Nonrandom cytogenetic alterations in hepatocellular carcinoma from transgenic mice overexpressing c-Myc and transforming growth factor-alpha in the liver

MicroRNA-25 Exerts an Oncogenic Function by Regulating the Ubiquitin Ligase Fbxw7 in Hepatocellular Carcinoma

BACKGROUND

MicroRNA (miRNA) expression abnormalities are implicated in tumor progression. Previous reports have indicated that microRNA-25 (miR-25) acts as a tumor suppressor or oncogene in diverse cancers. However, its molecular mechanisms in hepatocellular carcinoma (HCC) are still unclear. F-box and WD repeat domain 7 (Fbxw7) is a critical tumor suppressor and is one of the most important deregulated proteins of the ubiquitin-proteasome system in cancer. Our objective was to elucidate the role of miR-25 and Fbxw7 in HCC and to clarify the mechanism by which Fbxw7 is regulated.

METHODS

Fbxw7 expression was estimated in 210 fixed paraffin-embedded HCC samples by immunohistochemistry, and miR-25 expression was evaluated in 142 frozen HCC tissue samples by quantitative real-time PCR. Oncogenic functions of miR-25 and its role in the regulation of Fbxw7 expression were assayed in vitro.

RESULTS

miR-25 was overexpressed in HCC tissue compared with adjacent normal tissue and significantly correlated with a poorer prognosis. Moreover, it was inversely correlated with Fbxw7 expression in HCC tissues. Furthermore, miR-25 inhibition significantly reduced the proliferation, migration, and invasion of HCC cells in vitro.

CONCLUSION

miR-25 may promote tumor progression in HCC patients by repression of Fbxw7 and could serve as a promising molecular target for HCC treatment.

The epicenter of chromosomal fragility of Fra14A2, the mouse ortholog of human FRA3B common fragile site, is largely attached to the nuclear matrix in lymphocytes but not in other cell types that do not express such a fragility

Common fragile sites (CFSs) correspond to chromosomal regions susceptible to present breaks, discontinuities or constrictions in metaphase chromosomes from cells subjected to replication stress. They are considered as genomic regions intrinsically difficult to replicate and they are evolutionary conserved at least in mammals. However, the recent discovery that CFSs are cell-type specific indicates that DNA sequence by itself cannot account for CFS instability. Nevertheless, the large gene FHIT that includes FRA3B, the most highly expressed CFS in human lymphocytes, is commonly deleted in a variety of tumors suggesting a tumor suppressor role for its product. Here, we report that the epicenter of fragility of Fra14A2/Fhit, the mouse ortholog of human FRA3B/FHIT that like its human counterpart is the most highly expressed CFS in mouse lymphocytes, is largely attached to the nuclear matrix compartment in naive B lymphocytes but not in primary hepatocytes or cortical neurons that do not express such a CFS. Our results suggest a structural explanation for the difficult-to-replicate nature of such a region and so for its common fragility in lymphocytes, that is independent of the possible tumor suppressor role of the gene harboring such CFS.

Patient-derived multicellular tumor spheroids towards optimized treatment for patients with hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is one of the most common malignant tumors worldwide and has poor prognosis. Specially, patients with HCC usually have poor tolerance of systemic chemotherapy, because HCCs develop from chronically damaged tissue that contains considerable inflammation, fibrosis, and cirrhosis. Since HCC exhibits highly heterogeneous molecular characteristics, a proper in vitro system is required for the study of HCC pathogenesis. To this end, we have established two new hepatitis B virus (HBV) DNA-secreting HCC cell lines from infected patients.

Methods

Based on these two new HCC cell lines, we have developed chemosensitivity assays for patient-derived multicellular tumor spheroids (MCTSs) in order to select optimized anti-cancer drugs to provide more informative data for clinical drug application. To monitor the effect of the interaction of cancer cells and stromal cells in MCTS, we used a 3D co-culture model with patient-derived HCC cells and stromal cells from human hepatic stellate cells, human fibroblasts, and human umbilical vein endothelial cells to facilitate screening for optimized cancer therapy.

Results

To validate our system, we performed a comparison of chemosensitivity of the three culture systems, which are monolayer culture system, tumor spheroids, and MCTSs of patient-derived cells, to sorafenib, 5-fluorouracil, and cisplatin, as these compounds are typically standard therapy for advanced HCC in South Korea.

Conclusion

In summary, these findings suggest that the MCTS culture system is the best methodology for screening for optimized treatment for each patients with HCC, because tumor spheroids not only mirror the 3D cellular context of the tumors but also exhibit therapeutically relevant pathophysiological gradients and heterogeneity of in vivo tumors.

Electronic supplementary material

The online version of this article (10.1186/s13046-018-0752-0) contains supplementary material, which is available to authorized users.

MicroRNA-92a contributes to tumor growth of human hepatocellular carcinoma by targeting FBXW7

Deregulation of microRNA-92a (miR-92a) has been reported in several human cancers and is associated with prognosis of patients. However, the clinical significance of miR-92a and the underlying mechanisms involved in hepatocarcinogenesis remain to be determined. The aim of the present study was to determine the role of miR-92a in hepatocellular carcinoma (HCC). The results showed that the expression of miR-92a was upregulated in HCC tissues as compared with matched tumor-adjacent tissues. A high expression of miR-92a was observed in HCC cell lines as compared with a non-transformed hepatic cell line. The gain- and loss-of-function studies revealed that miR-92a significantly promoted proliferation and cell cycle transition from G1 to S phase, and inhibited apoptosis of HCC cell in vitro. In tumor‑bearing nude mice, the downregulation of miR-92a suppressed tumor growth of HCC in vivo. miR-92a was inversely correlated with F-box and WD repeat domain-containing 7 (FBXW7) expression in HCC tissues. Furthermore, miR-92a negatively regulated FBXW7 abundance in HCC cells. In the present study, FBXW7 was identified as a direct target of miR-92a. Notably, alterations of FBXW7 expression abrogated the effects of miR-92a on HCC cell proliferation, cell cycle and apoptosis. Clinical association analysis revealed that a high expression of miR-92a was correlated with poor prognostic characteristics of HCC. Notably, the high expression of miR-92a conferred a reduced 5-year overall survival (OS) and recurrence-free survival (RFS) of HCC patients. The multivariate Cox regression analysis demonstrated that miR-92a expression was an independent prognostic marker for predicting survival of HCC patients. In conclusion, the results of the present study suggested that miR-92a promotes the tumor growth of HCC by targeting FBXW7 and may serve as a novel prognostic biomarker and therapeutic target for HCC.

Role of DLC1 tumor suppressor gene and MYC oncogene in pathogenesis of human hepatocellular carcinoma: potential prospects for combined targeted therapeutics (review)

Hepatocellular carcinoma (HCC) is the third leading cause of cancer death, and its incidence is increasing worldwide in an alarming manner. The development of curative therapy for advanced and metastatic HCC is a high clinical priority. The HCC genome is complex and heterogeneous; therefore, the identification of recurrent genomic and related gene alterations is critical for developing clinical applications for diagnosis, prognosis and targeted therapy of the disease. This article focuses on recent research progress and our contribution in identifying and deciphering the role of defined genetic alterations in the pathogenesis of HCC. A significant number of genes that promote or suppress HCC cell growth have been identified at the sites of genomic reorganization. Notwithstanding the accumulation of multiple genetic alterations, highly recurrent changes on a single chromosome can alter the expression of oncogenes and tumor suppressor genes (TSGs) whose deregulation may be sufficient to drive the progression of normal hepatocytes to malignancy. A distinct and highly recurrent pattern of genomic imbalances in HCC includes the loss of DNA copy number (associated with loss of heterozygosity) of TSG-containing chromosome 8p and gain of DNA copy number or regional amplification of protooncogenes on chromosome 8q. Even though 8p is relatively small, it carries an unusually large number of TSGs, while, on the other side, several oncogenes are dispersed along 8q. Compelling evidence demonstrates that DLC1, a potent TSG on 8p, and MYC oncogene on 8q play a critical role in the pathogenesis of human HCC. Direct evidence for their role in the genesis of HCC has been obtained in a mosaic mouse model. Knockdown of DLC1 helps MYC in the induction of hepatoblast transformation in vitro, and in the development of HCC in vivo. Therapeutic interventions, which would simultaneously target signaling pathways governing both DLC1 and MYC functions in hepatocarcinogenesis, could result in progress in the treatment of liver cancer.

Genomic modeling of tumor onset and progression in a mouse model of aggressive human liver cancer

A comprehensive understanding of molecular mechanisms driving cancer onset and progression should provide a basis for improving early diagnosis, biomarker discovery and treatment options. A key value of genetically engineered mice for modeling human cancer is the possibility to analyze the entire process of tumor development. Here, we applied functional genomics approach to study step-by-step development of hepatocellular carcinoma (HCC) in the c-Myc/Tgfα transgenic mouse model of aggressive human liver cancer. We report that coexpression of c-Myc and Tgfα induces progressive and cumulative transcriptional alterations in the course of liver oncogenesis. Functional analysis of deregulated genes at the early stage of HCC disease supports a model of active hepatocyte proliferation on the background of chronic oxidative stress generated by a general metabolic disorder. In addition, early and persistent deregulation of numerous immune-related genes suggested that disruption of immune microenvironment may contribute to oncogenic process in this model of accelerated liver carcinogenesis. In particularly, by flow cytometry analysis, we found loss of the major histocompatibility complex class I expression in dysplastic hepatocytes followed by upregulation of numerous activating ligands for natural killer (NK) cells concomitant with a drastic decrease in hepatic NK cell frequency. In conclusion, our study provides a comprehensive characterization of sequential molecular changes during a stepwise progression of preneoplastic lesions toward HCC and highlights a critical role of metabolic disorders and innate immunity at the early stages of liver cancer.

Functional interactions between retinoblastoma and c-MYC in a mouse model of hepatocellular carcinoma

Inactivation of the RB tumor suppressor and activation of the MYC family of oncogenes are frequent events in a large spectrum of human cancers. Loss of RB function and MYC activation are thought to control both overlapping and distinct cellular processes during cell cycle progression. However, how these two major cancer genes functionally interact during tumorigenesis is still unclear. Here, we sought to test whether loss of RB function would affect cancer development in a mouse model of c-MYC-induced hepatocellular carcinoma (HCC), a deadly cancer type in which RB is frequently inactivated and c-MYC often activated. We found that RB inactivation has minimal effects on the cell cycle, cell death, and differentiation features of liver tumors driven by increased levels of c-MYC. However, combined loss of RB and activation of c-MYC led to an increase in polyploidy in mature hepatocytes before the development of tumors. There was a trend for decreased survival in double mutant animals compared to mice developing c-MYC-induced tumors. Thus, loss of RB function does not provide a proliferative advantage to c-MYC-expressing HCC cells but the RB and c-MYC pathways may cooperate to control the polyploidy of mature hepatocytes.

Evolution of genomic instability in diethylnitrosamine-induced hepatocarcinogenesis in mice

Diethylnitrosamine (DEN) is a hepatic procarcinogen which is frequently used as an inducer of hepatocellular carcinoma (HCC) in mice. Although mice after DEN exposure are among the most widely used models for liver tumorigenesis, a detailed, mechanistic characterization of the longitudinal changes in the respective tumor genomes has never been performed. Here we established the chronological order of genetic alterations during DEN carcinogenesis by examining mice at different points in time. Tumor samples were isolated by laser microdissection and subjected to array-comparative genomic hybridization (array-CGH) and sequencing analysis. Chromosomal gains and losses were observed in tumors by week 32 and increased significantly by week 56. Loss of distal chromosome 4q, including the tumor suppressors Runx3 and Nr0b2/Shp, was a frequent early event and persisted during all tumor stages. Surprisingly, sequencing revealed that β-catenin mutations occurred late and were clearly preceded by chromosomal instability. Thus, contrary to common belief, β-catenin mutations and activation of the Wnt/β-catenin pathway are not involved in tumor initiation in this model of chemical hepatocarcinogenesis.

CONCLUSION

Our study suggests that the majority of the current knowledge about genomic changes in HCC is based on advanced tumor lesions and that systematic analyses of the chronologic order including early lesions may reveal new, unexpected findings.

Gain of MYC underlies recurrent trisomy of the MYC chromosome in acute promyelocytic leukemia

The leukemogenic effects of Myc drive recurrent trisomy in a mouse model of acute myeloid leukemia.

Gain of chromosome 8 is the most common chromosomal gain in human acute myeloid leukemia (AML). It has been hypothesized that gain of the MYC protooncogene is of central importance in trisomy 8, but the experimental data to support this are limited and controversial. In a mouse model of promyelocytic leukemia in which the MRP8 promoter drives expression of the PML-RARA fusion gene in myeloid cells, a Myc allele is gained in approximately two-thirds of cases as a result of trisomy for mouse chromosome 15. We used this model to test the idea that MYC underlies acquisition of trisomy in AML. We used a retroviral vector to drive expression of wild-type, hypermorphic, or hypomorphic MYC in bone marrow that expressed the PML-RARA transgene. MYC retroviruses cooperated in myeloid leukemogenesis and suppressed gain of chromosome 15. When the PML-RARA transgene was expressed in a Myc haploinsufficient background, we observed selection for increased copies of the wild-type Myc allele concomitant with leukemic transformation. In addition, we found that human myeloid leukemias with trisomy 8 have increased MYC. These data show that gain of MYC can contribute to the pathogenic effect of the most common trisomy of human AML.

Quantifying growth and transformation frequency of oncogene-expressing mouse hepatocytes in vivo

Gene changes can affect cancer cells in many ways, but changes that increase disease severity--by allowing cells to proliferate when they should be quiescent, by enhancing their rate of growth under growth permissive conditions, or by increasing the risk that they will accumulate additional carcinogenic alterations--must be identified so that strategies to counter their effects can be developed. We describe a novel in vivo assay system based on hepatocyte transplantation that permits us to accomplish this objective for genetically modified hepatocytes. We find that the oncogenes c-myc and transforming growth factor alpha, but not simian virus 40 T-antigen, increase the rate of hepatocyte growth under growth permissive conditions. However, no single oncogene can induce hepatocyte growth in quiescent liver. In contrast, at least one oncogene combination, transforming growth factor alpha/T-antigen, was sufficient to direct cell autonomous growth even in this nonpermissive environment. Furthermore, we could quantify risk for progression to neoplasia associated with oncogene expression; increased transformation frequency was the principal carcinogenic effect of T-antigen.

CONCLUSION

This system identifies biological mechanistic role(s) in carcinogenesis for candidate genetic changes implicated in development of human liver cancer. The quantitative and comparative evaluation of gene effects on liver cancer allows us to prioritize targets for therapeutic intervention.

Transgenic oncogenes induce oncogene-independent cancers with individual karyotypes and phenotypes

Cancers are clones of autonomous cells defined by individual karyotypes, much like species. Despite such karyotypic evidence for causality, three to six synergistic mutations, termed oncogenes, are generally thought to cause cancer. To test single oncogenes, they are artificially activated with heterologous promoters and spliced into the germ line of mice to initiate cancers with collaborating spontaneous oncogenes. Because such cancers are studied as models for the treatment of natural cancers with related oncogenes, the following must be answered: 1) which oncogenes collaborate with the transgenes in cancers; 2) how do single transgenic oncogenes induce diverse cancers and hyperplasias; 3) what maintains cancers that lose initiating transgenes; 4) why are cancers aneuploid, over- and underexpressing thousands of normal genes? Here we try to answer these questions with the theory that carcinogenesis is a form of speciation. We postulate that transgenic oncogenes initiate carcinogenesis by inducing aneuploidy. Aneuploidy destabilizes the karyotype by unbalancing teams of mitosis genes. This instability thus catalyzes the evolution of new cancer species with individual karyotypes. Depending on their degree of aneuploidy, these cancers then evolve new subspecies. To test this theory, we have analyzed the karyotypes and phenotypes of mammary carcinomas of mice with transgenic SV40 tumor virus- and hepatitis B virus-derived oncogenes. We found that (1) a given transgene induced diverse carcinomas with individual karyotypes and phenotypes; (2) these karyotypes coevolved with newly acquired phenotypes such as drug resistance; (3) 8 of 12 carcinomas were transgene negative. Having found one-to-one correlations between individual karyotypes and phenotypes and consistent coevolutions of karyotypes and phenotypes, we conclude that carcinogenesis is a form of speciation and that individual karyotypes maintain cancers as they maintain species. Because activated oncogenes destabilize karyotypes and are dispensable in cancers, we conclude that they function indirectly, like carcinogens. Such oncogenes would thus not be valid models for the treatment of cancers.

Prognostic markers and putative therapeutic targets for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the fifth most frequent human cancer and a fatal disease. Therapies with pharmacological agents do not improve the prognosis of patients with unresectable HCC. This emphasizes the need to identify new targets for early diagnosis, chemoprevention, and treatment of the disease. Available evidence indicates that clinical outcome of HCC could reflect the genetic predisposition to cancer development and progression. Numerous loci controlling HCC progression have been identified in rodents. In this review, we describe results of recent studies on effector mechanisms of susceptibility/resistance genes, responsible for HCC progression, aimed at identifying new putative prognostic markers and therapeutic targets of this tumor. Highest c-myc amplification and overexpression, alterations of iNOS crosstalk with IKK/NF-kB and RAS/ERK signaling, ubiquitination of ERK and cell cycle inhibitors, and deregulation of FOXM1 and cell cycle key genes occur in rapidly progressing dysplastic nodules and HCC, induced in genetic susceptible rat strains, compared to the lesions of resistant rats. Notably, alterations of these mechanisms in human HCC subtypes with poorer or better prognosis, are similar to those present in genetically susceptible and resistant rats, respectively, and function as prognostic markers and therapeutic targets. Attempts to cure advanced HCC by molecular therapy directed against specific targets led to modest survival benefit. Thus, efforts are necessary to identify and test, in pre-clinical and clinical studies, new therapeutic targets for combined molecular treatments of HCC. They may take advantage from the comparative analysis of signal transduction in HCCs differently prone to progress, in rats and humans.

Recurrent and nonrandom DNA copy number and chromosome alterations in Myc transgenic mouse model for hepatocellular carcinogenesis: implications for human disease

Mouse models for hepatocellular carcinoma (HCC) provide an experimental ground for dissecting the genetic and biological complexities of human liver cancer and contribute to our ability to gain insights into the relevance of candidate cancer genes. We examined, using spectral karyotyping (SKY) and array-based CGH (aCGH), seven cell lines derived from HCC spontaneously developed in transgenic Myc mice (Myc), and four cell lines established from tumors induced in nude mice by inoculation with the original Myc cells (nuMyc). All the cell lines exhibited gain of material from chromosomes 5, 6, 8, 10, 11, 15, and 19 and DNA copy-number loss from chromosomes 2, 4, 7, 9, 12, 14, and X. In addition, several recurrent chromosome reorganizations were found, including del(3), t(3;8), del(4), t(4;11), t(6;5), del(7), del(8), del(9), t(10;14), del(11), and del(16). Chromosome breakpoints underlying rearrangements clustered in the regions previously identified as important for the early stages of Myc-induced hepatocarcinogenesis. The results strongly suggest the importance of recurrent breakage and loss of chromosomes 4, 9, and 14 and gain of chromosomes 15 and 19 in mouse liver neoplasia. Genomic changes observed in Myc HCC cell lines are also recurrent in HCC developed in other transgenic mouse models, in mouse spontaneous HCC and derivative cell lines, and in preneoplastic liver lesions induced with chemical carcinogens. Overall, the present results document selective, nonrandom genomic changes involving chromosomal regions homologous to those implicated in human HCC.

Production of C5a by ASP, a serine protease released from Aeromonas sobria

Aeromonas sobria causes pus and edema at sites of infection. However, the mechanisms underlying these effects have not been elucidated. C5a, the amino-terminal fragment of the complement 5th component (C5), mimics these events. To investigate the involvement of C5a in the pathophysiology of A. sobria infection, we examined release of C5a from human C5 by a serine protease (ASP), a putative virulence factor secreted by this bacterium. C5 incubated with enzymatically active ASP induced neutrophil migration in a dose-dependent manner from an ASP concentration of 3 nM and in an incubation time-dependent manner in as little as 7 min, with neutrophil accumulation in guinea pigs at intradermal injection sites and neutrophil superoxide release. These effects on neutrophils were inhibited by a C5a-receptor antagonist. The ASP incubation mixture with C5 but not C3 elicited vascular leakage in a dose- and incubation time-dependent manner, which was inhibited by a histamine H(1)-receptor antagonist. Together with these C5a-like activities, ASP cleaved C5 to release only one C5a Ag, the m.w. of which was similar to that of C5a. Immunoblotting using an anti-C5a Ab revealed generation of a C5a-like fragment from human plasma incubated with ASP. These results suggest that ASP-elicited neutrophil migration and vascular leakage via C5a production from C5 could occur in vivo, which was supported by that ASP did not affect functions of C5a and neutrophil C5a receptor. Through C5a generation, ASP could be associated with the induction of pus and edema caused by infection with this bacterium.

Decoding human liver cancer signatures

Because alterations of expression patterns and genomic copy numbers of thousands of genes are fundamental properties of cancer cells, and the application of high-throughput microarray-based genomic technologies for the analysis of cancer inevitably generate many false-positive results, it is rarely possible to select a reasonable number of candidate genes for therapeutic targets and/or biomarkers for diagnosis and prognosis. Therefore, it will be necessary to devise new experimental and analytical strategies to overcome this problem. This review summarizes recent advances in gene expression profiling of hepatocellular carcinoma and discusses future strategies for analyzing large and complicated data sets from microarray studies and how to integrate these with diverse genomic data.

Chromosomal changes in high- and low-invasive mouse lung adenocarcinoma cell strains derived from early passage mouse lung adenocarcinoma cell strains

The incidence of adenocarcinoma of the lung is increasing in the United States, however, the difficulties in obtaining lung cancer families and representative samples of early to late stages of the disease have lead to the study of mouse models for lung cancer. We used Spectral Karyotyping (SKY), mapping with fluorescently labeled genomic clones (FISH), comparative genomic hybridization (CGH) arrays, gene expression arrays, Western immunoblot and real time polymerase chain reaction (PCR) to analyze nine pairs of high-invasive and low-invasive tumor cell strains derived from early passage mouse lung adenocarcinoma cells to detect molecular changes associated with tumor invasion. The duplication of chromosomes 1 and 15 and deletion of chromosome 8 were significantly associated with a high-invasive phenotype. The duplication of chromosome 1 at band C4 and E1/2-H1 were the most significant chromosomal changes in the high-invasive cell strains. Mapping with FISH and CGH array further narrowed the minimum region of duplication of chromosome 1 to 71-82 centimorgans (cM). Expression array analysis and confirmation by real time PCR demonstrated increased expression of COX-2, Translin (TB-RBP), DYRK3, NUCKS and Tubulin-alpha4 genes in the high-invasive cell strains. Elevated expression and copy number of these genes, which are involved in inflammation, cell movement, proliferation, inhibition of apoptosis and telomere elongation, were associated with an invasive phenotype. Similar linkage groups are altered in invasive human lung adenocarcinoma, implying that the mouse is a valid genetic model for the study of the progression of human lung adenocarcinoma.

Hepatocellular carcinoma pathogenesis: from genes to environment

Hepatocellular carcinoma is among the most lethal and prevalent cancers in the human population. Despite its significance, there is only an elemental understanding of the molecular, cellular and environmental mechanisms that drive disease pathogenesis, and there are only limited therapeutic options, many with negligible clinical benefit. This Review summarizes the current state of knowledge of this, the most common and dreaded liver neoplasm, and highlights the principal challenges and scientific opportunities that are relevant to controlling this accelerating global health crisis.

Comparative and integrative functional genomics of HCC

Global gene expression profiling of hepatocellular carcinoma (HCC) is a promising new technology that has already refined the diagnosis and prognostic predictions of HCC patients. This has been accomplished by identifying genes whose expression pattern is associated with clinicopathological features of HCC tumors. Molecular characterization of HCC from gene expression profiling studies will undoubtedly improve the prediction of treatment responses, selection of treatments for specific molecular subtypes of HCC and ultimately the clinical outcome of HCC patients. The research focus is now shifting toward the identification of genetic determinants that are components of the specific regulatory pathways altered in cancers, and that may constitute novel therapeutic targets. Here we review the recent advances in gene expression profiling of HCC and discuss the future strategies for analysing large and complicated data sets from microarray studies and how to integrate these with diverse genomic data.

c-Myc, genome instability, and tumorigenesis: the devil is in the details

The c-myc oncogene acts as a pluripotent modulator of transcription during normal cell growth and proliferation. Deregulated c-myc activity in cancer can lead to excessive activation of its downstream pathways, and may also stimulate changes in gene expression and cellular signaling that are not observed under non-pathological conditions. Under certain conditions, aberrant c-myc activity is associated with the appearance of DNA damage-associated markers and karyotypic abnormalities. In this chapter, we discuss mechanisms by which c-myc may be directly or indirectly associated with the induction of genomic instability. The degree to which c-myc-induced genomic instability influences the initiation or progression of cancer is likely to depend on other factors, which are discussed herein.

Silencing of caspase-8 in murine hepatocellular carcinomas is mediated via methylation of an essential promoter element

BACKGROUND & AIMS

Caspase-8 is the apical caspase essential for triggering Fas-induced apoptosis. In this study, we investigated caspase-8 expression in hepatocellular carcinomas (HCCs) using recently described HCC mouse models (c-myc and IgEGF transgenes).

METHODS

HCCs were isolated from c-myc and IgEGF transgenic animals. Expression of caspase-8 was monitored by reverse-transcription polymerase chain reaction. The murine caspase-8 promoter was characterized by luciferase-reporter analysis and the analysis of promoter methylation was performed by bisulfite genomic sequencing.

RESULTS

In HCCs investigated, we frequently found a lack of caspase-8 messenger RNA expression. Genomic deletions at the caspase-8 locus did not contribute to caspase-8 silencing. We examined tumor-derived promoter sequences and found significant hypermethylation at distinct CpG sites. In parallel, we characterized the murine caspase-8 promoter and identified a 30-bp promoter element that is indispensable for basal promoter activity. This minimal promoter element contained SP1 binding motifs that are colocalized with CpG sites and were methylated in tumor-derived promoter sequences. Electrophoretic mobility shift assay analysis showed that methylation of these SP1 sites is sufficient to prevent SP1 complex formation. To support our data, we mimicked the methylation pattern of a tumor-derived caspase-8 promoter in vitro using CpG methylase and found a strong reduction of promoter activity.

CONCLUSIONS

We show that HCCs are correlated frequently with silencing of caspase-8 expression and provide data suggesting that caspase-8 silencing is a direct consequence of inhibiting SP1-dependent transactivation caused by CpG methylation at its essential binding sites in the promoter region. Our data support the hypothesis that inhibition of apoptosis triggers hepatocarcinogenesis.

Hepatocellular carcinoma as a complex polygenic disease. Interpretive analysis of recent developments on genetic predisposition

The different frequency of hepatocellular carcinoma (HCC) in humans at risk suggests a polygenic predisposition. However, detection of genetic variants is difficult in genetically heterogeneous human population. Studies on mouse and rat models identified 7 hepatocarcinogenesis susceptibility (Hcs) and 2 resistance (Hcr) loci in mice, and 7 Hcs and 9 Hcr loci in rats, controlling multiplicity and size of neoplastic liver lesions. Six liver neoplastic nodule remodeling (Lnnr) loci control number and volume of re-differentiating lesions in rat. A Hcs locus, with high phenotypic effects, and various epistatic gene-gene interactions were identified in rats, suggesting a genetic model of predisposition to hepatocarcinogenesis with different subset of low-penetrance genes, at play in different subsets of population, and a major locus. This model is in keeping with human HCC epidemiology. Several putative modifier genes in rodents, deregulated in HCC, are located in chromosomal segments syntenic to sites of chromosomal aberrations in humans, suggesting possible location of predisposing loci. Resistance to HCC is associated with lower genomic instability and downregulation of cell cycle key genes in preneoplastic and neoplastic lesions. p16(INK4A) upregulation occurs in susceptible and resistant rat lesions. p16(INK4A)-induced growth restraint was circumvented by Hsp90/Cdc37 chaperons and E2f4 nuclear export by Crm1 in susceptible, but not in resistant rats and human HCCs with better prognosis. Thus, protective mechanisms seem to be modulated by HCC modifiers, and differences in their efficiency influence the susceptibility to hepatocarcinogenesis and probably the prognosis of human HCC.

Transcriptional regulation and transformation by Myc proteins

Myc genes are key regulators of cell proliferation, and their deregulation contributes to the genesis of most human tumours. Recently, a wealth of data has shed new light on the biochemical functions of Myc proteins and on the mechanisms through which they function in cellular transformation.

Molecular mechanisms of hepatocarcinogenesis in transgenic mouse models of liver cancer

Overexpression of c-myc and transforming growth factor-alpha (TGF-alpha) has been frequently observed in human hepatocellular carcinoma (HCC),suggesting a pivotal role played by these protooncogenes in liver oncogenesis. In order to investigate the molecular events underlying human hepatic malignant transformation, we have generated c-myc and c-myc/ TGF-alpha transgenic mice that are prone to liver cancer. These transgenic mice develop HCCs with different incidence, kinetics and histopathological features. Indeed, co-expression of c-myc and TGF-alpha transgenes results in a dramatic synergistic effect on liver tumor development when compared with respective single transgenic lines, including a shorter latency period and a more aggressive phenotype. The more malignant histopathological features characteristic of c-myc/ TGF-alpha HCCs are the result of the increased proliferation and reduced apoptosis in this model of liver cancer when compared with single parental lines. Accordingly, c-myc and c-myc/l TGF-alpha transgenic mice display a different molecular pathogenesis of HCC. Importantly, the genetic and molecular mechanisms that are involved in c-myc and c-myc/ TGF-alpha liver cancer development are major oncogenic events in human hepatocarcinogenesis, indicating that these mouse models represent a useful tool to dissect and elucidate the molecular basis of human HCC.

Application of comparative functional genomics to identify best-fit mouse models to study human cancer

Genetically modified mice have been extensively used for analyzing the molecular events that occur during tumor development. In many, if not all, cases, however, it is uncertain to what extent the mouse models reproduce features observed in the corresponding human conditions. This is due largely to lack of precise methods for direct and comprehensive comparison at the molecular level of the mouse and human tumors. Here we use global gene expression patterns of 68 hepatocellular carcinomas (HCCs) from seven different mouse models and 91 human HCCs from predefined subclasses to obtain direct comparison of the molecular features of mouse and human HCCs. Gene expression patterns in HCCs from Myc, E2f1 and Myc E2f1 transgenic mice were most similar to those of the better survival group of human HCCs, whereas the expression patterns in HCCs from Myc Tgfa transgenic mice and in diethylnitrosamine-induced mouse HCCs were most similar to those of the poorer survival group of human HCCs. Gene expression patterns in HCCs from Acox1(-/-) mice and in ciprofibrate-induced HCCs were least similar to those observed in human HCCs. We conclude that our approach can effectively identify appropriate mouse models to study human cancers.

Vitamin E down-modulates iNOS and NADPH oxidase in c-Myc/TGF-alpha transgenic mouse model of liver cancer

BACKGROUND/AIMS

Co-expression of c-Myc and TGF-alpha in the mouse liver accelerates hepatocarcinogenesis and enhances DNA damage due to chronic oxidative stress. Dietary supplementation with vitamin E (VE) inhibits hepatocarcinogenesis and reduces chromosomal alterations in the same mice. Here we investigated the sources of reactive oxygen species (ROS) production in c-Myc/TGF-alpha transgenic mice.

METHODS

Inducible nitric oxide synthase (iNOS) and NADPH oxidase levels were determined in c-Myc, TGF-alpha and c-Myc/TGF-alpha mice by RT-PCR, western blot analysis and immunohistochemistry.

RESULTS

iNOS and nitrotyrosines levels were higher in the three transgenic lines when compared with wild-type mice. Preneoplastic and neoplastic lesions from c-Myc, TGF-alpha and c-Myc/TGF-alpha transgenic mice displayed upregulation of NADPH oxidase subunits p47-, 67-phox, Rac1, HSP 70, and HO-1. Importantly, dietary supplementation with vitamin E abolished iNOS expression, lowered nitrotyrosines, p47-, p67-phox, and Rac1 levels, and suppressed HSP 70 and HO-1 proteins in c-Myc/TGF-alpha livers.

CONCLUSIONS

The results suggest that iNOS and NADPH oxidase are involved in ROS generation during c-Myc/TGF-alpha hepatocarcinogenesis and are inhibited by VE treatment. The data provide additional evidence for the potential use of VE in treatment of chronic liver diseases and HCC prevention.

Developmental context determines latency of MYC-induced tumorigenesis

One of the enigmas in tumor biology is that different types of cancers are prevalent in different age groups. One possible explanation is that the ability of a specific oncogene to cause tumorigenesis in a particular cell type depends on epigenetic parameters such as the developmental context. To address this hypothesis, we have used the tetracycline regulatory system to generate transgenic mice in which the expression of a c-MYC human transgene can be conditionally regulated in murine hepatocytes. MYC's ability to induce tumorigenesis was dependent upon developmental context. In embryonic and neonatal mice, MYC overexpression in the liver induced marked cell proliferation and immediate onset of neoplasia. In contrast, in adult mice MYC overexpression induced cell growth and DNA replication without mitotic cell division, and mice succumbed to neoplasia only after a prolonged latency. In adult hepatocytes, MYC activation failed to induce cell division, which was at least in part mediated through the activation of p53. Surprisingly, apoptosis is not a barrier to MYC inducing tumorigenesis. The ability of oncogenes to induce tumorigenesis may be generally restrained by developmentally specific mechanisms. Adult somatic cells have evolved mechanisms to prevent individual oncogenes from initiating cellular growth, DNA replication, and mitotic cellular division alone, thereby preventing any single genetic event from inducing tumorigenesis.

A transgenic mouse model demonstrates that developmental context may be the reason why the spectrum of tumors differs in children and adults

Tissue-specific spatial organization of genomes

A systematic analysis of the spatial positioning of a subset of mouse chromosomes reveals that chromosomes exhibit tissue-specific organization in the nucleus.

Background

Genomes are organized in vivo in the form of chromosomes. Each chromosome occupies a distinct nuclear subvolume in the form of a chromosome territory. The spatial positioning of chromosomes within the interphase nucleus is often nonrandom. It is unclear whether the nonrandom spatial arrangement of chromosomes is conserved among tissues or whether spatial genome organization is tissue-specific.

Results

Using two-dimensional and three-dimensional fluorescence in situ hybridization we have carried out a systematic analysis of the spatial positioning of a subset of mouse chromosomes in several tissues. We show that chromosomes exhibit tissue-specific organization. Chromosomes are distributed tissue-specifically with respect to their position relative to the center of the nucleus and also relative to each other. Subsets of chromosomes form distinct types of spatial clusters in different tissues and the relative distance between chromosome pairs varies among tissues. Consistent with the notion that nonrandom spatial proximity is functionally relevant in determining the outcome of chromosome translocation events, we find a correlation between tissue-specific spatial proximity and tissue-specific translocation prevalence.

Conclusions

Our results demonstrate that the spatial organization of genomes is tissue-specific and point to a role for tissue-specific spatial genome organization in the formation of recurrent chromosome arrangements among tissues.

Disruption of beta-catenin pathway or genomic instability define two distinct categories of liver cancer in transgenic mice

BACKGROUND & AIMS

Human liver cancer can be divided into 2 categories that are characterized by activation of beta-catenin and genomic instability. Here we investigate whether similar categories exist among 5 transgenic models of liver cancer, including c-myc, transforming growth factor-alpha, E2F-1, c-myc/transforming growth factor-alpha, and c-myc/E2F-1 mice.

METHODS

The random amplified polymorphic DNA method was used to assess the overall genomic instability, and chromosomal loci affected by genomic alterations were determined by microsatellite analysis. beta-Catenin mutations and deletions were analyzed by polymerase chain reaction and sequencing screening. Cellular localization of beta-catenin and expression of alpha-fetoprotein, a prognostic marker of hepatocellular carcinoma, were investigated by immunohistochemistry.

RESULTS

Liver tumors from the transgenic mice could be divided into 2 broad categories characterized by extensive genomic instability (exemplified by the c-myc/transforming growth factor-alpha mouse) and activation of beta-catenin (exemplified by the c-myc/E2F-1 mouse). The c-myc/transforming growth factor-alpha tumors displayed extensive genomic instability with recurrent loss of heterozygosity at chromosomes 1, 2, 4, 6, 7, 9, 12, 14, and X and a low rate of beta-catenin activation. The genomic instability was evident from the early dysplastic stage and occurred concomitantly with increased expression of alpha-fetoprotein. The c-myc/E2F-1 tumors were characterized by a high frequency of beta-catenin activation in the presence of a relatively stable genome and low alpha-fetoprotein levels.

CONCLUSIONS

We have identified 2 prototype experimental models, i.e., c-myc/transforming growth factor-alpha and c-myc/E2F-1 mice, for the 2 categories of human hepatocellular carcinoma characterized by genomic instability and beta-catenin activation, respectively. These mouse models will assist in the elucidation of the molecular basis of human hepatocellular carcinoma.

Haploinsufficiency of Anx7 tumor suppressor gene and consequent genomic instability promotes tumorigenesis in the Anx7(+/-) mouse

Annexin 7 (ANX7) acts as a tumor suppressor gene in prostate cancer, where loss of heterozygosity and reduction of ANX7 protein expression is associated with aggressive metastatic tumors. To investigate the mechanism by which this gene controls tumor development, we have developed an Anx7(+/-) knockout mouse. As hypothesized, the Anx7(+/-) mouse has a cancer-prone phenotype. The emerging tumors express low levels of Anx7 protein. Nonetheless, the wild-type Anx7 allele is detectable in laser-capture microdissection-derived tumor tissue cells. Genome array analysis of hepatocellular carcinoma tissue indicates that the Anx7(+/-) genotype is accompanied by profound reductions of expression of several other tumor suppressor genes, DNA repair genes, and apoptosis-related genes. In situ analysis by tissue imprinting from chromosomes in the primary tumor and spectral karyotyping analysis of derived cell lines identify chromosomal instability and clonal chromosomal aberrations. Furthermore, whereas 23% of the mutant mice develop spontaneous neoplasms, all mice exhibit growth anomalies, including gender-specific gigantism and organomegaly. We conclude that haploinsufficiency of Anx7 expression appears to drive disease progression to cancer because of genomic instability through a discrete signaling pathway involving other tumor suppressor genes, DNA-repair genes, and apoptosis-related genes.

Metaphase FISHing of transgenic mice recommended: FISH and SKY define BAC-mediated balanced translocation

The evolving trend to use larger transgenes and their associated increased chance of unexpected genetic events mandates more careful characterization of transgenic mice. In characterizing our five new mouse strains transgenic for the BAC, bEMS4, we have identified the highest copy number reported to date: the stable incorporation of approximately 40 copies of a 194-kb expressed transgene in a single insertion site. We caution, however, that standard molecular techniques failed to identify a balanced translocation in another strain, and an inappropriate site of insertion in a third. Molecular cytogenetic analysis using metaphase FISH was the minimum level of characterization needed to reveal these unexpected genetic events. In addition, we combined FISH and SKY to identify the transgene at the breakpoints of the balanced translocation, t(3;9). This is the first description of a BAC-mediated chromosomal rearrangement and the first application of SKY to identify transgene-induced chromosomal rearrangements.

Dysregulation of DNA repair pathways in a transforming growth factor alpha/c-myc transgenic mouse model of accelerated hepatocarcinogenesis

Previous work from our laboratory has implicated oxidative DNA damage and genetic instability in the etiology of transforming growth factor-alpha (TGFalpha)/c-myc-associated hepatocarcinogenesis. In contrast, oxidative DNA damage was lower in c-myc single-transgenic mice, consistent with less chromosomal damage and with later and more benign tumor formation. We examined whether defects in the DNA repair pathways contribute to the acceleration of liver cancer in TGFalpha/c-myc mice. A cDNA expression array containing 140 known genes and multiplex RT-PCR were used to compare the basal levels of expression of DNA repair genes at the dysplastic stage. Thirty-five percent (8/23) and 43% (10/23) of DNA repair genes were constitutively up-regulated in 10-week-old TGFalpha/c-myc and c-myc transgenic livers, respectively, compared with wild-type controls. The commonly up-regulated genes were OGG1 and NTH1 of base excision repair; ERCC5, RAD23A, and RAD23B of nucleotide excision repair; and RAD50, RAD52, and RAD54 involved in DNA strand break repair. Additional treatment with a peroxisome proliferator, Wy-14,643, known to increase the level of oxidants in the liver, failed to induce a further increase in the expression level of DNA repair enzymes in TGFalpha/c-myc but not in c-myc or wild-type livers. Moreover, expression of several genes, including Ku80, PMS2, and ATM, was decreased in TGFalpha/c-myc livers, suggesting a fault or inefficient activation of the DNA repair pathway upon induction of oxidative stress. Together, the results show that DNA damage response is attenuated in TGFalpha/c-myc mice, creating a condition that may contribute to acceleration of liver cancer in this model.

Chromosome-mediated alterations of the MYC gene in human cancer

The step-wise accumulation of genetic and epigenetic alterations in cancer development includes chromosome rearrangements and viral integration-mediated genetic alterations that frequently involve proto-oncogenes. Proto-oncogenes deregulation lead to unlimited, self-sufficient cell growth and ultimately generates invasive and destructive tumors. C-MYC gene, the cellular homologue of the avian myelocitic leukemia virus, is implicated in a large number of human solid tumors, leukemias and lymphomas as well as in a variety of animal neoplasias. Deregulated MYC expression is a common denominator in cancer. Chromosomal rearrangements and integration of oncogenic viruses frequently target MYC locus, causing structural or functional alterations of the gene. In this article, we illustrate how genomic rearrangements and viruses integration affect MYC locus in certain human lymphomas and solid tumors.

Recurrent allelic deletions at mouse chromosomes 4 and 14 in Myc-induced liver tumors

Transgenic mice expressing the c-Myc oncogene driven by woodchuck hepatitis virus (WHV) regulatory sequences develop hepatocellular carcinoma with a high frequency. To investigate genetic lesions that cooperate with Myc in liver carcinogenesis, we conducted a genome-wide scan for loss of heterozygosity (LOH) and mutational analysis of beta-catenin in 37 hepatocellular adenomas and carcinomas from C57BL/6 x castaneus F1 transgenic mice. In a subset of these tumors, chromosome imbalances were examined by comparative genomic hybridization (CGH). Allelotyping with 99 microsatellite markers spanning all autosomes revealed allelic imbalances at one or more chromosomes in 83.8% of cases. The overall fractional allelic loss was rather low, with a mean index of 0.066. However, significant LOH rates involved chromosomes 4 (21.6% of tumors), 14, 9 and 1 (11 to 16%). Interstitial LOH on chromosome 4 was mapped at band C4-C7 that contains the INK4a/ARF and INK4b loci, and on chromosome 14 at band B-D including the RB locus. In man, the homologous chromosomal regions 9p21, 13q14 and 8p21-23 are frequently deleted in liver cancer. LOH at chromosomes 1 and 14, and beta-catenin mutations (12.5% of cases) were seen only in HCCs. All tumors examined were found to be aneuploid. CGH analysis of 10 representative cases revealed recurrent gains at chromosomes 16 and 19, but losses or deletions involving mostly chromosomes 4 and 14 generally prevailed over gains. Thus, Myc activation in the liver might select for inactivation of tumor suppressor genes on regions of chromosomes 4 and 14 in a context of low genomic instability. Myc transgenic mice provide a useful model for better defining crosstalks between oncogene and tumor suppressor pathways in liver tumorigenesis.

Integration of a c-myc transgene results in disruption of the mouse Gtf2ird1 gene, the homologue of the human GTF2IRD1 gene hemizygously deleted in Williams-Beuren syndrome

Transgenic mice expressing c-myc under the control of the albumin promoter and enhancer develop liver tumors and have served as a useful model for studying the progression of hepatocarcinogenesis. The chromosomes of one line of c-myc transgenic mice carry the reciprocal translocation t(5;6)(G1;F2) adjacent to the transgene insertion site on the 5G1-ter segment translocated to chromosome 6. To characterize the genomic alterations in the c-myc transgenic animals, we have cloned the mouse DNA flanking the transgene array. By linkage mapping, the transgene integration site was localized to the region of distal chromosome 5 syntenic to the region on human chromosome 7q11.23 that is hemizgygously deleted in Williams-Beuren syndrome, a multisystemic developmental disorder. Comparison of the genomic DNA structure in wildtype and transgenic mice revealed that the transgene integration had induced an approximately 40-kb deletion, starting downstream of the Cyln2 gene and including the first exon of the Gtf2ird1 gene. Gtf2ird1 encodes a polypeptide related to general transcription factor TFII-I, and it is the mouse orthologue of GTF2IRD1 (WBSCR11), one of the genes commonly deleted in Williams-Beuren syndrome patients. Loss of the 5' end of the Gtf2ird1 gene resulted in greatly reduced expression of Gtf2ird1 mRNA in mice homozygous for the transgene.

Cooperating oncogenic events in murine mammary tumorigenesis: assessment of ErbB2, mutant p53, and mouse mammary tumor virus

We are investigating cooperating genetic events in the genesis of breast cancer, using the mouse as a model system. We have shown cooperativity between a mutant allele of p53 (p53-172H) and overexpressed ErbB2 in mammary tumorigenesis in transgenic mice. We are now performing additional crosses to further examine oncogene cooperativity with ErbB2 and p53-172H. We attempted to test the dominant oncogenic potential of p53-172H in an in vivo setting by crossing the p53-172H transgene together with ErbB2 onto either a p53(-/-) or a p53(+/-) background. We show that the p53-172H allele and the heterozygous p53 genotype have an identical impact on the latency of ErbB2-induced mammary tumors; there was no evidence of additivity or synergy between p53-172H and the p53(+/-) genotype. On the p53(-/-) background, we obtained no mammary tumors due to the early onset of lymphomas and sarcomas, thus precluding assessment of the effect of the p53-172H transgene on mammary tumorigenesis in a p53-null background. Thus, in this in vivo model for breast cancer, we failed to find evidence that p53-172H can function as a dominant oncogenic allele, but rather found support for its being essentially equivalent to a null allele in its impact on ErbB2-induced mammary tumorigenesis. By comparative genome analysis, we showed that a common feature of tumors arising in ErbB2/mutant p53 mice (p53-null allele with or without p53-172H) is a loss of chromosome 4, a feature of many epithelial tumors in mice and one that is consistent with a role for loss of INK4a/ARF in such tumors. We also attempted to accelerate ErbB2-induced mammary tumorigenesis with mouse mammary tumor virus (MMTV) proviral tagging mutagenesis, but we were surprised to find that mice with MMTV alone had the same latency as mice with both MMTV and ErbB2, indicating no cooperativity between ErbB2 and MMTV. This may have been due to the mixed C3H/HeN x FVB strain background used in this cross.

Preliminary results of interferon-alpha therapy on woodchuck hepatitis virus-induced hepatocarcinogenesis: possible benefit in female transgenic mice

BACKGROUND

C-myc activation is a potent oncogenic event in hepatocarcinogenesis. The aim of this study was to test the preventive effect of interferon-alpha (IFN-alpha) on the development of dysplasia and subsequent hepatocellular carcinoma (HCC) in transgenic (Tg) mice overexpressing c-myc in the liver.

METHODS

The WHV/c-myc Tg mice recapitulating woodchuck hepatitis virus-induced hepatocarcinogenesis were treated with IFN-alpha, starting early in life until sacrifice at pre-neoplastic or neoplastic stages. Transgene expression was assessed by reverse transcription-polymerase chain reaction (RT-PCR), hepatocyte proliferation was assessed by bromodeoxyuridine incorporation and RT-PCR for proliferating cell nuclear antigen, and apoptosis was assessed by in situ nick-end-labeling of DNA.

RESULTS

C-myc expression and hepatocyte proliferation were significantly reduced in treated female mice, without modification of apoptosis, correlating with a lower severity of dysplasia in 9/12 treated animals at pre-neoplastic stages. At the neoplastic stage, 2/3 treated females neither exhibited carcinoma nor dysplasia, while all 6/6 untreated mice and 3/3 treated males developed carcinomas.

CONCLUSIONS

Inhibition of c-myc and hepatocyte proliferation by long-term administration of IFN-alpha was associated with a decrease, or a delay, of oncogenesis in the mouse Tg HCC model. Whether c-myc and hepatocyte proliferation down-regulation could be relevant parameters of IFN-alpha efficiency for hepatocarcinogenesis prevention in cirrhotic patients should be established.

Molecular cytogenetic evaluation of virus-associated and non-viral hepatocellular carcinoma: analysis of 26 carcinomas and 12 concurrent dysplasias

The worldwide incidence of hepatocellular carcinoma (HCC) is approximately one million cases a year. This makes HCC one of the most frequent human malignancies, especially in Asia and Africa, although the incidence is increasing also in the western world. HCC is a complication of chronic liver disease, with cirrhosis as the most important risk factor. Viral co-pathogenesis makes cirrhosis due to hepatitis B (HBV) and hepatitis C virus (HCV) infection a very important factor in the development of HCC. As curative therapy is often ruled out due to the late detection of HCC, it would be attractive to find parameters which predict malignant transformation in HBV- and HCV-infected livers. This study has used comparative genomic hybridization (CGH) to analyse 26 HCCs (11 non-viral, nine HBV, six HCV) and 12 concurrent dysplasias (five non-viral, five HBV, two HCV). Frequent gain (> or =25% of all tumours) was detected, in decreasing order of frequency, on 8q (69%), 1q (46%), 17q (46%), 12q (42%), 20q (31%), 5p (27%), 6q (27%), and Xq (27%). Frequent loss (> or =25% of all tumours) was found, in decreasing order of frequency, on 8p (58%), 16q (54%), 4q (42%), 13q (39%), 1p (35%), 4p (35%), 16p (35%), 18q (35%), 14q (31%), 17p (31%), 9p (27%), and 9q (27%). Minimal overlapping regions could be determined at multiple locations (candidate genes in parentheses). Minimal regions of overlap for deletions were assigned to 4p14-15 (PCDH7), 8p21-22 (FEZ1), 9p12-13, 13q14-31 (RB1), 14q31 (TSHR), 16p12-13.1 (GSPT1), 16q21-23 (CDH1), 17p12-13 (TP53), and 18q21-22 (DPC4, DCC). Minimal overlapping amplified sites could be seen at 8q24 (MYC), 12q15-21 (MDM2), 17q22-25 (SSTR2, GH1), and 20q12-13.2 (MYBL2, PTPN1). A single high level amplification was seen on 5q21 in an HBV-related tumour. Aberrations appeared more frequent in HBV-related HCCs than in HCV-associated tumours (p=0.008). This was most prominent with respect to losses (p=0.004), specifically loss on 4p (p=0.007), 16q (p=0.04), 17p (p=0.04), and 18q (p=0.03). In addition, loss on 17p was significantly lower in non-viral cancers than in HBV-related HCC (p<0.001). Furthermore, loss on 13q was more prevalent in HCCs in non-cirrhotic livers (p=0.02), thus suggesting a different, potentially more aggressive, pathway in neoplastic progression. A tendency (p=0.07) was observed for loss on 9q in high-stage tumours; no specific changes were found in relation to tumour grade. A subset of the HCC-associated genetic changes was disclosed in the preneoplastic stage, i.e. liver cell dysplasia. This group of dysplasias showed frequent gain on 17q (25%) and frequent loss on 16q (33%), 4q (25%), and 17p (25%). The majority of the dysplasias with alterations revealed genetic changes that were also present in the primary tumour. In conclusion, firstly, this study has provided a detailed map of genomic changes occurring in HCC of viral and non-viral origin, and has suggested candidate genes. Loss on 17p, including the TP53 region, appeared significantly more prevalent in HBV-associated liver cancers, whereas loss on 13q, with possible involvement of RB1, was distinguished as a possible genetic biomarker. Secondly, CGH analysis of liver cell dysplasia, both viral and non-viral, has revealed HCC-specific early genetic changes, thereby confirming its preneoplastic nature. Finally, genes residing in these early altered regions, such as CDH1 or TP53, might be associated with hepatocellular carcinogenesis.

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.

Transgenic mouse models in carcinogenesis research and testing

Double transgenic mice bearing fusion genes consisting of mouse albumin enhancer/promoter-mouse c-myc cDNA and mouse metallothionein 1 promoter-human TGF-alpha cDNA were generated to investigate the interaction of these genes in hepatic oncogenesis and to provide a general paradigm for characterizing both the interaction of nuclear oncogenes and growth factors in tumorigenesis. In addition, these mice provide an experimental model to test how environmental chemicals might interact with the c-myc and TGF-alpha transgenes during the neoplastic process. We show experimental evidence that co-expression of TGF-alpha and c-myc transgenes in mouse liver promotes overproduction of ROS and thus creates an oxidative stress environment. This phenomenon may account for the massive DNA damage and acceleration of hepatocarcinogenesis observed in the TGF-alpha/c-myc mouse model. Also, the role of mutagenesis in hepatocarcinogenesis induced by 2-amino-3,8-dimethylimidazo(4,5-f)-quinoxaline (MeIQx) was demonstrated in C57BL/lacZ (Muta Mice) and double transgenic c-myc/lacZ mice that carry the lacZ mutation reporter gene. The MeLQx hepatocarcinogenicity was associated with an increase in in vivo mutagenicity as scored by mutations in the lacZ reporter gene. These results suggest that transgenic mouse models may provide important tools for testing both the carcinogenic potential of environmental chemicals and the interaction/cooperation of these compounds with specific genes during the neoplastic process.

Vitamin E reduces chromosomal damage and inhibits hepatic tumor formation in a transgenic mouse model

We have previously shown that chronic activation of mitogenic signaling induced by over-expression of c-myc and transforming growth factor-alpha (TGFalpha) transgenes in mouse liver induces a state of oxidative stress. We therefore proposed that increased reactive oxygen species (ROS) generation might be responsible for the extensive chromosomal damage and acceleration of hepatocarcinogenesis characteristic for TGFalpha/c-myc mice. In this study, we show that vitamin E (VE), a potent free radical scavenging antioxidant, is able to protect liver tissue against oxidative stress and suppress tumorigenic potential of c-myc oncogene. Dietary supplementation with VE, starting from weaning, decreased ROS generation coincident with a marked inhibition of hepatocyte proliferation while increasing the chromosomal as well as mtDNA stability in the liver. Similarly, dietary VE reduced liver dysplasia and increased viability of hepatocytes. At 6 mo of age, VE treatment decreased the incidence of adenomas by 65% and prevented malignant conversion. These results indicate that ROS generated by over-expression of c-myc and TGFalpha in the liver are the primary carcinogenic agents in this animal model. Furthermore, the data demonstrate that dietary supplementation of VE can effectively inhibit liver cancer development.

Function of the c-Myc oncogenic transcription factor

The c-myc gene and the expression of the c-Myc protein are frequently altered in human cancers. The c-myc gene encodes the transcription factor c-Myc, which heterodimerizes with a partner protein, termed Max, to regulate gene expression. Max also heterodimerizes with the Mad family of proteins to repress transcription, antagonize c-Myc, and promote cellular differentiation. The constitutive activation of c-myc expression is key to the genesis of many cancers, and hence the understanding of c-Myc function depends on our understanding of its target genes. In this review, we attempt to place the putative target genes of c-Myc in the context of c-Myc-mediated phenotypes. From this perspective, c-Myc emerges as an oncogenic transcription factor that integrates the cell cycle machinery with cell adhesion, cellular metabolism, and the apoptotic pathways.