Point mutations of c-ras genes in human bladder cancer and kidney cancer

Role of bone morphogenetic proteins in transitional cell carcinoma cells

Bone morphogenetic proteins (BMPs) are pleiotropic growth factors that signal through an interaction with the membrane receptors-type--IA, -IB, and -II (BMP-RIA, -RIB, and -RII, respectively). Although the prototypical members of this group of growth factors were isolated as osteoinductive factors, recently accumulated data have suggested that these factors regulate malignant cells. Herein, we review the data concerning BMPs in transitional cell carcinoma cells.

Molecular pathways in bladder cancer

The aim of this review is to provide a contemporary outline of our current understanding of the molecular and genetic events associated with tumorigenesis and the progression of bladder cancer. A comprehensive review of the literature was performed on the molecular alterations associated with transitional cell carcinoma (TCC) of the bladder. Intense research efforts are being made to better identify and characterize various bladder cancers and their true biologic potential. The need to predict which superficial tumors will recur or progress, and which invasive tumors will metastasize has led to a much better understanding of the molecular pathways associated with bladder cancer. The molecular changes that occur in TCC of the bladder are numerous and can be categorized into: (1) chromosomal alterations leading to carcinogenesis, (2) loss of cell cycle regulation accounting for cellular proliferation, and (3) metastasis, guided by events such as angiogenesis. It is becoming apparent that the accumulation of genetic and molecular changes ultimately determines a tumors phenotype and subsequent clinical behavior. At the present time, conventional histopathologic evaluation of bladder cancer (tumor grade and stage) is inadequate to accurately predict the behavior of most bladder tumors. While new laboratory techniques have allowed us to better understand how bladder cancer develops and ultimately progresses, few of these techniques are currently available for use in the clinical setting. The ultimate goal is to develop reliable prognostic markers which will accurately predict not only the expected clinical course of an individual bladder tumor but also the response of that tumor to currently available therapies. More importantly, this information may be employed in the future to dictate altogether new treatments for the prevention and/or stabilization of the early molecular events that lead to the development of bladder cancer.

Molecular prognostication in bladder cancer--a current perspective

The optimal management of bladder cancer depends on the accurate assessment of the tumour's biological potential. Advances in molecular biology and cytogenetics have spurred intense research in identifying and characterising prognostic markers for patients with transitional cell carcinoma (TCC) of the bladder. The molecular changes that occur can be categorised into (1) chromosomal alterations leading to carcinogenesis, (2) cellular proliferation as a result of dysregulation of cell cycle control, and (3) growth control processes such as angiogenesis leading to metastasis. The accumulation of these changes ultimately determines a tumour's clinical behaviour and response to therapy. As the understanding of bladder cancer evolves, novel molecular markers for prognostication will make their way from the research laboratory to the clinical setting with the promise to improve patient care and outcomes.

[Expression of p21ras in locally confined renal adenocarcinoma and its prognostic implications]

OBJECTIVE

The p21ras protein is encoded by the three ras genes (H-, K- and N-ras) and participate in the regulation of normal cell growth and cell differentiation. The objective of this study is to determine the expression of this protein in locally confined renal cell carcinoma, as well as its relations with different histopathological variables and their prognostic implications.

METHOD

58 renal cell carcinomas, in pT1-T3a N0 M0 (TNM 1997) stages, treated by radical or partial nephrectomy with curative intention. We analysed different clinical and anatomopathological variables, as well as expression of p21ras in paraffinated tissue, using immunohistochemical techniques.

RESULTS

The mean percentage of stained nuclei was 6.1%, with a range lying between 0 and 45%. We did not obtain statistically significant association between expression of p21ras and the tumour size (p = 0.698), the nuclear grade (p = 0.676) or the histopathological stage (p = 0.095). The survival analysis also did not show significant differences when we stratified the patients using the mean value of the sample as reference point (p = 0.134).

CONCLUSIONS

Expression of p21ras was not demonstrated to be related to any of the histopathological variables analysed: size, grade and stage, or with survival. Therefore, this protein does not appear to be related to the evolution of renal cell carcinoma.

Genetic and molecular markers of urothelial premalignancy and malignancy

The molecular genetic changes reported in bladder tumors can be classified as primary and secondary aberrations. Primary molecular alterations may be defined as those directly related to the genesis of cancer. These are frequently found as the sole abnormality and are often associated with particular tumors. There are characteristic primary abnormalities involved in th production of low-grade/well-differentiated neoplasms, which destabilize cellular proliferation but have little effect on cellula "social" interactions or differentiation, as well as the rate of cell death or apoptosis. Other molecular events lead to high-grad neoplasms which disrupt growth control, including the cell cycle and apoptosis, and which have a major impact on biological behavior. A primary target leading to low-grade papillary superficial bladder tumors resides on chromosome 9, while p53 gene alterations are commonly seen in flat carcinoma in situ. Other molecular alterations must be elucidated, as many non-invasive neoplasms have neither chromosome 9 nor p53 alterations. Novel approaches utilizing tissue microdissection techniques an molecular genetic assays are needed to shed further light on this subject. Secondary genetic or epigenetic abnormalities may be fortuitous, or may determine the biological behavior of the tumor. Multiple molecular abnormalities are identified in most human cancers studied, including bladder neoplasms. The accumulation, rather than the order, of these genetic alterations may be the critical factor that grants synergistic activity. In this regard, it is noteworthy that many of the genes that are altered act upon the two recognized critical growth and senescenc pathways, TP53 and RB. These particular molecular aberrations may be especially important to evaluate for their use in the management of bladder cancer because of their commonality in progressive forms of the disease. Thus, clinical trials are underway to explore their use in specific situations, particularly in the surgical management of locally advanced disease, and to determine whether adjuvant chemotherapy in such patients may be of benefit. The use of molecular alterations in the management of non-invasive bladder neoplasms remains to be firmly established. Our knowledge of molecular alterations important in bladder cancer progression is far from complete, and further study is necessary to further elucidate cruci pathways involved in progression and therapeutic response. As per preneoplastic conditions, difficulties in identifying and interpreting the significance of phenotypic changes have imposed certain limitations, as has an evolving nomenclature and issues of reproducibility in interpreting morphologica criteria. Nevertheless, molecular alterations involving chromosome 9q and the INK4A locus in papillary superficial tumors vs changes in chromosomes 14q and 8q, p53 and RB in flat carcinoma in situ lesions may indicate a molecular basis for early events that lead to varying pathways in urothelial tumorigenesis. Studies aimed at revealing the clinical relevance of genet instability, as well as molecular or epigenetic alterations, in urothelium and preneoplastic lesions of otherwise morphologicall normal appearance are needed to further advance knowledge in the field. Clinical advances in bladder cancer will be facilitated by novel animal models paralleling the human disease. Molecular diagnostics, particularly specific antigen expression, fluorescence in situ hybridization and microsatellite analyses, have show great promise as screening and follow-up methodologies, and may supplement urine cytology in the diagnosis and characterization of new and recurrent disease. In addition, the use of high-throughput genomic/proteomic assays, linked to comprehensive databases, and coupled with robust bioinformatics will be key elements in elucidating the components of regulatory and signaling pathways involved in bladder tumorigenesis and cancer progression.

Risk and prognosis in renal neoplasms. A pathologist's prospective

The incidence of renal carcinoma has increased in the United States over the last two decades. An increased rate of detection of incidental tumors and a variety of exogenous risk factors may be responsible for this increase. Pathologic stage and nuclear grade remain the most important and practical prognostic features, however, the specific tumor type has emerged as important as the cytogenetic validation of recent renal carcinoma classification. Proliferation markers, DNA ploidy, and morphometry have powerful predictive value but are handicapped by cost and complexity. The search continues for molecules of diagnostic and prognostic utility that may also impact invasive and metastatic capability for this group of neoplasms whose course is principally determined by the completeness of the original resection.

Prognostic markers in bladder cancer: a contemporary review of the literature

PURPOSE

We provide a contemporary review of bladder tumor markers and summarize their role as prognostic indicators.

MATERIALS AND METHODS

A comprehensive review of the literature on prognostic markers for transitional cell carcinoma of the bladder was performed.

RESULTS

Intense research efforts are being made to identify and characterize better various bladder cancers and their true biological potential. The need to predict which superficial tumors will recur or progress and which invasive tumors will metastasize has led to the identification of a variety of potential prognostic markers. Blood group antigens, tumor associated antigens, proliferating antigens, oncogenes, peptide growth factors and their receptors, cell adhesion molecules, tumor angiogenesis and angiogenesis inhibitors, and cell cycle regulatory proteins have recently been identified. The potential clinical applications of these tumor markers are under active investigation. Recent attention has focused on which tumor markers may predict the responsiveness of a particular bladder cancer to systemic chemotherapy.

CONCLUSIONS

At present conventional histopathological evaluation of bladder cancer (tumor grade and stage) cannot predict accurately the behavior of most bladder tumors. With a better understanding of the cell cycle, and cell to cell and cell to extracellular matrix interactions as well as improved diagnostic techniques (immunohistochemistry), progress is being made to identify and characterize other potential prognostic markers for transitional cell carcinoma of the bladder. The ultimate goal is to develop reliable prognostic markers that will accurately predict not only the course but also the response of a tumor to therapy. This information may then be used to dictate more aggressive treatment for tumors that are likely to progress and less aggressive treatment for those that are unlikely to progress. In the future these biological markers may also be used in gene therapy for the treatment of bladder cancer.

Restriction endonuclease-mediated selective polymerase chain reaction: a novel assay for the detection of K-ras mutations in clinical samples

The enriched polymerase chain reaction (PCR) assay has been used extensively in the detection of ras gene mutations in many types of human malignancies. Although it is very sensitive, it has a number of features that limit its use in the routine diagnostic laboratory. The aim of this study was to develop a novel enriched PCR strategy, in which the concurrent activity of the restriction enzyme BstNI and Taq polymerase allowed the amplification of mutant K-ras while inhibiting the formation of wild-type product. This restriction endonuclease-mediated selective PCR assay uses three sets of primers, together with BstNI, in the reaction mix, and the amplification products are analyzed by gel electrophoresis. The reliability of the restriction endonuclease-mediated selective PCR assay to detect activated K-ras was determined in a variety of clinical samples, including 139 fresh colorectal carcinomas and 113 paraffin-embedded blocks from 80 separate tumors of the colon and rectum, pancreas, breast, or kidney. Codon 12 mutations of the K-ras oncogene were identified in DNA from both fresh and paraffin-embedded tumors in a rapid, sensitive, and reproducible manner. Mutations were detected in 33 (24%) of the fresh colorectal cancers and 16 (20%) of the paraffin-embedded tumors. These results were 97% concordant in cases in which paraffin blocks and fresh specimens from the same tumor were available for analysis. We conclude that restriction endonuclease-mediated selective PCR is a sensitive, rapid, and robust assay for the detection of point mutations in a variety of clinical samples. Importantly, there is no need for manipulation of the sample once the PCR has been set up, and therefore, the chance of contamination is significantly reduced. In contrast to previous assays, restriction endonuclease-mediated selective PCR is not labor intensive, and its format is suitable for use in routine diagnostic laboratory.

Screening of H-ras gene point mutations in 50 cases of bladder carcinoma

BACKGROUND

Mutation converts the H-ras gene into an activated oncogene in about 10% of human bladder cancers. Codons 12 and 61 are the major "hot spots" for activation. A simple and accurate method to detect point mutations in these codons may be clinically useful for early diagnosis of bladder cancer.

METHODS

Bladder cancer samples from 50 patients, plus 10 samples of normal bladder mucosa, were analyzed for possible point mutation of the H-ras gene at either codon 12 or codon 61. The H-ras gene DNA segments that include these 2 codons were amplified by PCR methods, then the possible presence of a point mutation was evaluated at each codon by susceptibility of the respective DNA segments to digestion with the restriction enzyme and by dot blot hybridization assay. A bladder cancer patient who had an H-ras gene mutation was examined to see whether the mutation was also detectable in the cells released in the urine.

RESULTS

Definite or possible point mutations were found in 6 (12%) out of 50 bladder cancer patients, while no mutation was detected in normal mucosa. A point mutation could also be detected in cells isolated from the patient's urine sample.

CONCLUSION

The prevalence of point mutations at codon 12 or codon 61 of the H-ras gene found in this study was similar to that previously estimated for human bladder cancer by DNA transfection assay. The method we have used for detecting point mutations of the H-ras gene provides a simple and highly accurate way to detect mutated cancer cells even in the urine. It may be clinically usable for early diagnosis of bladder cancer.

Molecular and genetic events in schistosomiasis-associated human bladder cancer: role of oncogenes and tumor suppressor genes

Carcinoma of the urinary bladder is the most common malignancy in many tropical and subtropical countries and is mainly due to endemic schistosomal infection. Schistosomiasis-associated bladder cancer defines a characteristic pathology and cellular and molecular biology that differs from urothelial carcinoma of non-schistosomal origin. N-Nitroso compounds are suspected etiologic agents in the process of bladder cancer induction during schistosomiasis. Elevated levels of DNA alkylation damage have been detected in schistosome-infected bladders and are accompanied by an inefficient capacity of DNA repair mechanisms. Consequently, high frequency of G --> A transition mutations were observed in the H-ras gene and at the CpG sequences of the p53 tumor suppressor gene. Genetic changes have also been detected in the c-erbB-1 and c-erbB-2 oncogenes and in the cdkn2 and Rb tumor suppressor genes. The potential application of these mutational patterns in providing a biological marker suitable for the biomonitoring and early detection of this neoplasm could indicate new avenues of approach that might alleviate the problem in the future. It can also assist in elucidating the mechanisms by which schistosomiasis augments human bladder cancers.

p53 mutations in transitional cell carcinomas of the urinary bladder in rats treated with N-butyl-N-(4-hydroxybutyl)-nitrosamine

Involvement of p53 gene alterations has been demonstrated in a variety of human neoplasias including urinary bladder carcinomas. N-Butyl-N-(4-hydroxybutyl)nitrosamine (BBN)-induced urinary bladder carcinogenesis models in rodents have been widely used to study carcinogenic processes in this organ. In the present study, transitional cell carcinomas induced in the urinary bladders of male F344 rats treated with 0.05% BBN for 16 or 32 weeks and then sacrificed at experimental week 32 were analyzed for mutational changes in the p53 and H-ras genes by polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis and subsequent DNA sequencing. The total p53 mutation incidences were 3/10 (30%) and 8/12 (66.7%) in rats treated with BBN for 16 weeks followed by 16 weeks' non-treatment, or in rats treated with BBN for 32 weeks, respectively, while the H-ras mutation incidences were 0/10 (0%), and 1/12 (8.3%), respectively. The present results indicate that mutations in the p53 gene might be involved in the process of urinary bladder carcinogenesis by BBN as part of a multistep pathway. However, considering the decreasing tendency in lesions with p53 mutations after stopping BBN administration, a p53 mutation alone would not appear to be sufficient to give a marked selective advantage to mutant cells. No evidence of H-ras mutation involvement was gained even for the late course of rat urinary bladder carcinogenesis.

Proliferative heterogeneity of human renal cell carcinomas and prevalence of ras gene point mutations

The variable prevalence and a possible stage-dependent increase of ras gene point mutations in human tumors might correspond to clonal growth advantages of ras-activated cells. Tumor areas with activated ras genes might thus differ in proliferative activity from those lacking ras gene activation. This hypothesis is studied in a series of human renal cell carcinomas that had been used previously for an analysis of proliferative compartments after post-operative vascular [3H]/[14C]thymidine perfusion [Rabes et al. (1979) Cancer 44: 799-813]. The growth fraction of different subcompartments of these tumors was studied by immunohistochemistry with mib1 antibody, recognizing a fixation- and embedding-resistant epitope of Ki-67 protein. Thirty subpopulations of 14 human renal cell carcinomas that exhibited a broad spectrum of proliferative activity were chosen for an analysis of the prevalence of K-ras point mutations in exon 1 by a mutation-enriching primer-mediated restriction-fragment-length-polymorphism analysis and/or direct sequencing of polymerase-chain-reaction-amplified material. The combined autoradiographic and immunohistochemical analysis confirmed the intra- and intertumoral proliferative heterogeneity. Compared to [3H]/[14C]thymidine labeling indices, mib1 labeling indices are higher. The ratio of mib1 to [3H]/[14C]thymidine labeling indices varies from 1.9 to 4.1 for the individual tumor subcompartments. However, neither in K-ras codons 12/13 nor in adjacent codons did we detect any mutations in the various tumor compartments. The results suggest that neither mode of proliferation nor type of differentiation is related to K-ras exon 1 point mutations in human renal cell carcinomas.

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.

High incidence of H-ras oncogene mutations in squamous cell carcinoma of lip vermilion

Nine specimens of well-differentiated squamous cell carcinoma of the lip vermilion have been analyzed for the presence of H-ras oncogene mutations, using the technique of hybridization with synthetic oligonucleotide probes on in vitro amplified tumour DNA. Five specimens harbored mutations: four in codon 12 and one in codon 13. This high incidence (55%) of mutated H-ras genes suggests that their activation may play an important role in lip tumour development and may be connected to the exposure to chemical and/or physical carcinogens.

K-ras codon 12 mutations in biliary tract tumors detected by polymerase chain reaction denaturing gradient gel electrophoresis

BACKGROUND

Although the prevalence of K-ras codon 12 mutations in biliary tract (BT) tumors has been addressed in previous studies, the results have shown large discrepancies in mutation frequency.

METHODS

K-ras codon 12 mutations were investigated by polymerase chain reaction (PCR)-denaturing gradient gel electrophoresis (DGGE), a sensitive method for detecting DNA base changes, in a large series of BT tumors.

RESULTS

In A-549 cells, which are known to contain a G to A change at the first base of K-ras codon 12, the mutation could be detected by DGGE even after 1:16 dilution with normal DNA. Tumor samples were microdissected from paraffin embedded tissue sections to ensure the presence of the tumor cells. K-ras mutations were detected in 13 of 23 bile duct tumors (56.5%) and in 9 of 23 gallbladder tumors (39.1%) by DGGE. However, no mutations were detected in normal, hyperplastic, and dysplastic BT epithelium or in tumorlike lesions, such as adenomyomatous hyperplasia, cholesterol polyps, and cystitis glandularis proliferans. The samples exhibiting abnormalities on DGGE showed a base change at K-ras codon 12 when examined by oligonucleotide hybridization.

CONCLUSIONS

K-ras codon 12 mutations are seen often in BT tumors, and a combination of microdissection and PCR-DGGE is an effective approach for their detection.

Concurrent mutations of coding and regulatory sequences of the Ha-ras gene in urinary bladder carcinomas

This report concerns the study of Ha-ras gene mutations and ras p21 expression in primary tumors of the urinary bladder. Polymerase chain reaction-based techniques and computerized image analysis were used. The data obtained were related to tumor grade, DNA ploidy, and tumor invasion. A point mutation (G-->T) at Ha-ras codon 12 was found in 30 of 67 tumors. The mutation frequency was greater in grade III (65%) than in grade II (44%) tumors; no mutations were observed in grade I tumors. The mutation was observed more often in aneuploid (58%) than in diploid (28%) tumors. No other substitution at codon 12 was seen and no codon 61 mutation was detected. The tumors were also tested for the A-->G mutation at position 2719 of Ha-ras intron D. Concurrent codon 12 and intron D mutations were identified in seven high-grade aneuploid tumors; six were invasive. The levels of the ras gene product p21 were approximately 10 times higher in tumors with intron D mutation than in those without. These findings confirm on human bladder tumors the observations of the effect of synchronous exon-intron mutations reported on the bladder cancer cell line T24. Our results are the first demonstration of Ha-ras intron D alterations in human tumor tissues and suggest that concurrent mutations at codon 12 and intron D of this gene within the same tumor may contribute to the aggressive behavior of human bladder carcinomas.

ras mutations in endocrine tumors: mutation detection by polymerase chain reaction-single strand conformation polymorphism

To elucidate the molecular basis for endocrine tumorigenesis, ras mutations in human endocrine tumors were analyzed using polymerase chain reaction-single strand conformation polymorphism (PCR-SSCP) analysis. Mutations of the H-, K-, N-ras genes were examined in genomic DNAs from 169 successfully amplified primary endocrine tumors out of 189 samples. Four out of 24 thyroid follicular adenomas analyzed contained mutated N-ras codon 61, and one contained the mutated H-ras codon 61. One of the 19 pheochromocytomas revealed mutation of the H-ras codon 13. No mutations of the ras gene were detected in pituitary adenomas, parathyroid tumors, thyroid cancers, endocrine pancreatic tumors, and adrenocortical tumors. Based on these findings we conclude that activation of the ras gene may play a role in the tumorigenesis of a limited number of thyroid follicular adenomas and pheochromocytomas, and that mutation of the ras gene is not frequent in other human endocrine tumors.

Chromosome losses in tumorigenic revertants of EJ/ras-expressing somatic cell hybrids

Tumorigenic transformation of SV40-immortalized human uroepithelial cells (SV-HUC) after transfection with EJ/ras was previously reported to be a rare event. To test the hypothesis that ras transformation requires loss of suppressor genes, somatic cell hybrids were generated between a rare tumorigenic transformant and an isogeneic nontumorigenic EJ/ras transfectant obtained in the same experiment. Both parental cell lines, as well as all hybrid progeny, expressed mutant p21 ras protein, but injections of three such independent hybrids into athymic nude mice at passage (P) 4 demonstrated that tumorigenicity was suppressed at 20 of 22 sites. Two tumors developed, after a relatively long 17-week latent period, as compared with a 4-week latent period for the tumorigenic parent. All three hybrids produced tumors at P8, but these showed different latent periods (3-14 weeks). Revertant hybrid tumors were high-grade carcinomas. Cell lines derived from these tumors expressed mutant p21 ras and retained at least 1 EJ/ras integration site. Karyotypic analysis of six independent hybrid tumor revertants showed that each had a unique clonal karyotype. Losses of two or more homologues of 1p, 3p, 4, 8, 10p, 11p, 13q, and 18 were identified in one or more tumorigenic revertants. Losses of all these chromosomes were previously associated with transformation of SV-HUC by EJ/ras, but were also associated with chemical transformation of SV-HUC in tumors that did not express mutant ras. Genetic losses involving most of these chromosomes have also been identified in clinical bladder cancers (i.e., 1p, 3p, 8, 11p, 13 and 18q). These data show that expression of EJ/ras does not negate or significantly alter requirements for multiple genetic losses in HUC tumorigenesis.

The molecular biology of urological tumors

This article reviews the present understanding of chromosomal aberrations and specific genetic mutations in renal, bladder, and prostate cancers. In kidney tumors, specific emphasis is given to chromosome 3 deletions in renal cell carcinoma and the characterization of the WT1 gene in Wilms' tumor. In all three urological tumors, the presence of mutations in the RAS, P53, and RB genes (all of which often occur in other tumors) is analyzed. The expression and properties of the androgen receptor in prostate cancer are also summarized.

Enhanced immunoreactivity of ras oncogene p21 protein in urinary bladder epithelium of rats treated with N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide

Normal urothelium and various lesions of the rat urinary bladder induced by the dietary administration of 0.2% N-[4-(5-nitro-2-furyl)-2-thiazolyl]formamide (FANFT) (up to 77 weeks) or by the combination of 0.2% FANFT and the subsequent administration of 5% sodium saccharin or 2% DL-tryptophan (up to 104 weeks) were evaluated for immunoreactivity with monoclonal antibody to ras p21 by avidin-biotin immunohistochemistry. Seventy-one to 100% of transitional cell carcinomas showed strong reactivity to the antibody to ras p21 depending on treatment with long-term administration of FANFT or by 6 weeks administration of FANFT followed by sodium saccharin or DL-tryptophan. Focal reactivity to the ras p21 antibody was frequently observed in the hyperplastic (57-96%) or normal appearing urinary bladder epithelium (50-100%) in rats treated with FANFT (FANFT alone or in combination with sodium saccharin or tryptophan) but not in hyperplasia or normal epithelium in rats given sodium saccharin or tryptophan alone, without pretreatment with FANFT or in untreated controls. The present results show that there is a close association of enhanced immunoreactivity with ras p21 antibody in the urinary bladder epithelium to FANFT treatment, and that ras p21 is expressed in normal, hyperplastic and neoplastic lesions of the bladder of rats treated with FANFT. These results suggest that enhanced immunoreactivity with ras p21 is observed as a consequence of the treatment with FANFT but it alone does not reflect the progression from benign to malignant lesions.

Analysis of ras DNA sequences in rat renal cell carcinoma

The DNA sequences for Ha-, Ki-, and N-ras were determined in six cell lines derived from independent rat hereditary renal cell carcinomas (RCC). Genomic regions encompassing codons 12, 13, and 61 of Ha-ras, Ki-ras, and N-ras, and codon 117 of Ha-ras were PCR amplified and directly sequenced. The DNA sequences of Ha-ras and Ki-ras were normal in all lines tested, as were the codon 12 and 61 sequences of N-ras. However, DNA sequence variations that could code for amino acid substitutions were observed in codons 13, 14, and 18 of N-ras in all the lines. The codon 13 Gly----Val alteration observed was consistent with activating N-ras mutations previously reported. When normal kidney DNA from rats with the hereditary tumor syndrome was sequenced, the same N-ras sequence variations observed in the tumor lines were found. DNA from outbred Long-Evans and inbred Fischer rats also had the altered N-ras sequences. The variant N-ras sequence was not observed in PCR-amplified N-ras cDNA from the RCC lines. Thus, tumor-associated activation of ras oncogene appears to be an infrequent event in spontaneous rat RCC. In addition, these data indicate that rats contain an N-ras DNA polymorphism that appears to be a species-specific anomaly.