p53 gene mutation and integrated hepatitis B viral DNA sequences in human liver cancer cell lines

Acquired expression of transcriptionally active p73 in hepatocellular carcinoma cells

p53 and p73 proteins activate similar target genes and induce apoptosis and cell cycle arrest. However, p53, but not p73 is considered a tumour-suppressor gene. Unlike p53, p73 deficiency in mice does not lead to a cancer-prone phenotype, and p73 gene is not mutated in human cancers, including hepatocellular carcinoma. Here we report that normal liver cells express only DeltaN-p73 transcript forms giving rise to the synthesis of N-terminally truncated, transcriptionally inactive and dominant negative p73 proteins. In contrast, most hepatocellular carcinoma cells express TA-p73 transcript forms encoding full-length and transcriptionally active p73 proteins, in addition to DeltaN-p73. We also show that together with the acquired expression of TA-p73, the 'retinoblastoma pathway' is inactivated, and E2F1-target genes including cyclin E and p14(ARF) are activated in hepatocellular carcinoma. However, there was no full correlation between 'retinoblastoma pathway' inactivation and TA-p73 expression. Most TA-p73-expressing hepatocellular carcinoma cells have also lost p53 function either by lack of expression or missense mutations. The p73 gene, encoding only DeltaN-p73 protein, may function as a tumour promoter rather than a tumour suppressor in liver tissue. This may be one reason why p73 is not a mutation target in hepatocellular carcinoma.

Sp1 plays a critical role in the transcriptional activation of the human cyclin-dependent kinase inhibitor p21(WAF1/Cip1) gene by the p53 tumor suppressor protein

In the present study we present evidence for the critical role of Sp1 in the mechanism of transactivation of the human cell cycle inhibitor p21(WAF1/Cip1) (p21) gene promoter by the tumor suppressor p53 protein. We found that the distal p53-binding site of the p21 promoter acts as an enhancer on the homologous or heterologous promoters in hepatoma HepG2 cells. In transfection experiments, p53 transactivated the p21 promoter in HaCaT cells that express Sp1 but have a mutated p53 form. In contrast, p53 could not transactivate the p21 promoter in the Drosophila embryo-derived Schneider's SL2 cells that lack endogenous Sp1 or related factors. Cotransfection of SL2 cells with p53 and Sp1 resulted in a synergistic transactivation of the p21 promoter. Synergistic transactivation was greatly decreased in SL2 cells and HaCaT cells by mutations in either the p53-binding site or in the -82/-77 Sp1-binding site indicating functional cooperation between Sp1 and p53 in the transactivation of the p21 promoter. Synergistic transactivation was also decreased by mutations in the transactivation domain of p53. Physical interactions between Sp1 and p53 proteins were established by glutathione S-transferase pull-down and coimmunoprecipitation assays. By using deletion mutants we found that the DNA binding domain of Sp1 is required for its physical interaction with p53. In conclusion, Sp1 must play a critical role in regulating important biological processes controlled by p53 via p21 gene activation such as DNA repair, cell growth, differentiation, and apoptosis.

Gene delivery using a receptor-mediated gene transfer system targeted to hepatocellular carcinoma cells

For gene therapy to be effective in cancers, it is necessary to deliver therapeutic genes into cells with high specificity and efficiency. In this study, we examined the in vitro and in vivo gene delivery efficiency of a new, growth receptor-mediated gene transfer system in hepatocellular carcinoma (HCC). The effects of transfection of wild-type p53 using this system were also studied. The system consisted of a ligand oligopeptide for epidermal growth factor receptor (EGFR) recognition, a polypeptide for DNA binding, and an endosome-releasing oligopeptide for endosomolysis. Two human HCC cell lines and a normal liver cell line were used, and pCMV-beta-galactosidase (beta-gal) was used as a reporter gene. Both HCC cell lines had strong expression of EGFR and the in vitro transfer efficiency peaked at day 5 at about 50%. This finding was in contrast to the normal liver cell line, which had weak EGFR expression and less than 1% transfer efficiency throughout. For in vivo gene transfer in tumors produced by inoculating HCC cells in nude mice and with the vector-beta-gal gene complex injected peritumorally, beta-gal expression was detected within the tumors at 12 hr, peaked at day 5 involving about 50% of the tumor cells and persisted at 2 weeks. Using this vector system, transfection of wild-type p53 into Huh-7 cells that had mutated p53 resulted in significant growth inhibition of cancer cells accompanied by a decreased G2/M phase and increased p53 protein. In conclusion, this receptor-mediated gene transfer system appears to work specifically in HCC cells with high efficiency, and may be promising in delivering apoptotic and other genes into HCC cells.

Distinctive gene expression profiles associated with Hepatitis B virus x protein

Hepatitis B virus (HBV) is a major risk factor for the development of hepatocellular carcinoma (HCC). HBV encodes the potentially oncogenic HBx protein, which mainly functions as a transcriptional co-activator involving in multiple gene deregulations. However, mechanisms underlying HBx-mediated oncogenicity remain unclear. To determine the role(s) of HBx in the early genesis of HCC, we utilized the NCI Oncochip microarray that contains 2208 human cDNA clones to examine the gene expression profiles in either freshly isolated normal primary adult human hepatocytes (Hhep) or an HCC cell line (SK-Hep-1) ecotopically expressing HBx via an adenoviral system. The gene expression profiles also were determined in liver samples from HBV-infected chronic active hepatitis patients when compared with normal liver samples. The microarray results were validated through Northern blot analysis of the expression of selected genes. Using reciprocally labeling hybridizations, scatterplot analysis of gene expression ratios in human primary hepatocytes expressing HBx demonstrates that microarrays are highly reproducible. The comparison of gene expression profiles between HBx-expressing primary hepatocytes and HBV-infected liver samples shows a consistent alteration of many cellular genes including a subset of oncogenes (such as c-myc and c-myb) and tumor suppressor genes (such as APC, p53, WAF1 and WT1). Furthermore, clustering algorithm analysis showed distinctive gene expression profiles in Hhep and SK-Hep-1 cells. Our findings are consistent with the hypothesis that the deregulation of cellular genes by oncogenic HBx may be an early event that favors hepatocyte proliferation during liver carcinogenesis.

Liver cancer

The prognosis of patients with HCC remains dismal. Even in the subgroups of patients who have the most favorable characteristics and are eligible for surgical resection, the 5-year survival rate is less than 25%. For patients with more advanced disease, the median survival time is less than 1 year. The good news in HCC research is that the disease can be prevented. In Taiwan, the rate of HCC in children aged 6 to 9 years decreased from 5.2 per million population before the neonatal vaccination program began in 1984 to 1.3 per million population in the first vaccinated cohort. Treatment of viral hepatitis with IFN may decrease the rates of long-term development of HCC. Other agents that may prevent second primary tumors following resection of HCC, such as polyprenoic acid and acylic retinoid, are also being investigated.

A monoclonal antibody against DNA binding helix of p53 protein

Three monoclonal antibodies (Mabs) were generated against p53 DNA-binding core domain. When tested by immunoprecipitation, Western blot and immunofluorescence techniques, Mab 9E4, as well as 7D3 and 6B10 reacted with both wild-type and various mutant p53 proteins. The epitopes recognized by Mabs 7D3, 9E4 and 6B10 were located respectively within the amino acid residues 211-220, 281-290 and 291-300 of human p53 protein. The epitope recognized by 9E4 Mab coincides with helix 2, also called p53 DNA binding helix, which allows the direct contact of the protein with its target DNA sequences. This antibody may be useful to study transcription-dependent and transcription-independent activities of wild-type and mutant p53 proteins.

The biochemistry and toxicity of atractyloside: a review

Atractyloside poisoning is an infrequent but often fatal form of herbal poisoning, which occurs worldwide but especially in Africa and the Mediterranean regions. The primary mechanism of atractyloside poisoning is known to be inhibition of the mitochondrial ADP transporter. Poisoning in humans may present with either acute hepatic or renal pathology and it is possible that there is a second, different mechanism of toxicity to the hepatocyte. Atractyloside in large amounts gives rise to massive necrosis, but in vitro studies have shown that at lower doses cells progress to apoptosis. Simple methods for the detection of atractyloside poisoning are at present restricted to thin-layer chromatography in urine and are useful only in the case of severe poisoning. Immunoassays, high-performance liquid chromatography, nuclear magnetic resonance, and a recently developed high-performance liquid chromatography/mass spectrometry method have yet to be applied to clinical diagnoses. There is at present no treatment, but a fuller understanding of the mechanisms of toxicity may lead to the application of a number of compounds that are effective in vitro.

Disruption of TGF-beta growth inhibition by oncogenic ras is linked to p27Kip1 mislocalization

Expression of oncogenic Ras in epithelial tumor cells is linked to the loss of transforming growth factor-beta (TGF-beta) anti-proliferative activity, and was proposed to involve inhibition of Smad2/3 nuclear translocation. Here we studied several epithelial cell lines expressing oncogenic N-RasK61 and show that TGF-beta-induced nuclear translocation of and transcriptional activation by Smad2/3 were unaffected. In contrast, oncogenic Ras mediated nuclearto-cytoplasmic mislocalization of p27KiP1 (p27) and of the cyclin-dependent kinase (CDK) CDK6, but not CDK2. Concomitantly, oncogenic Ras abrogated the ability of TGF-beta to release p27 from CDK6, to enhance its binding to CDK2 and to inhibit CDK2 activity. Inactivation of Ras by a specific antagonist restored the growth inhibitory response to TGF-beta with concurrent normalization of p27 and CDK6 localization. Therefore, the disruption of TGF-beta-mediated growth inhibition by oncogenic Ras appears to be due to lack of inhibition of CDK2, caused by the sequestration of p27 and CDK2 in different subcellular compartments and by the loss of TGF-beta-induced partner switching of p27 from CDK6 to CDK2.

Expression of the p53 tumor suppressor gene is up-regulated by depletion of intracellular zinc in HepG2 cells

Expression and activation of the p53 tumor suppressor protein are modulated by various cellular stimuli. The objective of this work was to examine the influence of zinc depletion on the expression of p53 in HepG2 cells. Two different low Zn (ZD) media, Zn-free Opti-MEM and a ZD medium containing Chelex-100 treated serum, were used to deplete cellular zinc over one passage. Cellular zinc levels of ZD cells were significantly lower than in their controls in both the Opti-MEM and Chelex studies. p53 mRNA abundance was 187% higher in ZD Opti-MEM cells and >100% higher in ZD Chelex cells compared with their respective controls. To examine whether the effects were specific to zinc depletion, a third, zinc-replenished group (ZDA) was included in the Opti-MEM study in which cells were cultured in ZD media for nearly one passage before a change was made to zinc-adequate (ZA) medium for the last 24 h. Zinc levels in the ZDA cells were significantly higher than in ZD cells, and p53 mRNA abundance was normalized to control levels. Nuclear p53 protein levels were >100% higher in the ZD Opti-MEM cells than in ZA cells. Interestingly, the ZDA Opti-MEM cells had significantly lower levels of nuclear p53 protein than both the ZA and ZD cells. These data suggest that expression of p53, a critical component in the maintenance of genomic stability, may be affected by reductions in cellular zinc.

A comparison of apoptosis and necrosis induced by hepatotoxins in HepG2 cells

7H-Dibenzo[c,g]carbazole (DBC), an N-heterocyclic aromatic hydrocarbon, is cytotoxic and carcinogenic in rodent liver. While DBC leads to necrotic lesions in the liver, the induction of apoptosis by DBC has not been investigated. The focus of this study was to determine the degree to which apoptosis and necrosis contributed to DBC cytotoxicity in a human hepatoma cell line (HepG2). To determine if these effects were unique to DBC, the results were compared to another hepatotoxin, aflatoxin B(1) (AFB(1)). DBC produced a distinct biphasic LDH release curve within 24 h of exposure. During the same time period lower concentrations of DBC (<10 microM) induced the formation of DBC-DNA adducts and increased p53 protein levels followed by apoptotic cell death. However, increasing the concentration of DBC to 80 microM led to lower DNA adduct and p53 protein levels. At this concentration, intracellular ATP levels were rapidly depleted followed by cell swelling and loss of membrane integrity consistent with necrotic cell death. In contrast to DBC, a biphasic LDH release curve was not observed for AFB(1). Instead, AFB(1) induced a concentration-dependent increase in apoptosis that reached two- to threefold higher levels than DBC. These results suggest that differences exist in the extent and type of cell death induced by DBC and AFB(1) at equimolar concentrations. Apoptosis and necrosis result from low and high concentrations of DBC, respectively, and may be dependent upon intracellular ATP levels.

The Fn14 immediate-early response gene is induced during liver regeneration and highly expressed in both human and murine hepatocellular carcinomas

Polypeptide growth factors stimulate mammalian cell proliferation by binding to specific cell surface receptors. This interaction triggers numerous biochemical responses including the activation of protein phosphorylation cascades and the enhanced expression of specific genes. We have identified several fibroblast growth factor (FGF)-inducible genes in murine NIH 3T3 cells and recently reported that one of them, the FGF-inducible 14 (Fn14) immediate-early response gene, is predicted to encode a novel, cell surface-localized type Ia transmembrane protein. Here, we report that the human Fn14 homolog is located on chromosome 16p13.3 and encodes a 129-amino acid protein with approximately 82% sequence identity to the murine protein. The human Fn14 gene, like the murine Fn14 gene, is expressed at elevated levels after FGF, calf serum or phorbol ester treatment of fibroblasts in vitro and is expressed at relatively high levels in heart and kidney in vivo. We also report that the human Fn14 gene is expressed at relatively low levels in normal liver tissue but at high levels in liver cancer cell lines and in hepatocellular carcinoma specimens. Furthermore, the murine Fn14 gene is rapidly induced during liver regeneration in vivo and is expressed at high levels in the hepatocellular carcinoma nodules that develop in the c-myc/transforming growth factor-alpha-driven and the hepatitis B virus X protein-driven transgenic mouse models of hepatocarcinogenesis. These results indicate that Fn14 may play a role in hepatocyte growth control and liver neoplasia.

Induction of apoptosis after switch-on of the hepatitis B virus X gene mediated by the Cre/loxP recombination system

The HBx protein of hepatitis B virus is a multifunctional protein that is implicated in the pathogenesis of hepatocellular carcinoma by regulating gene transcription, causing cell proliferation and, as shown recently, inducing cell death. However, analysis of the effects of HBx in stable cultured cell clones has been hampered because only cell lines that adapted to the effects of HBx were selected during the establishment of cell clones. Here, we describe a system in which transcription of the X gene of hepatitis B virus is switched on by the use of the site-specific Cre recombinase. Two human liver cell lines, HLF and HepG2, were used, the former with a mutant p53 allele and the latter with wild-type p53. The stable cell clones isolated, which carried the X gene in a transcriptionally silent state, were infected with recombinant adenovirus carrying Cre recombinase. Ninety-six hours after adenovirus infection, cell clones that expressed HBx had undergone TUNEL-positive cell death with characteristics of apoptosis. Apoptosis was induced despite concomitant inactivation of the p53 protein as a result of its cytoplasmic translocation by HBx. In contrast, neither the X gene-carrying cells infected with wild-type adenovirus nor various control cells infected with Cre-expressing adenovirus exhibited apoptosis. These results indicate that the expression of HBx protein leads to liver cell apoptosis independently of the p53 pathway. The significance of HBx-induced apoptosis in natural infection is unclear, but it may contribute to the development of hepatitis and serve to spread progeny virus to neighbouring cells while evading the host immune responses.

Mutational analysis of p73 and p53 in human cancer cell lines

p73 is a candidate tumor suppressor gene with substantial DNA and protein homology to the p53 tumor suppressor gene. We have investigated two hypotheses: (a) p73 is mutated in diverse types of human cancer, and (b) p73 is functionally redundant with p53 in carcinogenesis so that mutations would be exclusive in these two genes. The entire coding region and intronic splice junctions of p73 were examined in 54 cancer cell lines. Three lung cancer cell lines contained mutations that affected the amino acid sequence. One amino acid substitution was in a region with homology to the specific DNA binding region of p53 and two microdeletions were outside the region of homology. Two of the cell lines with p73 mutations also carried p53 mutations. Although our results are inconsistent with the two hypotheses tested, p73 mutations may contribute infrequently to the molecular pathogenesis of human lung cancer.

Genetic alterations in hepatocellular carcinomas: association between loss of chromosome 4q and p53 gene mutations

The major risk factors for hepatocellular carcinomas (HCC) in high incidence areas include infection with hepatitis B and C viruses (HBV, HCV) and exposure to aflatoxin. Genetic alterations in 24 liver resection specimens from Shanghai and Qidong were studied. Hepatitis B virus was integrated in all patient samples, and a null phenotype for the GSTM1 enzyme was present in 63% of patients. Alteration of p53 was present in 95% (23/24) of cases: mutations of the p53 gene in 12 HCC, p53 overexpression in 13 and loss of heterozygosity (LOH) of chromosome 17p in 17. All seven HCCs with a p53 mutation from Qidong and three of five from Shanghai had the aflatoxin-associated point mutation with a G to T transversion at codon 249, position 3. No HCC had microsatellite instability. LOH of chromosome 4q, 1p, 16q and 13q was present in 50%, 46%, 42% and 38%, respectively, and 4q was preferentially lost in HCCs containing a p53 mutation: LOH of 4q was present in 75% (9/12) of HCC with, but only 25% (3/12) of HCC without, a p53 gene mutation (P = 0.01). These data indicate a possible interaction between p53 gene mutation and 4q loss in the pathogenesis of HCC.

Downregulation of DNA excision repair by the hepatitis B virus-x protein occurs in p53-proficient and p53-deficient cells

Synergism between exposure to chemical carcinogens and infection with the hepatitis B virus (HBV) has been implicated in the high incidence of hepatocellular carcinoma. In this study we report that the HBV protein HBx, inhibits cellular DNA repair capacity in a p53-independent manner. Two alternative assays were used: the host cell reactivation assay, which measures the cell's capacity to repair DNA damage in a reporter plasmid, and unscheduled DNA synthesis, which measures the overall DNA repair capacity in damaged cells. Two p53-proficient cell lines, the hepatocellular carcinoma cell line HepG2 and liver epithelial cell line CCL13, were co-transfected with the pCMV-HBx reporter plasmid and the pCMV-CAT plasmid damaged with UVC radiation. Compared with cells transfected with control plasmid, the presence of HBx resulted in approximately 50% inhibition of the cell's capacity to reactivate CAT activity of UVC-damaged plasmid, and approximately 25% inhibition of unscheduled DNA synthesis in cells treated with either aflatoxin B1 epoxide or UVC radiation. Using the p53-deficient cell line Saos-2, we demonstrated that expression of HBx also resulted in diminished overall cellular DNA repair of damage induced by both aflatoxin B1 epoxide and UVC radiation, using both the host cell reactivation and unscheduled DNA synthesis assays. In summary, this study provides evidence for p53-independent regulation of DNA repair by HBx.

p53 activates the CD95 (APO-1/Fas) gene in response to DNA damage by anticancer drugs

Chemotherapeutic drugs cause DNA damage and kill cancer cells mainly by apoptosis. p53 mediates apoptosis after DNA damage. To explore the pathway of p53-dependent cell death, we investigated if p53-dependent apoptosis after DNA damage is mediated by the CD95 (APO-1/Fas) receptor/ligand system. We investigated hepatoma, gastric cancer, colon cancer, and breast cancer cell lines upon treatment with different anticancer agents known to act via p53 accumulation. Cisplatin, mitomycin, methotrexate, mitoxantrone, doxorubicin, and bleomycin at concentrations present in the sera of patients during therapy led to an upregulation of both CD95 receptor and CD95 ligand. Induction of the CD95 ligand occurred in p53 wild-type (wt), p53 mutant (mt), and p53 deficient (p53(-/-)) cell lines and at wt and mt conformation of temperature-sensitive p53 mutants. In contrast, upregulation of the CD95 receptor was observed only in cells with wt p53, not in cells with mt or without any p53. Restitution of inducible wt p53 function restored the ability of p53(-/-) Hep3B cells to upregulate the CD95 receptor in response to anticancer drugs. This rendered the cells sensitive to CD95-mediated apoptosis. In an attempt to understand how CD95 expression is regulated by p53, we identified a p53-responsive element within the first intron of the CD95 gene, as well as three putative elements within the promoter. The intronic element conferred transcriptional activation by p53 and cooperated with p53-responsive elements in the promoter of the CD95 gene. wt p53 bound to and transactivated the CD95 gene, whereas mt p53 failed to induce apoptosis via activation of the CD95 gene. These observations provide a mechanistic explanation for the ability of p53 to contribute to tumor progression and to resistance of cancer cells to chemotherapy.

Transactivation of the human MDR1 gene by hepatitis B virus X gene product

BACKGROUND/AIMS

Persistent hepatitis B virus (HBV) infection may cause hepatocellular carcinoma. Patients with hepatocellular carcinoma are characterized by nonresponsiveness to chemotherapeutic agents. While many studies have been devoted to understanding the hepatocarcinogenesis mechanism of HBV, the possible relationship between HBV and the drug sensitivity phenotype of cancer cells has rarely been addressed. The hepatitis B virus X gene encodes a transcription transactivator which has been suggested to be a potential factor in viral hepatocarcinogenesis. The role of HBV pX in mediating the drug resistance phenotype of hepatoma cell lines was examined in this study.

METHODS

Standard transfection and chloramphenicol acetyltransferase assay were utilized to examine the effect of HBV pX transactivator on a reporter gene under the control of the human multidrug resistance (MDR) 1 upstream regulatory elements. Selected Hep G2 clones with or without HBV pX expression were tested for their sensitivity towards various anti-cancer agents by utilization of MTT assay.

RESULTS

The expression of HBV pX in both Hep G2 (p53+) and Hep 3B (p53-) cells resulted in transactivation of the reporter gene under control of the human MDR1 upstream regulatory elements. Northern blot analysis indicated that expression of the endogenous MDR1 gene was also elevated in Hep G2 clones with HBV pX expression. Decreased drug sensitivity towards adriamycin, vinblastine, and VP-16 was observed in Hep G2 clones with HBV pX expression.

CONCLUSIONS

HBV pX can transactivate the MDR1 gene. Drug sensitivity was altered in Hep G2 cells with HBV pX expression.

Pathogenesis of hepatitis B and C-induced hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is estimated to have an annual worldwide incidence of 0.25 to 1.2 million new cases per year. Both the prevalence and incidence of HCC vary markedly as a function of geography and the local prevalence of chronic viral hepatitis. Both chronic hepatitis B and chronic hepatitis C are recognized as risk factors for HCC. The prevalence of cirrhosis in individuals with HCC and chronic hepatitis B or C is reported to be 80.9% and 75.8%, respectively. HCC occurs at a lower rate in chronic viral hepatitis in the absence of cirrhosis. Moreover, hepatitis C virus (HCV) rather than hepatitis B virus (HBV) is associated with the majority of non-cirrhotic cases of HCC. It is probable that the ongoing process of hepatocyte necrosis and liver cell renewal coupled with inflammation, which is characteristic of chronic viral hepatitis, causes not only nodular regeneration and cirrhosis but also progressive genomic errors in hepatocytes as well as unregulated growth and repair mechanisms leading to hepatocyte dysplasia and, in some cases, hepatic carcinoma. Current concepts concerning virus-induced HCC are reported and discussed in the following review.

Suppression of growth of hepatocellular carcinoma by sodium butyrate in vitro and in vivo

Treatment of HuH-7 human hepatocellular carcinoma (HCC) cells with 1-10 mM sodium butyrate (SB) resulted in growth inhibition in a dose-dependent manner. At 3 mM and higher concentrations, SB caused nuclear fragmentation and DNA ladder formation characteristic of apoptosis. In the treated cells, the expression of p21 (WAFI/CIPI) increased and that of alpha-fetoprotein (AFP) decreased. These characteristic changes were also observed with 5 other human HCC cell lines with or without mutation of the p53 gene. The ability of these cells to form colonies in soft agar was suppressed by either pretreating the cells with SB prior to soft agar plating or incubating untreated cells in SB-containing soft agar. Direct injection of SB into tumors developed from HuH-7 cells in nude mice resulted in an increase in the p21 level, a decrease in the tumor size and an increase in the survival time of mice. When the inoculation of HuH-7 cells into nude mice was immediately followed by subcutaneous injection of SB, development of tumors was either significantly delayed or completely suppressed. These results suggest that SB induces cellular differentiation and suppresses growth and tumorigenicity of HCC cells in vitro and in viva by a mechanism independent of p53 but possibly dependent on p21.

Accumulation of genetic alterations and their significance in each primary human cancer and cell line

Analyses of multiple genetic alterations accumulated in each cancer cell is expected to provide useful information to elucidate the molecular mechanisms involved in tumorigenesis. Here, we summarized the results of studies on aberrations of oncogenes and tumor suppressor genes by ourselves and other groups. DNAs analyzed were from particular sets of surgical specimens from human tumors and cancer cell lines derived from non-small cell lung cancers, pancreatic cancers, hepatocellular carcinomas and gliomas. Tumors could be grouped into two types based on the genetic alterations detected. Tumors in group 1 had mutations in genes encoding proteins involved in a limited number of signal transduction cascades such as p16-cyclin D1/CDK4-RB or MDM2-p53-p21, where the aberration of one component seems to be sufficient to cause dysfunction of the cascade. Group 2 contained a subset of tumors in which no alteration was detected in the genes analyzed, even in the advanced stage or established cancer cells, indicating the involvement of completely different oncogenic pathways.

Sebaceous carcinoma. Tumor progression through mutational inactivation of p53

BACKGROUND

Sebaceous carcinoma may masquerade for years as an inflammatory condition. In many cases, this may be because of the presence of longstanding intraepithelial disease (e.g., dysplasia or carcinoma in situ), which eventually progresses to invasive carcinoma recognized through tumefaction and a worsening clinical presentation. The mechanism for this tumor progression is unknown. In the Far East, human papilloma virus (HPV) has been suggested to play a role in the development of sebaceous carcinoma by inactivating tumor suppressor gene p53. Here, the authors explore the molecular basis of the progression of ocular sebaceous carcinoma.

METHODS

Cases of sebaceous carcinoma seen at the University of Virginia, Department of Ophthalmology, during the period from 1989 to 1996 were analyzed for HPV infection by in situ hybridization and polymerase chain reaction. The expression of p53, p21WAF-1, Bcl-2, and epithelial membrane antigen was examined by immunohistochemistry. In one of the cases, frozen tumor was available, allowing exons 5 through 9 of the p53 gene to be sequenced.

RESULTS

Seven cases were identified, all of which were from women. All were negative for HPV. In cases in which disease was restricted to dysplasia (carcinoma in situ), p53 but not p21WAF-1 was negative. In contrast, cases that contained a component of invasive or metastatic carcinoma showed striking hyperexpression of nuclear p53 in all of the malignant cells. In one of these cases, a G:C-->T:A transversion was found in the p53 gene. This mutation, characteristic of bulky carcinogens, substituted phenylalanine for cysteine 277, a residue that participates in hydrogen bonding to the p53 DNA binding consensus sequence.

CONCLUSIONS

Mutational inactivation of p53 may be involved in the progression of sebaceous carcinoma.

Screening the p53 status of human cell lines using a yeast functional assay

We have screened the p53 status of 156 human cell lines, including 142 tumor cell lines from 27 different tumor types and 14 cell lines from normal tissues by using functional analysis of separated alleles in yeast. This assay enables us to score wild-type p53 expression on the basis of the ability of expressed p53 to transactivate the reporter gene HIS3 via the p53-responsive GAL1 promotor in Saccharomyces cerevisiae. Of 142 tumor cell lines, at least 104 lines (73.2%) were found to express the mutated p53 gene: 94 lines (66.2%) were mutated in both alleles, three lines (2.1%) were heterozygous, and no p53 cDNA was amplified from seven lines (4.9%). Of the 14 cell lines originating from normal tissues, all the transformed or immortalized cell lines expressed mutant p53 only. Yeast cells expressing mutant p53 derived from 94 cell lines were analyzed for temperature-sensitive growth. p53 cDNA from eight cell lines showed p53-dependent temperature-sensitive growth, growing at 30 degrees C but not at 37 degrees C. Four temperature-sensitive p53 mutations were isolated: CAT-->CGT at codon 214 (H214R), TAC-->TGC at codon 234 (Y234C), GTG-->ATG at codon 272 (V272M), and GAG-->AAG (E285K). Functionally wild-type p53 was detected in 38 tumor cell lines (26.8%) and all of the diploid fibroblasts at early and late population doubling levels. These results strongly support the previous findings that p53 inactivation is one of the most frequent genetic events that occurs during carcinogenesis and immortalization.

ONYX-015, an E1B gene-attenuated adenovirus, causes tumor-specific cytolysis and antitumoral efficacy that can be augmented by standard chemotherapeutic agents

The 55-kilodalton (kDa) protein from the E1B-region of adenovirus binds to and inactivates the p53 gene, which is mutated in half of human cancers. We have previously shown that the replication and cytopathogenicity of an E1B, 55-kDa gene-attenuated adenovirus, ONYX-015, is blocked by functional p53 in RKO and U20S carcinoma lines. We now report that normal human cells were highly resistant to ONYX-015-mediated, replication-dependent cytolysis. In contrast, a wide range of human tumor cells, including numerous carcinoma lines with either mutant or normal p53 gene sequences (exons 5-9), were efficiently destroyed. Antitumoral efficacy was documented following intratumoral or intravenous administration of ONYX-015 to nude mouse-human tumor xenografts; efficacy with ONYX-015 plus chemotherapy (cisplatin, 5-fluorouracil) was significantly greater than with either agent alone.

Wild-type p53 gene-induced morphological changes and growth suppression in hepatoma cells

The human hepatocellular carcinoma (HCC) cell line, HLF, expresses only mutant-type p53 (mt-p53), which has an amino acid substitution at the 244th residue from glycine to alanine. HLF cells were transfected with wild-type p53 (wt-p53) cDNA construct pC53-SN3, mt-p53 cDNA construct pC53-SCX [which differs by a single nucleotide, resulting in alanine instead of valine at the 143rd residue in p53 (p53-143)], or pCMV-Neo-Bam, as a control, by a liposome method. After G418 selection, three wt-p53 stable transformants (WT), four mt-p53 transformants (MT), and three control vector transformants (VT) were obtained. We analyzed the cell growth and morphological changes of these transformants under different culture conditions [fetal calf serum (FCS), 10%, 1%, and 0%]. Whereas no difference from control in the growth rate and morphology was observed under the 10% FCS conditions, serum starvation induced remarkable phenotypical changes in all three WTs, but not in the other transformant. Corresponding to these phenotypical changes, the transcriptional activity of wt-p53 was increased more than nine fold. These results indicated that serum starvation would induce wt-p53 biological function, which is tightly linked to morphological changes and growth suppression. To induce these changes, the introduction of the wt-p53 gene itself was not sufficient, and additional triggering, i.e., serum starvation, was indispensable.

p53 and tumour viruses: catching the guardian off-guard

Oncogenic viruses have evolved direct and indirect mechanisms to overcome the tumour suppressor p53. Fortunately, tumour development is limited by the narrow cell tropisms of the viruses concerned and the host immune response. However, such viruses are helping to elucidate the p53 response pathway and may play a future role as novel cancer therapeutic agents.

Drug-induced apoptosis in hepatoma cells is mediated by the CD95 (APO-1/Fas) receptor/ligand system and involves activation of wild-type p53

Chemotherapeutic drugs are cytotoxic by induction of apoptosis in drug-sensitive cells. We investigated the mechanism of bleomycin-induced cytotoxicity in hepatoma cells. At concentrations present in the sera of patients during therapy, bleomycin induced transient accumulation of nuclear wild-type (wt) p53 and upregulated expression of cell surface CD95 (APO-1/Fas) receptor in hepatoma cells carrying wt p53 (HepG2). Bleomycin did not increase CD95 in hepatoma cells with mutated p53 (Huh7) or in hepatoma cells which were p53-/- (Hep3B). In addition, sensitivity towards CD95-mediated apoptosis was also increased in wt p53 positive HepG2 cells. Microinjection of wt p53 cDNA into HepG2 cells had the same effect. In contrast, bleomycin did not enhance susceptibility towards CD95-mediated apoptosis in Huh7 and in Hep3B cells. Furthermore, bleomycin treatment of HepG2 cells increased CD95 ligand (CD95L) mRNA expression. Most notably, bleomycin-induced apoptosis in HepG2 cells was almost completely inhibited by antibodies which interfere with CD95 receptor/ligand interaction. These data suggest that apoptosis induced by bleomycin is mediated, at least in part, by p53-dependent stimulation of the CD95 receptor/ligand system. The same applies to other anti-cancer drugs such as cisplatin and methotrexate. These data may have major consequences for drug treatment of cancer and the explanation of drug sensitivity and resistance.

Mutations of the p53 tumor suppressor gene and ras oncogenes in aflatoxin hepatocarcinogenesis

Aflatoxin B1 (AFB1) is classified as a group I carcinogen in humans by IARC. However, the exact mechanisms of AFB1 hepatocarcinogenesis have not been fully elucidated. Recent studies have suggested that oncogenes are critical molecular targets for AFB1, and AFB1 causes characteristic genetic changes in the p53 tumor suppressor gene and ras protooncogenes. Up to date, more than 1500 human hepatocellular carcinoma (HCC) samples have been examined for p53 mutations with respect to different AFB1 exposure levels. The most significant finding is that more than 50% of HCC patients from high aflatoxin exposure areas such as southern Africa and Qidong, China harboured a codon 249 G to T transversion in the p53 tumor suppressor gene, which is found to be consistent with the mutagenic specificity of AFB1 observed in vitro. In contrast, this mutational pattern is not found in HCC samples from moderate or low aflatoxin exposure countries or regions. Therefore, this hot-spot mutation is believed to be a molecular fingerprint linking the initial event of AFB1-DNA adduct formation with the ultimate development and progress of human HCC. However, some important points still remain to be explicated. First, in many of these studies, the systematic evaluation of AFB1 exposure is rather limited and the classification of AFB1 exposure level is speculative and confusing, without the definite evidence for the actual aflatoxin exposure level. Second, the role of hepadnaviral infection has to be considered in the induction of this unique mutational spectrum. On the other hand, ras oncogene mutations are frequently found in AFB1-induced HCC samples in experimental animals, while the frequency of ras mutation in human HCC in contrast is much lower than that of p53. Recent studies have provided additional evidence that reactive oxygen species (ROS) and oxidative DNA damage may be involved in AFB1-induced p53 and ras mutations. In future, follow-up cohorts exposed to different levels of AFB1 combined with the determination of putative gene markers are much needed.

Allele-specific PCR analysis of p53 codon 249 AGT transversion in liver tissues from patients with viral hepatitis

AGG to AGT mutations in codon 249 of the p53 tumor-suppressor gene are frequently observed in hepatocellular carcinomas (HCC) from areas where exposure to aflatoxin B1 (AFB) occurs. We developed a sensitive allele-specific polymerase chain reaction (AS-PCR) assay to detect this point mutation in non-neoplastic human liver tissues. Three oligonucleotide primers, 1 specific for the mutant allele and 2 specific for the wild-type allele were used. The mutant allele primer differed from the wild-type allele due to a G-to-T transversion in its terminal 3' nucleotide. The first stage involved amplification of exon 7 of p53 followed by a selective amplification of mutant codon 249 sequences. This method allowed for the detection of a mutant codon 249 allele in the presence of as many as 105 copies of the wild-type allele and was 100-fold more sensitive than the restriction fragment length polymorphism-PCR technique. We have applied this AS-PCR protocol to examine codon 249 AGT transversion in tumor and matched non-tumor liver samples from North American patients with hepatitis and from Mozambiquan patients exposed to AFB. Mutations were detected in 5 of 6 samples of non-neoplastic liver from Mozambiquan patients, all of whom were HBsAg- or HBcAg-positive and AFB-exposed. In contrast, no mutations were detected in non-neoplastic liver from North American patients with either HBV- or HCV-derived hepatitis and cirrhosis. This procedure is a simple and powerful approach for screening p53 codon 249 AGT mutation in heterogeneous non-neoplastic hepatocyte populations.

Inhibition of hepatitis-B-virus core promoter by p53: implications for carcinogenesis in hepatocytes

The incidence of hepatocellular carcinoma (HCC) is particularly high in regions of Asia and sub-Saharan Africa where rates of infection with human hepatitis-B virus (HBV) and aflatoxin-B1 contamination of food are high. In HCC tumors occurring in inhabitants of these regions, a G-to-T mutation frequently occurs at position 249 of the tumor-suppressor gene p53. This suggests that HBV and p53 mutation may collaborate in the carcinogenic process in liver. We have examined the effect of the HBV protein HBX in HCC lines with exogenous wild-type p53 or mutated p53 on transactivation of 2 different reporter genes. Transfection of HCC lines with wild-type p53 and a reporter with the promoter from the p53-responsive gene WAF1/p21 resulted in a high level of expression, as expected. When cells were co-transfected with a reporter gene driven by the HBV core promoter and with the HBX gene, expression was enhanced in the Hep 3B, HLE, PLC/PRF/5 and HuH 7 lines, but not in the HuH 1 line. Co-transfection of the reporter with a plasmid containing wild-type p53 resulted in significant inhibition of the HBV core promoter in all of the lines, whereas the mutated p53 gene had no effect. Our results indicate that wild-type p53 can inhibit transcription from the HBV core promoter. In similar experiments, both HBX and p53 were co-transfected into HCC lines with the WAF1/p2l reporter gene. HBX inhibited p53-induced expression in 4 of the 6 lines (Hep 3B, HuH 1, HuH 7 and HLE), there was no effect in one line (HLF), and enhancement was evident in PLC/PRF/5. Our results indicate that inhibition of p53 transcriptional activity by HBX does occur in HCC, but is highly cell-context-dependent. Inhibition of transcription from the HBV core promoter by wild-type p53 appears to be more universal, and may represent a mechanism by which wild-type p53 can protect against the carcinogenic process in liver.

Mutation of p53 gene in hepatocellular carcinoma cell lines with HBX DNA

It has been known that the incidence of p53 mutation is very rare in HBX-positive primary human hepatocellular carcinoma (HCC) tissues. The frequency of p53 mutation, however, in established cell lines with integrated HBV DNA and/or HBX has not been well studied. To know p53 mutational frequency, and to investigate whether the presence of HBX DNA sequence correlates with the absence of p53 mutation in the established HCC cell lines, we studied the p53 mutation and the presence of HBX sequence in 12 recently characterized HCC cell lines. As a result, all 12 (100%) lines showed mutation in the p53 gene. Three (25%) cell lines had transversion of codon 215 while no mutation of codon 249 was found. In contrast with previous reports, although HBX DNA was present in 11 cell lines, p53 mutation had occurred, indicating that the presence of HBX viral DNA does not correlate with a lack of p53 mutation in established HCC cell lines. Our results suggest that the frequency of p53 mutation is extremely high even in HBX DNA positive HCC cell lines.

Interactions of the transcription factors MIBP1 and RFX1 with the EP element of the hepatitis B virus enhancer

We previously demonstrated that MIBP1 and RFX1 polypeptides associate in vivo to form a complex that binds to the MIF-1 element in the c-myc gene and the major histocompatibility complex class II X-box recognition sequence. We now show that the EP element, a key regulatory sequence within hepatitis B virus enhancer I, also associates with MIBP1 and RFX1. Using polyclonal antisera directed against either oligonucleotide-purified MIBP1 or a peptide derived from the major histocompatibility complex class II promoter-binding protein RFX1, we showed that MIBP1 and RFX1 are both present in the DNA-protein complexes at the EP site. In addition, while the EP element can act cooperatively with several adjacent elements to transactivate hepatitis B virus expression, we demonstrated that the EP site alone can repress transcription of simian virus 40 promoter in a position- and orientation-independent manner, suggesting a silencer function in hepatocarcinoma cells.

Infrequent mutations of the TP53 gene and no amplification of the MDM2 gene in hepatoblastomas

We have investigated the mutation of the TP53 gene in hepatoblastomas (HBLs) by using polymerase chain reaction-single strand conformation polymorphism and direct sequencing in 38 HBL tumor samples and in two HBL cell lines. We detected the TP53 gene mutation in an anaplastic hepatoblastoma cell line, but no aberration of the TP53 gene (exons 5-9) was found in tumor samples and in the other HBL cell line. The mutation of the cell line was a missense mutation from GAC (asparagine) to CAC (histidine) at codon 281, which was different from the G-to-T transversion of codon 249 that is frequently found in adult hepatocellular carcinomas (HCCs). In addition, we performed Southern blot analysis of the MDM2 gene, but we did not find MDM2 gene amplification in 19 cases tested. Our results suggest that, in contrast to the findings in HCCs in adults, TP53 gene aberrations are not involved in the development or progression of HBLs in children.

Low incidence of p53 mutations in European hepatocellular carcinomas with heterogeneous mutation as a rare event

BACKGROUND/AIMS

The aim of this study was to evaluate the role of p53 mutations in European hepatocarcinogenesis.

METHODS

DNA extracts from 20 microdissected tumor samples were investigated. Nucleotide sequence analysis of subcloned polymerase chain reaction-fragments of the conserved domain exons 5-8 was performed in order to detect heterogeneous distribution of p53 mutated cells within the tumors. In a screening procedure four clones of each exon 5-8 were analyzed. To confirm the observed mutations polymerase chain reaction and subcloning was repeated.

RESULTS

Sequence analysis confirmed a mutation in only two cases (10%). One at codon 220 (exon 6) was a homogeneous transition in nearly all clones from TAT to TGT. The other mutation was a transition from cGG to CAG at the known hot spot codon 248 (exon 7). It was found in 30% of the clones. We conclude that the other mutations from the first step were artefacts due to the infidelity of the taq-polymerase. All tumors had wild type sequence at the reported hot spot codon 249. The minor importance of p53 gene alterations in European hepatocarcinogenesis was further confirmed at the protein level by immunohistochemistry. Only the tumors with the heterogeneous p53 mutation at codon 248 showed a p53 overexpression in nearly 30% of the nuclei. None of the other tumors showed higher levels of p53 expression.

CONCLUSIONS

We therefore conclude that the incidence of p53 mutations in European hepatocellular carcinomas is very low. Generally there may be no heterogeneous distribution of p53 mutated cells within a tumor. The contribution of this genetic alteration to hepatocarcinogenesis in Europe seems of little importance.

p53 expression in patients with cirrhosis with and without hepatocellular carcinoma

BACKGROUND

Mutated p53 acts as a dominant oncogene, whereas the wild type (wt) p53 gene product suppresses cell growth. Abnormalities in the p53 gene are reported in more than 50% of malignant tumors. Recently, an allelic loss of chromosome 17p, where the p53 gene is located, was found to be more frequent in hepatocellular carcinoma (HCC) cell lines and human tumors. In addition, in half of the cases of HCC from endemic areas for hepatitis B virus and aflatoxin, a hot spot point mutation at codon 249 was detected, as previously reported. Missense mutations in p53, mdm-2 complex formation, and other unknown mechanisms may lead to stabilization of the gene product, thus rendering it detectable by immunohistochemistry.

METHODS

To assess the relationship between p53 status at a premalignant stage and in HCC, the authors studied the immunohistologic expression of p53 in HCC and in the adjacent nontumorous resected liver tissue, using monoclonal antibody to wt and mutated p53.

RESULTS

Twelve of the 14 patients with liver tumors had HCC. Of the 12 patients with HCC and underlying cirrhosis, 8 (67%) had increased p53 expression in HCC cells. Eight of the 12 patients with p53-positive HCC cells had p53 overexpression in the nontumorous hepatocytes within regenerative nodules adjacent to HCC tissue. Three of 21 cirrhotic livers without a detectable tumor had increased p53 expression in the regenerative nodules. None of the 12 patients with chronic active hepatitis without cirrhosis or the 13 with a normal liver histology had increased p53 expression.

CONCLUSION

p53 overexpression in some cirrhotic livers and in nontumorous livers of patients with HCC may indicate a normal p53 gene response to cellular stress or, alternatively, to an abnormally or mutated p53 gene, and could occur before the development of HCC.

Family history of cancer, body weight, and p53 nuclear overexpression in Duke's C colorectal cancer

To examine the hypothesis that colorectal carcinomas with and without TP53 mutations may be characterised by aetiological heterogeneity, we analysed a group of 107 patients with primary Dukes' C colorectal cancer seen at the Memorial Sloan-Kettering Cancer Center (MSKCC) from 1986 to 1990. We assessed p53 overexpression using the monoclonal antibody PAb 1801, and identified 42 (39%) patients displaying p53-positive phenotype, defined as > or = 25% of positive cells. Patients with two or more first-degree relatives with cancer had an odds ratio (OR) of 2.9 (95% CI 1.0-8.3) for p53 overexpression in comparison with those without a family history of cancer (trend test, P = 0.11). A possible association between body weight and p53 overexpression was observed. The ORs were 1.9 for the second quartile, 1.9 for the third quartile and 3.4 for the highest quartile in comparison with the lowest quartile (trend test, P = 0.06). No association between occupational physical activity, smoking, drinking, parity and p53 overexpression was identified. The results suggest that p53 overexpression may be related to genetic predisposition to colorectal cancer, and p53-positive and p53-negative colorectal cancers may be controlled by different aetiological pathways.

p53-mediated cellular response to DNA damage in cells with replicative hepatitis B virus

Wild-type p53 acts as a tumor suppressor gene by protecting cells from deleterious effects of genotoxic agents through the induction of a G1/S arrest or apoptosis as a response to DNA damage. Transforming proteins of several oncogenic DNA viruses inactivate tumor suppressor activity of p53 by blocking this cellular response. To test whether hepatitis B virus displays a similar effect, we studied the p53-mediated cellular response to DNA damage in 2215 hepatoma cells with replicative hepatitis B virus. We demonstrate that hepatitis B virus replication does not interfere with known cellular functions of p53 protein.

Extensive oxidative DNA damage in hepatocytes of transgenic mice with chronic active hepatitis destined to develop hepatocellular carcinoma

A transgenic mouse strain that expresses the hepatitis B virus (HBV) large envelope protein in the liver was used to determine the extent of oxidative DNA damage that occurs during chronic HBV infection. This mouse strain develops a chronic necroinflammatory liver disease that mimics the inflammation, cellular hyperplasia, and increased risk for cancer that is evident in human chronic active hepatitis. When perfused in situ with nitroblue tetrazolium, an indicator for superoxide formation, the liver of transgenic mice displayed intense formazan deposition in Kupffer cells, indicating oxygen radical production, and S-phase hepatocytes were commonly seen adjacent to the stained Kupffer cells. Similar changes were not observed in nontransgenic control livers. To determine whether these events were associated with oxidative DNA damage, genomic DNA from the livers of transgenic mice and nontransgenic controls was isolated and examined for 8-oxo-2'-deoxyguanosine, an oxidatively modified adduct of deoxyguanosine. Results showed a significant, sustained accumulation in steady-state 8-oxo-2'-deoxyguanosine that started early in life exclusively in the transgenic mice and increased progressively with advancing disease. The most pronounced increase occurred in livers exhibiting microscopic nodular hyperplasia, adenomas, and hepatocellular carcinoma. Thus, HBV transgenic mice with chronic active hepatitis display greatly increased hepatic oxidative DNA damage. Moreover, the DNA damage occurs in the presence of heightened hepatocellular proliferation, increasing the probability of fixation of the attendant genetic and chromosomal abnormalities and the development of hepatocellular carcinoma.

Comparative biology and pathogenesis of AIDS and hepatitis B viruses: related but different

AIDS (HIV) and hepatitis B viruses are remarkably similar in their sharing of reverse transcription, in their ancestral origins and common genetic elements, and in their modes of transmission. Both are hypermutable and exist as quasispecies due primarily to errors in reverse transcription, though there is severe restriction in the replicative competence of most hepatitis B mutants. They differ in the lack of an integrase in hepatitis B virus and in their pathogenesis in the infected host. HIV survives mainly by antigenic variability, immune evasion, and impairment of immune function though viral regulatory control elements seek to restrict fatal damage to the host. Hepatitis B virus survives primarily by mutation of e antigen/core genes that directly obviates cytotoxic T cell destruction of infected liver cells, or indirectly limits destruction of infected cells through induction of anergy in the cytotoxic T cell response. Most persons infected with hepatitis B virus recover completely while recovery from HIV infection is rare if ever. Hepatitis B is highly preventable by vaccine while HIV vaccine is still seeking a meaningful immunoprophylactic target. AIDS and hepatitis B represent an extreme example, among the viruses of man, in their close similarities but distinct differences. In depth details and perspectives are presented in this review.

Development and characterization of recombinant adenoviruses encoding human p53 for gene therapy of cancer

We have constructed recombinant human adenoviruses that express wild-type human p53 under the control of either the Ad 2 major late promoter (MLP) or the human cytomegalovirus (CMV) immediate early gene promoter. Each construct replaces the Ad 5 E1a and E1b coding sequences necessary for viral replication with the p53 cDNA and MLP or CMV promoter. These p53/Ad recombinants are able to express p53 protein in a dose-dependent manner in infected human cancer cells. Tumor suppressor activity of the expressed p53 protein was assayed by several methods. [3H]Thymidine incorporation assays showed that the recombinant adenoviruses were capable of inhibiting DNA synthesis in a p53-specific, dose-dependent fashion. Ex vivo treatment of Saos-2 tumor cells, followed by injection of the treated cells into nude mice, led to complete tumor suppression using the MLP/p53 recombinant. Following a single injection of CMV/p53 recombinant adenovirus into the peritumoral space surrounding an in vivo established tumor derived from a human small cell lung carcinoma cell line (NIH-H69), we were able to detect p53 mRNA in the tumors at 2 and 7 days post-injection. Continued treatment of established H69 tumors with MLP/p53 recombinant led to reduced tumor growth and increased survival time compared to control treated animals. These results indicate that recombinant adenoviruses expressing wild-type p53 may be useful vectors for gene therapy of human cancer.

Overexpression and point mutations of p53 tumor suppressor gene in hepatocellular carcinomas in Hong Kong Chinese people

BACKGROUND

Gene deletion, point mutations, and abnormalities in expression of the tumor suppressor gene p53 in hepatocellular carcinoma have been reported to occur with varying frequency in different geographic regions.

METHODS

To assess the expression and point mutation of the p53 gene, 31 patients with hepatocellular carcinomas were examined using Northern blotting, immunohistochemical methods, and DNA sequencing. All patients were Chinese, and 90.3% were positive for hepatitis B surface antigen (HBsAg).

RESULTS

p53 transcript or protein was found in 14 (48.4%) of the 31 patients. Detectable p53 mRNA transcripts were found in 10 patients, and p53 protein was detected in 8 patients. In most cases of patients who had detectable p53 mRNA transcripts, the transcripts in the tumors were exhibited at a higher level than they were in the corresponding nontumorous livers. No p53 protein was detected in the nontumorous livers in all 31 patients. Six (23.1%) of the 26 tumors sequenced showed point mutation scattered in exons 5-9. Of these, only two were at codon-249, and the nature of these two mutations was G-to-T transversions. All but one of the six patients with point mutations had overexpression of the gene.

CONCLUSIONS

Our results show that scattered point mutations are not uncommon in hepatocellular carcinomas in patients from Hong Kong. The distribution pattern of the mutations seems to have no particular correlation with HBsAg status despite a high prevalence rate of HBsAg positivity in our patients. Consistent with a low aflatoxin exposure, aflatoxin-related specific mutation at codon-249 is much less related to the pathogenesis of hepatocellular carcinoma in Hong Kong Chinese people than in other regions with a high-aflatoxin exposure.

Prostaglandin E1 increases survival with extended anhepatic phase during liver transplantation

OBJECTIVE

The authors investigated the intraoperative treatment effects of Prostaglandin E1 (PGE1) for extension of the anhepatic phase and improvement of survival in a rat liver transplant model.

BACKGROUND

Cross-clamping the inferior vena cava and the portal vein during liver transplantation causes severe pathophysiologic changes during surgery. The time of the anhepatic phase is strictly limited and results in a very tenuous period during the liver transplant operation.

METHODS

Prostaglandin E1 was infused at 0.5 microgram/kg/min into five subgroups of rats with 20, 30, 40, 60, and 80 minutes of anhepatic phase during transplantation. Bile secretion, serum aspartate transaminase (AST), lactic dehydrogenase (LDH), and blood gas analysis were studied in the 30-minute subgroup. The results were compared with the sham-operated and control groups.

RESULTS

Intraoperative treatment with PGE1 extended the maximal anhepatic phase from 30 minutes in the sham-operated group up to 80 minutes, and increased survival. Significant changes in the PGE1 treated rats in the 30-minute subgroup included an increase of bile flow and bile salt output and decrease of AST and LDH activities after surgery. Blood gas analysis showed a decrease in acidosis and hypercarbia at the end of the anhepatic phase.

CONCLUSIONS

The PGE1 treatment increased survival with extended anhepatic phase during rat liver transplantation. The beneficial effects can be attributed to its biologic activities.

Hepatitis B virus X protein inhibits p53 sequence-specific DNA binding, transcriptional activity, and association with transcription factor ERCC3

Chronic active hepatitis caused by infection with hepatitis B virus, a DNA virus, is a major risk factor for human hepatocellular carcinoma. Since the oncogenicity of several DNA viruses is dependent on the interaction of their viral oncoproteins with cellular tumor-suppressor gene products, we investigated the interaction between hepatitis B virus X protein (HBX) and human wild-type p53 protein. HBX complexes with the wild-type p53 protein and inhibits its sequence-specific DNA binding in vitro. HBX expression also inhibits p53-mediated transcriptional activation in vivo and the in vitro association of p53 and ERCC3, a general transcription factor involved in nucleotide excision repair. Therefore, HBX may affect a wide range of p53 functions and contribute to the molecular pathogenesis of human hepatocellular carcinoma.

Bromobenzene detoxification in the human liver-derived HepG2 cell line

1. The applicability of the human hepatoma cell line, HepG2, as a cell culture model for studying xenobiotic liver toxicity has been investigated using the well-characterized hepatotoxic chemical, bromobenzene. 2. Bromobenzene caused a concentration- (0-10 mM) and time-dependent (0-180 min) decrease in HepG2 cell viability. The degree of toxicity was dependent upon the culture medium composition and the state of cell growth. Toxicity in Modified Earle's and Williams' E Media was maximal at 7 days growth compared with 3 and 10 days, and was greater in Williams' than in Earle's medium. Toxicity in Dulbecco's medium was apparent only at 10 days growth and was less than the maximum toxicity in the other media. 3. Bromobenzene was detoxified by epoxide hydrase. The question of metabolic activation by P450 remained unresolved, but any involvement of P450 was by forms not inhibited by ketoconazole. 4. The mechanism of bromobenzene toxicity did not appear to involve lipid peroxidation, depletion of reduced glutathione, calcium-mediated proteolysis or metabolic activation by prostaglandin synthetase, but may have involved direct solvent-induced cell damage. 5. This study demonstrates the potential usefulness of HepG2 cells in toxicity testing and highlights the importance of standardizing culture conditions.

Historical origins of current concepts of carcinogenesis

The first attempts to understand the causes of cancer were based on generalizations of what might now be termed a "holistic" nature, and hereditary influences were recognized at an early stage; these views survive principally through a supposed positive connection between psychological factors such as stress and diminished ability to combat the progressive development of tumors through some form of immunologically mediated rejection of potentially cancerous cells. While evidence for immunosurveillance is generally accepted, it is now widely regarded as almost wholly confined to instances where tumor viruses are involved as causative agents. The earliest theorists drew an analogy between the processes of carcinogenesis and of evolution; the cancer cells acquired the ability to outstrip their normal counterparts in their capacity for proliferation. This was even before evolution had been interpreted as involving a continuous succession of mutations. Evidence was already to hand before the end of the 18th century that exogenous agents, notably soot, a product of the "industrial revolution," could cause skin cancer. Somewhat over 100 years later, another industrial innovation, the manufacture of synthetic dyestuffs, implicated specific chemical compounds that could act systemically to cause bladder cancer. Meanwhile, the 19th century saw the establishment of the fundamentals of modern medical science; of particular relevance to cancer was the demonstration that it involved abnormalities in the process of cell division. The commencement of the 20th century was marked by a rediscovery of the concept of mutation; and it was proposed that cancer originated through uncontrolled division of somatically mutated cells. At around this time, two further important exogenous causative agents were discovered: X-rays and tumor viruses. In the late 1920s, x-radiation became the first established exogenous cause of mutagenesis. The discoverer of this phenomenon, H. J. Muller, suggested that while mutation in a single cell was the primary causative mechanism in carcinogenesis, its generally observed logarithmic increase in incidence with age reflected a "multihit" process, and that multiple successive mutations were required in the progeny of the original mutants. He also recognized that the rate of proliferation of potentially cancerous cells would markedly influence the probability of their subsequent mutation. These considerations are essentially the foundation of the generally accepted view of carcinogenesis that now seems unlikely to be superseded. However, this acceptance did not come about unopposed. The analogy between carcinogenesis and evolution was disliked by many biologists because it embodied the concept that cancer was an inevitable consequence of our evolutionary origins.(ABSTRACT TRUNCATED AT 400 WORDS)