Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0596263 (carcinogenesis)
 64,820 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In studies on bacteria, the excision repair of UVR-induced DNA base damage has been divided into two major pathways on the basis of physiologic requirements and genetic control. The major pathway requires a functional polA+ gene, does not need complete growth medium, is largely error free, and produces short patches during repair. The second pathway requires complete growth medium and functional recA+, recB+, recC+, lexA+, uvrD+, and polC+ genes, is mutagenic, and produces long patches during repair. A second type of ecision repair exists, in which the modified base is removed by a DNA glycosylase, and the chain is nicked by an apurinic (apyrimidinic) acid endonuclease. Subsequent events are presumed similar to the above excision repair process. The postreplication repair system has been divided into at least four distinct pathways, three of which depend on functional recB+, lexA+, and uvrD+ genes, and are error free. A fourth pathway depends on the above gene products but is blocked by postirradiation treatment with chloramphenicol, and may be the UV-inducible, error-prone, mutagenic pathway of repair ("SOS repair"). A possible fifth pathway is dependent on a functional recF+ gene and is independent of the recB+-dependent pathway. Mutagenesis is the result of error-prone DNA repair, and evidence is growing that carcinogenesis is also the result of error-prone repair. Therefore, a complete understanding of DNA repair is crucial to a complete understanding of the molecular basis of carcinogenesis.
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PMID:Multiple pathways of DNA repair and their possible roles in mutagenesis. 38 33

UV light-induced mutagenesis in bacteria is a genetically controlled process dependent on induction of some cellular functions, provoked initially by unrepaired photolesions in the DNA. Experiments on the extent and fidelity of in vitro DNA systhesis on UV-irradiated templates by bacterial mammalian DNA polymerases suggest a crucial role for 3' to 5' exonuclease (proofreading) activity in UV light-induced mutagenesis. Two-stage carcinogenesis (initiation and promotion) is discussed in terms of two-stage mutagenesis (mutation fixation in the DNA and mutation expression). A unifying concept for both mutational and viral malignant transformation is proposed.
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PMID:Mutagenesis and cell transformation by ultraviolet irradiation: many hypotheses for few results. 38 35

Clinical observations and epidemiologic studies indicate that the sun is the primary stimus for most human skin can formation. However, investigations directly confirming this association as well as defining the action spectra, time-dose relationships, energy level requirements, etc., have been confined to animal experimentation. Studies in which gross methods are used indicate that the experimental carcinogenic action spectrum falls primarily between 280 and 320 nm. Quantitative studies and tumor promotion investigations indicate that UV-induced cancer formation begins with the initial exposure. Heat, wind, and moisture stimulate UV carcinogenesis. Also, exogenous chemicals may influence carcinogenesis as photosensitizers such as 8-MOP, as additive carcinogens as noted with DMBA, or as promoters as described for Croton oil, retinoic acid, and BCNU. Qualitative studies indicate that progressive alterations occur in the epidermal-dermal basement membrane and dermal conncecive tissue and mucopolysaccharides associated with the progressive development of epidermal cancers. Malignant melanomas have also been induced experimentally in hairless mice with UV energy. Mechanistically, immunologic alterations and effects on DNA have received the most attention. Tumor-specific antigenicity as well as antigen deletion has been demonstrated. Immune suppression by antilymphocyte serum and certain chemicals has led to stimulation of tumor development. Perhaps the most exciting new information relates to the demonstration that chronically UV-irradiated mice have not rejected highly antigenic UV-induced cancers. This indicated that UV irradiation specifically altered the immunologic responses of the animals to these tumors. Within recent years, the influence of DNA injury and repair on cutaneous carcinogenesis has received a great deal of attention. This has been partly due to the demonstration of defective repair of UV-induced DNA damage in patients with XP. The primary photosensitive problem in these patients is an inordinate sensitivity to the carcinogenic effects of sunlight. However, correlation of DNA injury and repair directly with cancer formation has not been accomplished.
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PMID:Photocarcinogenesis: a review. 38 36

The mechanism of carcinogenesis is not yet understood. There is increasing evidence justifying the assumption that an unifying concept of carcinogenesis should be possible at the molecular level. New insights into the molecular mechanism of carcinogenesis were mainly obtained in studies on both chemical and viral carcinogenesis. In the present paper, selected results of these studies are reviewed. It is concluded that the interaction of different carcinogenic agents with the cellular DNA results in alterations of DNA. Only some of these alterations, however, seem to be relevant to carcinogenesis. Alterations of DNA can be caused by reaction of electrophilic agents with DNA constituents, by increased infidelity of DNA replication, by integration of viral genomes or by recombination events involving integrated proviruses.
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PMID:[Molecular aspects of carcinogenesis (author's transl)]. 39 99

The carcinogenic process is usually multifactor in its causation and multistep in its evolution. It is likely that entirely different molecular mechanisms underlie the many steps in this process. In contrast to initiating carcinogens, the action of the tumor-promoting phorbol esters does not appear to involve covalent binding to cellular DNA and they are not mutagenic. Recent studies in cell culture have revealed two interesting biologic effects of the phorbol esters and related macrocyclic plant diterpenes. The first is that at nanomolar concentrations they induce several changes that resemble those seen in cells transformed by chemical carcinogens or tumor viruses. These include altered morphology and increased saturation density, altered cell surface fucose-glycopeptides, decrease in the LETS protein, increased transport of deoxyglucose, and increased levels of plasminogen activator and ornithine decarboxylase. In transformed cells exposed to phorbol esters the expression of these features is further accentuated. Phorbol esters do not induce normal cells to grow in agar but they do enhance the growth in agar of certain transformed cells. The second effect of the phorbol esters is inhibition of terminal differentiation. This effect extends to a variety of programs of differentiation and is reversible when the agent is removed. With certain cell culture systems induction of differentiation, rather than inhibition, is observed. Both the transformation mimetic and the differentiation effects are exerted by plant diterpenes that have tumor-promoting activity but not by congeners that lack such activity. The primary target of phorbol esters appears to be the cell membrane. Early membrane-related effects include enhanced uptake of 2-deoxyglucose and other nutrients, altered cell adhesion, induction of arachidonic acid release and prostaglandin synthesis, inhibition of the binding of epidermal growth factor to cell surface receptors, altered lipid metabolism, and modifications in the activities of other cell surface receptors. A model of "two stage" carcinogenesis encompassing the known molecular and cellular effects of initiating carcinogens and tumor promoters is presented. According to this model, initiating carcinogens induce stable alterations in the cellular genome but these are not manifested until tumor promoters modulate programs of gene expression and induce the clonal outgrowth of the initiated cell.
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PMID:Action of phorbol esters in cell culture: mimicry of transformation, altered differentiation, and effects on cell membranes. 39 70

A maximum tolerated dose (15 mug/g) of the carcinogen 4-nitroquinoline 1-oxide (4NQO) induced neither fetal deaths nor malformations when given to pregnant ICR/Jcl mice at the sensitive stages (Days 9 to 11) for the induction of malformations, although these embryotoxicities were detected with urethan and X-ray. This may not be due to the lack of teratogenic actions of 4NQO, but to the difficulty this compound has in reaching the embryo, because direct injection of 4NQO into the amniotic cavity of the Day-11 embryo, so that exposure was more direct, induced a high incidence of malformations. Similarity of the mechanism of chemical carcinogen-initiated teratogenesis and carcinogenesis was also suggested by the following findings. Urethan-initiated teratogenesis was almost completely inhibited by posttreatment with caffeine during the period of 0 to 24 and 24 to 48 hr after urethan treatment, whereas it was not inhibited during the 48- to 72-hr post-urethan and the 6- to 30-hr pre-urethan period. The results are similar to those of 4NQO-initiated transformation in cultured mouse embryo cells and 4NQO- and urethan-initiated lung tumorigenesis in mice. Cells carrying preteratogenic or pretumorigenic damage produced by some chemical carcinogens may be extremely sensitive to caffeine treatment during and/or after the postcarcinogen DNA replication period, thus resulting in decrease of malformations and tumors. The process may be related to error-prone DNA repair, because caffeine is known to inhibit the postreplication repair in cultured mouse cells.
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PMID:Similarity of the mechanism of chemical carcinogen-initiated teratogenesis and carcinogenesis in mice. 40 2

Evidence for a mutation theory of cancer is presented by reviewing the experimental work on 4-nitroquinoline 1-oxide (4NQO) carcinogenesis. 4NQO almost completely mimics u.v. light and produces 4NQO-purine adducts on DNA. When 4NQO-treated cells are held in liquid medium under appropriate conditions, the 4NQO adducts disappear from DNA, in parallel to decrease of premutational damage in Escherichia coli, or pretransformational damage in cultured mouse cells. Post-treatment with caffeine greatly diminishes the yields by 4NQO of mutants in E. coli, malignant transformants in cultured mouse cells and tumour nodules in the lung of mice. Potentially tumourigenized stem cells in the lung remain sensitive to selective killing by caffeine for at least 5 days after 4NQO treatment, in spite of their DNA being apparently replicated, an indication that carcinogen-damaged DNA in the stem cell can be transmitted to its successive daughter stem cells for many generations. This peculiar characteristic is discussed as a possible lead to the crux of the mutation theory of cancer in vivo, and a model for carcinogenesis is proposed.
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PMID:A test for mutation theory of cancer: carcinogenesis by misrepair of DNA damaged by 4-nitroquinoline 1-oxide. 40 31

The effect of portacaval shunt on hepatocarcinogenesis was studied in rats fed 3'-methyl-4-dimethylaminoazobenzene. Portacaval anastomosis resulted in a decrease of hepatocarcinogenesis as reflected by a delay in the early peak of alpha-fetoproteins, an absence of late appearance of alpha-fetoproteins, and a significantly lower incidence of tumors than in nonshunted rats. Reduction of hepatocarcinogenesis in shunted rats was associated with a decrease of the binding of 3'-methy-4-dimethylamioazobenzene metabolites to liver proteins. This effect seemed to be related to modifications of carcinogen-metabolic pathways. While the detoxifying azoreductase activity was not affected by portal diversion, the activating pathway leading to the binding of 4-dimethylaminoazobenzene metabolites to DNA, a major step for cell carcinogenesis that is mediated by microsomal enzymes, was decreased in shunted rats to about 50 percent of control values. The decrease of liver weight that occurred in shunted rats without loss of body weight produced a very significant reduction of the total capacity of liver to activate 4-dimethylaminoazobenzene while the total capacity of detoxification remained unchanged. This could be a direct consequence of portacaval anastomosis, as has been shown for other microsomal enzymes.
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PMID:Modifications of 3'-methyl-4-dimethylaminoazobenzene carcinogenesis of rat liver and carcinogen metabolism by portacaval anastomosis. 41 69

The effect of 4-hydroxyaminoquinoline-1-oxide (4-HAQO) on DNA synthesis in the pancreas and liver, target and non-target organs for 4-HAQO carcinogenesis, respectively, were compared. Pancreatic and liver DNA synthesis were simultaneously induced in rats fed a protein deficient diet containing 0.5% DL-ethionine for 18 days, and DNA synthesis in both tissues was inhibited by hydroxyurea. A single i.v. injection of 4-HAQO at a dose of 7 mg/kg body weight also inhibited DNA synthesis in both tissues within 4 h. In the pancreas the inhibition was maximum at a dose of 7 mg/kg, and DNA synthesis was less than in the pancreas of rats fed a control grain diet. This inhibition continued for the subsequent 5 days which were tested. In the liver, the degree of inhibition was less than in pancreas but the value remained higher than in rats fed control diet. The inhibition of liver DNA synthesis at a dose of 7 mg/kg completely recovered within 1 day. These results suggest that the lesions of DNA induced by 4-HAQO and its repair might be different between the pancreas and the liver. A pancreatic chemical carcinogen, 4-HAQO, might thus have the same cytotoxic effect that liver carcinogens have toward the liver resulting in failure to respond to mitotic stimuli. This might be causally related to the organotropism of 4-HAQO toward the pancreas.
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PMID:Differential effects of 4-hydroxyaminoquinoline-1-oxide on pancreatic and liver DNA synthesis in rats. 41 97

The rapid development of the chemical industry, combustion of fossil fuels, and smoking of tobacco have resulted in contact of the general population with benzo(a)pyrene and other carcinogenic aromatic hydrocarbons. Persons especially at risk occupationally are those engaged in thermal processing of oil shale, coal, and heavy residual petroleum. It has been shown that polycyclic aromatic hydrocarbons require metabolic activation before they can act as mutagens or carcinogens. This metabolic activation results from interaction with microsomal enzymes present in many body cells, yielding reactive epoxides which react with DNA and produce mutations in the count frame shift or participate in covalent bounding. While opinions differ regarding the relative role of these processes in mutagenesis, considerable evidence exists which links mutagenesis and carcinogenesis. Metabolites of the polycyclic aromatic hydrocarbons which are carcinogenic are usually mutagenic, which supports the hypothesis that damage to chromosomes plays an important role in carcinogenesis. These facts open the possibility to monitoring the spread of carcinogenic substances in the biosphere by relatively simple tests whose endpoint is mutagenesis.
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PMID:Mutagenic and carcinogenic properties of polycyclic aromatic hydrocarbons. 44 50


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