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

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.

Regulation of PI 3-K, PTEN, p53, and mTOR in Malignant and Benign Tumors Deficient in Tuberin

The tuberous sclerosis complex (TSC) is caused by mutation in either of 2 tumor suppressor genes, TSC-1 (encodes hamartin) and TSC-2 (encodes tuberin). In humans, deficiency in TSC1/2 is associated with benign tumors in many organs, including renal angiomyolipoma (AML) but rarely renal cell carcinoma (RCC). In contrast, deficiency of TSC function in the Eker rat is associated with RCC. Here, we have investigated the activity of PI 3-K and the expression of PTEN, p53, tuberin, p-mTOR, and p-p70S6K in both Eker rat RCC and human renal AML. Compared to normal tissue, increased PI 3-K activity was detected in RCC of Eker rats but not in human AML tissue. In contrast, PTEN was highly expressed in AML but significantly reduced in the renal tumors of Eker rats. Phosphorylation on Ser(2448) of mTOR and Thr(389) of p70S6K were significantly increased in both RCC and AML compared to matching control tissue. Total tuberin was significantly decreased in AML while completely lost in RCC of Eker rats. Our data also show that while p53 protein expression is lost in rat RCC, it was highly elevated in AML. These novel data provide evidence that loss of TSC-2, PTEN, and p53 as well as activation of PI 3-K and mTOR is associated with kidney cancer in the Eker rat, while sustained expression of TSC-2, PTEN, and p53 may prevent progression of kidney cancer in TSC patients.

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.

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.

Nuclear p53 overexpression in bladder, prostate, and renal carcinomas

BACKGROUND

The aim of this study was to examine nuclear p53 overexpression in transitional cell carcinoma of the bladder, adenocarcinoma of the prostate, and renal cell carcinoma.

METHODS

Forty-four pathologic specimens from 39 bladder cancer patients, 41 prostatic adenocarcinoma, and 39 renal cell carcinoma specimens were analyzed immunohistochemically with D07 monoclonal antibody to detect the expression of the mutant p53 gene. Overexpression was said to occur when the number of positively-stained tumor nuclei were > or = 10% in each specimen. p53 overexpression was correlated with the clinical and histopathological features of these cancers.

RESULTS

Nuclear p53 overexpression occurred in 18.2% of transitional cell bladder cancer specimens, 12.2% of prostate cancer specimens, and 17.9% of renal cell cancer specimens. Statistical analyses showed that grade, vascular invasion, and necrosis in bladder cancer, a high Gleason score in prostate cancer, and the 1-year mortality rate in renal cancer were significantly related with p53 nuclear overexpression (P < 0.05).

CONCLUSION

Using the D07 monoclonal antibody, nuclear p53 overexpression is relatively uncommon in urologic malignancies, and moderately correlates with several histopathological and clinical features of urologic malignancies.

Studies of oncogene activation and tumor suppressor gene inactivation in normal and neoplastic rodent tissue

Emerging short-term bioassays for chemically-induced carcinogenesis are dependent for their relevance to human risk assessment on the degree of coincidence of human and rodent tumor pathways. Since these pathways do not always converge, these new tests may have a number of unanticipated pitfalls. Models of liver and renal tumors are described. The results from Rb and p53 tumor suppressor gene transgenic animals are compared to human tumor syndromes. The question of mutagenic and epigenetic fingerprints of chemicals versus the cell-specific selection of spontaneous mutations is debated. Examples of specific pitfalls, such as the recently discovered Helicobacter hepaticus promoted liver tumors in mice are presented. The rat pseudogenes for p53 and the rare role of p53 in most important rodent tumor models other than epithelial tumors present experimental quandaries. The differential effects of carcinogens during various stages of rodent perinatal and adult development are also discussed. It is concluded that the pathways of both animal models and their human counterparts should be better identified so that realistic endpoint markers can be chosen for human carcinogenic risk assessment.

Renal cell carcinoma development in the rat independent of alterations at the VHL gene locus

Germline alterations of the human von Hippel-Lindau (VHL) tumor suppressor gene predispose to renal cell carcinoma and a constellation of other tumor types found in VHL disease. This gene is also mutated or deleted in a high proportion of sporadic nonpapillary renal cell carcinomas. In the Eker rat model, spontaneous renal cell carcinoma develops with a high frequency. We therefore investigated the role of this tumor suppressor gene in the development of these hereditary rat tumors. By using reverse transcriptase (RT)-polymerase chain reaction (PCR) analysis, the sequence of the rat VHL gene was determined over the portion of the gene homologous to regions where most mutations in the human VHL gene occur. The sequence homology was 90% and the amino-acid identity 99% between the rat and human genes. A developmental and tumor-specific pattern of expression for the VHL gene was found; a ubiquitous 3.2-kb transcript was expressed in all rat tissues examined (neonatal kidney, lung, liver, brain, heart, kidney, spleen, testis, and stomach), and an additional 4.5-kb transcript was expressed in neonatal kidney and cell lines derived from Eker rat renal cell carcinomas (ERC cell lines). To determine whether mutations in the VHL gene were involved in tumor development in the Eker model, RT-PCR, single-strand conformation polymorphism (SSCP) analysis, and direct sequencing were used to search for alterations in this gene in the ERC cell lines. Alterations in the VHL gene were not detected by SSCP, and these data were confirmed by direct sequencing. Transformed rat kidney epithelial cell lines derived from Fisher rats also expressed the VHL gene but like the ERC cell lines did not contain mutations in the VHL gene. These data indicate that in the rat, transformation of kidney epithelial cells and the development of solid, nonpapillary renal cell carcinoma can occur via pathways that are independent of alterations at the VHL gene locus.

Hereditary renal cell carcinoma in the Eker rat: a unique animal model for the study of cancer susceptibility

A class of genes, the so-called tumor suppressor genes or anti-oncogenes, was originally identified as being responsible for germ-line transmission of cancer susceptibility in humans. Tumor suppressor genes are recessive at the cellular level with respect to oncogenesis but often manifest as dominantly inherited familial cancer syndromes. This type of cancer syndrome arises in the Eker rat due to a genetic defect in the tuberous sclerosis 2 (Tsc2) gene. The Eker rat familial cancer syndrome serves as a unique animal model in which to study the molecular pathways of renal tubular epithelial carcinogenesis as well as a valuable tool for studies that examine how chemical carcinogens interact with cancer susceptibility genes.

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.