Susceptibility to renal carcinoma in the Eker rat involves a tumor suppressor gene on chromosome 10

Choosing The Right Animal Model for Renal Cancer Research

The increase in the life expectancy of patients with renal cell carcinoma (RCC) in the last decade is due to changes that have occurred in the area of preclinical studies. Understanding cancer pathophysiology and the emergence of new therapeutic options, including immunotherapy, would not be possible without proper research. Before new approaches to disease treatment are developed and introduced into clinical practice they must be preceded by preclinical tests, in which animal studies play a significant role. This review describes the progress in animal model development in kidney cancer research starting from the oldest syngeneic or chemically-induced models, through genetically modified mice, finally to xenograft, especially patient-derived, avatar and humanized mouse models. As there are a number of subtypes of RCC, our aim is to help to choose the right animal model for a particular kidney cancer subtype. The data on genetic backgrounds, biochemical parameters, histology, different stages of carcinogenesis and metastasis in various animal models of RCC as well as their translational relevance are summarized. Moreover, we shed some light on imaging methods, which can help define tumor microstructure, assist in the analysis of its metabolic changes and track metastasis development.

Nox4 is a Target for Tuberin Deficiency Syndrome

The mechanism by which TSC2 inactivation or deficiency contributes to the pathology of tuberous sclerosis complex (TSC) is not fully clear. We show that renal angiomyolipomas from TSC patients and kidney cortex from Tsc2+/− mice exhibit elevated levels of reactive oxygen species (ROS). Downregulation of tuberin (protein encoded by TSC2 gene) in renal proximal tubular epithelial cells significantly increased ROS concomitant with enhanced Nox4. Similarly, we found elevated levels of Nox4 in the renal cortex of Tsc2+/− mice and in the renal angiomyolipomas from TSC patients. Tuberin deficiency is associated with activation of mTORC1. Rapamycin, shRNAs targeting raptor, or inhibition of S6 kinase significantly inhibited the expression of Nox4, resulting in attenuation of production of ROS in tuberin-downregulated proximal tubular epithelial cells. In contrast, activation of mTORC1 increased Nox4 and ROS. These results indicate that Nox4 may be a potential target for tuberin-deficiency-derived diseases. Using a xenograft model from tuberin-null tubular cells in nude mice, both anti-sense Nox4 and GKT137831, a specific inhibitor of Nox1/4, significantly inhibited the tumor growth. Thus, our results demonstrate the presence of an antagonistic relationship between tuberin and Nox4 to drive oncogenesis in the tuberin deficiency syndrome and identify Nox4 as a target to develop a therapy for TSC.

ERK crosstalks with 4EBP1 to activate cyclin D1 translation during quinol-thioether-induced tuberous sclerosis renal cell carcinoma

The mammalian target of rapamycin (mTOR) and mitogen-activated protein kinase signaling cascades have been implicated in a number of human cancers. The tumor suppressor gene tuberous sclerosis-2 (Tsc-2) functions as a negative regulator of mTOR. Critical proteins in both pathways are activated following treatment of Eker rats (Tsc-2(EK/+)) with the nephrocarcinogen 2,3,5-tris-(glutathion-S-yl)hydroquinone (TGHQ), which also results in loss of the wild-type allele of Tsc-2 in renal preneoplastic lesions and tumors. Western blot analysis of kidney tumors formed following treatment of Tsc-2(EK/+) rats with TGHQ for 8 months revealed increases in B-Raf, Raf-1, pERK, cyclin D1, 4EBP1, and p-4EBP1-Ser65, -Thr70, and -Thr37/46 expression. Similar changes are observed following TGHQ-mediated transformation of primary renal epithelial cells derived from Tsc-2(EK/+) rats (quinol-thioether rat renal epithelial [QTRRE] cells) that are also null for tuberin. These cells exhibit high ERK, B-Raf, and Raf-1 kinase activity and increased expression of all p-4EBP1s and cyclin D1. Treatment of the QTRRE cells with the Raf kinase inhibitor, sorafenib, or the MEK1/2 kinase inhibitor, PD 98059, produced a significant decrease in the protein expression of all p-4EBP1s and cyclin D1. Following siRNA knockdown of Raf-1, Western blot analysis revealed a significant decrease in Raf-1, cyclin D1, and all p-4EBP1 forms noted above. In contrast, siRNA knockdown of B-Raf resulted in a nominal change in these proteins. The data indicate that Raf-1/MEK/ERK participates in crosstalk with 4EBP1, which represents a novel pathway interaction leading to increased protein synthesis, cell growth, and kidney tumor formation.

Comparison of human and rat uterine leiomyomata: identification of a dysregulated mammalian target of rapamycin pathway

Uterine leiomyomata, or fibroids, are benign tumors of the uterine myometrium that significantly affect up to 30% of reproductive-age women. Despite being the primary cause of hysterectomy in the United States, accounting for up to 200,000 procedures annually, the etiology of leiomyoma remains largely unknown. As a basis for understanding leiomyoma pathogenesis and identifying targets for pharmacotherapy, we conducted transcriptional profiling of leiomyoma and unaffected myometrium from humans and Eker rats, the best characterized preclinical model of leiomyomata. A global comparison of mRNA from leiomyoma versus myometrium in human and rat identified a highly significant overlap of dysregulated gene expression in leiomyomata. An unbiased pathway analysis using a method of gene-set enrichment based on the sigPathway algorithm detected the mammalian target of rapamycin (mTOR) pathway as one of the most highly up-regulated pathways in both human and rat tumors. To validate this pathway as a therapeutic target for uterine leiomyomata, preclinical studies were conducted in Eker rats. These rats develop uterine leiomyomata as a consequence of loss of Tsc2 function and up-regulation of mTOR signaling. Inhibition of mTOR in female Eker rats with the rapamycin analogue WAY-129327 for 2 weeks decreased mTOR signaling and cell proliferation in tumors, and treatment for 4 months significantly decreased tumor incidence, multiplicity, and size. These results identify dysregulated mTOR signaling as a component of leiomyoma etiology across species and directly show the dependence of uterine leiomyomata with activated mTOR on this signaling pathway for growth.

Zebrafish Tsc1 reveals functional interactions between the cilium and the TOR pathway

The cell surface organelle called the cilium is essential for preventing kidney cyst formation and for establishing left-right asymmetry of the vertebrate body plan. Recent advances suggest that the cilium functions as a sensory organelle in vertebrate cells for multiple signaling pathways such as the hedgehog and the Wnt pathways. Prompted by kidney cyst formation in tuberous sclerosis complex (TSC) patients and rodent models, we investigated the role of the cilium in the TSC-target of rapamycin (TOR) pathway using zebrafish. TSC1 and TSC2 genes are causal for TSC, and their protein products form a complex in the TOR pathway that integrates environmental signals to regulate cell growth, proliferation and survival. Two TSC1 homologs were identified in zebrafish, which we refer to as tsc1a and tsc1b. Morpholino knockdown of tsc1a led to a ciliary phenotype including kidney cyst formation and left-right asymmetry defects. Tsc1a was observed to localize to the Golgi, but morpholinos against it, nonetheless, acted synthetically with ciliary genes in producing kidney cysts. Consistent with a role of the cilium in the same pathway as Tsc genes, the TOR pathway is aberrantly activated in ciliary mutants, resembling the effect of tsc1a knockdown. Moreover, kidney cyst formation in ciliary mutants was blocked by the Tor inhibitor, rapamycin. Surprisingly, we observed elongation of cilia in tsc1a knockdown animals. Together, these data suggest a signaling network between the cilium and the TOR pathway in that ciliary signals can feed into the TOR pathway and that Tsc1a regulates the length of the cilium itself.

Multiple roles of the tuberous sclerosis complex genes

Soon after proposing the "two-hit" hypothesis for tumorigenesis, Knudson pursued further experimental validation of the concept by using a rat model of dominantly inherited renal tumor. Today, the Eker rat is one of the best characterized models of tuberous sclerosis complex (TSC) and has been used extensively for study of the function of the TSC2 tumor suppressor gene. Along with TSC1, these two genes behave as expected for tumor suppressor genes with evidence for loss of heterozygosity in tumors and suppression of growth when expressed in proliferating cells. Despite much experimental work, the mechanisms of these genes have remained elusive until recently. This review summarizes some of the current concepts in our understanding of the biological and biochemical function of the TSC genes.

Polycystic kidney disease as a result of loss of the tuberous sclerosis 2 tumor suppressor gene during development

Somatic loss of function of the tuberous sclerosis 2 (TSC2) tumor suppressor gene leads to the development of benign and malignant lesions of the kidney, brain, uterus, spleen, and liver and germline loss of function of this tumor suppressor gene is embryonic lethal. In addition, the gene product of TSC2, tuberin, is necessary for normal function of the polycystic kidney disease 1 (PKD1) gene product, polycystin-1, which is required for normal cell-cell and cell-matrix interactions. We report here the development of severe polycystic kidney disease in three cases of young Eker rats carrying a germline inactivation of one allele of the Tsc2 gene. Extrarenal tumors were also noted in the spleen and uterus of these animals, which was remarkable given their young age and in the case of the spleen, diffuse involvement of the affected organ. A cell line (EKT2) was established from an affected kidney of one of these animals and used in conjunction with tissues from affected animals to elucidate the defect responsible for the development of these lesions. Affected cells were determined to have lost the wild-type Tsc2 allele while retaining two copies of chromosome 10 containing the mutant Tsc2 allele along with two normal copies of the Pkd1 gene. The genetic data, bilateral nature of the observed kidney disease, and extent of involvement of the spleen and kidney indicate that, in affected animals, loss of the wild-type Tsc2 allele occurred during embryogenesis, probably as a result of chromosome nondisjunction, with affected animals being mosaics for loss of Tsc2 gene function.

Renal carcinogenesis: genotype, phenotype and dramatype

Cancer is a heritable disorder of somatic cells. Environment and heredity are both important in the carcinogenic process. The Eker rat model of hereditary renal carcinoma (RC) is an example of a Mendelian dominantly inherited predisposition to a specific cancer in an experimental animal. Forty years after the discovery of the Eker rat in Oslo, we and Knudson's group independently identified a germline retrotransposon insertion in the rat homologue of the human tuberous sclerosis (TSC2) gene. To our knowledge, this was the first isolation of a Mendelian dominantly predisposing cancer gene in a naturally occurring animal model. Recently, we discovered a new hereditary renal carcinoma in the rat. This rat was named the "Nihon" rat and its predisposing (Nihon) gene could be a novel renal tumor suppressor gene. This article will review the utility of these unique models for the study of problems in carcinogenesis; e.g., species-specific differences in tumorigenesis, cell stage and tissue/cell-type specific tumorigenesis, multistep carcinogenesis, modifier gene(s) in renal carcinogenesis, cancer prevention and the development of therapeutic treatments which can be translated to human patients, as well as how environmental factors interact with cancer susceptibility gene(s).

Use of the spontaneous Tsc2 knockout (Eker) rat model of hereditary renal cell carcinoma for the study of renal carcinogens

The kidney is a frequent site for chemically induced cancers in rodents and among the 10 most frequent sites for cancer in human patients. Renal cell carcinoma (RCC) is the most frequent upper urinary tract cancer in humans and accounts for 80-85% of malignant renal tumors. Hereditary RCC occurs in Eker rats that are heterozygous for an insertion mutation in the Tsc2 tumor suppressor gene. The germline mutation renders heterozygous mutants highly susceptible to renal carcinogens. The utility of this model in studying potential renal carcinogens is due to an ordered progression of proliferative renal lesions that can be identified and counted microscopically. The quantitative nature of the model allows for the production of statistically powerful data to understand the relative degree and potency of chemical effects and allow analysis of genetic alterations that may be chemical specific.

Cell proliferation is insufficient, but loss of tuberin is necessary, for chemically induced nephrocarcinogenicity

Although 2,3,5-tris-(glutathion-S-yl)hydroquinone (TGHQ; 2.5 micromol/kg ip) markedly increased cell proliferation within the outer stripe of the outer medulla (OSOM) of the kidney in both wild-type (Tsc2(+/+)) and mutant Eker rats (Tsc2(EK/+)), only TGHQ-treated Tsc2(EK/+) rats developed renal tumors, indicating that cell proliferation per se was not sufficient for tumor development. Tuberin expression was initially induced within the OSOM after TGHQ treatment but was lost within TGHQ-induced renal tumors. High extracellular signal-regulated kinase (ERK) activity occurred in the OSOM of Tsc2(EK/+) rats at 4 mo and in TGHQ-induced renal tumors. Cyclin D1 was also highly expressed in TGHQ-induced renal tumors. Reexpression of Tsc2 in tuberin-negative cells decreased ERK activity, consistent with the growth-suppressive effects of this tumor suppressor gene. Thus 1) stimulation of cell proliferation after toxicant insult is insufficient for tumor formation; 2) tuberin induction after acute tissue injury suggests that Tsc2 is an acute-phase response gene, limiting the proliferative response after injury; and 3) loss of Tsc2 gene function is associated with cell cycle deregulation.

Confirmation of the mapping of a 12-O-tetradecanoylphorbol-13-acetate promotion susceptibility locus, Psl1, to distal mouse chromosome 9

Susceptibility to two-stage skin carcinogenesis in the mouse is affected by several genes. In addition, studies suggest that genes that modify the response of mice to skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) also may influence histologic changes in the skin as the result of TPA treatment. One TPA susceptibility locus, Psl1, previously was mapped to distal chromosome 9. The mapping of this locus was confirmed by marker-based genotypic selection. Furthermore, Psl1 or a gene closely linked to Psl1 influenced epidermal hyperplasia and epidermal labeling index of mice treated with TPA.

Multistep renal carcinogenesis as gene expression disease in tumor suppressor TSC2 gene mutant model — genotype, phenotype and environment

Cancer is an inheritable disorder of somatic cells. Environment and heredity both operate in the origins of human cancer. These environmental and genetic determinants of cancer can be classified into four groups designated "Oncodemes" [1]. Oncodeme 1 is the irreducible "background" level of cancer due to spontaneous mutagenesis. Oncodeme 2 is "environmentally induced" cancer, whose causative agents are chemical carcinogens, radiation and viruses. Oncodeme 3 is basically "environmentally induced" cancer, but there are genetically determined differences among persons, e.g. the activation or inactivation of carcinogenes. Most human cancers are believed to belong to Oncodemes 2 and/or 3 (about 80%), for which the probability of the occurrence of the initial carcinogenic step(s) is increased, although the number of steps is not decreased. Oncodeme 1 would contain the approximately 20% that would remain if "environmentally induced" cancers (Oncodeme 2 and/or 3) were prevented. Lastly, Oncodeme 4 is "hereditary" cancer. Hereditary cancers could prove valuable in elucidating carcinogenesis, even though only a small proportion of cancers belong to this group. Here, we present a unique animal model of Oncodeme 4 for the study of problems in carcinogenesis; e.g. cell stage and tissue/cell-type-specific tumorigenesis, multistep carcinogenesis, species-specific differences in tumorigenesis, modifier gene(s) in renal carcinogenesis and cancer prevention.

Transformation of kidney epithelial cells by a quinol thioether via inactivation of the tuberous sclerosis-2 tumor suppressor gene

Although hydroquinone (HQ) is a rodent carcinogen, because of its lack of mutagenicity in standard bacterial mutagenicity assays it is generally considered a nongenotoxic carcinogen. 2,3,5-Tris-(glutathion-S-yl)HQ (TGHQ) is a potent nephrotoxic metabolite of HQ that may play an important role in HQ-mediated nephrocarcinogenicity. TGHQ mediates cell injury by generating reactive oxygen species and covalently binding to tissue macromolecules. We determined the ability of HQ and TGHQ to induce cell transformation in primary renal epithelial cells derived from the Eker rat. Eker rats possess a germline inactivation of one allele of the tuberous sclerosis-2 (Tsc-2) tumor suppressor gene that predisposes the animals to renal cell carcinoma. Treatment of primary Eker rat renal epithelial cells with HQ (25 and 50 microM) or TGHQ (100 and 300 microM) induced 2- to 4-fold and 6- to 20-fold increases in cell transformation, respectively. Subsequently, three cell lines (The QT-RRE 1, 2, and 3) were established from TGHQ-induced transformed colonies. The QT-RRE cell lines exhibited a broad range of numerical cytogenetic alterations, loss of heterozygosity at the Tsc-2 gene locus, and loss of expression of tuberin, the protein encoded by the Tsc-2 gene. Only heterozygous (Tsc-2(EK/+)) kidney epithelial cells were susceptible to transformation by HQ and TGHQ, as wild-type cells (Tsc-2(+/+)) showed no increase in transformation frequency over background levels following chemical exposure. These data indicate that TGHQ and HQ are capable of directly transforming rat renal epithelial cells and that the Tsc-2 tumor suppressor gene is an important target of TGHQ-mediated renal epithelial cell transformation.

A novel gene "Niban" upregulated in renal carcinogenesis: cloning by the cDNA-amplified fragment length polymorphism approach

A modified AFLP (amplified fragment length polymorphism) method was employed to isolate genes differentially expressed in renal carcinogenesis of Tsc2 gene mutant (Eker) rats. One gene, selected for further investigation, was named "Niban" "second" in Japanese), because it is the second new gene to be found after Erc (expressed in renal carcinoma) in our laboratory. Importantly, "Niban" is well expressed even in small primary rat Eker renal tumors, more than in progressed cell lines, and is also expressed in human renal carcinoma cells, but not in normal human or rat kidneys. Chromosome assignment was to RNO 13 in the rat, and HSA 1. This "Niban" gene is a candidate as a marker for renal tumor, especially early-stage renal carcinogenesis.

Mapping and determination of the cDNA sequence of the Erc gene preferentially expressed in renal cell carcinoma in the Tsc2 gene mutant (Eker) rat model

The Eker rat develops hereditary renal carcinomas (RCs) due to two hit mutations of the tumor suppressor gene, Tsc2. We previously identified using representational difference analysis (RDA), four genes that were expressed more abundantly in an Eker rat RC cell line than in normal kidney tissue. One gene, Erc (expressed in renal carcinoma) showed sequence homology to the mouse and human megakaryocyte potentiating factor (MPF)/mesothelin gene. The present study determines the full sequence of the cDNA and the exon-intron structure of the rat Erc gene and maps its locus in the chromosome by fluorescence in situ hybridization. Rat Erc and its human homologue were localized in chromosomes 10q12-21 and 16p13.3, respectively, both of which coincided with the locus of the Tsc2/TSC gene. We also found that Erc was expressed at higher levels in primary RCs compared with the normal kidney of the Eker rat. Erc may be related to carcinogenesis in the Tsc2 gene mutant (Eker) rat model.

Genetic mapping of a naturally occurring hereditary renal cancer syndrome in dogs

Canine hereditary multifocal renal cystadenocarcinoma and nodular dermatofibrosis (RCND) is a rare, naturally occurring inherited cancer syndrome observed in dogs. Genetic linkage analysis of an RCND-informative pedigree has identified a linkage group flanking RCND (CHP14-C05.377-C05.414-FH2383-C05. 771-[RCND-CPH18]-C02608-GLUT4-TP53-ZuBe Ca6-AHT141-FH2140-FH2594) thus localizing the disease to a small region of canine chromosome 5. The closest marker, C02608, is linked to RCND with a recombination fraction (theta) of 0.016, supported by a logarithm of odds score of 16.7. C02608 and the adjacent linked markers map to a region of the canine genome corresponding to portions of human chromosomes 1p and 17p. A combination of linkage analysis and direct sequencing eliminate several likely candidate genes, including tuberous sclerosis 1 and 2 genes (TSC1 and TSC2) and the tumor suppressor gene TP53. These data suggest that RCND may be caused by a previously unidentified tumor suppressor gene and highlight the potential for canine genetics in the study of human disease predisposition.

Molecular genetics of renal carcinogenesis

Renal cell carcinoma (RCC) is the most common tumor of the adult kidney, accounting for approximately 85% of renal neoplasms. RCC is heterogeneous in appearance, displaying diverse histologic and cytologic characteristics, with the clear cell variant being the most common. Individuals at high risk for this disease include persons with end-stage renal disease, those with hereditary predispositions such as von Hippel-Lindau syndrome (VHL) or tuberous sclerosis (TSC), and individuals with significant environment exposures such as smoking or analgesic abuse. Recently, several of the genetic targets for alterations involved in the development of human RCC have been identified. Solid RCC of the clear cell type is associated with alterations in the VHL tumor suppressor gene and hereditary papillary RCC is associated with alterations of the c-met protooncogene. In the rat, the most commonly seen tumors are of the non-clear cell type and it is the Tsc-2 tumor suppressor gene, rather than the VHL tumor suppressor gene, that appears to be the primary target for both spontaneous and carcinogen-induced mutations in these animals. These data suggest that different variants of RCC have distinct molecular etiologies and that there are species-specific determinants that modulate the involvement of specific tumor suppressor genes in RCC. Interestingly, many of the genes involved in RCC also play significant roles in kidney development. The Wilm's tumor suppressor gene, WT-1, and Pax-2 regulate the mesenchymal epithelial transition that occurs during nephrogenesis and both these genes exhibit altered expression patterns and/or are mutated in renal tumors. Other genes such as c-met and its ligand hepatocyte growth factor are also involved in normal development and tumorigenesis, suggesting that tumors arise as a result of altered functions that are reflective of events that occur during nephrogenesis.

Identification of a leader exon and a core promoter for the rat tuberous sclerosis 2 (Tsc2) gene and structural comparison with the human homolog

Hereditary renal carcinoma in the Eker rat is an excellent example of predisposition to a specific cancer being transmitted as a dominant trait. Recently, we identified a germline mutation of the tuberous sclerosis 2 (Tsc2) gene in the Eker rat. In the present study, we analyzed the upstream region of the Tsc2 gene. A novel leader exon (exon 1a) in a CpG island was found, and core promoter activity was identified in a 242-bp region of this island. Exon 1a and the promoter region were conserved in the human TSC2 gene. In addition, a rat homolog of a gene found upstream of TSC2 in human has been identified, indicating that the genomic organization around Tsc2/TSC2 is conserved between the two species. Characterization of the 5' region of Tsc2 and TSC2 will facilitate studies of the regulation of the gene and its disregulation in tumorigenesis.

Somatic mutation of the tuberous sclerosis (Tsc2) tumor suppressor gene in chemically induced rat renal carcinoma cell

PURPOSE

von Hippel-Lindau (VHL) gene mutations are detected in noninherited, sporadic human renal cell carcinomas (RCs) at a high frequency. We recently identified a germline mutation in the rat homologue of the human tuberous sclerosis (TSC2) predisposing RC gene in the Eker rat model, and in this study we searched for mutations of the Tsc2 gene in chemically induced non-Eker rat RCs.

MATERIALS AND METHODS

Chemically [N-ethyl-N-hydroxyethylnitrosamine (EHEN)]-induced non-Eker rat RC lines (designated as BP13 and BP36B) were subjected to PCR-single strand conformation polymorphism (PCR-SSCP) analysis using specific primers covering entire exons of Tsc2 gene (41 coding exons and one non-coding exon). We simultaneously searched for mutations of Vhl gene, a rat homologue of von Hippel-Lindau disease gene (VHL) as well as Tsc2 gene.

RESULTS

BP36B showed an abnormal mobility shift from the normal tissue of the same rat in exon 35 on analysis by PCR-SSCP. This mutation was confirmed by direct sequencing and found to be a T-to-C transition at the second position of codon 1470, resulting in an amino acid change from leucine to proline (missense mutation).

CONCLUSIONS

This is the first demonstration of Tsc2 gene somatic mutation in non-Eker rat RCs. Our present findings call attention to further investigation of the role of Tsc2 gene mutations in rat renal carcinogenesis and possible Tsc2 gene mutations in human RCs, especially of the non-clear cell type, which are not related to the VHL gene.

Suppression of tumorigenicity by the wild-type tuberous sclerosis 2 (Tsc2) gene and its C-terminal region

The Tsc2 gene, which is mutationally inactivated in the germ line of some families with tuberous sclerosis, encodes a large, membrane-associated GTPase activating protein (GAP) designated tuberin. Studies of the Eker rat model of hereditary cancer strongly support the role of Tsc2 as a tumor suppressor gene. In this study, the biological activity of tuberin was assessed by expressing the wild-type Tsc2 gene in tumor cell lines lacking functional tuberin and also in rat fibroblasts with normal levels of endogenous tuberin. The colony forming efficiency of Eker rat-derived renal carcinoma cells was significantly reduced following reintroduction of wild-type Tsc2. Tumor cells expressing the transfected Tsc2 gene became more anchorage-dependent and lost their ability to form tumors in severe combined immunodeficient mice. At the cellular level, restoration of tuberin expression caused morphological changes characterized by enlargement of the cells and increased contact inhibition. As with the full-length Tsc2 gene, a clone encoding only the C terminus of tuberin (amino acids 1049-1809, including the GAP domain) was capable of reducing both colony formation and in vivo tumorigenicity when transfected into the Eker rat tumor cells. In normal Rat1 fibroblasts, conditional overexpression of tuberin also suppressed colony formation and cell growth in vitro. These results provide direct experimental evidence for the tumor suppressor function of Tsc2 and suggest that the tuberin C terminus plays an important role in this activity.

A genetic, physical, and comparative map of rat chromosome 10

A map of rat Chromosome (Chr) 10 was generated from 21 markers, mostly of conserved structural genes, by linkage analysis and fluorescence in situ hybridization. The study emphasizes the proximal third of the chromosome which, until now, has been relatively devoid of markers. Based on comparative analysis, our data suggest that genes on rat Chr 10 are conserved on mouse Chr 11, 16, 17 and human Chr 16, 5, and 17.

Cloning of the rat homologue of the von Hippel-Lindau tumor suppressor gene and its non-somatic mutation in rat renal cell carcinomas

Recently, von Hippel-Lindau (VHL) gene mutations were detected in non-inherited, sporadic human renal cell carcinomas (RCs) at a high frequency. In order to determine whether or not the VHL gene is also a critical gene in rat RCs, we cloned and sequenced the rat homologue of human VHL gene and searched for mutations of the VHL gene in rat RCs. Mutations in the VHL gene were not detected in spontaneous RCs of the Eker rat model or in ferric nitrilotriacetate-induced rat RCs using the polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) method. These data indicate that mutation of the VHL tumor suppressor gene is not an event in rat renal carcinogenesis, at least in our present systems.

Allelic loss at the tuberous sclerosis 2 locus in spontaneous tumors in the Eker rat

Somatic events leading to the inactivation of tumor suppressor genes often involve chromosomal alterations that can be detected as loss of heterozygosity (LOH). In the Eker rat, spontaneous tumors of the kidney, uterus, and spleen develop as a result of a germline mutation of the tuberous sclerosis 2 (Tsc2) gene. We examined the pattern and frequency of LOH at the predisposing locus in 77 primary tumors and cell lines to gain an understanding of the role of Tsc2 allelic loss in the pathogenesis of Eker-derived tumors. Although most renal and uterine tumors (primary and cell lines) displayed LOH, splenic hemangiosarcomas did not. Although the presence of normal tissue may account for some of this difference, the possibility exists that an alternative mechanism, such as subtle mutation or gene dosage effects, may be involved during splenic tumorigenesis. Northern analysis confirmed that LOH resulted in loss of the wild-type transcripts for the Tsc2 gene. Thus, the inactivation of both alleles plays an important role in renal and uterine tumor development, in keeping with Knudson's two-hit hypothesis. In addition, renal tumors that retained the wild-type allele also did not express the normal transcript, suggesting that the remaining Tsc2 alleles had acquired subtle mutations resulting in loss of gene function.

Allelic loss at the tuberous sclerosis (Tsc2) gene locus in spontaneous uterine leiomyosarcomas and pituitary adenomas in the Eker rat model

Hereditary renal carcinomas (RCs) develop in virtually all Eker rats by the age of one year. Investigation of extra-renal primary tumors co-occurring in Eker rats late in life (at 2 years) additionally revealed enhanced development of hemangiosarcomas of the spleen, uterine leiomyosarcomas and pituitary adenomas, although the demonstrated predilection for these extra-renal tumors was not as complete as with RCs. We identified the germline mutated tuberous sclerosis (Tsc2) gene as the predisposing Eker gene and revealed the tumor suppressor nature of Tsc2 gene function in renal carcinogenesis. In the present study, we examined allelic loss at the Tsc2 gene locus in uterine leiomyosarcomas and pituitary adenomas developing in hybrid F1 rats carrying the Eker mutation as well as in pituitary adenomas from non-carrier rats. We detected loss of heterozygosity in 4 of 11 uterine leiomyosarcomas (36%) and 11 of 31 pituitary adenomas (35%) from Eker rats but in none of 9 pituitary adenomas from non-carrier rats (P < 0.05), suggesting that inactivation of the Tsc2 gene is also a critical event in the pathogenesis of these extra-renal tumors. Our present data indicate that there might be different pathways for tumorigenesis of pituitary adenomas between Eker and

Renal carcinogenesis in the Eker rat

The Eker rat hereditary renal carcinoma is an excellent example of a Mendelian dominant predisposition to a specific cancer in an experimental animal. We recently reported that a germline insertion in the rat homologue of the human tuberous sclerosis (TSC2) gene gives rise to the dominantly inherited cancer in the Eker rat model. The function of the TSC2/Tsc2 gene product (called "tuberine" in the human case) is not yet understood, although it contains a short amino acid sequence homologous to the ras family GTPase-activating proteins (GAP3). In the study, we isolated subtracted cDNA clones having increased expression in Eker renal carcinoma cells, using a modified representational difference analysis method to search for additional genes specifically involved in renal carcinogenesis. Here we identified four genes: the third component of the complement (C3) gene, the fos-related antigen I (fra-1) gene, an unknown gene (designated as being expressed in renal carcinoma: erc) and the calpactine I heavy-chain (Annexin II) gene.

Molecular genetic basis of renal carcinogenesis in the Eker rat model of tuberous sclerosis (Tsc2)

We have recently identified on rat chromosome 10q a germline mutation in the tuberous sclerosis gene (Tsc2), the gene predisposing to renal carcinoma (RC) in the Eker rat. The homozygous mutant condition is lethal at around the 13th day of fetal life. In heterozygotes, RCs invariably develop in the first year of life. Histologically, RCs develop through multiple stages from early preneoplastic lesions (i.e., phenotypically altered tubules) to adenomas. The wild-type allele mutation has been found even in the earliest preneoplastic lesions, fitting Knudson's two-hit hypothesis and supporting the hypothesis that Tsc2 is a tumor suppressor gene. In this study, homozygous deletion of the Ink4 homologue on rat chromosome 5q was observed in 14 of 24 (58%) RC-derived cell lines. This may represent involvement of a second tumor suppressor gene, contributing to tumor progression. Considering previous results of studies of homozygous deletion of the Ifn alpha gene in five of 24 cases (21%) and the Ifn beta gene in one of 24 cases (4%), the order of the genes may be Ink4-Ifn alpha-Ifn beta. Microsatellite instability was not observed in 26 Eker rat tumors.

cDNA structure, alternative splicing and exon-intron organization of the predisposing tuberous sclerosis (Tsc2) gene of the Eker rat model

The Eker rat hereditary renal carcinoma (RC) is an excellent example of a Mendelian dominant predisposition to a specific cancer in an experimental animal. We recently reported that a germline insertion in the rat homologue of the human tuberous sclerosis gene (TSC2) gives rise to the dominantly inherited cancer in the Eker rat model. We now describe the entire cDNA (5375 bp without exons 25 and 31) and genomic structure of the rat Tsc2 gene. The deduced amino acid sequence (1743 amino acids) shows 92% identity to the human counterpart. Surprisingly, there are a great many (> or = 41) coding exons with small sized introns spanning only approximately 35 kb of genomic DNA. Two alternative splicing events [involving exons 25 (129 bp) and 31 (69 bp)] make for a complex diversity of the Tsc2 product. The present determination of the Tsc2 gene and establishment of strong conservation between the rat and man provide clues for assessing unknown gene functions apart from that already predicted from the GTPase activating proteins (GAP3) homologous domain and for future analysis of intragenic mutations in tumors using methods such as PCR-SSCP and for insights into diverse phenotypes between species.

Spontaneous renal tubular carcinoma in Fischer-344 rat littermates

Two of 632 Fischer-344 rats in a food restriction study had spontaneous, bilateral, multicentric renal tubular cell carcinomas. Although there were 104 litters represented in this study, both rats that developed this rare neoplasm were from the same litter. The littermates, one male and one female, were in the food-restricted treatment groups (60% of ad libitum intake) and were 550 and 447 days old, respectively, at death. The probability that the two rare bilateral renal neoplasms occurred by a chance event in littermates is approximately 0.8%. The apparent familial predisposition for development of specific types of neoplasms emphasizes the importance of randomization of individuals into treatment groups and consideration of lineage for rare tumors.

[Model systems for investigation of genetic factors in tumorigenesis]

The steadily rising public concern about the number and amounts of carcinogenic agents in our environment has led to a decline in interest in another aspect of tumorigenesis, namely the involvement of genetic factors in the processes that lead to malignant tumors. It is becoming evident that both the noxious influences in the environment and the genetic make-up of cells or the whole individual are involved in cancerous processes to a similar extent. The usefulness of experimental animal models for analysis of the extreme complexity of the molecular mechanisms underlying tumor formation is demonstrated by recent results in experimental oncology.

p53 status in spontaneous and dimethylnitrosamine-induced renal cell tumors from rats

Rats carrying the Eker tumor-susceptibility mutation (Eker rats) are predisposed to developing renal cell carcinoma. Rats heterozygous for the Eker mutation develop spontaneous multiple bilateral renal cell tumors by the age of 1 yr. In a previous study, Eker-mutation carrier and noncarrier rats were exposed to the renal carcinogen dimethylnitrosamine (DMN), and male rats carrying the Eker mutation exhibited a 70-fold increase in the induction of renal adenomas and carcinomas when compared with noncarrier rats. In this study, spontaneous and DMN-induced rat renal cell tumors (adenomas and carcinomas) were analyzed for mutations of the p53 gene by direct sequencing of cDNA polymerase chain reaction products. There were no mutations in p53 cDNA derived from renal tumors from six untreated rats. Mutations were found in one of 15 of the DMN-induced tumors: a transition at codon 140, CCT-->CTT, in a renal adenoma. Additionally, seven cell lines derived from spontaneous renal cell tumors did not contain mutations in p53. The low frequency of p53 mutations (one of 21 renal cell tumors and none of seven cell lines derived from renal cell tumors) indicates that the development of both spontaneous and carcinogen-induced renal tumors involved a non-p53-dependent pathway. As p53 is infrequently mutated in human renal cell carcinomas and in rat renal mesenchymal tumors, it is likely that a tumor suppressor gene or genes other than p53 are involved in the development of renal cancer.

A germline insertion in the tuberous sclerosis (Tsc2) gene gives rise to the Eker rat model of dominantly inherited cancer

The Eker rat hereditary renal carcinoma (RC) is an excellent example of a mendelian dominant predisposition to a specific cancer in an experimental animal. We have previously established a new conserved linkage group on rat chromosome 10q and human chromosome 16p13.3, and shown that the Eker mutation is tightly linked to the tuberous sclerosis (Tsc2) gene. We now describe a germline mutation in the gene encoding Tsc2 caused by the insertion of an approximately 5 kilobase DNA fragment in the Eker rat, resulting in aberrant RNA expression from the mutant allele. The phenotype of tuberous sclerosis in humans differs from that of the Eker rat, except for the occurrence of renal tumours. The Eker rat may therefore provide insights into species-specific differences in tumourigenesis and/or phenotype-specific mutations.

Predisposition to renal carcinoma in the Eker rat is determined by germ-line mutation of the tuberous sclerosis 2 (TSC2) gene

Genetic predisposition to neoplasia often involves tumor suppressor genes. One such model of hereditary renal carcinoma was described in the rat by Eker. These tumors share morphologic similarities with human renal cancer. Linkage analysis localized the inherited mutation to rat chromosome band 10q12. This region is syntenic with human chromosome band 16p13.3, the site of the tuberous sclerosis 2 (TSC2) gene. A specific rearrangement of the rat homologue of TSC2 was found to cosegregate with carriers of the predisposing mutation. Tumors with or without loss of heterozygosity expressed only the mutant allele, consistent with the two-hit hypothesis. This mutation gave rise to an aberrant transcript that deletes the 3' end normally containing a region of homology with the catalytic domain of rap1GAP.

Atypical tubule hyperplasia and renal tubule tumors in conventional rats on 90-day toxicity studies

Bilateral, multicentric renal tubule tumors were found in 4 rats at the termination of 3 separate 90-day toxicity studies during the safety evaluation of 3 unrelated chemicals. The 3 studies were conducted at 2 separate locations, but the rats used were obtained from the same commercial source. The rat strains were Fischer-344 (1 male and 1 female case) and Sprague-Dawley (2 female cases). Three of the renal tumor cases were from either the high-dose or mid-dose treatment groups, and 1 case was an untreated control. The tumors were accompanied by multiple foci of atypical tubule hyperplasia but only in the tumor-bearing rats. There were no lesions associated with renal tumor pathogenesis in any of the remaining treated or untreated animals in the 3 studies. In addition, there was no indication of nephrotoxicity in the treated or untreated animals. Tumor morphology was characterized by a generally vacuolated appearance, eosinophilia, cytoplasmic and nuclear pleomorphism, and conspicuously hypertrophied nucleoli. The renal tubule tumors in these 90-day studies were compared to hereditary renal tubule tumors occurring in the Eker rat, a Long-Evans derivative with a genetic predisposition to this tumor type. The multiplicity of renal tubule tumors, early age of onset, and tumor morphology described in the cases from the 90-day studies were very similar to those characterizing the hereditary renal tumor model.(ABSTRACT TRUNCATED AT 250 WORDS)

Antioncogenes and human cancer

The antioncogenes, or tumor suppressor genes, as negative regulators of cell division, stand in contrast to oncogenes. For most human cancers, the more frequently mutated genes are the antioncogenes, the principal exception being the leukemias and lymphomas. Persons heterozygous for germ-line mutations in antioncogenes are strongly predisposed to one or more kinds of cancer, and most dominantly inherited cancer is attributable to such heterozygosity. Seven antioncogenes have been cloned through the study of these persons, and several others have been mapped. An eighth one was mapped and cloned through the investigation of tumors and is not yet known in hereditary form. Three dominantly inherited forms of cancer are not attributable to mutations in antioncogenes. The corresponding nonhereditary forms of most cancers generally reveal abnormalities of the same antioncogenes that are found in the hereditary forms but may also show additional ones. Some cancers, especially the embryonal tumors of children, have a small number of antioncogene mutations; some others, such as most sarcomas, have more, and the common carcinomas have the most, reflecting a hierarchy of controls over growth of stem cell populations. Still more members of this gene category remain to be mapped and cloned through the study of cancer families and of tumors. The genes that have been cloned act at diverse points in the signal transduction pathway in cells, from the outer cell membranes to sites of gene transcription, in some cases as negative regulators of oncogene expression.