Antioxidant protein Peroxiredoxin V (PrxV) is located in mitochondria and peroxisomes but is also present in the nucleus. Here, we show that nuclear PrxV associates with coilin-containing bodies suggesting possible interaction of this protein with transcription complexes. We also studied etoposideinduced phosphorylation of histone H2AX (c-H2AX) in human cells in which PrxV activity was downregulated (knockdown, KD-clones) or compromised by overexpression of redox-negative (RD) protein. In KD clones, but not in RD-clones, formation of etoposide-induced c-H2AX was increased, indicating that PrxV inhibits conversion of topoisomerase II cleavage complexes into double-strand DNA breaks but this inhibition is not caused by its antioxidant activity.

Chinese hamster cells have large interstitial (TTAGGG) bands (ITs) which are unstable and should be protected by an unknown mechanism. Here, we expressed in Chinese hamster V79 cells green fluorescent protein (GFP)-tagged human TRF1, and found that a major fraction of GFP-TRF1 bound to ITs is diffusionally mobile. This fraction strongly decreases after treatment of cells with wortmannin, a protein kinase inhibitor, and this drug also increases the frequency of chromosome aberrations. Ionizing radiation does not induce detectable translocation of GFP-TRF1 to the sites of random double-strand breaks visualized using antibodies against histone c-H2AX. TRF1 is known to be eliminated from telomeres by overexpression of tankyrase 1 which induces TRF1 poly(ADP-ribosyl)ation. We transfected V79 cells by plasmid encoding tankyrase 1 and found that the frequency of chromosome rearrangements is increased in these cells independently of their treatment by IR. Taken together, our results suggest that TRF1 is involved in sequence-specific protection of internal nontelomeric (TTAGGG)n repeats.

Inhaled cigarette smoke induces oxidative stress in the epithelium of airways. Peroxiredoxin V (PRXV) is a potent antioxidant protein, highly expressed in cells of the airway epithelium. The goal of our study was to determine whether cigarette smoke extract (CSE) influenced expression of this protein in airway epithelia in vivo and in vitro. In Sprague-Dawley rats, we determined effects of CSE on airway epithelial permeability, mRNA levels and expression of PRXV protein. Exposure of isolated tracheal segment in vitro to 20% CSE for 4 h resulted in development of increased permeability to albumin, significantly reduced mRNA levels for PRXV, and reduced amounts of PRXV protein in the epithelium. In cultures of the airway epithelial cell lines (Calu-3, JME), primary airway cell culture (cow), and alveolar epithelial cells A549, CSE also significantly decreased transepithelial electrical resistance and expression of PRXV protein, and induced glutathione and protein oxidation. To demonstrate functional importance of PRXV, we exposed clones of HeLa cells with siRNA-downregulated PRXV to hydrogen peroxide, which resulted in increased rate of cell death and protein oxidation. CSE directly downregulates expression of functionally important antioxidant enzyme PRXV in the epithelial cells of airways, which represents one pathophysiological mechanism of cigarette smoke toxicity.

In this study, we examined DNA repair synthesis in human cells treated with the radiomimetic drug bleomycin, which efficiently induces double-strand breaks (DSBs). Using tyramide-biotin to amplify fluorescent signals, discrete nuclear foci from the incorporation of 5-iododeoxyuridine (IdU) were detected in proliferating human cells treated with bleomycin. We believe this comes from the repair of DSBs. An increase in the number of foci (>5 per nucleus) was detected in a major fraction (75%) of non-S-phase cells labeled for 30 min with IdU 1 h after the end of bleomycin treatment. The fraction of cells with multiple IdU-containing foci was found to decrease 18 h after treatment. The average number of foci per nucleus detected 1 h after bleomycin treatment was found to decrease twofold between 1 and 3.5 h, indicating that the foci may be associated with the slow component of DSB repair. The presence of DSBs in bleomycin-treated cells was confirmed using antibodies against phosphorylated histone H2AX (gamma-H2AX), which is strictly associated with this type of DNA damage. After treatment with bleomycin, non-S-phase cells also displayed heterogeneous nuclear foci containing tightly bound proliferating cell nuclear antigen (PCNA), suggesting an ongoing process of unscheduled DNA synthesis. PCNA is known to be involved in base excision repair, but a fraction of the PCNA foci may also be associated with DNA synthesis occurring during the repair of DSBs.

Karyotype analysis of the Syrian hamster (Mesocricetus auratus) was performed after DAPI-banding of metaphase chromosomes obtained from cultivated skin fibroblasts of a newborn animal. Fluorescence in situ hybridization with telomeric FITC-conjugated peptide nucleic acid probe was applied to map interstitial blocks of (TTAGGG)_n repeats. Strong fluorescence in situ hybridization signals corresponded to interstitial telomeric repeats in pericentromeric chromatin bands of chromosomes 2, 4, 14, 20, and X. High-resolution DAPI-banding allowed specifying the arrangement of bands in the pericentromeric regions of these chromosomes.