γ-H2AX is a sensitive marker of DNA damage induced by metabolically activated 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone

Investigating the neuroprotective effects of polyunsaturated fatty acids in egg yolk phospholipids upon oxidative damage in HT22 cells

Egg yolk phospholipids are primarily composed of various fatty acids, lysophosphatidylcholine and lysophosphatidylethanolamine. Existing studies have revealed the neuroprotective activity of egg yolk phospholipids. However, it is not clear which digestion products of phospholipids exert neuroprotective activity. The objective of this study was to investigate the neuroprotective effects of different structural components in egg yolk phospholipids based on a DMNQ-induced oxidative damage in HT22 cells. The findings demonstrated that pre-treatment with diverse egg yolk phospholipid components, particularly the polyunsaturated fatty acids, markedly elevated the cell viability and superoxide dismutase activity, diminished the ROS generation, reduced the malondialdehyde levels and elevated the mitochondrial membrane potential. Furthermore, RNA-Seq analysis demonstrated that unsaturated fatty acids exert its neuroprotective effects by upregulating the genes involved in cell proliferation (Jag2 and Ypel3), nervous system development (Ntf5), DNA damage repair (H2ax), and other related processes. These findings provide a theoretical basis for future studies on the characteristic structure of egg yolk phospholipids with profound neuroprotective effects.

Cigarette sidestream smoke-induced cellular senescence and the protective role of histone H2AX

Cigarette smoke imposes serious health hazards such as cancer and cardiovascular diseases but is also associated with cellular senescence. Recently, histone loss and modifications are reported as one of the characteristics of cellular senescence. In this study, we examined the relationship between cigarette smoke-induced cellular senescence and histone H2A variant H2AX, an important player in DNA damage response. We exposed normal human skin diploid fibroblast ASF-4-1 to cigarette sidestream smoke (CSS) extract and successfully induced premature senescence. Persistent DNA damages are known to induce cellular senescence. Double strand breaks (DSBs) formation was detected in CSS-treated cells, indicating DSBs could be the cause for the CSS-induced cellular senescence. In the senescent cells, persistent phosphorylation of histone H2AX (γ-H2AX) and unexpected increase of H2AX protein expression was observed. To elucidate the role of H2AX in CSS-induced cellular senescence, we depleted H2AX in ASF-4-1 cells with siRNA. In H2AX-depleted cells, CSS-induced elevated β-galactosidase activity was more prominent. CSS concentration-dependent increase of reactive oxygen species and DSBs formation was also facilitated by H2AX depletion. These results suggest that histone H2AX may have a protective role against DNA damage-induced premature senescence.

Mechanistic Insights into Toxicity of Titanium Dioxide Nanoparticles at the Micro- and Macro-levels

Titanium oxide nanoparticles (TiO2 NPs) have been regarded as a legacy nanomaterial due to their widespread usage across multiple fields. The TiO2 NPs have been and are still extensively used as a food and cosmetic additive and in wastewater and sewage treatment, paints, and industrial catalysis as ultrafine TiO2. Recent developments in nanotechnology have catapulted it into a potent antibacterial and anticancer agent due to its excellent photocatalytic potential that generates substantial amounts of highly reactive oxygen radicals. The method of production, surface modifications, and especially size impact its toxicity in biological systems. The anatase form of TiO2 (<30 nm) has been found to exert better and more potent cytotoxicity in bacteria as well as cancer cells than other forms. However, owing to the very small size, anatase particles are able to penetrate deep tissue easily; hence, they have also been implicated in inflammatory reactions and even as a potent oncogenic substance. Additionally, TiO2 NPs have been investigated to assess their toxicity to large-scale ecosystems owing to their excellent reactive oxygen species (ROS)-generating potential compounded with widespread usage over decades. This review discusses in detail the mechanisms by which TiO2 NPs induce toxic effects on microorganisms, including bacteria and fungi, as well as in cancer cells. It also attempts to shed light on how and why it is so prevalent in our lives and by what mechanisms it could potentially affect the environment on a larger scale.

A Dietary Antioxidant Formulation Ameliorates DNA Damage Caused by γ-Irradiation in Normal Human Bronchial Epithelial Cells In Vitro

Antioxidants can be used as radioprotectants to reduce DNA damage due to exposure to radiation that could result in malignancies, including lung cancer. Mortality rates are consistently higher in lung cancer, which is usually diagnosed at later stages of cancer development and progression. In this preliminary study, we examined the potential of an antioxidant formulation (AOX2) to reduce DNA damage using a cell model of human normal bronchial epithelial cells (BEAS-2B). Cells were exposed to γ-irradiation or smoke-related hydrocarbon 4[(acetoxymethyl)nitrosamino]-1 (3-pyridyl) 1-butanone (NNKOAc) to induce DNA damage. We monitored intracellular reactive oxygen species (ROS) levels and evidence of genotoxic damage including DNA fragmentation ELISA, γ-H2AX immunofluorescence, and comet assays. Pre-incubation of the cells with AOX2 before exposure to γ-irradiation and NNKOAc significantly reduced DNA damage. The dietary antioxidant preparation AOX2 significantly reduced the induction of the tumor suppressor protein p53 and DNA damage-associated γ-H2AX phosphorylation by radiation and the NNKOAc treatment. Thus, AOX2 has the potential to act as a chemoprotectant by lowering ROS levels and DNA damage caused by exposure to radiation or chemical carcinogens.

γH2AX, a DNA Double-Strand Break Marker, Correlates with PD-L1 Expression in Smoking-Related Lung Adenocarcinoma

In recent years, the choice of immune checkpoint inhibitors (ICIs) as a treatment based on high expression of programmed death-ligand 1 (PD-L1) in lung cancers has been increasing in prevalence. The high expression of PD-L1 could be a predictor of ICI efficacy as well as high tumor mutation burden (TMB), which is determined using next-generation sequencing (NGS). However, a great deal of effort is required to perform NGS to determine TMB. The present study focused on γH2AX, a double-strand DNA break marker, and the suspected positive relation between TMB and γH2AX was investigated. We assessed the possibility of γH2AX being an alternative marker of TMB or PD-L1. One hundred formalin-fixed, paraffin-embedded specimens of lung cancer were examined. All of the patients in the study received thoracic surgery, having been diagnosed with lung adenocarcinoma or squamous cell carcinoma. The expressions of γH2AX and PD-L1 (clone: SP142) were evaluated immunohistochemically. Other immunohistochemical indicators, p53 and Ki-67, were also used to estimate the relationships of γH2AX. Positive relationships between γH2AX and PD-L1 were proven, especially in lung adenocarcinoma. Tobacco consumption was associated with higher expression of γH2AX, PD-L1, Ki-67, and p53. In conclusion, the immunoexpression of γH2AX could be a predictor for the adaptation of ICIs as well of as PD-L1 and TMB.

Circular RNA circNIPBL promotes NNK-induced DNA damage in bronchial epithelial cells via the base excision repair pathway

Environmental chemical exposure often causes DNA damage, which leads to cellular dysfunction and the development of diseases. 4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), a tobacco-specific carcinogen that is known to cause DNA damage, while remains unknown about the underlying mechanism. In this study, simulated doses of NNK exposure in smokers, ranging from 50 to 300 μM, were used to detect the DNA damage effects of NNK in two human bronchial epithelial cells, 16HBE and BEAS-2B. The comet assay revealed increased DNA damage in response to NNK treatment, as measured by increased Olive tail moment (OTM). NNK treatment also led to elevated foci formation and protein expression of γ-H2AX, a DNA damage sensor. Dysregulation of proliferation, cell cycle arrest and apoptosis, was also observed in NNK-treated cells. Furthermore, the most effective dose of NNK (300 μM) was used in subsequent mechanistic studies. A circular RNA circNIPBL was identified to be significantly up-regulated in NNK-treated cells, circNIPBL knockdown successfully alleviated NNK-induced DNA damage and reversed the cellular dysregulation, while circNIPBL overexpression had the opposite effect. Mechanistically, we identified an interaction between circNIPBL and PARP1, a critical enzyme of the base excision repair (BER) pathway. CircNIPBL silencing successfully alleviated the NNK-induced inhibition of BER pathway proteins, including PARP1, XRCC1, PCNA and FEN1, while overexpression of circNIPBL had the opposite effect. In summary, our study shows for the first time that circNIPBL promotes NNK-induced DNA damage and cellular dysfunction through the BER pathway. In addition, our findings reveal the crucial role of epigenetic regulation in carcinogen-induced genetic lesions and further our understanding of environmental carcinogenesis.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone-Induced Histone Acetylation via α7nAChR-Mediated PI3K/Akt Activation and Its Impact on γ-H2AX Generation

A typical tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is known as a strong carcinogen. We previously reported that metabolized NNK induced histone H2AX phosphorylation (γ-H2AX), a DNA damage-induced histone modification. In this study, we found that NNK globally acetylated histone H3, which affected γ-H2AX generation. Human lung adenocarcinoma A549 was treated with several doses of NNK. NNK induced dose-dependent global histone H3 acetylation (Ac-H3), at 2 to 12 h after the treatment, independent of the cell cycle. The Ac-H3 pattern was not affected by CYP2A13 overexpression unlike γ-H2AX, indicating no requirement of NNK metabolism to induce Ac-H3. Immunofluorescence staining of Ac-H3 was uniform throughout the nucleus, whereas γ-H2AX was formed as foci and did not coincide with Ac-H3. Nicotinic receptor antagonist methyllycaconitine inhibited Ac-H3 and also γ-H2AX. Phosphoinositide-3-kinase (PI3K)/Akt inhibitors, LY294002, wortmannin, and GSK690693, also suppressed both Ac-H3 and γ-H2AX, whereas KU-55933, an inhibitor of ataxia telangiectasia mutated (ATM) upstream of γ-H2AX, inhibited γ-H2AX but not Ac-H3. These results suggested that binding of NNK to the nicotinic acetylcholine receptor (α7nAChR) activated the PI3K/Akt pathway, resulting in Ac-H3. The activated pathway leading to Ac-H3 enhanced γ-H2AX, suggesting that NNK-induced DNA damage is impacted by the α7nAChR-mediated signal transduction pathway.

Genetic and Enzymatic Characteristics of CYP2A13 in Relation to Lung Damage

Cytochrome P450 2A13 is an omitted brother of CYP2A6 that has an important role in the drug metabolism of liver. Due to extrahepatic expression, it has gained less attention than CYP2A6, despite the fact that it plays a significant role in toxicant-induced pulmonary lesions and, therefore, lung cancer. The purpose of this mini-review is to summarize the basic knowledge about this enzyme in relation to the substrates, inhibitors, genetic polymorphisms, and transcriptional regulation that are known so far (September 2021).

Vitamin-Containing Antioxidant Formulation Reduces Carcinogen-Induced DNA Damage through ATR/Chk1 Signaling in Bronchial Epithelial Cells In Vitro

Lung cancer has the highest mortality rate worldwide and is often diagnosed at late stages, requiring genotoxic chemotherapy with significant side effects. Cancer prevention has become a major focus, including the use of dietary and supplemental antioxidants. Thus, we investigated the ability of an antioxidant formulation (AOX1) to reduce DNA damage in human bronchial epithelial cells (BEAS-2B) with and without the combination of apple peel flavonoid fraction (AF4), or its major constituent quercetin (Q), or Q-3-O-d-glucoside (Q3G) in vitro. To model smoke-related genotoxicity, we used cigarette-smoke hydrocarbon 4-[(acetoxymethyl)nitrosamino]-1-(3-pyridyl)-1-butanone (NNKOAc) as well as methotrexate (MTX) to induce DNA damage in BEAS-2B cells. DNA fragmentation, γ-H2AX immunofluorescence, and comet assays were used as indicators of DNA damage. Pre-exposure to AOX1 alone or in combination with AF4, Q, or Q3G before challenging with NNKOAc and MTX significantly reduced intracellular reactive oxygen species (ROS) levels and DNA damage in BEAS-2B cells. Although NNKOAc-induced DNA damage activated ATM-Rad3-related (ATR) and Chk1 kinase in BEAS-2B cells, pre-exposure of the cells with tested antioxidants prior to carcinogen challenge significantly reduced their activation and levels of γ-H2AX (p ≤ 0.05). Therefore, AOX1 alone or combined with flavonoids holds promise as a chemoprotectant by reducing ROS and DNA damage to attenuate activation of ATR kinase following carcinogen exposure.

Telomere Dysfunction in Oocytes and Embryos From Obese Mice

Maternal obesity impairs oocyte quality and embryo development. However, the potential molecular pathways remain to be explored. In the present study, we examined the effects of obesity on telomere status in oocytes and embryos obtained from mice fed with high-fat diet (HFD). Of note, telomere shortening was observed in both oocytes and early embryos from obese mice, as evidenced by the reduced expression of telomerase reverse transcriptase and activity of telomerase. Moreover, quantitative analysis of telomere dysfunction-induced foci (TIFs) revealed that maternal obesity induces the defective telomeres in oocytes and embryos. Meanwhile, the high frequency of aneuploidy was detected in HFD oocytes and embryos as compared to controls, accompanying with the increased incidence of apoptotic blastocysts. In conclusion, these results indicate that telomere dysfunction might be a molecular pathway mediating the effects of maternal obesity on oocyte quality and embryo development.

Anthocyanin-rich haskap (Lonicera caerulea L.) berry extracts reduce nitrosamine-induced DNA damage in human normal lung epithelial cells in vitro

Diets rich in polyphenols are known to reduce cancer among high-risk populations. Haskap (Lonicera caerulea L.) berry has abundant phenolic acids and flavonoids, especially anthocyanins. Tobacco-specific nitrosamine, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) present in cigarette smoke, is a major lung carcinogenic factor. We analyzed the efficacy of anthocyanin-rich haskap berry extracts in preventing DNA damage induced by 4-[(acetoxymethyl) nitrosamino]-1-(3-pyridyl)-1-butanone (NNKOAc), a precursor of NKK, in human lung epithelial BEAS-2B cells in vitro. A cocktail of monomeric polyphenols from haskap berries was extracted separately in ethanol and water and profiled. Sub-lethal concentrations of NNKOAc were used to induce DNA damage in BEAS-2B cells, and a cell viability assay was performed to confirm that the tested concentrations of haskap extracts were not cytotoxic to BEAS-2B cells. Cells were pre-treated with the haskap extracts prior to NNKOAc exposure. Dose-dependent DNA damage was observed with carcinogenic NNKOAc, but did not occur in the presence of the haskap extracts. Pre-treatment of the cells with the haskap extracts significantly reduced NNKOAc-induced DNA damage, DNA fragmentation, and intracellular reactive oxygen species and upregulated the ATM-dependent DNA damage repair cascade compared to non-treated BEAS-2B cells. The protective effect of haskap extracts could be related to their polyphenol content and high antioxidant capacity.

Effect of oocyte vitrification on DNA damage in metaphase II oocytes and the resulting preimplantation embryos

As an assisted reproduction technology, vitrification has been widely used for oocyte and embryo cryopreservation. Many studies have indicated that vitrification affects ultrastructure, gene expression, and epigenetic status. However, it is still controversial whether oocyte vitrification could induce DNA damage in metaphase II (MII) oocytes and the resulting early embryos. This study determined whether mouse oocytes vitrification induce DNA damage in MII oocytes and the resulting preimplantation embryos, and causes for vitrification-induced DNA damage. The effects of oocyte vitrification on reactive oxygen species (ROS) levels, γ-H2AX accumulation, apoptosis, early embryonic development, and the expression of DNA damage-related genes in early embryos derived by in vitro fertilization were examined. The results indicated that vitrification significantly increased the number of γ-H2AX foci in zygotes and two-cell embryos. Trp53bp1 was upregulated in zygotes, two-cell embryos and four-cell embryos in the vitrified group, and Brca1 was increased in two-cell embryos after vitrification. Vitrification also increased the ROS levels in MII oocytes, zygotes, and two-cell embryos and the apoptotic rate in blastocysts. Resveratrol (3,5,4'-trihydroxystilbene) treatment decreased the ROS levels and the accumulation of γ-H2AX foci in zygotes and two-cell embryos and the apoptotic rate in blastocysts after vitrification. Overall, vitrification-induced abnormal ROS generation, γ-H2AX accumulation, an increase in the apoptotic rate and the disruption of early embryonic development. Resveratrol treatment could decrease ROS levels, γ-H2AX accumulation, and the apoptotic rate and improve early embryonic development. Vitrification-associated γ-H2AX accumulation is at least partially due to abnormal ROS generation.

Effects of cellular differentiation in human primary bronchial epithelial cells: Metabolism of 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone

Many of the toxicants in tobacco smoke undergo biotransformation in the lungs of smokers, both to reactive and to detoxified derivatives. Human air-liquid-interface (ALI) airway tissue models have emerged as an advanced in vitro model for evaluating the toxicity of inhaled substances; however, the metabolic potential of these cultures has not been evaluated extensively. In this study, we compared the metabolic activities of an ALI tissue model to the undifferentiated normal human primary bronchial epithelial (NHBE) cells from which it was derived. Measurement of the basal levels of gene expression for 84 phase I drug metabolism enzymes indicated that most genes were upregulated in ALI cultures compared to NHBE cells. Furthermore, the enzymatic activities of three cytochrome P450s involved in the bioactivation of tobacco-specific nitrosamines were higher in the ALI cultures, and the bioactivation of 4-(methylnitrosamine)-1-(3-pyridyl)-1-butanone (NNK), as measured by the formation of two of its major metabolites, i.e., keto acid and 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), was significantly greater in the ALI cultures. Finally, NNK was a direct-acting genotoxicant in the ALI cultures, while the genotoxicity of NNK was detected in NHBE cells only in the presence of an exogenous liver S9 activation system. Taken together, our findings demonstrate the greater metabolic potential of well-differentiated ALI cultures than primary NHBE cells, supporting the potential use of ALI airway cultures as an alternative in vitro model for evaluating inhaled toxicants that require metabolic transformation.

Using Phytochemicals to Investigate the Activation of Nicotine Detoxification via Upregulation of CYP2A6 in Animal Models Exposed Tobacco Smoke Condensate by Intratracheal Instillation

This study examined the efficacy of standardized Smilax china L. root extract (SSCR) containing chlorogenic acid on detoxifying nicotine from tobacco smoke condensate (TSC) in vitro and in vivo. Chlorogenic acid is an identified bioactive component in SSCR by ultraperformance liquid chromatography/photodiode array/electrospray ionization/mass spectroscopy (UPLC/PDA/ESI/MS). HepG2 liver cells and A549 lung cells were carried for measuring ROS and antioxidant enzymes. Sprague-Dawley rats were treated with nicotine by intratracheal instillation (ITI). Cell viabilities by pretreatments of 5, 12.5, and 25, 50 μg SSCR/mL ranged from 41 to 76% in HepG2 and 65 to 95% in A549. Pretreatments of SSCR inhibited TSC-mediated production of reactive oxygen species (ROS) by 8 and 10% in HepG2 and A549 cells, respectively. However, the expression of CAT, SOD1, and AOX1 was downregulated by SSCR in the both cells. The highest conversion of cotinine was observed at 50 μg/mL of SSCR after 120 min of incubation. SSCR upregulated CYP2A6 3-fold in A549 cells regardless of TSC cotreatment. When Sprague-Dawley rats were treated with nicotine by ITI or subjected to SSCR administration for 14 days, the levels of cotinine in urine increased in SSCR treatment only. The cellular level of antioxidant capacity at 10 or 100 mg/kg body weight/day of SSCR treatment was 1.89 and 1.86 times higher than those of nicotine-control. Results suggest that the intake of SSCR can detoxify nicotine by elevating nicotine conversion to cotinine and antioxidant capacity.

Simultaneous delivery of olaparib and carboplatin in PEGylated liposomes imparts this drug combination hypersensitivity and selectivity for breast tumor cells

Combination regiments involving platinum anticancer drugs and agents with unrelated mechanisms of action are a subject of widespread interest. Here, we show that synergistic toxic action in cancer cells of combinations of antitumor platinum drug carboplatin and effective PARP inhibitor olaparib is considerably improved if these combined drugs are encapsulated into liposomes. Notably, the formation of such nano-formulations, called OLICARB, leads to a marked enhancement of activity in human cancer cell lines (including those resistant to conventional platinum antitumor drugs) and selectivity towards tumor cells. We used immunofluorescence analysis of γH2AX expression and examined DNA damage in cancerous cells treated with the investigated compounds. We find that the synergistic toxic effects in cancer cells of both drugs used in combination, nonencapsulated or embedded in the OLICARB nanoparticles, positively correlates with DNA damage. These results also suggest that the enhancement of the toxic effects of carboplatin by olaparib in cancer cells is a consequence of an accumulation of cytotoxic lesions in DNA due to the inhibition of repair of platinated DNA augmented by the synergistic action of olaparib as an effective PARP inhibitor. Our findings also reveal that the combination of olaparib with carboplatin encapsulated in the OLICARB nanoparticles is particularly effective to inhibit the growth of 3D mammospheres. Collectively, the data provide convincing evidence that the encapsulation of carboplatin and olaparib into liposomal constructs to form the OLICARB nanoparticles may represent the viable approach for the treatment of tumors with the aim to eliminate the possible effects of acquired resistance.

γH2AX is immunohistochemically detectable until 7 days after exposure of N-bis (2-hydroxypropyl) nitrosamine (DHPN) in rat lung carcinogenesis

It is known that γH2AX, which is formed when there is a double-strand break in DNA, can act as a sensitive marker of genomic instability. In this experiment, the time-course manner of the expression of γH2AX in the lung was examined in the early phase after treatment with a lung carcinogen, N-bis (2-hydroxypropyl) nitrosamine (DHPN). The expression of γH2AX is expected to be one of the useful markers for lung carcinogenesis in early stages. Rats were separated into 10 groups of 5 rats. The DHPN groups were administered 0.1% DHPN in drinking tap water for two weeks, while the control group received drinking tap water. At 0, 1, 3, 7, and 14 days after finishing DHPN treatment, one group each from the DHPN and control groups was sacrificed. The removed lung tissues were examined for immunostaining of γH2AX and PCNA, and positive cells were counted. The γH2AX levels of the DHPN-treated groups were found to be increased significantly at 0, 1, 3, and 7 days (4.4 ± 1.4, 5.1 ± 2.7, 3.3 ± 1.0, and 4.1 ± 1.3%, respectively), and they dropped significantly on day 14 (1.1 ± 0.4%). The experiment showed that the γH2AX-positive score could be effectively measured for up to 7 days after exposure, as a significance difference was observed between the treated group and the control group. It can be deduced that γH2AX is an effective marker for DHPN-induced double-strand breaks in pulmonary epithelial cells.

Genotoxicity analysis of five particle matter toxicants from cigarette smoke based on γH2AX assay combined with Hill/Two-component model

To investigate the genotoxic characteristics of typical toxicants in particle phase of cigarette smoke, including B[a]P, nicotine, tar, NNN and NNK. The in vitro γH2AX assay was used to detect the DNA double-strand breaks (DSBs) in A549 cells using high content screening (HCS). The results showed all toxicants had a dose/time-dependent effects on induction of γH2AX except for NNN and NNK. Based on dose-response of γH2AX and Hill model, the ability to induce DSBs was evaluated: NNN-acetate > B[a]P > NNK-acetate > tar > nicotine. Based on time-course of γH2AX and two-component model, the complex DNA damage was the main subtypes of DNA damage induced by these toxicants. Overall, all toxicants were genotoxic in A549 cells in a dose- or time- dependent manner except for NNN and NNK based on the γH2AX HCS assay. NNN-acetate had more potential to induce DSBs, which was followed by B[a]P, NNK-acetate, tar and nicotine.

Functional characterization of 9 CYP2A13 allelic variants by assessment of nicotine C-oxidation and coumarin 7-hydroxylation

Cytochrome P450 2A13 (CYP2A13) is responsible for the metabolism of chemical compounds such as nicotine, coumarin, and tobacco-specific nitrosamine. Several of these compounds have been recognized as procarcinogens activated by CYP2A13. We recently showed that CYP2A13*2 contributes to inter-individual variations observed in bladder cancer susceptibility because CYP2A13*2 might cause a decrease in enzymatic activity. Other CYP2A13 allelic variants may also affect cancer susceptibility. In this study, we performed an in vitro analysis of the wild-type enzyme (CYP2A13.1) and 8 CYP2A13 allelic variants, using nicotine and coumarin as representative CYP2A13 substrates. These CYP2A13 variant proteins were heterologously expressed in 293FT cells, and the kinetic parameters of nicotine C-oxidation and coumarin 7-hydroxylation were estimated. The quantities of CYP2A13 holoenzymes in microsomal fractions extracted from 293FT cells were determined by measuring reduced carbon monoxide-difference spectra. The kinetic parameters for CYP2A13.3, CYP2A13.4, and CYP2A13.10 could not be determined because of low metabolite concentrations. Five other CYP2A13 variants (CYP2A13.2, CYP2A13.5, CYP2A13.6, CYP2A13.8, and CYP2A13.9) showed markedly reduced enzymatic activity toward both substrates. These findings provide insights into the mechanism underlying inter-individual differences observed in genotoxicity and cancer susceptibility.

gamma-H2AX: Can it be established as a classical cancer prognostic factor?

Double-strand breaks are among the first procedures taking place in cancer formation and progression as a result of endogenic and exogenic factors. The histone variant H2AX undergoes phosphorylation at serine 139 due to double-strand breaks, and the gamma-H2AX is formatted as a result of genomic instability. The detection of gamma-H2AX can potentially serve as a biomarker for transformation of normal tissue to premalignant and consequently to malignant tissues. gamma-H2AX has already been investigated in a variety of cancer types, including breast, lung, colon, cervix, and ovary cancers. The prognostic value of gamma-H2AX is indicated in certain cancer types, such as breast or endometrial cancer, but further investigation is needed to establish gamma-H2AX as a prognostic marker. This review outlines the role of gamma-H2AX in cell cycle, and its formation as a result of DNA damage. We investigate the role of gamma-H2AX formation in several cancer types and its correlation with other prognostic factors, and we try to find out whether it fulfills the requirements for its establishment as a classical cancer prognostic factor.

Role of DNA Repair Factor Xeroderma Pigmentosum Protein Group C in Response to Replication Stress As Revealed by DNA Fragile Site Affinity Chromatography and Quantitative Proteomics

Replication stress (RS) fuels genomic instability and cancer development and may contribute to aging, raising the need to identify factors involved in cellular responses to such stress. Here, we present a strategy for identification of factors affecting the maintenance of common fragile sites (CFSs), which are genomic loci that are particularly sensitive to RS and suffer from increased breakage and rearrangements in tumors. A DNA probe designed to match the high flexibility island sequence typical for the commonly expressed CFS (FRA16D) was used as specific DNA affinity bait. Proteins significantly enriched at the FRA16D fragment under normal and replication stress conditions were identified using stable isotope labeling of amino acids in cell culture-based quantitative mass spectrometry. The identified proteins interacting with the FRA16D fragment included some known CFS stabilizers, thereby validating this screening approach. Among the hits from our screen so far not implicated in CFS maintenance, we chose Xeroderma pigmentosum protein group C (XPC) for further characterization. XPC is a key factor in the DNA repair pathway known as global genomic nucleotide excision repair (GG-NER), a mechanism whose several components were enriched at the FRA16D fragment in our screen. Functional experiments revealed defective checkpoint signaling and escape of DNA replication intermediates into mitosis and the next generation of XPC-depleted cells exposed to RS. Overall, our results provide insights into an unexpected biological role of XPC in response to replication stress and document the power of proteomics-based screening strategies to elucidate mechanisms of pathophysiological significance.