Search results for "Alkyltransferase"
showing 10 items of 13 documents
Flipping of alkylated DNA damage bridges base and nucleotide excision repair
2009
Alkyltransferase-like proteins (ATLs) share functional motifs with the cancer chemotherapy target O6-alkylguanine-DNA alkyltransferase (AGT) and paradoxically protect cells from the biological effects of DNA alkylation damage, despite lacking the reactive cysteine and alkyltransferase activity of AGT. Here we determine Schizosaccharomyces pombe ATL structures without and with damaged DNA containing the endogenous lesion O6-methylguanine or cigarette-smoke-derived O6-4-(3-pyridyl)-4-oxobutylguanine. These results reveal non-enzymatic DNA nucleotide flipping plus increased DNA distortion and binding pocket size compared to AGT. Our analysis of lesion-binding site conservation identifies new A…
Transgenic systems in studies on genotoxicity of alkylating agents: critical lesions, thresholds and defense mechanisms
1998
Abstract Transgenic systems, both cell lines and mice with gain or loss of function, are being used in order to modulate the expression of DNA repair proteins, thus allowing to assess their contribution to the defense against genotoxic mutagens and carcinogens. In this review, questions have been addressed concerning the use of transgenic systems in elucidating critical primary DNA lesions, their conversion into genotoxic endpoints, low-dose effects, and the relative contribution of individual cellular functions in defense. It has been shown that the repair protein alkyltransferase (MGMT) is decisive for protection against methylating and chloroethylating compounds. Protection pertains also…
MGMT: Key node in the battle against genotoxicity, carcinogenicity and apoptosis induced by alkylating agents
2007
O(6)-methylguanine-DNA methyltransferase (MGMT) plays a crucial role in the defense against alkylating agents that generate, among other lesions, O(6)-alkylguanine in DNA (collectively termed O(6)-alkylating agents [O(6)AA]). The defense is highly important, since O(6)AA are common environmental carcinogens, are formed endogenously during normal cellular metabolism and possibly inflammation, and are being used in cancer therapy. O(6)AA induced DNA damage is subject to repair, which is executed by MGMT, AlkB homologous proteins (ABH) and base excision repair (BER). Although this review focuses on MGMT, the mechanism of repair by ABH and BER will also be discussed. Experimental systems, in wh…
Mismatch G-T binding activity and MSH2 expression is quantitatively related to sensitivity of cells to methylating agents
1998
To elucidate mechanisms involved in alkylating drug resistance, Chinese hamster cells resistant to methylating agents have been generated upon transfection with human DNA. Here it is shown that these Chinese hamster ovary (CHO) variants exhibit the tolerance phenotype: they are alkyltransferase deficient (Mex-), cross-resistant to 6-thioguanine, exhibit reduced G-T binding (MutS alpha) activity and express the mismatch repair protein MSH2 at a significantly lower level than the corresponding control. By comparing wild-type cells with different tolerant strains that show gradual differences in resistance to methylating agents, it was shown that both the G-T binding activity and the amount of…
Induction of the alkyltransferase (MGMT) gene by DNA damaging agents and the glucocorticoid dexamethasone and comparison with the response of base ex…
1996
Repair of alkylated bases in DNA is performed by O6-methylguanine-DNA methyltransferase (MGMT) and a set of enzymes of the base excision repair pathway involving N-methylpurine-DNA glycosylase (MPG), apurinic endonuclease (APE), DNA polymerase beta (Pol beta) and DNA ligase. The level of expression of these enzymes may exert a profound effect on resistance of cells towards alkylating drugs. We have comparatively analyzed the expression of MGMT and the different base excision repair genes in rat hepatoma cells (line H4IIE) after exposure to alkylating agents, X-rays and the glucocorticoid hormone dexamethasone. Furthermore, the effect of these agents on the activity of the cloned human MGMT …
Acquired resistance of melanoma cells to the antineoplastic agent fotemustine is caused by reactivation of the DNA repair gene mgmt
2001
Acquired resistance to antineoplastic agents is a frequent obstacle in tumor therapy. Malignant melanoma cells are particularly well known for their unresponsiveness to chemotherapy; only about 30% of tumors exhibit a transient clinical response to treatment. In our study, we investigated the molecular mechanism of acquired resistance of melanoma cells (MeWo) to the chloroethylating drug fotemustine. Determination of O6-methylguanine-DNA methyltransferase (MGMT) activity showed that MeWo cells that acquired resistance to fotemustine upon repeated treatment with the drug display high MGMT activity, whereas the parental cell line had no detectable MGMT. The resistant cell lines exhibit cross-…
Inactivation of O(6)-methylguanine-DNA methyltransferase by glucose-conjugated inhibitors.
2001
The DNA-repair protein O6-methylguanine-DNA methyltransferase (MGMT) is a decisive determinant of resistance of tumor cells to methylating and chloroethylating anti-cancer drugs. Therefore, selective inhibition of MGMT in tumors is expected to cause tumor sensitization. Several inhibitors of MGMT have been developed which function in both tumors and normal tissue. To deplete MGMT preferentially in tumors, strategies to target the inhibitor to the tumor tissue need to be developed. Here, we report on the properties of glucose-conjugated MGMT inhibitors that might be useful for tumor targeting since tumor cells frequently over-express glucose transporter. O6-Benzylguanine (O6BG), 8-aza-O6-ben…
MGMT in primary and recurrent human glioblastomas after radiation and chemotherapy and comparison with p53 status and clinical outcome
2007
The DNA repair protein O(6)-methylguanine-DNA methyltransferase (MGMT) plays a pivotal role in alkylating drug resistance. Here, we determined MGMT activity in primary and recurrent glioblastomas (GBM, WHO grade IV) of patients who received radiation therapy (RT) or RT plus chemotherapy with alkylating agents (temozolomide, chloroethylnitrosoureas). The mean MGMT activity of untreated GBM was 37 +/- 45 (range 0-205) fmol/mg proteins. In the 1st, 2nd and 3rd recurrences, MGMT activity increased from 66 +/- 50 (13-194) to 68 +/- 44 (14-143) and 182 +/- 163 (64-423) fmol/mg protein, respectively. Comparing patients who received RT only with RT plus chemotherapy, a significant increase of MGMT …
Activity of O(6)-methylguanine-DNA methyltransferase in relation to p53 status and therapeutic response in ovarian cancer.
1999
The DNA-repair protein O(6)-methylguanine-DNA methyltransferase (alkyltransferase; MGMT) is a major determinant of resistance of cells to various alkylating cytostatic drugs. Its expression in tissues is highly variable, indicating complex regulatory mechanisms involved. Transfection-mediated expression of wild-type p53 has been shown to negatively regulate basal promoter activity of MGMT in vitro. To elucidate whether p53 is involved in regulation of MGMT in tumor tissue, we examined MGMT expression and the p53 status of 140 primary ovarian carcinomas and analyzed the data as to the correlation between MGMT and p53, as well as the survival response of the patients after chemotherapy. We sh…
DNA Repair and Damage Response Following Exposure of Cells to Alkylating Carcinogens
2012
Abstract Alkylating carcinogens are widely distributed in the environment and are present in food, beverages and tobacco. They are also endogenously formed in stomach and gut. These agents induce a dozen different DNA lesions, and some of them have been identified to be carcinogenic, clastogenic, recombinogenic and cytotoxic. A critical DNA adduct is O6-methylguanine (O6MeG). This damage causes mutations and is responsible for most of the carcinogenic effects of simple alkylating agents. At the same time, O6MeG is a highly powerful cytotoxic lesion, giving rise to the induction of apoptosis, necrosis and autophagy. The damage is repaired by the suicide enzyme alkyltransferase (MGMT), which …