Tumorigenicity of simian virus 40-hepatocyte cell lines: effect of in vitro and in vivo passage on expression of liver-specific genes and oncogenes

Generation of Hepatic Progenitor Cells from the Primary Hepatocytes of Nonhuman Primates Using Small Molecules

BACKGROUND

Since primates have more biological similarities to humans than do other animals, they are a valuable resource in various field of research, including biomedicine, regenerative medicine, and drug discovery. However, there remain limitations to maintenance and expansion of primary hepatocytes derived from nonhuman primates. To overcome these limitations, we developed a novel culture system for primate cells.

METHODS

Primary hepatocytes from Macaca fascicularis (mf-PHs) were isolated from hepatectomized liver. To generate chemically derived hepatic progenitor cells (mf-CdHs), mf-PHs were cultured with reprogramming medium containing A83-01, CHIR99021, and hepatocyte growth factor (HGF). The bi-potent differentiation capacity of mf-CdHs into hepatocytes and biliary epithelial cells was confirmed by treatment with hepatic differentiation medium (HDM) and cholangiocytic differentiation medium (CDM), respectively.

RESULTS

mf-PHs cultured with reprogramming medium showed rapid proliferation capacity in vitro and expressed progenitor-specific markers. Moreover, when cultured in HDM, these progenitor cells stably differentiated into hepatocyte-like cells expressing the mature hepatic markers. On the other hand, when cultured in CDM, the differentiated biliary epithelial cells expressed mature cholangiocyte characteristics.

CONCLUSION

The results of the present study demonstrate that we successfully induced the formation of hepatic progenitor cells from mf-PHs by culturing them with a combination of small molecules, including growth factors. These results offer a means of expanding nonhuman primate hepatocytes without genetic manipulation for cellular resource, preclinical applications and regenerative medicine for the liver.

Establishment and characterization of immortalized porcine neonatal hepatocytes without the use of viral components

Porcine hepatocytes are a promising option for xenotransplantation in light of the critical shortage of orthotopic donor livers. Because primary hepatocytes have limited ability to proliferate in vitro, several immortalized hepatocyte lines have been established. However, these cells have typically been generated using a virus-dependent transfection methodology and express viral oncogenes that introduce potential risks in clinical applications. In our study, we established immortalized porcine neonatal hepatocytes by introduction of a plasmid-based hTERT gene expression system by electroporation, without the use of viral components. We detected stable expression of hTERT by RT-PCR and Western blot. The immortalized hepatocytes exhibit a high growth rate, but retain the normal morphology of freshly isolated primary hepatocytes. To date, these immortalized hepatocytes have been expanded for over 80 passages. In addition, no significant differences were detected in glycogen synthesis, secretion of serum albumin, or lipid accumulation between the primary hepatocytes and our immortalized hepatocytes. The cells also exhibit serum-dependent growth and have no capacity for anchorage-independent growth in vitro, demonstrating that they have not been transformed in vitro. Our immortalized porcine hepatocytes will be useful for elucidating the pathogenesis of liver disease and developing efficient treatments. Furthermore, these immortalized hepatocytes may provide a safer source of cells for application in xenotransplantation, compared with immortalized cells generated using viral components.

Potential for Isolation of Immortalized Hepatocyte Cell Lines by Liver-Directed In Vivo Gene Delivery of Transposons in Mice

Isolation of hepatocytes and their culture in vitro represent important avenues to explore the function of such cells. However, these studies are often difficult to perform because of the inability of hepatocytes to proliferate in vitro. Immortalization of isolated hepatocytes is thus an important step toward continuous in vitro culture. For cellular immortalization, integration of relevant genes into the host chromosomes is a prerequisite. Transposons, which are mobile genetic elements, are known to facilitate integration of genes of interest (GOI) into chromosomes in vitro and in vivo. Here, we proposed that a combination of transposon- and liver-directed introduction of nucleic acids may confer acquisition of unlimited cellular proliferative potential on hepatocytes, enabling the possible isolation of immortalized hepatocyte cell lines, which has often failed using more traditional immortalization methods.

Strategies for immortalization of primary hepatocytes

The liver has the unique capacity to regenerate in response to a damaging event. Liver regeneration is hereby largely driven by hepatocyte proliferation, which in turn relies on cell cycling. The hepatocyte cell cycle is a complex process that is tightly regulated by several well-established mechanisms. In vitro, isolated hepatocytes do not longer retain this proliferative capacity. However, in vitro cell growth can be boosted by immortalization of hepatocytes. Well-defined immortalization genes can be artificially overexpressed in hepatocytes or the cells can be conditionally immortalized leading to controlled cell proliferation. This paper discusses the current immortalization techniques and provides a state-of-the-art overview of the actually available immortalized hepatocyte-derived cell lines and their applications.

Immortalization of Human Fetal Hepatocyte by Ectopic Expression of Human Telomerase Reverse Transcriptase, Human Papilloma Virus (E7) and Simian Virus 40 Large T (SV40 T) Antigen Towards Bioartificial Liver Support

BACKGROUND

Generation of genetically stable and non-tumoric immortalization cell line from primary cells would be enormously useful for research and therapeutic purposes, but progress towards this goal has so far been limited. It is now universal acceptance that immortalization of human fetal hepatocytes based on recent advances of telomerase biology and oncogene, lead to unlimited population doubling could be the possible source for bioartificial liver device.

METHODS

Immortalization of human fetal hepatocytes cell line by ectopic expression of human telomerase reverse transcriptase (hTERT), human papilloma virus gene (E7) and simian virus 40 large T (SV40 T) antigens is main goal of present study. We used an inducible system containing human telomerase and E7, both of which are cloned into responder constructs controlled by doxycycline transactivator. We characterized the immortalized human fetal hepatocyte cells by analysis of green fluorescent cells (GFP) positive cells using flow cytometry (FACs) cell sorting and morphology, proliferative rate and antigen expression by immunohistochemical analysis. In addition to we analysized lactate formation, glucose consumption, albumin secretion and urea production of immortalized human fetal hepatocyte cells.

RESULTS

After 25 attempts for transfection of adult primary hepatocytes by human telomerase and E7 to immortalize them, none of the transfection systems resulted in the production of a stable, proliferating cell line. Although the transfection efficiency was more than 70% on the first day, the vast majority of the transfected hepatocytes lost their signal within the first 5-7 days. The remaining transfected hepatocytes persisted for 2-4 weeks and divided one or two times without forming a clone. After 10 attempts of transfection human fetal hepatocytes using the same transfection system, we obtained one stable human fetal hepatocytes cell line which was able albumin secretion urea production and glucose consumption.

CONCLUSION

We established a conditional human fetal hepatocytes cell line with mesenchymal characteristics. Thus immortalization of human fetal hepatocytes cell line by telomerase biology offers a great challenge to examine basic biological mechanisms which are directly related to human and best cell source having unlimited population doubling for bioartificial support without any risk of replicative senescence and pathogenic risks.

Phenotypic and in vivo functional characterization of immortalized human fetal liver cells

We report the establishment and characterization of immortalized human fetal liver progenitor cells by expression of the Simian virus 40 large T (SV40 LT) antigen. Well-characterized cells at various passages were transplanted into nude mice with acute liver injury and tested for functional capacity. The SV40LT antigen-immortalized fetal liver cells showed a morphology similar to primary cells. Cultured cells demonstrated stable phenotypic expression in various passages, of hepatic markers such as albumin, CK 8, CK18, transcription factors HNF-4α and HNF-1α and CYP3A/7. The cells did not stain for any of the tested cancer-associated markers. Albumin, HNF-4α and CYP3A7 expression was confirmed by reverse transcription polymerase chain reaction (RT-PCR). Flow cytometry showed expression of some progenitor cell markers. In vivo study showed that the cells expressed both fetal and differentiated hepatocytes markers. Our study suggests new approaches to expand hepatic progenitor cells, analyze their fate in animal models aiming at cell therapy of hepatic diseases.

Establishment and characterization of immortalized porcine hepatocytes for the study of hepatocyte xenotransplantation

BACKGROUND

In light of the critical shortage of donor livers, xenogeneic sources offer the best alternative to human hepatocytes for the treatment of acute liver failure. This study investigated whether a combination of simian virus 40 large T antigen (SV40 LT) and human telomerase catalytic subunit (hTERT) genes could immortalize primary porcine hepatocytes that could reverse acute liver failure (ALF) in rats.

METHODS

We cotransfected SV40 LT and hTERT genes into primary porcine hepatocytes to examine the features of the transfected cell lines. We characterized the potentially therapeutic effect of immortalized porcine hepatocytes in a rat model of ALF induced by 90% hepatectomy.

RESULTS

An immortalized porcine hepatocyte cell line, HepLi, was expanded by >250 passages. HepLi cells maintained the defining characteristics of primary porcine hepatocytes, including porcine albumin secretion, urea production, and diazepam metabolism. Intrasplenic transplantation of HepLi cells significantly improved liver function, and significantly prolonging the survival of rats with ALF.

CONCLUSIONS

Cotransfection of SV40 LT and hTERT immortalized primary porcine hepatocytes without tumorigenicity in vitro. The Immortalized porcine hepatocytes served as a potential cell resource for xenotransplantation.

Serum proteomics of lung adenocarcinomas induced by targeted overexpression of c-raf in alveolar epithelium identifies candidate biomarkers

We previously reported a proteome map of lung adenocarcinomas in serine-threonine kinase of the Raf family (c-raf) transgenic mice. We now extend our initial studies to serum proteins at early stage (1 month) and advanced stages of tumorigenesis (12 months). Notably, serum proteins from wild-type and tumor bearing mice were extracted with a lysis buffer containing 5 mol/L urea, 2 mol/L thiourea, 40 mmol/L Tris, 4% CHAPS, 100 mmol/L DTT, 0.5% BioLyte 3-10, separated by 2-DE and studied by image analysis. On average 400 protein spots per gel were excised and analyzed by MALDI-TOF MS. We identified 45 common and 5 uniquely expressed proteins in wild-type and tumor bearing mice. Apart from uniquely identified proteins we observed for n = 9 proteins differential expression when wild-type and tumor bearing mice were compared. This included serpins and other protease inhibitors, lipocalins, transthyretins, globins, and Igs. Notably, we demonstrate significant regulation of alpha-1-antitrypsin, alpha-2-macroglobulin, hemoglobin subunit alpha, vitamin D-binding protein, major urinary proteins, and transthyretin (up to eight-fold) in serum of lung tumor bearing mice. Disease association of these proteins in human malignancies has been reported. Thus, an identification of regulated serum proteins in this lung cancer disease model provides excellent opportunities for the search of novel biomarkers.

Liver cell lines for the study of hepatocyte functions and immunological response

BACKGROUND

Liver cell lines closely resembling primary hepatocyte are essential for research on hepatitis viruses and hepatocyte function. Currently used cell lines are derived from hepatic tumours and have altered gene expression.

AIMS

The generation and characterisation of novel human hepatocyte lines (HHLs) derived from healthy human liver, retaining the primary hepatocyte phenotype.

RESULTS

Primary hepatocytes were immortalised with Moloney's mouse leukaemia virus expressing E6 and E7 proteins of human papillomavirus, and cultures propagated long-term. All HHLs contained markers of hepatocyte and biliary phenotype (cytokeratins 7, 8, 18 and 19), Cytochrome P450 and albumin. The HHLs did not express high levels of p53 or alpha-fetoprotein. When grown in a collagen sandwich culture, or at the air-liquid interface, HHLs were maintained as monolayer whereas Huh-7 and HepG2 formed thick layers. All HHLs showed increased capacity to bind recombinant hepatitis C virus-like particles in comparison with Huh-7 and HepG2. We also demonstrate that HHLs contained active gap junctions, and that the cells respond to stimulation with IFN-alpha by upregulation of major histocompatibility complex (MHC)-I and -II.

CONCLUSIONS

These HHLs retain primary hepatocyte phenotype and should be useful for investigating mechanisms of entry and replication of hepatotropic viruses, and should also be valuable in the study of hepatocyte biology and pathology.

Spontaneous transformation of an immortalized hepatocyte cell line: potential role of a nuclear protease

In this study, we utilized an in vitro model of spontaneous transformation/progression, an SV40 large T antigen-immortalized rat hepatocyte cell line (designated CWSV14) that is very weakly tumorigenic at low-passage, but acquires a transformed phenotype upon extended passage in cell culture. Here we show that this mid-passage transformation is accompanied by development of aneuploidy and disorganization of the actin cytoskeleton, concomitant with a large increase in a chymotrypsin-like nuclear protease activity which we have previously implicated in chemical transformation of fibroblasts and ras-transformation of hepatocytes. Passage of the CWSV14 cells with AAPF(cmk), a relatively selective inhibitor of the nuclear protease activity, abrogates the acquisition of the transformed phenotype and prevents the changes in the actin cytoskeleton. We hypothesize that the nuclear protease may play a role in initiating development of genomic instability, paralleling the archetypical role of proteases in paradigms such as the SOS-type responses in bacteria and yeast.

Mitochondrial and microsomal derived reactive oxygen species mediate apoptosis induced by transforming growth factor-beta1 in immortalized rat hepatocytes

Transforming growth factor-beta1 (TGFbeta1) is a multifunctional cytokine that is over expressed during liver hepatocytes injury and regeneration. SV40-transformed CWSV-1 rat hepatocytes that are p53-defective undergo apoptosis in response to choline deficiency (CD) or TGFbeta1, which mediates CD-apoptosis. Reactive oxygen species (ROS) are essential mediators of apoptosis. We have shown that apoptosis induced by TGFbeta1 is accompanied by ROS generation and the ROS-trapping agent N-acetylcysteine (NAC) inhibits TGFbeta1-induced apoptosis. While persistent induction of ROS contributes to this form of apoptosis, the source of ROS generated downstream of TGFbeta1 is not clear. The mitochondria and the endoplasmic reticulum both harbor potent electron transfer chains that might be the source of ROS essential for completion of TGFbeta1-apoptosis. Here we show that CWSV-1 cells treated with cyclosporine A, which prevents opening of mitochondrial membrane pores required for ROS generation, inhibits TGFbeta1-induced apoptosis. A similar effect was obtained by treating these cells with rotenone, an inhibitor of complex 1 of the mitochondrial electron transfer chain. However, we demonstrate that TGFbeta1 induces cytochrome P450 1A1 and that metyrapone, a potent inhibitor of cytochrome P450 1A1, inhibits TGFbeta1-induced apoptosis. Therefore, our studies indicate that concurrent with promoting generation of ROS from mitochondria, TGFbeta1 also promotes generation of ROS from the cytochrome P450 electron transfer chain. Since inhibition of either of these two sources of ROS interferes with apoptosis, it is reasonable to conclude that the combined involvement of both pathways is essential for completion of TGFbeta1-induced apoptosis.

Altered mitochondrial function and overgeneration of reactive oxygen species precede the induction of apoptosis by 1-O-octadecyl-2-methyl-rac-glycero-3-phosphocholine in p53-defective hepatocytes

The mechanism of induction of apoptosis by the novel anti-cancer drug 1-O-octadecyl-2-methyl-rac-glycero-3-phosphocholine (ET-18-OCH3) was investigated in p53-defective SV40 immortalized rat hepatocytes (CWSV1). Exposure to 12 microM ET-18-OCH3 for 36 h induced apoptosis as determined using classical morphological features and agarose gel electrophoresis of genomic DNA. Increased levels of reactive oxygen species (ROS) were detected spectrophotometrically using a nitroblue tetrazolium (NBT) assay in cells treated with ET-18-OCH3. Both the increased generation of ROS and the induction of apoptosis were inhibited when cells were treated concurrently with ET-18-OCH3 in the presence of the antioxidant alpha-tocopherol. Similar results were achieved when cells were switched acutely to choline-deficient (CD) medium in the presence of the antioxidant. The possible role of mitochondria in the generation of ROS was investigated. Both ET-18-OCH3 and CD decreased the phosphatidylcholine (PC) content of mitochondrial and associated membranes, which correlated with depolarization of the mitochondrial membrane as analyzed using 5,5',6,6'-tetramethylbenzimidazolcarbocyanine iodide (JC-1), a sensitive probe of mitochondrial membrane potential. Rotenone, an inhibitor of the mitochondrial electron transport chain, significantly reduced the intracellular level of ROS and prevented mitochondrial membrane depolarization, correlating with a reduction of apoptosis in response to either ET-18-OCH3 or CD. Taken together, these results suggest that the form of p53-independent apoptosis induced by ET-18-OCH3 is mediated by alterations in mitochondrial membrane PC, a loss of mitochondrial membrane potential, and the release of ROS, resulting in completion of apoptosis.

Regulation of heme metabolism in rat hepatocytes and hepatocyte cell lines: delta-aminolevulinic acid synthase and heme oxygenase are regulated by different heme-dependent mechanisms

Regulation of delta-aminolevulinic acid (ALA) synthase and heme oxygenase was analyzed in primary rat hepatocytes and in two immortalized cell lines, CWSV16 and CWSV17 cells. ALA synthase was induced by 4,6-dioxohepatnoic acid (4,6-DHA), a specific inhibitor of ALA dehydratase, in all three systems; however, the induction in CWSV17 cells was greater than in either of the other two systems. Therefore, CWSV17 cells were used to explore the regulation of both enzymes by heme and 4,6-DHA. Data obtained from detailed concentration curves demonstrated that 4,6-DHA induced the activity of ALA synthase once ALA dehydratase activity became rate-limiting for heme biosynthesis. Heme induced heme oxygenase activity with increases occurring at concentrations of 10 microM or greater. Heme blocked the 4,6-DHA-dependent induction of ALA synthase with an EC50 of 1.25 microM. Heme-dependent decreases of ALA synthase mRNA levels occurred more quickly and at lower concentrations than heme-dependent increases of heme oxygenase mRNA levels. ALA synthase mRNA remained at reduced levels for extended periods of time, while the increases in heme oxygenase mRNA were much more transient. The drastic differences in concentrations and times at which heme-dependent effects were observed strongly suggest that two-different heme-dependent mechanisms control the ALA synthase and heme oxygenase mRNAs. In CWSV17 cells, heme decreased the stability of ALA synthase mRNA from 2.5 to 1.3 h, while 4,6-DHA increased the stability of the mRNA to 5.2 h. These studies demonstrate that regulation of ALA synthase mRNA levels by heme in a mammalian system is mediated by a change in ALA synthase mRNA stability. The results reported here demonstrate the function of the regulatory heme pool on both ALA synthase and heme oxygenase in a mammalian hepatocyte system.

Proteoglycan production by immortalized human chondrocyte cell lines cultured under conditions that promote expression of the differentiated phenotype

Large and small proteoglycans are essential components of articular cartilage. How to induce chondrocytes to repair damaged cartilage with normal ratios of matrix components after their loss due to degenerative joint disease has been a major research focus. We have developed immortalized human chondrocyte cell lines for examining the regulation of cartilage-specific matrix gene expression. However, the decreased synthesis and deposition of cartilage matrix associated with a rapid rate of proliferation has presented difficulties for further examination at the protein level. In these studies, proteoglycan synthesis was characterized in two chondrocyte cell lines, T/C-28a2 and tsT/AC62, derived, respectively, from juvenile costal and adult articular cartilage, under culture conditions that either promoted or decreased cell proliferation. Analysis of proteo[36S]glycans by Sepharose CL-4B chromatography and SDS-PAGE showed that the large proteoglycan aggrecan and the small, leucine-rich proteoglycans, decorin and biglycan, were produced under every culture condition studied. In monolayer cultures, a high initial cell density and conditions that promoted proliferation (presence of serum for T/C-28a2 cells or permissive temperature for the temperature-sensitive tsT/AC62 cells) favored cell survival and ratios of proteoglycans expected for differentiated chondrocytes. However, the tsT/AC62 cells produced more proteoglycans at the nonpermissive temperature. Culture of cells suspended in alginate resulted in a significant decrease in proteoglycan production in all culture conditions. While the tsT/AC62 cells continued to produce a larger amount of aggrecan than small proteoglycans, the T/C-28a2 cells lost the ability to produce significant amounts of aggrecan in alginate culture. In addition, our data indicate that immortalized chondrocytes may alter their ability to retain pericellular matrix under changing culture conditions, although the production of the individual matrix components does not change. These findings provide critical information that will assist in the development of a reproducible chondrocyte culture model for the study of regulation of proteoglycan biosynthesis in cartilage.

Hepatitis C virus core protein promotes immortalization of primary human hepatocytes

Hepatitis C virus (HCV) core protein has many intriguing properties as a viral factor and is implicated in cell growth regulation. In this study, the cell growth regulation potential of HCV core protein was investigated by introduction of the core genomic region into primary human hepatocytes, a natural host for virus replication and tropism. Core-transfected primary human hepatocytes displayed altered cell morphology resembling that of low-differentiated epithelial cells. Those cells retained an immortalized phenotype and exhibited continuous growth after more than 50 passages over 2 years. Stable hepatocyte transfectants exhibited albumin secretion and HCV core protein expression. Telomerase activity, a characteristic of immortalized or transformed cells, was evident in the transfected hepatocytes immediately after senescence. Anchorage-independent growth of the immortalized hepatocytes provided further evidence for a transformed phenotype. Results from these studies suggest that the HCV core protein promotes primary human hepatocytes to an immortalized phenotype, which may predispose cells over an extended period of time to undergo a transforming event. Thus, HCV core protein appears to contribute to virus-mediated pathogenesis in a persistently infected host.

Characterization and evaluation of detoxification functions of a nontumorigenic immortalized porcine hepatocyte cell line (HepLiu)

Primary porcine hepatocytes (PPH) are currently used in research and therapeutic applications as the biological component of extracorporeal liver assist devices to overcome the shortage of human hepatocytes. However, their finite life span and typically rapid loss of functions limit their utility. An immortalized, nontumorigenic, highly differentiated porcine hepatocyte cell line was developed in our laboratory to resolve these disadvantages. PPH were transfected with simian virus 40 (SV40) T antigen under the control of the SV40 early promoter. From the established 69 clones, 23 clones displaying hepatocyte-like morphology were screened for diazepam metabolism. One clone, HepLiu D63, has been maintained in culture for > 2 years, through more than 60 passages and 240 divisions. Albumin protein, present in early passages, was lost at later passages, but albumin transcript still was detectable in later passages. Carbamoyl phosphate synthetase, a gateway enzyme of the urea cycle, was consistently detectable in HepLiu cells. Cytokeratin 18, a characteristic marker of primary hepatocytes, was detected by both immunofluorescent staining and Western blot in HepLiu cells. Furthermore, maintenance of P450 functions in HepLiu cells was evidenced by diazepam and 7-ethoxycoumarin metabolites measured by HPLC. Phase II conjugative function was measured as acetaminophen glucuronidation. P450 dealkylase was demonstrated microscopically by the conversion of a nonfluorescent substrate to a fluorescent product. Both Northern blot analysis and immunofluorescent staining showed SV40 T antigen expression in the nuclei of HepLiu cells. No tumor formation occurred when HepLiu cells were injected into severe combined immunodeficient (SCID) mice nor was the TAI (a tumor marker) mRNA expressed, even in later passages. This immortalized, nontumorigenic, highly functional cell line may provide a valuable tool for drug/toxicological studies, liver biologic regulation studies, and artificial liver support systems.

Methyl-group donors cannot prevent apoptotic death of rat hepatocytes induced by choline-deficiency

Choline-deficiency causes liver cells to die by apoptosis, and it has not been clear whether the effects of choline-deficiency are mediated by methyl-deficiency or by lack of choline moieties. SV40 immortalized CWSV-1 hepatocytes were cultivated in media that were choline-sufficient, choline-deficient, choline-deficient with methyl-donors (betaine or methionine), or choline-deficient with extra folate/vitamin B12. Choline-deficient CWSV-1 hepatocytes were not methyl-deficient as they had increased intracellular S-adenosylmethionine concentrations (132% of control; P < 0.01). Despite increased phosphatidylcholine synthesis via sequential methylation of phosphatidylethanol-amine, choline-deficient hepatocytes had significantly decreased (P < 0.01) intracellular concentrations of choline (20% of control), phosphocholine (6% of control), glycerophosphocholine (15% of control), and phosphatidylcholine (55% of control). Methyl-supplementation in choline-deficiency enhanced intracellular methyl-group availability, but did not correct choline-deficiency induced abnormalities in either choline metabolite or phospholipid content in hepatocytes. Methyl-supplemented, choline-deficient cells died by apoptosis. In a rat study, 2 weeks of a choline deficient diet supplemented with betaine did not prevent the occurrence of fatty liver and the increased DNA strand breakage induced by choline-deficiency. Though dietary supplementation with betaine restored hepatic betaine concentration and increased hepatic S-adenosylmethionine/S-adenosylhomocysteine ratio, it did not correct depleted choline (15% of control), phosphocholine (6% control), or phosphatidylcholine (48% of control) concentrations in deficient livers. These data show that decreased intracellular choline and/or choline metabolite concentrations, and not methyl deficiency, are associated with apoptotic death of hepatocytes.

Apoptosis induced by tumor necrosis factor-alpha in rat hepatocyte cell lines expressing hepatitis B virus

Three well differentiated SV40-immortalized rat hepatocyte cell lines, CWSV1, CWSV2, and CWSV14, and Hepatitis B Virus (HBV)-producing cell lines derived from them were examined for sensitivity to tumor necrosis factor (TNF)-alpha. CWSV1, CWSV2, and CWSV14 cells were co-transfected with a DNA construct containing a dimer of the HBV genome and the neo gene and selected in G418 to generate stable cell lines. Characterization of these cell lines indicated that they contain integrated HBV DNA, contain low molecular weight HBV DNA compatible with the presence of HBV replication intermediates, express HBV transcripts, and produce HBV proteins. The viability of CWSV1, CWSV2, and CWSV2 cells was not significantly altered when they were treated with TNF-alpha at concentrations as high as 20,000 U/ml. The HBV-expressing CWSV1 cell line, SV1di36, and the HBV-expressing CWSV14 cell line, SV14di208, were also not killed when treated with TNF-alpha. However, the HBV-expressing CWSV2 cell line, SV2di366, was extensively killed when treated with TNF-alpha at concentrations ranging from 200 to 20,000 U/ml. Analysis of several different HBV-producing CWSV2 cell lines indicated that TNF-alpha killing depended upon the level of HBV expression. The TNF-alpha-induced cell killing in high HBV-producing CWSV2 cell lines was accompanied by the presence of an oligonucleosomal DNA ladder characteristic of apoptosis.

Responsiveness of an SV40-immortalized hepatocyte cell line to growth hormone

The response of an SV40-immortalized hepatocyte cell line (CWSV-1) derived from adult male rat hepatocytes to human growth hormone (hGH) was investigated. CWSV-1 cells, which have been characterized extensively, retain certain differentiated functions of normal liver (Woodworth and Isom, Mol Cell Biol 7: 3740-3748, 1987). This cell line consists of tightly associated polygonal, mononucleated cells that grow as monolayers. These cells showed no significant morphological changes with the addition of hGH. Northern blot analysis showed that continuous treatment of the CWSV-1 cells with hGH induced the expression of insulin-like growth factor I (IGF-I) and 5 alpha-reductase RNAs. In addition, continuous exposure to hGH resulted in the induction of expression of the growth hormone receptor/growth hormone binding protein (GHR/GHBP) genes. This study indicates that the CWSV-1 cells may serve as a valuable in vitro model system for studying the signaling pathway of GH.

Porcine vascular smooth muscle cells immortalized with SV40 ori-defective DNA: characteristics of cell growth and collagen synthesis

A cell line derived from medial smooth muscle cells (SMC) was established from the porcine coronary artery by transfection with ori-defective simian virus 40 plasmid DNA (SV40 DNA). The characteristics of transfected cells (SV40-SMC) such as cell growth, collagen and non-collagen syntheses were investigated. SV40-SMC expressed SV40 large T antigen, c-myc and c-myb encoded proteins in the nuclei. SV40-SMC demonstrated a 'hills and valleys'-like arrangement in overconfluence and actin filaments upon immunofluorescent staining. Under electron microscopic observation, SV40-SMC had larger amounts of synthetic organelles and smaller amounts of filament bundles than those of SMC. SV40-SMC demonstrated three times higher growth activity and 4.4 times greater cellular density than SMC. Smooth muscle cells did not grow in media containing 5% plasma derived serum (PDS) instead of normal serum, whereas SV40-SMC proliferated in this medium. SV40-SMC did not grow in soft agar gel, while HeLa S3 cells, a cell line of human cervical carcinoma, formed colonies in this gel. By immunofluorescent (IF) staining, collagen phenotypes I, III, IV and V were detected in both SV40-SMC and SMC. However, protein synthesis including collagen and non-collagen was higher in SV40-SMC than in the control sample. It was concluded that SV40-SMC were a continuous cell line for vascular SMC regarding morphological characteristics, and demonstrated a higher growth activity, with increased collagen and non-collagen syntheses. This cell line is useful for the investigation of atherogenesis in relation to a proliferation of SMC and an accumulation of extracellular matrices in vascular intima.

The hepatocyte-specific phenotype of murine liver cells correlates with high expression of connexin32 and connexin26 but very low expression of connexin43

This investigation was initiated in order to find out whether expression of the hepatocyte-specific phenotype is accompanied by expression of certain connexin genes coding for gap junctional protein subunits. Several clones of mouse embryonic hepatocytes immortalized in serum-free MX83 medium by infection with recombinant retrovirus-expressed transcripts for connexin32, connexin26, albumin, alpha-fetoprotein, tyrosine aminotransferase, as well as aldolase A and B, at more than half of the levels found in primary mouse hepatocytes. In addition the immortalized hepatocyte clones contained low levels of connexin43 mRNA of which only trace amounts were detected in primary embryonic mouse hepatocytes and in rat liver. Two of the immortalized hepatocyte clones were shifted from serum-free MX83 medium to Dulbecco's modified Eagle medium (DMEM) containing 10% fetal calf serum and, after 2, 14, or 180 days, back to MX83 medium. We found that expression of connexin32 and connexin26 mRNAs as well as transcripts of other liver-specific proteins was reversibly decreased in serum-containing medium, whereas the expression level of connexin43 transcripts was increased in serum-containing DMEM compared to serum-free MX83 medium. The expression levels of connexin26, connexin32, or connexin43 mRNAs were altered by the addition of fetal calf serum or arginine or by the absence of hydrocortisone in MX83 medium, all of which contributed to the shift in phenotype. Furthermore several dedifferentiated cell lines derived from rat or mouse liver and cultivated in serum-containing medium were found to express little connexin32 or connexin26 mRNA but relatively high levels of connexin43 mRNA.

Losses of 3p, 11p, and 13q in EJ/ras-transformable simian virus 40-immortalized human uroepithelial cells

Five independent clones of Simian virus 40 (SV40)-immortalized human uroepithelial cells (CK/SV-HUC) were established after transfection of HUC cultures from the same tissue donor with plasmids encoding SV40 large T and small t antigen genes. Each CK/SV-HUC clone contained a unique SV40 integration site, and all expressed similar levels of SV40 mRNA. All five clones were nontumorigenic, but clones 2, 4, and 5 tumorigenically transformed after transfection at P19 with mutant EJ/ras and also spontaneously after 40 serial passages in vitro. In contrast, CK/SV-HUC clones 1 and 3 did not transform when either approach was used. These differences in transformability among CK/SV-HUC clones could not be predicted based on differences in SV40 gene expression nor on any in vitro growth property tested. In cytogenetic analyses, a transformable clone showed losses of three chromosome arms containing putative cancer suppressor gene regions, including 3p14----pter, 13q, and 11p, whereas the nontransformable clones showed none of these losses. Thus these data indicate that genetic losses on 3p, 11p, and 13q may contribute to tumorigenic transformation of SV40-immortalized human uroepithelial cells.

Cytogenetic analysis of hepatic cell lines derived from SV40-T antigen gene-harboring transgenic mice

A total of five hepatic cell lines were established from SV40-T transgenic mice at different stages of development. Karyotype analysis performed on these cell lines revealed 1) chromosomal instability manifested by numerous karyotypic alterations, 2) non-random numerical changes of chromosome number 18 and 3) frequent occurrence of marker chromosomes in four of the five lines. These findings indicate that genetic abnormalities occur very frequently in hepatocytes of the transgenic mice, most probably caused by the mutagenic action of T-antigen, raising the possibility that they play essential roles in initiation and progression in this model of murine hepatocarcinogenesis.

Retinoic acid modulation of mRNA levels in malignant, nontransformed, and immortalized osteoblasts

Clonal cell lines presumably "arrested" at a particular stage of differentiation are useful models to study the processes of differentiation in osteoblasts. UMR-201 is a presumptive preosteoblastic nontransformed rat clonal cell line with a limited life span in culture. Two immortalized cell lines, UMR-201-10A (10A) and UMR-201-10B (10B), were derived from UMR-201 by stable transfection with simian virus (SV) 40 large T antigen. This study compares the growth and profile of gene expression of the immortalized cell lines with those of UMR-201 and UMR-106-06, a rat clonal cell line with well-defined osteoblast-like phenotypic characteristics. All four cell lines constitutively expressed the mRNA for the gamma, alpha, and beta receptors for retinoic acid (RA), the growth hormone receptor, pro-alpha 1(I) collagen, osteonectin, bone proteoglycan I, and bone morphogenetic proteins (BMP) 1 and 2A. Alkaline phosphatase mRNA was absent in the preosteoblast cell lines but was induced by treatment with 10(-6) M RA, which also increased the steady-state levels of mRNA for osteopontin and BMP1. mRNA for matrix gla protein was constitutively present and further induced by RA in UMR-201 and 10B only. Messenger RNA for bone sialoprotein and bone morphogenetic protein 3 were constitutively expressed in UMR-106-06 and UMR-201 but absent in the immortalized cell lines. None of the cell lines expressed measurable mRNA for bone gla protein or bone proteoglycan II. 10B grew more rapidly than UMR-201, but unlike UMR-201, it was also able to proliferate in serum-free medium and exhibit anchorage-independent growth. In summary, this study identifies novel retinoic acid effects on gene expression in these cells. Differences noted in the expression of mRNAs between UMR-106-06 and the other cell lines may provide some insight into the sequence of expression of these phenotypic characteristics as osteoblasts differentiate.

In vitro progression-associated c-H-ras activation in neoplastic hepatocyte lines established from SV40-T antigen gene-harboring transgenic mice

In order to investigate the molecular mechanisms of multistep hepatocarcinogenesis in SV40-T antigen gene-harboring transgenic mice, 9 hepatocellular carcinoma (HCC) lines and 10 "preneoplastic" hepatocyte lines were established from the animals and their biological and molecular changes during culture were investigated. Three of the 9 HCC lines showed progression during culture in terms of growth rate and growth capability in soft agar and in nude mice. This progression was associated with the appearance of activated c-H-ras oncogene. Including these 3 lines, H-ras activation was observed in a total of 7 of the 9 HCC lines (78%), whereas it was found only in 1 of 10 (10%) "preneoplastic" hepatocyte lines. These data thus indicate that H-ras activation may be an event occurring at a relatively late stage of hepatocarcinogenesis in this transgenic mouse system and that it may serve towards completion of the carcinogenic process together with the T-antigen.

Expression of transforming growth factor-beta 1 mRNA in human hepatocellular carcinoma

We investigated the expression of transforming growth factor beta 1 (TGF-beta 1) mRNA in tumor tissues surgically removed from ten patients with hepatocellular carcinoma (HCC). All HCC tissues expressed TGF-beta 1 mRNA at different levels, indicating the presence of activated transcription of TGF-beta 1 gene in human HCC tissues in vivo. The level of TGF-beta 1 mRNA expression showed no relationship to main tumor size of plasma alpha-fetoprotein level. Some HCC tissues presenting a relatively low grade of histological differentiation showed the highest levels of TGF-beta 1 mRNA expression.

Immortalization of primary cells by DNA tumor viruses

Cellular senescence is characterized by a decline in sensitivity to growth factors resulting in cessation of cellular growth. The expression of cellular or viral oncogenes may result in the establishment of cell lines with unlimited proliferative potential ("immortalization"). A variety of viral and cellular oncogenes have been reported to immortalize cells, suggesting that multiple mechanisms may lead to an escape from senescence. Immortalization has been reported to occur as a result of an interaction of viral proteins with cellular suppressor gene products or may result from the elevated expression of "transforming" oncoproteins (such as the polyomavirus middle-t antigen). Here we speculate that a selection for cells with a further decreased probability of cell cycle withdrawal can occur during the growth of cells expressing viral early genes, resulting in a process of tumor progression. Explaining immortalization in terms of mitogenic stimulation due to the expression of viral oncogenes followed by genetic/epigenetic changes may help to explain why lytic DNA viruses have a biological activity which may not be necessary for their life cycle.

Complete transformation of embryonal rat fibroblasts by polyomavirus occurs during passage in vitro

The tumorigenicity of secondary rat embryo fibroblasts transfected with a plasmid harboring a replication origin-defective polyomavirus was found to increase during in vitro propagation. Thus, polyomavirus-transfected cells were found to be more than 10,000-fold more tumorigenic when injected into syngenic rats at 3 months after transfection compared to those injected at an earlier time point. Furthermore, most clones of polyomavirus-transfected cells did not grow in semisolid medium at 52 days after transfection but did grow at 95 days. Addition of glucocorticoid hormones, but not of 25% fetal calf serum, to the growth medium of the early passage cells resulted in limited anchorage-independent growth. An altered level of expression of a number of proteins was found in cells analyzed at different times after transfection. Notably, the expression of a component of the actin filament system, tropomyosin 2, was shown to decrease during growth in vitro. The development of a more fully transformed phenotype at late passages correlated with loss of the requirement for large T-antigen for growth. Thus, cells transfected with a polyomavirus mutant encoding a thermolabile large T-antigen did not grow at the restrictive temperature at 6 weeks after transfection, but grew well at 5 months after transfection. We suggest that these phenomena may be explained by assuming that establishment of rodent fibroblasts, and thereby sensitivity to transformation by middle T-antigen, is not an immediate consequence of expression of large T-antigen but occurs after a period of growth in vitro.

Rat vascular smooth muscle cells immortalized with SV40 large T antigen possess defined smooth muscle cell characteristics including growth inhibition by heparin

Rat aortic smooth muscle cells (SMC) have been established by retroviral delivery of the complementary DNA (cDNA) for the simian virus 40 large T antigen (SV40LT) and examined for SMC phenotypic markers and growth characteristics, including responsiveness to the antiproliferative effects of heparin. The transfected cells (SV40LT-SMC) maintain defined SMC characteristics for more than 215 population doublings (PD) as judged by muscle-specific actin expression and growth inhibition by heparin. SV40LT-SMC greater than 129 PD become transformed while SV40LT-SMC less than 77 PD resemble nontransfected SMC morphologically and are nontumorigenic. SV40LT-SMC apparently release a growth factor which acts in an autocrine fashion, since (1) suramin inhibits SV40LT-SMC proliferation, (2) SV40LT-SMC-conditioned medium (CM) contains mitogenic activity, and (3) SV40LT-SMC CM suppresses the binding of platelet-derived growth factor to SMC. Heparin (10-100 micrograms/ml) is a potent inhibitor of both early (less than 80 PD) and late-passage (greater than 80 PD) SV40LT-SMC proliferation. The antiproliferative effects of heparin are similar to those previously observed for SMC by several criteria; the dose-response inhibition curves are indistinguishable from those obtained with nontransfected cells, other glycosaminoglycans have little effect on SV40LT-SMC growth, the antiproliferative effects of heparin are reversed in the presence of epidermal growth factor, and heparin displays high-affinity saturable binding to SV40LT-SMC. In conclusion, SV40LT-SMC are a continuous line of SMC-like cells that are sensitive to the growth inhibitor, heparin. SV40LT-SMC should facilitate studies of heparin inhibition and may be applicable for the study of other SMC characteristics as well.