Liver enriched transcription factors and differentiation of hepatocellular carcinoma

Therapeutic potential of lipin inhibitors for the treatment of cancer

Lipins are phosphatidic acid phosphatases (PAP) that catalyze the conversion of phosphatidic acid (PA) to diacylglycerol (DAG). Three lipin isoforms have been identified: lipin-1, -2 and -3. In addition to their PAP activity, lipin-1 and -2 act as transcriptional coactivators and corepressors. Lipins have been intensely studied for their role in regulation of lipid metabolism and adipogenesis; however, lipins are hypothesized to mediate several pathologies, such as those involving metabolic diseases, neuropathy and even cognitive impairment. Recently, an emerging role for lipins have been proposed in cancer. The study of lipins in cancer has been hampered by lack of inhibitors that have selectivity for lipins, that differentiate between lipin family members, or that are suitable for in vivo studies. Such inhibitors have the potential to be extremely useful as both molecular tools and therapeutics. This review describes the expression and function of lipins in various tissues and their roles in several diseases, but with an emphasis on their possible role in cancer. The mechanisms by which lipins mediate cancer cell growth are discussed and the potential usefulness of selective lipin inhibitors is hypothesized. Finally, recent studies reporting the crystallization of lipin-1 are discussed to facilitate rational design of novel lipin inhibitors.

A Kaleidoscope of Keratin Gene Expression and the Mosaic of Its Regulatory Mechanisms

Keratins are a family of intermediate filament-forming proteins highly specific to epithelial cells. A combination of expressed keratin genes is a defining property of the epithelium belonging to a certain type, organ/tissue, cell differentiation potential, and at normal or pathological conditions. In a variety of processes such as differentiation and maturation, as well as during acute or chronic injury and malignant transformation, keratin expression undergoes switching: an initial keratin profile changes accordingly to changed cell functions and location within a tissue as well as other parameters of cellular phenotype and physiology. Tight control of keratin expression implies the presence of complex regulatory landscapes within the keratin gene loci. Here, we highlight patterns of keratin expression in different biological conditions and summarize disparate data on mechanisms controlling keratin expression at the level of genomic regulatory elements, transcription factors (TFs), and chromatin spatial structure.

Transcriptional Regulation of Liver-Type OATP1B3 (Lt-OATP1B3) and Cancer-Type OATP1B3 (Ct-OATP1B3) Studied in Hepatocyte-Derived and Colon Cancer-Derived Cell Lines

Due to alternative splicing, the SLCO1B3 gene encodes two protein variants; the hepatic uptake transporter liver-type OATP1B3 (Lt-OATP1B3) and the cancer-type OATP1B3 (Ct-OATP1B3) expressed in several cancerous tissues. There is limited information about the cell type-specific transcriptional regulation of both variants and about transcription factors regulating this differential expression. Therefore, we cloned DNA fragments from the promoter regions of the Lt-SLCO1B3 and the Ct-SLCO1B3 gene and investigated their luciferase activity in hepatocellular and colorectal cancer cell lines. Both promoters showed differences in their luciferase activity depending on the used cell lines. We identified the first 100 bp upstream of the transcriptional start site as the core promoter region of the Ct-SLCO1B3 gene. In silico predicted binding sites for the transcription factors ZKSCAN3, SOX9 and HNF1α localized within these fragments were further analyzed. The mutagenesis of the ZKSCAN3 binding site reduced the luciferase activity of the Ct-SLCO1B3 reporter gene construct in the colorectal cancer cell lines DLD1 and T84 to 29.9% and 14.3%, respectively. In contrast, using the liver-derived Hep3B cells, 71.6% residual activity could be measured. This indicates that the transcription factors ZKSCAN3 and SOX9 are important for the cell type-specific transcriptional regulation of the Ct-SLCO1B3 gene.

Mechanism of paracrine communications between hepatic progenitor cells and endothelial cells

Hepatic progenitor cells (HPCs) are facultative tissue-specific stem cells lining reactive ductules, which are ubiquitously observed in chronic liver diseases and cancer. Although previous research mainly focused on their contribution to liver regeneration, it turned out that in vivo differentiation of HPCs into hepatocytes only occurs after extreme injury. While recent correlative evidence implies the association of HPCs with disease progression, their exact role in pathogenesis remains largely unknown. Our previous research demonstrated that HPCs expressing angiogenic paracrine factors accumulate in the peritumoral area and are positively correlated with the extent of intratumoral cell proliferation and angiogenesis in the livers of patients with liver cancer. Given the crucial roles of angiogenesis in liver disease progression and carcinogenesis, we aimed to test the hypothesis that HPCs secrete paracrine factors to communicate with endothelial cells, to determine molecular mechanisms mediating HPCs-endothelial interactions, and to understand how the paracrine function of HPCs is regulated. HPCs promoted viability and tubulogenesis of human umbilical vein endothelial cells (HUVECs) and upregulated genes known to be involved in angiogenesis, endothelial cell function, and disease progression in a paracrine manner. The paracrine function of HPCs as well as expression of colony stimulating factor 1 (CSF1) were inhibited upon differentiation of HPCs toward hepatocytes. Inhibition of CSF1 receptor partly suppressed the paracrine effects of HPCs on HUVECs. Taken together, our study indicates that inhibition of the paracrine function of HPCs through modulation of their differentiation status and inhibition of CSF1 signaling is a promising strategy for inhibition of angiogenesis during pathological progression.

Transcriptional control by HNF-1: Emerging evidence showing its role in lipid metabolism and lipid metabolism disorders

The present review focuses on the roles and underlying mechanisms of action of hepatic nuclear factor-1 (HNF-1) in lipid metabolism and the development of lipid metabolism disorders. HNF-1 is a transcriptional regulator that can form homodimers, and the HNF-1α and HNF-1β isomers can form heterodimers. Both homo- and heterodimers recognize and bind to specific cis-acting elements in gene promoters to transactivate transcription and to coordinate the expression of target lipid-related genes, thereby influencing the homeostasis of lipid metabolism. HNF-1 was shown to restrain lipid anabolism, including synthesis, absorption, and storage, by inhibiting the expression of lipogenesis-related genes, such as peroxisome proliferator-activated receptor γ (PPARγ) and sterol regulatory element-binding protein-1/2 (SREBP-1/2). Moreover, HNF-1 enhances the expression of various genes, such as proprotein convertase subtilisin/kexin type 9 (PCSK9), glutathione peroxidase 1 (GPx1), and suppressor of cytokine signaling-3 (SOCS-3) and negatively regulates signal transducer and activator of transcription (STAT) to facilitate lipid catabolism in hepatocytes. HNF-1 reduces hepatocellular lipid decomposition, which alleviates the progression of nonalcoholic fatty liver disease (NAFLD). HNF-1 impairs preadipocyte differentiation to reduce the number of adipocytes, stunting the development of obesity. Furthermore, HNF-1 reduces free cholesterol levels in the plasma to inhibit aortic lipid deposition and lipid plaque formation, relieving dyslipidemia and preventing the development of atherosclerotic cardiovascular disease (ASCVD). In summary, HNF-1 transcriptionally regulates lipid-related genes to manipulate intracorporeal balance of lipid metabolism and to suppress the development of lipid metabolism disorders.

The CpG Island-Binding Protein SAMD1 Contributes to an Unfavorable Gene Signature in HepG2 Hepatocellular Carcinoma Cells

The unmethylated CpG island-binding protein SAMD1 is upregulated in many human cancer types, but its cancer-related role has not yet been investigated. Here, we used the hepatocellular carcinoma cell line HepG2 as a cancer model and investigated the cellular and transcriptional roles of SAMD1 using ChIP-Seq and RNA-Seq. SAMD1 targets several thousand gene promoters, where it acts predominantly as a transcriptional repressor. HepG2 cells with SAMD1 deletion showed slightly reduced proliferation, but strongly impaired clonogenicity. This phenotype was accompanied by the decreased expression of pro-proliferative genes, including MYC target genes. Consistently, we observed a decrease in the active H3K4me2 histone mark at most promoters, irrespective of SAMD1 binding. Conversely, we noticed an increase in interferon response pathways and a gain of H3K4me2 at a subset of enhancers that were enriched for IFN-stimulated response elements (ISREs). We identified key transcription factor genes, such as IRF1, STAT2, and FOSL2, that were directly repressed by SAMD1. Moreover, SAMD1 deletion also led to the derepression of the PI3K-inhibitor PIK3IP1, contributing to diminished mTOR signaling and ribosome biogenesis pathways. Our work suggests that SAMD1 is involved in establishing a pro-proliferative setting in hepatocellular carcinoma cells. Inhibiting SAMD1's function in liver cancer cells may therefore lead to a more favorable gene signature.

HepG2-Based Designer Cells with Heat-Inducible Enhanced Liver Functions

Functional human hepatocytes have been a pivotal tool in pharmacological studies such as those investigating drug metabolism and hepatotoxicity. However, primary human hepatocytes are difficult to obtain in large quantities and may cause ethical problems, necessitating the development of a new cell source to replace human primary hepatocytes. We previously developed genetically modified murine hepatoma cell lines with inducible enhanced liver functions, in which eight liver-enriched transcription factor (LETF) genes were introduced into hepatoma cells as inducible transgene expression cassettes. Here, we establish a human hepatoma cell line with heat-inducible liver functions using HepG2 cells. The genetically modified hepatoma cells, designated HepG2/8F_HS, actively proliferated under normal culture conditions and, therefore, can be easily prepared in large quantities. When the expression of LETFs was induced by heat treatment at 43 °C for 30 min, cells ceased proliferation and demonstrated enhanced liver functions. Furthermore, three-dimensional spheroid cultures of HepG2/8F_HS cells showed a further increase in liver functions upon heat treatment. Comprehensive transcriptome analysis using DNA microarrays revealed that HepG2/8F_HS cells had enhanced overall expression of many liver function-related genes following heat treatment. HepG2/8F_HS cells could be useful as a new cell source for pharmacological studies and for constructing bioartificial liver systems.

Hepatocellular Carcinoma Differentiation: Research Progress in Mechanism and Treatment

Hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver. Although progress has been made in diagnosis and treatment, morbidity and mortality continue to rise. Chronic liver disease and liver cirrhosis are still the most important risk factors for liver cancer. Although there are many treatments, it can only be cured by orthotopic liver transplantation (OLT) or surgical resection. And the worse the degree of differentiation, the worse the prognosis of patients with liver cancer. Then it can be considered that restoring a better state of differentiation may improve the prognosis. The differentiation treatment of liver cancer is to reverse the dedifferentiation process of hepatocytes to liver cancer cells by means of drugs, improve the differentiation state of the tumor, and restore the normal liver characteristics, so as to improve the prognosis. Understanding the mechanism of dedifferentiation of liver cancer can provide ideas for drug design. Liver enrichment of transcription factors, imbalance of signal pathway and changes of tumor microenvironment can promote the occurrence and development of liver cancer, and restoring its normal level can inhibit the malignant behavior of tumor. At present, some drugs have been proved to be effective, but more clinical data are needed to support the effectiveness and reliability of drugs. The differentiation treatment of liver cancer is expected to become an important part of the treatment of liver cancer in the future.

Transcriptional control by HNF-1: Emerging evidence showing its role in lipid metabolism and lipid metabolism disorders

The present review focuses on the roles and underlying mechanisms of action of hepatic nuclear factor-1 (HNF-1) in lipid metabolism and the development of lipid metabolism disorders. HNF-1 is a transcriptional regulator that can form homodimers, and the HNF-1α and HNF-1β isomers can form heterodimers. Both homo- and heterodimers recognize and bind to specific cis-acting elements in gene promoters to transactivate transcription and to coordinate the expression of target lipid-related genes, thereby influencing the homeostasis of lipid metabolism. HNF-1 was shown to restrain lipid anabolism, including synthesis, absorption, and storage, by inhibiting the expression of lipogenesis-related genes, such as peroxisome proliferator-activated receptor γ (PPARγ) and sterol regulatory element-binding protein-1/2 (SREBP-1/2). Moreover, HNF-1 enhances the expression of various genes, such as proprotein convertase subtilisin/kexin type 9 (PCSK9), glutathione peroxidase 1 (GPx1), and suppressor of cytokine signaling-3 (SOCS-3) and negatively regulates signal transducer and activator of transcription (STAT) to facilitate lipid catabolism in hepatocytes. HNF-1 reduces hepatocellular lipid decomposition, which alleviates the progression of nonalcoholic fatty liver disease (NAFLD). HNF-1 impairs preadipocyte differentiation to reduce the number of adipocytes, stunting the development of obesity. Furthermore, HNF-1 reduces free cholesterol levels in the plasma to inhibit aortic lipid deposition and lipid plaque formation, relieving dyslipidemia and preventing the development of atherosclerotic cardiovascular disease (ASCVD). In summary, HNF-1 transcriptionally regulates lipid-related genes to manipulate intracorporeal balance of lipid metabolism and to suppress the development of lipid metabolism disorders.

Signaling molecules orchestrating liver regenerative medicine

The liver is in charge of more than 500 functions in the human body, which any damage and failure to the liver can significantly compromise human life. Numerous studies are being carried out in regenerative medicine, as a potential driving force, toward alleviating the need for liver donors and fabrication of a 3D-engineered transplantable hepatic tissue. Liver tissue engineering brings three main factors of cells, extracellular matrix (ECM), and signaling molecules together, while each of these three factors tries to mimic the physiological state of the tissue to direct tissue regeneration. Signaling molecules play a crucial role in directing tissue fabrication in liver tissue engineering. When mimicking the natural in vivo process of regeneration, it is tightly associated with three main phases of differentiation, proliferation (progression), and tissue maturation through vascularization while directing each of these phases is highly regulated by the specific signaling molecules. The understanding of how these signaling molecules guide the dynamic behavior of regeneration would be a tool for further tailoring of bioengineered systems to help the liver regeneration with many cellular, molecular, and tissue-level functions. Hence, the signaling molecules come to aid all these phases for further improvements toward the clinical use of liver tissue engineering as the goal.

Dedifferentiation of hepatocellular carcinoma: molecular mechanisms and therapeutic implications

Hepatocellular carcinoma (HCC) is a common cancer with high morbidity and mortality. Poorer differentiation status indicates worse prognosis of HCC patients. Regain of better differentiation status may improve the prognosis. Differentiation therapy for HCC is based on the fact that agents may reverse the dedifferentiation process from hepatocytes to HCC cells and thus improve tumor differentiation status. Reversal of progenitor-like property and restoration of hepatic characteristics are main objectives of HCC differentiation therapy. Comprehending the mechanisms of HCC dedifferentiation provides ideas for drug design. Diverse dysregulated molecules and signalings cooperatively cause HCC dedifferentiation. Dysregulation of liver enriched transcription factors, especially hepatocyte nuclear factor 4α, was a critical determinant of HCC dedifferentiation. Aberrant pivotal signaling molecules such as transforming factor-β, β-catenin and Yes-associated protein caused disordered signalings, which promoted HCC dedifferentiation. Loss of epithelial morphology during epithelial-mesenchymal transition (EMT) concurred with HCC dedifferentiation. Some EMT-related molecules exerted double-sided role in concurrently inducing EMT and HCC dedifferentiation. Besides, microRNAs (e.g. miR-122 and miR-148a) as well as some impressive proteins (i.e. KLF4, gankyrin and CHD1L) functioned in manipulating HCC differentiation status. Restoring normal expression levels of these molecules could induce HCC differentiation and inhibited malignant tumor behaviors. Based on the knowledge above, some agents have been found effective in lab, but need more data to support their reliability. Additionally, peretinoin as a potential drug is in progress of several phase III clinical trials. It's promising that differentiation therapy for HCC may be a part of options in future HCC treatment.

Tissue-specific transcription reprogramming promotes liver metastasis of colorectal cancer

Metastasis, the development of secondary malignant growths at a distance from a primary tumor, is the cause of death for 90% of cancer patients, but little is known about how metastatic cancer cells adapt to and colonize new tissue environments. Here, using clinical samples, patient-derived xenograft (PDX) samples, PDX cells, and primary/metastatic cell lines, we discovered that liver metastatic colorectal cancer (CRC) cells lose their colon-specific gene transcription program yet gain a liver-specific gene transcription program. We showed that this transcription reprogramming is driven by a reshaped epigenetic landscape of both typical enhancers and super-enhancers. Further, we identified that the liver-specific transcription factors FOXA2 and HNF1A can bind to the gained enhancers and activate the liver-specific gene transcription, thereby driving CRC liver metastasis. Importantly, similar transcription reprogramming can be observed in multiple cancer types. Our data suggest that reprogrammed tissue-specific transcription promotes metastasis and should be targeted therapeutically.

Effects of C2-Ceramide and Oltipraz on Hepatocyte Nuclear Factor-1 and Glutathione S-Transferase A1 in Acetaminophen-Mediated Acute Mice Liver Injury

In this study, acetaminophen (APAP)-induced acute liver injury mice model was used to investigate the effects of C2-ceramide and oltipraz on hepatocyte nuclear factor 1 (HNF-1) and glutathione S-transferase A1 (GSTA1). Notably, C2-ceramide caused alteration in mice serum transaminases and liver tissue indexes, and aggravated hepatic injury, while oltipraz alleviated hepatic injury. By screening, the optimal concentrations of C2-ceramide and oltipraz were confirmed to be 120 and 150 μmol/L, respectively. In histopathology, karyolysis and more necrotic cells and bleeding spots were appeared on administration of C2-ceramide, but only a small amount of inflammatory cells infiltration was seen after oltipraz treatment. In addition, RT-PCR and western blot results revealed that the mRNA and protein expression levels of HNF-1 and GSTA1 in liver were significantly decreased (p < 0.01) with the administration of 120 μmol/L C2-ceramide. Meanwhile, GSTA1 content in serum increased up to 1.27-fold. In contrast, 150 μmol/L oltipraz incorporation to APAP model mice resulted in obvious elevation (p < 0.01) in the mRNA and protein expression levels of HNF-1 and GSTA1 in liver, and serum GSTA1 content decreased up to 0.77-fold. In conclusion, C2-ceramide could down-regulate the expression of HNF-1 and GSTA1 which exacerbated hepatic injury, while oltipraz could up-regulate the expression of HNF-1 and GSTA1 which mitigated hepatic injury.

HNF-4α promotes multidrug resistance of gastric cancer cells through the modulation of cell apoptosis

Multidrug resistance (MDR) typically leads to treatment failure, and is associated with disease progression of gastric cancer (GC). In the present study, a total of 15 aberrantly activated transcription factors (TFs) were detected in chemo-resistant GC cells using a TF Activation Profiling Plate Array. Among these TFs, hepatocyte nuclear factor (HNF)-4α was significantly upregulated in multidrug-resistant GC cells (P=0.019). The overexpression of HNF-4α was able to cause resistance to multiple chemotherapeutics, whereas inhibition of HNF-4α appeared to reverse cancer cell resistance. Further studies demonstrated that HNF-4α had no clear influence on drug transportation; however, inhibition of drug-induced cell apoptosis occurred as B-cell lymphoma 2 (Bcl-2) expression increased in GC cells. Additionally, immunohistochemistry demonstrated that HNF-4α was overexpressed in human GC tissues, and associated with tumor stage and lymph node metastasis. In conclusion, the results of the present study indicate the involvement of TFs in MDR in GC, and suggest that HNF-4α may enhance MDR in GC by regulating cell apoptosis and Bcl-2 expression.

Characterization of genetically engineered mouse hepatoma cells with inducible liver functions by overexpression of liver-enriched transcription factors

New cell sources for the research and therapy of organ failure could significantly alleviate the shortage of donor livers that are available to patients who suffer from liver disease. Liver carcinoma derived cells, or hepatoma cells, are the ideal cells for developing bioartificial liver systems. Such cancerous liver cells are easy to prepare in large quantities and can be maintained over long periods under standard culture conditions, unlike primary hepatocytes. However, hepatoma cells possess only a fraction of the functions of primary hepatocytes. In a previous study, by transducing cells with liver-enriched transcription factors that could be inducibly overexpressed-hepatocyte nuclear factor (HNF)1α, HNF1β, HNF3β [FOXA2], HNF4α, HNF6, CCAAT/enhancer binding protein (C/EBP)α, C/EBPβ and C/EBPγ-we created mouse hepatoma cells with high liver-specific gene expression called the Hepa/8F5 cell line. In the present study, we performed functional and genetic analyses to characterize the Hepa/8F5 cell line. Further, in three-dimensional cultures, the function of these cells improved significantly compared to parental cells. Ultimately, these cells might become a new resource that can be used in basic and applied hepatic research.

Oroxylin A activates PKM1/HNF4 alpha to induce hepatoma differentiation and block cancer progression

Liver cancer is the second cause of death from cancer worldwide, without effective treatment. Traditional chemotherapy for liver cancer has big side effects for patients, whereas targeted drugs, such as sorafenib, commonly have drug resistance. Oroxylin A (OA) is the main bioactive flavonoids of Scutellariae radix, which has strong anti-hepatoma effect but low toxicity to normal tissue. To date, no differentiation-inducing agents have been reported to exert a curative effect on solid tumors. Here our results demonstrated that OA restrained the proliferation and induced differentiation of hepatoma both in vitro and in vivo, via inducing a high PKM1 (pyruvate kinase M1)/PKM2 (pyruvate kinase M2) ratio. In addition, inhibited expression of polypyrimidine tract-binding protein by OA was in charge of the decrease of PKM2 and increase of PKM1. Further studies demonstrated that increased PKM1 translocated into the nucleus and bound with HNF-4α (hepatocyte nuclear factor 4 alpha) directly, promoting the transcription of HNF-4α-targeted genes. This work suggested that OA increased PKM1/PKM2 ratio, resulting in HNF-4α activation and hepatoma differentiation. Especially, OA showed reliable anticancer effect on both human primary hepatocellular carcinoma cells and patient-derived tumor xenograft model for hepatoma, and slowed down the development of primary hepatoma, suggesting that OA could be developed into a novel differentiation inducer agent for hepatoma.

Salvianolic acid B protects against chronic alcoholic liver injury via SIRT1-mediated inhibition of CRP and ChREBP in rats

Salvianolic acid B (SalB), a water-soluble polyphenol extracted from Radix Salvia miltiorrhiza, has been reported to possess many pharmacological activities. This study investigated the hepatoprotective effects of SalB in chronic alcoholic liver disease (ALD) and explored the related signaling mechanisms. In vivo, SalB treatment significantly attenuated ethanol-induced liver injury by blocking the elevation of serum aminotransferase activities and markedly decreased hepatic lipid accumulation by reducing serum and liver triglyceride (TG) and total cholesterol (TC) levels. Moreover, SalB treatment ameliorated ethanol-induced hepatic inflammation by decreasing the levels of hepatotoxic cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). Importantly, SalB pretreatment significantly increased the expression of SIRT1 and downregulated the expression of inflammatory mediator C-reactive protein (CRP) and lipoprotein carbohydrate response element-binding protein (ChREBP). In vitro, SalB significantly reversed ethanol-induced down-regulation of SIRT1 and increased CRP and ChREBP expression. Interestingly, the effects of SalB on SIRT1, CRP and ChREBP were mostly abolished by treatment with either SIRT1 siRNA or EX527, a specific inhibitor of SIRT1, indicating that SalB decreased CRP and ChREBP expression by activating SIRT1. SalB exerted anti-steatotic and anti-inflammatory effects against alcoholic liver injury by inducing SIRT1-mediated inhibition of CRP and ChREBP expression.

Cross Talk Between GH-Regulated Transcription Factors HNF6 and CUX2 in Adult Mouse Liver

Hepatocyte-enriched nuclear factor (HNF)6 and CUX2 are GH and STAT5-regulated homeobox transcription factors. CUX2 shows female-specific expression and contributes to liver sex differences by repressing many male-biased genes and inducing many female-biased genes, whereas HNF6 is expressed at similar levels in male and female liver. In cell-based transfection studies, CUX2 inhibited HNF6 transcriptional regulation of the sex-specific gene promoters CYP2C11 and CYP2C12, blocking HNF6 repression of CYP2C11 and HNF6 activation of CYP2C12. These inhibitory actions of CUX2 can be explained by competition for HNF6 DNA binding, as demonstrated by in vitro EMSA analysis and validated in vivo by global analysis of the HNF6 cistrome. Approximately 40 000 HNF6-binding sites were identified in mouse liver chromatin, including several thousand sites showing significant sex differences in HNF6 binding. These sex-biased HNF6-binding sites showed strong enrichment for correspondingly sex-biased DNase hypersensitive sites and for proximity to genes showing local sex-biased chromatin marks and a corresponding sex-biased expression. Further, approximately 90% of the genome-wide binding sites for CUX2 were also bound by HNF6. These HNF6/CUX2 common binding sites were enriched for genomic regions more accessible in male than in female mouse liver chromatin and showed strongest enrichment for male-biased genes, suggesting CUX2 displacement of HNF6 as a mechanism to explain the observed CUX2 repression of male-biased genes in female liver. HNF6 binding was sex independent at a majority of its binding sites, and HNF6 peaks were frequently associated with cobinding by multiple other liver transcription factors, consistent with HNF6 playing a global regulatory role in both male and female liver.

Regulation of Liver Enriched Transcription Factors in Rat Hepatocytes Cultures on Collagen and EHS Sarcoma Matrices

Liver-enriched transcription factors (LETF) play a crucial role in the control of liver-specific gene expression and for hepatocytes to retain their molecular and cellular functions complex interactions with extra cellular matrix (ECM) are required However, during cell isolation ECM interactions are disrupted and for hepatocytes to regain metabolic competency cells are cultured on ECM substrata. The regulation of LETFs in hepatocytes cultured on different ECM has not been studied in detail. We therefore compared two common sources of ECM and evaluated cellular morphology and hepatocyte differentiation by investigating DNA binding activity of LETFs at gene specific promoters and marker genes of hepatic metabolism. Furthermore, we studied testosterone metabolism and albumin synthesis to assess the metabolic competence of cell cultures. Despite significant difference in morphological appearance and except for HNF1β (p<0.001) most LETFs and several of their target genes did not differ in transcript expression after Bonferroni adjustment when cultured on collagen or Matrigel. Nonetheless, Western blotting revealed HNF1β, HNF3α, HNF3γ, HNF4α, HNF6 and the smaller subunits of C/EBPα and C/EBPβ to be more abundant on Matrigel cultured cells. Likewise, DNA binding activity of HNF3α, HNF3β, HNF4α, HNF6 and gene expression of hepatic lineage markers were increased on Matrigel cultured hepatocytes. To further investigate hepatic gene regulation, the effects of Aroclor 1254 treatment, e.g. a potent inducer of xenobiotic defense were studied in vivo and in vitro. The gene expression of C/EBP-α increased in rat liver and hepatocytes cultured on collagen and this treatment induced DNA binding activity of HNF4α, C/EBPα and C/EBPβ and gene expression of CYP1A1 and CYP1A2 in vivo and in vitro. Taken collectively, two sources of ECM greatly affected hepatocyte morphology, activity of liver enriched transcription factors, hepatic gene expression and metabolic competency that should be considered when used in cell biology studies and drug toxicity testing.

TCP10L acts as a tumor suppressor by inhibiting cell proliferation in hepatocellular carcinoma

TCP10L (T-complex 10 (mouse)-like) has been identified as a liver and testis-specific gene. Although a potential transcriptional suppression function of TCP10L has been reported previously, biological function of this gene still remains largely elusive. In this study, we reported for the first time that TCP10L was significantly down-regulated in clinical hepatocellular carcinoma (HCC) samples when compared to the corresponding non-tumorous liver tissues. Furthermore, TCP10L expression was highly correlated with advanced cases exceeding the Milan criteria. Overexpression of TCP10L in HCC cells suppressed colony formation, inhibited cell cycle progression through G0/G1 phase, and attenuated cell growth in vivo. Consistently, silencing of TCP10L promoted cell cycle progression and cell growth. Therefore, our study has revealed a novel suppressor role of TCP10L in HCC, by inhibiting proliferation of HCC cells, which may facilitate the diagnosis and molecular therapy in HCC.

Primary hepatocyte cultures for pharmaco-toxicological studies: at the busy crossroad of various anti-dedifferentiation strategies

Continuously increasing understanding of the molecular triggers responsible for the onset of diseases, paralleled by an equally dynamic evolution of chemical synthesis and screening methods, offers an abundance of pharmacological agents with a potential to become new successful drugs. However, before patients can benefit of newly developed pharmaceuticals, stringent safety filters need to be applied to weed out unfavourable drug candidates. Cost effectiveness and the need to identify compound liabilities, without exposing humans to unnecessary risks, has stimulated the shift of the safety studies to the earliest stages of drug discovery and development. In this regard, in vivo relevant organotypic in vitro models have high potential to revolutionize the preclinical safety testing. They can enable automation of the process, to match the requirements of high-throughput screening approaches, while satisfying ethical considerations. Cultures of primary hepatocytes became already an inherent part of the preclinical pharmaco-toxicological testing battery, yet their routine use, particularly for long-term assays, is limited by the progressive deterioration of liver-specific features. The availability of suitable hepatic and other organ-specific in vitro models is, however, of paramount importance in the light of changing European legal regulations in the field of chemical compounds of different origin, which gradually restrict the use of animal studies for safety assessment, as currently witnessed in cosmetic industry. Fortunately, research groups worldwide spare no effort to establish hepatic in vitro systems. In the present review, both classical and innovative methodologies to stabilize the in vivo-like hepatocyte phenotype in culture of primary hepatocytes are presented and discussed.

IKKα activation of NOTCH links tumorigenesis via FOXA2 suppression

Proinflammatory cytokine TNFα plays critical roles in promoting malignant cell proliferation, angiogenesis, and tumor metastasis in many cancers. However, the mechanism of TNFα-mediated tumor development remains unclear. Here, we show that IKKα, an important downstream kinase of TNFα, interacts with and phosphorylates FOXA2 at S107/S111, thereby suppressing FOXA2 transactivation activity and leading to decreased NUMB expression, and further activates the downstream NOTCH pathway and promotes cell proliferation and tumorigenesis. Moreover, we found that levels of IKKα, pFOXA2 (S107/111), and activated NOTCH1 were significantly higher in hepatocellular carcinoma tumors than in normal liver tissues and that pFOXA2 (S107/111) expression was positively correlated with IKKα and activated NOTCH1 expression in tumor tissues. Therefore, dysregulation of NUMB-mediated suppression of NOTCH1 by TNFα/IKKα-associated FOXA2 inhibition likely contributes to inflammation-mediated cancer pathogenesis. Here, we report a TNFα/IKKα/FOXA2/NUMB/NOTCH1 pathway that is critical for inflammation-mediated tumorigenesis and may provide a target for clinical intervention in human cancer.

Pathophysiologic role of hepatocyte nuclear factor 6

Hepatocyte nuclear factor 6 (HNF6) is one of liver-enriched transcription factors. HNF6 utilizes the bipartite onecut-homeodomain sequence to localize the HNF6 protein to the nuclear compartment and binds to specific DNA sequences of numerous target gene promoters. HNF6 regulates an intricate network and mediates complex biological processes that are best known in the liver and pancreas. The function of HNF6 is correlated to cell proliferation, cell cycle regulation, cell differentiation and organogenesis, cell migration and cell-matrix adhesion, glucose metabolism, bile homeostasis, inflammation and so on. HNF6 controls the transcription of its target genes in different ways. The details of the regulatory pathways and their mechanisms are still under investigation. Future study will explore HNF6 novel functions associated with apoptosis, oncogenesis, and modulation of the inflammatory response. This review highlights recent progression pertaining to the pathophysiologic role of HNF6 and summarizes the potential mechanisms in preclinical animal models. HNF6-mediated pathways represent attractive therapeutic targets for the treatment of the relative diseases such as cholestasis.

The uptake transporter OATP8 expression decreases during multistep hepatocarcinogenesis: correlation with gadoxetic acid enhanced MR imaging

OBJECTIVES

To clarify the changes in organic anion-transporting polypeptide 8 (OATP8) expression and enhancement ratio on gadoxetic acid-enhanced MR imaging in hepatocellular nodules during multistep hepatocarcinogenesis.

METHODS

In imaging analysis, we focused on 71 surgically resected hepatocellular carcinomas (well, moderately and poorly differentiated HCCs) and 1 dysplastic nodule (DN). We examined the enhancement ratio in the hepatobiliary phase of gadoxetic acid enhanced MR imaging [(1/postcontrast T1 value-1/precontrast T1 value)/(1/precontrast T1 value)], then analysed the correlation among the enhancement ratio, tumour differentiation grade and intensity of immunohistochemical OATP8 expression. In pathological analysis, we focused on surgically resected 190 hepatocellular nodules: low-grade DNs, high-grade DNs, early HCCs, well-differentiated, moderately differentiated and poorly differentiated HCCs, including cases without gadoxetic acid-enhanced MR imaging. We evaluated the correlation between the immunohistochemical OATP8 expression and the tumour differentiation grade.

RESULTS

The enhancement ratio of HCCs decreased in accordance with the decline in tumour differentiation (P < 0.0001, R = 0.28) and with the decline of OATP8 expression (P < 0.0001, R = 0.81). The immunohistochemical OATP8 expression decreased from low-grade DNs to poorly differentiated HCCs (P < 0.0001, R = 0.15).

CONCLUSIONS

The immunohistochemical expression of OATP8 significantly decreases during multistep hepatocarcinogenesis, which may explain the decrease in enhancement ratio on gadoxetic acid-enhanced MR imaging.

Inhibition of the liver enriched protein FOXA2 recovers HNF6 activity in human colon carcinoma and liver hepatoma cells

Recently, we demonstrated that the transcription factors HNF6 and FOXA2 function as key regulators in human colorectal liver metastases. To better understand their proposed inhibitory crosstalk, the consequences of functional knockdown of FOXA2 on HNF6 and C/EBPα activity were investigated in the human colon Caco-2 and HepG2 carcinoma cell lines. Specifically, siRNA-mediated gene silencing of FOXA2 repressed transcript expression by >80%. This resulted in a statistically significant 6-, 3-, 4-, and 8-fold increase in mRNA expression of HNF6 and of genes targeted by this transcription factor, e.g., HSP105B, CYP51, and C/EBPα, as determined by qRT-PCR. Thus, functional knockdown of FOXA2 recovered HNF6 activity. Furthermore, with nuclear extracts of Caco-2 cells no HNF6 DNA binding was observed, but expression of HNF1α, FOXA2, FOXA3, and HNF4α protein was abundant. We therefore transfected a plasmid encoding HNF6 into Caco-2 cells but also employed a retroviral vector to transfect HNF6 into HepG2 cells. This resulted in HNF6 protein expression with DNA binding activity being recovered as determined by EMSA band shift assays. Furthermore, by flow cytometry the consequences of HNF6 expression on cell cycle regulation in transfected cells was studied. Essentially, HNF6 inhibited cell cycle progression in the G2/M and G1 phase in Caco-2 and HepG2 cell lines, respectively. Here, proliferation was reduced by 80% and 50% in Caco-2 and HepG2 cells, respectively, as determined by the BrdU labeling assay. Therefore functional knockdown of FOXA2 recovered HNF6 activity and inhibited growth of tumor-cells and may possibly represent a novel therapeutic target in primary and secondary liver malignancies.

Preservation of hepatocellular functionality in cultures of primary rat hepatocytes upon exposure to 4-Me2N-BAVAH, a hydroxamate-based HDAC-inhibitor

Great efforts are being put in the development/optimization of reliable and highly predictive models for high-throughput screening of efficacy and toxicity of promising drug candidates. The use of primary hepatocyte cultures, however, is still limited by the occurrence of phenotypic alterations, including loss of xenobiotic biotransformation capacity. In the present study, the differentiation-stabilizing effect of a new histone deacetylase inhibitor 5-(4-dimethylaminobenzoyl)-aminovaleric acid hydroxamide (4-Me(2)N-BAVAH), a structural Trichostatin A (TSA)-analogue with a more favourable pharmaco-toxicological profile, was studied at a genome-wide scale by means of microarray analysis. Several genes coding for xenobiotic biotransformation enzymes were found to be positively regulated upon exposure to 4-Me(2)N-BAVAH. For CYP1A1/2B1/3A2, these observations were confirmed by qRT-PCR and immunoblot analysis. In addition, significantly higher 7-ethoxyresorufin-O-deethylase and 7-pentoxyresorufin-O-dealkylase activity levels were measured. These effects were accompanied by an increased expression of CCAAT/enhancer binding protein alpha and hepatic nuclear factor (HNF)4α, but not of HNF1α. Finally, 4-Me(2)N-BAVAH was found to induce histone H3 acetylation at the proximal promoter of the albumin, CYP1A1 and CYP2B1 genes, suggesting that chromatin remodelling is directly involved in the transcriptional regulation of these genes. In conclusion, histone deacetylase inhibitors prove to be efficient agents for better maintaining a differentiated hepatic phenotype in rat hepatocyte cultures.

Roles of hepatocyte nuclear factors (HNF) in the regulation of reproduction in teleosts

Hepatocyte nuclear factor (HNF) families are composed of liver-enriched transcription factors and upstream regulators of many liver-specific genes. HNF are involved in liver-specific gene expression, metabolism, development, cell growth and many cellular functions in the body. HNF genes can be activated or influenced by several hormones and insulin-like growth factors (IGF), and different combinations of the four HNF factors form a network in controlling the expression of liver-specific or liver-enriched genes. The functions of these factors and their interactions within the gonads of bony fishes, however, are not well understood, and the related literature is scant. Recently, several members of the HNF families have been detected in teleost gonads together with their downstream genes (IGF-I and IGF-II), suggesting that these HNF could be upregulated in vitro by steroid hormones. Thus, the hormone-HNF-IGF-gonad interaction may be an alternative axis in the reproductive mechanism that acts in concert with the conventional hypothalamus-pituitary-gonad pathway. This may help the early development and maturation of the gonad or gamete, sexual maturity or reversion and spawning-regulating mechanisms among fishes to be understood.

Growth hormone-activated STAT5 may indirectly stimulate IGF-I gene transcription through HNF-3{gamma}

IGF-I is abundantly expressed in the liver under the stimulation of GH. We showed previously that expression of hepatocyte nuclear factor (HNF)-3gamma, a liver-enriched transcription factor, was strongly stimulated by GH in bovine liver. In this study, we determined whether GH-increased HNF-3gamma might contribute to GH stimulation of IGF-I gene expression in bovine liver and the underlying mechanism. A sequence analysis of the bovine IGF-I promoter revealed three putative HNF-3 binding sites, which all appear to be conserved in mammals. Chromatin immunoprecipitation assays showed that GH injection increased binding of HNF-3gamma to the IGF-I promoter in bovine liver. Gel-shift assays indicated that one of the three putative HNF-3 binding sites, HNF-3 binding site 1, bound to the HNF-3gamma protein from bovine liver with high affinity. Cotransfection analyses demonstrated that this HNF-3 binding site was essential for the transcriptional response of the IGF-I promoter to HNF-3gamma in CHO cells and to GH in primary mouse hepatocytes. Using similar approaches, we found that GH increased binding of the signal transducer and activator of transcription 5 (STAT5) to the HNF-3gamma promoter in bovine liver, that this binding occurred at a conserved STAT5 binding site, and that this STAT5 binding site was necessary for the HNF-3gamma promoter to respond to GH. Taken together, these results suggest that in addition to direct action, GH-activated STAT5 may also indirectly stimulate IGF-I gene transcription in the liver by directly enhancing the expression of the HNF-3gamma gene.

Specific expression and regulation of hepassocin in the liver and down-regulation of the correlation of HNF1alpha with decreased levels of hepassocin in human hepatocellular carcinoma

Hepassocin (HPS), is a liver-specific gene with mitogenic activity on isolated hepatocytes. It is up-regulated following partial hepatectomy and down-regulated frequently in heptocellular carcinoma (HCC). However, very little is known about the HPS transcription regulation mechanism. In this study, we identified HNF1alpha (hepatocyte nuclear factor-1alpha) as an important liver-specific cis-acting element for HPS using in vivo luciferase assays. Deletion of the HNF1 binding site not only led to a complete loss of HPS promoter activity in vivo but also abolished the induction of the HPS promoter by HNF1alpha. An electrophoretic mobility shift assay demonstrated that HNF1alpha interacted with the HPS gene promoter in vitro. Chromatin immunoprecipitation showed that HNF1alpha interacted with HMGB1 and CREB-binding protein, and all of them were recruited to the HPS promoter in vivo. Moreover, HNF1alpha expression was lower in HCC cell lines and tissues and correlated significantly with the down-regulation of HPS expression. Re-expression of HNF1alpha in human hepatoma HepG2 cells reinduced HPS expression. In contrast, knockdown of endogenous HNF1alpha expression by small interfering RNA resulted in a significant reduction of HPS expression. Furthermore, we found that partial hepatectomy and IL-6 significantly induced promoter activity of HPS, depending on STAT3 and HNF1 binding sites in the HPS promoter. These results demonstrate that the HNF1 binding site and HNF1alpha are critical to liver-specific expression of HPS, and down-regulation or loss of HNF1alpha causes, at least in part, the transcriptional down-regulation of HPS in HCC.

Transcription factor HNF and hepatocyte differentiation

To know the precise mechanisms underlying the life or death and the regeneration or differentiation of cells would be relevant and useful for the development of a regenerative therapy for organ failure. Liver-specific gene expression is controlled primarily at a transcriptional level. Studies on the transcriptional regulatory elements of genes expressed in hepatocytes have identified several liver-enriched transcriptional factors, including hepatocyte nuclear factor (HNF)-1, HNF-3, HNF-4, HNF-6 and CCAAT/enhancer binding protein families, which are key components of the differentiation process for the fully functional liver. The transcriptional regulation by these HNFs, which form a hierarchical and cooperative network, is both essential for hepatocyte differentiation during mammalian liver development and also crucial for metabolic regulation and liver function. Among these liver-enriched transcription factors, HNF-4 is likely to act the furthest upstream as a master gene in transcriptional cascade and interacts with other liver-enriched transcriptional factors to stimulate hepatocyte-specific gene transcription. A link between the extracellular matrix, changes in cytoskeletal filament assembly and hepatocyte differentiation via HNF-4 has been shown to be involved in the transcriptional regulation of liver-specific gene expression. This review provides an overview of the roles of liver-enriched transcription factors in liver function.

Translational control plays a prominent role in the hepatocytic differentiation of HepaRG liver progenitor cells

BACKGROUND

We investigated the molecular events associated with the differentiation of liver progenitor cells into functional and polarized hepatocytes, using human HepaRG cells that display potent hepatocytic differentiation-inducible properties and share some features with liver progenitor cells.

RESULTS

Profiling of total and of polysome-bound transcripts isolated from HepaRG cells undergoing hepatocytic differentiation was performed. A group of 3,071 probe sets was reproducibly regulated by at least 2-fold in total or in polysome-bound RNA populations, upon differentiation. The fold changes in the total and the polysome-bound RNA populations for these 3,071 probe sets were poorly correlated (R = 0.38). Moreover, while the majority of the regulated polysome-bound RNA probe sets were up-regulated upon differentiation, the majority of the regulated probe sets selected from the total RNA population was down-regulated. Genes translationally up-regulated were associated with cell cycle inhibition, increased susceptibility to apoptosis and innate immunity. In contrast, genes transcriptionally up-regulated during differentiation corresponded in the majority to liver-enriched transcripts involved in lipid homeostasis and drug metabolism. Finally, several epithelial and hepato-specific transcripts were strongly induced in the total RNA population but were translationally repressed.

CONCLUSION

Translational regulation is the main genomic event associated with hepatocytic differentiation of liver progenitor cells in vitro and targets genes critical for moderating hepatocellular growth, cell death and susceptibility to pathogens. Transcriptional regulation targets specifically liver-enriched transcripts vital for establishing normal hepatic energy homeostasis, cell morphology and polarization. The hepatocytic differentiation is also accompanied by a reduction of the transcript content complexity.

Hypoxia and hepatocellular carcinoma: The therapeutic target for hepatocellular carcinoma

Hypoxia enhances proliferation, angiogenesis, metastasis, chemoresistance, and radioresistance of hepatocellular carcinoma (HCC); suppresses differentiation and apoptosis of HCC; and consequently leads to resistance of transarterial embolization (with or without chemotherapy). Because transarterial embolization contributes to angiogenesis via inducing hypoxia, therapy combined with transarterial embolization and antiangiogenic therapy provides a new strategy for the treatment of HCC. Unfortunately, hypoxia leads to the escape of HCC cells from transarterial embolization and antiangiogenic therapy. Thus combined therapy that induces and targets hypoxia may be of benefit to HCC patients. Because angiogenesis plays an important role in recurrence of HCC after resection, antiangiogenic therapy is beneficial to HCC patients following surgical resection of the tumor.

Mammalian target of rapamycin activation impairs hepatocytic differentiation and targets genes moderating lipid homeostasis and hepatocellular growth

The mammalian target of rapamycin (mTOR) pathway, a major regulator of translation, is frequently activated in hepatocellular carcinomas. We investigated the effects of mTOR activation in the human HepaRG cells, which possess potent hepatocytic differentiation capability. Differentiation of HepaRG cells into functional and polarized hepatocyte-like cells correlated with a decrease in mTOR and Akt activities. Stable cell lines expressing an activated mutant of mTOR were generated. Sustained activation of mTOR impaired the hepatocytic differentiation capability of these cells as shown by impaired formation of bile canaliculi, absence of polarity, and reduced secretion of alpha1-antitrypsin. An inhibitor of mTOR, rapamycin, was able to revert this phenotype. Furthermore, increased mTOR activity in HepaRG cells resulted in their resistance to the antiproliferative effects of transforming growth factor-beta1. Profiling of polysome-bound transcripts indicated that activated mTOR specifically targeted genes posttranscriptionally regulated on hepatocytic differentiation. Three major biological networks targeted by activated mTOR were identified: (a) cell death associated with tumor necrosis factor superfamily members, IFNs and caspases; (b) lipid homeostasis associated with the transcription factors PPARalpha, PPARdelta, and retinoid X receptor beta; and (c) liver development associated with CCAAT/enhancer binding protein alpha and hepatic mitogens. In conclusion, increased mTOR activity conferred a preneoplastic phenotype to the HepaRG cells by altering the translation of genes vital for establishing normal hepatic energy homeostasis and moderating hepatocellular growth.

The locus control region activates serpin gene expression through recruitment of liver-specific transcription factors and RNA polymerase II

The human serine protease inhibitor (serpin) gene cluster at 14q32.1 comprises 11 serpin genes, many of which are expressed specifically in hepatic cells. Previous studies identified a locus control region (LCR) upstream of the human alpha1-antitrypsin (alpha1AT) gene that is required for gene activation, chromatin remodeling, and histone acetylation throughout the proximal serpin subcluster. Here we show that the LCR interacts with multiple liver-specific transcription factors, including hepatocyte nuclear factor 3beta (HNF-3beta), HNF-6alpha, CCAAT/enhancer binding protein alpha (C/EBPalpha), and C/EBPbeta. RNA polymerase II is also recruited to the locus through the LCR. Nongenic transcription at both the LCR and an upstream regulatory region was detected, but the deletion of the LCR abolished transcription at both sites. The deletion of HNF-3 and HNF-6 binding sites within the LCR reduced histone acetylation at both the LCR and the upstream regulatory region and decreased the transcription of the alpha1AT, corticosteroid binding globulin, and protein Z-dependent protease inhibitor genes. These results suggest that the LCR activates genes in the proximal serpin subcluster by recruiting liver-specific transcription factors and components of the general transcription machinery to regulatory regions upstream of the alpha1AT gene.

Bone marrow cells: the source of hepatocellular carcinoma?

Whether the stem cells or the mature cells are the origination of hepatocellular carcinoma is uncertain. Recently, researches have shown that some cancer stem cells could derive from adult stem cells. Moreover, gastric cancer could originate from bone marrow stem cells. Hematopoiesis and the hepatic environment are known to have a close relationship at the time of hepatic development and systemic diseases. Here we propose a new carcinogenetic model of hepatocellular carcinoma. Chronic liver injury could recruit bone marrow stem cells to the liver. Bone marrow cells take part in liver regeneration by differentiating to oval cells and hepatocytes. Persistent regeneration results in hyperproliferation, an increased rate of transforming mutations. Extracellular matrix remodeling triggers a cascade of events that inhibits the transactivation potential of liver-specific transcription factors, blocks the maturation of stem cells, and then results in hepatocellular carcinoma.

The hepatocyte nuclear factor 6 (HNF6) and FOXA2 are key regulators in colorectal liver metastases

The molecular causes leading to secondary liver malignancies are unknown. Here we report regulation of major hepatic nuclear factors in human colorectal liver metastases and primary colonic cancer. Notably, the genes coding for HNF6, HNF1beta, and C/EBPgamma were selectively regulated in liver metastases. We therefore studied protein expression of regulated transcription factors and found unacetylated HNF6 to be a hallmark of colorectal liver metastases. For its known interaction with HNF6, we investigated expression of FOXA2, which we found to be specifically induced in colorectal liver metastases. By electromobility shift assay, we examined DNA binding of disease regulated transcription factors. Essentially, no HNF6 DNA binding was observed. We also searched for sequence variations in the DNA binding domains of HNF6, but did not identify any mutation. Furthermore, we probed for expression of 28 genes targeted by HNF6. Mostly transcript expression was repressed except for tumor growth. In conclusion, we show HNF6 protein expression to be driven by the hepatic environment. Its expression is not observed in healthy colon or primary colonic cancer. HNF6 DNA binding is selectively abrogated through lack of post-translational modification and interaction with FOXA2. Targeting of FOXA2 and HNF6 may therefore enable mechanism-based therapy for colorectal liver metastases.

Expression of hepatocyte nuclear factor 4α and 3β in human tissues

AIM: To investigate the expression patterns of hepatocyte nuclear factor 4α (HNF-4α) and HNF-3b in normal human tissues, so as to provide the bases for further exploration of their relationships with hepatitis B virus (HBV) replication in hepatitis B patients.

METHODS: Immunohistochemistry was used to detect the expression of HNF-4α and HNF-3b in human tissues of liver, brain, lung, kidney, heart, spleen, intestine, pancreas, stomach and thyroid from 14 corpses. The differences of their expression in different tissues were analyzed.

RESULTS: The expression patterns of HNF-4α and HNF-3b was different among the 10 kinds of human tissues (HNF-4α: F = 22.479, P < 0.01; HNF-3b: F = 13.021, P < 0.01). Both HNF-4α and HNF-3b expression were not detected in brain, lung, stomach, appendix, thymus, adrenal gland and tonsil. Besides the tissues mentioned above, the expression of HNF-4α was significantly higher in liver, kidney, heart, spleen and intestines than that in the other tissues; the expression of HNF-3b was markedly higher in liver, kidney, heart and pancreas than that in the other tissues. The difference between high-level expression and low-level expression group has statistical significance (P < 0.05); however, the difference among those tissues with high-level expression had no statistical significance (P > 0.05).

CONCLUSION: The expression of HNF-4a and HNF-3b are different among human tissues, and they are highly expressed in some tissues such as liver. This result indicates that HNF-4a and HNF-3b might participate in the tissue-specific replication of HBV.

Hepatocyte nuclear factor (HNF) 1 and HNF4 mediate hepatic multidrug resistance protein 2 up-regulation during hepatitis C virus gene expression

Hepatitis C virus (HCV) is known to induce hepatic oxidative stress that is implicated in the up-regulation of multidrug resistance proteins (MRPs). The relationship between increased prooxidant production, MRPs, and HCV has not been investigated. Here, we report that a homeodomain-containing transcription factor, hepatocyte nuclear factor (HNF) 1, plays a central role in liver gene regulation during HCV gene expression and/or subgenome replication. MRP2 protein and mRNA expression were increased and MRP2 promoter activity was increased 7-fold. Mutations within the putative HNF1 binding site of the human MRP2 promoter abrogated HCV-induced activation, implicating HNF1 in the induction of MRP2 by HCV. The mechanism by which HNF1-mediated activation occurs seems to be transcriptional, because the regulated expression of HNF4, which is known to control HNF1 expression, was also increased. Consistent with this finding, HNF1 mRNA was increased 10-fold. A promoter-luciferase construct of the human HNF1 gene was activated in an HNF4-dependent manner, and a mutant construct lacking the HNF4 binding site was not activated in HCV-positive cells. Consistent with this hypothesis, HNF4 protein and mRNA levels as well as HNF4 promoter activity and DNA binding activity were increased. The expression of HNF1 seems to play a critical role in the induction of hepatic MRP2 secondary to HCV subgenomic replication. The ability of HCV to induce HNF1 and HNF4 is attributed to 1) increased oxidative stress and 2) direct protein-protein interactions between HCV nonstructural component (NS) 5A and HNF1, leading to enhanced HNF1 DNA binding. In conclusion, we describe a novel mechanism by which HCV gene expression may induce adaptive responses involving MRP2 via HNF1 activation. This may constitute, in part, the cellular detoxification task force during HCV infection.

Sequential exposure to cytokines reflecting embryogenesis: the key for in vitro differentiation of adult bone marrow stem cells into functional hepatocyte-like cells

Differentiation of adult bone marrow stem cells (BMSC) into hepatocyte-like cells is commonly performed by continuous exposure to a cytokines-cocktail. Here, it is shown that the differentiation efficacy in vitro can be considerably enhanced by sequential addition of liver-specific factors (fibroblast growth factor-4, hepatocyte growth factor, insulin-transferrin-sodium selenite, and dexamethasone) in a time-dependent order that closely resembles the secretion pattern during in vivo liver embryogenesis. Quantitative RT-PCR analysis and immunocytochemistry showed that, upon sequential exposure to liver-specific factors, different stages of hepatocyte differentiation, as seen during liver embryogenesis, can be mimicked. Indeed, expression of the early hepatocyte markers alpha-fetoprotein and hepatocyte nuclear factor (HNF)3beta decreased as differentiation progressed, whereas levels of the late liver-specific markers albumin (ALB), cytokeratin (CK)18, and HNF1alpha were gradually upregulated. In contrast, cocktail treatment did not significantly alter the expression pattern of the hepatic markers. Moreover, sequentially exposed cells featured highly differentiated hepatic functions, including ALB secretion, glycogen storage, urea production, and inducible cytochrome P450-dependent activity, far more efficiently compared to the cocktail condition. In conclusion, sequential induction of the differentiation process, analogous to in vivo liver development, is crucial for in vitro differentiation of adult rat BMSC into functional hepatocyte-like cells. This model may not only be applicable for in vitro studies of endoderm differentiation but it also provides a "virtually unlimited" source of functional hepatocytes, suitable for preclinical pharmacological research and testing, and cell and organ development.

Choroid plexus tumors differ from metastatic carcinomas by expression of the excitatory amino acid transporter-1

Tumors of the choroid plexus (CPTs) are rare neoplasms of neuroectodermal origin usually arising in pediatric patients. However, CPT may occur at any age, and their distinction from metastatic carcinomas is often difficult in adult cases. Because CPTs frequently show focal glial differentiation, we now investigated 35 CPTs (19 males and 16 females 0.3-70 years old; median age, 25.0 years), including 21 choroid plexus papillomas (CPPs), 5 atypical CPP, and 9 choroid plexus carcinomas regarding their expression of the excitatory amino acid transporter-1 (EAAT1, corresponding to rodent GLAST/GLAST-1) by immunohistochemistry. In addition, 77 metastatic carcinomas, including 64 adenocarcinomas with mostly papillary formations, derived from different organs were examined. Of the 35 CPTs, 23 (66%) showed membranous EAAT1 expression in variable numbers of tumor cells, including all atypical CPP and 3 of 9 choroid plexus carcinomas (33%). None of the metastatic carcinomas showed membranous immunostaining. Excitatory amino acid transporter-1 expression in CPT was significantly age dependent (P < .0001), with the proportion of EAAT1-positive tumor cells increasing with age, but not sex dependent. There was a highly significant difference between EAAT1 expression in CPT and in metastatic carcinomas (P < .0001). Establishing a cutoff value of 1% immunoreactive tumor cells served in adult cases to distinguish CPT from metastatic adenocarcinomas with 100% specificity and 70% sensitivity and was associated with positive and negative predictive values of 100% and 91%, respectively. Our findings indicate that EAAT1 immunohistochemistry may be useful in differentiating CPT from metastatic carcinomas.

Farnesoid X receptor, hepatocyte nuclear factors 1alpha and 3beta are essential for transcriptional activation of the liver-specific organic anion transporter-2 gene

BACKGROUND

We isolated the human liver-specific organic anion transporter gene, LST-2 (OATP8/SLCO1B3), which is exclusively expressed in the basolateral membrane of the hepatocytes. In this study, we analyzed the transcriptional regulation of the LST-2 gene in hepatocyte-derived cells and the effect of bile acid.

METHODS

Transcriptional activity of the LST-2 gene was measured using a human LST-2 promoter-luciferase reporter plasmid under various concentrations of bile acids. Electrophoresis mobility shift assays of farnesoid X receptor (FXR), hepatocyte nuclear factor (HNF) 1alpha, and HNF3beta were performed.

RESULTS

Luciferase analysis showed that the 5'-flanking region from -180 to -20 bp is responsible for LST-2 transcriptional activity. By site-directed mutation analysis, it was revealed that the consensus binding sites for FXR, HNF1alpha, and HNF3beta play important roles in the transcriptional activity of the LST-2 gene. By electrophoresis mobility shift assay, we observed specific protein-DNA complexes of FXR, HNF1alpha, and HNF-3beta. Luciferase activity was increased fivefold when chenodeoxycholate or deoxycholate were added. Northern blot analyses revealed that the expression of LST-2 was increased by addition of chenodeoxycholate or deoxycholate in a dose-dependent manner.

CONCLUSIONS

This study demonstrated that the transcription of the LST-2 gene is regulated by three transcription factors, FXR, HNF1alpha, and HNF3beta. HNF1alpha and HNF3beta might contribute to its liver-specific expression, and FXR might play a role in its transcriptional activation by bile acids.

Transcriptional regulation and characterization of the promoter region of the human ABCC6 gene

ABCC6, a member of the adenosine 5'-triphosphate-binding cassette family of genes, encodes multidrug resistance-associated protein 6, a putative transmembrane transporter expressed primarily in the liver and to a significantly lower extent in other tissues. Mutations in ABCC6 result in pseudoxanthoma elasticum, a multi-system heritable connective tissue disorder with variable phenotypic expression. To examine the transcriptional regulation and tissue-specific expression of this gene, we cloned 2.6 kb of human ABCC6 promoter and developed a series of 5'-deletion constructs linked to luciferase reporter gene. Transient transfections in a number of cultured cell lines of diverse origin identified a specific NF-kappaB-like sequence (-235/-226), which conferred high level of expression in HepG2 hepatoma cells, inferring liver specificity. The functionality of the promoter fragments was confirmed in vivo by tail vein injection followed by luciferase reporter assay. Testing of selected cytokines revealed that transforming growth factor (TGF)-beta upregulated, while tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma downregulated the promoter activity in HepG2 cells. The responsiveness to TGF-beta was shown to reside primarily within an Sp1/Sp3 cognate-binding site at -58 to -49. The expression of the ABCC6 promoter was also shown to be markedly enhanced by Sp1 protein, as demonstrated by cotransfection of ABCC6 promoter-luciferase constructs and an Sp1 expression vector in Drosophila SL2 cells, which are devoid of endogenous Sp1. Furthermore, four additional transcription factors, with their cognate-binding sequences present in DNA, were shown to bind the 2.6-kb promoter fragment by protein/DNA array. Collectively, the results indicate that human ABCC6 displays tissue-specific gene expression, which can be modulated by proinflammatory cytokines. These findings may have implications for phenotypic expression of heritable and acquired diseases involving abnormality in the ABCC6 gene.

Species-specific effects of the hepatocarcinogens 3'-methyl-4-dimethyl-aminoazobenzene and ortho-aminoazotoluene in mouse and rat liver

The effects of rat-specific hepatocarcinogen 3'-methyl-4-dimethylaminoazobenzene (3'-MeDAB), mouse-specific hepatocarcinogen ortho-aminoazotoluene (OAT), non-species-specific hepatocarcinogen diethylnitrosamine (DENA), and non-carcinogenic 4'-methyl-4-dimethylaminoazobenzene (4'-MeDAB) on glucocorticoid induction of tyrosine aminotransferase (TAT) and DNA-binding activity of hepatocyte nuclear factor 3 (HNF3) family of transcription factors were investigated with carcinogen-susceptible and -resistant animals. Species-specific hepatocarcinogens 3'-MeDAB and OAT strongly inhibited glucocorticoid induction of TAT in the liver of susceptible but not resistant animals. DENA, which is highly carcinogenic for the liver of both rats and mice inhibited glucocorticoid induction of TAT in both species, while non-carcinogenic 4'-MeDAB was absolutely ineffective both in rats and mice. The inhibition of TAT activity by the carcinogens was due to reduced levels of TAT mRNA, which is most likely to be a result of the reduced rate of transcription initiation of the TAT gene. In all cases, the TAT inhibition was accompanied by significant reduction of DNA-binding activity of the HNF3 transcription factor, which is known to be critical to glucocorticoid regulation of TAT gene. We also demonstrated that the described species-specific effects of OAT and of 3'-MeDAB on HNF3 DNA-binding activity may be initiated not only by administration in vivo, but also by their direct administration to homogenate, intact nuclei or nuclear lysate, but not to nuclear extract fraction, obtained by precipitation with 0.32 g/mL of ammonium sulfate (Fraction I). We showed, that a factor responsible for this effect might be precipitated in 0.32-0.47 g/mL interval of ammonium sulfate concentration. In contrast, non-specific hepatocarcinogen DENA was effective upon being added directly to Fraction I, implying a different mechanism of its action.