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

The DNA sequence of 11 in vivo-arising intragenic deletion junctions occurring in the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene of human T-lymphocytes was determined. These deletions ranged in size from 16 bp to 4057 bp. Extensive homology was not found at the deletion breaksites, indicating that non-homologous recombination was responsible for these deletions. Short regions of homology (1-3 nucleotides) at the deletion termini, which may direct the recombination event, were found in seven of the mutations. Only one mutation had an unaccounted for nucleotide at the junction. V(D)J recombinase recognition sequences, previously identified at other hprt deletion breaksites, were not present. Such features are also found at the deletion and translocation junctions of rearranged oncogenes and suppressor oncogenes. The ability to isolate and molecularly analyze deletion mutations occurring in vivo in peripheral human T-lymphocytes allows the assay of DNA breakage/rejoining events. Such a system may serve as a biomarker of exposure to environmental and occupational agents which may be important in the etiology of cancer.
Carcinogenesis 1994 Jul
PMID:Deletion mutations in the hprt gene of T-lymphocytes as a biomarker for genomic rearrangements important in human cancers. 803 26

The mutagenic potential of the epoxide metabolites of butadiene (BD) was measured at the tk and hprt loci in TK6 human lymphoblastoid cells. TK6 cells were exposed for 24 h to 0-400 microM 1,2-epoxybutene (EB), 0-800 microM 3,4-epoxy-1,2-butanediol (EBD), or 0-6 microM 1,2,3,4-diepoxybutane (DEB). Treated cells were allowed to grow for several days and then seeded in medium containing either 6-thioguanine or trifluorothymidine to select for hprt- or tk-/- mutants, respectively. All three metabolites were mutagenic at both loci, with DEB exhibiting activity at concentrations approximately 100-fold lower than EB or EBD. At the hprt locus, an induced mutation frequency of 5 x 10(-6) (approximately twice background hprt- frequency) was produced by treatment with 3.5 microM DEB, 150 microM EB and 450 microM EBD. At the tk locus, a similar increase in mutation frequency (total tk-/- frequency) was produced by treatment with 1.0 microM DEB, 100 microM EB and 350 microM EBD. Each epoxide tested was capable of inducing slow growth tk-/- mutants. This mutant phenotype, as shown previously by others, results from large alterations in the tk region which completely remove the active tk allele. In addition, Southern blot analysis revealed that approximately half of DEB-induced hprt- mutants displayed loss of wild-type hprt restriction fragments. No statistically significant increase in the fraction of hprt deletions among EB mutants was observed. The ability of DEB to induce deletions may be related to its ability to form DNA-DNA and DNA-protein cross-links.
Carcinogenesis 1994 Apr
PMID:Mutagenicity of butadiene and its epoxide metabolites: I. Mutagenic potential of 1,2-epoxybutene, 1,2,3,4-diepoxybutane and 3,4-epoxy-1,2-butanediol in cultured human lymphoblasts. 814 85

The mutagenic potential and mutational spectra of butadiene (BD), 1,2-epoxybutene (EB), and diepoxybutane (DEB) were determined in splenic T cells from exposed B6C3F1 mice. Mice exposed by inhalation to 625 p.p.m. BD for 2 weeks displayed an average hprt- mutation frequency of 6.2 x 10(-6) compared to 1.2 x 10(-6) in controls. Mice were also given three daily i.p. doses of 60, 80 and 100 mg EB/kg or 7, 14 and 21 mg DEB/kg. Average hprt- frequencies of 5.4 x 10(-6), 4.1 x 10(-6) and 8.6 x 10(-6) were seen in the EB groups, respectively, while average frequencies of 4.6 x 10(-6), 9.4 x 10(-6) and 13 x 10(-6) were seen in the DEB groups. DNA sequencing revealed that approximately half of the mutations induced in vivo by BD, EB and DEB were frameshift mutations. A +1 frameshift 'hotspot' in six consecutive guanine bases in exon 3 was observed with all three compounds. The remaining mutations produced by BD, EB and DEB were transition and transversion mutations at both AT and GC base pairs. Base pair substitutions induced by BD were biased in favor of mutation at AT base pairs. The mutational spectra produced by BD, EB and DEB were very similar to that observed previously with ethylene oxide, suggesting that these epoxide agents may be working through a similar mutagenic mechanism.
Carcinogenesis 1994 Apr
PMID:Mutagenicity of butadiene and its epoxide metabolites: II. Mutational spectra of butadiene, 1,2-epoxybutene and diepoxybutane at the hprt locus in splenic T cells from exposed B6C3F1 mice. 814 86

N-Ethyl-N-nitrosourea (ENU) forms several major adducts upon reaction with DNA, of which ethylation at the O6 position of guanine and the O4, O2 and N3 positions of thymine have been implicated to be mutagenic lesions. To investigate what specific kinds of ENU-induced mutations were affected by the repair ability of O6-alkylguanine-DNA alkyltransferase (AGT), we examined the mutations in the hypoxanthine (guanine) phosphoribosyltransferase gene (hprt) in 87 independent mutants derived from ENU-treated AGT proficient (Mer+) or deficient (Mer-) diploid human fibroblasts. Of the characterized mutations, 97% were single base substitutions. The major difference in the mutation spectra was that the frequency of G.C to A.T transitions was significantly higher in Mer- mutants (16/38) than in Mer+ mutants (4/33). The results indicate that AGT removes O6-ethylguanine, thus protecting human cells from parts of the cytotoxic and mutagenic effects of ENU. A high frequency of T.A to A.T transversions induced by ENU was observed in both Mer+ (52%) and Mer- (34%) mutants. This type of mutation was less frequently observed (10%) in N-methyl-N'-nitro-N-nitrosoguanidine (MNNG)-induced mutants derived from the same Mer+ cells in our previous report (J. Mol. Biol., 221, 421, 1991). Comparison of alkylating lesions formed by MNNG and ENU indicates that O2-ethylthymine and N3-ethylthymine are potent mutational adducts for T to A transversions. The occurrence of ENU-induced T.A base pair transversions showed a strong strand bias; 35/37 were located on the non-transcribed strand, assuming thymine is the mutagenic lesion. The result suggests a difference in repair capacity of ethylthymine on the two strands. In addition, this type of mutation preferentially occurred at 5'-Pu-T sequences.
Carcinogenesis 1994 May
PMID:Comparison of mutation spectra induced by N-ethyl-N-nitrosourea in the hprt gene of Mer+ and Mer- diploid human fibroblasts. 820 99

6-Nitrochrysene can be activated to genotoxic derivatives by two major metabolic pathways: nitroreduction to N-hydroxy-6-aminochrysene, and a combination of ring-oxidation and nitroreduction that involves the intermediate formation of trans-1,2-dihydro-1,2-dihydroxy-6-aminochrysene (6-AC-1,2-dihydrodiol). The DNA adduct formed from this latter pathway was evaluated by reacting individual deoxynucleoside 5'-monophosphates with 6-AC-1,2-dihydrodiol in the presence of liver microsomal enzymes from 3-methylcholanthrene-pretreated rats. Binding was greatest to deoxyguanosine monophosphate and the major deoxyguanosine (dG) adduct co-chromatographed with the single major adduct formed from the microsome-catalyzed reaction of 6-AC-1,2-dihydrodiol with DNA. In order to characterize the mutational changes associated with the 6-AC-1,2-dihydrodiol pathway, we analyzed the mutational spectrum produced by 6-AC-1,2-dihydrodiol in the hypoxanthine-guanine phosphoribosyltransferase (hprt) gene of CHO-K1 cells. cDNA was synthesized from the RNA of 28 6-thioguanine-resistant mutants, the hprt coding region amplified by the polymerase chain reaction, and the DNA products directly sequenced. Twenty independent primary mutations were found: 12 G:C-->T:A transversions, three G:C-->C:G transversions, one G:C-->A:T transition, one A:T-->T:A transversion, two -1 frameshift mutations in sequences containing consecutive guanines, and one 11 bp deletion. All G:C basepair substitutions had the mutated dG on the non-transcribed strand and 86% of the G:C basepair substitutions had one purine 3' to the mutated dG. The pattern of 6-AC-1,2-dihydrodiol-induced basepair substitutions was distinct from the pattern observed in solvent control mutants. These results are consistent with the formation of a promutagenic dG adduct from a metabolite of 6-AC-1,2-dihydrodiol.
Carcinogenesis 1993 Oct
PMID:Trans-1,2-dihydro-1,2-dihydroxy-6-aminochrysene is metabolized to form a major adduct with deoxyguanosine and produces mutations in the hprt gene of Chinese hamster ovary cells at G:C basepairs. 822 62

To investigate which specific kinds of base changes are induced by psoralen adducts in the genomic DNA of diploid human fibroblasts, cells were exposed to 8-methoxypsoralen (8-MOP) at 2-12 microM followed by one dose of UVA (365 nm) irradiation (PUVA-I treatment) or two doses of UVA (PUVA-II treatment). While PUVA-I treatment produced little effect on the induction of cytotoxicity, PUVA-II treatment significantly reduced the fibroblasts' colony-forming ability and resulted in about 10-fold increases in mutation frequency at the D0 dose. Mutations in the hypoxanthine (guanine) phosphoribosyltransferase (hprt) gene of 36 independent PUVA-II mutants were characterized by direct sequencing of cDNA amplified by the polymerase chain reaction (PCR). Seventeen mutants contained single base substitutions and the other 19 mutants either lacked one or more exons, or had deleted or gained nucleotides in the exon boundaries in their cDNA. The intron--exon boundaries of 10 of these 19 putative splicing mutants were further characterized by direct sequencing of the PCR-amplified hprt gene. The results showed that nine contained single base substitutions at the consensus splicing donor and acceptor sites. One splicing mutant possessed two base substitutions located at exon 8, whereas its splicing sites were intact. Most of the base substitutions occurred at T-A base pairs (24/29). The majority of T.A changes occurred at thymine of 5'TA and 5'ATA on the non-transcribed strand. Four of the five G.C base substitutions were located at guanines of 5'TG sites adjacent 3' to AT or TA sequences. In addition, the occurrence of a specific type of mutation was highly correlated to the 5' flanking bases of TA sites. The mutagenesis of 13 of the 16 mutational events at 5'TA sites on the non-transcribed strand can be explained by the preferential incisions of the photoadducts on the transcribed strand followed by misalignment--realignment during translesion repair synthesis of the bulky lesions on the non-transcribed strand.
Carcinogenesis 1994 Feb
PMID:Mutation specificity of 8-methoxypsoralen plus two doses of UVA irradiation in the hprt gene in diploid human fibroblasts. 831 9

We have characterized the mutational spectrum of 6-nitrosochrysene in the hprt gene of Chinese hamster ovary (CHO-K1) cells and also examined the adducts formed by this compound in CHO-K1 cells by quantitative 32P-postlabeling analysis. Seventy percent of the identified mutations were simple basepair substitutions, and they occurred more often at A:T (14/17) than at G:C. Furthermore, 13 of the basepair substitutions at A:T had the mutated dA, the probable adducted residue, on the non-transcribed DNA strand. The preference for mutation at A:T contrasted sharply with the distribution of adducts formed by 6-nitrosochrysene: 80% of the identified adducts were with dG, while only 20% were probably formed through binding with dA. Analyses conducted with excision-repair-defective CHO-UV5 cells revealed both a preference for basepair substitution at A:T and an adduct profile that were similar to those found for repair-proficient CHO-K1 cells. However, basepair substitutions from CHO-UV5 cell mutants had the mutated dAs distributed randomly between the non-transcribed and transcribed DNA strands. The mutational spectra found for solvent control CHO-K1 and CHO-UV5 cells differed from those of the 6-nitrosochrysene-treated cultures. These findings suggest that 6-nitrosochrysene-induced mutations are targeted to DNA damage, but that 6-nitrosochrysene-derived dA adducts are much more effective at producing mutations than 6-nitrosochrysene-derived dG adducts. The extreme strand bias for mutated dAs in the CHO-K1 mutational spectrum appears to result from preferential removal of 6-nitrosochrysene-induced DNA lesions from the transcribed DNA strand.
Carcinogenesis 1993 Sep
PMID:Molecular analysis of DNA adducts and hprt mutations produced by 6-nitrosochrysene in Chinese hamster ovary cells. 840 11

Monoclonal antibodies specific for N2,3-ethenodeoxyguanosine (N2,3-epsilon dGuo) and 1,N2-ethenodeoxyguanosine (1,N2-epsilon dGuo) were developed. In a competitive ELISA, 50% inhibition of binding of the N2,3-epsilon dGuo specific antibody (ETH1) was achieved with 18 fmol of N2,3-epsilon dGuo. Fifty per cent inhibition of the 1,N2-epsilon dGuo-specific antibody (ETH2) required 11 pmol 1,N2-epsilon dGuo. Immunoassays for N2,3-epsilon dGuo and 1,N2-epsilon dGuo in single-stranded DNA were developed using these antibodies. The immunoassays could detect as little as 48 fmol of N2,3-epsilon dGuo or 340 fmol 1,N2-epsilon dGUO in 25 micrograms of single stranded DNA. These assays and previously developed immunoassays for 1,N6-ethenodeoxy-adenosine (1,N6-epsilon dAdo) and 3,N4-ethenodeoxycytidine (3,N4-epsilon dCyd) were used to measure etheno adduct levels in DNA of cells exposed to chloroacetaldehyde. The cells used were V79 cells with an inactivated hprt gene and a single copy of the bacterial gpt gene (G12 cells). The most abundant etheno adduct was 1,N6-epsilon dAdo, followed by 3,N4-epsilon dCyd and N2,3-epsilon dGuo. 1,N2-epsilon dGuo was not detected in chloro-acetaldehyde-treated G12 cells. Chloroacetaldehyde was also shown to be mutagenic in these same cells.
Carcinogenesis 1993 Jan
PMID:Development of monoclonal antibodies specific for 1,N2-ethenodeoxyguanosine and N2,3-ethenodeoxyguanosine and their use for quantitation of adducts in G12 cells exposed to chloroacetaldehyde. 842 58

N-Methyl-N-nitrosourea (MNU) reacts with DNA to produce a variety of lesions, of which O6-methylguanine (O6-MeG) has been implicated in the mutagenic and carcinogenic effects of this agent. The present study aimed to investigate the types and position specificities of mutations induced by MNU. Mutational sequence alterations were determined for 53 independent mutations induced by MNU in a cDNA of the human hprt gene, which is stably integrated into chromosomes of the mouse cell line VH12. The majority of the mutations induced by MNU were base substitutions (85%), mostly GC to AT transitions (41/43), and the remainder (15%) were frameshift or deletion mutations resulting from loss or addition of a few bases. The transition mutations occurred preferentially at the middle G in 5'-purine-G-N-3' sequences in the non-transcribed strand, and were distributed nonrandomly over the coding region of the gene. Analysis of the results suggests that, when interpreting mutational specificity and distribution, not only the nature of the mutational target sequence, but also the functional domains of the protein should be considered.
Carcinogenesis 1993 Apr
PMID:Specificity of mutations induced by N-methyl-N-nitrosourea in a cDNA of the hprt gene. 847 39

Colon cancer and an increasing number of other cancers have been found to exhibit instability of DNA microsatellite sequences. Such tumors have been designated as replication errors (RER) tumors. However, as microsatellites are only rarely found within coding regions of the genome, instability of these sequences cannot directly contribute to carcinogenesis. Recently, we have shown RER colon cancers also demonstrate a marked 100-fold increase in mutation rates measured within an expressed gene, hprt, suggesting the mutator phenotype in these tumors extends beyond microsatellite sequences. To determine whether the RER phenotype indeed destabilizes non-repetitive DNA sequences we have sequenced hprt gene mutations recovered from the RER colon cancer cell line RKO. Greater than 10% of hprt mutants proved to be a single 3 bp deletion located in a nonrepetitive ATTAT sequence motif. Additionally, 1-4 bp deletions or insertions were found to be randomly located throughout the hprt gene. Lastly, one third of hprt mutations proved to be transitions or transversions. The microsatellite instability demonstrated in RKO is thus a global mutator phenotype which destabilizes DNA sequences both inside and outside of repetitive sequence elements and which augments base substitutions as well as frameshifts. These findings extend the characteristics of mutations associated with RER tumors and suggest additional mechanisms by which mutator phenotypes may alter oncogenes and tumor suppressor genes.
 ...
PMID:Diverse hypermutability of multiple expressed sequence motifs present in a cancer with microsatellite instability. 862 58


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>