Spontaneous neoplastic transformation of WB-F344 rat liver epithelial cells

Applicability of Scrape Loading-Dye Transfer Assay for Non-Genotoxic Carcinogen Testing

Dysregulation of gap junction intercellular communication (GJIC) is recognized as one of the key hallmarks for identifying non-genotoxic carcinogens (NGTxC). Currently, there is a demand for in vitro assays addressing the gap junction hallmark, which would have the potential to eventually become an integral part of an integrated approach to the testing and assessment (IATA) of NGTxC. The scrape loading-dye transfer (SL-DT) technique is a simple assay for the functional evaluation of GJIC in various in vitro cultured mammalian cells and represents an interesting candidate assay. Out of the various techniques for evaluating GJIC, the SL-DT assay has been used frequently to assess the effects of various chemicals on GJIC in toxicological and tumor promotion research. In this review, we systematically searched the existing literature to gather papers assessing GJIC using the SL-DT assay in a rat liver epithelial cell line, WB-F344, after treating with chemicals, especially environmental and food toxicants, drugs, reproductive-, cardio- and neuro-toxicants and chemical tumor promoters. We discuss findings derived from the SL-DT assay with the known knowledge about the tumor-promoting activity and carcinogenicity of the assessed chemicals to evaluate the predictive capacity of the SL-DT assay in terms of its sensitivity, specificity and accuracy for identifying carcinogens. These data represent important information with respect to the applicability of the SL-DT assay for the testing of NGTxC within the IATA framework.

Ring1 promotes the transformation of hepatic progenitor cells into cancer stem cells through the Wnt/β-catenin signaling pathway

The proliferation of hepatic progenitor cells (HPCs) is observed in reactive conditions of the liver and primary liver cancers. Ring1 as a member of polycomb-group proteins which play vital roles in carcinogenesis and stem cell self-renewal was increased in HCC patients and promoted proliferation and survival of cancer cell by degrading p53. However, the mechanisms of Ring1 driving the progression of hepatocarcinogenesis have not been elucidated. In this study, forced expression Ring1 and Ring1 siRNA lentiviral vectors were utilized to stably overexpression and silence Ring1 in HPC cell line (WB-F344), respectively. Our finding indicated that overexpression of Ring1 in HPCs promoted colony formation, cell multiplication, and invasion in vitro, conversely depletion of Ring1 repressed the biological functions of HPCs relative to controls. The expression of β-catenin was upregulated in the HPCs with overexpression of Ring1, and the correlation analysis also showed that β-catenin and Ring1 had a significant correlation in the liver cancer tissues and adjacent tissues. The activation of the Wnt/β-catenin signaling pathway significantly increased the expression of liver cancer stem cells related (LCSCs)-related molecular markers CD90 and EpCAM, which led to the transformation of HPCs into LCSCs. Most importantly, the injection of HPCs with overexpressed Ring1 into the subcutaneous of nude mice leads to the formation of poorly differentiated HCC neoplasm. Our findings elucidate that overexpression of Ring1 the activated Wnt/β-catenin signaling pathway and drove the transformation of HPCs into cancer stem cell-like cells, suggesting Ring1 has extraordinary potential in early diagnosis of HCC.

Dysregulation of Bmi1 promotes malignant transformation of hepatic progenitor cells

Adult hepatic progenitor cells (HPCs) are involved in a wide range of human liver diseases, including hepatocellular carcinoma (HCC). Bmi1 has been reported to have vital roles in stem cell self-renewal and carcinogenesis. We have previously demonstrated that Bmi1 is upregulated in HCC with bile duct tumor thrombi, a subtype of HCC characterized by profuse expression of hepatic stem cell markers. However, the function of Bmi1 in HPCs has not yet been well elucidated. The current study was designed to investigate the effects of Bmi1 on the biological properties of rat HPCs. To accomplish this, Bmi1 was silenced or enhanced in two HPC cell lines (WB-F344 and OC3) by, respectively, using either small interfering RNA against Bmi1 or a forced Bmi1 expression retroviral vector. The biological functions of Bmi1 in HPCs were investigated through cell proliferation assays, colony-formation assays, cell cycle analysis and invasion assays, as well as through xenograft-formation assays. In this study, genetic depletion of Bmi1 repressed cell proliferation, colony formation and invasion in both assessed HPC cell lines relative to controls. Conversely, forced expression of Bmi1 in two HPCs cell lines promoted cell proliferation, colony formation and invasion in vitro. Aldehyde dehydrogenase (ALDH) assay revealed a significant increase in the number of ALDH-positive cells following the forced expression of Bmi1 in HPCs. Most importantly, transplantation of forced Bmi1 expression HPCs into nude mice resulted in the formation of tumors with histological features of poorly differentiated HCC. Taken together, our findings indicate that forced expression of Bmi1 promotes the malignant transformation of HPCs, suggesting Bmi1 might be a potential molecular target for the treatment of HCC.

The challenge of cholangiocarcinoma: dissecting the molecular mechanisms of an insidious cancer

Cholangiocarcinoma is a fatal cancer of the biliary epithelium and has an incidence that is increasing worldwide. Survival beyond a year of diagnosis is less than 5%, and therapeutic options are few. Known risk factors include biliary diseases such as primary sclerosing cholangitis and parasitic infestation of the biliary tree, but most cases are not associated with any of these underlying diseases. Numerous in vitro and in vivo models, as well as novel analytical techniques for human samples, are helping to delineate the many pathways implicated in this disease, albeit at a frustratingly slow pace. As yet, however, none of these studies has been translated into improved patient outcome and, overall, the pathophysiology of cholangiocarcinoma is still poorly understood. There remains an urgent need for new approaches and models to improve management of this insidious and devastating disease. In this review, we take a bedside-to-bench approach to discussing cholangiocarcinoma and outline research opportunities for the future in this field.

Patterns of microRNA expression in non-human primate cells correlate with neoplastic development in vitro

MicroRNAs (miRNAs) are small noncoding RNAs that negatively regulate gene expression post-transcriptionally. They play a critical role in developmental and physiological processes and have been implicated in the pathogenesis of several diseases including cancer. To identify miRNA signatures associated with different stages of neoplastic development, we examined the expression profile of 776 primate miRNAs in VERO cells (a neoplastically transformed cell line being used for the manufacture of viral vaccines), progenitor primary African green monkey kidney (pAGMK) cells, and VERO cell derivatives: spontaneously immortalized, non-tumorigenic, low-passage VERO cells (10-87 LP); tumorigenic, high-passage VERO cells (10-87 HP); and a cell line (10-87 T) derived from a 10-87 HP cell tumor xenograft in athymic nude mice. When compared with pAGMK cells, the majority of miRNAs were expressed at lower levels in 10-87 LP, 10-87 HP, and 10-87 T cells. We identified 10 up-regulated miRNAs whose level of expression correlated with VERO cell evolution from a non-tumorigenic phenotype to a tumorigenic phenotype. The overexpression of miR-376a and the polycistronic cluster of miR-376a, miR-376b and miR-376c conferred phenotypic changes to the non-tumorigenic 10-87 LP cells that mimic the tumorigenic 10-87 HP cells. Thirty percent of miRNAs that were components of the identified miRNAs in our spontaneously transformed AGMK cell model are also dysregulated in a variety of human tumors. These results may prove to be relevant to the biology of neoplastic development. In addition, one or more of these miRNAs could be biomarkers for the expression of a tumorigenic phenotype.

Accumulation of neoplastic traits prior to spontaneous in vitro transformation of rat cholangiocytes determines susceptibility to activated ErbB-2/Neu

Cholangiocarcinoma, a severe form of biliary cancer, has a high mortality rate resulting partially from the advanced stage of disease at earliest diagnosis. A better understanding of the progressive molecular and cellular changes occurring during spontaneous cholangiocarcinogenesis is needed to identify potential biomarkers for diagnosis/prognosis or targets for novel therapeutics. Here, we show that with continued passage (p) in vitro, rat bile duct epithelial cells (BDEC) accumulated neoplastic characteristics that by mid-passage (p31-85) included alterations in morphology, increased growth rate, growth factor independence, decreased cell adhesion, loss of cholangiocyte markers expressed at low passage (p<30), and onset of aneuploidy. At high passage (p>85), BDEC cultures showed increasing numbers of cells expressing activated, tyrosine phosphorylated ErbB-2/Neu, a receptor tyrosine kinase previously reported to be at elevated levels in cholangiocarcinomas. Enrichment for high passage ErbB-2/Neu-positive cells yielded several anchorage-independent sub-lines with elevated levels of activated ErbB-2/Neu and increased expression of cyclooxygenase-2 (COX-2). When injected into immunodeficient beige/nude/xid mice, these sub-lines formed poorly differentiated cystic tumors strongly positive for rat cholangiocyte markers, a finding consistent with a previous report showing the susceptibility of high passage, non-tumorigenic BDEC to transformation by activated ErbB-2/Neu. Mid passage BDEC, in contrast, were resistant to the transforming activity of activated ErbB-2/Neu and remained anchorage dependent in vitro and non-tumorigenic in vivo following stable transfection. Based on these findings, we concluded that during progression to high passage, cultured BDEC undergo preneoplastic changes that enhance their susceptibility to transformation by ErbB-2/Neu. The ability to generate cells at different points in the process of spontaneous neoplastic transformation offers a valuable model system for identifying molecular features that determine whether over-expression of activated ErbB-2/Neu is necessary and sufficient to induce neoplastic conversion.

Sequential loss of cell cycle checkpoint control contributes to malignant transformation of murine embryonic fibroblasts induced by 20-methylcholanthrene

Definitive information about the number and nature of discrete steps of tumorigenesis is enigmatic. To understand the multistep nature of carcinogenesis, an in vitro model of 20-Methylcholanthrene-treated primary fibroblast cells CNCI-PM-20, from 20-day old Swiss mouse embryo was used. Visible neoplastic changes with distinct morphological variations along with specific chromosomal aberrations like Robertsonian metacentrics, double and single-minute chromosomes and aneuploidy were observed from Passage-20 onwards. The cell cycle profile showed gradual increase in G(2)/M population till P-32, followed by evasion of block from P-36 onwards. Gradual increase in expression of C-myc, CyclinD1 and a decrease in expression of P21 was observed from P-20 onwards. CDC25A expression was significantly increased at P-27 and remained more or less constant in subsequent passages. Additionally, an increased P16 and P53 expression were seen at P-20 followed by their significant down-regulation at P-32. An increased level of phosphorylated retinoblastoma (ppRb) was observed from P-27, probably responsible for a compromised G(1)/S checkpoint. The inactivation of p21 and p16 might be due to their promoter hyper-methylation as suggested through de-methylation experiment by 5-aza-deoxycytidine at P-42. G(2)/M checkpoint abrogation was marked by gradual increase in expression of CyclinB1 and Cdc20, and a significant increase of Mad2 at P-20. Interestingly, increased expression of phospho-ATM, ATR and phospho-Chk1 were also seen at P-20 followed by their down-regulation at subsequent passages, indicating a perturbation of DNA damage response pathway at early passages. Our findings therefore dramatize the multiple genetic events that can cooperate to promote tumorigenesis.

Dynamic alteration of protein expression profiles during neoplastic transformation of rat hepatic oval-like cells

To explore the molecular basis of neoplastic transformation of hepatic oval cells, a proteomic strategy was utilized to examine the global protein expression alterations during neoplastic transformation of rat hepatic oval-like cells. N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-initiated WB-F344 cells were treated with H(2)O(2) for neoplastic transformation. The transformed cells were identified by soft agar assay and MTT assay. The subsequent proteomic separation and identification were performed with 2-DE followed by MALDI-TOF-MS/MS analysis. Of the 148 differentially displayed protein spots analyzed, 121 spots representing 79 distinct proteins were finally identified. The expression levels of interested proteins were validated by western blotting including 40 S ribosomal protein A (RPSA) and cytokeratin 8. Bioinformatics annotations indicated that these identified proteins were enriched with oxidoreduction and stress response; transcription, translation, and protein processing; and energy/metabolism functions. Interestingly, 17 of the identified proteins were also found to be involved in early hepatic differentiation of mouse embryonic stem (ES) cells in our previous study. Twenty-six proteins had been reported as being dysregulated in hepatocellular carcinoma and other cancers. It suggested that these changed proteins may be implicated in neoplastic transformation of WB-F344 cells. The results may provide some clues for understanding the molecular mechanisms of hepatocarcinogenesis as viewed from dysregulation of differentiation.

A novel "patient-like" model of cholangiocarcinoma progression based on bile duct inoculation of tumorigenic rat cholangiocyte cell lines

Intrahepatic cholangiocarcinoma typically presents in an advanced stage in which treatment options are limited. In an effort to recapitulate key biological and clinical features of the progressive disease, we established a novel rat model based on bile duct inoculation of rat cholangiocyte cell lines in different stages of tumor progression. Our BDEneu cell line, which is highly tumorigenic, originated from an immortalized rat cholangiocyte cell line (BDE1 cells) that was stably transfected to constitutively overexpress mutationally activated rat neu oncogene. Our less aggressive tumorigenic BDEsp cholangiocyte cell line was derived from the spontaneous in vitro neoplastic transformation of the same parent BDE1 cell line. Unlike BDEneu cells, BDEsp cells expressed wild-type c-neu and exhibited in vitro growth rates intermediate between those of BDEneu and BDE1 cholangiocytes. Cyclooxygenase-2 and activated Akt were significantly overexpressed in BDEsp cells over those of BDE1 cells, and at higher levels than those expressed in BDEneu cells. Only BDEneu cells overexpressed activated p185(neu), which was associated with a significant increase in phospho-p44/42 mitogen-activated protein kinase (MAPK). Mucin 1 (MUC1) messenger RNA (mRNA), an indicator of cholangiocarcinoma cell progression, was also significantly overexpressed in BDEneu cells over that of BDEsp cells. BDEneu cells inoculated into the bile duct of isogenic rats resulted over a 21- to 26-day period in rapid exponential cholangiocarcinoma tumor growth within liver, paralleled by increases in bile duct obstruction and gross peritoneal metastases. Under comparable conditions, BDEsp cells yielded only small nonmetastatic intrahepatic cholangiocarcinomas without bile duct obstruction.

CONCLUSIONS

A novel model of cholangiocarcinoma progression mimicking progressive development of the advanced human disease has been established, which may serve as a powerful preclinical platform to study cholangiocarcinoma progression and for rapidly testing treatment approaches.

Deletion of the Met tyrosine kinase in liver progenitor oval cells increases sensitivity to apoptosis in vitro

The hepatocyte growth factor (HGF)/Met signaling system is essential for liver development, homeostasis, and function. In this study, we took advantage of a liver-specific, Met-conditional knockout mouse generated in our laboratory to address the molecular mechanisms of HGF/Met signaling in adult liver progenitor cell (oval cell) biology. For this purpose, we isolated oval cells from 3,5-diethoxycarbonyl-1,4-dihydro-collidine-treated Met(flx/flx) mice and established oval cell-derived cell lines that carried either functional (Met(flx/flx)) or a nonfunctional (Met(-/-)) met gene using virus-mediated Cre-loxP recombination. Oval cells lacking Met tyrosine kinase activity displayed neither Met phosphorylation nor activation of downstream targets and were refractory to HGF stimulation. Although Met(-/-) and Met(flx/flx) cells proliferated at similar rates under 10% serum, Met-deficient cells demonstrated decreased cell viability and were more prone to apoptosis when challenged with either serum starvation or the pro-apoptotic cytokine transforming growth factor-beta. Treatment with HGF reduced transforming growth factor-beta-mediated cell death in Met(flx/flx) but not Met(-/-) cells. Importantly, Met(flx/flx) and Met(-/-) cells both constitutively expressed hgf, and conditioned medium from serum-starved oval cells exhibited anti-apoptotic activity in Met(flx/flx) cells. Furthermore, serum-starved Met(flx/flx) cells showed persistent activation of the Met tyrosine kinase, suggesting HGF/Met autocrine regulation. In conclusion, these data reveal a critical, functional role for Met in oval cell survival through an autocrine mechanism.

Epithelial cells with hepatobiliary phenotype: is it another stem cell candidate for healthy adult human liver?

AIM

To investigate the presence and role of liver epithelial cells in the healthy human adult liver.

METHODS

Fifteen days after human hepatocyte primary culture, epithelial like cells emerged and started proliferating. Cell colonies were isolated and subcultured for more than 160 d under specific culture conditions. Cells were analyzed for each passage using immunofluorescence, flow cytometry and reverse transcription-polymerase chain reaction (RT-PCR).

RESULTS

Flow cytometry analysis demonstrated that liver epithelial cells expressed common markers for hepatic and stem cells such as CD90, CD44 and CD29 but were negative for CD34 and CD117. Using immunofluorescence we demonstrated that liver epithelial cells expressed not only immature (alpha-fetoprotein) but also differentiated hepatocyte (albumin and CK-18) and biliary markers (CK-7 and 19), whereas they were negative for OV-6. RT-PCR analysis confirmed immunofluorescence data and revealed that liver epithelial cells did not express mature hepatocyte markers such as CYP2B6, CYP3A4 and tyrosine amino-transferase. Purified liver epithelial cells were transplanted into SCID mice. One month after transplantation, albumin positive cell foci were detected in the recipient mouse parenchyma.

CONCLUSION

According to their immature and bipotential phenotype, liver epithelial cells might represent a pool of precursors in the healthy human adult liver other than oval cells.

Spontaneous differentiation of adult rat marrow stromal cells in a long-term culture

It is well recognized that bone marrow stromal cells (MSCs) can differentiate into neuron-like cells when supplemented with growth factors and/or chemical treatments. We demonstrated that primary MSCs obtained from adult rats could spontaneously differentiate into neural precursor cells after long-term culture. During the outset of in vitro culture, less than 0.1% of adult rat primary MSCs expressed nestin, the common protein of neural precursors. These MSCs didn't show neuronal morphology nor express neuronal antigens. In contrast, after continuous maintenance for 6 weeks, a significant subpopulation of MSCs formed cellular clumps and expressed nestin (32.3 +/- 6.3%). Less than 0.1% of cells expressing immature neuron marker betaIII-tubulin could be detected in these prolonged cultured MSCs. After serum deprivation and growth factor supplement, these nestin-positive cells could express neuron-like morphology and neuron-specific markers NF-H, betaIII-tubulin, tau, and neurotransmitter GABA. In contrast, the MSCs without prolonged culture didn't show neuronal morphology nor neuronal markers even after serum withdrawal and growth factors stimulation. These results demonstrated that neural precursors could be obtained from long-term cultured MSCs, and suggested that MSCs should be useful as a potential source for treatment of neurological disease.

Role of oval cells in carcinogenesis of experimental hepatocellular carcinoma in rats

AIM: To discuss the role of oval cells in the carcinogenesis and progression of hepatocellular carcinoma.

METHODS: A total of 60 male Sprague Dawley rats were divided into experiment group (n = 48) and control group (n = 12). 3'-methyl-4-dimethylaminoazobenzene (3'-Me-DAB) was used to induce hepatocellular carcinoma, and the presence of oval cells, the expression of p53 gene and P53 protein were dynamically (4, 8, 12, 16, 20, 24 wk) detected by immunohistochemistry, reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively.

RESULTS: Large numbers of oval cells appeared in the periportal regions 4 wk after the induction of carcinoma, and these cells were OV-6-positive. Cancer nodules were observed at the 16^th wk, and the oval cells were located in and around the cancer nodule. A part of these proliferated cells were P53-positive, and the two kinds of cells were almost located in the same region. Twenty weeks after cancer induction, the levels of p53 mRNA (F = 4.78, P < 0.05) and P53 protein in the cancer tissues of rat liver were significantly elevated (F = 2.46, P < 0.05).

CONCLUSION: Oval cells are involved in the process of rat hepatocarcinogesis induced by 3'-Me-DAB, and its mechanism may be related to the mutation of p53 gene.

erbB-2/neu transformed rat cholangiocytes recapitulate key cellular and molecular features of human bile duct cancer

BACKGROUND & AIMS

Cholangiocarcinomas appear to arise from the malignant transformation of cholangiocytes lining the biliary tract. Because the development of an in vitro model of malignant transformation can provide a powerful new tool for establishing critical events governing the molecular pathogenesis of cholangiocarcinoma, we investigated the potential of achieving malignant transformation of cultured rat cholangiocytes in relation to aberrant overexpression of mutationally activated erbB-2/neu.

METHODS

Malignant neoplastic transformation was achieved after infection of the rat cholangiocyte cell line, designated BDE1, with the retrovirus Glu664-neu, containing the transforming rat erbB-2/neu oncogene.

RESULTS

Compared with untransformed control cells, malignant transformants carrying the activating erbB-2/neu mutation prominently overexpressed p185neu receptor protein, which was phosphorylated strongly at its major autophosphorylation site at tyrosine 1248. Moreover, erbB-2/neu transformation of BDE1 cells resulted in increased telomerase activity, up-regulation of cyclooxygenase-2 with overproduction of prostaglandin E(2), enhanced phosphorylation of mitogen-activated protein kinase and of serine/threonine kinase Akt/PKB, overexpression of vascular endothelial growth factor, and increased mucin 1 messenger RNA expression. Only erbB-2/neu transformants were tumorigenic when transplanted into isogeneic rats, yielding a 100% incidence of tumors closely resembling human desmoplastic ductal cholangiocarcinomas in their morphology. Malignant cholangiocytes in the tumors were strongly immunoreactive for biliary cytokeratin 19, p185neu, and cyclooxygenase-2.

CONCLUSIONS

This unique malignant transformation model recapitulates key molecular features of the human disease and appears to be well suited for testing novel molecular therapeutic strategies against cholangiocarcinoma.

Emerging insights into liver-directed cell therapy for genetic and acquired disorders

Treatment of acute or chronic liver diseases by cell transplantation is an attractive prospect because organ shortages greatly restrict liver transplantation. Moreover, a variety of genetic deficiency states affecting extrahepatic organs are amenable to liver-directed cell therapy. While the initial clinical experience with liver cell transplantation has been encouraging, further advances in several areas are necessary to improve these results. Insights into how engraftment and proliferation of transplanted cells may be modulated to obtain therapeutically effective masses of transplanted cells will be important in this pursuit. Studies of cell therapy in animal models of specific diseases have provided insights into the development of clinically relevant strategies for various disorders. Also, identification of suitable cell types, including stem/progenitor cells that could be expanded and manipulated in cell culture conditions, has begun to provide important new information for cell therapy. Similarly, advances in cryopreservation of cells and prevention of allograft rejection offer ways to accomplish cell therapy in an effective manner. Taken together, these advances indicate that liver-directed cell therapy will be well positioned in the near future to play significant roles in transplantation medicine.

Telomerase regulation and progressive telomere shortening of rat hepatic stem-like epithelial cells during in vitro aging

Rat hepatic stem-like epithelial cells, LE/2, LE/6, and WB-F344, share some phenotypic properties with oval cells, observed in the early stages of hepatocarcinogenesis. Here, we describe regulations of telomerase and telomere length during in vitro aging of LEs and WB-F344. These cells displayed no apparent aging phenotypes for over 140 passages. Telomerase activity and telomere length of these cells progressively decreased with the passages, and at the late passages, telomere shortening appeared to be reduced as telomerase activity increased. Regulation of TERT and TR, key components of telomerase, was similar to that of the telomerase activity. LEs possessed weak telomerase activity with a slow rate of proliferation compared to WB-F344, and were not tumorigenic, whereas WB-F344 was transformed in vitro from intermediate passage. In conclusion, LEs and WB-F344 have different biochemical properties, and telomerase activation and short telomeres are unlikely necessary for the transformation of WB-F344. TERT and TR seem to be the regulators of the telomerase activity. The relationship between telomere length and telomerase activity suggests that telomerase contributes to the regulation of telomere length in these cells. Our findings provide a better understanding of mechanisms in neoplastic transformation of rat hepatic stem-like epithelial cells.