Oncogene expression in liver regeneration and hepatocarcinogenesis

Detecção imunoistoquímica das oncoproteínas p21ras, c-myc E p53 no carcinoma hepatocelular e no tecido hepático não-neoplásico

RACIONAL: A hepatocarcinogênese é um processo no qual as alterações genéticas e epigenéticas são bem conhecidas em modelos animais, mas carece de estudos no homem. OBJETIVOS: Analisar a freqüência das oncoproteínas p21ras, c-myc e p53 no carcinoma hepatocelular e no fígado não-neoplásico. Verificar ainda a associação destas oncoproteínas com os padrões e graus histológicos, assim como com as infecções pelos vírus das hepatites B e C. MÉTODOS: Foi analisada por método imunoistoquímico a detecção das oncoproteínas p21ras, c-myc e p53 em 47 casos de carcinoma hepatocelular e no tecido não-neoplásico circunjacente ao tumor (40 casos). RESULTADOS: As oncoproteínas p21ras, c-myc e p53 foram detectadas, respectivamente, em 44,7%, 53,2% e 36,2% dos casos de carcinoma hepatocelular. A imunorreatividade do p21ras e c-myc mostrou uma associação significativa. Contudo, não houve associação significativa entre a detecção do p21ras, c-myc e p53 com os diferentes graus e padrões histológicos, nem tampouco com as infecções pelos vírus das hepatites B e C. A mesma associação significativa entre o p21ras e c-myc foi encontrada no tecido não-neoplásico dos casos de cirrose em relação aos que não apresentaram cirrose, enquanto que o p53 foi negativo em todos os casos. CONCLUSÕES: A imunorreatividade das oncoproteínas p21ras, c-myc e p53 corrobora evidências prévias de sua detecção no carcinoma hepatocelular, o que sugere poder haver participação destas proteínas na hepatocarcinogênese humana. A significativa associação entre as proteínas p21ras, c-myc e p53 no carcinoma hepatocelular e na cirrose pode apontar uma interação entre as mesmas, sobretudo na hepatocarcinogênese pela via da cirrose.

[11C]choline uptake in regenerating liver after partial hepatectomy or CCl4-administration

To characterize [methyl-(11)C]choline ([(11)C]choline) as an oncologic PET radiopharmaceutical, [(11)C]choline uptake in regenerating livers after partial hepatectomy as a model of typical proliferating tissue and after CCl(4) insult as that of proliferating tissue with inflammation, was studied in rats. [(11)C]Choline, [(18)F]2-fluoro-2-deoxy-D-glucose ([(18)F]FDG) and [2-(14)C]thymidine ([(14)C]TdR) uptake was studied in regenerating rat liver after 70% partial hepatectomy or CCl(4)-administration. [(11)C]Choline uptake in regenerating liver after partial hepatectomy was significantly increased with [(14)C]TdR uptake as a marker of DNA synthesis at 18 hours after surgery. On the other hand, the uptake was not accelerated by CCl(4)-administration, though it significantly increased [(14)C]TdR uptake. There were no differences of [(11)C]choline uptake acceleration following partial hepatectomy among the three parts of the regenerating liver. [(18)F]FDG uptake was accelerated in the regenerating liver on either partial hepatectomy or CCl(4)-administration. The magnitude of the increase in [(18)F]FDG uptake in the regenerating liver induced by partial hepatectomy was greater than that for [(11)C]choline. [(11)C]Choline uptake in the liver was accelerated by partial hepatectomy, but not by CCl(4)-administration. This might be expected given that the differentiation between proliferating tissues such as tumor and inflammatory tissue was possible by [(11)C]choline-PET.

Effect of peroxisome proliferators on the methylation and protein level of the c-myc protooncogene in B6C3F1 mice liver

Peroxisome proliferators in general are nongenotoxic mouse liver carcinogens for which DNA hypomethylation and altered gene expression are proposed mechanisms. Therefore, the peroxisome proliferators 2,4-dichlorophenoxyacetic acid (2,4-D), dibutyl phthalate (DBP), gemfibrozil, and Wy-14,643 were evaluated for the ability to alter the methylation and expression of the c-myc protooncogene. Male B6C3F1 mice were administered for 6 days in their diet Wy-14,643 (5-500 ppm), 2,4-D (1,680 ppm), DBP (20,000 ppm), or gemfibrozil (8,000 ppm). All four peroxisome proliferators caused hypomethylation of the c-myc gene in the liver. Wy-14,643 appeared to be the most efficacious with a threshold between 10 and 50 ppm. The level of the c-myc protein was increased by Wy-14,643, but not the other peroxisome proliferators. When female B6C3F1 mice received a two-thirds partially hepatectomy and 16 h later were administered 50 mg/kg Wy-14,643 by gavage, hypomethylation of the gene occurred 24 h later. Hypomethylation was not found in mice that received Wy-14,643 following a sham operation. Hypomethylation of the c-myc gene within 24 h of administering Wy-14,643 after a partial hepatectomy but not after a sham operation supports the hypothesis that the peroxisome proliferators prevent methylation of hemimethylated sites formed by DNA replication.

ATA2-mediated amino acid uptake following partial hepatectomy is regulated by redistribution to the plasma membrane

System A, the Na(+)-dependent amino acid transport activity, is encoded by the ATA2 gene and up-regulated following partial hepatectomy (PH), and its competitive inhibition interferes with liver regeneration. Rabbit polyclonal antibody was raised against a portion of the ATA2 gene product followed by immunodetection of ATA2 in isolated liver plasma membrane and lysate. The level of ATA2 increased in the plasma membrane following PH, while the relatively high quantity of ATA2 found in liver lysate remained constant. We also have shown that Northern analysis of steady-state ATA2 mRNA revealed no significant change following PH. These data show that ATA2-mediated transport is not regulated by the steady-state level of ATA2 mRNA but is regulated by the amount of ATA2 and redistribution to the plasma membrane. We hypothesize that ATA2 activity is regulated by recruitment of ATA2 protein from an intracellular compartment. In addition, the pattern of expression of System A activity in oocytes, transport kinetics, and sensitivity to chemical modification indicate the presence of a second System A isoform in liver that differs substantially from ATA2.

Induction of ribosomal genes and hepatocyte hypertrophy by adenovirus-mediated expression of c-Myc in vivo

Overexpression of c-Myc in immortalized cells increases cell proliferation, inhibits cell differentiation, and promotes cell transformation. Recent evidence suggests that these effects, however, do not necessarily occur when c-Myc is overexpressed in primary mammalian cells. We sought to determine the immediate effects of transient overexpression of c-Myc in primary cells in vivo by using recombinant adenovirus to overexpress human MYC in mouse liver. Mice were intravenously injected with adenoviruses encoding MYC (Ad/Myc), E2F-1 (Ad/E2F-1), or beta-galactosidase (Ad/LacZ). Transgene expression was detectable 4 days after injection. Expression of ectopic c-Myc was immediately accompanied by enlarged and dysmorphic hepatocytes in the absence of significant cell proliferation or apoptosis. These findings were not present in the livers of mice injected with Ad/E2F-1 or Ad/LacZ. Prominent hepatocyte nuclei and nucleoli were associated with the up-regulation of large- and small-subunit ribosomal and nucleolar genes, suggesting that c-Myc may induce their expression to increase cell mass. Our studies support a role for c-Myc in the in vivo control of vertebrate cell size and metabolism independent of cell proliferation.

Effect of trichloroethylene on DNA methylation and expression of early-intermediate protooncogenes in the liver of B6C3F1 mice

Trichloroethylene (TCE) is a multimedia environmental pollution that is carcinogenic in mouse liver. The ability of TCE to modulate DNA methylation and the expression of immediate-early protooncogenes was evaluated. Female B6C3F1 mice were administered 1000 mg/kg TCE by gavage 5 days/week and killed after 5, 12, or 33 days of exposure. Methylation of DNA as 5-methylcytosine was decreased by 5 days of treatment with TCE and remained reduced for 33 days. TCE also decreased the methylation of the promoter regions for the protooncogenes, c-jun and c-myc. The expression of the mRNA for the two protooncogenes was increased between 60 and 120 minutes after administering the last dose of TCE and returned to control level by 24 hours. The expression of the mRNA for c-fos remained undetectable after administering TCE. Hence, TCE decreased the methylation both of total DNA and the promoters for the c-jun and c-myc genes and increased the expression of their mRNA. The decreased methylation and increased expression of the two immediate-early protooncogenes might be associated with TCE-induced increase in cell proliferation and promotion of tumors.

Differential protooncogene expression in Sprague Dawley and Fischer 344 rats during 1,2-dichlorobenzene-induced hepatocellular regeneration

Significant differences in hepatotoxic injury of 1,2-dichlorobenzene (o-DCB) have been reported (Gunawardhana, L., Sipes, I.G., 1991. Dichlorobenzene hepatotoxicity strain differences and structure activity relationships. Adv. Exp. Med. Biol. 283, 731-734; Stine, E.R., Gunawardhana, L., Sipes, I.G., 1991. The acute hepatotoxicity of the isomers of dichlorobenzene in Fischer 344 and Sprague-Dawley rats: isomer specific and strain-specific differential toxicity. Toxicol. Appl. Pharmacol. 109, 472-481; Valentovic, M.A., Ball, J. G., Anestis, D., Madan E., 1993a. Acute hepatic and renal toxicity of dichlorobenzene isomers in Fischer 344 rats. J. Appl. Toxicol. 13, 1-7; Kulkarni, S.G., Duong, H., Gomila, R., Mehendale, H.M., 1996. Strain differences in tissue repair response to 1,2-dichlorobenzene. Arch. Toxicol. 70, 714-723. Kulkarni, S.G., Warbritton, A., Bucci, T., Mehendale, H.M., 1997. Antimitotic intervention with colchicine alters the outcome of o-DCB-induced hepatotoxicity in Fischer 344 rats. Toxicology. 120, 79-88). Although, hepatotoxic injury of o-DCB is greater in Fischer 344 (F344) when compared with Sprague Dawley (S-D) rats, this interstrain difference does not transcend into any difference in lethal effects of o-DCB. Interstrain difference in compensatory tissue repair has been suggested as the underlying mechanism for the lack of strain differences in lethality (Kulkarni et al., 1996; Kulkarni et al., 1997, see these refs. above). However, the mechanism(s) for this interstrain difference in tissue repair is (are) not currently understood. The objectives of the present study were (1) to investigate if the differences in compensatory tissue repair are reflected in differential protooncogene expression in S-D versus F344 rat livers and (2) to investigate if changes in protooncogene expression could explain the decrease and delay in tissue repair response beyond a threshold of 0.6 ml o-DCB/kg. Male S-D and F344 rats (8/9 weeks old) were administered either 0.6 or 1.2 ml o-DCB/kg and changes in expression of protooncogenes c-myc (immediate early) and Ha-ras (delayed early) were examined over a time course. Findings of this study indicate that the timing and extent of c-myc and Ha-ras expression varies in the two strains following administration of o-DCB. Thus, the timing and extent of compensatory liver regeneration that ensues following o-DCB administration in S-D and F344 rats is temporally concordant with the protooncogene expression in the two strains.

Cyclin A2 and c-myc mRNA expression in ethinyl estradiol induced liver proliferation

The time-course of c-myc and cyclin A2 mRNA expression was determined in the liver of male Sprague-Dawley rats during transient liver cell proliferation induced by a single dose of ethinyl estradiol (EE), and was compared to that during liver regeneration following two-thirds hepatectomy (PH). Cell proliferation was assessed in terms of 5'-bromodeoxyuridine (BrdU) labeling. EE administration and PH both increased BrdU labeling between 18 and 48 h, with peak values at 18 and 24 h. An early (2 h) increase in BrdU labeling was observed after EE but not PH. Maximal increases in cyclin A2 mRNA levels and BrdU labeling coincided after both EE and PH, and cyclin A2 mRNA expression was proportional to the intensity of the proliferative response. In contrast, the degree of c-myc mRNA expression was similar after EE administration and PH, but the time course was different: c-myc gene expression rose concomitantly with DNA replication after EE, while after PH it increased during the prereplicative phase. This indicates that the pattern of c-myc gene expression in the liver is strongly related to the type of proliferative response.

Potential effect of sodium nitrite on the expression of nuclear proto-oncogenes during 2-acetyl aminofluorene-induced hepatocarcinogenesis in rats

2-acetyl aminofluorene (AAF) reacts in acidic conditions with nitrous fume yielding N-nitroso-AAF (N-NO-AAF), as previously described, that exerts more toxic and mutagenic effects than its parental compound. In this study, the effect of sodium nitrite (NaNO2) on the tumorigenicity of AAF in rats fed with AAF and NaNO2 was observed. Wistar rats were divided into five groups: group I served as control; group II were treated with NaNO2 (0.3%); group III was given 0.02% AAF alone; groups IV and V received both AAF and NaNO2 (0.2 and 0.3% respectively) in their diet for 12 weeks. At the end of the experiment, all rats in groups III, IV and V developed early stage phenomena of hepatocellular carcinoma, including hepatomegaly with variable-sized foci and neoplastic nodules. Severe damage was observed in the rats treated with AAF and NaNO2. Feeding of AAF (0.02%) for 3 months elevated the levels of c-Fos, c-Jun and c-Myc proteins in the rat livers. The AAF-induced c-Jun, c-Fos and c-Myc expressions were significantly magnified (P < 0.001) by NaNO2. These data confirmed that the strengthening of AAF-induced hepatocarcinogenesis by NaNO2 should be associated with its enhancing effect on the AAF-induced increases in the expressions of c-Jun, c-Fos and c-Myc.

p53 expression in hepatocellular carcinoma in Greece. Correlation with epidemiological and histopathological data

Localization of p53 oncoprotein was investigated in 60 hepatocellular carcinomas (HCCs) from patients resident in the Northwest and Central Greece. The streptavidin-biotin complex immunoperoxidase method was performed in archival formalin-fixed, paraffin-embedded material, using the monoclonal antibody DO-1. The aim of our study was to correlate p53 expression with histological and epidemiological data. p53 overexpression in patients with serological hepatitis B or C was greater (47%) as compared to that observed in patients without these markers (p < 0.01). Morphologically normal liver tissue (NLT) and liver cell dysplasia (LCD) was recognized adjacent to HCC developing on non-alcoholic cirrhotic livers in patients with "NonA, NonB hepatitis" from between 1975-1986. NLT and LCD and p53 oncoprotein was expressed in 10% of the cases. No relationship was observed between p53 expression and tumor histological grade, patients' age and sex. These results suggest that in Northwest and Central Greece, p53 oncosupressor gene may be involved in some HCCs; it may be associated with viral chronic infection disease (HBV or HCV), and as yet with uncharacterized viruses which remain to be determined.

Role of nutrition in the survival after hepatotoxic injury

Nutritional status is an important factor in determining susceptibility to toxic chemicals. While macro and micronutrients may affect many aspects of Stage I and Stage II of toxicity, in this paper, the influence of macronutrients as sources of energy required for cell division and tissue repair mechanisms on the outcome of hepatic injury is discussed. Male Sprague-Dawley rats maintained on normal rodent chow and 15% glucose (as a source of energy for the centrilobular hepatocytes) in drinking water for 7 days experienced an increased lethality from structurally and mechanistically different centrilobular hepatotoxicants (acetaminophen, thioacetamide, chloroform and carbon tetrachloride), while male Sprague-Dawley (S-D) rats fed rat chow containing palmitic acid (PA, 8% w/w, as a source of energy for the periportal hepatocytes) and L-carnitine (LC, 2 mg/ml, as a mitochondrial carrier for the supplemented fatty acids) in drinking water for 7 days were protected from a LD100 dose (600 mg/kg, i.p.) of thioacetamide (TA). Indices of cell division revealed that cell cycle progression in the liver played a very critical role in determining the final outcome of hepatotoxic injury. These results confirmed our hypothesis that cell division and tissue repair play a critical role in survival after life-threatening hepatotoxic injury. Any manipulation directed towards altering a prompt and exacting compensatory cell division and tissue repair responses after hepatotoxic injury would also alter the final outcome of the toxicity. These studies indicate that the source of cellular energy can decisively influence the compensatory response of the target tissue to alter the outcome of hepatotoxic injury. Since nutritional status is known to vary widely among human populations, these could contribute enormously to susceptibility of human populations to toxic chemicals.

2-Mercaptopropionylglycine modulates the expression of c-jun and c-Ha-ras in regenerating rat liver

Changes in the expression of two proto-oncogenes, c-jun and c-Ha-ras and their modulation by MPG were studied in regenerating rat liver. A significant increase in c-jun and c-Ha-ras mRNA levels was noted after partial hepatectomy. However, the increase in c-Ha-ras mRNA was much less when compared with c-jun mRNA levels. Metallothionein (MT-I) mRNA levels showed a gradual decrease following partial hepatectomy. However, the decrease in MT-I mRNA levels was not significant when intertime comparisons were made. MPG caused a significant reduction in the levels of c-jun and c-Ha-ras mRNA in the regenerating rat liver compared to untreated controls, but had very little effect on MT-I mRNA levels. Selective reduction in the expression of proto-oncogenes by MPG suggests that MPG may affect the cell proliferation by modulating the expression of these genes.

The G-C specific DNA binding drug, mithramycin, selectively inhibits transcription of the C-MYC and C-HA-RAS genes in regenerating liver

Expression of the c-myc and c-Ha-ras protooncogenes is dramatically increased in regenerating rat liver as an early response to partial hepatectomy. Nuclear runon transcription studies confirm that the increased c-myc and c-Ha-ras mRNA levels in regenerating livers reflect transcriptional activation of these genes. Mithramycin, a G-C specific DNA binding drug, prevents the increased transcriptional activity of c-myc and c-Ha-ras genes after hepatectomy but does not alter the transcriptional activity of the beta-actin gene. Continuous exposure of rats to mithramycin after hepatectomy prevents the increase in both c-myc and c-Ha-ras expression and blocks the increased cellular proliferation characteristic of regeneration. The delayed increase in c-myc and c-Ha-ras gene expression is associated with a delay in cellular proliferation. The inhibition of c-myc and c-Ha-ras transcription by mithramycin, the delay in cellular proliferation, and the ability of mithramycin to prevent protein binding to the c-myc promoter, suggest that the increased expression of these genes is a necessary component of liver regeneration.

Expression of myc, fos, and Ha-ras in the livers of furan-treated F344 rats and B6C3F1 mice

Furan administered by gavage for 2 yr has been reported to induce hepatocellular carcinomas in male and female B6C3F1 mice and in male but not female F344 rats. Chronic exposure studies in our laboratory using bioassay conditions showed extensive hepatocellular toxicity and sustained increases in regenerative cell proliferation after 1, 3, and 6 wk of treatment in male and female rats and male mice. Altered expression of growth-control genes associated with this hyperproliferative state may enhance the susceptibility of these genes to mutation or may provide a selective growth advantage to preneoplastic cells. Quantitative northern blot analysis of mRNA was used to examine the expression of the oncogenes myc, fos, and Ha-ras in the livers of animals treated with furan. In male rats, a single administration of 30 mg/kg furan produced necrosis and a subsequent wave of cell proliferation 48 h after treatment and induced transient peaks in the expression of myc, fos, and Ha-ras 6-24 h after treatment. In male rat liver from our cell proliferation studies, only a slight increase in myc expression was seen at the end of week 1 of treatment. However, beginning at week 3 and increasing at week 6, up to a 15-fold increase over control values was observed in the expression of myc in the treated animals. The only other notable increase in expression observed in any animals from the cell proliferation study was a threefold increase in myc at week 6 in treated female rats. The absence of an increase in Ha-ras expression in the male mouse liver suggests that the unique pattern of Ha-ras mutations previously reported in furan-induced mouse liver tumors is not due to increased mutational susceptibility related to overexpression of this gene. The lack of sustained expression of myc, fos, and Ha-ras in rapidly proliferating liver suggests that continuous expression of these genes is not necessary to maintain increased rates of cell replication. The large increase in myc expression in male but not female rats suggests an adaptive change that may be related to the sex-specific incidence of furan-induced hepatocellular carcinomas in rats.

Variation in expression of genes used for normalization of Northern blots after induction of cell proliferation

Quantitative knowledge of gene expression can provide valuable information for understanding the action of chemicals that alter cell proliferation and cancer. Accurate quantification of mRNA levels requires the normalization of the gene of interest to a gene with transcriptional levels that do not vary through the cell cycle or with a particular treatment. Changes in expression were examined in proliferating or non-proliferating rat liver for three constitutively expressed 'housekeeping' genes commonly used to normalize mRNA levels from Northern blots. In addition, a direct method of quantifying poly(A)+ mRNA by hybridization with a radiolabelled polythymidylate--poly(T)--probe was compared with traditional methods. Hepatocyte cytolethality and a subsequent wave of hepatocyte proliferation were induced in male Fischer-344 rats by treatment with a single gavage dose of carbon tetrachloride. Induced cell proliferation peaked at 48 h after treatment. Expression of the housekeeping genes actin, glyceraldehyde-3-phosphate-dehydrogenase (GAPDH) and albumin, as well as the proto-oncogene H-ras, was determined by Northern blot analysis at times from 0.5 h to 4 days after treatment. Time-dependent changes were observed in the expression of these genes relative to the levels observed in the untreated control animals. Actin expression peaked at 3.4-fold over control and GAPDH expression was increased by 1.9-fold over control. Albumin mRNA levels varied the least, 1.4-fold over control, indicating that this gene is more appropriate than actin or GAPDH for normalization of proto-oncogene expression under experimental conditions that induce cell proliferation in rat liver. The direct quantification of poly(A)+ mRNA using a poly(T) probe was not influenced by the induction of cell proliferation. This method may be useful when the expression of housekeeping genes is affected by treatment.

Increased yield in GST-P-positive liver pre-neoplastic foci induced by DENA or ENU in rats pre-treated with estradiol or tamoxifen

We investigated the mechanisms by which partial hepatectomy (PH) increases the ability of chemical hepatocarcinogens to induce pre-neoplastic liver foci. Comparison of the effects of pre-treatment with PH, estradiol (E2) or tamoxifen (TAM) on the yield in glutathione-S-transferase(GST-P)-positive preneoplastic foci in rat liver induced by subsequent treatment with ethylnitrosourea (ENU) or diethylnitrosamine (DENA) showed that pre-treatment with E2 increased the yield in foci induced by subsequent treatment with ENU or DENA, as compared with that in animals not pre-treated, the increase being of similar magnitude with either carcinogen. Compared with that of PH, the effect of the hormone was much more pronounced than would be expected from the relative mitogenic effect of the hormonal and surgical pre-treatments if the mitotic rate were the cause. On the other hand, the average volume of pre-neoplastic liver lesions in rats treated with ENU or DENA was 2.5 to 5.0 times higher than in rats not pretreated whenever PH was included in the pre-treatment, whereas it was not affected by any other pre-treatment.

The hepatic extracellular matrix. II. Ontogenesis, regeneration and cirrhosis

The unique nature of the hepatic extracellular matrix (ECM) is predicted by the special configuration of the space of Disse. Whereas other epithelial organs have two basement membranes (BM) and a substantial ECM interposed between endothelial and epithelial cells, the liver lobule has no BM and only an attenuated ECM, consisting mostly of fibronectin (FN), some collagen type I, and minor quantities of types III, IV, V, and VI. This configuration, together with the abundant fenestrations and gaps of the sinusoidal endothelial cells, seems ideally suited to facilitate the rapid bidirectional exchange of macromolecules normally taking place between plasma and hepatocytes. During organogenesis, the liver anlage is vascularized by continuous capillaries with BM, but by day 13.5 of development (in the rat) the vessels in the immediate proximity of hepatocytes become fenestrated, lacking specialized junctions and BM, suggesting that the hepatocytes produce signals capable of modulating the endothelial phenotype. In regeneration, hepatocyte proliferation precedes vascular proliferation resulting in the formation of hepatocyte clusters that, temporarily, lack sinusoids. Eventually, vascular proliferation follows and the normal hepatocyte-vascular relationships are restored. During this period laminin synthesis by Ito cells is prominent. As soon as hepatocytes become stable, secretion of the sinusoid phenotype-maintaining factors resumes and laminin synthesis and secretion terminates. The interplay between extracellular matrix and liver cells is essential for normal homeostasis and its modification results in deranged hepatic function.

Immunolocalization of ras oncogene p21 in human liver diseases

Fifty-five cases representing a spectrum of disease states of the human liver and 10 normal liver controls were examined for the presence of the ras oncogene product p21. Conventional formalin-fixed, paraffin-embedded sections were immunostained by the avidin-biotin complex method with the broadly reactive ras p21 monoclonal antibody (Mab) RAP-5. The specificity of the reactions was confirmed by immunostaining selected samples with Mab Y13-259. In the normal liver, virtually no hepatocytic immunostaining was noted. Variable, often extensive, and convincing immunoreactions were noted in diverse forms of hepatitis, cirrhosis, and allograft rejection; the strongest immunostaining was found in samples of focal nodular hyperplasia. Hepatic adenomas and hepatocellular carcinomas showed unevenly distributed, moderate to weak reactions or no reaction at all; cholangiocarcinomas did not immunostain. In reactive but non-transformed liver cell populations, enhanced p21 ras reactions seemed to correlate with the severity of the injury and the intensity of the proliferative response. The uneven and comparatively weak ras p21 reactions noted in adenomas and carcinomas suggest that this oncogene product may be involved only transitorily in their transformation processes and possibly may not be involved in certain variants thereof.

Expression of oncogenes and tumor suppressor genes in human hepatocellular carcinoma and hepatoblastoma cell lines

The expression of nine oncogenes (c-myc, N-myc, N-ras, H-ras, k-ras, abl, fos, src, and raf) and two tumor suppressor genes (p53 and RB) were studied by northern blot hybridization in six human hepatocellular carcinoma or hepatoblastoma cell lines (PLC/PRF/5, Hep3B, Hep G2, 2.2.15, HLE, and HLF) and in a human embryonic lung fibroblast cell line (WI-38) to look for differences that might be associated with the presence (PLC/PRF/5, Hep3B, and 2.2.15) or absence (Hep G2, HLE, and HLF) of integrated hepatitis B virus (HBV) DNA. The levels of expression of the oncogenes and tumor suppressor genes were unrelated to the presence or absence of integrated HBV-DNA. Furthermore, the intensity of expression of these oncogenes was no greater in the 2.2.15 cell line (consisting of Hep G2 cells transfected with hepatitis B virus) than in untransfected Hep G2 cells.

Transcription induction of c-Ki-ras with the tumour promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) in normal and transformed liver cells

Results from nuclear run-off assays show that exposure of hepatocytes and Reuber H35B hepatoma cells to the tumour promoter, 12-O-tetradecanoylphorbol-13-acetate (TPA), leads to enhanced transcription of c-Ki-ras gene. This increase in transcription in turn results in an accumulation of the functionally active c-Ki-ras message. The half life of c-Ki-ras message in both normal and transformed livers cells is not altered by TPA and is determined to be 3.5 hr. The induction of c-Ki-ras message is accompanied by an increase in the level of c-Ki-ras protein.

Hepatitis B virus infection and primary hepatocellular carcinoma

For many years, epidemiological studies have demonstrated a strong link between chronic hepatitis B virus (HBV) infection and the development of primary hepatocellular carcinoma (PHC). Other hepatocarcinogens such as hepatitis C virus and aflatoxin also contribute to hepatocarcinogenesis either in conjunction with HBV infection or alone. Cellular and molecular biological studies are providing explanations for the HBV-PHC relationship, and models are now being formulated to further test the relative importance of various factors such as viral DNA integration, activation of oncogenes, genetic instability, loss of tumor suppressor genes, and trans-activating properties of HBV to the pathogenesis of PHC. Further research will probably define more than a single mechanism whereby chronic HBV infection results in PHC.

Fractal geometry of mosaic pattern demonstrates liver regeneration is a self-similar process

Partial hepatectomy causes compensatory, nonneoplastic growth and regeneration in mammalian liver. Compensatory liver growth can be used to examine aspects of patterns of cell division in regenerating tissue. Chimeric animals provide markers of cell lineage which are independent of growth and can be used to follow cell division patterns. Previous experimental evidence suggests that compensatory liver growth is uniform, without focal centers of proliferation. In this study we have extended that observation to include genes important in regeneration and cell cycle control in order to establish that nascent growth centers are not present in regenerating liver. There is a uniform spatial distribution of expression of these genes which is not related to mosaic pattern in the chimeras. While these genes may help regulate hepatocyte proliferation they do not appear to regulate patch pattern in the chimeras. With this information confirming uniform growth it was possible to use fractal analysis to test various hypothesized patterns of regenerative growth in the liver. The results of this analysis indicate that mosaic pattern does not change substantially during the regenerative process. Patch area and perimeter (the area occupied by or perimeter around cells of like lineage) increase during compensatory liver growth in chimeric rats without alteration of the geometric complexity of patch boundaries (boundaries around cells of like lineage). These tissue findings are consistent with previously reported computer models of growth in which repetitive application of simple decisions assuming uniform growth created complex mosaic patterns. They support the notion that an iterating (repeating), self-similar (a pattern in which parts are representative of, but not identical to the whole) cell division program is sufficient for the regeneration of liver tissue following partial hepatectomy. Iterating, self-similar cell division programs are important because they suggest a way in which complex patterns (or morphogenesis) can be efficiently created from a small amount of stored information.

Spatiotemporal changes in Ha-ras p21 expression through the hepatocyte cell cycle during liver regeneration

The protein product of the ras oncogene, Ha-ras (p21), is thought to be an important regulator of cell growth. The cytoplasmic relocalization of p21 in the cell during the cell cycle suggests a transient signaling role for this protein in association with its signal transduction function. Because of the importance of this role we examined spatial patterns in vivo of p21 expression at the protein and mRNA levels in hepatocytes during compensatory growth in rat liver following partial hepatectomy. A low level of p21 was immunolocalized on the cytoplasmic membrane of nonregenerating hepatocytes. The level of hepatic p21 increased significantly and without spatial restriction within the liver from 36 to 60 hr after partial hepatectomy (PH). p21 was localized in the cytoplasm of dividing hepatocytes and on the hepatic cytoplasmic membrane. The elevated p21 level decreased and was found mainly on hepatocyte plasma membranes by 96 hr after PH. Immunogold electron microscopy showed p21 localized over mitochondrial membranes and nuclei in nondividing regenerating hepatocytes. Approximately 50% of nonregenerating hepatocytes show nuclear localization of p21. This percentage changes with time following PH. The decrease in nuclear localization was accompanied with an increase in the low number of hepatocytes which demonstrated cytoplasmic localization in nondividing hepatocytes in regenerating liver. Flow cytometric analysis revealed a significant increase of p21 at 36 hr after PH which was 12 hr after the initial induction of ras mRNA. ras mRNA level increased 1.5-fold at 24 hr after PH and a maximum twofold induction was observed at 48 hr. Cell-cycle analysis of regenerating hepatocytes indicated a synchronized first peak of cell division 36-40 hr after PH. Dual parameter flow cytometry revealed that the level of p21 in hepatocytes in S phase and G2/M phase of the cell cycle was significantly higher than that in G0/G1 phase during regeneration. These findings suggest that p21 is important for the progression of regenerating hepatocytes to S phase and then to G2/M phase.

The role of capillarization in hepatic failure: studies in carbon tetrachloride-induced cirrhosis

During the cirrhotic process, the hepatic microvascular phenotype is transformed from sinusoids (discontinuous capillaries) into continuous capillaries. This transformation has been termed capillarization. Many hepatic functions depend on the rapid, bidirectional exchange of macromolecules between plasma and hepatocytes. To determine whether capillarization contributes to hepatic failure in cirrhosis, we decided to study the plasma clearance (125I) and hepatocyte uptake (electron microscopy) of three tracers in normal and cirrhotic rats. The tracers chosen were a hemeundecapeptide with peroxidatic activity (fluid-phase pinocytosis), asialofetuin (receptor-mediated endocytosis of a medium size protein) and ferritin (receptor-mediated endocytosis of a large size protein). The results demonstrate a decreased hepatocyte uptake of hemeundecapeptide; a significant delay in plasma clearance of asialofetuin; and a minor delay in plasma clearance of ferritin, but a striking trapping of ferritin in the cirrhotic capillary basement membrane. The delayed plasma clearance in cirrhosis cannot be ascribed to a decreased number of surface receptors because, in isolated hepatocytes, the number of molecules bound per cell was equivalent in normal and cirrhotic livers. These findings support the concept of capillarization, with the formation of continuous diffusion and filtration barriers between plasma and hepatocytes, representing a significant hindrance to the bidirectional macromolecular exchange normally taking place between these two compartments. Furthermore, at least in the case of ferritin, the capillary basement membrane of cirrhotic livers seems to be the major filtration barrier. This hindrance to hepatocyte uptake, and presumably also to secretion, may be the cause (or at least a major determinant) of the hepatic failure characteristic of cirrhosis.

Depression of liver-specific gene expression in regenerating rat liver: a putative cause for liver dysfunction after hepatectomy

We carried out studies on the expression of liver-specific genes during regeneration of the liver and searched for changes in the expression of oncogenes and housekeeping genes. Albumin and ornithine transcarbamylase genes were the liver-specific genes examined by Northern blot analysis, using total RNAs isolated from residual livers of Sprague-Dawley rats subjected to a 68% partial hepatectomy. The mRNA levels of both genes began to decrease 8 hr after hepatectomy, both reaching the lowest levels at 24 hr, and then recovered to some extent at 48 hr. In contrast, these levels in the housekeeping and growth-related genes were augmented during this period. This would suggest that there is a selective expression of growth-related and housekeeping genes, in preference to liver-specific genes during liver regeneration. The expression of these genes in the regenerating liver was simulated in primary cultured hepatocytes during the dedifferentiation processes. It would appear that the first step in regeneration of the residual liver is dedifferentiation, in which the depression of liver-specific genes may be linked to liver dysfunction following hepatectomy.

Site-specific hypomethylation of c-myc protooncogene in liver nodules and inhibition of DNA methylation by N-nitrosomorpholine

The protooncogene c-myc was investigated in N-nitrosomorpholine-induced rat liver nodules to elucidate the role of altered DNA methylation in chemical carcinogenesis. Furthermore, Micrococcus luteus DNA and chicken erythrocyte DNA were modified in vitro by reactive metabolites of N-nitrosomorpholine, generated by P450-dependent monooxygenases. The modified DNAs were less methylated in vitro than control DNAs by DNA-(cytosine-5)-methyltransferase (DNA methylase). The DNA methylase assay and 32P-postlabeling analysis revealed lowered levels of DNA methylation in nodular DNA. In nodular tissue, c-myc messenger RNA levels were found to be increased compared to normal liver. DNA methylation analysis using the restriction endonucleases HpaII/MspI indicated hypomethylation in the first intron of c-myc DNA in liver nodules. The results suggest that genotoxic lesions may cause stably inherited, aberrant DNA methylation patterns which may be responsible for site-specific hypomethylation of the c-myc protooncogene in liver nodules.

Nutritional model of hepatocarcinogenesis. Rats fed choline-devoid diet

Rats fed a choline-devoid diet as the sole treatment develop hepatocellular carcinomas, the pathogenesis of which appears to reside exclusively in effects of the diet on the liver. Among the latter, most prominent is the induction of repeating cycles of liver cell injury, death, and regeneration. Two other models have been described recently in the literature, in which development of hepatic neoplastic lesions occurs after protracted periods of liver cell injury, death, and regeneration, without exposure of the animals to chemical carcinogens. The possibility is considered that an abnormal increase in cell turnover may result in all of the genomic alterations that are required for initiation, promotion, and neoplastic transformation of liver cells in these models of hepatocarcinogenesis. The possible involvement, in the same models, of endogenously initiated liver cells also is discussed briefly.

Oncogene expression in the liver tissue of patients with nonneoplastic liver disease

The expression of cellular oncogenes in nonneoplastic human liver tissue was examined to determine if there was a correlation between oncogene expression and physiologic regeneration in liver disease. Human liver tissue specimens from 70 patients with various histologic findings from almost normal to cirrhosis were examined (using northern blot analysis) for the expression of nine cellular oncogenes. With c-K-ras, four RNA bands (5.6-kilobase [kb], 2.1-kb, 1.5-kb, and 1.2-kb RNA species) were detected in all liver tissue examined. Expression of c-fos was also detected in a few samples examined when 50-micrograms samples of total RNA were applied. Other oncogenes such as H-ras, myc, erbB, raf, fms, fes, and myb were not detected. These results indicate that particular oncogene(s) may not be highly expressed during liver regeneration in human liver disease, or that populations of regenerating hepatocytes may be too small to show significant elevations of oncogene expression. The new finding of a constant expression of c-K-ras in human liver tissue suggests that it is linked to essential hepatocellular function rather than carcinogenesis.

Specific gangliosides increase rapidly in rat liver following partial hepatectomy

Rat liver gangliosides (sialic acid containing glycosphingolipids) were analyzed by HPTLC and HPLC following either partial hepatectomy or sham operation. Analysis of whole liver gangliosides by HPTLC demonstrated that within 6 h after partial (68%) hepatectomy, there was a significant increase in GM1 compared to both sham and control animals. By 48 h, GM1 was further increased and the polysialylgangliosides GD1a, GD1b and GT1b had also risen significantly, whereas changes in GM3 were negligible. Gangliosides associated with the plasma membrane were increased up to 3.5-fold in regenerating liver compared to sham-hepatectomized controls as assessed by HPLC. Although elevations in membrane gangliosides were associated with hepatocyte proliferation, they did not closely follow the growth curve. The time course of changes in ganglioside biosynthesis suggests differential upregulation of GM3 synthase and GD3 synthase in regenerating livers.

Ethanol inhibits liver regeneration in rats without reducing transcripts of key protooncogenes

The mechanisms responsible for ethanol-associated inhibition of liver regeneration are poorly understood but may involve the modulation of protooncogene expression. To test this hypothesis, the steady-state messenger RNA levels of several protooncogenes involved in cellular proliferation were measured in livers obtained from ethanol-fed rats and isocalorically maintained controls before and during surgically-induced liver regeneration. Regeneration was significantly inhibited in ethanol-fed rats as evidenced by delayed induction of ornithine decarboxylase activity and reduced thymidine incorporation, mitotic index, and restoration of liver mass after partial hepatectomy. As previously reported, partial hepatectomy induced the time-dependent expression of mRNA for c-fos, c-myc, and c-Ha-ras. However, the transcript levels of these protooncogenes were indistinguishable in ethanol and control livers at various time points between 0-72 hours after partial hepatectomy. Although regeneration after partial hepatectomy is significantly delayed in ethanol-fed rats, the transcription of certain protooncogenes, which encode for both DNA-binding and signal-transducing proteins, appears to proceed normally. Consequently, ethanol-associated impairment of liver regeneration cannot be explained by altered transcription of these protooncogenes. The results suggest that either the expression of these protooncogenes alone may not be sufficient to trigger liver regeneration or that ethanol inhibits protooncogene-mediated events at posttranscriptional levels.

Consideration of both genotoxic and nongenotoxic mechanisms in predicting carcinogenic potential

Bacterial and cell culture genotoxicity assays have proven to be valuable in the identification of DNA reactive carcinogens because mutational events that alter the activity or expression of growth control genes are a key step in carcinogenesis. The addition of metabolizing enzymes to these assays have expanded the ability to identify agents that require metabolic activation. However, chemical carcinogenesis is a complex process dependent on toxicokinetics and involving at least steps of initiation, promotion and progression. Identification of those carcinogens that are activated in a manner unique to the whole animal, such as 2,6-dinitrotoluene, require in vivo genotoxicity assays. There are many different classes of non-DNA reactive carcinogens ranging from the potent promoter 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) that acts through a specific receptor, to compounds that alter growth control, such as phenobarbital. Many compounds, such as saccharin, appear to exhibit initiating, promotional and/or carcinogenic activity as events secondary to induced cytotoxicity and cell proliferation seen only at the chronic lifetime maximum tolerated doses mandated in rodent bioassays. Simple plus/minus vs. carcinogen/noncarcinogen comparisons used to validate the predictivity of bacterial and cell culture genotoxicity assays have revealed that a more comprehensive analysis will be required to account for the carcinogenicity of so many diverse chemical agents. Predictive assays and risk assessments for the numerous types of nongenotoxic carcinogens will require understanding of their mechanism of action, reasons for target organ and species specificity, and the quantitative dose-response relationships between endpoints such as induced cell proliferation and carcinogenic potential.

Simultaneous activation of heat shock protein (hsp 70) and nucleolin genes during in vivo and in vitro prereplicative stages of rat hepatocytes

Rapidly growing cells usually have high levels of ribosome biogenesis. The sequential expression of protooncogenes during the transition of quiescent hepatocytes to the replicative stage was assumed to be followed by activation of cellular genes related to cell growth such as ribosome biosynthesis. First, the expression of major nucleolar protein (nucleolin or C23) and major heat-shock protein (hsp 70) genes was examined during rat liver regeneration. hsp 70 may function in cell growth and has a characteristic nucleolar location after heat shock. Both nucleolin and hsp 70 mRNA began to increase simultaneously after peaks of c-fos and c-myc, showed a peak 6 h after partial hepatectomy, and declined to the control levels around 20 h. That is, the peaks of nucleolin and hsp 70 mRNA precede the peak of ribosome formation (12-20 h) and DNA replication (24 h). Second, the behavior of nucleolin and hsp 70 mRNA was examined in primary cultured hepatocytes during their G0-G1 transition. Although the amounts of c-myc mRNA reached a plateau around 20 h after the initiation of culture and remained at these levels, DNA synthesis has never been found to start without the addition of EGF and insulin to this system. Both nucleolin and hsp 70 mRNA began to increase at around 20 h (prereplicative stage) and simultaneously decreased in inverse proportion to DNA synthesis induced by these growth factors. Thus, it is possible that the simultaneous enhancement of nucleolin and hsp 70 genes as described above is not merely coincidental, but is important biologically during the transition of quiescent hepatocytes to proliferative cells.

Transient induction of c-jun during hepatic regeneration

The cellular oncogene c-jun is transiently expressed in cultured cells stimulated to proliferate but has not been identified in normal liver. Because partial hepatectomy results in coordinated cell proliferation in the remaining liver, we investigated c-jun expression after partial hepatectomy in mice. Northern analysis of whole liver mRNA demonstrated a transient increased expression of c-jun within half an hour of the operation. The related gene junB increased only 50%, whereas c-jun expression increased 13-fold compared with sham-operated controls. To determine the cell of origin of the c-jun transcript, both in situ hybridization and Northern analysis of mRNAs from parenchymal and nonparenchymal cell fractions were performed 2 hr after partial hepatectomy. C-jun expression was found in both cell populations. To investigate the mechanism of increased c-jun expression, cycloheximide was given to some animals preoperatively. C-jun induction occurred with cycloheximide alone, but partial hepatectomy further increased c-jun expression, indicating that new protein synthesis was not required for this effect. Furthermore, run-on transcriptional assay demonstrated a twofold increase in c-jun expression. Thus c-jun expression increases after hepatectomy by transcriptional and posttranscriptional mechanisms. Because the extracellular matrix-degrading enzyme transin, which bears the recognition site for jun/AP-1, showed sustained induction after hepatectomy, we speculate that an important function of c-jun expression could be the remodeling of extracellular matrices to accommodate cell proliferation.

An immunohistochemical analysis of ras oncogene expression in epithelial neoplasms of the colon

Colonic epithelial tumors (101) including villoglandular adenomas, carcinomas in situ, adenocarcinomas, and neuroendocrine (NE) carcinomas were studied immunohistochemically with monoclonal antibodies (MoAb) RAP-5 and RAS-10 recognizing altered and unaltered ras oncogene products. In addition, 20 samples from multiple polyposis including adenomas with and without dysplasia, carcinomas in situ, and invasive carcinomas were studied. Using immunostaining techniques, normal mucosa was weakly stained, whereas the mucosa in the vicinity of tumors or inflammation showed enhanced staining. More tumors stained intensely with MoAb RAP-5 than with MoAb RAS-10. With MoAb RAP-5, most benign and malignant tumors showed enhanced staining. No significant differences in staining were noted in relation to superficial versus deeply invasive carcinomas or clinical staging. Immunostaining was also noted in some metastases. No significant differences in enhanced staining were found in carcinomas. Interestingly, the most extensive and enhanced immunostaining was noted in the villoglandular adenomas, dysplastic adenomas, and carcinomas in situ. The authors conclude that (1) ras protein expression is detectable in most benign, borderline, and malignant epithelial tumors of the colon as determined with MoAb RAP-5 and RAS-10, whereas enhanced expression is more often detected with RAP-5; (2) enhanced ras product expression in colon carcinomas does not seem to correlate with advanced tumor stages or with exocrine, NE, or phenotypically mixed tumors; and (3) the finding of the most intensely enhanced ras products expression in villoglandular polyps and carcinomas in situ suggests a possibly significant role for the oncogene in the early phases of transformation.

Modulation of c-myc expression by transforming growth factor beta 1 in human hepatoma cell lines

The effects of transforming growth factor beta 1 (TGF-beta 1) on cell proliferation of human hepatoma cell lines, PLC/PRF/5 and Mahlavu, were investigated under serum-free conditions. DNA synthesis was strongly inhibited in the PLC/PRF/5 cells by addition of TGF-beta 1 (0.5 to 4.0 ng/ml), but remained unchanged in the Mahlavu cells. Also the expression of c-myc mRNA was suppressed by the addition of TGF-beta 1 in the PLC/PRF/5 cells but not in the Mahlavu cells. These results indicate that TGF-beta 1 might regulate cell growth, in part, by modulating c-myc expression, although there is no direct proof that c-myc expression is really relevant to DNA synthesis mediated by TGF-beta 1.

Expression of c-myc, c-raf-1, and c-Ki-ras in azaserine-induced pancreatic carcinomas and growing pancreas in rats

We examined the pattern of expression of several proto-oncogenes during nonneoplastic growth and in acinar cell neoplasms in the rat pancreas. The levels of c-myc, c-raf-1, and c-Ki-ras mRNAs were increased in regenerating pancreata following surgical partial pancreatectomy and following administration of camostat. We also investigated proto-oncogene expression associated with the progression of pancreatic cancers in azaserine-treated rats. Injection of a single dose (30 mg/kg) of azaserine (O-diazoacetyl-L-serine) to 14-d-old rats leads to a variety of neoplastic lesions in the rat pancreas. Total RNA was isolated from lesions in various stages of tumor progression, including adenomas, carcinomas in situ, and invasive carcinomas. We observed increased expression of c-myc, c-raf-1, and c-Ki-ras in azaserine-induced adenomas and carcinomas. Actin expression was also increased in these tissues, whereas amylase expression was variable. However, when compared to the normal growing pancreas, the level of proto-oncogene expression in the adenomas and carcinomas was disproportionate to the degree of cellular division in those tissues. Thus, the alterations induced by azaserine apparently caused a deregulated increase in expression of cellular oncogenes associated with growth regulation.

Heterogeneity of enzyme-altered foci in rat liver

Enzyme-altered foci (EAF) in liver are assumed to be precursor lesions for tumors in this organ. Results obtained with selected hepatocarcinogens which produce lesions of differing phenotype and growth behavior indicate that not the total number of enzyme-altered cells but rather the proliferation of individual cell clones is of major importance for additional changes leading to malignancy. Analyses including multiple marker enzymes demonstrate a relationship between foci phenotype and proliferation. The inducibility of certain downregulated enzymes in EAF indirectly suggests disturbances in the expression of regulatory genes such as proto-oncogenes. Data on Ha-ras and c-myc proto-oncogene expression in EAF are presented.

Oncogene expression in cholangiocarcinoma and in normal hepatic development

The expression of the proteins encoded by the ras, myc, and erb B-2 oncogenes was examined in 63 paraffin-embedded human cholangiocarcinomas of Thai and English origin using immunohistochemistry. The observed distributions were compared with oncogene expression in a series of human hepatocellular carcinomas. In an attempt to relate expression of these three oncogenes to specific stages of normal tissue differentiation, tissue sections of normal fetal, infant, and adult human livers were also examined. Of 63 cholangiocarcinomas, 59 (95%) expressed p62 c-myc, 47 (75%) expressed p21 c-ras, and 46 (73%) expressed p190 c-erbB-2. The expression of c-myc and c-ras but not of c-erb B-2 correlated directly with tumor differentiation as judged by morphologic criteria. No difference was observed in oncogene expression between intrahepatic and extrahepatic cholangiocarcinomas. Twelve of 14 hepatocellular carcinomas (86%) stained positively for all three oncoproteins. During normal liver development, expression of c-myc and c-ras was shown to occur from 18 weeks' gestation until 5 years of age, but not thereafter. Expression of c-myc, c-ras, and c-erbB-2 oncogenes may be used as immunohistochemical markers to distinguish cholangiocarcinoma from nonneoplastic biliary tissues, and may provide useful information concerning the cell biology of tumor differentiation.

Compensatory ovarian hypertrophy occurs by a mechanism distinct from compensatory growth in the regenerating liver

The mechanism by which compensatory ovarian growth occurs is complex and not completely understood. To compare the molecular events in compensatory ovarian growth with those known to occur in other compensatory growth processes such as the regenerating liver, the temporal pattern of proto-oncogene expression and dexoyribonucleic acid synthesis was investigated in rat ovarian tissue after unilateral castration. One hundred fifty female rats were subjected to either a left hemioophorectomy or a sham oophorectomy. Twenty-four rats from each group were put to death at 3 and 14 days after the initial procedure and the ovaries were weighed. There was a mean compensatory weight increase in the right ovaries of the hemioophorectomy group of 7.9% at 3 days and 22.5% at 14 days. The temporal pattern of proto-oncogene expression was determined by removing the right ovary from six rats in each group at 4, 8, 12, 24, 36, and 48 hours after the initial procedure. The ovaries were paired into three samples in each group for each time point and the ribonucleic acid was extracted. Dot blot hybridization was performed on each ribonucleic acid sample with radiolabeled complementary deoxyribonucleic acid probes for the proto-oncogenes c-myc, c-HA-ras, and c-fos. There was no significant increase in proto-oncogene expression in the right ovaries of the hemioophorectomy group when compared with the right ovaries of the sham oophorectomy group. The temporal pattern of dexoyribonucleic acid synthesis was determined by removing the right ovary from three rats in each group at 8, 12, 24, 36, and 48 hours after the initial procedure. Each rat had been injected intraperitoneally with [3H]thymidine 2 hours before the right oophorectomy. The specific activity of dexoyribonucleic acid extracted from each ovarian sample did not demonstrate a significant increase in ovarian dexoyribonucleic acid synthesis after hemioophorectomy or any significant difference in dexoyribonucleic acid synthesis between the hemioophorectomy and the sham oophorectomy groups. This report concludes that compensatory ovarian growth occurs by a mechanism distinct from compensatory growth in the regenerating liver.

Dissociation of cellular proliferation and c-myc expression by buttercup extract

Buttercup extract (BE), an extract of the buttercup plant (Zanthoriza simplicissima), inhibits RNA and DNA synthesis by HL-60 promyelocytic leukemia cells. Exposure of these cells to 3% BE for 48 hours results in dramatic inhibition of RNA synthesis without loss of cell viability. The effect of BE is partially reversible over 12-24 hours with the level of RNA synthesis returning nearly to control levels during this time period. DNA synthesis is also reversibly inhibited by exposure to BE. Despite the inhibition of RNA synthesis in HL-60 cells, there is no decrease in the level of c-myc mRNA, even at high BE concentrations. The level of gene-specific mRNA for the c-Ha-ras, c-fms, and c-mos genes in these cells also remained constant during exposure to BE. Ribosomal RNA is not degraded during 24 hours of BE treatment in vitro, suggesting that BE does not maintain the relative mRNA level for these genes by selective degradation of other RNA species. The inhibition of RNA and DNA synthesis by BE without a corresponding alteration in the level of expression of the c-myc gene suggests that this agent dissociates c-myc expression and cellular proliferation in these cells.

Cellular analysis of c-Ha-ras gene expression in rat liver after CCl4 administration

Expression of the c-Ha-ras proto-oncogene is specifically enhanced during liver regeneration, in parallel with increased DNA replication, which suggests that c-Ha-ras may play a role in the control of regeneration. In this study, an in situ hybridization technique was applied for analysis of expression of the c-Ha-ras gene at the cellular level during liver regeneration induced by CCl4 administration. The in situ hybridization was compared with the observation for the p21c-Ha-ras protein, the corresponding protein of the c-Ha-ras gene, by immunohistochemistry. In normal rat liver, a few hepatocytes expressed the mRNAs and the corresponding proteins without any preferential localization. Zonal heterogeneity of c-Ha-ras gene expression first became evident at 12 hr after CCl4 administration, a higher number of gene products being detected in the pericentral zone than in the periportal zone. This heterogeneity became maximal at 24 hr after CCl4 administration. Zonal heterogeneity in the level of the p21c-Ha-ras protein paralleled that in the level of gene expression. Furthermore, both hepatocytes and nonparenchymal cells participated in expression of the c-Ha-ras gene during liver regeneration.

Human chorionic gonadotropin and alpha-fetoprotein in cholangiocarcinoma in relation to the expression of ras p21: an immunohistochemical study

The immunohistochemical localization of human chorionic gonadotropin (HCG) and alpha-fetoprotein (AFP) was studied in 44 cases with cholangiocarcinoma (CC) to determine the correlation to the expression of ras oncogene product p21 on tumor cells. HCG-immunoreactivity was found in 10 of 44 cases (23%) and AFP in only one (2.3%), whereas the expression of ras p21 was demonstrated in 39 (88.6%). The incidence of HCG-positive cells within the tumor was less than 1% in 8 of 10. The incidence of AFP-positive cells was less than 0.01%. All were histologically classified as adenocarcinoma and none of them had histologic features of trophoblastic tumors, yolk sac tumor or hepatocellular carcinoma. Nine of 10 HCG-positive and one AFP-positive CC expressed ras p21 on their tumor cells. However, one HCG-positive CC was negative for ras p21, though the incidence of HCG-positive cells within the tumor was 25%. HCG- and AFP-immunoreactivity was more frequently observed in poorly or undifferentiated tumor cells than in moderately or well-differentiated areas, whereas the expression of ras p21 was more diffuse in well-differentiated tumor and stronger in moderately differentiated areas, but rarely found in poorly and undifferentiated tumor. These results suggest that HCG production by CC of the usual adenocarcinoma variety is not rare, when compared to AFP production, and is preferentially localized in a small number of poorly differentiated and undifferentiated carcinoma cells, and there is no correlation between the production of HCG or AFP and the expression of ras p21 in CCs.

Inhibition of in vivo DNA synthesis in regenerating rat liver following thermal injury

Hepatic repair and regeneration which is extremely important after thermal injuries can be inhibited by the acute inflammatory reaction. Since thermal injury initiates this acute inflammatory reaction, DNA synthesis was studied in the regenerating liver following this injury. In vivo incorporation of [3H]-thymidine into hepatic DNA, autoradiographic determination of a labeling index, and thymidine kinase activity were determined. Incorporation of [3H]-thymidine into hepatic DNA and labeling indices were markedly diminished at 24 hours if partial hepatectomy and thermal injury were carried out concurrently. After partial hepatectomy, the expected elevations in thymidine kinase activity were inhibited by the thermal injury (p less than 0.01) and elevation of serum fibrinogen, a marker of the acute phase reaction that normally follows thermal injury, was blunted by the partial hepatectomy (p less than 0.05). The combination of thermal injury and partial hepatectomy resulted in a greatly diminished DNA replicative response as compared to partial hepatectomy alone and suggests that multiplicative injury is more likely to result in multi-system failure.

Expression of c-raf-1 and A-raf-1 during regeneration of rat liver following surgical partial hepatectomy

The major objective of this study was to investigate the expression of members of the raf family of proto-oncogenes during rat liver regeneration. The steady-state level of expression of both c-raf-1 and A-raf-1 increased three- to fivefold 18-24 h following partial hepatectomy, and it returned to basal levels by 72 h. Expression of c-myc and Ha-ras mRNA was increased at 3 and 18-24 h, respectively, confirming previous reports. Increased steady-state levels of c-raf-1, A-raf-1, and Ha-ras mRNA were also detected in hepatocytes isolated from rat liver 24 h after partial hepatectomy. Thus, elevated expression of the raf genes closely correlated with that of Ha-ras, beginning at 12 h and reaching maximal levels during the first peak of DNA synthesis following partial hepatectomy.

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

Five simian virus 40 (SV40)-hepatocyte cell lines were examined for tumorigenicity and the effect of in vitro passage on the expression of four liver-specific genes (albumin, transferrin, alpha 1-antitrypsin, and phosphoenolpyruvate carboxykinase), two oncogenes (c-Ha-ras and c-raf), and two genes associated with hepatocarcinogenesis (alpha-fetoprotein and placental-type glutathione-S-transferase). At low passage (12 to 22), all five cell lines expressed the four liver-specific genes at levels similar to those in the liver and were not tumorigenic or were weakly tumorigenic. At high passage (33 to 61), the cell lines formed carcinomas, and four out of five cell lines produced primary tumors that metastasized. At least two cell lines produced well-differentiated hepatocellular carcinomas that expressed liver-specific RNAs. Levels of expression of liver-specific genes changed with time in culture. Some of the changes in liver-specific gene expression in the tumor tissue (such as for the phosphoenolpyruvate carboxykinase gene) paralleled those that occurred with in vitro passage, while other changes (such as for the albumin gene) did not parallel those that occurred with in vitro passage. Correlations between enhanced expression of c-Ha-ras and tumorigenic potential and between the process of SV40 immortalization and induced expression of c-raf and glutathione-S-transferase-P were observed. Induction of alpha-fetoprotein was detected with in vitro and in vivo passage only in the CWSV14 cell line and was paralleled by diminished albumin expression. In conclusion, we developed a model system with five SV40-hepatocyte cell lines, tumors induced by them, and tumor cell lines to examine changes in gene expression that accompany the progression from a normal cell to a hepatocellular carcinoma. Because the SV40-hepatocyte cell lines and tumor cell lines remain highly differentiated and vary in the magnitude of expression of specific genes, they can be used to study the molecular mechanisms regulating gene expression, in particular those regulating specific genes associated with differentiation.

The use of primary cultures of adult rat hepatocytes to study induction of enzymes and DNA synthesis: effect of nafenopin and electroporation

Primary cultures of adult rat hepatocytes maintained in a well-differentiated state, in a chemically defined medium containing 2% DMSO, have been utilized to study the effect of non-mutagenic hepatocarcinogens such as the peroxisome proliferator nafenopin. The parameters chosen in this in vitro system were those that paralleled the major in vivo effects of nafenopin on the liver, mainly: the proliferation of the endoplasmic reticulum and induction of cytochrome P-452, the proliferation of the peroxisome compartment and the induction of cyanide-insensitive beta-oxidation of fatty acids and the stimulation of liver growth as measured by the DNA synthetic activity of the hepatocytes. In this review, we also describe the morphology of hepatocyte cultures prepared from previously electroporated hepatocytes and the potential for the use of electroporation to introduce growth related genes into hepatocyte cells to study the mechanisms of hepatocyte growth at the molecular level. In addition we describe the formation of endoplasmic reticulum whorls in these cultures as a consequence of nafenopin treatment. 'Whorl formation' by hepatotrophic chemicals has been previously shown to occur in vivo; in this report, it is described for the first time in vitro.

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

Five simian virus 40 (SV40)-hepatocyte cell lines were examined for tumorigenicity and the effect of in vitro passage on the expression of four liver-specific genes (albumin, transferrin, alpha 1-antitrypsin, and phosphoenolpyruvate carboxykinase), two oncogenes (c-Ha-ras and c-raf), and two genes associated with hepatocarcinogenesis (alpha-fetoprotein and placental-type glutathione-S-transferase). At low passage (12 to 22), all five cell lines expressed the four liver-specific genes at levels similar to those in the liver and were not tumorigenic or were weakly tumorigenic. At high passage (33 to 61), the cell lines formed carcinomas, and four out of five cell lines produced primary tumors that metastasized. At least two cell lines produced well-differentiated hepatocellular carcinomas that expressed liver-specific RNAs. Levels of expression of liver-specific genes changed with time in culture. Some of the changes in liver-specific gene expression in the tumor tissue (such as for the phosphoenolpyruvate carboxykinase gene) paralleled those that occurred with in vitro passage, while other changes (such as for the albumin gene) did not parallel those that occurred with in vitro passage. Correlations between enhanced expression of c-Ha-ras and tumorigenic potential and between the process of SV40 immortalization and induced expression of c-raf and glutathione-S-transferase-P were observed. Induction of alpha-fetoprotein was detected with in vitro and in vivo passage only in the CWSV14 cell line and was paralleled by diminished albumin expression. In conclusion, we developed a model system with five SV40-hepatocyte cell lines, tumors induced by them, and tumor cell lines to examine changes in gene expression that accompany the progression from a normal cell to a hepatocellular carcinoma. Because the SV40-hepatocyte cell lines and tumor cell lines remain highly differentiated and vary in the magnitude of expression of specific genes, they can be used to study the molecular mechanisms regulating gene expression, in particular those regulating specific genes associated with differentiation.

Electroporation of cultured adult rat hepatocytes with the c-myc gene potentiates DNA synthesis in response to epidermal growth factor

The human c-myc gene was introduced and transiently expressed in adult rat hepatocyte cultures by the technique of electroporation and its effect on DNA synthesis was examined. Epidermal growth factor (EGF) has been found to stimulate a wave of DNA synthesis in electroporated rat hepatocytes. Hepatocyte cultures electroporated with the c-myc gene showed a potentiation of this EGF effect exhibiting rates of DNA synthesis up to 50% greater than those of control electroporated cultures, as determined by [3H]thymidine labeling of cell nuclei. This potentiation was dependent on the amount of c-myc DNA transfected. The potentiation was due neither to an alteration in the dose-response of the stimulatory effect of EGF nor to a change in the time course of the DNA synthesis wave.