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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Retinoblastoma is the most frequent malignant tumour of the eye in the child; the median age at diagnosis is two years. A model of carcinogenesis by two successive mutations has been devised for this tumour and explains the two forms of the disease, hereditary and non-hereditary. It is most often manifested by a whitish pupillary reflection (leukocoria) or internal strabismus. Funduscopy using general anaesthesia is used to confirm diagnosis and assess endo-ocular extension. When the disease is confined to the retina, local treatment (enucleation, radiation therapy) leads to cure in a very large majority of cases. When diagnosis is made early, particularly as in familial cases, conservative treatment is possible. In intra- and extra-retinal disease, chemotherapy and radiation therapy can improve prognosis.
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PMID:[Retinoblastoma]. 814 37

Expression of a recessive phenotype can occur by a number of different mechanisms, such as chromosomal deletion, recombination, and intragenic frameshift mutation or base substitution. To examine the contribution of different mutational events, we isolated and characterized a human fibroblast cell line heterozygous at the adenine phosphoribosyltransferase (APRT) locus. Cells that subsequently lost APRT activity were selected, cloned, and analyzed for the mechanisms contributing to the loss of APRT activity. Loss of APRT activity occurred at a rate of 7.8 x 10(-5) per allele per cell generation. Molecular analysis of DNA from 21 independent APRT- clones demonstrated that 62% of mutants had lost the functional allele and that the rest had incurred intragenic mutations. Loss of the functional allele was frequently accompanied by loss of the proximal marker D16S77 but not the more distant proximal marker D16S4, indicating that a high frequency of mitotic recombination or deletion occurred at the region between D16S77 and D16S4 on chromosome 16. Loss of APRT activity in the remaining 38% of the clones was predominantly due to point mutations. These data demonstrate that the mechanisms for loss of heterozygosity at the APRT locus are similar to those found in retinoblastoma and other tumors. The autosomal location of the APRT gene and the ease with which its phenotype can be selected make this gene useful for modeling mutational events at loci important to carcinogenesis.
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PMID:Loss of heterozygosity: the most frequent cause of recessive phenotype expression at the heterozygous human adenine phosphoribosyltransferase locus. 821 32

Esophageal carcinomas from 24 patients, most of whom were smokers and consumed alcoholic beverages daily, were analyzed for mutations in exons 5-8 of the p53 tumor suppressor gene. Mutations were identified by polymerase chain reaction amplification and direct sequencing in 12 of 24 (50%) of the samples; almost half of the mutations were at A:T base pairs. Nuclear accumulation of p53 protein, determined by immunohistochemistry with the CM-1 polyclonal antibody, was observed in all cases in which a missense mutation in the p53 gene was detected. None of the 24 carcinomas had amplification of the mdm2 gene, an alternate pathway to p53 loss of function. Alterations involving three other cancer-related genes associated with human esophageal carcinogenesis, c-erbB-1/epidermal growth factor receptor (EGFR), c-myc, and retinoblastoma (Rb), were examined by Southern blot or immunohistochemical analysis in the same sample set to explore the possibility of a link between oncogene activation and loss of tumor suppressor function. While no associations were observed between amplification of the c-myc or EGFR genes and p53 abnormalities, a significant correlation (P < 0.01) was seen between the presence of p53 mutation and EGFR overexpression. Absence of Rb protein, measured immunohistochemically, was observed in four tumors, none of which had aberrations of the p53 gene.
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PMID:Correlation of p53 mutations with epidermal growth factor receptor overexpression and absence of mdm2 amplification in human esophageal carcinomas. 828 Mar 79

The recent advances in molecular biology have led to a concept that carcinomas arise from the accumulation of a series of genetic alterations involving activation of protooncogenes and inactivation of tumor suppressor genes. The present study was designed to elucidate that such processes take place in the tumorigenesis of the uterine endometrium as well. The incidence of ras gene mutation, which were mostly composed of the point mutations of k-ras codons 12 and 13, was higher in carcinomas (31%) than atypical hyperplasias (15%), with marginal significance, but has not been associated with aggressiveness of the carcinomas. Thus, k-ras activations may occur as an early event in tumorigenesis. Mutations of tumor suppressor gene, p53, were detected in 24% of carcinomas and 8% of atypical hyperplasia, while they are not statistically different. The p53 mutations were associated with poorly differentiated adenocarcinomas. The most common pattern of the base change detected in endometrial carcinomas was the transition from G:C to A:T. The p53 mutations at CpG sites were frequent, especially at codon 248. Loss of heterozygosity (LOH) was more frequently detected than the mutations and most cases with LOH harbored the mutations, suggesting that allelic loss may precede the mutation in the tumorigenesis of endometrium. Expression of p53 was well correlated with type of the p53 mutation and its overexpression is associated with aggressive clinical behavior, suggesting the possible application of p53 as a prognostic indicator. The other tumor suppressor genes, Retinoblastoma gene (RB) and DCC gene, were also involved in the endometrial carcinogenesis. LOH and abnormal m-RNA of RB were detected in 15% and 33% of carcinomas, respectively, and associated with advanced clinical stage and poorly differentiated adenocarcinomas. LOH of DCC was also detected in some cases while that of APC was not detected. Thus, tumor suppressor genes may also play an important role as later events in carcinogenesis by inactivation mechanism consisting of the loss of one chromosomal allele and/or mutation of the gene in the remaining allele. Human papillomavirus (HPV) DNA type 16 was curiously detected in 5% of cases by both Southern blot and in situ hybridization analyses. Consequently, two third of endometrial carcinomas examined in the present study for ras, p53, RB, DCC, APC and HPV showed abnormality of at least one of these genes. The abnormality of multiple genes may contribute as an etiologic role to multisteps in carcinogenesis of the endometrium.
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PMID:[Genetic alterations and transformations in development and establishment of uterine endometrial carcinomas]. 837 Oct 6

The authors have established an in vitro model system which demonstrates the progression of the transformed phenotypes of human cervical epithelial cells transfected with human papillomavirus (HPV) type 16 and 18 DNAs. Both viral DNAs exhibit immortalizing potential; however, only HPV 18-immortalized cell lines progress to exhibit anchorage-independent growth and, in a limited number of cases, tumorigenesis. In this paper, the authors have examined the genetic basis for this in vitro progression step by step, including immortalization, anchorage-independent growth, and tumorigenicity of the HPV-transfected human cervical epithelial cells by cell fusion. The results suggest that (a) all three transformed phenotypes, i.e., immortalization, anchorage-independent growth, and tumorigenesis, in this in vitro cervical carcinogenesis model are a result of recessive changes in genes or processes involved; (b) inactivation of p53 and retinoblastoma protein is not sufficient for immortalization of human cervical epithelial cells; (c) HPV expression per se does not account for immortalization of human cervical epithelial cells; (d) immortalization of human cervical epithelial cells initiated by HPV can occur through different processes, although one of them is the most preferred; and (e) probably only one group of recessive genes appears to be involved in the loss of anchorage-dependent growth for HPV-immortalized human cervical cells.
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PMID:Genetic analysis of in vitro progression of human papillomavirus-transfected human cervical cells. 838 57

Cyclin A associates with both the p34 cdc2 and p33 cdk2 kinases and is involved at two major check-points (G1-S and G2-M) of the cell cycle. The cyclin has been identified in multimeric protein complexes that incorporate the E2F transcription factor, the p33 cdk2 kinase, and p107, which is related to the retinoblastoma protein. Therefore, cyclin A provides a link between studies on the cell-cycle machinery and those aiming to elucidate the modulation of cell proliferation and regulation of gene expression by oncogenes and growth-suppressor proteins. The modification of cyclin A expression in a human liver cancer by the insertion of hepatitis B viral DNA into the cyclin A gene, and binding of cyclin A to the oncogenic E1A viral protein in adenovirus-infected cells suggest that the cyclin is implicated in human carcinogenesis. In addition, cyclin A might also be considered as a marker for tumor-cell proliferation in oncology. With these views in mind, it is now important to extend these observations to other types of cancer.
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PMID:Oncogenic activation of cyclin A. 838 33

The effect of the human papillomavirus (HPV) oncogenes E6 and E7 was examined in transgenic mice with a construct containing the human beta-actin promoter regulating HPV16 E6 and E7 open reading frames. In the sole line of mice that transmitted the transgene, neuroepithelial tumors appeared at 2.5 months of life, and by 10 months, 87 of 122 (71%) of the animals were dead from brain tumors. The most frequent type of tumor (74%) was an anaplastic neuroepithelial tumor associated with the ependyma of the third and fourth ventricles, which locally invaded adjacent brain tissue and spread for considerable distances along the ventricular surface. The other two types of tumor were well-differentiated choroid plexus carcinomas (26%) and rare pituitary carcinomas (8.7%). HPV16 E6 RNA and E7 oncoprotein expression were demonstrated in tumor tissue and primary cell lines derived from the tumors. Examination of two tumor suppressor gene products, the retinoblastoma protein and p53, known to bind to HPV16 E7 and E6 oncoproteins, respectively, showed both were expressed in the primary tumor cell lines. These data support a causative role for the HPV oncoproteins in epithelial carcinogenesis.
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PMID:Neuroepithelial carcinomas in mice transgenic with human papillomavirus type 16 E6/E7 ORFs. 838 43

Since multistage carcinogenesis is frequently associated with the loss of suppressor gene activity, and since in over 90% of cases of nasopharyngeal carcinoma (NPC) p53 alterations are not involved [Sun, Y., Hegamyer, G.H., Cheng, Y.-J., Hildesheim, A., Chen, J.-Y., Chen, I.-H., Cao, Y., Yao, K.-T. & Colburn, N.H. (1992). Proc. Natl. Acad. Sci. USA, 89, 6516-6520] we investigated the possible involvement of the inactivation of the retinoblastoma susceptibility gene (RB) in nasopharyngeal carcinogenesis. We analysed the expression, gross structure and possible point mutation of the RB gene in an NPC cell line as well as seven NPC biopsies obtained from seven patients. The NPC cell line expresses the RB gene with a normal size and abundance, as assayed by reverse transcriptase polymerase chain reaction (RT-PCR) and Northern hybridization. No point mutation was detected in two independent E1A/large T-binding regions, which are the common sites for mutations in the RB gene. NPC biopsies also showed no point mutations at four exon-intron boundaries at which point mutations have been reported in other human carcinomas. The biopsies and cell line had no deletions in the promoter region of the gene and showed no gross deletions or rearrangements. Taken together, we conclude that, in contrast to multistage carcinogenesis leading to human retinoblastoma, osteogenic sarcomas and carcinomas of lung, breast, bladder and prostate, nasopharyngeal carcinogenesis appears unlikely to involve RB gene alterations.
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PMID:Nasopharyngeal carcinoma shows no detectable retinoblastoma susceptibility gene alterations. 843 63

Two distinct gene classes have been implicated in colorectal carcinogenesis. Tumour promoter genes (oncogenes, dominant oncogenes) produce an excessive positive stimulus to cell proliferation. The ras family of oncogenes are an example. Acquired mutations of the c-k-ras gene are commonly found in colonic adenomas and carcinomas. Tumour suppressor genes (anti-oncogenes, recessive oncogenes) normally constrain or regulate cell proliferation. Loss of this function through gene deletion or mutation is oncogenic. Inherited tumour suppressor gene mutations have now been identified in several of the familial cancer syndromes. Acquired tumour suppressor gene mutations are found in both sporadic and hereditary cancers. Together with the tumour promoter genes they provide the genetic basis for the cellular changes occurring during carcinogenesis. The retinoblastoma gene was the first human tumour suppressor gene to be characterized and exemplifies the class. More recently, linkage studies in the hereditary cancer syndromes and the detection of specific deletions in sporadic tumours have helped to identify several new tumour suppressor genes. At least four of these (MCC, APC, p53 and DCC) apparently contribute to sporadic colorectal carcinogenesis. Germ line APC mutations produce the inherited colorectal cancer syndrome familial adenomatous polyposis (FAP). Detection of these mutations using linked markers has already found clinical application in the screening of families with this disease. In the future, genetic diagnosis of hereditary non-polyposis colorectal cancer (HNPCC) and the recognition of those genetically susceptible to sporadic colorectal cancer may become possible. At the same time, as our understanding of the genes involved improves, new avenues for treatment and prevention of colorectal cancer may emerge.
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PMID:Tumour suppressor genes and colorectal neoplasia. 847 56

Mutations of the p53 tumor suppressor gene are the most common defined genetic alterations seen in a wide variety of human cancers. In contrast, little is known about the importance of the p53 gene in chemically induced tumors of rodents, which are widely used as models for the evaluation of human health risks. In this study we examined 54 methylene chloride-induced and seven spontaneously arising lung tumors from female B6C3F1 mice for losses of heterozygosity (LOH) at markers near the p53 gene on chromosome 11. LOH was detected in seven methylene chloride-induced lung carcinomas by Southern analysis of a restriction fragment length polymorphism and PCR analysis of five simple sequence length polymorphisms. In each case allele loss was observed at all six markers; thus, these chromosomal alterations were likely to have resulted from mitotic nondisjunction. In contrast, LOH was not detected in 20 liver tumors from methylene chloride-treated mice at the Acrb locus, which is tightly linked to the p53 gene on chromosome 11. In addition single strand conformation polymorphism analysis was performed to screen for mutations in the most conserved regions of the p53 gene (exons 5 to 8). Consequently, potential mutations identified by direct sequencing, were only detected in four of the seven tumor samples with LOH, but not in any of the remaining lung tumors. Overexpression of the p53 protein by immunohistochemical staining was detected only in the four tumors that contained p53 point mutations and in a focal area of another tumor. Finally, using a simple sequence length polymorphism within the retinoblastoma tumor suppressor gene, LOH on mouse chromosome 14 was also detected in three lung carcinomas and one liver tumor. Inactivation of p53 and possibly the retinoblastoma tumor suppressor gene appear to be infrequent events in lung and liver tumors from methylene chloride treated mice.
Carcinogenesis 1993 May
PMID:Characterization of p53 mutations in methylene chloride-induced lung tumors from B6C3F1 mice. 850 69


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