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

Diagnostic biomarker of asbestos-related mesothelioma: example of translational research

Mesothelioma is an aggressive tumor arising from the mesothelium, and is usually associated with previous exposure to asbestos. The incubation period of asbestos-related mesothelioma is estimated to be approximately 30-40 years. Once mesothelioma has occurred, there is no effective treatment. So, identification of tumor markers and a method for early diagnosis using such markers are urgently needed. Recently, several enzyme-linked immunosorbent assay systems for Erc/mesothelin have been developed, the reported usefulness of which has been assessed and demonstrated as a diagnostic tool. Asbestos-related mesothelioma should be ascribed as a typical environmental carcinogen. In this review, we will present asbestos-related mesothelioma for the study of problems in environmental carcinogenesis.

Tuberin: a stimulus-regulated tumor suppressor protein controlled by a diverse array of receptor tyrosine kinases and G protein-coupled receptors

Tuberin, a tumor suppressor protein, is involved in various cellular functions including survival, proliferation, and growth. It has emerged as an important effector regulated by receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCRs). Regulation of tuberin by RTKs and GPCRs is highly complex and dependent on the type of receptors and their associated signaling molecules. Apart from Akt, the first kinase recognized to phosphorylate and inactivate tuberin upon growth factor stimulation, an increasing number of kinases upstream of tuberin have been identified. Furthermore, recruitment of different scaffolding adaptor components to the activated receptors appears to play an important role in the regulation of tuberin activity. More recently, the differential regulation of tuberin by various G protein family members have also been intensively studied, it appears that G proteins can both facilitate (e.g., G(i/o)) as well as inhibit (e.g., G(q)) tuberin phosphorylation. In the present review, we attempt to summarize our emerging understandings of the roles of RTKs, GPCRs, and their cross-talk on the regulation of tuberin.

The Mcs7 quantitative trait locus is associated with an increased susceptibility to mammary cancer in congenic rats and an allele-specific imbalance

Identification of high-penetrance breast cancer genes such as Brca1 has been accomplished by analysing familial cases. However, these genes occur at low frequency and do not account for the majority of genetic risk. Identification of low-penetrance alleles that occur commonly in populations may benefit from unbiased genome-wide screening. One such approach uses linkage studies in rodent models to identify homologous human candidates. The Wistar Kyoto (WKy) rat is resistant to mammary carcinomas induced with 7,12-dimethybenz[a]anthracene (DMBA), whereas the Wistar Furth (WF) strain is susceptible. Previous genome-wide linkage studies in crosses of these strains identified three WKy resistance quantitative trait loci, Mcs5, Mcs6 and Mcs8, and one predicted to increase susceptibility, Mcs7. The Mcs7 region on rat chromosome 10 (RNO10) is orthologous to human 17q, a common site of genetic aberrations in breast cancer. Here, we establish the independent phenotype conferred by Mcs7 using congenic rats carrying the WKy Mcs7 locus on a WF background. Tumor multiplicity was significantly higher ( approximately 50%) in DMBA-treated congenics homozygous and heterozygous for the WKy allele at the Mcs7 locus, compared to controls. We also investigated allelic imbalance (AI) in mammary carcinomas from (WKy x WF)F1 rats and Mcs7 heterozygous congenics. Of the four known WKy Mcs loci tested, only Mcs7 displayed AI. The pattern of AI in carcinomas from both F1 and Mcs7 congenic rats was similar, suggesting a WF allelic loss. Together, these data suggest that one or more breast cancer-related genes are located within the dominantly acting WKy allele at the Mcs7 locus.

Genetic and environmental factors in hereditary predisposition to tumors: a conceptual overview

Cancer is a heritable disorder of somatic cells. Carcinogenesis at the cellular level is like an opened Japanese fan, because initiated cells grow in several directions and tumors suggest the edge of the fan by having many gene abnormalities. We discuss here the primal force and gene networks (federal headship) in renal carcinogenesis. The Eker (Tsc2 mutant) rat model of hereditary renal carcinoma (RC) is an example of a Mendelian dominantly inherited predisposition to a specific cancer in an experimental animal. Recently, we discovered a new hereditary renal carcinoma in the rat in Japan, and the rat was named the "Nihon" rat. We suggest that its predisposing (Bhd) gene is a novel renal tumor suppressor gene. We present these unique models as part of the study of problems in carcinogenesis; e.g., multistep carcinogenesis, cancer prevention and the development of the therapeutic treatments that can be translated to human patients, as well as how environmental factors interact with cancer susceptibility gene(s).

The phakomatoses

The "phakomatosis" concept was formulated early in the twentieth century by the ophthalmologist van der Hoeve. He included 3 disorders in the group-neurofibromatosis, tuberous sclerosis complex, and von Hippel-Lindau syndrome--on the basis of the occurrence of patchy ophthalmologic manifestations in each disorder. Since the name was coined, much has been learned about the pathogenesis of these 3 disorders. It is clear that 2 of them--neurofibromatosis and tuberous sclerosis--are collective terms for multiple disorders. Each of the conditions is caused by distinct genetic defects, with little commonality in terms of protein function. Yet, in some respects, the disorders share a pathogenetic mechanism, that of the tumor suppressor gene. This review will briefly describe these disorders in light of what has been learned about underlying molecular pathogenesis. In each case, genetic testing is beginning to be available; principles of the use of genetic tests will be described.

The transcriptional profile of the kidney in Tsc2 heterozygous mutant Long Evans (Eker) rats compared to wild-type

Hereditary renal cell carcinoma (RCC) in Eker rats results from an inherited insertional mutation in the Tsc2 tumor suppressor gene and provides a valuable experimental model to characterize the function of the Tsc2 gene product, tuberin in vivo. The Tsc2 mutation predisposes the Eker rat to develop renal tumors at an early age. The exact mechanism of Tsc2 mediated tumor suppression is not known, however, there is evidence that it is most likely mediated by changes in cell cycle regulation via the PI3K/Akt pathway. The present study was designed to identify if gene expression was different in Tsc2 heterozygous mutant rat kidney compared to wild-type and if any of those differences are associated with tumorigenesis. cDNA microarray analysis of the untreated Tsc2 (+/-) mutant Long Evans (Eker) rat was compared to the Tsc2 (+/+) wild-type Long Evans rat to search for patterns that might be indicative of the intrinsic role of Tsc2. Of 4395 genes queried, 3.2% were significantly altered in kidneys from heterozygous mutant rats, of which 110 (76%) were up-regulated and 34 (24%) were down-regulated relative to the wild-type. The genes with altered expression belonged to the functional categories of cell cycle regulation, cell proliferation, cell adhesion and endocytosis. Many of these genes appear to be directly or indirectly regulated by the PI3K/Akt pathway. In addition to the PI3K/Akt pathway, other signaling pathways were also differentially expressed in Tsc2 mutant Eker rat kidneys compared to wild-type rats. The gene expression profiles of the Tsc2 heterozygous mutant and wild-type animals highlights new pathways for investigation that may be associated with the tumorigenic activity of tuberin loss and correlate with the enhanced susceptibility of the Tsc2 mutant animal's tendency to develop renal cell carcinoma.

Hereditary renal carcinogenesis fitting Knudson's two-hit model: genotype, environment, and phenotype

Cancer is a heritable disorder of somatic cells. Environment and heredity both operate in the origin of human cancer. The Eker (Tsc2 gene mutant) rat model of hereditary renal carcinoma (RC) is an example of Mendelian dominantly inherited predisposition to a specific cancer in an experimental animal. To the best of 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 in Japan, and the rat was named the "Nihon" rat, and its predisposing (Nihon) gene could be a novel renal tumor suppressor gene. We present these unique models, comparing these two predisposing genes (both are located on rat chromosome 10), for the study of problems in carcinogenesis, for instance, species-specific difference in tumorigenesis, cell stage and tissue/cell-type specific tumorigenesis, multistep carcinogenesis, modifier gene(s) in renal carcinogenesis, cancer prevention, and the development of the therapeutic treatments that can be translated to human patients, as well as how environmental factors interact with cancer susceptibility gene(s).

Tumour suppressors hamartin and tuberin: intracellular signalling

Tumour suppressors hamartin and tuberin, encoded by tuberous sclerosis complex 1(TSC1) and TSC2 genes, respectively, are critical regulators of cell growth and proliferation. Mutations in TSC1 and TSC2 genes are the cause of an autosomal dominant disorder known as tuberous sclerosis complex (TSC). Another genetic disorder, lymphangioleiomyomatosis (LAM), is also associated with mutations in the TSC2 gene. Hamartin and tuberin control cell growth by negatively regulating S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E binding protein 1 (4E-BP1), potentially through their upstream modulator mammalian target of rapamycin (mTOR). Growth factors and insulin promote Akt/PKB-dependent phosphorylation of tuberin, which in turn, releases S6K1 from negative regulation by tuberin and results in the activation of S6K1. Although much has been written regarding the molecular genetics of TSC and LAM, which is associated with either the loss of or mutation in the TSC1 and TSC2 genes, few reviews have addressed the intracellular signalling pathways regulated by hamartin and tuberin. The current review will fill the gap in our understanding of their role in cellular signalling networks, and by improving this understanding, an integrated picture regarding the normal function of tuberin and hamartin is beginning to emerge.

Down-regulation of cyclooxygenase-2 expression but up-regulation of cyclooxygenase-1 in renal carcinomas of the Eker (TSC2 gene mutant) rat model

Although it is generally accepted that cyclooxygenase (Cox)-2 is overexpressed in carcinomas, few studies have examined Cox-2 expression in renal carcinoma (RC). The Eker rat RC is an example of a Mendelian dominantly inherited carcinoma, and in the present study, expression of Cox-2 in the Eker rat RC was examined. Reverse transcription polymerase chain reaction indicated constitutive expression of Cox-2 mRNA in the normal control kidney and non-tumor part of Eker rat kidney. Unexpectedly, expression of Cox-2 mRNA was down-regulated in four Eker RCs from two Eker rats, and in the cell line Lk9ds. Immunohistochemical analysis failed to reveal Cox-2 protein staining in Eker RCs. As a control to Cox-2 expression, Cox-1 expression was examined. Interestingly, in contrast to the down-regulated Cox-2 expression, Cox-1 mRNA expression was induced in these four Eker RCs and cell lines. Cox-2 and Cox-1 expression were further examined in six additional Eker RCs. In total, Cox-2 mRNA expression was down-regulated in eight out of ten Eker RCs and cell lines, while Cox-1 mRNA expression was up-regulated in nine out of ten Eker RCs and cell lines.

N-ethyl-N-hydroxyethylnitrosamine (EHEN)-induced renal and hepatocarcinogenesis in the tumor suppressor Tsc2 transgenic rat

Hereditary renal carcinomas (RCs) develop in Tsc2 gene mutant (Eker) rats around the age of 1 year. We previously reported that Tsc2 mutations were detected in chemically (N-ethyl-N-hydroxyethylnitrosamine (EHEN) and diethylnitrosamine)-induced non-Eker rat RCs, suggesting an involvement of Tsc2 alteration in rat RC development. In this study, we evaluated the effect of extra copies of the Tsc2 gene on renal and hepatocarcinogenesis that was induced by EHEN in vivo. The incidence of RCs in non-transgenic rats (2/17) is slightly higher than in transgenic rats (0/32), although it is statistically not significant. These results suggest the presence of other target RC gene(s) in chemically (EHEN)-induced renal carcinogenesis. We observed no difference in the numbers and areas of the hepatic glutathione S-transferase placental type positive foci.