Proliferation Of Normal Hepatocytes Research Articles

Metabolic reprogramming in Nrf2-driven proliferation of normal rat hepatocytes.

Cancer cells reprogram their metabolic pathways to support bioenergetic and biosynthetic needs and to maintain their redox balance. In several human tumors, the Keap1-Nrf2 system controls proliferation and metabolic reprogramming by regulating the pentose phosphate pathway (PPP). However, whether this metabolic reprogramming also occurs in normal proliferating cells is unclear. To define the metabolic phenotype in normal proliferating hepatocytes, we induced cell proliferation in the liver by 3 distinct stimuli: liver regeneration by partial hepatectomy and hepatic hyperplasia induced by 2 direct mitogens: lead nitrate (LN) or triiodothyronine. Following LN treatment, well-established features of cancer metabolic reprogramming, including enhanced glycolysis, oxidative PPP, nucleic acid synthesis, NAD + /NADH synthesis, and altered amino acid content, as well as downregulated oxidative phosphorylation, occurred in normal proliferating hepatocytes displaying Nrf2 activation. Genetic deletion of Nrf2 blunted LN-induced PPP activation and suppressed hepatocyte proliferation. Moreover, Nrf2 activation and following metabolic reprogramming did not occur when hepatocyte proliferation was induced by partial hepatectomy or triiodothyronine. Many metabolic changes in cancer cells are shared by proliferating normal hepatocytes in response to a hostile environment. Nrf2 activation is essential for bridging metabolic changes with crucial components of cancer metabolic reprogramming, including the activation of oxidative PPP. Our study demonstrates that matured hepatocytes exposed to LN undergo cancer-like metabolic reprogramming and offers a rapid and useful in vivo model to study the molecular alterations underpinning the differences/similarities of metabolic changes in normal and neoplastic hepatocytes.

Integerrima A-E, phenylethanoid glycosides from the stem of Callicarpa integerrima.

Five new phenylethanoid glycosides integerrima A-E (1-5) were isolated from the stem of Callicarpa integerrima for the first time. Their structures were elucidated by extensive spectroscopic analyses. In addition, cytotoxicity, anti-adipogenic and antioxidant activities were evaluated. All the phenylethanoid glycosides would be nontoxic to the normal human hepatocytes LO-2 and pre-adipocytes 3T3-L1 cell lines, significantly promote the proliferation of normal hepatocytes, thus displaying the potential for hepatoprotective. Integerrima A (1), C (3) and D (4) exhibited selectively moderate cytotoxic activity against the hepatoma cell lines Bel-7402, with the IC50 value at 72.66, 80.43 and 84.88μmol/L, respectively. Moreover, integerrima D (4) had significant activities on reducing lipid droplet formation, with the inhibition rate of 48.02% on the concentration of 200μg/mL. Finally, the result of FRAP assays exhibited remarkable antioxidant activity in integerrima E (5), which was close to the positive control ascorbic acid with the concentration of 100μg/mL.

Hypomethylation-mediated upregulation of the WASF2 promoter region correlates with poor clinical outcomes in hepatocellular carcinoma

BackgroundHepatocellular carcinoma (HCC) is one of the most common and lethal cancers worldwide. Wiskott–Aldrich syndrome protein family member 2 (WASF2) is an integral member of the actin cytoskeleton pathway, which plays a crucial role in cell motility. In this study, we aimed to explore the role of WASF2 in HCC carcinogenesis and its regulatory mechanism.MethodsWASF2 expression in HCC was analyzed using six public RNA-seq datasets and 66 paired tissues from patients with HCC. The role of WASF2 in normal hepatocyte cell phenotypes was evaluated using a WASF2 overexpression vector in vitro; it was evaluated in HCC cell phenotypes using small interfering RNA (siRNA) in vitro and in vivo. Epigenetic regulatory mechanism of WASF2 was assessed in the Cancer Genome Atlas liver hepatocellular carcinoma project (TCGA_LIHC) dataset and also validated in 38 paired HCC tissues. Site mutagenesis, bisulfite sequencing polymerase chain reaction (BSP), methylation-specific polymerase chain reaction (MSP), and quantitative MSP (qMSP) were used for evaluating WASF2 methylation status.ResultsWASF2 is overexpressed in HCC and is clinically correlated with its prognosis. WASF2 overexpression promoted normal hepatocyte proliferation. WASF2 inactivation decreased the viability, growth, proliferation, migration, and invasion of Huh-7 and SNU475 HCC cells by inducing G2/M phase arrest. This induced cell death and inhibited epithelial–mesenchymal transition, hindering actin polymerization. In addition, WASF2 knockdown using siWASF2 in a xenograft mouse model and a lung metastasis model exerted tumor suppressive effect. There was a negative correlation between WASF2 methylation status and mRNA expression. The methylation pattern of CpG site 2 (− 726 bp), located in the WASF2 promoter, plays an important role in the regulation of WASF2 expression. Furthermore, the cg242579 CpG island in the WASF2 5′ promoter region was hypomethylated in HCC compared to that in the matched non-tumor samples. Patients with high WASF2 methylation and low WASF2 expression displayed the highest overall survival.ConclusionsWASF2 is overexpressed and hypomethylated in HCC and correlates with patient prognosis. WASF2 inactivation exerts anti-tumorigenic effects on HCC cells in vitro and in vivo, suggesting that WASF2 could be a potential therapeutic target for HCC.

MALAT1-mediated EZH2 Recruitment to the GFER Promoter Region Curbs Normal Hepatocyte Proliferation in Acute Liver Injury.

The goal of this study was to investigate the mechanism by which the long noncoding RNA MALAT1 inhibited hepatocyte proliferation in acute liver injury (ALI). Lipopolysaccharide (LPS) was used to induce an ALI cellular model in HL7702 cells, in which lentivirus vectors containing MALAT1/EZH2/GFER overexpression or knockdown were introduced. A series of experiments were performed to determine their roles in liver injury, oxidative stress injury, and cell biological processes. The interaction of MALAT1 with EZH2 and enrichment of EZH2 and H3K27me3 in the GFER promoter region were identified. Rats were treated with MALAT1 knockdown or GFER overexpression before LPS induction to verify the results derived from the in vitro assay. MALAT1 levels were elevated and GFER levels were reduced in ALI patients and the LPS-induced cell model. MALAT1 knockdown or GFER overexpression suppressed cell apoptosis and oxidative stress injury induced cell proliferation, and reduced ALI. Functionally, MALAT1 interacted directly with EZH2 and increased the enrichment of EZH2 and H3K27me3 in the GFER promoter region to reduce GFER expression. Moreover, MALAT1/EZH2/GFER was activated the AMPK/mTOR signaling pathway. Our study highlighted the inhibitory role of reduced MALAT1 in ALI through the modulation of EZH2-mediated GFER.

MicroRNA-22-3p and MicroRNA-149-5p Inhibit Human Hepatocellular Carcinoma Cell Growth and Metastasis Properties by Regulating Methylenetetrahydrofolate Reductase.

microRNAs are small endogenous noncoding RNAs that have emerged as key negative regulators that target gene expression through RISC. Our previous study showed that the methylenetetrahydrofolate reductase gene (MTHFR) plays a key role in one carbon metabolism, which is downregulated by miR-22-3p and miR-149-5p, and that it could exert a potential anti-cancer effect. Whether miR-22-3p/miR-149-5p can regulate MTHFR to exert anti-cancer effects has become the focus of our research. Normal (HL-7702 cells) and cancerous (QGY-7703/HepG2 cells) human hepatocellular cells were transfected with 100 nM hsa-miR-22-3p/hsa-miR-149-5p mimic or controls. After 24, 48, and 72 h, cell proliferation ability was tested using CCK-8. The changes in MTHFR expression at both the transcriptional and translational levels were determined by RT-qPCR and Western blotting, respectively. Cancerous cell invasion and migration ability were confirmed by means of a transwell assay. We found that ectopic miR-22-3p/miR-149-5p inhibits hepatocellular carcinoma cell proliferation but does not inhibit normal human hepatocyte proliferation. The transfection of ectopic miR-22-3p/miR-149-5p downregulated the MTHFR expression in QGY-7703 and HepG2 but not in HL-7702. QGY-7703 and HepG2 migration and invasion were inhibited by ectopic miR-22-3p/miR-149-5p. Additionally, we found that ectopic miR-22-3p/miR-149-5p significantly increased the expression of TP53INP1 and PDCD4 in QGY-7703. The results of the study suggest that miRNA-22-3p and miRNA-149-5p inhibit tumor growth and metastasis properties may be by regulating MTHFR and that they exert anticancer effects in hepatocellular carcinoma cells.

Chemical characters and protective effect of Baqi Lingmao formula on experimental liver injury.

To investigate the chemical characters of water-extract of Baqi Lingmao formula (BQLM formula) and its effects on anti-liver injury in model mice and live cells. BQLM formula was composed of ten herbal medicines. We determined the contents of alkaloids, saponins, phenolic acids and flavonoid in BQLM formula by UV spectrophotometry. The active components of alkaloids and phenolic acids in BQLM formula were identified by HPLC chromatography. The anti-hepatic injury effects of BQLM formula were investigated with concanavalin A (ConA)-induced hepatitis model of mice, human liver LO2 and HepG2.2.15 cells. BQLM formula (2 and 10 g/kg, orally) significantly improved the damages of liver tissues and functions caused by ConA in mice, reduced the infiltration of inflammatory cells into liver and inhibited the inflammatory cytokine secretion of interferon-γ, tumor necrosis factor-α and interleukin-6. BQLM formula simultaneously decreased the levels of alanine aminotransferase and aspartate aminotransferase of liver and serum, and recovered the superoxide dismutase and catalase activities of liver to normal levels in ConA-induced hepatic-injury mice. The serum of BQLM formula group stimulated the human liver LO2 cell proliferation in vitro. Further, BQLM formula obviously promoted the proliferation of normal hepatocytes (LO2 cells) and inhibited the hepatocytes death induced by ConA. It also significantly inhibited the proliferation of HepG2.2.15 cells and decreased the secretion of HBsAg and HBeAg in vitro. BQLM formula has anti-inflammation and anti-hepatitis virus Beffects, and is capable of improving liver injury in vivo and in vitro.

MiR-126 Regulates Properties of SOX9+ Liver Progenitor Cells during Liver Repair by Targeting Hoxb6

SummaryLiver progenitor cells (LPCs) have a remarkable contribution to the hepatocytes and ductal cells when normal hepatocyte proliferation is severely impaired. As a biomarker for LPCs, Sry-box 9 (Sox9) plays critical roles in liver homeostasis and repair in response to injury. However, the regulation mechanism of Sox9 in liver physiological and pathological state remains unknown. In this study, we found that miR-126 positively regulated the expression of Sox9, the proliferation and differentiation of SOX9+ LPCs by suppressing the translation of homeobox b6 (Hoxb6). As a transcription factor, HOXB6 directly binds to the promoter of Sox9 to inhibit Sox9 expression, resulting in the destruction of the properties of SOX9+ LPCs in CCl4-induced liver injury. These findings revealed the role of miR-126 in regulating SOX9+ LPCs fate by targeting Hoxb6 in liver injury repair. Our findings suggest the potential role of miR-126 as a nucleic acid therapy drug target for liver failure.

Expression of the type 3 InsP3 receptor is a final common event in the development of hepatocellular carcinoma

Background & objectivesHepatocellular carcinoma (HCC) is the second leading cause of cancer death worldwide. Several types of chronic liver disease predispose to HCC, and several different signalling pathways have been...

Boiling Licorice Produces Self-Assembled Protein Nanoparticles: A Novel Source of Bioactive Nanomaterials.

As a popular ingredient for western and traditional Chinese medicine, the root and rhizome of Chinese licorice (Glycyrrhiza uralensis Fisch.) is often administered in the form of a decoction. The protein nanoparticles (NPs) self-assembled during the process of decoction. A major constitutive protein (GLP) was purified and determined to have a molecular weight of 28 kDa with an N-terminal sequence of NPDGL IACYC GQYCW. Over 80% of the purified GLP self-assembled into spherical NPs with diameters of 74.1 ± 0.7 nm and ζ-potential of -24.3 ± 1.7 mV when boiled in Tris-HCl buffer (pH = 7.9, 20 mM) at 100 °C for 60 min. Each nanoparticle was estimated by the SEC-MALLS approach to be composed of approximately 23 protein molecules. The NPs and GLP showed low cellular toxicity upon four types of cells including MDCK, L-02, HepG2, and Caco2 cells, while the NPs promoted proliferation of normal hepatocytes by 67%. The NPs solubilized the insoluble astragaloside IV by encapsulation. The results suggest a great potential for GLP-NPs as a promising prototype of a type of drug vehicle, a novel source of bioactive nanomaterials from herbal proteins, as well as a new mode of function with herbal components.

Evidence for a Novel Regulatory Interaction Involving Cyclin D1, Lipid Droplets, Lipolysis, and Cell Cycle Progression in Hepatocytes.

During normal proliferation, hepatocytes accumulate triglycerides (TGs) in lipid droplets (LDs), but the underlying mechanisms and functional significance of this steatosis are unknown. In the current study, we examined the coordinated regulation of cell cycle progression and LD accumulation. As previously shown, hepatocytes develop increased LD content after mitogen stimulation. Cyclin D1, in addition to regulating proliferation, was both necessary and sufficient to promote LD accumulation in response to mitogens. Interestingly, cyclin D1 promotes LD accumulation by inhibiting the breakdown of TGs by lipolysis through a mechanism involving decreased lipophagy, the autophagic degradation of LDs. To examine whether inhibition of lipolysis is important for cell cycle progression, we overexpressed adipose TG lipase (ATGL), a key enzyme involved in TG breakdown. As expected, ATGL reduced LD content but also markedly inhibited hepatocyte proliferation, suggesting that lipolysis regulates a previously uncharacterized cell cycle checkpoint. Consistent with this, in mitogen‐stimulated cells with small interfering RNA‐mediated depletion of cyclin D1 (which inhibits proliferation and stimulates lipolysis), concurrent ATGL knockdown restored progression into S phase. Following partial hepatectomy, a model of robust hepatocyte proliferation in vivo, ATGL overexpression led to decreased LD content, cell cycle inhibition, and marked liver injury, further indicating that down‐regulation of lipolysis is important for normal hepatocyte proliferation. Conclusion: We suggest a new relationship between steatosis and proliferation in hepatocytes: cyclin D1 inhibits lipolysis, resulting in LD accumulation, and suppression of lipolysis is necessary for cell cycle progression.

Myc and ChREBP transcription factors cooperatively regulate normal and neoplastic hepatocyte proliferation in mice

Analogous to the c-Myc (Myc)/Max family of bHLH-ZIP transcription factors, there exists a parallel regulatory network of structurally and functionally related proteins with Myc-like functions. Two related Myc-like paralogs, termed MondoA and MondoB/carbohydrate response element-binding protein (ChREBP), up-regulate gene expression in heterodimeric association with the bHLH-ZIP Max-like factor Mlx. Myc is necessary to support liver cancer growth, but not for normal hepatocyte proliferation. Here, we investigated ChREBP's role in these processes and its relationship to Myc. Unlike Myc loss, ChREBP loss conferred a proliferative disadvantage to normal murine hepatocytes, as did the combined loss of ChREBP and Myc. Moreover, hepatoblastomas (HBs) originating in myc-/-, chrebp-/-, or myc-/-/chrebp-/- backgrounds grew significantly more slowly. Metabolic studies on livers and HBs in all three genetic backgrounds revealed marked differences in oxidative phosphorylation, fatty acid β-oxidation (FAO), and pyruvate dehydrogenase activity. RNA-Seq of livers and HBs suggested seven distinct mechanisms of Myc-ChREBP target gene regulation. Gene ontology analysis indicated that many transcripts deregulated in the chrebp-/- background encode enzymes functioning in glycolysis, the TCA cycle, and β- and ω-FAO, whereas those dysregulated in the myc-/- background encode enzymes functioning in glycolysis, glutaminolysis, and sterol biosynthesis. In the myc-/-/chrebp-/- background, additional deregulated transcripts included those involved in peroxisomal β- and α-FAO. Finally, we observed that Myc and ChREBP cooperatively up-regulated virtually all ribosomal protein genes. Our findings define the individual and cooperative proliferative, metabolic, and transcriptional roles for the "Extended Myc Network" under both normal and neoplastic conditions.

Increasing 3D Matrix Rigidity Strengthens Proliferation and Spheroid Development of Human Liver Cells in a Constant Growth Factor Environment.

Mechanical forces influence the growth and shape of virtually all tissues and organs. Recent studies show that increased cell contractibility, growth and differentiation might be normalized by modulating cell tensions. Particularly, the role of these tensions applied by the extracellular matrix during liver fibrosis could influence the hepatocarcinogenesis process. The objective of this study is to determine if 3D stiffness could influence growth and phenotype of normal and transformed hepatocytes and to integrate extracellular matrix (ECM) stiffness to tensional homeostasis. We have developed an appropriate 3D culture model: hepatic cells within three-dimensional collagen matrices with varying rigidity. Our results demonstrate that the rigidity influenced the cell phenotype and induced spheroid clusters development whereas in soft matrices, Huh7 transformed cells were less proliferative, well-spread and flattened. We confirmed that ERK1 played a predominant role over ERK2 in cisplatin-induced death, whereas ERK2 mainly controlled proliferation. As compared to 2D culture, 3D cultures are associated with epithelial markers expression. Interestingly, proliferation of normal hepatocytes was also induced in rigid gels. Furthermore, biotransformation activities are increased in 3D gels, where CYP1A2 enzyme can be highly induced/activated in primary culture of human hepatocytes embedded in the matrix. In conclusion, we demonstrated that increasing 3D rigidity could promote proliferation and spheroid developments of liver cells demonstrating that 3D collagen gels are an attractive tool for studying rigidity-dependent homeostasis of the liver cells embedded in the matrix and should be privileged for both chronic toxicological and pharmacological drug screening.

The Effect of ADAM8 on the Proliferation and Apoptosis of Hepatocytes and Hepatoma Carcinoma Cells.

This study was undertaken to evaluate the effect of ADAM8 on the proliferation and apoptosis of hepatocytes and hepatoma carcinoma cells during hepatocellular carcinoma (HCC) progression. The expression of ADAM8 was significantly increased with good correlation of PCNA expression increasing and cells apoptosis decreasing during the progression of HCC in the liver of mice. Proliferation experiment in vitro showed that recombinant ADAM8 could induce the expression of PCNA in L02 cells, but not in HepG2 cells. Apoptosis experiment in vitro showed that recombinant ADAM8 did not induce or inhibit the expression of apoptosis-related factors Bcl2, Bax, and Caspase3 in L02 cells, but significantly induced the expression of Bcl2, inhibited the expression of Bax and Caspase3 in HepG2 cells. In conclusion, our study suggested that ADAM8 could promote the proliferation of normal hepatocytes and render hepatoma carcinoma cells more resistant to apoptosis to play important roles during the progression of HCC. ADAM8; Proliferation; Apoptosis.

Role and Regulation of PDGFRα Signaling in Liver Development and Regeneration

Aberrant platelet-derived growth factor receptor-α (PDGFRα) signaling is evident in a subset of hepatocellular cancers (HCCs). However, its role and regulation in hepatic physiology remains elusive. In the current study, we examined PDGFRα signaling in liver development and regeneration. We identified notable PDGFRα activation in hepatic morphogenesis that, when interrupted by PDGFRα-blocking antibody, led to decreased hepatoblast proliferation and survival in embryonic liver cultures. We also identified temporal PDGFRα overexpression, which is regulated by epidermal growth factor (EGF) and tumor necrosis factor α, and its activation at 3 to 24 hours after partial hepatectomy. Through generation of hepatocyte-specific PDGFRA knockout (KO) mice that lack an overt phenotype, we show that absent PDGFRα compromises extracelluar signal-regulated kinases and AKT activation 3 hours after partial hepatectomy, which, however, is alleviated by temporal compensatory increases in the EGF receptor (EGFR) and the hepatocyte growth factor receptor (Met) expression and activation along with rebound activation of extracellular signal-regulated kinases and AKT at 24 hours. These untimely increases in EGFR and Met allow for normal hepatocyte proliferation at 48 hours in KO, which, however, are aberrantly prolonged up to 72 hours. Intriguingly, such compensation also was visible in primary KO hepatocyte cultures but not in HCC cells after siRNA-mediated PDGFRα knockdown. Thus, temporal activation of PDGFRα in liver development is important in hepatic morphogenesis. In liver regeneration, despite increased signaling, PDGFRα is dispensable owing to EGFR and Met compensation, which is unique to normal hepatocytes but not HCC cells.

Selective poisoning of Ctnnb1-mutated hepatoma cells in mouse liver tumors by a single application of acetaminophen

Mouse liver tumors that harbor activating mutations in Ctnnb1, encoding β-catenin, express high levels of various cytochromes P450 (CYP), including CYP2E1 and CYP1A2. Acetaminophen (AAP) is metabolized in hepatocytes by these CYPs to the reactive intermediate N-acetyl-p-benzoquinone-imine, which is toxic to hepatocytes at high doses where depletion of glutathione occurs. We have induced liver tumors in mice by treatment with the liver carcinogen N-nitrosodiethylamine followed by chronic treatment with the tumor promoter phenobarbital. Under this protocol, ~80 % of tumors display Ctnnb1 mutations and express high levels of various CYP isoforms. Tumor-bearing animals were given a single intraperitoneal injection of 300 mg/kg body weight AAP, which was well tolerated by the animals. This dose, however, eradicated essentially all larger Ctnnb1-mutated, CYP-positive liver tumors, killing >90 % of hepatoma cells: at 2 days after AAP, large necrotic areas filled with cell debris were observed in tumors. These were infiltrated in the following days by immune cells starting from the outer parts of the damaged areas slowly closing the "wounds" left from the poisoned tumor cells. During this period, there was increased proliferation of normal hepatocytes, but some residual tumor cells were also proliferating. Our results show that a selective poisoning of Ctnnb1-mutated liver tumors by administration of AAP is possible in this experimental system. Application of an adapted protocol could be envisaged for neo-adjuvant treatment of human hepatoblastoma which are frequently mutated in CTNNB1 and often show high expression of CYP2E1.

A Calcium Ion-Dependent Dimeric Bean Lectin with Antiproliferative Activity Toward Human Breast Cancer MCF-7 Cells

In this study, a 60.8-kDa dimeric lectin was isolated from the Phaseolus vulgaris cv. jade bean and characterized. The lectin was bound on Blue Sepharose 6 and Q Sepharose and was finally purified by size exclusion chromatography on Superdex 200. Its hemagglutinating activity toward rabbit erythrocytes was dependent on divalent cations, especially calcium ions. Various carbohydrates tested were devoid of any effect on the hemagglutinating activity. The lectin was stable at pH between 4.5 and 9.4 and temperatures between 30 and 70°C. It did not exert antifungal activity toward Valsa mali, Setosphaeria turcica, Mycosphaerella arachidicola, Fusarium oxysporum and Bipolaris maydis. The IC50 of the antiproliferative activity of the lectin toward MCF-7 human breast cancer cells was 174μM. It did not inhibit proliferation of WRL-68 human normal embryonic hepatocytes. The lectin was dependent on calcium ions for hemagglutinating activity and possessed a blocked N-terminus. These two characteristics make the lectin unique among Phaseolus lectins.

The inhibitory effect of rapamycin on the oval cell response and development of preneoplastic foci in the rat

Oval cell activation occurs under conditions of severe liver injury when normal hepatocyte proliferation is blocked. Recent studies have shown that a subset of hepatocellular carcinomas expresses oval cell markers, suggesting that these cells are targets of hepatocarcinogens. However, the signaling pathways that control oval cell activation and proliferation are not well characterized. Based on the role of the nutrient signaling kinase complex, mTORC1, in liver development, we investigated the role of this pathway in oval cell activation. Oval cell proliferation was induced in male Fisher rats by a modification of the traditional choline deficient plus ethionine model (CDE) or by 2-acetylaminoflourene treatment followed by 2/3 partial hepatectomy with or without initiation by diethylnitrosamine. To assess the role of mTOR in the oval cell response and development of preneoplastic foci, the effect of the mTORC1 inhibitor, rapamycin, was studied in all models. Rapamycin induced a significant suppression of the oval cell response in both models, an effect that coincided with a decrease in oval cell proliferation. Rapamycin administration did not affect the abundance of neutrophils or natural killer cells in CDE-treated liver or the expression of key cytokines. Gene expression studies revealed the fetal hepatocyte marker MKP-4 to be expressed in oval cells. In an experimental model of hepatic carcinogenesis, rapamycin decreased the size of preneoplastic foci and the rate of cell proliferation within the foci. mTORC1 signaling plays a key role in the oval cell response and in the development of preneoplastic foci. This pathway may be a target for the chemoprevention of hepatocellular carcinoma.

KIF20A mRNA and Its Product MKlp2 Are Increased During Hepatocyte Proliferation and Hepatocarcinogenesis

Mitotic kinesin-like protein 2 (MKlp2), a microtubule-associated motor, is required during mitosis exit for the final step of cytokinesis. It also contributes to retrograde vesicular trafficking from the Golgi apparatus to the endoplasmic reticulum in interphase. The KIF20A gene encoding MKlp2 is controlled by the E2F-retinoblastoma protein-p16 pathway, and its widely expressed mRNA is found in fetal and proliferating adult tissues. The expression pattern and function of MKlp2 in the adult liver, however, have not been investigated. We report herein that MKlp2 transiently accumulates in vivo during mouse liver regeneration after partial hepatectomy and is strongly overexpressed in preneoplastic and neoplastic mouse liver. In vitro in mitogen-stimulated primary hepatocytes, MKlp2 accumulated in the nucleus during the G2 phase of the cell cycle coincident with the mitotic kinase Aurora B. Human hepatoma cell lines exhibited high levels of MKlp2; however, it was undetectable in normal human hepatocytes. RNAi-mediated MKlp2 knockdown in hepatoma cells induced polyploidization consistent with its essential function in promoting cytokinesis and inhibited cell proliferation without inducing apoptosis. KIF20A mRNA was strongly accumulated in a large series of human hepatocellular carcinomas, with the highest expression observed in tumors with genomic instability. Accumulation of MKlp2 in normal proliferating, preneoplastic, and transformed hepatocytes suggests that MKlp2 contributes to both normal and pathologic hepatocyte proliferation and is linked to tumor aggressiveness in human hepatocellular carcinomas.

Toll-like receptor 4 and myeloid differentiation factor 88 provide mechanistic insights into the cause and effects of interleukin-6 activation in mouse liver regeneration

Partial hepatectomy (PH) consistently results in an early increase of circulating interleukin-6 (IL-6), which is thought to play a major role in liver regeneration. Activation of this cytokine after PH requires the adaptor protein, MyD88, but the specific MyD88-related receptors involved remain unidentified. It is also unknown whether the magnitude of IL-6 elevation determines the extent of subsequent hepatocyte proliferation. Here, we uncovered artifacts in the assessment of circulating IL-6 levels when using cardiac puncture in mice after PH. By using retro-orbital bleed sampling, we show that the circulating levels of IL-6 after PH were not directly correlated with the extent of hepatocyte DNA synthesis in individual mice. The IL-6 increase after PH was attenuated in all lipopolysaccharide-hyporesponsive mouse strains studied (e.g., C3H/HeJ, Tlr4 null, Cd14 null, Tlr2,4,9 null, and Tlr2,4-Caspase1 null) and was severely abrogated in Myd88 null mice. Despite attenuated IL-6 levels, Tlr4 null mice showed normal signaling downstream of IL-6 and normal hepatocyte proliferation. In contrast, Myd88 null mice showed severe impairments in signal transducer and activator of transcription 3 phosphorylation and Socs3 induction, but had enhanced and prolonged extracellular signal-related kinase 1 and 2 phosphorylation in the first 6 hours after PH. Unexpectedly, these changes were associated with accelerated initiation of hepatocyte proliferation, as assessed by hepatocyte bromodeoxyuridine incorporation, phospho-histone H3 immunostaining, and cyclin E and A protein expression. TLR-4 signaling contributes to IL-6 activation after PH, but the Tlr4-independent component appears sufficient for ensuring intact signaling downstream of IL-6. The lack of correlation between IL-6 levels and hepatocyte proliferation after PH, and the accelerated start of hepatocyte proliferation in Myd88 null mice despite abrogated cytokine activation, may highlight relevant antiproliferative effects of IL-6 signaling, possibly via Socs3, in the regulation of liver regeneration.

Long-Term Ethanol Consumption Promotes Hepatic Tumorigenesis but Impairs Normal Hepatocyte Proliferation in Rats

Chronic and excessive alcohol consumption has been related to an increased risk of several cancers, including that of the liver; however, studies in animal models have yet to conclusively determine whether ethanol acts as a tumor promoter in hepatic tumorigenesis. We examined whether prolonged alcohol consumption could act as a hepatic tumor promoter after initiation by diethylnitrosamine (DEN) in a rat model. Male Sprague-Dawley rats were injected with 20 mg DEN/kg body weight 1 wk before introduction of either an ethanol liquid diet or an isoenergic control liquid diet. Hepatic pathological lesions, hepatocyte proliferation, apoptosis, PPARα and PPARγ, and plasma insulin-like growth factor 1 (IGF-1) levels were assessed after 6 and 10 mo. Mean body and liver weights, plasma IGF-1 concentration, hepatic expressions of proliferating cellular nuclear antigen and Ki-67, and cyclin D1 in ethanol-fed rats were all significantly lower after 10 mo of treatment compared with control rats. In addition, levels of hepatic PPARγ protein, not PPARα, were significantly higher in the ethanol-fed rats after prolonged treatment. Although ethanol feeding also resulted in significantly fewer altered hepatic foci, hepatocellular adenoma was detected in ethanol-fed rats at 10 mo, but not in control rats given the same dose of DEN. Together, these results indicate that chronic, excessive ethanol consumption impairs normal hepatocyte proliferation, which is associated with reduced IGF-1 levels, but promotes hepatic carcinogenesis.