Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.7.7 (DNA polymerase)
 17,007 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Frameshift mutations induced by acridines in bacteriophage T4 have been shown to be due to the ability of these mutagens to cause DNA cleavage by the type II topoisomerase of T4 and the subsequent processing of the 3' ends at DNA nicks by DNA polymerase or its associated 3' exonuclease followed by ligation of the processed end to the original 5' end. An analysis of the ability of nick-processing models is presented here to test the ability of nick processing to account for the DNA sequences of duplications and deletions induced in the aprt gene of CHO cells by teniposide (VM-26) [Han et al. (1993) J. Mol. Biol., 229, 52]. Although teniposide is not an acridine, it induces topoisomerase II-mediated DNA cutting in aprt sequences in vitro and mutagenesis in vivo. Although the previous study noted a correlation between mutation sites and nearby DNA discontinuities induced by the enzyme in vitro, neither the nick-processing model responsible for T4 mutations, nor double-strand break models alone were able to account for most of the mutant sequences. Thus, no single model explained the correlation between teniposide-induced DNA cleavage and mutagenic specificity. This report describes an expanded analysis of the ways that nick-processing models might be related to mutagenesis and demonstrates that a modified nick-processing model provides a biochemical rationale for the mutant specificities. The successful nick-processing model proposes that either 3' ends at nicks are elongated by DNA polymerase and/or that 5' ends of nicks are subject to nuclease activity; 3'-nuclease activity is not implicated. The mutagenesis model for nick-processing of teniposide-induced nicks in CHO cells when compared to the mechanism of nick-processing in bacteriophage T4 at acridine-induced nicks provides a framework for considering whether the differences may be due to cell-specific modes of DNA processing and/or due to the precise characteristics of topoisomerase-DNA intermediates created by teniposide or acridine that lead to mutagenesis.
 ...
PMID:Deletion and duplication sequences induced in CHO cells by teniposide (VM-26), a topoisomerase II targeting drug, can be explained by the processing of DNA nicks produced by the drug-topoisomerase interaction. 751 Aug 33

Topoisomerase II (Top II) is the target enzyme for many antineoplastic drugs such as epipodophyllotoxins, anthracyclines, and acridines. Cell lines with alterations in Top II are resistant to drugs that interact with the enzyme. Studies of the Top II from a Chinese hamster ovary line, VpmR-5, that is resistant to VP-16 and VM-26, demonstrated that it is very similar, qualitatively and quantitatively, to its normal counterpart except that DNA cleavage by the VpmR-5 enzyme is not stimulated by VP-16 or VM-26. To understand the basis for the drug-resistant phenotype, the Top II cDNAs were isolated from both Chinese hamster ovary (CHO) and VpmR-5 cells by cDNA cloning with lambda gt22, and the entire cDNAs were sequenced. A mutation of G-->A at nucleotide 1478 was the only alteration observed in the VpmR-5 Top II cDNA compared with the wild-type gene. The mutation in VpmR-5 was confirmed by sequencing DNA fragments amplified from the genomic DNA by the polymerase chain reaction. Southern blot hybridization analysis of genomic DNA demonstrated loss of a Top II allele in VpmR-5 probably occurred during the development of resistance to etoposide. The mutation in VpmR-5 changes amino acid 493 from arginine to glutamine and is located adjacent to a putative ATP binding site of Top II. Mutations in an analogous region have been identified in two human leukemia cell lines by amplification of segments of Top II cDNA with Taq DNA polymerase. Taken together, these observations suggest that mutations in this region of the gyrase B domain of mammalian topoisomerase II may be capable of conferring resistance to antineoplastic agents that interact with this enzyme.
 ...
PMID:Molecular cloning and identification of a point mutation in the topoisomerase II cDNA from an etoposide-resistant Chinese hamster ovary cell line. 838 May 92

Multidrug resistance (MDR), characterized by a cross-resistance to many natural toxin-related compounds, may be caused either by overexpression of a drug efflux pump such as P-glycoprotein, (P-gP), multidrug resistance proteins MRP1-3, or BCRP/MXR or, in the case of DNA topoisomerase II active drugs, by a decrease in the enzymatic activity of the target molecule termed altered topoisomerase MDR (at-MDR). However, human small cell lung carcinoma (SCLC) cell lines showed a collateral sensitivity to 2',2'-difluorodeoxycytidine (gemcitabine, dFdC) and 1-beta-D-arabinofuranosylcytosine (ara-C). H69/DAU, a daunorubicin (DAU)-resistant variant of H69 with a P-gP overexpression, and NYH/VM, a VM-26 (teniposide)-resistant variant of NYH with an at-MDR, were both 2-fold more sensitive to gemcitabine and 7- and 2-fold more sensitive to ara-C, respectively. MDR variants had a 4.3- and 2.0-fold increased activity of deoxycytidine kinase (dCK), respectively. dCK catalyzes the first rate-limiting activation step of both gemcitabine and ara-C. In addition, deoxycytidine deaminase, responsible for inactivation of dFdC and ara-C, was 9.0-fold lower in H69/DAU cells. The level of thymidine kinase 2, a mitochondrial enzyme that can also phosphorylate deoxycytidine and gemcitabine, was not significantly different between the variants. These differences most likely caused an increased accumulation of the active metabolites (dFdCTP, 2.1- and 1.6-fold in NYH/VM and H69/DAU cells, respectively) and of ara-CTP (1.3-fold in NYH/VM cells). Ara-CTP accumulation was not detectable in either H69 variant. The pools of all ribonucleoside and deoxyribonucleoside triphosphates were at least 3- to 4-fold higher in the NYH variants compared to the H69 variants; for dCTP and dGTP this difference was even larger. The higher ribonucleotide pools might explain the >10-fold higher accumulation of dFdCTP in NYH compared to H69 variants. Since dCTP is low, H69 cells might not need a high ara-CTP accumulation to inhibit DNA polymerase. This might be related to the lack of ara-CTP in H69 variants. In addition, the increased CTP, ATP, and UTP pools in the MDR variants might explain the increased ara-CTP and dFdCTP accumulation. In conclusion, the MDR variants of the human SCLC cell lines were collaterally sensitive due to an increased dCK activity, and consequently an increased ara-CTP and dFdCTP accumulation.
 ...
PMID:Collateral sensitivity to gemcitabine (2',2'-difluorodeoxycytidine) and cytosine arabinoside of daunorubicin- and VM-26-resistant variants of human small cell lung cancer cell lines. 1133 Oct 76