Immortalization of epithelial-like cells from human liver tissue with SV40 T-antigen gene

A robust reprogramming strategy for generating hepatocyte-like cells usable in pharmaco-toxicological studies

BACKGROUND

High-throughput pharmaco-toxicological testing frequently relies on the use of established liver-derived cell lines, such as HepG2 cells. However, these cells often display limited hepatic phenotype and features of neoplastic transformation that may bias the interpretation of the results. Alternate models based on primary cultures or differentiated pluripotent stem cells are costly to handle and difficult to implement in high-throughput screening platforms. Thus, cells without malignant traits, optimal differentiation pattern, producible in large and homogeneous amounts and with patient-specific phenotypes would be desirable.

METHODS

We have designed and implemented a novel and robust approach to obtain hepatocytes from individuals by direct reprogramming, which is based on a combination of a single doxycycline-inducible polycistronic vector system expressing HNF4A, HNF1A and FOXA3, introduced in human fibroblasts previously transduced with human telomerase reverse transcriptase (hTERT). These cells can be maintained in fibroblast culture media, under standard cell culture conditions.

RESULTS

Clonal hTERT-transduced human fibroblast cell lines can be expanded at least to 110 population doublings without signs of transformation or senescence. They can be easily differentiated at any cell passage number to hepatocyte-like cells with the simple addition of doxycycline to culture media. Acquisition of a hepatocyte phenotype is achieved in just 10 days and requires a simple and non-expensive cell culture media and standard 2D culture conditions. Hepatocytes reprogrammed from low and high passage hTERT-transduced fibroblasts display very similar transcriptomic profiles, biotransformation activities and show analogous pattern behavior in toxicometabolomic studies. Results indicate that this cell model outperforms HepG2 in toxicological screening. The procedure also allows generation of hepatocyte-like cells from patients with given pathological phenotypes. In fact, we succeeded in generating hepatocyte-like cells from a patient with alpha-1 antitrypsin deficiency, which recapitulated accumulation of intracellular alpha-1 antitrypsin polymers and deregulation of unfolded protein response and inflammatory networks.

CONCLUSION

Our strategy allows the generation of an unlimited source of clonal, homogeneous, non-transformed induced hepatocyte-like cells, capable of performing typical hepatic functions and suitable for pharmaco-toxicological high-throughput testing. Moreover, as far as hepatocyte-like cells derived from fibroblasts isolated from patients suffering hepatic dysfunctions, retain the disease traits, as demonstrated for alpha-1-antitrypsin deficiency, this strategy can be applied to the study of other cases of anomalous hepatocyte functionality.

Rapidly Functional Immobilization of Immortalized Human Hepatocytes Using Cell Adhesive GRGDS Peptide-Carrying Cellulose Microspheres

With the development of biotechnology, hepatic support by a hybrid artificial liver (HAL) using hepatocytes has been given much attention. Because the availability of human livers is limited, we have established a tightly regulated immortal human hepatocyte cell line, NKNT-3, for developing HAL. Because high-density cell culture allows the compactness of the HAL device and its easy use under emergency circumstances, we have developed cell adhesive GRGDS peptide-containing cellulose microspheres (GRGDS/CMS). The GRGDS/CMS efficiently immobilized NKNT-3 cells within 24 h in a stirred suspension culture. Electron microscopic examinations demonstrated glycogen granules and well-developed endoplasmic reticulum and mitochondria in NKNT-3 cells attached to the GRGDS/CMS. The cells showed ammonia clearance activity, whereas HepG2-transformed human liver cells did not remove the loaded ammonia. An efficient adenoviral delivery of the lacZ reporter gene was performed in GRGDS/CMS-immobilized NKNT-3 cells. In this study we present rapid immobilization of NKNT-3 immortal human hepatocytes using cellulose microspheres carrying GRGDS peptides. These microspheres satisfied immediate preparation of NKNT-3 cells in sufficient quantity and of adequate quality.

The immortalisation of rat hepatocytes by transfection with SV40 sequences

Abbreviations EGTA - ethylene bis(oxyethylenenitrilo)-tetraacetic acid; F12 - Ham's F12; FBS - foetal bovine serum; HBSS - Hank's balanced salt solution; HDM - hormonally defined medium; HEPES - 4-(2-hydroxyethyl)-1-piperazine ethanesulphonic acid; NBS - new born calf serum; WME - Williams' medium E.

Establishment of Immortalized Human Hepatocytes by Introduction of HPV16 E6/E7 and hTERT as Cell Sources for Liver Cell-Based Therapy

For future cell-based therapies for liver diseases, the shortage of cell sources must be resolved. Immortalized human hepatocytes are expected to be among the new sources. In addition to telomerase activation by the introduction of human telomerase reverse transcriptase (hTERT), inactivation of the p16/RB pathway and/or p53 by E6/E7 of human papillomavirus type 16 (HPV16) has been shown to be useful for efficient immortalization of several human cell types. Here we report the immortalization of human hepatocytes by the introduction of HPV16 E6/E7 and hTERT. Human adult hepatocytes were lentivirally transduced with HPV16 E6/E7 and hTERT. Two human immortalized hepatocyte cell lines were established and were named HHE6E7T-1 and HHE6E7T-2. Those cells proliferated in culture beyond 200 population doublings (PDs). Albumin synthesis and expression of liver-enriched genes were confirmed, but gradually decreased as passages progressed. Karyotype analysis showed that HHE6E7T-1 cells remained near diploid but that HHE6E7T-2 cells showed severe aneuploidy at 150 PDs. Subcutaneous injection of these cells into severe combined immunodeficiency (SCID) mice did not induce tumor development. Intrasplenic transplantation of dedifferentiated HHE6E7T-1 cells over 200 PDs significantly improved the survival of acetaminophen-induced acute liver failure SCID mice. In conclusion, we successfully established immortalized human hepatocytes that retain the characteristics of differentiated hepatocytes. We also showed the reduction of hepatocyte-specific functions in long-term culture. However, the results of intrasplenic transplantation to SCID mice with acetaminophen-induced acute liver failure showed the possibility of HHE6E7T-1 serving as a cell source for hepatocyte transplantation.

Hepatocyte cell lines: their use, scope and limitations in drug metabolism studies

Gaining knowledge on the metabolism of a drug, the enzymes involved and its inhibition or induction potential is a necessary step in pharmaceutical development of new compounds. Primary human hepatocytes are considered a cellular model of reference, as they express the majority of drug-metabolising enzymes, respond to enzyme inducers and are capable of generating in vitro a metabolic profile similar to what is found in vivo. However, hepatocytes show phenotypic instability and have a restricted accessibility. Different alternatives have been explored in the past recent years to overcome the limitations of primary hepatocytes. These include immortalisation of adult or fetal human hepatic cells by means of transforming tumour virus genes, oncogenes, conditionally immortalised hepatocytes, and cell fusion. New strategies are currently being used to upregulate the expression of drug-metabolising enzymes in cell lines or to derive hepatocytes from progenitor cells. This paper reviews the features of liver-derived cell lines, their suitability for drug metabolism studies as well as the state-of-the-art of the strategies pursued in order to generate metabolically competent hepatic cell lines.

A new method to immortalize primary cultured rat hepatocytes

BACKGROUND

In conventional methods of establishing hepatocyte cell lines, the immortalizing gene alone is introduced into hepatocytes. We designed a new method in which not only the immortalizing gene, the simian virus-40 large T-antigen (SV-40 Tag) gene, but also a drug-resistant gene, under the control of an albumin enhancer/promoter, were introduced into hepatocytes to efficiently obtain immortalized hepatocyte cell lines.

METHODS

The plasmid pAPUR contains the puromycin-resistant gene under the control of an albumin enhancer/promoter, and the pSVTag contains the early region of SV-40 enhancer/promoter and the SV-40 Tag gene. Both pAPUR and pSVTag were transferred into isolated rat hepatocytes by electroporation. After these cells were cultured on a collagen-coated dish for 24 hours, puromycin selection was started. Expression levels of albumin, alpha-fetoprotein (AFP), SV-40 Tag, and cytokeratin 19 (CK 19) in the transformed cells were evaluated by western analysis, immunocytochemical staining, and RT PCR.

RESULTS

Approximately 3 weeks after transfection, five or six colonies appeared on the dish. Twenty strains were obtained by cloning these cells. All strains that were similar to immature hepatocytes expressed albumin and SV-40 Tag, although CK 19 was not detected. AFP expression was detected in 33% of these strains.

CONCLUSIONS

All clones cotransfected by pAPUR and pSVTag expressed albumin. Our new method may be useful to establish hepatocyte cell lines.

Establishment of a highly differentiated immortalized human cholangiocyte cell line with SV40T and hTERT

BACKGROUND

Cholangiocytes perform an essential role in important pathophysiologic functions in the liver. Establishment of a human cholangiocyte line facilitates advances in cholangiocyte research and clinical applications for cell therapies. Here, we describe the immortalization of human cholangiocytes using serial transfection of simian virus 40 large T (SV40T) followed by human telomerase reverse transcriptase (hTERT).

METHODS

SV40T-transduced human liver OUMS-21 cells were superinfected with a retroviral vector SSR#197 encoding hTERT and green fluorescent protein (GFP) cDNAs. Resulting cell lines were evaluated for gene expression, functional cholangiogenic characteristics in vitro and in vivo, and response to lipopolysaccharide (LPS).

RESULTS

One of the SV40T- and hTERT-immortalized cholangiocyte clones, MMNK-1, was established. MMNK-1 expressed cholangiocyte markers, including cytokeratin (CK)-7 and -19 and exhibited cholangiogenic tubule formation in a Matrigel assay. When transplanted into the immunodeficient mice, MMNK-1 cells developed bile duct-like structures in the spleen. After LPS treatment, MMNK-1 cells produced interleukin-6 and failed to form well-developed tubular structures in Matrigel.

CONCLUSION

We have established an immortalized cholangiocyte cell line, MMNK-1, using SV40T and hTERT transduction.

Recent developments on human cell lines for the bioartificial liver

Most bioartificial liver (BAL) devices contain porcine primary hepatocytes as their biological component. However, alternatives are needed due to xenotransplantation associated risks. Human liver cell lines have excellent growth characteristics and are therefore candidates for application in BAL devices. Tumour-derived cell lines HepG2 and C3A express a variety of liver functions, but some specific liver functions, like ammonia detoxification and ureagenesis are insufficient. Immortalised human hepatocytes might offer better prospects. The balance between immortalisation and transformation with dedifferentiation of cells seems controllable by conditional immortalisation and/or the use of telomerase as immortalising agent. Another promising approach will be the use of embryonic or adult human stem cells. Rodent stem cells have been directed to hepatic differentiation in vitro, which might be applicable to human stem cells. However, both functionality and safety of immortalised human liver cell lines and differentiated stem cells should be improved before successful use in BAL devices becomes reality.

Construction of a differentiated human hepatocyte cell line expressing the herpes simplex virus-thymidine kinase gene

Transient support using a hybrid artificial liver (HAL) device is a promising treatment for the patients with acute liver failure. Primary human hepatocytes are an ideal source for HAL therapy; however, the number of human livers available for hepatocyte isolation is limited by competition for use in whole organ transplantation. To overcome this problem, we previously established a highly differentiated human fetal hepatocyte cell line OUMS-29. Considering the potential risk when using these genetically engineered cells in humans, additional safeguards should be added to make the cells more clinically useful. In this work, the herpes simplex virus thymidine kinase (HSVtk) gene was retrovirally introduced into OUMS-29 cells. One of the HSVtk-expressed clones, OUMS-29/thymidine kinase (TK), grew in chemically defined serum free medium and expressed the genes of albumin, asialoglycoprotein receptor, glutamine synthetase, glutathione-S-transferase pi, and blood coagulation factor X. In vitro sensitivity of the cells to ganciclovir was evaluated. Intrasplenic transplantation of 50 x 10(6) OUMS-29/TK cells prolonged the survival of 90% hepatectomized rats compared with medium injection alone (control). In the present study, we have established highly differentiated immortalized human hepatocytes with tight regulation. The cells may be clinically useful for HAL treatment.

Establishment of a human hepatocyte line (OUMS-29) having CYP 1A1 and 1A2 activities from fetal liver tissue by transfection of SV40 LT

Immortalized human hepatocytes that can retain functions of drug-metabolizing enzymes would be useful for medical and pharmacological studies and for constructing an artificial liver. The aim of this study was to establish immortalized human hepatocyte lines having differentiated liver-specific functions. pSVneo deoxyribonucleic acid, which contains large and small T genes in the early region of simian virus 40, was introduced into hepatocytes that had been obtained from the liver of a 21-wk-old fetus. Neomycin-resistant immortalized colonies were cloned and expanded to mass cultures to examine hepatic functions. Cells were cultured in a chemically defined serum-free medium, ASF104, which contains no peptides other than recombinant human transferrin and insulin. As a result, an immortal human hepatocyte cell line (OUMS-29) having liver-specific functions was established from one of the 13 clones. Expression of CYP 1A1 and 1A2 messenger ribonucleic acid by the cells was induced by treatment with benz[a]pyrene, 3-methylcholanthrene, and benz[a]anthracene. OUMS-29 cells had both the polycyclic aromatic hydrocarbon receptor (AhR) and AhR nuclear translocator. Consequently 7-ethoxyresorufin deethylase activity of the cells was induced time- and dose-dependently by these polycyclic aromatic hydrocarbons. This cell line is expected to be instrumental as an alternative method in animal experiments for studying hepatocarcinogenesis, drug metabolisms of liver cells, and hepatic toxicology.

Which hepatocyte will it be? Hepatocyte choice for bioartificial liver support systems

Liver failure, notwithstanding advances in medical management, remains a cause of considerable morbidity and mortality in the developed world. Although bioartificial liver (BAL) support systems offer the potential of significant therapeutic benefit for such patients, many issues relating to their use are still to be resolved. In this review, these issues are examined in terms of the functions required, the cells of choice in such a system, and the most appropriate environment to optimize the function of such cells. The major functions identified to date for a BAL are ammonia detoxification and biotransformation of toxic compounds, although this somewhat belies the complexity of the functions required. Two practical choices for cell type within such a system are xenogenic hepatocytes and immortalized human hepatocyte lines. Both these choices have drawbacks, such as the transmission of zoonoses and malignant infiltration, respectively. Finally, improvements in culture conditions, such as supplemented media, biodegradable scaffolds, and coculture, offer the possibility of prolonging the differentiated function of hepatocytes in a BAL.

Treatment of surgically induced acute liver failure with transplantation of highly differentiated immortalized human hepatocytes

Primary human hepatocytes are an ideal source of hepatic function in bioartficial liver (BAL), but the shortage of human livers available for hepatocyte isolation limits this modality. To resolve this issue, primary human fetal hepatocytes were immortalized using simian virus 40 large T antigen. One of the immortal cell lines, OUMS-29, showed highly differentiated liver functions. Intrasplenic transplantation of OUMS-29 cells protected 90% hepatectomized rats from hyperammonemia and significantly prolonged their survival. Essentially unlimited availability of OUMS-29 cells supports their clinical use for BAL treatment.

Transplantation of highly differentiated immortalized human hepatocytes to treat acute liver failure

BACKGROUND

Temporary support of a damaged liver by a bioartificial liver (BAL) devise is a promising approach for the treatment of acute liver failure. Although human primary hepatocytes are an ideal source of hepatic function in BAL, shortage of human livers available for hepatocyte isolation is the limiting factor for the use of this modality. A clonal human hepatocyte cell line that can grow economically in culture and exhibit liver-specific functions should be an attractive solution to this problem.

METHODS

To test this alternative, primary human fetal hepatocytes were immortalized using Simian virus 40 large T antigen. To investigate the potential of the immortalized cells for BAL, we transplanted the cells into the spleen of adult rats and performed a 90% hepatectomy 12 hr later.

RESULTS

One of the cloned human liver cell lines, OUMS-29, showed highly differentiated liver functions. Intrasplenic transplanting of 20x10(6) OUMS-29 cells protected the animals from hyperammonemia and the associated hepatic encephalopathy. Survival was significantly prolonged in 90% of hepatectomized rats receiving OUMS-29 cells.

CONCLUSIONS

A highly differentiated immortalized human hepatocyte cell line, OUMS-29, was able to provide metabolic support during acute liver failure induced by 90% hepatectomy in rats. Essentially unlimited availability of OUMS-29 cells may be clinically useful for BAL treatment.

Development of a mouse cell line containing the PhiX174 am3 allele as a target for detecting mutation

Transgenic mice containing multiple copies of the PhiX174 am3 allele are being developed as a model for detecting tissue-specific in vivo mutation. In order to derive an analogous system for measuring am3 mutation in vitro, cells were cultured from 15-day-old C57Bl/6J mouse embryos that were homozygous for the transgene and these cells were transfected with a plasmid expressing the SV40 large T-antigen. Two G418-resistant colonies were isolated from this culture and expanded to continuously proliferating cell lines (PX-1 and PX-2). Line PX-2 was treated with up to 1.0 mg/ml of N-ethyl-N-nitrosourea (ENU), assayed for survival by cloning efficiency after overnight culture, and assayed for am3 mutations after 5 days of culture. Survival decreased to 31% at the highest dose of ENU, while mutant frequency increased with dose from approximately 2 x 10(-7) in the untreated cells to 13 x 10(-7) in cultures treated with 0.6 mg/ml of ENU. PX-2 cells also were treated with 0 and 0.6 mg/ml of ENU and mutant frequency assays were performed after 5, 24, 48 and 72 h of growth. The mutant frequency in the treated culture increased to 20 x 10(-7) at 48 h and remained approximately the same at 72 h. These results indicate that PX-2 cells should be a useful resource for developing the in vivo am3 mutant assay and for evaluating the sensitivity of the am3 allele to various classes of mutagens.

Expression of liver functions in immortalised rat hepatocyte cell lines

The differentiated hepatic function of two rat liver cell lines, P9 and SV40RH1, immortalised by transfection with SV40 DNA has been investigated in terms of the glutathione synthesis, and the activities of gamma-glutamyltransferase, glutathione-S-transferase and UDP-glucuronosyltransferase. SV40RH1 is a highly differentiated cell line at early passage, but the expression of some aspects of its differentiated phenotype is unstable and some functions are lost by passage 12-13. P9 is a less-well differentiated cell line, with relatively stable expression of functions between passages 4 and 13. In terms of differentiated function both cell lines represent a marked improvement over primary cultures of rat hepatocytes which de-differentiate rapidly within 24-48 h in culture. This retention of liver function in proliferating cell lines offers the opportunity to use such cells in in vitro toxicological studies.