The mechanism of radiotherapy for lung adenocarcinoma in promoting protein SIRT6-mediated deacetylation of RBBP8 to enhance the sensitivity of targeted therapy.

BACKGROUND: Lung cancer has the fastest increase in morbidity and mortality, and is one of the most threatening malignant tumors to human health and life. Both radiotherapy and targeted therapy are typical treatments after lung cancer surgery. Radiotherapy is a means of locally killing cancer lesions, and it plays an important role in the entire management of lung cancer. Gefitinib is one of the most commonly used targeted therapy drugs in the treatment of lung cancer. The purpose of this project is to explore the mechanism by which deacetylation of RBBP8 mediated by radiotherapy-promoting protein SIRT6 in lung adenocarcinoma enhances the sensitivity of targeted therapy. METHODS: In both the cell experiments and the animal experiments, the samples were divided into five groups: Model group, RT group, CT group, RT+CT group, and RT+CT+inhibitor group. The CCK8 method was used to detect the viability of each group of cells. The flow cytometry experiment was used to analyze the apoptotic characteristics of each group of cells. The scratch test was used to detect the migration ability of each group of cells. Transwell invasion test was used to determine the invasion ability of each group of cells. The lung tumor tissues of each group of mice were collected to analyze the tumor size, volume, and metastasis characteristics. The TUNEL experiment was used to detect the apoptosis characteristics of the cells in the lung cancer tissues of each group mice. Immunohistochemistry experiments were used to analyze the distribution and relative expression characteristics of protein SIRT6 in mouse lung cancer tissues. The colorimetric experiments were used to detect the activity of Caspase 3 and Caspase 8 in each group. Western blot method was used to detect the expression of SIRT6, RBBP8, and MYC in each group. RESULTS: In each experiment, the results of the experiment have mutually proven consistency, and there is no contradiction. In addition to the Model group, the other 4 groups used different treatment methods. The better the curative effect, the lower the cell viability of cancer cells and the higher the apoptotic ratio. This is reflected in the CCK8 test, flow cytometry analysis, cell scratch test, Transwell cell migration test, and TUNEL detection. At the same time, colorimetric detection and Western blot analysis also analyzed the levels of SIRT6, RBBP8 and other cancer-related proteins in each group at the molecular level, implying the importance of SIRT6 protein in the treatment process. CONCLUSION: Our project has proved that radiotherapy can promote the protein SIRT6 to deacetylate RBBP8 proteins, and ultimately enhance targeted therapy drug sensitivity.

Chronic coexposure to arsenic and estrogen potentiates genotoxic estrogen metabolic pathway and hypermethylation of DNA glycosylase MBD4 in human prostate epithelial cells.

BACKGROUND: Previously we reported that arsenic and estrogen cause synergistic effects in the neoplastic transformation of human prostate epithelial cells. In addition to receptor-mediated pathways, DNA-reactive estrogen metabolites have also been shown to play a critical role in mutagenicity and carcinogenicity. Both estrogen and arsenic are known prostate carcinogens, however, the effect of coexposure to these two chemicals on genes involved in estrogen metabolism is not known. Therefore, the objective of this study was to evaluate the role of arsenic and estrogen coexposure on the expression of estrogen receptors and estrogen metabolism-associated genes. Earlier, we also reported the synergistic effect of arsenic and estrogen on decreased expression of MBD4 genes that play an important role in DNA repair through its DNA glycosylase activity. To further understand the mechanism, the promoter methylation of this gene was also analyzed. METHODS: Total RNA and protein were isolated from RWPE-1 human prostate epithelial cells that were coexposed to arsenic and estrogen for a chronic duration (6 months). The expression of estrogen receptors, estrogen metabolism associated phase I genes (CYP 1A1, 1A2, 3A4, and 1B1) and phase II gene catechol-O-methyltransferase (COMT), as well as antioxidant MnSOD, were analyzed either at the RNA level by quantitative reverse transcriptase-polymerase chain reaction or at the protein level by western blot. Promoter methylation of MBD4 was analyzed by pyrosequencing. RESULTS: Expression of MnSOD and phase I genes that convert E2 into genotoxic metabolites 2-OH-E2 and 4-OH-E2 were significantly increased, whereas the expression of phase II gene COMT that detoxifies estrogen metabolites was significantly decreased in arsenic and estrogen coexposed cells. MBD4 promoter was hypermethylated in arsenic and estrogen coexposed cells. Coexposure to arsenic and estrogen has synergistic effects on the expression of these genes as well as in MBD4 promoter hypermethylation. CONCLUSIONS: These novel findings suggest that coexposure to arsenic and estrogen acts synergistically in the activation of not only the estrogen receptors but also the genes associated with genotoxic estrogen metabolism and epigenetic inactivation of DNA glycosylase MBD4. Together, these genetic and epigenetic aberrations provide the molecular basis for the potentiation of carcinogenicity of arsenic and estrogen coexposure in prostate epithelial cells.

Bid-Induced Release of AIF/EndoG from Mitochondria Causes Apoptosis of Macrophages during Infection with Leptospira interrogans.

Leptospirosis is a global zoonotic infectious disease caused by pathogenic Leptospira species. Leptospire-induced macrophage apoptosis through the Fas/FasL-caspase-8/3 pathway plays an important role in the survival and proliferation of the pathogen in hosts. Although, the release of mitochondrial apoptosis-inducing factor (AIF) and endonuclease G (EndoG) in leptospire-infected macrophages has been described, the mechanisms linking caspase and mitochondrion-related host-cell apoptosis has not been determined. Here, we demonstrated that leptospire-infection induced apoptosis through mitochondrial damages in macrophages. Apoptosis was caused by the mitochondrial release and nuclear translocation of AIF and/or EndoG, leading to nuclear DNA fragmentation. However, the mitochondrion-related CytC-caspase-9/3 pathway was not activated. Next, we found that the release and translocation of AIF and/or EndoG was preceded by the activation of the BH3-interacting domain death agonist (Bid). Furthermore, our data demonstrated that caspase-8 was activated during the infection and caused the activation of Bid. Meanwhile, high reactive oxygen species (ROS) trigged by the infection caused the dephosphorylation of Akt, which also activated Bid. In conclusion, Bid-mediated mitochondrial release of AIF and/or EndoG followed by nuclear translocation is a major mechanism of leptospire- induced apoptosis in macrophages, and this process is modulated by both caspase-8 and ROS-Akt signal pathways.

Zebrafish Models for the Mechanosensory Hair Cell Dysfunction in Usher Syndrome 3 Reveal That Clarin-1 Is an Essential Hair Bundle Protein.

Usher syndrome type III (USH3) is characterized by progressive loss of hearing and vision, and varying degrees of vestibular dysfunction. It is caused by mutations that affect the human clarin-1 protein (hCLRN1), a member of the tetraspanin protein family. The missense mutation CLRN1(N48K), which affects a conserved N-glycosylation site in hCLRN1, is a common causative USH3 mutation among Ashkenazi Jews. The affected individuals hear at birth but lose that function over time. Here, we developed an animal model system using zebrafish transgenesis and gene targeting to provide an explanation for this phenotype. Immunolabeling demonstrated that Clrn1 localized to the hair cell bundles (hair bundles). The clrn1 mutants generated by zinc finger nucleases displayed aberrant hair bundle morphology with diminished function. Two transgenic zebrafish that express either hCLRN1 or hCLRN1(N48K) in hair cells were produced to examine the subcellular localization patterns of wild-type and mutant human proteins. hCLRN1 localized to the hair bundles similarly to zebrafish Clrn1; in contrast, hCLRN1(N48K) largely mislocalized to the cell body with a small amount reaching the hair bundle. We propose that this small amount of hCLRN1(N48K) in the hair bundle provides clarin-1-mediated function during the early stages of life; however, the presence of hCLRN1(N48K) in the hair bundle diminishes over time because of intracellular degradation of the mutant protein, leading to progressive loss of hair bundle integrity and hair cell function. These findings and genetic tools provide an understanding and path forward to identify therapies to mitigate hearing loss linked to the CLRN1 mutation. SIGNIFICANCE STATEMENT: Mutations in the clarin-1 gene affect eye and ear function in humans. Individuals with the CLRN1(N48K) mutation are born able to hear but lose that function over time. Here, we develop an animal model system using zebrafish transgenesis and gene targeting to provide an explanation for this phenotype. This approach illuminates the role of clarin-1 and the molecular mechanism linked to the CLRN1(N48K) mutation in sensory hair cells of the inner ear. Additionally, the investigation provided an in vivo model to guide future drug discovery to rescue the hCLRN1(N48K) in hair cells.

DNA damage in blood cells exposed to low-level lasers.

BACKGROUND AND OBJECTIVE: In regenerative medicine, there are increasing applications of low-level lasers in therapeutic protocols for treatment of diseases in soft and in bone tissues. However, there are doubts about effects on DNA, and an adequate dosimetry could improve the safety of clinical applications of these lasers. This work aimed to evaluate DNA damage in peripheral blood cells of Wistar rats induced by low-level red and infrared lasers at different fluences, powers, and emission modes according to therapeutic protocols. MATERIAL AND METHODS: Peripheral blood samples were exposed to lasers and DNA damage was accessed by comet assay. In other experiments, DNA damage was accessed in blood cells by modified comet assay using formamidopyrimidine DNA glycosylase (Fpg) and endonuclease III enzymes. RESULTS: Data show that exposure to low-level red and infrared lasers induce DNA damage depending on fluence, power and emission mode, which are targeted by Fpg and endonuclease III. CONCLUSION: Oxidative DNA damage should be considered for therapeutic efficacy and patient safety in clinical applications based on low-level red and infrared lasers.

Mitochondrially targeted Endonuclease III has a powerful anti-infarct effect in an in vivo rat model of myocardial ischemia/reperfusion.

Recent reports indicate that elevating DNA glycosylase/AP lyase repair enzyme activity offers marked cytoprotection in cultured cells and a variety of injury models. In this study, we measured the effect of EndoIII, a fusion protein construct that traffics Endonuclease III, a DNA glycosylase/AP lyase, to the mitochondria, on infarct size in a rat model of myocardial ischemia/reperfusion. Open-chest, anesthetized rats were subjected to 30 min of occlusion of a coronary artery followed by 2 h of reperfusion. An intravenous bolus of EndoIII, 8 mg/kg, just prior to reperfusion reduced infarct size from 43.8 ± 1.4% of the risk zone in control animals to 24.0 ± 1.3% with no detectable hemodynamic effect. Neither EndoIII's vehicle nor an enzymatically inactive EndoIII mutant (K120Q) offered any protection. The magnitude of EndoIII's protection was comparable to that seen with the platelet aggregation inhibitor cangrelor (25.0 ± 1.8% infarction of risk zone). Because loading with a P2Y12 receptor blocker to inhibit platelets is currently the standard of care for treatment of acute myocardial infarction, we tested whether EndoIII could further reduce infarct size in rats treated with a maximally protective dose of cangrelor. The combination reduced infarct size to 15.1 ± 0.9% which was significantly smaller than that seen with either cangrelor or EndoIII alone. Protection from cangrelor but not EndoIII was abrogated by pharmacologic blockade of phosphatidylinositol-3 kinase or adenosine receptors indicating differing cellular mechanisms. We hypothesized that EndoIII protected the heart from spreading necrosis by preventing the release of proinflammatory fragments of mitochondrial DNA (mtDNA) into the heart tissue. In support of this hypothesis, an intravenous bolus at reperfusion of deoxyribonuclease I (DNase I) which should degrade any DNA fragments escaping into the extracellular space was as protective as EndoIII. Furthermore, the combination of EndoIII and DNase I produced additive protection. While EndoIII would maintain mitochondrial integrity in many of the ischemic cardiomyocytes, DNase I would further prevent mtDNA released from those cells that EndoIII could not save from propagating further necrosis. Thus, our mtDNA hypothesis would predict additive protection. Finally to demonstrate the toxicity of mtDNA, isolated hearts were subjected to 15 min of global ischemia. Infarct size doubled when the coronary vasculature was filled with mtDNA fragments during the period of global ischemia. To our knowledge, EndoIII and DNase are the first agents that can both be given at reperfusion and add to the protection of a P2Y12 blocker, and thus should be effective in today's patient with acute myocardial infarction.

Zinc Finger Nuclease induced DNA double stranded breaks and rearrangements in MLL.

Radiation treatment or chemotherapy has been linked with a higher risk of secondary cancers such as therapy related Acute Myeloid Leukemia (tAML). Several of these cancers have been shown to be correlated to the introduction of double stranded breaks (DSB) and rearrangements within the Mixed Lineage Leukemia (MLL) gene. We used Zinc Finger Nucleases (ZFNs) to introduce precise cuts within MLL to examine how a single DNA DSB might lead to chromosomal rearrangements. A ZFN targeting exon 13 within the Breakpoint Cluster Region of MLL was transiently expressed in a human lymphoblast cell line originating from a CML patient. Although FISH analysis showed ZFN DSB at this region increased the rate of MLL fragmentation, we were unable to detect leukemogenic rearrangements or translocations via inverse PCR. Interestingly, gene fragmentation as well as small interstitial deletions, insertions and base substitutions increased with the inhibition of DNA-PK, suggesting repair of this particular DSB is linked to non-homologous end joining (NHEJ). Although mis-repair of DSBs may be necessary for the initiation of leukemogenic translocations, a MLL targeted DNA break alone is insufficient.

Improving the efficiency of CHO cell line generation using glutamine synthetase gene knockout cells.

Although Chinese hamster ovary (CHO) cells, with their unique characteristics, have become a major workhorse for the manufacture of therapeutic recombinant proteins, one of the major challenges in CHO cell line generation (CLG) is how to efficiently identify those rare, high-producing clones among a large population of low- and non-productive clones. It is not unusual that several hundred individual clones need to be screened for the identification of a commercial clonal cell line with acceptable productivity and growth profile making the cell line appropriate for commercial application. This inefficiency makes the process of CLG both time consuming and laborious. Currently, there are two main CHO expression systems, dihydrofolate reductase (DHFR)-based methotrexate (MTX) selection and glutamine synthetase (GS)-based methionine sulfoximine (MSX) selection, that have been in wide industrial use. Since selection of recombinant cell lines in the GS-CHO system is based on the balance between the expression of the GS gene introduced by the expression plasmid and the addition of the GS inhibitor, L-MSX, the expression of GS from the endogenous GS gene in parental CHOK1SV cells will likely interfere with the selection process. To study endogenous GS expression's potential impact on selection efficiency, GS-knockout CHOK1SV cell lines were generated using the zinc finger nuclease (ZFN) technology designed to specifically target the endogenous CHO GS gene. The high efficiency (∼2%) of bi-allelic modification on the CHO GS gene supports the unique advantages of the ZFN technology, especially in CHO cells. GS enzyme function disruption was confirmed by the observation of glutamine-dependent growth of all GS-knockout cell lines. Full evaluation of the GS-knockout cell lines in a standard industrial cell culture process was performed. Bulk culture productivity improved two- to three-fold through the use of GS-knockout cells as parent cells. The selection stringency was significantly increased, as indicated by the large reduction of non-producing and low-producing cells after 25 µM L-MSX selection, and resulted in a six-fold efficiency improvement in identifying similar numbers of high-productive cell lines for a given recombinant monoclonal antibody. The potential impact of GS-knockout cells on recombinant protein quality is also discussed.

Mitochondrial DNA integrity may be a determinant of endothelial barrier properties in oxidant-challenged rat lungs.

In cultured pulmonary artery endothelial cells and other cell types, overexpression of mt-targeted DNA repair enzymes protects against oxidant-induced mitochondrial DNA (mtDNA) damage and cell death. Whether mtDNA integrity governs functional properties of the endothelium in the intact pulmonary circulation is unknown. Accordingly, the present study used isolated, buffer-perfused rat lungs to determine whether fusion proteins targeting 8-oxoguanine DNA glycosylase 1 (Ogg1) or endonuclease III (Endo III) to mitochondria attenuated mtDNA damage and vascular barrier dysfunction evoked by glucose oxidase (GOX)-generated hydrogen peroxide. We found that both Endo III and Ogg1 fusion proteins accumulated in lung cell mitochondria within 30 min of addition to the perfusion medium. Both constructs prevented GOX-induced increases in the vascular filtration coefficient. Although GOX-induced nuclear DNA damage could not be detected, quantitative Southern blot analysis revealed substantial GOX-induced oxidative mtDNA damage that was prevented by pretreatment with both fusion proteins. The Ogg1 construct also reversed preexisting GOX-induced vascular barrier dysfunction and oxidative mtDNA damage. Collectively, these findings support the ideas that mtDNA is a sentinel molecule governing lung vascular barrier responses to oxidant stress in the intact lung and that the mtDNA repair pathway could be a target for pharmacological intervention in oxidant lung injury.

Clearance and characterization of residual HSV DNA in recombinant adeno-associated virus produced by an HSV complementation system.

Encapsidation of cellular- or plasmid-derived DNA sequences during recombinant adeno-associated virus (rAAV) production has been well documented. However, most of the published data were generated from rAAV vectors manufactured by the plasmid transient transfection method. We previously reported a novel, scalable method for rAAV manufacturing based on a recombinant herpes simplex virus (rHSV) complementation system. In this report, we evaluated clearance of DNA impurities during rAAV purification, by determining the quantity of residual herpes simplex virus and cellular DNA at each process step. A single Benzonase treatment during the upstream process effectively reduced unprotected HSV and cellular DNA to <300 bp fragments, and subsequent chromatography steps completely removed these small DNA fragments. Further analysis showed that trace amounts of residual, DNase-resistant HSV and cellular DNA were present at static concentrations during subsequent purification steps, and the residual HSV DNA sequences were single stranded, ranging from 0.8 to 4.2 kb. After transduction of human embryonic kidney 293 cells with purified rAAV, the residual HSV DNA fragments were neither transcribed nor translated into HSV proteins. In summary, this manufacturing process for rAAV production was effective in removing DNA and protein contaminants and achieving a highly purified product, suitable for human clinical application.

Antitumor activity of apoptotic nuclease TBN1 from L. esculentum.

Nuclease from tomato (TBN1) was produced by in planta biotechnology purified and tested for its anticarcinogenic properties. The nuclease was cytostatic after its intratumoral administration to nude mice bearing human melanoma or prostate carcinoma or after tumor targeting by TBN1 administration intravenously as conjugate with polyethylene glycol (PEG). Inhibitory effects of TBN1 on tumor growth were comparable to effects of bovine seminal RNase (BS-RNase), but the inhibition was reached at about ten times lower protein concentration. Simultaneously, TBN1 exhibited a lower degree of embryotoxicity compared to BS-RNAse and other nucleases. TBN1 showed significant stability in vivo, because it was readily detected after its administration intratumorally or intravenously by the fluorescence methods. Intravenous administration of TBN1-PEG caused significant inhibition of tumor proliferation without obvious degenerative changes, while direct administration of TBN1 into melanoma tumors led to rapid tumor tissue degeneration. The fact can be essential for the mode of TBN1 biological action that mature nuclease is a small (36 kDa) thermostable glycoprotein that has ability to destroy human 28S, 18S, 7S and 5.8S RNA, circular RNAs, double-stranded RNA in vitro and shows DNase and 3'nucleotidase activities.

[Benzonase--possibility of practical application]. / Benzonaza--mozliwosci praktycznych zastosowan.

Benzonase nuclease degrades all forms of DNA and RNA while having no photolytic activity. In this study we check possibility of use this reagent to prepare proteins to microcalorymetric experiments.

DNase1L2 suppresses biofilm formation by Pseudomonas aeruginosa and Staphylococcus aureus.

BACKGROUND: The formation of biofilms, which is an important step in bacterial colonization, can be inhibited by deoxyribonuclease (DNase)-mediated breakdown of extracellular DNA. We have recently demonstrated that epidermal keratinocytes strongly express DNase1-like 2 (DNase1L2) in a differentiation-associated manner. OBJECTIVES: To determine whether enzymatically active DNase1L2 is present in human stratum corneum and whether it is able to suppress bacterial biofilm formation. METHODS: DNase1L2 was extracted from normal human stratum corneum, immunocaptured and incubated with plasmid DNA. DNA hydrolysis was monitored by gel electrophoresis and ethidium bromide staining. The effect of DNase1L2 on biofilm formation was assayed by cultivation of Pseudomonas aeruginosa and Staphylococcus aureus in the presence or absence of purified recombinant DNase1L2 in microtitre plates and subsequent quantification of biofilm-forming bacteria by crystal violet staining. RESULTS: DNase1L2 was found to be present in an enzymatically active form in the stratum corneum of human skin. In an in vitro assay, purified recombinant DNase1L2 efficiently suppressed the formation of biofilms by P. aeruginosa and S. aureus. CONCLUSIONS: Our data suggest that DNase1L2 is a novel component of the innate antimicrobial defence of the epidermis.

Mechanistic aspects of the deoxyribonuclease activity of diphtheria toxin.

Here we examined the intrinsic nuclease activity of diphtheria toxin (DTx) to determine the mechanism by which it catalyzes DNA degradation. Results show that DTx degrades double-stranded DNA (dsDNA) by non-processive, endonucleolytic attack, without apparent specificity for nucleotide sequence. Moreover, divalent cation composition determines whether supercoiled dsDNA is cleaved by the introduction of single-strand nicks or double-strand breaks. Circular single-stranded DNA (ssDNA) is also a substrate for endonucleolytic attack. Pre-incubation of DTx with a 2000-fold excess of NAD, the natural substrate for the toxin's ADP-ribosyltransferase (ADPrT) activity, inhibited the transfer of radiolabeled ADP-ribose to elongation factor 2 but had no effect on the degradation of radiolabeled DNA. Based on this result and the fact that compounds known to inhibit the ADPrT activity of DTx had no effect on its nuclease activity and pre-incubation of DTx with DNA had no effect on ADPrT activity, we conclude that the ADPrT and nuclease active sites of DTx are functionally and spatially distinct. Moreover, studies with an ADPrT-inactivated form of DTx indicate that nuclease activity alone can lead to target cell lysis.

Ceramide synthase is essential for endonuclease-mediated death of renal tubular epithelial cells induced by hypoxia-reoxygenation.

Ceramide is known to play a role in the cell signaling pathway involved in apoptosis. Most studies suggest that enhanced ceramide generation is the result of hydrolysis of sphingomyelin by sphingomyelinases. However, the role of ceramide synthase in enhanced ceramide generation has not been previously examined in hypoxia-reoxygenation injury. In the present study, we demonstrated that 60-min hypoxia of rat renal tubular epithelial NRK-52E cells in a gas chamber with 95% N2-5% CO2 with glucose deprivation resulted in a significant increase in ceramide generation. The ceramide level further increased after reoxygenation for 60 min. Exposure of cells to hypoxia-reoxygenation resulted in a significant increase in ceramide synthase activity without any significant change in acid or neutral sphingomyelinase. The hypoxia-reoxygenation of NRK-52E cells was also associated with the release of endonuclease G (EndoG) from mitochondria to cytoplasm measured by Western blot analysis and endonuclease activity assay. It further led to the fragmentation of DNA and cell death. A specific inhibitor of ceramide synthase, fumonisin B1 (50 microM), suppressed hypoxia-reoxygenation-induced ceramide generation and provided protection against hypoxia-reoxygenation-induced EndoG release, DNA fragmentation, and cell death. Taken together, our data suggest that hypoxia-reoxygenation results in an activation of ceramide synthase rather than sphingomyelinase and that ceramide synthase-dependent ceramide generation is a key modulator of EndoG-mediated cytotoxicity in hypoxia-reoxygenation injury to renal tubular epithelial cells.

Effect of S. cerevisiae APN1 protein on mammalian DNA base excision repair.

Mammalian cells transfected with the S. cerevisiae APN1 protein acquire resistance to oxidizing agents, the damage of which is mainly repaired via DNA base excision repair (BER). We have recently hypothesized that this effect might be linked to the possible capacity of APN1 to accelerate mammalian BER by its 3' diesterase activity. We have investigated here the effect of pure APN1 protein on BER performed by mouse embryonic fibroblast extracts. No significant acceleration was observed in the repair of either a single AP site cleaved by the bifunctional glycosylase NTH of E. coli or the repair of a single 8-oxoguanine, initiated by the bifunctional glycosylase OGG1. Similarly, no significant effect was observed on the repair of a single U (initiated by the monofunctional glycosylase U DNA glycosylase) or the repair of a single natural abasic site. The inability of APN1 to increase the efficiency of BER initiated by bifunctional glycosylases indicates that removal of 3' blocking fragments is not the rate-limiting step of this repair pathway.

Human-yeast chimeric repair protein protects mammalian cells against alkylating agents: enhancement of MGMT protection.

Chemotherapeutic DNA alkylating agents are common weapons employed to fight both pediatric and adult cancers. In addition to cancerous cells, nontarget tissues are subjected to the cytotoxicity of these agents, and dose-limiting toxicity in the form of myelosuppression is a frequent result of treatment. One approach to prevent myelosuppression that results from the use of chemotherapeutic agents is to increase the levels of DNA repair proteins in bone marrow cells. Here we report our second successful attempt to create a fusion protein that possesses both direct reversal and base excision repair pathway DNA repair activities. The chimeric protein is composed of the human O(6)-Methylguanine-DNA Methyltransferase (MGMT) and the yeast Apn1 proteins and retains both MGMT and AP endonuclease activities as determined by biochemical analysis. We have also demonstrated that the chimeric protein is able to protect mammalian cells from the DNA alkylating agents 1,3-bis (2-chloroethyl)-1-nitrosourea (BCNU) and methyl methanesulfonate (MMS). The protection by the chimeric protein against BCNU is even greater than MGMT alone, which has potential translational significance given that MGMT is currently in clinical trials. Additionally, we show that the chimeric MGMT-Apn1 protein can protect mammalian cells from dual treatments of BCNU and MMS and that this effect is greater than that provided by MGMT alone. The data support our previous finding that a protein with multiple DNA repair activities can be constructed and that this and other constructs may play an important clinical role in guarding against dose-limiting effects of chemotherapy, particularly in situations of multiple drug use.

Nuclear translocation of DNase II and acid phosphatase during radiation-induced apoptosis in HL60 cells.

DNase II is involved in DNA fragmentation induced by a variety of treatments. However, according to past reports DNase II does not directly generate TUNEL (in situ DNA end labeling)-positive cells. The purpose of this study was to investigate the participation of acid phosphatase in the generation of TUNEL-positive cells. DNase II-like proteins, whose molecular weights were 32-kDa, were detected in nuclear extracts of HL60 human myeloid leukemia cells post gamma-irradiation by SDS-PAGE and immunohistochemistry. Acidic nuclease activity was especially active in 32-kDa bands TUNEL assay was positive post gamma-irradiation. From measurements of the activity of acid phosphatase, the activity in nuclear extracts increased remarkably post gamma-irradiation. Gamma-irradiation can directly or indirectly activate DNase II. Once DNase II and acid phosphatase have been translocated from lysosomes into the nuclei, DNase II generates TUNEL reactive ends in combination with acid phosphatase.

DNA is a target of the photodynamic effects elicited in A2E-laden RPE by blue-light illumination.

PURPOSE: When the pyridinium bisretinoid A2E, an age-related fluorophore in the retinal pigment epithelium (RPE), is irradiated with blue light, photochemical events are initiated that can ultimately provoke cell death. This study was designed to determine whether DNA is a target of the cellular damage. METHODS: ARPE-19 cells accumulated A2E before exposure to blue light. DNA damage was assayed in individual cells by alkaline gel electrophoresis (comet assay), with and without the addition of the repair enzymes formamidopyrimidine N-glycosylase (Fpg), endonuclease III (endo III) and T4-endonuclease V (T4-endo V) to characterize DNA lesions. Damage was quantified as comet tail moment. The base lesion 8-oxo-deoxyguanosine (8-oxo-dG) was detected by immunoperoxidase and histochemical methods. The singlet oxygen quencher, sodium azide, was tested for its ability to reduce DNA damage, and cell viability was quantified. RESULTS: DNA damage was induced in A2E-containing RPE exposed to 430-nm illumination. The extent of damage, measured as tail moment, was proportional to exposure duration and was reduced by preincubation with sodium azide. The detection of FPG- and endo III-sensitive DNA lesions revealed the presence of oxidized purine and pyrimidine bases, whereas labeling with specific antibody and binding of fluorescein-labeled avidin indicated that guanine bases were oxidatively modified to 8-oxo-dG. The ability of the cells to repair the DNA damage declined as the severity was increased, and kinetic studies disclosed rapid and slow stages of repair. CONCLUSIONS: DNA is one of the cellular constitutents that can be damaged by the interaction of A2E and blue light. At least some of the DNA lesions are oxidative base modifications.

Endonuclease III, formamidopyrimidine-DNA glycosylase, and proteinase K additively enhance arsenic-induced DNA strand breaks in human cells.

We report here that sequential digestion with endonuclease III, formamidopyrimidine-DNA glycosylase, and proteinase K in Tris buffer markedly increased the sensitivity for detecting DNA damage in arsenic-treated cells. These three enzymes increased DNA strand breaks in an additive manner. By using this sequential-enzyme-digestion comet assay, we demonstrated that trivalent inorganic arsenic induced more DNA damage than monomethylarsonous acid, monomethylarsonic acid, and dimethylarsinic acid in human blood cell lines. However, trivalent inorganic arsenic was far less potent than monomethylarsonous acid in inhibiting pyruvate dehydrogenase activity. Therefore, different mechanisms are involved in inhibiting pyruvate dehydrogenase activity and inducing DNA damage. Our results also indicate while trivalent inorganic arsenic induced more endonuclease III-digestible adducts, monomethylarsonous acid and monomethylarsonic acid induced more proteinase K-digestible adducts. These results suggest there is a difference in the mechanism for inducing DNA damage between inorganic and organic methylated arsenic compounds.