Protein-DNA cross-linking

The key to hexavalent chromium s mutagenicity and possible carcinogenicity is the abiHty of this oxidation state to penetrate the cell membrane. The Cr(VI) Species promotes DNA strand breaks and initiates DNA—DNA and DNA-protein cross-links both in cell cultures and in vivo (105,112,128—130). The mechanism of this genotoxic interaction may be the intercellular reduction of Cr(VI) in close proximity to the nuclear membrane. When in vitro reductions of hexavalent chromium are performed by glutathione, the formation of Cr(V) and glutathione thiyl radicals are observed, and these are beHeved to be responsible for the formation of the DNA cross-links (112). 

Cross-linkage - bifunctional agents may form covalent bonds with each of two adjacent guanine residues and such inter-strand cross-links will lead to inhibition of DNA replication and transcription. Intra-strand and DNA-protein cross-links may also be formed ... 

Chromosomal aberrations Gene mutation Dominant lethal mutation Micronucleus formation Micronucleus formation Micronucleus formation Chromosomal aberrations Sister chromatid exchange Micronucleus formation Chromosomal aberrations Sister chromatid exchange DNA-protein cross-links Nondisjunction of Y chromosome in sperm DNA damage (single-strand breaks)... 

Nackerdien, Z., Rao, G., Cacciuttolo, M.A., Gajewski, E. and Dizdaroglu, M. (1991). Chemical nature of DNA-protein cross-links produced in mammalian chromatin by hydrogen peroxide in the presence of iron or copper ions. Biochemistry 30, 4872-4879. 

Interestingly, the nucleophilic addition of water in the sequence of events giving rise to 41 represents a relevant model system for investigating the mechanism of the generation of DNA-protein cross-links under radical-mediated oxidative conditions [80, 81]. Thus, it was shown that lysine tethered to dGuo via the 5 -hydroxyl group is able to participate in an intramolecular cyclization reaction with the purine base at C-8, subsequent to one electron oxidation [81]. 

Ewig, R.A.C., and Kohn, K.W. (1977) DNA - protein cross-linking and DNA interstrand cross-linking by haloethylnitrosoureas in L1210 cells. Cancer Res. 38, 3197. 

Nickel chloride has been reported to induce DNA strand breaks in CHO cells [435] in a concentration, which did not significantly injure normal cellular division, and DNA-protein cross-links, which were concentration- and time-dependent and preferentially occurred in cells in the late S phase of the cell cycle [436], The nickel cross-linked proteins included nonhistone chromatin proteins, nonhistone DNA-binding proteins and a 30 kDa protein that comigrated electrophoretically with histone HI. Moreover, blocking of cell growth in S phase [249] and induction of DNA repair synthesis in CHO cells [437] and reduction in the fidelity of DNA synthesis [438, 439], have been reported. 

The biological significance of long-lived monofunctional adducts on DNA remains to be determined, but these alone may be sufficient to kill cells if they are not repaired, which seems to be the case for the active trans iminoether complex 18 (60). Long-lived monofunctional adducts may also promote the formation of DNA-protein cross-links. 

A similar pattern of reactivity has been observed by Burrows and coworkers for the reaction between A -acetyllysine methyl ester (Lys) and dG. This reaction was studied in order to gain an understanding of structural aspects of DNA-protein cross-links (DPCs). These cross-links are regarded as a common lesion of oxidative damage to cells, but remain, from a chemical point, a poorly understood DNA lesion. As pointed out by Burrows, oxidation of protein-DNA complexes should occur preferentially at the primary amines since these sites have a lower oxidation potential (1.1 V vs. NHE, pH 10) than G. While protonation of the primary amine inhibits the oxidative process, transient deprotonation of a lysine residue would give rise to a lysine aminyl radical (or aminium radical cation). Using... 

Patiemo SR, Costa M. 1985. DNA-protein cross-links induced by nickel compounds in intact cultured mammalian cells. Chem Biol Interact 55 75-91. 

DNA-DNA and DNA-protein cross-links were formed in the livers and lungs of mice exposed to butadiene at 250, 500 or 1000 ppm [550, 1100 or 2200 mg/m ] for 7 h. Exposures of up to 2000 ppm [4400 mg/m ] for 8 li per day for seven days did not induce cross-links in the liver or lung DNA of rats. Single-strand breaks were induced in mouse and rat liver DNA following exposure to 2000 ppm for 7 h per day for seven days and in mouse lung and liver following a 16-h exposure to 200 ppm [440 mg/iii of butadiene. 

Dichloromethane induced DNA-protein cross-links in vitro in hepatocytes of male B6C3Fi mice but not in hepatocytes of Fischer 344 rats, Syrian hamsters or in human hepatocytes with functional GSTTl genes. DNA-protein cross-links were also induced in Chinese hamster ovary CHO cells exposed to dichloromethane with or without exogenous metabolic activation. DNA damage was greater, however, in the presence of metabolic activation. 

DIA, DNA-protein cross-links, B6C3Fi mouse hepatocytes in vitro... 

DIA, DNA single-strand breaks and DNA-protein cross-links, Chinese (+) + 3975 Graves Green ... 

DVA, DNA-protein cross-links, B6C3Fi/CrlBR mouse liver in vivo -1- 498 ppm inh 6 h/d. Casanova ef al. ... 

DNA-protein cross-links caused by formaldehyde, a metabolite from the GST pathway, have been demonstrated in mice but not hamsters exposed to dichloromethane (Casanova et al., 1992). Similarly, in-vitro studies have not demonstrated DNA-protein cross-links in rat, hamster or human hepatocytes exposed to concentrations of dichloromethane of up to 5 mM. This is equivalent to the time-weighted average concentration predicted to occur in mouse liver during a 6-h inhalation exposure to a dichloromethane concentration of > 10 000 ppm [34 700 mg/m ] (Casanova et al., 1997). 

Casanova. M., Conolly, R.B. Heck, H.d A. (1996) DNA-protein cross-links (DPX) and cell proliferation in B6C3F, mice but not Syrian golden hamsters exposed to dichloromethane phannacokinetics and risk assessment with DPX as dosimeter. Fundam. appl. Toxicol, 31, 103— 116... 

Acetaldehyde caused DNA strand breaks and cross-links in human lymphocytes in vitro without metabolic activation, but not in human bronchial epithelial cells and in human leukocytes. It has been shown to bind covalently to deoxynucleotides in vitro to form DNA-protein cross-links in rat nasal mucosa. Acetaldehyde-DNA adducts have been found in vitro in calf thymus DNA, in 2 -dcoxyguanosinc-3 -monophosphatc and in liver from mice treated with ethanol (Fang Vaca, 1995). Abnormal sperm morphology or spennocyte micronuclei were not observed in mice treated with an intraperitoneal injection of acetaldehyde. 

DIA, DNA-protein cross-links, Fischer 344 rat nasal mucosa cells in vitro + NT 4410 Lam et al. (1986)... 

In mammalian cells, it induced sister chromatid exchanges, micronuclei and gene mutations in vitro. In one study, it induced DNA-protein cross-links in rat nasal epithelial cells treated in vitro. In human cells in vitro, hexamethylphosphoramide induced micronuclei and sister chromatid exchanges. 

A very interesting aspect of platinum-DNA interactions concerns the nature of the resulting adducts and their relative quantities. Due to the bifunctional nature of cis-Pt, several types of adducts in the DNA can be expected to be formed, to be distinguished in (1) interstrand chelates (binding of two nucleobases that are each positioned in one of the complementary DNA strands), (2) intrastrand chelates (binding of two nucleobases within the same DNA strands), (3) intrabase chelates (binding to two different atoms in one base), and (4) DNA-protein cross-links. 

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