Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.30.2 (endonuclease)
 18,621 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

A dose-limiting toxicity of certain chemotherapeutic alkylating agents is their toxic effects on nontarget tissues such as the bone marrow. To overcome the myelosuppression observed by chemotherapeutic alkylating agents, one approach is to increase the level of DNA repair proteins in hematopoietic stem and progenitor cells. Toward this goal, we have constructed a human fusion protein consisting of O6-methylguanine DNA methyltransferase coupled with an apurinic endonuclease, resulting in a fully functional protein for both O6-methylguanine and apurinic/apyrimidinic (AP) site repair as determined by biochemical analysis. The chimeric protein protected AP endonuclease-deficient Escherichia coli cells against methyl methanesulfonate and hydrogen peroxide (H2O2) damage. A retroviral construct expressing the chimeric protein also protected HeLa cells against 1,3-bis(2-chloroethyl)-1-nitrosourea and methyl methanesulfonate cytotoxicity either when these agents were used separately or in combination. Moreover, as predicted from previous analysis, truncating the amino 150 amino acids of the apurinic endonuclease portion of the O6-methylguanine DNA methyltransferase-apurinic endonuclease protein resulted in the retention of O6-methylguanine DNA methyltransferase activity but loss of all AP endonuclease activity. These results demonstrate that the fusion of O6-methylguanine DNA methyltransferase and apurinic endonuclease proteins into a combined single repair protein can result in a fully functional protein retaining the repair activities of the individual repair proteins. These and other related constructs may be useful for protection of sensitive tissues and, therefore, are candidate constructs to be tested in preclinical models of chemotherapy toxicity.
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PMID:Creation of a fully functional human chimeric DNA repair protein. Combining O6-methylguanine DNA methyltransferase (MGMT) and AP endonuclease (APE/redox effector factor 1 (Ref 1)) DNA repair proteins. 942 28

Previously we showed that a mismatch repair (MMR)-deficient cell line, HCT116 (hMLH1 mut), unlike a MMR wild-type cell line, SW480, was more resistant to the therapeutic methylating agent, temozolomide (TMZ), because the MMR complex fails to recognize TMZ-induced O6-methylguanine DNA adduct mispairings with thymine that arise after replication. TMZ also produces N7-methylguanine and N3-methyladenine adducts that are processed efficiently by the base excision repair (BER) system. After removal of the methylated base by methylpurine glycosylase, which creates the abasic or apurinic-apyrimidinic (AP) site, the phosphodiester bond is hydrolyzed immediately by AP endonuclease, initiating the repair of the AP site. Methoxyamine (MX) reacts with the abasic site and prevents AP endonuclease cleavage, disrupting DNA repair. MX potentiated the cytotoxic effect of TMZ with a dose modification factor (DMF) of 2.3+/-0.12 in SW480 and 3.1+/-0.16 in HCT116. When combined with O6-benzylguanine (BG), MX and TMZ dramatically increased TMZ cytotoxicity (65.8-fold) in SW480, whereas no additive effect was seen in HCT116. This suggests that N7-methylguanine and N3-methyladenine adducts are cytotoxic lesions in MMR-deficient and wild-type cells when BER is interrupted. Because poly(ADP-ribose) polymerase (PARP) aids in processing of DNA strand breaks induced during MMR and BER, we asked whether PARP inhibitors would also affect BER-mediated cell killing. We found that PARP inhibitors PD128763, 3-aminobenzimide, and 6-aminonicotinamide increased the sensitivity to TMZ in both HCT116 MMR-deficient cells and SW480 MMR wild-type cells. In HCT116 cells, PD128763 remarkably decreased resistance to TMZ, with a DMF of 4.7+/-0.2. However, the combination of PD128763, BG, and TMZ had no greater effect, indicating that persistent O6-methylguanine had no effect on cytotoxicity. In SW480, the DMF for TMZ cytotoxicity was 3.1+/-0.12 with addition of PD128763 and 36 with addition of PD128763 and BG. Synergy analysis by median effect plots indicated a high degree of synergy between TMZ and MX or PD128763. In contrast, 1,3-bis(2-chloroethyl)-1-nitrosourea combined with either MX or PD128763 showed little if any potentiation observed in the absence of BG in either cell line, suggesting that BER pathway has little impact on cytotoxic processing of 1,3-bis(2-chloroethyl)-1-nitrosourea-induced adducts. These studies indicate that targeting BER with MX or PARP inhibitors enhances the cytotoxicity of methylating agents, even in MMR-deficient cells.
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PMID:Pharmacologic disruption of base excision repair sensitizes mismatch repair-deficient and -proficient colon cancer cells to methylating agents. 1053 60

Apurinic/apyrimidinic (AP) endonuclease 1 (APE1) is the primary enzyme in mammals for the repair of abasic sites in DNA, as well as a variety of 3' damages that arise upon oxidation or as products of enzymatic processing. If left unrepaired, APE1 substrates can promote mutagenic and cytotoxic outcomes. We describe herein a dominant-negative form of APE1 that lacks detectable nuclease activity and binds substrate DNA with a 13-fold higher affinity than the wild-type protein. This mutant form of APE1, termed ED, possesses two amino acid substitutions at active site residues Glu(96) (changed to Gln) and Asp(210) (changed to Asn). In vitro biochemical assays reveal that ED impedes wild-type APE1 AP site incision function, presumably by binding AP-DNA and blocking normal lesion processing. Moreover, tetracycline-regulated (tet-on) expression of ED in Chinese hamster ovary cells enhances the cytotoxic effects of the laboratory DNA-damaging agents, methyl methanesulfonate (MMS; 5.4-fold) and hydrogen peroxide (1.5-fold). This MMS-induced, ED-dependent cell killing coincides with a hyperaccumulation of AP sites, implying that excessive DNA damage is the cause of cell death. Because an objective of the study was to identify a protein reagent that could be used in targeted gene therapy protocols, the effects of ED on cellular sensitivity to a number of chemotherapeutic compounds was tested. We show herein that ED expression sensitizes Chinese hamster ovary cells to the killing effects of the alkylating agent 1,3-bis(2-chloroethyl)-1-nitrosourea (also known as carmustine) and the chain terminating nucleoside analogue dideoxycytidine (also known as zalcitabine), but not to the radiomimetic bleomycin, the nucleoside analogue beta-D-arabinofuranosylcytosine (also known as cytarabine), the topoisomerase inhibitors camptothecin and etoposide, or the cross-linking agents mitomycin C and cisplatin. Transient expression of ED in the human cancer cell line NCI-H1299 enhanced cellular sensitivity to MMS, 1,3-bis(2-chloroethyl)-1-nitrosourea, and dideoxycytidine, demonstrating the potential usefulness of this strategy in the treatment of human tumors.
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PMID:A dominant-negative form of the major human abasic endonuclease enhances cellular sensitivity to laboratory and clinical DNA-damaging agents. 1725 46