The cloning and expression of human deoxyribonuclease II. A possible role in apoptosis

Caspase inhibition improves viability and efficiency of liposomal transfection

High transfection efficiency is the most important point for experiments of DNA and RNA introduction into cells. Decrease of cell viability during the transfection procedure is a crucial issue, resulting in transfection failure. However, the mechanism underlying cell growth inhibition has not been fully elucidated. Lipofection is frequently used for transfection experiments, whereases, depending on cell type, it causes a decrease in cell viability. The present study demonstrates here that a potent pan-caspase inhibitor Q-VD-OPh blocked cell death during the lipofection, indicating apoptosis was induced in lipofection. Moreover, Q-VD-OPh drastically increased transfected cells. This method provides easier and more effective transfection system of lipofection and may be useful for transfection of not only cell lines but also clinical uses such as gene therapy and nucleic acids vaccine.

Deoxyribonucleases and Their Applications in Biomedicine

Extracellular DNA, also called cell-free DNA, released from dying cells or activated immune cells can be recognized by the immune system as a danger signal causing or enhancing inflammation. The cleavage of extracellular DNA is crucial for limiting the inflammatory response and maintaining homeostasis. Deoxyribonucleases (DNases) as enzymes that degrade DNA are hypothesized to play a key role in this process as a determinant of the variable concentration of extracellular DNA. DNases are divided into two families-DNase I and DNase II, according to their biochemical and biological properties as well as the tissue-specific production. Studies have shown that low DNase activity is both, a biomarker and a pathogenic factor in systemic lupus erythematosus. Interventional experiments proved that administration of exogenous DNase has beneficial effects in inflammatory diseases. Recombinant human DNase reduces mucus viscosity in lungs and is used for the treatment of patients with cystic fibrosis. This review summarizes the currently available published data about DNases, their activity as a potential biomarker and methods used for their assessment. An overview of the experiments with systemic administration of DNase is also included. Whether low-plasma DNase activity is involved in the etiopathogenesis of diseases remains unknown and needs to be elucidated.

Omeprazole Induces Apoptosis in Jurkat Cells

We report for the first time a potent apoptotic effect of omeprazole (OM). Apoptosis was induced in Jurkat cells in a time and concentration-dependent mode. Caspase 3 and PARP were rapidly cleaved in response to OM, but apoptosis was only partially inhibited by the caspase 3 inhibitor DEVD-CHO. OM also induced an early lysosomal destabilization which increased progressively and was correlated with a parallel increase in apoptotic cells. The cysteine protease inhibitor E64d gave strong protection against apoptosis thus proving the involvement of lysosomal enzymes in OM-induced apoptosis whereas, it did not impede the caspase 3 cleavage. Instead ZVAD-fmk, a general caspase inhibitor, also able to inhibit cathepsin activity, protected cells completely from OM-induced apoptosis. It therefore seems that both caspases and cysteine cathepsins are involved in the execution stage of OM-induced apoptosis.

Loss of DNase II function in the gonad is associated with a higher expression of antimicrobial genes in Caenorhabditis elegans

Three waves of apoptosis shape the development of Caenorhabditis elegans. Although the exact roles of the three DNase II genes (nuc-1, crn-6 and crn-7), which are known to mediate degradation of apoptotic DNA, in the embryonic and larval phases of apoptosis have been characterized, the DNase II acting in the third wave of germ cell apoptosis remains undetermined. In the present study, we performed in vitro and in vivo assays on various mutant nematodes to demonstrate that NUC-1 and CRN-7, but not CRN-6, function in germ cell apoptosis. In addition, in situ DNA-break detection and anti-phosphorylated ERK (extracellular-signal-regulated kinase) staining illustrated the sequential and spatially regulated actions of NUC-1 and CRN-7, at the pachytene zone of the gonad and at the loop respectively. In line with the notion that UV-induced DNA fragment accumulation in the gonad activates innate immunity responses, we also found that loss of NUC-1 and CRN-7 lead to up-regulation of antimicrobial genes (abf-2, spp-1, nlp-29, cnc-2, and lys-7). Our observations suggest that an incomplete digestion of DNA fragments resulting from the absence of NUC-1 or CRN-7 in the gonad could induce the ERK signalling, consequently activating antimicrobial gene expression. Taken together, the results of the present study demonstrate for the first time that nuc-1 and crn-7 play a role in degrading apoptotic DNA in distinct sites of the gonad, and act as negative regulators of innate immunity in C. elegans.

A novel Schistosoma japonicum endonuclease homologous to DNase II

Background

Recent advances in studies of the Schistosoma japonicum genome have opened new avenues for the elucidation of parasite biology and the identification of novel targets for vaccines, drug development and early diagnostic tools.

Results

In this study, we surveyed the S. japonicum genome database for genes encoding nucleases. A total of 130 nucleases of 3 classes were found. Transcriptional analysis of these genes using a genomic DNA microarray revealed that the majority of the nucleases were differentially expressed in parasites of different developmental stages or different genders, whereas no obvious transcriptional variation was detected in parasites from different hosts. Further analysis of the putative DNases of S. japonicum revealed a novel DNase II homologue (Sjda) that contained a highly conserved catalytic domain. A recombinant Sjda-GST protein efficiently hydrolysed genomic DNA in the absence of divalent iron. Western-blot and immunofluorescence assays showed that Sjda was mainly expressed on the teguments of female adult parasites and induced early humoral immune responses in infected mice.

Conclusions

A novel DNase II homologue, Sjda, was identified in S. japonicum. Sjda was mainly distributed on the teguments of adult female parasites and possessed a typical divalent iron-independent DNA catalytic activity. This protein may play an important role in the host–parasite interaction.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1319-5) contains supplementary material, which is available to authorized users.

Apoptosis-inducing factor (AIF) and leukocyte elastase inhibitor/L-DNase II (LEI/LDNaseII), can interact to conduct caspase-independent cell death

Programmed cell death is an important factor in tissue homeostasis. Lot of work has been performed to characterize the caspase-dependent cell death. Caspase-independent cell death, although important in many physiological situations, is less investigated. In this work we show that two caspase-independent effectors of cell death, namely apoptosis-inducing factor and leukocyte elastase inhibitor derived DNase II interact and can cooperate to induce cell death. These results contribute to the knowledge of molecular pathways of cell death, an important issue in the development of new therapeutic strategies for the treatment of cancer or neurodegenerative diseases.

Role of ion transport in control of apoptotic cell death

Cell shrinkage is a hallmark and contributes to signaling of apoptosis. Apoptotic cell shrinkage requires ion transport across the cell membrane involving K(+) channels, Cl(-) or anion channels, Na(+)/H(+) exchange, Na(+),K(+),Cl(-) cotransport, and Na(+)/K(+)ATPase. Activation of K(+) channels fosters K(+) exit with decrease of cytosolic K(+) concentration, activation of anion channels triggers exit of Cl(-), organic osmolytes, and HCO3(-). Cellular loss of K(+) and organic osmolytes as well as cytosolic acidification favor apoptosis. Ca(2+) entry through Ca(2+)-permeable cation channels may result in apoptosis by affecting mitochondrial integrity, stimulating proteinases, inducing cell shrinkage due to activation of Ca(2+)-sensitive K(+) channels, and triggering cell-membrane scrambling. Signaling involved in the modification of cell-volume regulatory ion transport during apoptosis include mitogen-activated kinases p38, JNK, ERK1/2, MEKK1, MKK4, the small G proteins Cdc42, and/or Rac and the transcription factor p53. Osmosensing involves integrin receptors, focal adhesion kinases, and tyrosine kinase receptors. Hyperosmotic shock leads to vesicular acidification followed by activation of acid sphingomyelinase, ceramide formation, release of reactive oxygen species, activation of the tyrosine kinase Yes with subsequent stimulation of CD95 trafficking to the cell membrane. Apoptosis is counteracted by mechanisms involved in regulatory volume increase (RVI), by organic osmolytes, by focal adhesion kinase, and by heat-shock proteins. Clearly, our knowledge on the interplay between cell-volume regulatory mechanisms and suicidal cell death is still far from complete and substantial additional experimental effort is needed to elucidate the role of cell-volume regulatory mechanisms in suicidal cell death.

Induction of apoptosis through caspase-independent or caspase-9-dependent pathway in mouse and human osteosarcoma cells by a new nitroxyl spin-labeled derivative of podophyllotoxin

Previous study has found that a new nitroxyl spin-labeled derivative of podophyllotoxin, 4-[4"-(2",2",6",6"-tetramethyl-1"-piperidinyloxy)amino]-4'-demethyl-epipodophyllotoxin (GP7), can induce apoptosis in human leukemia cells. However, there have been no studies about the effects of GP7 on osteosarcoma (OS) cells. Here, we observed the anti-OS effects of GP7 in mouse and human OS cells with the comparison of etoposide. GP7 and etoposide inhibited the proliferation of a panel of mouse and human OS cells in a concentration- or time-dependent manner, and the inhibitory effect of GP7 on the proliferation of mouse LM8 or human U2OS cells was 1.28- or 1.35-fold higher than that of etoposide. GP7 or etoposide augmented the anti-OS effects of methotrexate, adriamycin, cisplatin, or their combination, and the combined inhibitory effects of GP7 with MTX on the proliferation of LM8 cells was higher than those of etoposide with MTX. GP7 arrested the cell cycle in S phase but etoposide in G(2)/M phase. GP7 or etoposide induced sub-G(1) peak, apoptotic DNA fragmentation, activations of caspase-3, -8, -9, and DNA fragmentation factor, downregulation of Bcl-2 and Bcl-xL, upregulation of Bax and Bak, and cytochrome-c release from mitochondria in both mouse and human OS cells. GP7 or etoposide also induced endonuclease G translocation from mitochondria into cytosol in mouse cells. GP7- or etoposide-induced apoptotic DNA fragmentation of human OS cells was inhibited by the pan caspase inhibitor and caspase-9 inhibitor, not by caspase-8 inhibitor whereas it was not inhibited by the pan caspase inhibitor in mouse OS cells. Our findings indicate that GP7 is effective against mouse and human OS cells in vitro. The apoptotic DNA fragmentation in mouse OS cells may be mediated by caspase-independent pathway with the involvement of endonuclease G whereas in human OS cells by caspase-9-dependent pathway downstream of the cytochrome-c-initiated caspase cascade.

Cladribine enhances apoptotic cell death in lung carcinoma cells over-expressing DNase γ

Worldwide, lung cancer is the most common form of cancer and often has a poor prognosis. Establishment of effective therapies for lung cancer is a major concern in clinical cancer research. We compared the cytotoxic effects of chemotherapeutic agents including cisplatin, 5-fluorouracil, vinorelbine and cladribine, on a human lung cancer cell line, A549, and its derivative transfected with the DNase γ gene. We observed selective cytotoxicity of cladribine on the DNase γ-expressing sub-cell line of A549. Cladribine induces selective apoptosis in DNase γ-expressing A549 cells, which depends on activation of caspases. These results suggest that a combination therapy that includes cladribine along with the introduction of DNase γ has potential as a new therapeutic strategy for lung cancer.

Apoptotic and Inflammatory Effects Induced by Different Particles in Human Alveolar Macrophages

Pollutant particles induce apoptosis and inflammation, but the relationship between these two biological processes is not entirely clear. In this study, we compared the proapoptotic and proinflammatory effects of four particles: residual oil fly ash (ROFA), St. Louis particles SRM 1648 (SL), Chapel Hill PM10 (CHP), and Mount St. Helens dust (MSH). Human alveolar macrophages (AM) were incubated with these particles at 100 microg/ml. Cell death was assessed by annexin V (AV) expression, histone release, nuclear morphology, caspase 3-like activity and release of caspase 1 for apoptosis, and propidium iodide (PI) for necrosis, and inflammation was measured by interleukin (IL)-1beta and IL-6. We found that particle effects on these cell death measurements varied, and ROFA affected most (four out of five) endpoints, including nuclear morphological changes. CHP and SL also caused necrosis. For cytokine release, the potency was CHP > SL > ROFA > MSH. The proapoptotic and proinflammatory effects induced by the whole particles were unaltered after the particles were washed with water. The water-soluble fraction was relatively inactive, as were individual soluble metals (V, Ni, Fe). ROFA-induced nuclear fragmentation was associated with upregulation and mitochondrial release of apoptosis-inducing factor (AIF), a caspase-independent chromatin condensation factor, and upregulation of DNase II, a lysosomal acid endonuclease. These results indicate that the potential for particles to induce apoptosis does not correlate with their proinflammatory properties, although active components for both processes reside in the water-insoluble core. Both apoptosis and inflammatory endpoints should be included when the toxicity of different pollutant particles is assessed.

The functions of Deoxyribonuclease II in immunity and development

Apoptosis, which is usually accompanied by DNA degradation, is important not only for the homeostasis of metazoans but also for mammalian development. If DNA is not properly degraded in these processes, it can cause diverse diseases, such as anemia, cataracts, and some autoimmune diseases. A large effort has been made to identify these nucleases that are responsible for these effects. In contrast to Deoxyribonuclease I (DNase I), Deoxyribonuclease II (DNase II) has been less well characterized in these processes. Additionally, enzymes of DNase II family in Trichinella spiralis, which is an intracellular parasitic nematode, are also considered involved in the development of the nematode. We have compiled information from studies on DNase II from various organisms and found some nonclassic features in these enzymes of T. spiralis. Here we have reviewed the characterization and functions of DNase II in these processes and predicted the functions of these enzymes in T. spiralis during host invasion and development.

Sensitivity of human prostate cancer cells to chemotherapeutic drugs depends on EndoG expression regulated by promoter methylation

Analysis of promoter sequences of all known human cytotoxic endonucleases showed that endonuclease G (EndoG) is the only endonuclease that contains a CpG island, a segment of DNA with high G+C content and a site for methylation, in the promoter region. A comparison of three human prostate cancer cell lines showed that EndoG is highly expressed in 22Rv1 and LNCaP cells. In PC3 cells, EndoG was not expressed and the EndoG CpG island was hypermethylated. The expression of EndoG correlated positively with sensitivity to cisplatin and etoposide, and the silencing of EndoG by siRNA decreased the sensitivity of the cells to the chemotherapeutic agents in the two EndoG-expressing cell lines. 5-aza-2'-deoxycytidine caused hypomethylation of the EndoG promoter in PC3 cells, induced EndoG mRNA and protein expression, and made the cells sensitive to both cisplatin and etoposide. The acetylation of histones by trichostatin A, the histone deacetylase inhibitor, induced EndoG expression in 22Rv1 cells, while it had no such effect in PC3 cells. These data are the first indication that EndoG may be regulated by methylation of its gene promoter, and partially by histone acetylation, and that EndoG is essential for prostate cancer cell death in the used models.

BRCA1-mediated ubiquitination inhibits topoisomerase II alpha activity in response to oxidative stress

Topoisomerase IIalpha is known to be critically involved in both cell proliferation and cell death. The mechanisms responsible for stress-dependent topoisomerase IIalpha alterations, however, remain unclear. This study focused on the behavior of topoisomerase IIalpha in response to oxidative stress induced by hydrogen peroxide (H(2)O(2)). The catalytic activity of topoisomerase IIalpha in MOLT-4 cells treated with H(2)O(2) decreased in parallel with the alteration of topoisomerase IIalpha expression. The ubiquitination of topoisomerase IIalpha was dependent on oxidative stress. BRCA1, a tumor-suppressor gene, appeared to be involved in these alterations in topoisomerase IIalpha. Furthermore, the retinoblastoma protein (pRb) was required for the ubiquitination of topoisomerase IIalpha by BRCA1. We conclude that the functions of topoisomerase IIalpha are regulated by ubiquitination on exposure to oxidative stress.

Induction of renal endonuclease G by cisplatin is reduced in DNase I-deficient mice

Nephrotoxicity from the chemotherapeutic drug cisplatin is associated with DNA fragmentation and cell death. We have recently demonstrated that DNase I knockout mice are significantly protected against cisplatin nephrotoxicity, but it is unknown whether the DNA fragmentation that occurs is produced by DNase I or another endonuclease. In this study we assessed the expression of several endonucleases involved in cell death after injection of cisplatin and found that the expression of endonuclease G (EndoG) increased whereas the expression of DNase I decreased almost to zero. Immunostaining showed that some nuclei contained both fragmented DNA and EndoG, suggesting that EndoG may cause DNA fragmentation induced by cisplatin. The increase in expression of EndoG was greater in wild-type mice than in DNase I knockout mice, indicating a potential link between the two endonucleases. In support of such a link, overexpression of DNase I in cultured mouse tubular epithelial cells also induced EndoG. Furthermore, gene silencing of EndoG in vitro provided significant protection against cell death. Taken together, our data suggest that both DNase I and EndoG mediate cisplatin injury to tubular epithelial cells.

Conformational modification of serpins transforms leukocyte elastase inhibitor into an endonuclease involved in apoptosis

The best-characterized biochemical feature of apoptosis is degradation of genomic DNA into oligonucleosomes. The endonuclease responsible for DNA degradation in caspase-dependent apoptosis is caspase-activated DNase. In caspase-independent apoptosis, different endonucleases may be activated according to the cell line and the original insult. Among the known effectors of caspase-independent cell death, L-DNase II (LEI [leukocyte elastase inhibitor]-derived DNase II) has been previously characterized by our laboratory. We have thus shown that this endonuclease derives from the serpin superfamily member LEI by posttranslational modification (A. Torriglia, P. Perani, J. Y. Brossas, E. Chaudun, J. Treton, Y. Courtois, and M. F. Counis, Mol. Cell. Biol. 18:3612-3619, 1998). In this work, we assessed the molecular mechanism involved in the change in the enzymatic activity of this molecule from an antiprotease to an endonuclease. We report that the cleavage of LEI by elastase at its reactive center loop abolishes its antiprotease activity and leads to a conformational modification that exposes an endonuclease active site and a nuclear localization signal. This represents a novel molecular mechanism for a complete functional conversion induced by changing the conformation of a serpin. We also show that this molecular transformation affects cellular fate and that both endonuclease activity and nuclear translocation of L-DNase II are needed to induce cell death.

Endonuclease G promotes cell death of non-invasive human breast cancer cells

The invasiveness of breast cancer cells was shown to be associated with the suppressed ability to develop apoptosis. The role of cell death DNases/endonucleases has not been previously examined in relation with the invasiveness of breast cancer cells. We have compared the activity of the endonucleases in seven human breast cancer cell lines different in the level of invasiveness and differentiation. The invasiveness of cell lines was confirmed by an in vitro Matrigel-based assay. The total endonuclease activity in the differentiated non-invasive (WDNI) cell lines was higher than that in the poorly differentiated invasive (PDI) cells. The expression of EndoG strongly correlated with the degree of estrogen receptor expression and showed an inverse correlation with vimentin and matrix metalloproteinase-13. The EndoG-positive WDNI cells were more sensitive to etoposide- or camptothecin-induced cell death than EndoG-negative PDI cells. Silencing of EndoG caused inhibited of SK-BR-3 WDNI cell death induced by etoposide. Human ductal carcinomas in situ expressed high levels of EndoG, while invasive medullar and ductal carcinomas had significantly decreased expression of EndoG. This correlated with decreased apoptosis as measured by TUNEL assay. Our findings suggest that the presence of EndoG in non-invasive breast cancer cells determines their sensitivity to apoptosis, which may be taken into consideration for developing the chemotherapeutic strategy for cancer treatment.

Endonuclease activation and chromosomal DNA fragmentation during apoptosis in leukemia cells

Apoptotic endonuclease is a key enzyme that mediates regulated DNA fragmentation and chromatin condensation in response to apoptotic signals such as the Fas ligand, ionizing radiation, and anticancer agents. An endonuclease that is activated specifically by caspase-3 has been identified in humans and mice. The human gene for this protein has been termed DFF40 (DNA fragmentation factor, 40-kd subunit) or caspase-activated nuclease (CPAN), whereas the mouse homologue has been named caspase-activated deoxyribonuclease (CAD). Although CAD/DFF40 is known as a major apoptotic nuclease, mice lacking inhibitor of CAD (ICAD) (also known as DFF45) are viable and still show DNA fragmentation, suggesting that alternative endonucleases play an important role during apoptosis. Endonuclease G has been reported to possibly be responsible for DNA fragmentation in various cells during apoptosis. Furthermore, we also have found that apurinic/apyrimidinic endonuclease 1 (Ape1) and its N-terminal-truncated form (AN34) are involved in DNA fragmentation during apoptosis in leukemia cells. In this review, we describe the features of several endonucleases that are involved in the apoptosis of human leukemia cells. Apoptotic endonuclease may vary among different leukemia cell types.

Acid DNases and their interest among apoptotic endonucleases

Apoptosis is characterized by cell shrinkage, nuclear condensation and internucleosomal DNA cleavage. Besides the central role of caspases and other proteases, cell death triggers DNA degradation so that DNases have an active role in apoptotic cell death. The best-characterized apoptotic DNase is CAD, a neutral Mg-dependent endonuclease. Its activity is regulated by its inhibitor, ICAD, which is cleaved by caspases. Other neutral DNases have been shown to cleave nuclear DNA in apoptotic conditions: endonuclease G, GADD. In cells, the cytosolic pH is maintained to 7.2, mostly due to the activity of the Na(+)/H(+) exchanger. In many apoptotic conditions, a decrease of the intracellular pH has been shown. This decrease may activate different acid DNases, mostly when pH decreases below 6.5. Three acidic DNases II are so far known: DNase II alpha, DNase II beta and L-DNase II, a DNase II, derived from the serpin LEI (Leukocyte Elastase Inhibitor). Their activation during cell death is discussed in this review.

Cloning and expression of deoxyribonuclease II from chicken

Acid endonucleases of the deoxyribonuclease II (DNase II, EC 3.1.22.1) family have been implicated in the degradation of DNA from apoptotic cell corpses formed in the process of normal mammalian development. Although a predicted DNase II has been detected in the chicken through expressed sequence tag (EST) analysis, to date no homolog of these important enzymes has been identified in vivo in any avian species. Here we report the cloning and expression of DNase II from the chicken, Gallus gallus. When expressed, the 363 amino acid glycoprotein is observed to be approximately 45 kDa in size and to exhibit DNA hydrolytic activity at pH 5 consistent with DNase II in other species. Furthermore, chicken DNase II sequence is compared with an identified partial sequence from the zebra finch, Taeniopygia guttata, as well as the previously identified homologs found in the fowlpox and canarypox viruses and the previously cloned mammalian DNases II. Through analysis of its amino acid sequence, comparative gene structure, and conserved synteny, chicken DNase II appears to represent a member of the DNase IIbeta subfamily and the apparent lack of a DNase IIalpha homolog in the chicken has important evolutionary implications for the study of this gene family.

Fusion and differentiation of murine C2C12 skeletal muscle cells that express Trichinella spiralis p43 protein

The ability of a 43 kDa stichocyte protein from Trichinella spiralis (Tsp43) to interfere with mammalian skeletal muscle gene expression was investigated. A MYC-tagged Tsp43 construct was expressed as a recombinant protein in C2C12 myoblasts. Transfection with low amounts of expression plasmid was required for successful expression of the protein. This construct had apparent toxic effects on transfected myoblasts and ectopic green fluorescent protein expression was suppressed in myoblasts co-transfected with the Tsp43 construct. These effects may result from similarities of Tsp43 to DNase II. Use of the general DNase inhibitor aurintricarboxylic acid (ATA) enhanced expression of MYC-Tsp43 in transfected muscle cells. Myoblasts transfected with Tsp43 did not fuse well when cultured under differentiation conditions without ATA. In contrast, transfected myoblasts transiently cultured with ATA underwent fusion and differentiation. Under short-term differentiation conditions without ATA, unfused myoblasts nevertheless expressed both MYC-Tsp43 and myosin heavy chain. Collectively, the results support that Tsp43 has a role in the T. spiralis life cycle that is distinct from repressing muscle gene expression during the muscle phase of infection. While the function of Tsp43 as a DNase is under debate, the effects of ATA on transfected muscle cells were consistent with this possibility.

Cisplatin Nephrotoxicity Is Mediated by Deoxyribonuclease I

Cisplatin is commonly used for chemotherapy in a wide variety of tumors; however, its use is limited by kidney toxicity. Although the exact mechanism of cisplatin-induced nephrotoxicity is not understood, several studies showed that it is associated with DNA fragmentation induced by an unknown endonuclease. It was demonstrated previously that deoxyribonuclease I (DNase I) is a highly active renal endonuclease, and its silencing by antisense is cytoprotective against the in vitro hypoxia injury of kidney tubular epithelial cells. This study used recently developed DNase1 knockout (KO) mice to determine the role of this endonuclease in cisplatin-induced nephrotoxicity. The data showed that DNase I represents approximately 80% of the total endonuclease activity in the kidney and cultured primary renal tubular epithelial cells. In vitro, primary renal tubular epithelial cells isolated from KO animals were resistant to cisplatin (8 microM) injury. DNase I KO mice were also markedly protected against the toxic injury induced by a single injection of cisplatin (20 mg/kg), by both functional (blood urea nitrogen and serum creatinine) and histologic criteria (tubular necrosis and in situ DNA fragmentation assessed by the terminal deoxynucleotidyl transferase nick end-labeling). These data provide direct evidence that DNase I is essential for kidney injury induced by cisplatin.

Identification of mouse retinal genes differentially regulated by dim and bright cyclic light rearing

Bright cyclic light rearing protects BALB/c mice from light-induced photoreceptor apoptosis compared to dim cyclic light rearing. We used a microarray approach to search for putative neuroprotection genes that were up- or down-regulated under these environmental conditions. Retinal protection by bright cyclic rearing was determined by quantitative histology and DNA fragmentation analysis. Total RNA was isolated from 5-week-old mice raised in bright (400 lux) or dim (5 lux) cyclic light and prepared for analysis on microarrays produced using a 70-mer oligonucleotide library that represented 16,463 mouse genes. Genes of interest were identified using statistically robust bioinformatics analysis methods that were developed in-house. Changes in some genes were confirmed with quantitative real time PCR. We found that 952 genes were up- or down-regulated by bright cyclic light rearing compared to dim cyclic light rearing. One hundred and eighty-four of them, having >/=2-fold differences, were grouped into 13 categories, and selected for further consideration. Eleven up-regulated and two down-regulated genes were confirmed by semi-quantitative PCR. Five neuroprotection-associated genes were up-regulated by bright cyclic light rearing as confirmed by real-time PCR. The human orthologue chromosomal location of 22 differentially expressed genes map to known retinal degeneration loci. Using PathwayAssist software, we modeled the pathway networks of up- and down-regulated genes that are functionally related to the retina. We identified retinal genes that are differentially regulated by environmental light history. Those that directly affect cell processes such as survival, apoptosis, and transcription are likely play a pivotal role in the regulation of retinal neuroprotection against light-induced photoreceptor apoptosis.

Plancitoxins, lethal factors from the crown-of-thorns starfish Acanthaster planci, are deoxyribonucleases II

Two lethal factors (named plancitoxins I and II for major and minor toxins, respectively) with the same LD50 (i.v. injection into mice) of 140 microg/kg were purified from spines of the crown-of-thorns starfish Acanthaster planci. Injection of a sublethal dose of plancitoxin I or II into mice remarkably elevated serum levels of glutamic oxaloacetic transaminase and glutamic pyruvic transaminase, demonstrating that both toxins are potently hepatotoxic. Analysis by SDS-PAGE revealed that both plancitoxins are composed of two subunits (alpha-subunit of 10 kDa and beta-subunit of 27 kDa) bridged by a disulfide bond. Based on the determined N-terminal amino acid sequences of alpha- and beta-subunits, the full-length cDNA (1820 bp) encoding plancitoxin I was cloned by RT-PCR, 3'-RACE and 5'-RACE. alpha-Subunit (92 amino acid residues) and beta-subunit (240 residues) are coded in this order by the same cDNA. Interestingly, the deduced amino acid sequence of plancitoxin I showed 40-42% homologies with mammalian deoxyribonucleases II (DNases II). In addition, plancitoxin I exhibited DNA degrading activity with an optimum pH of 7.2. Plancitoxin I is the first example of toxic DNases II whose structures have been elucidated.

Apoptotic pathways in ischemic acute renal failure

The study of cell death has emerged as an important and exciting area of research in cell biology. Although two kinds of cell death, apoptosis and necrosis, are recognized, one of the major advances in our understanding of cell death has been the recognition that the pathways traditionally associated with apoptosis may be very critical in the form of cell injury associated with necrosis. Renal tubular epithelial cell injury from ischemia has been generally regarded as a result of necrotic form of cell death. We briefly describe recent evidence indicating that pathways generally associated with apoptosis, including endonuclease activation, role of mitochondria and caspases, are important in renal tubular injury. It is likely that the cascades that lead to apoptotic or necrotic mode of cell death are activated almost simultaneously and may share some common pathways.

Restricted cytokine production from mouse peritoneal macrophages in culture in spite of extensive uptake of plasmid DNA

The production of inflammatory cytokines from macrophages (Mphi), upon stimulation with plasmid DNA (pDNA) containing CpG motifs, is a critical process for DNA-based therapies such as DNA vaccination and gene therapy. We compared Mphi activation, following stimulation with naked pDNA, based on the production of cytokines from cell lines (RAW264.7 and J774A1) and peritoneal Mphis in primary culture. The Mphi cell lines RAW264.7 and J774A1 produced a significant amount of tumour necrosis factor-alpha (TNF-alpha) upon stimulation with naked pDNA and this response required endosomal acidification. On the other hand, peritoneal Mphis (both resident and elicited) in primary culture did not secrete TNF-alpha or interleukin-6, although they contain the mRNA of toll-like receptor-9 (TLR-9) and are able to respond to CpG oligodeoxynucleotides. This unresponsiveness was not a result of impaired cellular uptake of pDNA because the primary cultured Mphis showed a higher uptake of pDNA than the RAW264.7 and J774A1 cell lines. These findings have important implications for Mphi activation by naked pDNA as it has been generally assumed that pDNA that contains CpG motifs is a potent agent for inducing inflammatory cytokines in vivo, based on evidence from in vitro studies using Mphi cell lines.

LDFF, the large molecular weight DNA fragmentation factor, is responsible for the large molecular weight DNA degradation during apoptosis in Xenopus egg extracts

DNA degradation is a biochemical hallmark in apoptosis. It has been demonstrated in many cell types that there are two stages of DNA fragmentation during the apoptotic execution. In the early stage, chromatin DNA is cut into large molecular weight DNA fragments, although the responsible nuclease(s) has not been recognized. In the late stage, the chromatin DNA is cleaved further into short oligonucleosomal fragments by a well-characterized nuclease in apoptosis, the caspase-activated DNase (CAD/DFF40). In this study, we demonstrate that large molecular weight DNA fragmentation also occurs in Xenopus egg extracts in apoptosis. We show that the large molecular weight DNA fragmentation factor (LDFF) is not the Xenopus CAD homolog XCAD. LDFF is activated by caspase-3. The large molecular weight DNA fragmentation activity of LDFF is Mg2+-dependent and Ca2+-independent, can occur in both acidic and neutral pH conditions and can tolerate 45 degrees C treatment. These results indicate that LDFF in Xenopus egg extracts might be a new DNase (or DNases) responsible for the large DNA fragmentation.

DNase II: genes, enzymes and function

Deoxyribonuclease (DNase) II, which was discovered more than 50 years ago, is a mammalian endonuclease that functions optimally at acid pH in the absence of divalent cations. Its lysosomal localization and ubiquitous tissue distribution suggested that this enzyme played a role in the degradation of exogenous DNA encountered by phagocytosis, although the relative importance of such a role was unknown. Subsequent investigations also suggested that DNase II was important for DNA fragmentation and degradation during cell death. Within the last few years, our work and that of others has lead to the cloning of various mammalian DNase II genes as well as the identification and characterization of highly homologous genes in the invertebrates Caenorhabditis elegans and Drosophila melanogaster. Interestingly, studies of the C. elegans DNase II homolog NUC-1 were the first to suggest that DNase II enzymes were fundamentally important in engulfment-mediated DNA degradation, particularly that associated with programmed cell death, due to the presence of persistent apoptotic-cell nuclei within phagocytic cells in nuc-1 mutants. Similarly, mutation of the Drosophila DNase II-like gene was found to result in the accumulation of low-molecular-weight DNA throughout the animals. Homozygous mutation (knockout) of the DNase II gene in mice revealed a much more complex and extensive phenotype including perinatal lethality. The lethality of DNase II-knockout mice is likely the result of multiple developmental defects, the most obvious being a loss of definitive erythropoiesis. Closer examination revealed that a defect in engulfment-mediated DNA degradation is the primary defect in DNase II-null mice. In this review, we have compiled information from studies on DNase II from various organisms to provide a consensus model for the role of DNase II enzymes in DNA degradation.

Deoxyribonuclease II is a lysosomal barrier to transfection

DNA delivered in nonviral vectors or as naked DNA must overcome a number of extracellular and intracellular barriers to transfection. Since many vectors deliver DNA into cells by the endocytic route, DNA degradation by lysosomal nucleases has been proposed as a significant barrier to transfection, despite the fact that this has not yet been formally demonstrated to occur. To test this hypothesis, we have investigated the role of deoxyribonuclease II (DNase II), the primary acidic endonuclease active in the lysosome, in transfection. Two genetic systems were engineered in which mammalian cells either overexpressed DNase II or were knocked out for the enzyme. In both models, higher levels of DNase II correlated with decreased transfection efficiency by nonviral DNA delivery vectors. These data provide direct evidence implicating lysosomal DNase II as a barrier to transfection.

Human apurinic/apyrimidinic endonuclease (Ape1) and its N-terminal truncated form (AN34) are involved in DNA fragmentation during apoptosis

We previously isolated a 34-kDa nuclease (AN34) from apoptotic human leukemia cells. Here, we identify AN34 as an N-terminally truncated form of human AP endonuclease (Ape1) lacking residues 1-35 (delta35-Ape1). Although Ape1 has hitherto been considered specific for damaged DNA (specific to AP site), recombinant AN34 (delta35-Ape1) possesses significant endonuclease activity on undamaged (normal) DNA and in chromatin. AN34 also displays enhanced 3'-5' exonuclease activity. Caspase-3 activates AN34 in a cell-free system, although caspase-3 cannot cleave Ape1 directly in vitro. We also found that Ape1 itself preferentially cleaves damaged chromatin DNA isolated from cells treated with apoptotic stimuli and that silencing of Ape1 expression decreases apoptotic DNA fragmentation in DFF40/CAD-deficient cells. Thus, we propose that AN34 and Ape1 participate in the process of chromatin fragmentation during apoptosis.

Recombinogenic flap ligation mediated by human topoisomerase I

Aberration of eukaryotic topoisomerase I catalysis leads to potentially recombinogenic pathways by allowing the joining of heterologous DNA strands. Recently, a new ligation pathway (flap ligation) was presented for vaccinia virus topoisomerase I, in which blunt end cleavage complexes ligate the recessed end of duplex acceptors having a single-stranded 3'-tail. This reaction was suggested to play an important role in the repair of topoisomerase I-induced DNA double-strand breaks. Here, we characterize flap ligation mediated by human topoisomerase I. We demonstrate that cleavage complexes containing the enzyme at a blunt end allow invasion of a 3'-acceptor tail matching the scissile strand of the donor, which facilitates ligation of the recessed 5'-hydroxyl end. However, the reaction was strictly dependent on the length of double-stranded DNA of the donor complexes, and longer stretches of base-pairing inhibited strand invasion. The stabilization of the DNA helix was most probably provided by the covalently bound enzyme itself, since deleting the N-terminal domain of human topoisomerase I stimulated flap ligation. We suggest that stabilization of the DNA duplex upon enzyme binding may play an important role during normal topoisomerase I catalysis by preventing undesired strand transfer reactions. For flap ligation to function in a repair pathway, factors other than topoisomerase I, such as helicases, would be necessary to unwind the DNA duplex and allow strand invasion.

Structural requirements of human DNase II alpha for formation of the active enzyme: the role of the signal peptide, N-glycosylation, and disulphide bridging

DNase II alpha (EC 3.1.22.1) is an endonuclease, which is active at low pH, that cleaves double-stranded DNA to short 3'-phosphoryl oligonucleotides. Although its biochemistry is well understood, its structure-activity relationship has been largely unexamined. Recently, we demonstrated that active DNase II alpha consists of one contiguous polypeptide, heavily glycosylated, and containing at least one intrachain disulphide linkage [MacLea, Krieser and Eastman (2002) Biochem. Biophys. Res. Commun. 292, 415-421]. The present paper describes further work to examine the elements of DNase II alpha protein required for activity. Truncated forms and site-specific mutants were expressed in DNase II alpha-null mouse cells. Results indicate that the signal-peptide leader sequence is required for correct glycosylation and that N-glycosylation is important for formation of the active enzyme. Despite this, enzymic deglycosylation of wild-type protein with peptide N-glycosidase F reveals that glycosylation is not intrinsically required for DNase activity. DNase II alpha contains six evolutionarily conserved cysteine residues, and mutations in any one of these cysteines completely ablated enzymic activity, consistent with the importance of disulphide bridging in maintaining correct protein structure. We also demonstrate that a mutant form of DNase II alpha that lacks the purported active-site His(295) can still bind DNA, indicating that this histidine residue is not simply involved in DNA binding, but may have a direct role in catalysis. These results provide a more complete model of the DNase II alpha protein structure, which is important for three-dimensional structural analysis and for production of DNase II alpha as a potential protein therapeutic for cystic fibrosis or other disorders.

Apoptosis induced by Na+/H+ antiport inhibition activates the LEI/L-DNase II pathway

L-DNase II is derived from its precursor leucocyte elastase inhibitor (LEI) by post-translational modification. In vitro, the conversion of LEI into L-DNase II can be induced by incubation of LEI at an acidic pH. In this study, we proposed to analyze the effects of intracellular acidification on this transformation. Amiloride derivatives, like hexamethylene amiloride (HMA), are known to provoke a decrease of cytosolic pH by inhibiting the Na(+)/H(+) antiport. In BHK cells, treatment with HMA-induced apoptosis accompanied by an increase in L-DNase II immunoreactivity and L-DNase II enzymatic activity. Overexpression of L-DNase II precursor led to a significant increase of apoptosis in these cells supporting the involvement of L-DNase II in HMA induced apoptosis. As previously shown in other cells, etoposide-induced apoptosis did not activate L-DNase. On the contrary, LEI overexpression significantly increased cell survival in etoposide-induced apoptosis. Together these results suggest differential roles of LEI and L-DNase II in response to different types of apoptotic inducers.

Sequence, gene structure, and expression pattern of CTNNBL1, a minor-class intron-containing gene--evidence for a role in apoptosis

We have identified and characterized a cDNA designated CTNNBL1 (catenin (cadherin-associated protein), beta-like 1) coding for a protein of 563 amino acids having predicted structural homology to beta-catenin and other armadillo (arm) family proteins. CTNNBL1 is expressed in multiple human tissues, and its sequence is conserved across widely divergent species. The human CTNNBL1 gene on chromosome 20q11.2 contains 16 exons spanning > 178 kb. Intron 4 is a minor-class intron bearing AT at the 5' splice site and AC at the 3' splice site. An acidic domain, as well as a putative bipartite nuclear localization signal, a nuclear export signal, a leucine-isoleucine zipper, and phosphorylation motifs are present in the protein sequence. Transient expression of CTNNBL1 in CHO cells results in localization to the nucleus and apoptosis. The rate of cell death was higher when cells were transfected with a carboxy-terminal fragment of CTNNBL1, suggesting that the apoptosis-inducing activity is a function of this region.

A family history of deoxyribonuclease II: surprises from Trichinella spiralis and Burkholderia pseudomallei

Deoxyribonuclease IIalpha (DNase IIalpha) is an acidic endonuclease found in lysosomes and nuclei, and it is also secreted. Though its Caenorhabditis elegans homolog, NUC-1, is required for digesting DNA of apoptotic cell corpses and dietary DNA, it is not required for viability. However, DNase IIalpha is required in mice for correct development and viability, because undigested cell corpses lead to lesions throughout the body. Recently, we showed that, in contrast to previous reports, active DNase IIalpha consists of one contiguous polypeptide. To better analyze DNase II protein structure and determine residues important for activity, extensive database searches were conducted to find distantly related family members. We report 29 new partial or complete homologs from 21 species. Four homologs with differences at the purported active site histidine residue were detected in the parasitic nematodes Trichinella spiralis and Trichinella pseudospiralis. When these mutations were reconstructed in human DNase IIalpha, the expressed proteins were inactive. DNase II homologs were also identified in non-metazoan species. In particular, the slime-mold Dictyostelium, the protozoan Trichomonas vaginalis, and the bacterium Burkholderia pseudomallei all contain sequences with significant similarity and identity to previously cloned DNase II family members. We report an analysis of their sequences and implications for DNase II protein structure and evolution.

Role of nitric oxide and peroxynitrite in apoptosis - relation to endonuclease activity

Apoptosis is a form of cell death utilized physiologically to maintain tissue homeostasis, as well as in response to various toxic and inflammatory stimuli or anticancer drugs. Since the process of apoptosis is followed by phagocytosis, the cleavage of DNA to low molecular weight material may serve as a protective function limiting the probability of gene transfer to the nuclei of viable neighbor cells. Many different endonucleases have been proposed as candidates responsible for the internucleosomal cleavage of the genomic DNA observed during apoptosis. The main effect was attributed to the alkaline DNase I (Mg 2+ and caspase-dependent) and acid-DNase II. It was also documented that both of them contain a potential protease (caspase) cleavage site, but they can be also activated upon the influence of other "fragmentation factors", including nitric oxide (NO). The complexity of biological effects induced by NO may be the result of the cell redox state changes, due to its potential interaction with superoxide. The apoptotic effect of both, nitric oxide (NO) and peroxynitrite (ONOO) are dose-dependent and cell-specific may point out the existence of possible "inducible" form of endonuclease.

Apoptotic pathways of oxidative damage to renal tubular epithelial cells

Toxic renal failure induced by gentamicin, glycerol, or cisplatin, as well as ischemic renal failure in vivo and hypoxia/reoxygenation of tubular epithelial cells in vitro, induces the production of reactive oxygen metabolites (ROM). Generation of ROM is responsible for the induction of tubular epithelial cell death, which is mediated by caspases and/or endonucleases. Scavenging of ROM protects tubular epithelium from caspase and endonuclease activation and from cell death. Thus, the inhibition of ROM production combined with the pharmacological control of caspase and endonuclease pathways may provide future modalities in the prevention or treatment of acute renal failure in humans.

Deoxyribonuclease IIalpha is required during the phagocytic phase of apoptosis and its loss causes perinatal lethality

Deoxyribonuclease IIalpha (DNase IIalpha) is one of many endonucleases implicated in DNA digestion during apoptosis. We produced mice with targeted disruption of DNase IIalpha and defined its role in apoptosis. Mice deleted for DNase IIalpha die at birth with many tissues exhibiting large DNA-containing bodies that result from engulfed but undigested cell corpses. These DNA-containing bodies are pronounced in the liver where fetal definitive erythropoiesis occurs and extruded nuclei are degraded. They are found between the digits, where apoptosis occurs, and in many other regions of the embryo. Defects in the diaphragm appear to cause death of the mice due to asphyxiation. The DNA in these bodies contains 3'-hydroxyl ends and therefore stain positive in the TUNEL assay. In addition, numerous unengulfed TUNEL-positive cells are observed throughout the embryo. Apoptotic cells are normally cleared rapidly from a tissue; hence the persistence of the DNA-containing bodies and TUNEL-positive cells identifies sites where apoptosis occurs during development. These results demonstrate that DNase IIalpha is not required for the generation of the characteristic DNA fragmentation that occurs during apoptosis but is required for degrading DNA of dying cells and this function is necessary for proper fetal development.

Involvement of DNase gamma in apoptosis associated with myogenic differentiation of C2C12 cells

Nucleosomal DNA fragmentation is detected in myoblasts only when apoptosis is induced under differentiating conditions. However, the molecular mechanisms and the DNase responsible for the differentiation-dependent apoptotic DNA laddering are poorly understood. Here we show that a Ca(2+)/Mg(2+)-dependent endonuclease, DNase gamma, is induced in C2C12 myoblasts during myogenic differentiation and catalyzes apoptotic DNA fragmentation in differentiating myoblasts. A Ca(2+)/Mg(2+)-dependent, Zn(2+)-sensitive endonuclease activity appears in C2C12 myoblasts during myogenic differentiation. The enzymatic properties of the inducible DNase were found to be quite similar to those of DNase I family of DNases. Reverse transcriptase-PCR analysis revealed that the induction of DNase gamma, a member of the DNase I family of DNases, is correlated with the appearance of inducible DNase activity. The induction of DNase gamma occurs simultaneously with myogenin induction but precedes the up-regulation of p21. A high level of DNase gamma expression was also detected in differentiated myotubes but not in skeletal muscle fibers in which DNase X is highly expressed. The role of DNase gamma in myoblast apoptosis was evaluated in the following experiments. Proliferating myoblasts acquire DNA ladder producing ability by the ectopic expression of DNase gamma, but not DNase X, suggesting that the expression level of DNase gamma is the determinant of the differentiation-dependent apoptotic DNA laddering observed in myoblasts. DNA fragmentation during differentiation-induced apoptosis is strongly suppressed by the antisense-mediated down-regulation of DNase gamma. Importantly, the extent of DNA laddering is well correlated with the level of endogenous DNase gamma activity. Our data demonstrate that DNase gamma is the endonuclease responsible for DNA fragmentation in apoptosis associated with myogenic differentiation.

Up-regulation of human deoxyribonuclease II gene expression during myelomonocytic differentiation of HL-60 and THP-1 cells

Several recent studies have suggested that intracellular deoxyribonuclease II (DNase II) is responsible for the degradation of DNA from apoptotic cells that are engulfed by macrophages. In this study, we studied DNase II expression during the phorbol 12-myristate-13-acetate (PMA)-induced differentiation of HL-60 and THP-1 cells. Basal levels of DNase II mRNA and protein were low, with expression being up-regulated approximately 15- and 7-fold, respectively, in HL-60 and THP-1 cells 72 h after PMA treatment. Nuclear run-on and luciferase reporter assays showed that transcription of DNase II gene was increased in PMA-treated cells. Together, these results demonstrate that DNase II gene transcription is increased during myelomonocytic differentiation, resulting in increased levels of mRNA and protein. This increase in DNase II levels in differentiated HL-60 and THP-1 cells suggests that it may play an important role in macrophages.

Drosophila acid DNase is a homolog of mammalian DNase II

Mammalian DNase II enzymes and the Caenorhabditis elegans homolog NUC-1 have recently been shown to be critically important during engulfment-mediated clearance of DNA. In this report, we describe the cloning and characterization of the gene encoding Drosophila DNase II. Database queries using the C. elegans NUC-1 protein sequence identified a highly homologous open reading frame in Drosophila (CG7780) that could encode a similar enzyme. Analysis of crude protein extracts revealed that wild-type Drosophila contain a potent acid endonuclease activity with cleavage preferences similar to DNase II/NUC1, while the same activity was markedly reduced in an acid DNase hypomorphic mutant line. Furthermore, the pattern of cleavage products generated from an end-labeled substrate by hypomorphic-line extracts was significantly altered in comparison to the pattern generated by wild-type extracts. Sequence analysis of CG7780 DNA and mRNA revealed that the hypomorphic line contains a missense mutation within the coding region of this gene. Additionally, Northern analysis demonstrated that CG7780 expression is normal in the mutant line, which in combination with the lowered/altered enzymatic activity and sequencing data suggested a defect in the CG7780 protein. To conclusively determine if CG7780 encoded the Drosophila equivalent of DNase II/NUC-1, transgenic lines expressing wild-type CG7780 in the mutant background were generated and subsequently shown to complement the mutant phenotype. Our results, therefore, provide compelling evidence that the predicted gene CG7780 encodes Drosophila DNase II (dDNase II), an enzyme related in sequence and activity to mammalian DNase II. Interestingly, overexpression of CG7780 both ubiquitously and in specific tissues failed to elicit any discernable phenotype.

Revised structure of the active form of human deoxyribonuclease IIalpha

Deoxyribonuclease IIalpha (DNase IIalpha) is an acid endonuclease found in lysosomes, nuclei, and various secretions. Murine DNase IIalpha is required for digesting the DNA of apoptotic cells after phagocytosis and for correct development and viability. DNase IIalpha purified from porcine spleen was previously shown to contain three peptides, two of which were thiol crosslinked, all derived by processing of a single polypeptide. Commercial bovine protein is consistent with this structure. However, screening of 18 human cell lines failed to demonstrate this processing, rather a 45 kDa protein was consistently observed. Incubation of cells with the N-glycosylation inhibitor tunicamycin resulted in a 37 kDa protein, which is close to the predicted formula weight. The protein also contains at least one thiol crosslink. Similar results were obtained with overexpressed DNase IIalpha. These results suggest that active DNase IIalpha consists of one contiguous polypeptide. We suggest the previous structure reflects proteolysis during protein purification.

Implications of CAD and DNase II in ischemic neuronal necrosis specific for the primate hippocampus

The exact molecular mechanism of ischemic neuronal death still remains unclear from rodents to primates. A number of studies using lower species animals have suggested implication of apoptosis cascade, while using monkeys the authors recently claimed necrosis cascade by calpain-induced leakage of lysosomal cathepsins (calpain-cathepsin hypothesis). This paper is to study implications of apoptotic versus necrotic cascades for the development of hippocampal CA1 neuronal death in the primate brain undergoing complete global ischemia. Here, we focused on two terminal cell death effectors; caspase-activated DNase (CAD) and lysosomal enzyme DNase II, in the monkey CA1 sector undergoing 18 min ischemia. The expressions of their mRNA and proteins, and the subcellular localizations as well as ultrastructure and specific DNA gel electrophoresis were examined. Expression of CAD was much less in the normal brain, compared with the lymph node or heart tissues. On day 1 after ischemia, however, CAD mRNA and protein were significantly increased in the CA1 sector, and then CAD protein immunohistochemically showed a translocation from the perikarya into the nucleus. Activated DNase II protein was significantly increased on days 2 and 3 after ischemia, and also showed a similar translocation indicating lysosomal leakage. Although the post-ischemic CA1 neurons showed positive terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL) staining on days 3-5, they showed eosinophilic coagulation necrosis on light microscopy, and frank membrane disruption and mild chromatin condensation on electron microscopy. Furthermore, DNA smear pattern typical for necrosis was observed instead of DNA laddering. These data altogether suggest that the post-ischemic CA1 neuronal death of the monkey occurs not by apoptosis but by necrosis with participations of lysosomal enzymes DNase II and cathepsins as well as CAD. The interactions between apoptotic (caspase-3 and CAD) and necrotic (calpain, cathepsin and DNase II) cascades should be studied further.

Isolation and characterization of the DLAD/Dlad genes, which lie head-to-head with the genes for urate oxidase

We previously found that a novel DNA endonuclease named DLAD (DNase II-Like Acid DNase) is specifically expressed in murine liver. Here, we describe the isolation and characterization of the human DLAD and mouse Dlad genes. Both DLAD and Dlad consist of 6 exons. DLAD encodes a 361 amino acid protein sharing 34.6% amino acid identity with human DNase II. Although a recombinant protein for the putative human DLAD has a divalent cation-independent acid DNase activity, expression of the DLAD mRNA containing the entire open reading frame was not detected in any human tissues tested, except for lung, in which a short 1.1 kb transcript lacking the first two exons is expressed. Interestingly, sequence analysis of Dlad showed that the 1st exon of the urate oxidase gene, Uox, is located on the opposite strand in its 5'-flanking region. The head-to-head organization of DLAD and UOX is conserved in the human genomic sequence. Promoter analysis revealed that the intergenic region between Dlad and Uox has promoter activity for both the Dlad and Uox directions, however, the corresponding human genomic fragment has promoter activity only for DLAD. It is known that murine Uox is expressed only in the liver, whereas human UOX has been inactivated as a pseudogene. On the basis of these results, the expression of DLAD/Dlad and UOX/Uox is suggested to be coordinated by a common regulatory mechanism(s), and the balance between the two enzymes is thought to be important for maintaining the purine nucleotide pool in the liver.

The white spot syndrome virus DNA genome sequence

White spot syndrome virus (WSSV) is at present a major scourge to worldwide shrimp cultivation. We have determined the entire sequence of the double-stranded, circular DNA genome of WSSV, which contains 292,967 nucleotides encompassing 184 major open reading frames (ORFs). Only 6% of the WSSV ORFs have putative homologues in databases, mainly representing genes encoding enzymes for nucleotide metabolism, DNA replication, and protein modification. The remaining ORFs are mostly unassigned, except for five, which encode structural virion proteins. Unique features of WSSV are the presence of a very long ORF of 18,234 nucleotides, with unknown function, a collagen-like ORF, and nine regions, dispersed along the genome, each containing a variable number of 250-bp tandem repeats. The collective information on WSSV and the phylogenetic analysis on the viral DNA polymerase suggest that WSSV differs profoundly from all presently known viruses and that it is a representative of a new virus family.

The cloning, genomic structure, localization, and expression of human deoxyribonuclease IIβ

Acidic endonuclease activity is present in all cells in the body and much of this can be attributed to the previously cloned and ubiquitously expressed deoxyribonuclease II (DNase II). Database analysis revealed the existence of expressed sequence tags and genomic segments coding for a protein with considerable homology to DNase II. This report describes the cloning of this cDNA, which we term deoxyribonuclease IIbeta (DNase IIbeta) and comparison of its expression to that of the originally cloned DNase II (now termed DNase IIalpha). The cDNA encodes a 357 amino acid protein. This protein exhibits extensive homology to DNase IIalpha including an amino-terminal signal peptide and a conserved active site, and has many of the regions of identity that are conserved in homologs in other mammals as well as C. elegans and Drosophila. The gene encoding DNase IIbeta has identical splice sites to DNase IIalpha. Human DNase IIbeta is highly expressed in the salivary gland, and at low levels in trachea, lung, prostate, lymph node, and testis, whereas DNase IIalpha is ubiquitously expressed in all tissues. The expression pattern of human DNase IIbeta suggests that it may function primarily as a secreted enzyme. Human saliva was found to contain DNase IIalpha, but after immunodepletion, considerable acid-active endonuclease remained which we presume is DNase IIbeta. We have localized the gene for human DNase IIbeta to chromosome 1p22.3 adjacent (and in opposing orientation) to the human uricase pseudogene. Interestingly, murine DNase IIbeta is highly expressed in the liver. Uricase is also highly expressed in mouse but not human liver and this may explain the difference in expression patterns between human and mouse DNase IIbeta.

Involvement of L-DNase II in nuclear degeneration during chick retina development

During the development of the neural retina, 50% of the neurons die physiologically by apoptosis. In the chick embryo, the apoptotic wave starts at E8 and ends at E18, with a peak at E11. The onset of apoptosis is accompanied by the activation of several degradative enzymes. Among these, the activation of the endonucleases leads to the degradation of the genomic DNA of the cell which is thought to be the final event in apoptosis. Here, we have investigated the endonucleases activated during apoptosis associated with retinal development. We have found that Ca2+-Mg2+-dependent endonucleases, as well as acid endonucleases are activated. The results obtained in vitro using purified nuclei from chicken retina indicate that the endonuclease activity resulting from the activation of L-DNase II, an acid DNase is responsible for most of the DNA degradation observed in these cells.

Ca2+-sensitive cytosolic nucleases prevent efficient delivery to the nucleus of injected plasmids

BACKGROUND

Efficient gene delivery by synthetic vectors is a major challenge in gene therapy. However, inefficient nuclear delivery of cDNA is thought to be a major limiting step in gene transfer using non-viral vectors. It is commonly thought that, in the cytosol, cDNA has to be released from its vector before importation to the nucleus. The stability of naked cDNA in the cytoplasm is not well established.

METHODS

cDNA plasmids, either free or complexed with poly(ethyleneimine) (PEI), were microinjected into the cytoplasm of mammalian cells and their turnover was assessed by fluorescence in situ hybridization (FISH). Incubations of cDNA plasmids in cytosolic extracts were also performed.

RESULTS

FISH experiments showed that naked cDNA rapidly fade with time when injected into the cytosol. Fading was not observed when naked cDNA plasmids were injected into the nucleus. Incubation of naked cDNA in a cytosolic fraction isolated from mammalian cells reproduced cDNA degradation as observed in microinjection experiments. Nuclease inhibitors, including aurin tricarboxylic acid or Zn2+, prevented in vitro cDNA degradation. The cytosolic nuclease activity was optimal at physiological pH and physiological Ca2+ concentration. By contrast, it was insensitive to Mg2+ or Na+ concentrations. Finally, cDNA complexation with PEI or addition of oligonucleotides prevented in vitro cDNA degradation.

CONCLUSION

Altogether, these experiments suggest that cDNA digestion by cytosolic nucleases occur when the decomplexed transgene is present in the cytosol. We propose that the inefficient transfer of cDNA into the nucleus during transfection with synthetic vectors may result from rapid digestion of naked cDNA by a Ca2+-sensitive cytosolic nuclease.

Characterization of human DNase I family endonucleases and activation of DNase gamma during apoptosis

We describe here the characterization of the so far identified human DNase I family DNases, DNase I, DNase X, DNase gamma, and DNAS1L2. The DNase I family genes are found to be expressed with different tissue specificities and suggested to play unique physiological roles. All the recombinant DNases are shown to be Ca(2+)/Mg(2+)-dependent endonucleases and catalyze DNA hydrolysis to produce 3'-OH/5'-P ends. High activities for DNase I, DNase X, and DNase gamma are observed under neutral conditions, whereas DNAS1L2 shows its maximum activity at acidic pH. These enzymes have also some other peculiarities: different sensitivities to G-actin, aurintricarboxylic acid, and metal ions are observed. Using a transient expression system in HeLa S3 cells, the possible involvement of the DNases in apoptosis was examined. The ectopic expression of each DNase has no toxic effect on the host cells; however, extensive DNA fragmentation is observed only in DNase gamma-transfected cells after the induction of apoptosis. Furthermore, DNase gamma is revealed to be located at the perinuclear region in living cells, and to translocate into the nucleus during apoptosis. Our results demonstrate that DNase I, DNase X, DNase gamma, and DNAS1L2 have similar but unique endonuclease activities, and that among DNase I family DNases, DNase gamma is capable of producing apoptotic DNA fragmentation in mammalian cells.

In vivo reactivation of DNases in implanted human prostate tumors after administration of a vitamin C/K(3) combination

Human prostate cancer cells (DU145) implanted into nude mice are deficient in DNase activity. After administration of a vitamin C/vitamin K(3) combination, both alkaline DNase (DNase I) and acid DNase (DNase II) activities were detected in cryosections with a histochemical lead nitrate technique. Alkaline DNase activity appeared 1 hr after vitamin administration, decreased slightly until 2 hr, and disappeared by 8 hr after treatment. Acid DNase activity appeared 2 hr after vitamin administration, reached its highest levels between 4 and 8 hr, and maintained its activity 24 hr after treatment. Methyl green staining indicated that DNase expression was accompanied by a decrease in DNA content of the tumor cells. Microscopic examination of 1-microm sections of the tumors indicated that DNase reactivation and the subsequent degradation of DNA induced multiple forms of tumor cell death, including apoptosis and necrosis. The primary form of vitamin-induced tumor cell death was autoschizis, which is characterized by membrane damage and the progressive loss of cytoplasm through a series of self-excisions. These self-excisions typically continue until the perikaryon consists of an apparently intact nucleus surrounded by a thin rim of cytoplasm that contains damaged organelles.

Recombinogenic flap ligation pathway for intrinsic repair of topoisomerase IB-induced double-strand breaks

Topoisomerase IB catalyzes recombinogenic DNA strand transfer reactions in vitro and in vivo. Here we characterize a new pathway of topoisomerase-mediated DNA ligation in vitro (flap ligation) in which vaccinia virus topoisomerase bound to a blunt-end DNA joins the covalently held strand to a 5' resected end of a duplex DNA containing a 3' tail. The joining reaction occurs with high efficiency when the sequence of the 3' tail is complementary to that of the scissile strand immediately 5' of the cleavage site. A 6-nucleotide segment of complementarity suffices for efficient flap ligation. Invasion of the flap into the duplex apparently occurs while topoisomerase remains bound to DNA, thereby implying a conformational flexibility of the topoisomerase clamp around the DNA target site. The 3' flap acceptor DNA mimics a processed end in the double-strand-break-repair recombination pathway. Our findings suggest that topoisomerase-induced breaks may be rectified by flap ligation, with ensuing genomic deletions or translocations.