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)

The distribution of O6-methylguanine-DNA methyltransferase (MGMT) activity in extracts of tumors from 74 patients was measured. The results demonstrated that there was considerable variation of MGMT activity in different human tumor tissues as well as in different individuals. The mean values (X +/- SD, pmol/mg of protein) in breast cancer, stomach cancer, small cell lung cancer, non-small cell lung cancer, renal cell carcinoma, esophageal carcinoma, brain tumors, colon carcinoma and malignant melanoma were 1.071 +/- 0.374 (9), 0.515 +/- 0.107 (5), 0.509 +/- 0.251 (5), 0.461 +/- 0.227 (24), 0.329 +/- 0.246 (5), 0.273 +/- 0.376 (5), 0.244 +/- 0.175 (14), 0.242 +/- 0.308 (5) and 0.201 +/- 0.161 (2) respectively. It was notable that six samples (1/24 non-small cell lung cancer, 3/5 esophageal carcinoma, 1/14 brain tumors and 1/5 colon carcinoma) did not have any detectable level of MGMT activity. Activity of glutamine pyruvic transaminase (GPT) was also measured in the same extracts used for the assay of MGMT activity. The activity of GPT in these samples with undetectable level of MGMT activity was similar to those with significant MGMT activity. These results further strengthen the assumption that a certain fraction of human tumors are Mer-.
Carcinogenesis 1992 Sep
PMID:O6-methylguanine-DNA methyltransferase activity in human tumors. 139 31

A non-transformed human fibroblast strain, GM11, established from the skin of a therapeutically aborted fetus, has been reported to exhibit the Mer- phenotype, i.e. inability to support the growth of adenovirus 5 damaged with 1-methyl-3-nitro-1-nitrosoguanidine. In the present study we determined (i) loss of colony-forming ability and frequency of mutants resistant to 6-thioguanine (6TG) on exposure to the SN1 alkylating agent methylnitrosourea (MNU) and (ii) amount of O6-methylguanine-DNA methyltransferase (MGMT), the protein responsible for repairing O6-methylguanine (O6mG) produced by MNU, in GM11 cells compared to GM10, a Mer+ human fetal fibroblast strain. Irrespective of in vitro culture age, GM10 cells responded normally to the cytotoxic action of the alkylating agent, i.e. their clonogenic survival curves exhibited a shoulder at low MNU concentrations (less than or equal to 0.4 mM) and a D10 (dose reducing survival to 10%) of approximately 1.4 mM. By contrast, no shoulder was observed on the survival curves of GM11 cells and their D10 values decreased from approximately 0.6 mM at passage 4 to 0.1 mM at passage 27. In GM10 (Mer+) cells, unlike the biphasic dose response seen for cell killing, the frequency of 6TG-resistant mutants increased as a linear function of chemical concentration delivered (range 0.05-1.2 mM); the induced mutation frequency in these cells (passage 16-20) was equal to 220 x 10(-6)/mM MNU, a yield some 5-fold greater than that reported by others for non-fetal human fibroblasts. GM11 cells proved to be only approximately 1.5 times more mutable by MNU than GM10 cells at late passage, and the susceptibility of the former strain to MNU-induced mutations did not change significantly as a function of culture age (i.e. 316 x 10(-6) and 326 x 10(-6) mutants/mM MNU at passages 4 and 16-20 respectively). The GM10 strain contained approximately 75,000 MGMT molecules/cell at all passages (4-20) examined, whereas the GM11 strain harbored deficient amounts of the protein (approximately 22,500 molecules/cell) at the lowest passage available (4), and this residual activity decreased precipituously to undetectable amounts by passage 16. Together, these data demonstrate that in the two human fetal strains examined the constitutive level of cellular MGMT activity correlates much better with resistance to reproductive inactivation than with mutagenesis by MNU, implying that inefficient repair of O6meG lesions impacts more severely on cell lethality than on mutation induction in at least some biological systems.
Carcinogenesis 1992 Jul
PMID:Cytotoxic and mutagenic effects of methylnitrosourea in two human fetal fibroblast strains differing in O6-methylguanine-DNA methyltransferase activity. 163 85

The level of the DNA repair enzyme O6-alkylguanine-DNA alkyltransferase (MGMT) was examined in benign and malignant skin tumors induced with different initiating and promoting agents and from both SENCAR and Sensitive SENCAR Inbred (SSIN) mice. The MGMT levels in the tumors were approximately one-half the level observed in normal surrounding epidermis and in keratinocytes from untreated controls. In addition, a carcinoma-producing cell line, VT 17DT, derived from papillomas in SENCAR mice had no detectable MGMT activity (Mer- phenotype), whereas in the non-tumor forming line, 3PC, MGMT activity was comparable to that in papillomas. The comparatively low level of MGMT in papillomas may contribute to their ease of conversion to squamous cell carcinomas by N-ethyl-N-nitrosourea or n-methyl-N'-nitro-N-nitrosoguanidine. MGMT activity was also determined in the epidermis of non-exposed mice of various stocks and strains. Epidermal MGMT activity was similar to levels in the corresponding livers and was, in general, parallel with stock/strain susceptibility to tumor formation. This is the first report that examined MGMT activity in skin tumors and normal keratinocytes in the mice of several stocks and strains.
Carcinogenesis 1992 Jul
PMID:O6-alkylguanine-DNA alkyltransferase activity in epidermal tumor and normal epidermal cells of mice of various stocks and strains. 163 96

The inactivation of human and Escherichia coli O6-alkylguanine-DNA alkyltransferase by O6-methylguanine and O6-benzylguanine was compared. When HT29 cell extracts or E. coli Ada protein were incubated in the presence of 200 microM O6-methylguanine for 1 h, alkyltransferase activity was reduced to 44 and 39% of control levels respectively. However, under the same conditions O6-benzylguanine completely depleted alkyltransferase activity in the extract from human cells but had virtually no effect on the Ada protein. Incubation of the HT29 cell alkyltransferase with O6-benzyl[3H]guanine resulted in a time-dependent production of [3H]guanine. No similar production of [3H]guanine was observed in the presence of the Ada protein. In CHO cells transfected with the bacterial ada gene (CHO-ada) or the human alkyltransferase cDNA (CHO-MGMT), treatment with 500 microM O6-methylguanine inhibited both alkyltransferases by greater than 85%. In contrast, 2 microM O6-benzylguanine inhibited human alkyltransferase expressed in CHO-MGMT cells by greater than 99% though concentrations as high as 25 microM for 24 h had no inhibitory effects on the bacterial alkyltransferase expressed in CHO-ada cells. This selective inhibition was also observed in vivo in transgenic mice expressing ada in the liver where O6-benzylguanine caused a decrease of only 40% in total hepatic alkyltransferase activity compared to 95% in non-transgenic mice, consistent with inhibition of only the mammalian alkyltransferase and maintenance of bacterial alkyltransferase activity in these animals. Thus, while O6-methylguanine at high concentrations inactivates both bacterial and mammalian alkyltransferases, O6-benzylguanine is a substrate only for the mammalian protein and is unable, perhaps due to steric hindrance, to inhibit the Ada protein.
Carcinogenesis 1991 Dec
PMID:Comparison of the inactivation of mammalian and bacterial O6-alkylguanine-DNA alkyltransferases by O6-benzylguanine and O6-methylguanine. 174 32

We have constructed a plasmid in which the expression of human O6-methylguanine-DNA methyltransferase (MGMT) cDNA is driven by the Rous sarcoma virus promoter sequence. Transfection of this plasmid into Chinese hamster ovary (CHO) cells results in expression of MGMT and in cellular resistance to N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and 1-(2-chloroethyl)-1-nitrosourea (CNU), but not to N-nitroso-N-ethylurea. The specific activity of MGMT in transfected CHO cells correlated well with their resistance to MNNG and CNU. Southern analysis showed that the plasmid had been integrated into the CHO cell genome. Western analysis of extracts from transfected CHO cells using an antibody against a peptide corresponding to the carboxyl-terminal end of the human MGMT protein demonstrated a single band with a molecular size of 24-25 kDa; no such band was observed in extracts from wild-type CHO cells. These transfected cells may therefore be used to study the role of MGMT in the repair of alkylating DNA lesions and to determine its importance in carcinogenesis as well as in chemotherapy.
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PMID:Expression of human O6-methylguanine-DNA methyltransferase in Chinese hamster ovary cells and restoration of cellular resistance to certain N-nitroso compounds. 179 86

Because interindividual variations in the activities of DNA repair enzymes may be a risk factor in the pathogenesis of lung diseases, O(6)-methylguanine-DNA methyltransferase (O(6)-MT) and uracil DNA glycosylase (UDG) were measured in broncho-alveolar lavage cell (BALC) and peripheral blood mononuclear cell (PBM) samples from 57 healthy volunteers (25 smokers and 32 non-smokers). According to cotinine determination in 39 cases where serum for this was available, 38% of the self-acclaimed non-smokers had greater than 10 ng/ml of cotinine in their serum. Whether grouped into smokers and non-smokers according to clinical history or by serum cotinine, there were no statistically significant differences between these groups in O(6)-MT or UDG in either of the cell types. However, a tendency towards lower values in smokers was seen. The highest intraindividual variation in O(6)-MT activity was 7-fold, while the highest interindividual variation reached 18-fold. For UDG, the respective values were 24- and 307-fold. Although the distribution of O(6)-MT in BALC was different from that in PBM, the data are consistent with unimodality in both of the cell types. These findings suggest that exposure to cigarette smoke is not entirely responsible for the wide interindividual variation in O(6)-MT and UDG DNA repair activities.
Carcinogenesis 1991 Aug
PMID:O(6)-methylguanine-DNA methyltransferase and uracil DNA glycosylase in human broncho-alveolar lavage cells and peripheral blood mononuclear cells from tobacco smokers and non-smokers. 186 Jan 59

When animals are treated with carcinogenic agents that alkylate O6-guanine residues, the incidence of tumors in specific tissues often relates inversely to the level of the DNA repair enzyme O6-methylguanine-DNA methyltransferase (MGMT) present in the tissue. Similarly, the hypersensitivity to anticancer chloroethylnitrosoureas of some human tumor cell lines is believed to result from their deficiency in MGMT. We have undertaken a comprehensive investigation of MGMT expression in a panel of nine characterized human glioma cell lines. Methyltransferase activity determined by incubating protein extracts of these glioma lines with [3H]methylated DNA ranged from undetectable in six lines (the Mer- phenotype) to greater than 0.8 pmol/mg in two lines (U-373 MG and D-392 MG). MGMT protein was undetectable in Western blots of the Mer- cell extracts probed with specific anti-MGMT monoclonal antibodies. Consistent with these results, steady-state levels of MGMT mRNA, determined by Northern blot analysis, were detectable only in the three Mer+ glioma lines (U-373 MG, D-392 MG, D-263 MG). Southern analysis of EcoRI-digested DNA probed with MGMT cDNA revealed no amplification, rearrangement or deletions of the MGMT gene in any of the glioma cell lines. This is the first report that examines MGMT expression at the biochemical, molecular and genetic levels in a particular tumor type. These studies suggest that transcriptional regulation is the basis of the Mer- phenotype in these malignant human glioma cell lines, since no gross structural or quantitative abnormalities of the MGMT gene were seen in the phenotypically Mer- lines.
Carcinogenesis 1991 Sep
PMID:Expression of O6-methylguanine-DNA methyltransferase in malignant human glioma cell lines. 189 34

Previous studies have shown that in about one-fifth of human tumor cell strains, the activity of O6-methylguanine-DNA methyltransferase (MGMT), which can repair O6-alkylguanine in DNA produced by alkylating agents, is deficient. These strains are termed Mer- cells. To see if there is any human tumor lacking MGMT activity, we measured the MGMT activity in extracts from liver tumors of 21 patients, and compared it to the activity in normal peritumoral tissues derived from the same patients. The MGMT activity was assayed by measuring the 3H radioactivity transferred from the substrate DNA containing [methyl-3H]-labeled O6-methylguanine to an acid-insoluble protein fraction. There was considerable variation in MGMT activity among individual extracts; the interindividual variation was approximately 6-fold in normal liver tissue and much larger in liver tumors. Although in many cases similar high levels of MGMT activity were found both in liver tumors and in the normal counterpart, six tumors had greater than 3-fold less activity compared with the normal liver tissue from the same patient. Liver tumors from two patients did not have any detectable level of MGMT activity by the present method used, in spite of the fact that the corresponding normal liver samples demonstrated significant activities. We also measured in the same tissue extracts the activities of two common enzymes, glutamic pyruvic transaminase (GPT) and lactic dehydrogenase (LDH). The activities of GPT and LDH in the liver tumor samples that showed undetectable levels of MGMT activity were similar to those in the surrounding normal liver tissues. These results may suggest the existence of human Mer- tumors, deficient or very low MGMT activity.
Carcinogenesis 1991 Jul
PMID:O6-methylguanine-DNA methyltransferase activity in human liver tumors. 207 Apr 98

An attempt was made to characterize the genetic regulation of the human DNA repair protein O(6)-alkylguanine-DNA alkyltransferase (AGT) in the absence of the cloned gene. Four human cell lines, differing in AGT activity from very proficient to essentially absent, were assayed for gene amplification as a possible mediator of the methylation repair phenotype (Mer+, AGT activity and MER-, no AGT activity) using in-gel DNA renaturation and G-banded karyotype analysis. The former technique allows subsequent analysis of amplification units and cloning of observed amplified DNA fragments, a hopeful approach to the isolation of the human AGT gene. Within the sensitivities of the techniques, no correlation between AGT activity and gene amplification was observed in the four cell lines tested.
Carcinogenesis 1990 Mar
PMID:Gene amplification affecting O(6)-alkylguanine-DNA alkyltransferase activity is not detected in nitrosourea resistant or sensitive human cell lines. 231 Nov 91

O6-methylguanine-DNA methyltransferase (MGMT) was measured in partially synchronized cultures of C3H/10T1/2 mouse embryo cells as a function of cell cycle. The degree of synchrony and progression of the cell cycle were monitored by flow cytometry. The MGMT level was significantly reduced prior to the onset of S-phase. This reduction was concomitant with the inhibition of in vivo repair of O6-methylguanine in DNA of S-phase cells as observed earlier. The recovery of the MGMT level paralleled the progression of synchronized cells into G2. S-phase cells purified by cell sorting contained approximately 15% of the MGMT present in G0 or early G1 cells. A comparison of the in vivo repair of O6-methylguanine and MGMT levels suggests that the lack of repair of O6-methylguanine in DNA of the mouse embryo cells is due only in part to a temporal loss of MGMT.
Carcinogenesis 1986 May
PMID:Cell cycle-dependent modulation of O6-methylguanine-DNA methyltransferase in C3H/10T1/2 cells. 369 7


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