore, spherically cultured FHPCs can grow in semi-solid agar and tend to maintain the morphology and characteristics of stem cells compared with growth in rat tail collagen. Notably, we also demonstrate that the C-terminus of HBx stimulates the proliferation of FHPCs, but is not required for the formation of spheroids, similar to hepatic cancer stem cells. These findings enhance our understanding of the HBx-induced tumourigenicity of FHPCs and may aid in the treatment of HCC.

The Role of Integrin α6 (CD49f) in Stem Cells: More than a Conserved Biomarker

Stem cells have the capacity for self-renewal and differentiation into specialized cells that form and repopulated all tissues and organs, from conception to adult life. Depending on their capacity for differentiation, stem cells are classified as totipotent (ie, zygote), pluripotent (ie, embryonic stem cells), multipotent (ie, neuronal stem cells, hematopoietic stem cells, epithelial stem cells, etc.), and unipotent (ie, spermatogonial stem cells). Adult or tissue-specific stem cells reside in specific niches located in, or nearby, their organ or tissue of origin. There, they have microenvironmental support to remain quiescent, to proliferate as undifferentiated cells (self-renewal), and to differentiate into progenitors or terminally differentiated cells that migrate from the niche to perform specialized functions. The presence of proteins at the cell surface is often used to identify, classify, and isolate stem cells. Among the diverse groups of cell surface proteins used for these purposes, integrin α6, also known as CD49f, may be the only biomarker commonly found in more than 30 different populations of stem cells, including some cancer stem cells. This broad expression among stem cell populations indicates that integrin α6 may play an important and conserved role in stem cell biology, which is reaffirmed by recent demonstrations of its role maintaining self-renewal of pluripotent stem cells and breast and glioblastoma cancer stem cells. Therefore, this review intends to highlight and synthesize new findings on the importance of integrin α6 in stem cell biology.

In Vitro Screening for Cytotoxic Activity of Herbal Extracts

Experimental studies have shown that a variety of chemopreventive plant components affect tumor initiation, promotion, and progression and the main difference, between botanical medicines and synthetic drugs, resides in the presence of complex metabolite mixtures shown by botanical medicine which in turn exert their action on different levels and via different mechanisms. In the present study, we performed an in vitro screening of ethanol extracts from commercial plants in order to investigate potential antitumor activity against human tumor cell lines. Experimental results obtained through a variety of methods and techniques indicated that extracts of I. verum, G. glabra, R. Frangula, and L. usitatissimum present significant reduction in in vitro tumor cell proliferation, suggesting these extracts as possible chemotherapeutical adjuvants for different cancer treatments.

Cancer stem cells in human gastrointestinal cancer

Cancer stem cells (CSCs) are thought to be responsible for tumor initiation, drug and radiation resistance, invasive growth, metastasis, and tumor relapse, which are the main causes of cancer-related deaths. Gastrointestinal cancers are the most common malignancies and still the most frequent cause of cancer-related mortality worldwide. Because gastrointestinal CSCs are also thought to be resistant to conventional therapies, an effective and novel cancer treatment is imperative. The first reported CSCs in a gastrointestinal tumor were found in colorectal cancer in 2007. Subsequently, CSCs were reported in other gastrointestinal cancers, such as esophagus, stomach, liver, and pancreas. Specific phenotypes could be used to distinguish CSCs from non-CSCs. For example, gastrointestinal CSCs express unique surface markers, exist in a side-population fraction, show high aldehyde dehydrogenase-1 activity, form tumorspheres when cultured in non-adherent conditions, and demonstrate high tumorigenic potential in immunocompromised mice. The signal transduction pathways in gastrointestinal CSCs are similar to those involved in normal embryonic development. Moreover, CSCs are modified by the aberrant expression of several microRNAs. Thus, it is very difficult to target gastrointestinal CSCs. This review focuses on the current research on gastrointestinal CSCs and future strategies to abolish the gastrointestinal CSC phenotype.

Existence of cancer stem cells in hepatocellular carcinoma: myth or reality?

The cancer stem cell (CSC) hypothesis has been disproved in many cancers. CSCs may exist in blood cancer, while many epithelial cancers may not have CSCs but tumor-initiating cells (TICs). Several independent studies have provided strong evidence for existence of CSCs in brain, skin, and colon cancers (Mani et al. in Cell 133:704-715, 2008, Joseph et al. in Cancer Cell 13:129-140, 2008, Reya et al. in Nature 414:105-111, 2001), while the CSC hypothesis remains controversial (Magee et al. in Cancer Cell 21:283-296, 2012). Liver TICs have bipotential to give rise to two different lineage types: hepatocellular carcinoma (HCC) and cholangiocarcinoma (CC). In the liver cancer field, the origin of HCC and CC is extensively debated. Several groups have validated that TICs gave rise to HCC and CC. Hepatocytes gave rise to HCC. Several groups have demonstrated that oval cells (or liver progenitor cells) give rise to TICs. However, CSCs may be a myth in gastrointestinal cancer, while many groups have validated liver TICs. The definition of CSCs includes pluripotency, while TICs do not have to have pluripotency and only need to have bi- or multipotential to give rise to diverse tumor types and tumor initiation potential in mouse models. The CSC hypothesis therefore controversial (Magee et al. in Cancer Cell 21:283-296, 2012). Cancer tissues contain subpopulations of cells known as tumor-initiating stem-like cells (TICs, so-called CSCs) that have been identified as key drivers of tumor growth and malignant progression with drug resistance. Stem cells proliferate via self-renewing division in which the two daughter cells differ in proliferative potential, with one displaying differentiated phenotype and the other retaining self-renewing activity.

Epigenome-wide DNA methylation analysis implicates neuronal and inflammatory signaling pathways in adult murine hepatic tumorigenesis following perinatal exposure to bisphenol A

Developmental exposure to the endocrine-active compound bisphenol A (BPA) has been linked to epigenotoxic and potential carcinogenic effects in rodent liver, prostate, and mammary glands. A dose-dependent increase in hepatic tumors in 10-month mice perinatally exposed to one of three doses of BPA (50 ng, 50 µg, or 50 mg BPA/kg chow) was previously reported. These tumors represent early-onset disease and lack classical sexual dimorphism in incidence. Here, adult epigenome-wide liver DNA methylation profiles to identify gene promoters associated with perinatal BPA exposure and disease in 10-month mice with and without liver tumors were investigated. Mice with hepatic tumors showed 12,822 (1.8%) probes with differential methylation as compared with non-tumor animals, of which 8,656 (67.5%) were hypomethylated. A significant enrichment of differential methylation in Gene Ontology (GO) terms and biological processes related to morphogenesis and development, and epigenomic alteration were observed. Pathway enrichment revealed a predominance of hypermethylated neuronal signaling pathways linked to energy regulation and metabolic function, supporting metabolic consequences in the liver via BPA-induced disruption of neuronal signaling pathways. Hypothesis-driven pathway analysis revealed mouse and human genes linked to BPA exposure related to intracellular Jak/STAT and MAPK signaling pathways. Taken together, these findings are indicators of the relevance of the hepatic tumor phenotype seen in BPA-exposed mice to human health. This work demonstrated that epigenome-wide discovery experiments in animal models were effective tools for identification and understanding of paralagous epimutations salient to human disease. Environ. Mol. Mutagen. 57:435-446, 2016. © 2016 Wiley Periodicals, Inc.

Toll-like receptor 3 mediates PROMININ-1 expressing cell expansion in biliary atresia via Transforming Growth Factor-Beta

BACKGROUND

In biliary atresia (BA), epithelial-mesenchymal hepatic progenitor cells (HPC) expressing the stem/progenitor cell marker PROMININ-1 (PROM1) undergo expansion and subsequent transdifferentiation into collagen-producing myofibroblasts within regions of evolving biliary fibrosis under the regulation of Transforming Growth Factor-β (TGFβ) signaling. We hypothesized that pro-inflammatory Toll-like Receptor-3 (TLR3) signal activation promotes the differentiation of PROM1+ HPC via TGFβ pathway activation in vitro.

METHODS

PROM1+ Mat1a(-/-) HPC were treated with a double-stranded RNA analog, polyionosinic-polycytidylic acid (Poly I:C), ± small molecule inhibitors nafamostat, or SB431542.

RESULTS

Poly I:C induced myofibroblastic-like morphologic changes, degradation of IκB-α consistent with TLR3-NFκB activation, a 15-fold increase in the expression of Vimentin, a 9-fold increase in Collagen-1a, a 4.6-fold increase in Snail at 24h (p<0.05), and an 8.2-fold increase in Prom1 at 72h (p<0.0001) by qPCR. Immunofluorescence demonstrated nuclear phosphorylated SMAD3, TLR3, and COLLAGEN-1α staining following Poly I:C treatment. Degradation of IκBα was inhibited by nafamostat. Co-treatment with either nafamostat or SB431542 blocked the morphologic change and abrogated the increased expression of Cd133, Collagen, Vimentin, and Snail1.

CONCLUSIONS

TLR3 activation induces myofibroblastic differentiation of PROM1+ HPC in part via TGFβ pathway activation to promote BA-associated biliary fibrosis.

Cancer Stem Cells: Formidable Allies of Cancer

Cancer stem cells (CSC) represent the subpopulation of cells within a tumour showing two fundamental properties of stem cells - self-renewal (the ability to make more of their own kind) and differentiation (the ability to generate diverse cell types present within a tissue). The CSC hypothesis posits that CSCs play an important role in tumour initiation, maintenance and progression. Furthermore, owing to their intrinsic drug resistance, they remain refractory to currently used therapy, thereby contributing to tumour relapse. Thus, targeting or taming CSCs can lead to more effective cancer treatment in the coming decades. In this review, we will discuss about the origin of CSC hypothesis, evidence showing their existence, clinical relevance and translational significance.

Cancer stem cells and personalized cancer nanomedicine

Despite the progress in cancer treatment over the past years advanced cancer is still an incurable disease. Special attention is pointed toward cancer stem cell (CSC)-targeted therapies, because this minor cell population is responsible for the treatment resistance, metastatic growth and tumor recurrence. The recently described CSC dynamic phenotype and interconversion model of cancer growth hamper even more the possible success of current cancer treatments in advanced cancer stages. Accordingly, CSCs can be generated through dedifferentiation processes from non-CSCs, in particular, when CSC populations are depleted after treatment. In this context, the use of targeted CSC nanomedicines should be considered as a promising tool to increase CSC sensitivity and efficacy of specific anti-CSC therapies.

NANOG Metabolically Reprograms Tumor-Initiating Stem-like Cells through Tumorigenic Changes in Oxidative Phosphorylation and Fatty Acid Metabolism

Stem cell markers, including NANOG, have been implicated in various cancers; however, the functional contribution of NANOG to cancer pathogenesis has remained unclear. Here, we show that NANOG is induced by Toll-like receptor 4 (TLR4) signaling via phosphorylation of E2F1 and that downregulation of Nanog slows down hepatocellular carcinoma (HCC) progression induced by alcohol western diet and hepatitis C virus protein in mice. NANOG ChIP-seq analyses reveal that NANOG regulates the expression of genes involved in mitochondrial metabolic pathways required to maintain tumor-initiating stem-like cells (TICs). NANOG represses mitochondrial oxidative phosphorylation (OXPHOS) genes, as well as ROS generation, and activates fatty acid oxidation (FAO) to support TIC self-renewal and drug resistance. Restoration of OXPHOS activity and inhibition of FAO renders TICs susceptible to a standard care chemotherapy drug for HCC, sorafenib. This study provides insights into the mechanisms of NANOG-mediated generation of TICs, tumorigenesis, and chemoresistance through reprogramming of mitochondrial metabolism.

Turning hepatic cancer stem cells inside out--a deeper understanding through multiple perspectives

Hepatocellular carcinoma (HCC), a highly malignant disease and the third leading cause of all cancer mortalities worldwide, often responses poorly to current treatments and results in dismal outcomes due to frequent chemoresistance and tumor relapse. The heterogeneity of HCC is an important attribute of the disease. It is the outcome of many factors, including the cross-talk between tumor cells within the tumor microenvironment and the acquisition and accumulation of genetic and epigenetic alterations in tumor cells. In addition, there is accumulating evidence in recent years to show that the malignancy of HCC can be attributed partly to the presence of cancer stem cell (CSC). CSCs are capable to self-renew, differentiate and initiate tumor formation. The regulation of the stem cell-like properties by several important signaling pathways have been found to endow the tumor cells with an increased level of tumorigenicity, chemoresistance, and metastatic ability. In this review, we will discuss the recent findings on hepatic CSCs, with special emphasis on their putative origins, relationship with hepatitis viruses, regulatory signaling networks, tumor microenvironment, and how these factors control the stemness of hepatic CSCs. We will also discuss some novel therapeutic strategies targeted at hepatic CSCs for combating HCC and perspectives of future investigation.

TLR4-dependent tumor-initiating stem cell-like cells (TICs) in alcohol-associated hepatocellular carcinogenesis

Alcohol abuse predisposes individuals to the development of hepatocellular carcinoma (HCC) and synergistically heightens the HCC risk in patients infected with hepatitis C virus (HCV). The mechanisms of this synergism have been elusive until our recent demonstration of the obligatory role of ectopically expressed TLR4 in liver tumorigenesis in alcohol-fed HCV Ns5a or Core transgenic mice. CD133+/CD49f+ tumor-initiating stem cell-like cells (TICs) isolated from these models are tumorigenic in a manner dependent on TLR4 and NANOG. TICs' tumor-initiating activity and chemoresistance are causally associated with inhibition of TGF-β tumor suppressor pathway due to NANOG-mediated expression of IGF2BP3 and YAP1. TLR4/NANOG activation causes p53 degradation via phosphorylation of the protective protein NUMB and its dissociation from p53 by the oncoprotein TBC1D15. Nutrient deprivation reduces overexpressed TBC1D15 in TICs via autophagy-mediated degradation, suggesting a possible role of this oncoprotein in linking metabolic reprogramming and self-renewal.

Oncogenic signaling pathways and origins of tumor-initiating stem-like cells of hepatocellular carcinomas induced by hepatitis C virus, alcohol and/or obesity

This review article discusses the importance and oncogenic signaling pathways of tumor-initiating cells (TICs) in several etiologies of hepatocellular carcinomas (HCCs) induced by hepatitis C virus (HCV), alcohol, obesity and/or chemicals. Stem cells may be present in cancer tissue, and a hierarchy of cells is formed, as is the case for normal tissue. Tumor formation, growth and propagation are maintained by a small proportion of cells with stem cell-like properties. TICs are present in alcohol-fed HCV transgenic mice, diethylnitrosamine/phenobarbital-treated mice (chemical carcinogenesis) and Spnb2 +/- mice (defective TGF-β signal). Alcohol/obesity-associated endotoxemia induces the stem cell marker Nanog through TLR4 signaling to generate TICs and liver tumors in several HCC models. The oncogenic pathway (such as the STAT3 and TLR4-NANOG pathway) and mechanism of generation of TICs of HCCs associated with HCV, alcohol and obesity are discussed. Understanding the molecular stemness signaling and cellular hierarchy and defining key TIC-specific genes will accelerate the development of novel biomarkers and treatment strategies. This review highlights recent advances in understanding the pathogenesis of liver TICs and discusses unanswered questions about the concept of liver TICs. (This project was supported by NIH grants 1R01AA018857 and P50AA11999).

UVB-induced gene expression in the skin of Xiphophorus maculatus Jp 163 B

Xiphophorus fish and interspecies hybrids represent long-standing models to study the genetics underlying spontaneous and induced tumorigenesis. The recent release of the Xiphophorus maculatus genome sequence will allow global genetic regulation studies of genes involved in the inherited susceptibility to UVB-induced melanoma within select backcross hybrids. As a first step toward this goal, we report results of an RNA-Seq approach to identify genes and pathways showing modulated transcription within the skin of X. maculatus Jp 163 B upon UVB exposure. X. maculatus Jp 163 B were exposed to various doses of UVB followed by RNA-Seq analysis at each dose to investigate overall gene expression in each sample. A total of 357 genes with a minimum expression change of 4-fold (p-adj<0.05) were identified as responsive to UVB. The molecular genetic response of Xiphophorus skin to UVB exposure permitted assessment of; (1) the basal expression level of each transcript for each skin sample, (2) the changes in expression levels for each gene in the transcriptome upon exposure to increasing doses of UVB, and (3) clusters of genes that exhibit similar patterns of change in expression upon UVB exposure. These data provide a foundation for understanding the molecular genetic response of fish skin to UVB exposure.

Fibroblast growth factor family as a potential target in the treatment of hepatocellular carcinoma

Hepatocellular cancer (HCC) is currently the third leading cause of cancer death worldwide. The prognosis of patients diagnosed with late-stage disease is dismal due to high resistance to conventional systemic therapies. The introduction of sorafenib, despite its limited efficacy, as the standard systemic therapy for advanced HCC has paved a way for targeted molecular therapies for HCC. Fibroblast growth factor (FGF) signaling plays an important role in the developing embryo and the adult. The FGF signaling pathway is often hijacked by cancer cells, including HCC. Several alterations in FGF signaling correlate with poor outcome in HCC patients, suggesting that this family of signaling molecules plays an important role in the development of HCC. Multikinase inhibitors targeting FGF signaling are currently under investigation in clinical trials. This review discusses the current understanding of the biological and clinical implications of aberrant FGF signaling in the prognosis, diagnosis, and treatment of HCC.

Cellular reprogramming and hepatocellular carcinoma development

Hepatocellular carcinoma (HCC) is one of the most common cancers, and is also the leading cause of death worldwide. Studies have shown that cellular reprogramming contributes to chemotherapy and/or radiotherapy resistance and the recurrence of cancers. In this article, we summarize and discuss the latest findings in the area of cellular reprogramming in HCC. The aberrant expression of transcription factors OCT4, KLF4, SOX2, c-MYC, NANOG, and LIN28 have been also observed, and the expression of these transcription factors is associated with unfavorable clinical outcomes in HCC. Studies indicate that cellular reprogramming may play a critical role in the occurrence and recurrence of HCC. Recent reports have shown that DNA methylation, miRNAs, tumor microenvironment, and signaling pathways can induce the expression of stemness transcription factors, which leads to cellular reprogramming in HCC. Furthermore, studies indicate that therapies based on cellular reprogramming could revolutionize HCC treatment. Finally, a novel therapeutic concept is discussed: reprogramming control therapy. A potential reprogramming control therapy method could be developed based on the reprogramming demonstrated in HCC studies and applied at two opposing levels: differentiation and reprogramming. Our increasing understanding and control of cellular programming should facilitate the exploitation of this novel therapeutic concept and its application in clinical HCC treatment, which may represent a promising strategy in the future that is not restricted to liver cancer.

Reciprocal regulation by TLR4 and TGF-β in tumor-initiating stem-like cells

Tumor-initiating stem-like cells (TICs) are resistant to chemotherapy and associated with hepatocellular carcinoma (HCC) caused by HCV and/or alcohol-related chronic liver injury. Using HCV Tg mouse models and patients with HCC, we isolated CD133(+) TICs and identified the pluripotency marker NANOG as a direct target of TLR4, which drives the tumor-initiating activity of TICs. These TLR4/NANOG-dependent TICs were defective in the TGF-β tumor suppressor pathway. Functional oncogene screening of a TIC cDNA library identified Yap1 and Igf2bp3 as NANOG-dependent genes that inactivate TGF-β signaling. Mechanistically, we determined that YAP1 mediates cytoplasmic retention of phosphorylated SMAD3 and suppresses SMAD3 phosphorylation/activation by the IGF2BP3/AKT/mTOR pathway. Silencing of both YAP1 and IGF2BP3 restored TGF-β signaling, inhibited pluripotency genes and tumorigenesis, and abrogated chemoresistance of TICs. Mice with defective TGF-β signaling (Spnb2(+/-) mice) exhibited enhanced liver TLR4 expression and developed HCC in a TLR4-dependent manner. Taken together, these results suggest that the activated TLR4/NANOG oncogenic pathway is linked to suppression of cytostatic TGF-β signaling and could potentially serve as a therapeutic target for HCV-related HCC.

Understanding and targeting cancer stem cells: therapeutic implications and challenges

Cancer stem cells (CSCs) have been identified as rare cell populations in many cancers, including leukemia and solid tumors. Accumulating evidence has suggested that CSCs are capable of self-renewal and differentiation into various types of cancer cells. Aberrant regulation of gene expression and some signaling pathways has been observed in CSCs compared to other tumor cells. CSCs are thought to be responsible for cancer initiation, progression, metastasis, recurrence and drug resistance. The CSC hypothesis has recently attracted much attention due to the potential for discovery and development of CSC-related therapies and the identification of key molecules involved in controlling the unique properties of CSC populations. Over the past several years, a tremendous amount of effort has been invested in the development of new drugs, such as nanomedicines, that can take advantage of the "Achilles' heel" of CSCs by targeting cell-surface molecular markers or various signaling pathways. Novel compounds and therapeutic strategies that selectively target CSCs have been identified, some of which have been evaluated in preclinical and clinical studies. In this article, we review new findings related to the investigation of the CSC hypothesis, and discuss the crucial pathways involved in regulating the development of CSC populations and the advances in studies of drug resistance. In addition, we review new CSC-targeted therapeutic strategies aiming to eradicate malignancies.

Tumor-initiating stem-like cells and drug resistance: carcinogenesis through Toll-like receptors, environmental factors, and virus

Neoplasms contain distinct subpopulations of cells known as tumor-initiating stem-like cells (TICs) that have been identified as key drivers of tumor growth and malignant progression with drug resistance. Stem cells normally proliferate through self-renewing divisions in which the two daughter cells differ markedly in their proliferative potential, with one displaying the differentiation phenotypes and another retaining self-renewing activity. Therefore, understanding the molecular mechanisms of hepatocarcinogenesis will be required for the eventual development of improved therapeutic modalities for treating hepatocellular carcinoma (HCC). Hepatitis C virus (HCV) and hepatitis B virus is a major cause of HCC. Compelling epidemiologic evidence identifies obesity and alcohol as co-morbidity factors that can increase the risk of HCV patients for HCC, especially in alcoholics or obese patients. The mechanisms underlying liver oncogenesis, and how environmental factors contribute to this process, are not yet understood. The HCV-Toll-like receptor 4 (TLR4)-Nanog signaling network is established since alcohol/obesity-associated endotoxemia then activates TLR4 signaling, resulting in the induction of the stem cell marker Nanog expression and liver tumors. Liver TICs are highly sensitized to leptin and exposure of TICs to leptin increases the expression and activity of an intrinsic pluripotency-associated transcriptional network comprised of signal transducer and activator of transcription 3, SOX2, OCT4, and Nanog. Stimulation of the pluripotency network may have significant implications for hepatocellular oncogenesis via genesis and maintenance of TICs. It is important to understand how HCV induces liver cancer through genesis of TICs so that better prevention and treatment can be found. This article reviews the oncogenic pathways to generate TICs.

Enhanced tumorigenesis and lymphatic metastasis of CD133+ hepatocarcinoma ascites syngeneic cell lines mediated by JNK signaling pathway in vitro and in vivo

Cancer stem cells (CSCs), stem-like cells, or tumor-initiating cells (TICs) may initiate tumorigenesis and metastasis, but neither the basic cell biology of CSCs nor the mechanisms of CSC-mediated tumor growth and lymphoid node metastasis are understood. Evidence suggests that CSC phenotype is maintained, at least in part, by altered JNK signaling. In this study, factors influencing the growth and metastatic potential of CSCs were examined by comparing CD133 surface antigen expression, proliferation, clonogenicity, invasive capacity, tumorigenicity, and expression of JNK-associated signaling molecules between the highly metastatic mouse hepatocarcinoma ascites syngeneic cell line Hca-F and the low metastasis potential line Hca-P. The Hca-F line exhibited higher clonogenic, proliferative, and invasive capacities than Hca-P cells, and a greater proportion of Hca-F cells were CD133 positive. In both cell lines, the CD133+ subpopulation showed significantly enhanced tumorigenicity and metastatic potential. An in vivo tumorigenicity assay in nude mice indicated that Hca-F cells possessed significantly higher tumorigenicity than Hca-P cells as indicated by larger tumors after inoculation. Expression levels of E-cadherin (CDH1), annexin VII, and JNK1 proteins were inversely correlated with CD133 expression in both Hca-F and Hca-P cells. These results demonstrate that CD133+ subpopulations of both Hca-F and Hca-P lines show CSC-like properties. However, Hca-F cells showed greater tumorigenicity and invasiveness, consistent with greater lymphatic metastasis capacity. We propose that tumorigenesis and lymphatic metastasis are regulated by JNK/P53/annexin VII and JNK/ATF-2/CDH1/annexin VII signal transduction pathways.

Fibroblast growth factor receptor-mediated activation of AKT-β-catenin-CBP pathway regulates survival and proliferation of murine hepatoblasts and hepatic tumor initiating stem cells

Fibroblast Growth Factor (FGF)-10 promotes the proliferation and survival of murine hepatoblasts during early stages of hepatogenesis through a Wnt-β-catenin dependent pathway. To determine the mechanism by which this occurs, we expanded primary culture of hepatoblasts enriched for progenitor markers CD133 and CD49f from embryonic day (E) 12.5 fetal liver and an established tumor initiating stem cell line from Mat1a(-/-) livers in media conditioned with recombinant (r) FGF10 or rFGF7. FGF Receptor (R) activation resulted in the downstream activation of MAPK, PI3K-AKT, and β-catenin pathways, as well as cellular proliferation. Additionally, increased levels of nuclear β-catenin phosphorylated at Serine-552 in cultured primary hepatoblasts, Mat1a(-/-) cells, and also in ex vivo embryonic liver explants indicate AKT-dependent activation of β-catenin downstream of FGFR activation; conversely, the addition of AKT inhibitor Ly294002 completely abrogated β-catenin activation. FGFR activation-induced cell proliferation and survival were also inhibited by the compound ICG-001, a small molecule inhibitor of β-catenin-CREB Binding Protein (CBP) in hepatoblasts, further indicating a CBP-dependent regulatory mechanism of β-catenin activity.

CONCLUSION

FGF signaling regulates the proliferation and survival of embryonic and transformed progenitor cells in part through AKT-mediated activation of β-catenin and downstream interaction with the transcriptional co-activator CBP.

S-adenosylmethionine in liver health, injury, and cancer

S-adenosylmethionine (AdoMet, also known as SAM and SAMe) is the principal biological methyl donor synthesized in all mammalian cells but most abundantly in the liver. Biosynthesis of AdoMet requires the enzyme methionine adenosyltransferase (MAT). In mammals, two genes, MAT1A that is largely expressed by normal liver and MAT2A that is expressed by all extrahepatic tissues, encode MAT. Patients with chronic liver disease have reduced MAT activity and AdoMet levels. Mice lacking Mat1a have reduced hepatic AdoMet levels and develop oxidative stress, steatohepatitis, and hepatocellular carcinoma (HCC). In these mice, several signaling pathways are abnormal that can contribute to HCC formation. However, injury and HCC also occur if hepatic AdoMet level is excessive chronically. This can result from inactive mutation of the enzyme glycine N-methyltransferase (GNMT). Children with GNMT mutation have elevated liver transaminases, and Gnmt knockout mice develop liver injury, fibrosis, and HCC. Thus a normal hepatic AdoMet level is necessary to maintain liver health and prevent injury and HCC. AdoMet is effective in cholestasis of pregnancy, and its role in other human liver diseases remains to be better defined. In experimental models, it is effective as a chemopreventive agent in HCC and perhaps other forms of cancer as well.