Methods to Study Trinucleotide Repeat Instability Induced by DNA Damage and Repair.

Trinucleotide repeat (TNR) instability (expansion and deletion) is associated with more than 42 human neurodegenerative diseases and cancer and mediated by DNA replication, repair, recombination, and gene transcription. Somatic TNR instability is involved in the progression of TNR expansion diseases and can be modulated by DNA damage repair and gene transcription. Recent studies from our group and others have shown that DNA base damage and its repair play an active role in modulating TNR instability and are responsible for somatic age-dependent CAG repeat expansion in neurons of Huntington's disease mice induced by oxidative DNA damage.

Electron-Mediated Aminyl and Iminyl Radicals from C5 Azido-Modified Pyrimidine Nucleosides Augment Radiation Damage to Cancer Cells.

Two classes of azido-modified pyrimidine nucleosides were synthesized as potential radiosensitizers; one class is 5-azidomethyl-2'-deoxyuridine (AmdU) and cytidine (AmdC), while the second class is 5-(1-azidovinyl)-2'-deoxyuridine (AvdU) and cytidine (AvdC). The addition of radiation-produced electrons to C5-azido nucleosides leads to the formation of π-aminyl radicals followed by facile conversion to σ-iminyl radicals either via a bimolecular reaction involving intermediate α-azidoalkyl radicals in AmdU/AmdC or by tautomerization in AvdU/AvdC. AmdU demonstrates effective radiosensitization in EMT6 tumor cells.

Pyrimidine Nucleosides with a Reactive (β-Chlorovinyl)sulfone or (β-Keto)sulfone Group at the C5 Position, Their Reactions with Nucleophiles and Electrophiles, and Their Polymerase-Catalyzed Incorporation into DNA.

Transition-metal-catalyzed chlorosulfonylation of 5-ethynylpyrimidine nucleosides provided ()-5-(β-chlorovinyl)sulfones , which undergo nucleophilic substitution with amines or thiols affording . The treatment of vinyl sulfones with ammonia followed by acid-catalyzed hydrolysis of the intermediary β-sulfonylvinylamines gave 5-(β-keto)sulfones . The latter reacts with electrophiles, yielding α-carbon-alkylated or -sulfanylated analogues .

Modulation of trinucleotide repeat instability by DNA polymerase β polymorphic variant R137Q.

Trinucleotide repeat (TNR) instability is associated with human neurodegenerative diseases and cancer. Recent studies have pointed out that DNA base excision repair (BER) mediated by DNA polymerase β (pol β) plays a crucial role in governing somatic TNR instability in a damage-location dependent manner. It has been shown that the activities and function of BER enzymes and cofactors can be modulated by their polymorphic variations.

Arsenic trioxide co-exposure potentiates benzo(a)pyrene genotoxicity by enhancing the oxidative stress in human lung adenocarcinoma cell.

Although both arsenic trioxide (As2O3) and benzo(a)pyrene (BaP) are well-established human carcinogens, the interaction between As2O3 and BaP is synergistic or antagonistic remains controversial in terms of the existing studies. In addition, the mechanisms responsible for the combined effects are still unclear. In this study, we examined the potential interactive effects between As2O3 (1, 5, and 10 μM) and BaP (5, 10, and 20 μM) in cultured A549 cells by treating with BaP and As2O3 alone or in combination at various concentrations for 24 h.

DNA polymerase beta is involved in the protection against the cytotoxicity and genotoxicity of cigarette smoke.

Reactive oxygen species (ROS) and oxidative DNA damage have been implicated in the cigarette smoke-induced cytotoxicity and genotoxicity. DNA polymerase β (polβ), a key base excision repair (BER) enzyme in repairing oxidative DNA damage, may play a crucial role in fighting against the cytotoxicity and genotoxicity of cigarette smoke. In this study, we applied a novel approach to collect cigarette smoke extract (CSE) and investigated the cytotoxic and genotoxic effects of CSE by using the mouse embryo fibroblasts that express wild-type of polβ (polβ(+/+)), null of polβ (polβ(-/-)) and overexpression of polβ (polβ(oe)).