Search results for "Alkylating Agents"
showing 10 items of 26 documents
Activation of c-Jun N-terminal kinase 1 by UV irradiation is inhibited by wortmannin without affecting c-iun expression.
1999
Activation of c-Jun N-terminal kinases (JNKs)/stress-activated protein kinases is an early response of cells upon exposure to DNA-damaging agents. JNK-mediated phosphorylation of c-Jun is currently understood to stimulate the transactivating potency of AP-1 (e.g., c-Jun/c-Fos; c-Jun/ATF-2), thereby increasing the expression of AP-1 target genes. Here we show that stimulation of JNK1 activity is not a general early response of cells exposed to genotoxic agents. Treatment of NIH 3T3 cells with UV light (UV-C) as well as with methyl methanesulfonate (MMS) caused activation of JNK1 and an increase in c-Jun protein and AP-1 binding activity, whereas antineoplastic drugs such as mafosfamide, mito…
Primary mouse fibroblasts deficient for c-Fos, p53 or for both proteins are hypersensitive to UV light and alkylating agent-induced chromosomal break…
2000
The important regulatory proteins, c-Fos and p53 are induced by exposure of cells to a variety of DNA damaging agents. To investigate their role in cellular defense against genotoxic compounds, we comparatively analysed chromosomal aberrations and apoptosis induced by ultraviolet (UV-C) light and the potent alkylating agent methyl methanesulfonate (MMS) in primary diploid mouse fibroblasts knockout for either c-Fos or p53, or double knockout for both genes. We show that c-Fos and p53 deficient fibroblasts are more sensitive than the corresponding wild-type cells as to the induction of chromosomal aberrations and apoptosis. Double knockout fibroblasts lacking both c-Fos and p53 are viable an…
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…
Nuclear Translocation of Mismatch Repair Proteins MSH2 and MSH6 as a Response of Cells to Alkylating Agents
2000
Mammalian mismatch repair has been implicated in mismatch correction, the prevention of mutagenesis and cancer, and the induction of genotoxicity and apoptosis. Here, we show that treatment of cells specifically with agents inducing O(6)-methylguanine in DNA, such as N-methyl-N'-nitro-N-nitrosoguanidine and N-methyl-N-nitrosourea, elevates the level of MSH2 and MSH6 and increases GT mismatch binding activity in the nucleus. This inducible response occurs immediately after alkylation, is long-lasting and dose-dependent, and results from translocation of the preformed MutSalpha complex (composed of MSH2 and MSH6) from the cytoplasm into the nucleus. It is not caused by an increase in MSH2 gen…
Mechanisms and consequences of methylating agent-induced SCEs and chromosomal aberrations: a long road traveled and still a far way to go.
2003
Since the milestone work of Evans and Scott, demonstrating the replication dependence of alkylation-induced aberrations, and Obe and Natarajan, pointing to the critical role of DNA double-strand breaks (DSBs) as the ultimate trigger of aberrations, the field has grown extensively. A notable example is the identification of DNA methylation lesions provoking chromosome breakage (clastogenic) effects, which made it possible to model clastogenic pathways evoked by genotoxins. Experiments with repair-deficient mutants and transgenic cell lines revealed both O<sup>6</sup>-methylguanine (O<sup>6</sup>MeG) and N- methylpurines as critical lesions. For S<sub>N</sub&g…
Exposure to N-ethyl-N-nitrosourea in adult mice alters structural and functional integrity of neurogenic sites.
2011
BackgroundPrevious studies have shown that prenatal exposure to the mutagen N-ethyl-N-nitrosourea (ENU), a N-nitroso compound (NOC) found in the environment, disrupts developmental neurogenesis and alters memory formation. Previously, we showed that postnatal ENU treatment induced lasting deficits in proliferation of neural progenitors in the subventricular zone (SVZ), the main neurogenic region in the adult mouse brain. The present study is aimed to examine, in mice exposed to ENU, both the structural features of adult neurogenic sites, incorporating the dentate gyrus (DG), and the behavioral performance in tasks sensitive to manipulations of adult neurogenesis.Methodology/principal findin…
Influence of DNA Repair on Nonlinear Dose-Responses for Mutation
2013
Recent evidence has challenged the default assumption that all DNA-reactive alkylating agents exhibit a linear dose-response. Emerging evidence suggests that the model alkylating agents methyl- and ethylmethanesulfonate and methylnitrosourea (MNU) and ethylnitrosourea observe a nonlinear dose-response with a no observed genotoxic effect level (NOGEL). Follow-up mechanistic studies are essential to understand the mechanism of cellular tolerance and biological relevance of such NOGELs. MNU is one of the most mutagenic simple alkylators. Therefore, understanding the mechanism of mutation induction, following low-dose MNU treatment, sets precedence for weaker mutagenic alkylating agents. Here, …
An approach to the evaluation of the activity of the DNA repair enzyme O6-methylguanine-DNA-methyl-transferase in tumor tissue in vivo: syntheses of …
2002
Abstract The resistance of tumor cells to the cytostatic activity of methylating and chloroethylating anticancer drugs is determined by the level of expression of the DNA repair protein O 6 -methylguanine-DNA-methyl-transferase (MGMT). The synthesis of labelled 6-benzyloxy-9H-purin-2-ylamine derivatives should hence allow a quantification of the MGMT status of tumor and non-target tissue in vivo. 6-benzyloxy-9-(2-fluoroethyl)-9H-purin-2-yl-amine and 6-benzyloxy-7-(2-fluoroethyl)-7H-purin-2-yl-amine were synthesized and evaluated in vitro, both showing an affinity of 1.8 μM. 6-benzyloxy-9-(2-[ 18 F]fluoroethyl)-9H-purin-2-yl-amine and 6-benzyloxy-7-(2-[ 18 F]fluoroethyl)-7H-purin-2-yl-amine …
Suture Removal After Trabeculectomy With Fornix-based Conjunctival Flap Leads to Faster Visual Recovery but Not Reduced Astigmatism
2019
PReCIS:: The closing limbal suture after trabeculectomy with a fornix-based conjunctival flap plays no critical role in the development of corneal astigmatism and intraocular pressure (IOP). A standard removal is not recommended. Purpose To investigate the effect of removal of the conjunctival suture after trabeculectomy with fornix-based conjunctival flap on corneal astigmatism, visual acuity, and IOP. Methods Eighty-seven cases of trabeculectomy with mitomycin C with a fornix-based conjunctival flap performed in the eyes of 82 patients (5 patients underwent bilateral trabeculectomy) were enrolled in a prospective randomized study. All surgeries were conducted by the same surgeon (J.W.) in…
Constitutive expression and inducibility of O6-methylguanine-DNA methyltransferase and N-methylpurine-DNA glycosylase in rat liver cells exhibiting d…
1995
AbstractWe have analyzed the expression of the DNA repair genes O6-methylguanine-DNA methyltransferase (MGMT) and N-methylpurine-DNA glycosylase (MPG) at RNA and protein activity level in primary rat hepatocytes in vitro and various rat hepatoma cell lines exhibiting different status of differentiation. The basal level of MGMT mRNA and activity correlated well with the degree of differentiation, as measured by tyrosine aminotransferase (TAT) mRNA expression. Induction of MGMT mRNA and protein activity by X-ray and Nmethyl-N′-nitro-N-nitrosoguanidine (MNNG) treatment was most pronounced in the well-differentiated hepatocytes and in various differentiated hepatoma cell lines (up to 6-fold). T…