Identification of an endonuclease responsible for apoptosis in rat thymocytes

Zn2+-Dependent Nuclease Is Involved in Nuclear Degradation during the Programmed Cell Death of Secretory Cavity Formation in Citrus grandis 'Tomentosa' Fruits

Zn2+- and Ca2+-dependent nucleases exhibit activity toward dsDNA in the four classes of cation-dependent nucleases in plants. Programmed cell death (PCD) is involved in the degradation of cells during schizolysigenous secretory cavity formation in Citrus fruits. Recently, the Ca2+-dependent DNase CgCAN was proven to play a key role in nuclear DNA degradation during the PCD of secretory cavity formation in Citrus grandis ‘Tomentosa’ fruits. However, whether Zn2+-dependent nuclease plays a role in the PCD of secretory cells remains poorly understood. Here, we identified a Zn2+-dependent nuclease gene, CgENDO1, from Citrus grandis ‘Tomentosa’, the function of which was studied using Zn2+ ions cytochemical localization, DNase activity assays, in situ hybridization, and protein immunolocalization. The full-length cDNA of CgENDO1 contains an open reading frame of 906 bp that encodes a protein 301 amino acids in length with a S1/P1-like functional domain. CgENDO1 degrades linear double-stranded DNA at acidic and neutral pH. CgENDO1 is mainly expressed in the late stage of nuclear degradation of secretory cells. Further spatiotemporal expression patterns of CgENDO1 showed that CgENDO1 is initially located on the endoplasmic reticulum and then moves into intracellular vesicles and nuclei. During the late stage of nuclear degradation, it was concentrated in the area of nuclear degradation involved in nuclear DNA degradation. Our results suggest that the Zn2+-dependent nuclease CgENDO1 plays a direct role in the late degradation stage of the nuclear DNA in the PCD of secretory cavity cells of Citrus grandis ‘Tomentosa’ fruits.

Comparison of the secretory murine DNase1 family members expressed in Pichia pastoris

Soluble nucleases of the deoxyribonuclease 1 (DNase1) family facilitate DNA and chromatin disposal (chromatinolysis) during certain forms of cell differentiation and death and participate in the suppression of anti-nuclear autoimmunity as well as thrombotic microangiopathies caused by aggregated neutrophil extracellular traps. Since a systematic and direct comparison of the specific activities and properties of the secretory DNase1 family members is still missing, we expressed and purified recombinant murine DNase1 (rmDNase1), DNase1-like 2 (rmDNase1L2) and DNase1-like 3 (rmDNase1L3) using Pichia pastoris. Employing different strategies for optimizing culture and purification conditions, we achieved yields of pure protein between ~3 mg/l (rmDNase1L2 and rmDNase1L3) and ~9 mg/l (rmDNase1) expression medium. Furthermore, we established a procedure for post-expressional maturation of pre-mature DNase still bound to an unprocessed tri-N-glycosylated pro-peptide of the yeast α-mating factor. We analyzed glycosylation profiles and determined specific DNase activities by the hyperchromicity assay. Additionally, we evaluated substrate specificities under various conditions at equimolar DNase isoform concentrations by lambda DNA and chromatin digestion assays in the presence and absence of heparin and monomeric skeletal muscle α-actin. Our results suggest that due to its biochemical properties mDNase1L2 can be regarded as an evolutionary intermediate isoform of mDNase1 and mDNase1L3. Consequently, our data show that the secretory DNase1 family members complement each other to achieve optimal DNA degradation and chromatinolysis under a broad spectrum of biological conditions.

DNASE1L3 as a Prognostic Biomarker Associated with Immune Cell Infiltration in Cancer

Objectives

Deoxyribonuclease 1 like 3 (DNASE1L3) is critically involved in apoptosis and immune response, however, its role in cancer has yet to be deciphered. We aimed to explore the prognostic value of DNASE1L3 across a series of malignancies.

Methods

Based on Oncomine database and Tumor Immune Estimation Resource (TIMER), expression profiling of DNASE1L3 was detailed in malignancies. Using PrognoScan, Kaplan-Meier Plotter, GEPIA2, and bc-GenEcMiner v4.5, prognostic value of DNASE1L3 was estimated in diverse cancers. Based on TIMER, association between DNASEL13 expression and immune infiltration was examined in various cancers. Then, mRNA level of DNASE1L3 in hepatocellular carcinoma (HCC) samples (n=22) and stomach adenocarcinoma (STAD) samples (n=17) was measured with qRT-PCR. Immunohistochemistry was performed to confirm expression of DNASE1L3 in paraffin-embedded tissues of HCC (n=9) and lung adenocarcinoma (n=20).

Results

DNASE1L3 was downregulated in multiple cancers, including breast invasive carcinoma (BRCA), cholangiocarcinoma (CHOL), liver hepatocellular carcinoma (LIHC), and lung adenocarcinoma (LUAD). A lower level of DNASE1L3 correlated with poorer prognosis in various cancers, especially in breast, liver, kidney, stomach, lung adenocarcinoma and sarcoma (SARC). Moreover, DNASE1L3 was positively related to immune cell infiltration in many cancers, including BRCA, LIHC, STAD, LUAD, and SARC. DNASE1L3 was significantly associated with CCR7/CCL19 in cancers. DNASE1L3 was downregulated in HCC and STAD tissues as demonstrated by qRT-PCR, as well as in HCC and LUAD samples, as shown by immunohistochemistry.

Conclusion

DNASE1L3 has potential to serve as a prognostic biomarker in cancer of the breast, kidney, liver, stomach, lung adenocarcinoma and sarcoma. Down-regulation of DNASE1L3 may participate in immune escape via CCR7/CCL19 axis.

The Role of Nucleases and Nucleic Acid Editing Enzymes in the Regulation of Self-Nucleic Acid Sensing

Detection of microbial nucleic acids by the innate immune system is mediated by numerous intracellular nucleic acids sensors. Upon the detection of nucleic acids these sensors induce the production of inflammatory cytokines, and thus play a crucial role in the activation of anti-microbial immunity. In addition to microbial genetic material, nucleic acid sensors can also recognize self-nucleic acids exposed extracellularly during turn-over of cells, inefficient efferocytosis, or intracellularly upon mislocalization. Safeguard mechanisms have evolved to dispose of such self-nucleic acids to impede the development of autoinflammatory and autoimmune responses. These safeguard mechanisms involve nucleases that are either specific to DNA (DNases) or RNA (RNases) as well as nucleic acid editing enzymes, whose biochemical properties, expression profiles, functions and mechanisms of action will be detailed in this review. Fully elucidating the role of these enzymes in degrading and/or processing of self-nucleic acids to thwart their immunostimulatory potential is of utmost importance to develop novel therapeutic strategies for patients affected by inflammatory and autoimmune diseases.

Proteomic analysis of the response of Trichinella spiralis muscle larvae to exogenous nitric oxide

Trichinella spiralis mainly dwells in the muscle tissue of its host and is the main causative agent of trichinellosis in humans. Nitric oxide (NO), an important intracellular signaling molecule that may restrict pathogen growth in infected hosts, has been known for its anti-pathogenic activity, including resistance to T. spiralis. Herein, we applied label-free analysis to investigate the effect of sodium nitroprusside (SNP, a NO donor compound) on the proteome of T. spiralis muscle larvae (ML), followed by Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway cluster analyses. Of the 1,476 proteins detected in the ML, 121 proteins showed differential expression, including 50 significantly upregulated and 71 downregulated proteins. The functions of the 108 annotated proteins were primarily related to signal transduction, transcription/translation, material metabolism, protein synthesis/assembly/degradation, and stress/defense/antioxidation. Quantitative real-time polymerase chain reaction (qRT-PCR) assay verified that FRMD5 and CUT-1 gene expression levels were significantly increased, while COX2 gene expression level was significantly decreased. GO annotation and KEGG pathway analyses showed that the majority of differentially expressed proteins were mainly involved in the molecular function of the catalytic activity, biological process of the immune system process, metabolic process, cellular component organization, biological adhesion, and cellular component of the macromolecular complex. Our results demonstrate the first comprehensive protein expression profile of the ML in response to NO stress and provide novel references for understanding the potential mechanism underlying the effects of NO on trichinellosis.

Immuno-proteomic analysis of Trichinella spiralis, T. pseudospiralis, and T. papuae extracts recognized by human T. spiralis-infected sera

The present study explored potentially immunogenic proteins of the encapsulated (Trichinella spiralis) and non-encapsulated (T. pseudospiralis, T. papuae) species within the genus Trichinella. The somatic muscle larval extracts of each species were subjected to immunoblotting analysis using human T. spiralis-infected serum samples. Fifteen reactive bands of all three species were selected for further protein identification by liquid chromatography-tandem mass spectrometry, and their possible functions were ascertained using the gene ontology. Our findings showed immunogenic protein patterns with molecular mass in the range of 33-67 kDa. Proteomic and bioinformatic analysis revealed a wide variety of functions of 17 identified proteins, which are associated with catalytic, binding, and structural activities. Most proteins were involved in cellular and metabolic processes that contribute in the invasion of host tissues and the larval molting processes. The parasite proteins were identified as actin-5C, serine protease, deoxyribonuclease-2, and intermediate filament protein ifa-1. This information may lead to alternative tools for selection of potential diagnostic protein markers or aid in the design of vaccine candidates for prevention and control of Trichinella infection.

Cytotoxic and genotoxic affects of acid mine drainage on fish Channa punctata (Bloch)

The investigation deals with the effects of Acid Mine Drainage (AMD) of coal mine on fish Channa punctata (Bloch) by examining the incidence of haematological, morphological, histological changes and DNA fragmentation in tissues of C. punctata in laboratory condition. For this study fishes were exposed to 10% of AMD for a period of 30 days. The fusion of the primary and secondary gill lamellae, distortion, loss of alignment, deposition of worn out tissues and mucous on the surface of the lamella in the gills; degeneration of morphological architecture, loss of alignment of tubules, mucous deposition in the kidney; cellular damage, cellular necrosis, extraneous deposition on the surface, pore formation in the liver are some important changes detected by scanning electron microscopy. Fishes of AMD treated group showed gradual significant decrease in TEC, Hb and, increase in TLC and DLC as compared to that of the control. DNA fragmentation observed in kidney of fishes from treated group indicates an intricate pollutant present in the AMD. The high incidence of morphological and histological alterations, haematological changes along with DNA breakage in C. punctata is an evidence of the cytotoxic and genotoxic potential of AMD of coal mines.

Dnases in health and disease

DNA degradation is critical to healthy organism development and survival. Two nuclease families that play key roles in development and in disease are the Dnase1 and Dnase2 families. While these two families were initially characterized by biochemical function, it is now clear that multiple enzymes in each family perform similar, non-redundant roles in many different tissues. Most Dnase1 and Dnase2 family members are poorly characterized, yet their elimination can lead to a wide range of diseases, including lethal anemia, parakeratosis, cataracts and systemic lupus erythematosus. Therefore, understanding these enzyme families represents a critical field of emerging research. This review explores what is currently known about Dnase1 and Dnase2 family members, highlighting important questions about the structure and function of family members, and how their absence translates to disease.

Dnase1L3 Regulates Inflammasome-Dependent Cytokine Secretion

Pediatric-onset systemic lupus erythematosus arises in humans and mice lacking the endonuclease Dnase1L3. When Dnase1L3 is absent, DNA from circulating apoptotic bodies is not cleared, leading to anti-DNA antibody production. Compared to early anti-DNA and anti-chromatin responses, other autoantibody responses and general immune activation in Dnase1L3^−/− mice are greatly delayed. We investigated the possibility that immune activation, specifically inflammasome activation, is regulated by Dnase1L3. Here, we report that Dnase1L3 inhibition blocked both NLR family, pyrin domain containing 3 (NLRP3) and NLRC4 inflammasome-mediated release of high-mobility group box 1 protein and IL-1β. In contrast to IL-1β release, Dnase1L3 inhibition only mildly impaired NLRP3-dependent pyroptosis, as measured by propidium iodide uptake or LDH release. Mechanistically, we found that Dnase1L3 was needed to promote apoptosis-associated speck-like protein containing a caspase activation and recruitment domain (ASC) nuclear export and speck formation. Our results demonstrate that Dnase1L3 inhibition separates cytokine secretion from pyroptosis by targeting ASC. These findings suggest that Dnase1L3 is necessary for cytokine secretion following inflammasome activation.

Identification of novel drugs to target dormant micrometastases

BACKGROUND

Cancer-specific survival has changed remarkably little over the past half century, mainly because metastases that are occult at diagnosis and generally resistant to chemotherapy subsequently develop months, years or even decades following definitive therapy. Targeting the dormant micrometastases responsible for these delayed or occult metastases would represent a major new tool in cancer patient management. Our hypothesis is that these metastases develop from micrometastatic cells that are suppressed by normal extracellular matrix (ECM).

METHODS

A new screening method was developed that compared the effect of drugs on the proliferation of cells grown on a normal ECM gel (small intestine submucosa, SISgel) to cells grown on plastic cell culture plates. The desired endpoint was that cells on SISgel were more sensitive than the same cells grown as monolayers. Known cancer chemotherapeutic agents show the opposite pattern.

RESULTS

Screening 13,000 compounds identified two leads with low toxicity in mice and EC50 values in the range of 3-30 μM, depending on the cell line, and another two leads that were too toxic to mice to be useful. In a novel flank xenograft method of suppressed/dormant cells co-injected with SISgel into the flank, the lead compounds significantly eliminated the suppressed cells, whereas conventional chemotherapeutics were ineffective. Using a 4T1 triple negative breast cancer model, modified for physiological metastatic progression, as predicted, both lead compounds reduced the number of large micrometastases/macrometastases in the lung. One of the compounds also targeted cancer stem cells (CSC) isolated from the parental line. The CSC also retained their stemness on SISgel. Mechanistic studies showed a mild, late apoptotic response and depending on the compound, a mild arrest either at S or G2/M in the cell cycle.

CONCLUSIONS

In summary we describe a novel, first in class set of compounds that target micrometastatic cells and prevent their reactivation to form recurrent tumors/macrometastases.

First evidence of fish genotoxicity induced by heavy metals from landfill leachates: the advantage of using the RAPD-PCR technique

Municipal leachates are loaded with heavy metals that can contaminate surface water before discharge into a receiving body of water. The aim of this study is to evaluate the genotoxic effects of heavy metals generated by domestic waste on the common roach Rutilus rutilus in the last of the four interconnected ponds at the Etueffont landfill. We used random amplified polymorphic DNA (RAPD) since it has been shown to be a powerful means of detecting a broad range of DNA damage due to environmental contaminants. Our results show the ability of RAPD analysis to detect significant genetic alterations in roach DNA, after contamination with a set of metals contained in the landfill leachates in comparison to a roach from a non-polluted reference pond. Analysis of electrophoresis profiles indicates apparent changes such as the appearance of new bands or disappearance of bands as compared to the control. In fact, mixed smearing and laddering of DNA fragments in muscle samples support the genotoxic effects of metal deposits in the roach. This study is the first evidence found via the RAPD-PCR technique in the detection of pollutant impacts on fish exposed to landfill leachates.

Proteomic analysis of surface proteins of Trichinella spiralis muscle larvae by two-dimensional gel electrophoresis and mass spectrometry

Background

Trichinella spiralis is a zoonotic tissue-dwelling parasitic nematode that infects humans and other mammals. Its surface proteins are recognized as antigenic in many infected hosts, being directly exposed to the host’s immune system and are the main target antigens that induce the immune responses. The larval surface proteins may also interact with intestinal epithelial cells and may play an important role in the invasion and development process of T. spiralis. The purpose of this study was to analyze and characterize the surface proteins of T. spiralis muscle larvae by two-dimensional gel electrophoresis (2-DE) and mass spectrometry.

Methods

The surface proteins of T. spiralis muscle larvae were stripped from the cuticle of live larvae by the cetyltrimethylammonium bromide (CTAB) and sodium deoxycholate. The surface protein stripping was examined by an immunofluorescent test (IFT). The surface proteins were analyzed by SDS-PAGE and Western blotting, and then identified by 2-DE and MALDI-TOF/TOF mass spectrometry analysis.

Results

The IFT results showed that the surface proteins-stripped larvae were not recognized by sera of mice immunized with surface antigens. Western blotting showed 7 of 12 protein bands of the surface proteins were recognized by mouse infection sera at 18 dpi and at 42 dpi. The 2-DE results showed that a total of approximately 33 proteins spots were detected with molecular weights varying from 10 to 66 kDa and isoelectric point (pI) from 4 to 7. Twenty-seven of 33 protein spots were identified and characterized to correlate with 15 different proteins. Out of the 14 proteins identified as T. spiralis proteins, 5 proteins (partial P49 antigen, deoxyribonuclease II family protein, two serine proteases, and serine proteinase) had catalytic and hydrolase activity. All of these 5 proteins were also associated with metabolic processes and 2 of the five proteins were associated with cellular processes.

Conclusions

In this study, T. spiralis muscle larval surface proteins have been identified, which will provide useful information to elucidate the host-parasite interaction, identify the invasion-related proteins, early diagnostic antigens and the targets for a vaccine.

Endonucleases and apoptosis in animals

Endonucleases are the main instruments of obligatory DNA degradation in apoptosis. Many endonucleases have marked processive action; initially they split DNA in chromatin into very large domains, and then they perform in it internucleosomal fragmentation of DNA followed by its hydrolysis to small fragments (oligonucleotides). During apoptosis, DNA of chromatin is attacked by many nucleases that are different in activity, specificity, and order of action. The activity of every endonuclease is regulated in the cell through its own regulatory mechanism (metal ions and other effectors, possibly also S-adenosylmethionine). Apoptosis is impossible without endonucleases as far as it leads to accumulation of unnecessary (defective) DNA, disorders in cell differentiation, embryogenesis, the organism's development, and is accompanied by various severe diseases. The interpretation of the structure and functions of endonucleases and of the nature and action of their modulating effectors is important not only for elucidation of mechanisms of apoptosis, but also for regulation and control of programmed cell death, cell differentiation, and development of organisms.

Proteomic analysis of Trichinella spiralis muscle larval excretory-secretory proteins recognized by early infection sera

Although the excretory-secretory (ES) proteins of Trichinella spiralis muscle larvae are the most commonly used diagnostic antigens for trichinellosis, their main disadvantage is the false negative results during the early stage of infection and cross-reaction of their main components (43, 45, 49, and 53 kDa) with sera of patients with other helminthiasis. The aim of this study was to identify early specific diagnostic antigens in T. spiralis ES proteins with 30–40 kDa. The ES proteins were analyzed by two-dimensional electrophoresis (2-DE), and a total of approximately 150 proteins spots were detected with isoelectric point (pI) varying from 4 to 7 and molecular weight from 14 to 66 kDa. When probed with sera from infected mice at 18 days postinfection, ten protein spots with molecular weight of 30–40 kDa were recognized and identified by MALDI-TOF/TOF-MS. All of ten spots were successfully identified and characterized to correlate with five different proteins, including two potential serine proteases, one antigen targeted by protective antibodies, one deoxyribonuclease (DNase) II, and one conserved hypothetical protein. These proteins might be the early specific diagnostic antigens for trichinellosis.

Apoptotic DNA fragmentation may be a cooperative activity between caspase-activated deoxyribonuclease and the poly(ADP-ribose) polymerase-regulated DNAS1L3, an endoplasmic reticulum-localized endonuclease that translocates to the nucleus during apoptosis

Caspase-activated DNase (CAD) is the most favorable candidate for chromatin degradation during apoptosis. Ca(2+)-dependent endonucleases are equally important in internucleosomal DNA fragmentation (INDF), including the PARP-1-regulated DNAS1L3. Despite the elaborate work on these endonucleases, the question of whether these enzymes cooperate during INDF was not addressed. Here, we show a lack of correlation between INDF and CAD expression levels and inactivation by cleavage of its inhibitor (ICAD) during apoptosis. The cells that failed to induce INDF accumulated large amounts of 50-kb breaks, which is suggestive of incomplete chromatin processing. Similarly, INDF was blocked by Ca(2+) chelation without a block in ICAD cleavage or caspase-3 activation, which is consistent with the involvement of CAD in 50-kb DNA fragmentation and its Ca(2+) independence. However, DNAS1L3 expression in INDF-deficient cells promoted INDF during apoptosis and was blocked by Ca(2+) chelation. Interestingly, expression of DNAS1L3 in ICAD-deficient cells failed to promote tumor necrosis factor α-induced INDF but required the coexpression of ICAD. These results suggest a cooperative activity between CAD and DNAS1L3 to accomplish INDF. In HT-29 cells, endogenous DNAS1L3 localized to the endoplasmic reticulum (ER) and translocated to the nucleus upon apoptosis induction but prior to INDF manifestation, making it the first reported Ca(2+)-dependent endonuclease to migrate from the ER to the nucleus. The nuclear accumulation of DNAS1L3, but not its exit out of the ER, required the activity of cysteine and serine proteases. Interestingly, the endonuclease accumulated in the cytosol upon inhibition of serine, but not cysteine, proteases. These results exemplify the complexity of chromatin degradation during apoptosis.

Apoptotic Volume Decrease (AVD) Is Independent of Mitochondrial Dysfunction and Initiator Caspase Activation

Persistent cell shrinkage is a major hallmark of apoptotic cell death. The early-phase shrinkage, which starts within 30−120 min after apoptotic stimulation and is called apoptotic volume decrease (AVD), is known to be accomplished by activation of K⁺ channels and volume-sensitive outwardly rectifying (VSOR) Cl⁻ channels in a manner independent of caspase-3 activation. However, it is controversial whether AVD depends on apoptotic dysfunction of mitochondria and activation of initiator caspases. Here, we observed that AVD is induced not only by a mitochondrial apoptosis inducer, staurosporine (STS), in mouse B lymphoma WEHI-231 cells, but also by ligation of the death receptor Fas in human B lymphoblastoid SKW6.4 cells, which undergo Fas-mediated apoptosis without involving mitochondria. Overexpression of Bcl-2 failed to inhibit the STS-induced AVD in WEHI-231 cells. These results indicate that AVD does not require the mitochondrial pathway of apoptosis. In human epithelial HeLa cells stimulated with anti-Fas antibody or STS, the AVD induction was found to precede activation of caspase-8 and caspase-9 and to be resistant to pan-caspase blockers. Thus, it is concluded that the AVD induction is an early event independent of the mitochondrial apoptotic signaling pathway and initiator caspase activation.

Confocal microscopy as a tool to examine DNA fragmentation, chromatin condensation and other apoptotic changes in Parkinson's disease

There is considerable controversy regarding the possibility that nigral dopaminergic neurons may die via apoptosis in Parkinson's disease. It is now clear that both single- and/or double-stranded DNA breaks can be generated in the apoptotic degradative process. Since these breaks may also be present in necrotic cell death, in situ end labeling cannot be used in isolation to identify apoptotic neurons. We have developed a fluorescent double-labeling method that combines in situ end labeling with the simultaneous visualization of chromatin condensation. When viewed with laser confocal scanning microscopy, the structural detail of the nucleus is provided to unequivocally identify apoptotic nuclei.

Global genetic analysis of all single nucleotide polymorphisms in exons of the human deoxyribonuclease I-like 3 gene and their effect on its catalytic activity

Deoxyribonucleases (DNases) have been suggested to be implicated in the pathophysiology of autoimmune diseases. In the DNASE1L3 gene encoding human DNase I-like 3 (DNase 1L3), a member of the DNase I family, only two non-synonymous (R178 H and R206C) single nucleotide polymorphisms (SNPs) have been examined [Ueki et al., Clin. Chim. Acta 2009, 407, 20-24]. Three other non-synonymous (G82R, K96N, and I243M) and four synonymous (S17S, T84T, R92R, and A181A) SNPs, in addition to R206C and R178H, have been identified in DNASE1L3. We investigated the distribution of all these SNPs in exons of the gene in eight Asian, three African, and three Caucasian populations worldwide using newly devised genotyping methods. SNP T84T showed polymorphism in all the populations, and R92R was polymorphic in the three African and three Caucasian populations; R206C was distributed only in Caucasian populations. In contrast, no minor allele was found in five SNPs (S17S, G82R, K96N, A181A, and I243M) in DNASE1L3. Generally, the DNase 1L3 gene shows relatively low genetic diversity with regard to exonic SNPs. When the effect of amino acid/nucleotide substitutions resulting from the SNPs on DNase 1L3 activity was examined, none of the synonymous SNPs had any effect on the DNase 1L3 activity, whereas among non-synonymous SNPs, SNP G82R diminished the activity of the enzyme, being similar to R206C. These findings permit us to assume that, although only R206 exhibits polymorphisms in a Caucasian-specific manner, at least SNPs G82R and R206C in DNASE1L3 might be potential risk factors for autoimmune disease.

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.

The release of high mobility group box 1 in apoptosis is triggered by nucleosomal DNA fragmentation

High mobility group box 1 (HMGB1) initially identified as a non-histone chromosomal protein, which mainly functions as chromatin structure and transcriptional regulation, has been recently reported to be secreted into extracellular milieu in necrosis and apoptosis, and act as a proinflammatory mediator. However, the mechanism by which apoptotic cells release HMGB1 is not clear. In this study, we found that staurosporine (apoptosis-inducer)-induced HMGB1 release was associated with nucleosomal DNA fragmentation catalyzed by caspase-activated DNase (CAD) in WEHI-231 cells. Importantly, this event was effectively attenuated by the treatment of a pan-caspase inhibitor, Z-VAD-fmk, and by the inhibition of CAD-mediated DNA fragmentation by the expression of caspase-resistant inhibitor of CAD (ICAD-CR). In WEHI-231/ICAD-CR and WEHI-231/Puro cells, DNase γ-catalyzed nucleosomal DNA fragmentation occurred by anti-IgM antibody treatment was critical for HMGB1 release. Furthermore, in DNase γ stably-expressing HeLa S3 cells (HeLa S3/γ), the release of HMGB1 accompanied with nucleosomal DNA fragmentation was more apparent than that in parental HeLa S3 cells in which DNA fragmentation was scarcely observed. Taken together, these date suggest that nucleosomal DNA fragmentation catalyzed by CAD or DNase γ plays a pivotal role in HMGB1 release.

Caucasian-specific allele in non-synonymous single nucleotide polymorphisms of the gene encoding deoxyribonuclease I-like 3, potentially relevant to autoimmunity, produces an inactive enzyme

BACKGROUND

Deoxyribonuclease I-like 3 (DNase Il3), a member of human DNase I family, is postulated to be involved in the genesis of autoimmune diseases. In the DNase Il3 gene, 2 non-synonymous SNPs, R178H and R206C, have been identified, however relevant population data are not available.

METHODS

Genotyping of the SNPs was performed in healthy subjects belonging to 3 ethnic groups (n=1708), including nine different populations, using an amplification refractory mutation system and the PCR-RFLP technique.

RESULTS

All of the 9 populations were typed as a single genotype in R178H. All Asian and African populations exhibited only a homozygous C686 allele in R206C, whereas a heterozygote, C686/T686, was found (frequency of 3.5-15.4%) in three Caucasian populations (Turk, German and Mexican); Caucasian-specific allele T686 was identified. The substitution of Arg by Cys corresponding to R206C resulted in elimination of DNase Il3 activity.

CONCLUSION

A Caucasian-specific allele in SNP R206C produces an inactive form of DNase Il3. It seems plausible that levels of DNase Il3 activity in Caucasian subjects with the heterozygote in R206C are lower than those in individuals with the predominant homozygote. Our results may have clinical implications in relation to the prevalence of autoimmune diseases.

Murine serum nucleases--contrasting effects of plasmin and heparin on the activities of DNase1 and DNase1-like 3 (DNase1l3)

DNase1 is regarded as the major serum nuclease; however, a systematic investigation into the presence of additional serum nuclease activities is lacking. We have demonstrated directly that serum contains DNase1-like 3 (DNase1l3) in addition to DNase1 by an improved denaturing SDS-PAGE zymography method and anti-murine DNase1l3 immunoblotting. Using DNA degradation assays, we compared the activities of recombinant murine DNase1 and DNase1l3 (rmDNase1, rmDNase1l3) with the serum of wild-type and DNase1 knockout mice. Serum and rmDNase1 degrade chromatin effectively only in cooperation with serine proteases, such as plasmin or thrombin, which remove DNA-bound proteins. This can be mimicked by the addition of heparin, which displaces histones from chromatin. In contrast, serum and rmDNase1l3 degrade chromatin without proteolytic help and are directly inhibited by heparin and proteolysis by plasmin. In previous studies, serum DNase1l3 escaped detection because of its sensitivity to proteolysis by plasmin after activation of the plasminogen system in the DNA degradation assays. In contrast, DNase1 is resistant to plasmin, probably as a result of its di-N-glycosylation, which is lacking in DNase1l3. Our data demonstrate that secreted rmDNase1 and murine parotid DNase1 are mixtures of three different di-N-glycosylated molecules containing two high-mannose, two complex N-glycans or one high-mannose and one complex N-glycan moiety. In summary, serum contains two nucleases, DNase1 and DNase1l3, which may substitute or cooperate with each other during DNA degradation, providing effective clearance after exposure or release from dying cells.

An endogenous calcium-dependent, caspase-independent intranuclear degradation pathway in thymocyte nuclei: antagonism by physiological concentrations of K(+) ions

Calcium ions have been implicated in apoptosis for many years, however the precise role of this ion in the cell death process remains incomplete. We have extensively examined the role of Ca(2+) on nuclear degradation in vitro using highly purified nuclei isolated from non-apoptotic rat thymocytes. We show that these nuclei are devoid of CAD (caspase-activated DNase), and DNA degradation occurs independent of caspase activity. Serine proteases rather than caspase-3 appear necessary for this Ca(2+) -dependent DNA degradation in nuclei. We analyzed nuclei treated with various concentrations of Ca(2+) in the presence of both a physiological (140 mM) and apoptotic (40 mM) concentration of KCl. Our results show that a 5-fold increase in Ca(2+) is required to induce DNA degradation at the physiological KCl concentration compared to the lower, apoptotic concentration of the cation. Ca(2+) -induced internucleosomal DNA degradation was also accompanied by the release of histones, however the apoptotic-specific phosphorylation of histone H2B does not occur in these isolated nuclei. Interestingly, physiological concentrations of K(+) inhibit both Ca(2+) -dependent DNA degradation and histone release suggesting that a reduction of intracellular K(+) is necessary for this apoptosis-associated nuclear degradation in cells. Together, these data define an inherent caspase-independent catabolic pathway in thymocyte nuclei that is sensitive to physiological concentrations of intracellular cations.

Cytoprotective effects of melatonin against necrosis and apoptosis induced by ischemia/reperfusion injury in rat liver

Melatonin protects against organ ischemia; this effect has mainly been attributed to the antioxidant properties of the indoleamine. This study examined the cytoprotective properties of melatonin against injury to the liver caused by ischemia/reperfusion (I/R). Rats were subjected to 60 min of ischemia followed by 5 hr of reperfusion. Melatonin (10 mg/kg) or the vehicle was administered intraperitoneally 15 min before ischemia and immediately before reperfusion. The serum aminotransferase activity and lipid peroxidation levels were increased markedly by hepatic I/R, which were suppressed significantly by melatonin. In contrast, the glutathione content, which is an index of the cellular redox state, and mitochondrial glutamate dehydrogenase activity, which is a maker of the mitochondrial membrane integrity, were lower in the I/R rats. These decreases were attenuated by melatonin. The rate of mitochondrial swelling, which reflects the extent of the mitochondrial permeability transition, was higher after 5 hr of reperfusion but was attenuated by melatonin. Melatonin limited the release of cytochrome c into the cytosol and the activation of caspase-3 observed in the I/R rats. The melatonin-treated rats showed markedly fewer apoptotic (TUNEL positive) cells and DNA fragmentation than did the I/R rats. These results suggest that melatonin ameliorates I/R-induced hepatocytes damage by inhibiting the level of oxidative stress and the apoptotic pathway. Consequently, melatonin may provide a new pharmacological intervention strategy for hepatic I/R injuries.

The role of apoptosis in Listeria monocytogenes neural infection: listeriolysin O interaction with neuroblastoma Neuro-2a cells

Listeria monocytogenes is the etiological agent of meningitis that affects individuals at high risk such as pregnant women, neonates, the elderly and immunocompromised individuals. Infection by this intracellular pathogen can be lethal if not diagnosed and treated. Mouse neuroblastoma Neuro-2a cells, a neuron-like cell line, were infected with L. monocytogenes. In this study apoptotic changes of neuroblastoma Neuro-2a cells infected with strains of Listeria producing different listeriolysin O levels are investigated by cytotoxicity assay, cellular viability assay, DAPI staining, intranucleosomal DNA fragmentation test, and monoclonal antibodies against ss-DNA. Results show that after internalization, the bacteria induced morphological, functional and genetic changes in the cells characteristic of apoptosis, which was dose-and time-dependent on listeriolysin O. Neuroblastoma Neuro-2a cells represent an interesting model cell line to further the understanding of Listeria pathogenesis within the central nervous system.

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.

Stage-specific expression of DNaseγ during B-cell development and its role in B-cell receptor-mediated apoptosis in WEHI-231 cells

Here, we describe the non-redundant roles of caspase-activated DNase (CAD) and DNasegamma during apoptosis in the immature B-cell line WEHI-231. These cells induce DNA-ladder formation and nuclear fragmentation by activating CAD during cytotoxic drug-induced apoptosis. Moreover, these apoptotic manifestations are accompanied by inhibitor of CAD (ICAD) cleavage and are abrogated by the constitutive expression of a caspase-resistant ICAD mutant. No such nuclear changes occur during oxidative stress-induced necrosis, indicating that neither CAD nor DNasegamma functions under necrotic conditions. Interestingly, the DNA-ladder formation and nuclear fragmentation induced by B-cell receptor ligation occur in the absence of ICAD cleavage and are not significantly affected by the ICAD mutant. Both types of nuclear changes are preceded by the upregulation of DNasegamma expression and are strongly suppressed by 4-(4,6-dichloro-[1, 3, 5]-triazin-2-ylamino)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-benzoic acid (DR396), which is a specific inhibitor of DNasegamma. Our results suggest that DNasegamma provides an alternative mechanism for inducing nuclear changes when the working apoptotic cascade is unsuitable for CAD activation.

Action of apoptotic endonuclease DNase γ on naked DNA and chromatin substrates

The internucleosomal cleavage of genomic DNA is a biochemical hallmark of apoptosis. DNase gamma, a Mg2+/Ca2+-dependent endonuclease, has been suggested to be one of the apoptotic endonucleases, but its biochemical characteristic has not been fully elucidated. Here, using recombinant DNase gamma, we showed that DNase gamma is a Mg2+/Ca2+-dependent single-stranded DNA nickase and has a high activity at low ionic strength. Under higher ionic strength, such as physiological buffer conditions, the endonuclease activity of DNase gamma is restricted, but its activity is enhanced in the presence of linker histone H1, which explains DNA cleavage at linker regions of apoptotic nuclei.

Cells die with increased cytosolic ATP during apoptosis: a bioluminescence study with intracellular luciferase

Apoptosis is a distinct form of cell death, which requires energy. Here, we made real-time continuous measurements of the cytosolic ATP level throughout the apoptotic process in intact HeLa, PC12 and U937 cells transfected with the firefly luciferase gene. Apoptotic stimuli (staurosporine (STS), tumor necrosis factor alpha (TNFalpha), etoposide) induced significant elevation of the cytosolic ATP level. The cytosolic ATP level remained at a higher level than in the control for up to 6 h during which activation of caspase-3 and internucleosomal DNA fragmentation took place. When the STS-induced ATP response was abolished by glucose deprivation-induced inhibition of glycolysis, both caspase activation and DNA laddering were completely inhibited. Annexin V-binding induced by STS or TNFalpha was largely suppressed by glycolysis inhibition. Thus, it is suggested that the cells die with increased cytosolic ATP, and elevation of cytosolic ATP level is a requisite to the apoptotic cell death process.

Comparative characterization of rat deoxyribonuclease 1 (Dnase1) and murine deoxyribonuclease 1-like 3 (Dnase1l3)

Deoxyribonuclease 1 (DNASE1, DNase I) and deoxyribonuclease 1-like 3 (DNASE1L3, DNase gamma, DNase Y, LS-DNase) are members of a DNASE1 protein family that is defined by similar biochemical properties such as Ca2+/Mg2+-dependency and an optimal pH of about 7.0 as well as by a high similarity in their nucleic acid and amino acid sequences. In the present study we describe the recombinant expression of rat Dnase1 and murine Dnase1l3 as fusion proteins tagged by their C-terminus to green fluorescent protein in NIH-3T3 fibroblasts and bovine lens epithelial cells. Both enzymes were translocated into the rough endoplasmic reticulum, transported along the entire secretory pathway and finally secreted into the cell culture medium. No nuclear occurrence of the nucleases was detectable. However, deletion of the N-terminal signal peptide of both nucleases resulted in a cytoplasmic and nuclear distribution of both fusion proteins. Dnase1 preferentially hydrolysed 'naked' plasmid DNA, whereas Dnase1l3 cleaved nuclear DNA with high activity. Dnase1l3 was able to cleave chromatin in an internucleosomal manner without proteolytic help. By contrast, Dnase1 was only able to achieve this cleavage pattern in the presence of proteases that hydrolysed chromatin-bound proteins. Detailed analysis of murine sera derived from Dnase1 knockout mice revealed that serum contains, besides the major serum nuclease Dnase1, an additional Dnase1l3-like nucleolytic activity, which, in co-operation with Dnase1, might help to suppress anti-DNA autoimmunity by degrading nuclear chromatin released from dying cells.

A novel inhibitor that protects apoptotic DNA fragmentation catalyzed by DNase γ

The internucleosomal cleavage of genomic DNA is the biochemical hallmark of apoptosis. DNase gamma, a Ca(2+)/Mg(2+)-dependent endonuclease, has been suggested to be one of the apoptotic endonucleases. We identified here 4-(4,6-dichloro-[1,3,5]-triazin-2-ylamino)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-benzoic acid (DR396) as a novel and potent DNase gamma inhibitor using stable HeLa S3 transfectants of DNase gamma (HeLa-gamma cells). DR396 inhibited apoptotic DNA fragmentation in HeLa-gamma cells induced by staurosporine (STS) and in rat splenocytes exposed to gamma-ray irradiation in a dose-dependent manner. This compound potently and selectively inhibited DNase gamma activity with an IC(50) value of 3.2 microM. DR396 did not delay the apoptotic processes as judged by the morphological changes and the cleavage of a death substrate, poly(ADP-ribose) polymerase (PARP). Furthermore, the compound did not prevent apoptotic DNA fragmentation in Jurkat cells induced by anti-Fas antibody (Ab), which is catalyzed by caspase-activated DNase (CAD). These findings clearly indicate that DR396 exerts chemical knockdown effect of DNase gamma on cells, suggesting that the compound could be an attractive tool for understanding of the physiological significance of DNase gamma.

Semi-artificial Fluorescent Molecular Machine for DNA Damage Detection

The design of artificial molecular machines is complicated because the mechanics used in macromachines is not readily adaptable for nano environments. We constructed a semi-artificial molecular device, which contains a naturally occurring molecular machine-a vaccinia virus encoded protein-linked with an artificial part. The self-assembled construct makes two fluorescently labeled detector units. It is the first sensor capable of selectively detecting different types of DNA breaks, exemplifying a practical approach to the design of molecular devices.

Involvement of apoptosis in syncytial cell death induced by canine distemper virus

The Yanaka strain, a field isolate of Canine distemper virus (CDV), caused extensive syncytial cytopathic effects (CPEs) followed by cell death in vitro. Syncytium formation is an important aspect of CDV pathogenicity, but the mechanism of the fusion-induced cell death is still not understood. In this study, the involvement of apoptosis in the CDV-induced CPE was investigated. We also examined apoptosis in cells infected with a persistent strain of CDV, the Yanaka-BP strain derived from the Yanaka strain, because this strain does not cause obvious CPE. DNA laddering together with Terminal transferase dUTP nick endlabeling (TUNEL) assay indicated that the Yanaka strain infection, but not the Yanaka-BP infection induced apoptosis. In addition, flow cytometric analysis similarly indicated that the Yanaka-BP strain induced apoptosis significantly less frequently than the Yanaka strain did. Thus, absence of apoptosis may be implicated in the CPE and establishment of persistent CDV infection.

Differential DNases are selectively used in neuronal apoptosis depending on the differentiation state

In this study, we investigate the roles of two apoptotic endonucleases, CAD and DNase gamma, in neuronal apoptosis. High expression of CAD, but not DNase gamma, is detected in proliferating N1E-115 neuroblastoma cells, and apoptotic DNA fragmentation induced by staurosporine under proliferating conditions is abolished by the expression of a caspase-resistant form of ICAD. After the induction of neuronal differentiation, CAD disappearance and the induction of DNase gamma occur simultaneously in N1E-115 cells. Apoptotic DNA fragmentation that occurs under differentiating conditions is suppressed by the downregulation of DNase gamma caused by its antisense RNA. The induction of DNase gamma is also observed during neuronal differentiation of PC12 cells, and apoptotic DNA fragmentation induced by NGF deprivation is inhibited by the antisense-mediated downregulation of DNase gamma. These observations suggest that DNA fragmentation in neuronal apoptosis is catalyzed by either CAD or DNase gamma depending on the differentiation state. Furthermore, DNase gamma is suggested to be involved in naturally occurring apoptosis in developing nervous systems.

Aging increases DNase γ, an apoptosis-related endonuclease, in rat liver nuclei: effect of dietary restriction

Organ-specific endonuclease might play a role in the age-related increase in apoptosis in laboratory rodent tissues. In nuclear extracts from liver tissues of male F344 rats, the DNase activity gel system identified DNase gamma, Ca(2+)/Mg(2+)-dependent endonuclease. The enzyme activity, which was measured at 3, 6, 16, and 24 months (mo) of age, was significantly increased between 16 and 24mo in control rats fed ad libitum (AL). The expression level of DNase gamma-mRNA, estimated by a semi-quantitative reverse transcription-polymerase chain reaction method, was also increased at 24mo in group AL. The proportion of immunohistochemically DNase gamma-positive cells, most of which were light-microscopically confined to apoptotic cells, was also significantly increased between 16 and 24mo. Dietary restriction, a powerful anti-aging intervention, which was achieved by providing 70% of the mean food intake in group AL from 6 weeks of age, inhibited the age-related increase in the enzyme activity and the proportion of immunostained cells; for the mRNA level, statistical significance was not obtained. The present study suggests that DNase gamma is involved in an age-related increase in the apoptosis of rat liver, and that CR inhibits the increase as it minimized the age-related increase in the fraction of DNA-damaged hepatocytes susceptible to apoptosis.

Arrested apoptosis of nurse cells during Hydra oogenesis and embryogenesis

During Hydra oogenesis, an aggregate of germ cells differentiates into one oocyte and thousands of nurse cells. Nurse cells display a number of features typical of apoptotic cells and are phagocytosed by the growing oocyte. Yet, these cells remain unchanged in morphology and number until hatching of the polyp, which can occur up to 12 months later. Treatments with caspase inhibitors can block oocyte development during an early phase of oogenesis, but not after nurse cell phagocytosis has taken place, indicating that initiation of nurse cell apoptosis is essential for oocyte development. The genomic DNA of the phagocytosed nurse cells in the oocyte and embryo shows large-scale fragmentation into 8- to 15-kb pieces, but there is virtually none of the internucleosomal degradation typically seen in apoptotic cells. The arrested nurse cells exhibit high levels of peroxidase activity and are prevented from entering the lysosomal pathway. After hatching of the polyp, apoptosis is resumed and the nurse cells are degraded within 3 days. During this final stage, nurse cells become TUNEL-positive and enter secondary lysosomes in a strongly degraded state. Our results suggest that nurse cell apoptosis consists of caspase-dependent and caspase-independent phases. The independent phase can be arrested at an advanced stage for several months, only to resume after the primary polyp hatches.

Changes in the topological expression of markers of differentiation and apoptosis in defined stages of human cervical dysplasia and carcinoma

OBJECTIVE

We compared the capacity of cells in normal cervical epithelium, progressive stages of CIN, and invasive carcinoma to proliferate, differentiate, and undergo apoptosis.

METHODS

We investigated 30 conizations showing regular squamous epithelium of the ectocervix, all stages of cervical preinvasive neoplastic lesions (CIN I to III), or invasive carcinoma. The expression of the cell proliferation and differentiation marker Ki67 and Mad-1, respectively, and of the apoptosis-related proteins bcl-2, active caspase-3, and DNase I was analyzed on paraffin sections by immunohistochemistry. The expression of DNase I or -like enzymes was also analyzed at the level of their gene transcripts by in situ hybridization. In addition, apoptotic events were identified by in situ end labeling of fragmented DNA (ISEL).

RESULTS

Expression of Ki67 was restricted to suprabasal cells in normal cervical epithelium but increased with CIN severity and invasive carcinoma. ISEL demonstrated apoptosis in superficial layers of normal, CIN I, and CIN II epithelium, whereas in CIS (CIN III) and invasive carcinoma, ISEL-positive cells were additionally observed at varying epithelial locations. Bcl-2 immunostaining remained restricted to the basal layer of all preneoplastic and neoplastic stages. Active caspase-3 was present in the suprabasal layer and extended to all upper layers in normal epithelium and slightly decreased with increasing dysplasia. In invasive carcinoma it was restricted to few scattered cells. The differentiation marker Mad-1 extended from the spinous to the superficial layer in regular epithelium, but gradually shifted to more superficial layers with increasing CIN grade and invasive carcinoma. A similar topological change was observed for DNase I with increasing CIN grade. In CIS and invasive carcinoma, DNase I immunopositive cells were solely interspersed within neoplastic cells. In contrast, DNase I specific mRNA was present in all epithelial layers in CIN III and neoplasia, suggesting a translational block of the expression of DNase I or -like enzymes.

CONCLUSION

Our data indicate that the elevated proliferation observed with increasing CIN severity and carcinoma was not paralleled by a similar increase in cell elimination. Most of the dysplastic and neoplastic cervical epithelial cells appeared incapable of entering terminal differentiation and complete it by apoptosis, possibly due to their failure to express or activate apoptosis executing enzymes.

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.

Ca2+-dependent and Caspase-3–independent Apoptosis Caused by Damage in Golgi Apparatus due to 2,4,5,7-Tetrabromorhodamine 123 Bromide–induced Photodynamic Effects¶

To clarify the role of the Golgi apparatus in photodynamic therapy-induced apoptosis, its signaling pathway was studied after photodynamic treatment of human cervix carcinoma cell line HeLa, in which a photosensitizer, 2,4,5,7-tetrabromorhodamine 123 bromide (TBR), was incorporated into the Golgi apparatus. Laser scanning microscopic analysis of TBR-loaded HeLa cells confirmed that TBR was exclusively located in the Golgi apparatus. HeLa cells incubated with TBR for 1 h were then exposed to visible light using an Xe lamp. Light of wavelength below 670 nm was eliminated with a filter. Morphological observation of nuclei stained with Hoechst 33342 revealed that apoptosis of cells was induced by exposure to light. Electron spin resonance spectrometry showed that light-exposed TBR produced both singlet oxygen (1O2) and superoxide anion (O2-). Apoptosis induction by TBR was inhibited by pyrrolidine dithiocarbamate, an O2- scavenger, but not by NaN3, a quencher of 1O2. Furthermore, TBR-induced apoptosis was inhibited by aurintricarboxylic acid and ZnCl2, which are known as inhibitors of deoxyribonuclease (DNase) gamma, and (acetoxymethyl)-1,2-bis(o-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, a chelator of Ca2+, but not by acetyl Asp-Glu-Val-Asp-aldehyde, an inhibitor of caspase-3. These results suggested that O2- was responsible for TBR-induced apoptosis, and Ca(2+)-dependent and caspase-3-independent nuclease such as DNase gamma played an important role in apoptotic signaling triggered by Golgi dysfunction.

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.

Nuclear apoptosis detection by flow cytometry: influence of endogenous endonucleases

Nuclear apoptosis is characterized by chromatin condensation and progressive DNA cleavage into high-molecular-weight fragments and oligonucleosomes. These complex phenomena can be mediated by the activation of a multiplicity of enzymes, characterized by specific patterns of cation dependance, pH requirement, and mode of activation. The significance of this multiplicity of enzymes that cleave genomic DNA has been attributed to the need of death effector pathways specific for cell types/tissues, the level of cell differenciation, and the nature of the apoptotic stimuli. The activation of these factors contributes to the development of alterations that can be detected specifically by flow cytometric assays, namely, propidium iodide assays, acridine orange/ethidium bromide double staining, the TUNEL and ISNT techniques, and the assays of DNA sensitivity to denaturation. Although applicable to a wide spectrum of cell types, an increasing body of literature indicates that these techniques cannot be universally applied to all cell lines and apoptotic conditions: The requirement of a particular mediator(s) of nuclear apoptosis or the absence of endonuclease activity can limit the relevance of certain techniques. Finally, endonucleases recruited during primary necrosis can introduce nuclear alterations detected by some assays and raise the problem of their specificity. This review underlines the need for strategies to accurately detect and quantify nuclear apoptosis by flow cytometry when new cell systems and apoptotic conditions are considered.

Macrophages are involved in DNA degradation of apoptotic cells in murine thymus after administration of hydrocortisone

In the present study, we undertook kinetic analyses of DNA degradation and acid DNase activity in murine thymus after administration of hydrocortisone. Hydrocortisone induced apoptosis in thymocytes, and a large number of cortical thymocytes became TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP biotin nick end labelling)-positive (TUNEL+). F4/80+ macrophages infiltrated through the cortico-medullay junction into the cortical region, and thereafter engulfed apoptotic cells in the cortex of thymus. The distribution of acid DNase-active cells appeared to be similar to that of F4/80+ macrophages. Eighteen hours after the injection, although the foci of apoptotic cells were situated within massively distended F4/80+ macrophages, oligonucleosomal DNA fragments on an agarose gel were undetectable. Our results showed that macrophages were involved in the disappearance of oligonucleosomal DNA fragments in apoptotic thymocytes. Taken together, macrophages play a role in the hydrolysis of DNA in apoptotic cells upon their phagocytosis of the dead cells.

Regulation of DNAS1L3 endonuclease activity by poly(ADP-ribosyl)ation during etoposide-induced apoptosis. Role of poly(ADP-ribose) polymerase-1 cleavage in endonuclease activation

Several endonucleases are implicated in the internucleosomal DNA fragmentation associated with apoptosis. The human Ca2+- and Mg2+-dependent endonuclease DNAS1L3 is inhibited by poly(ADP-ribosyl)ation in vitro, and its activation during apoptosis shows a time course similar to that of the cleavage of poly(ADP-ribose) polymerase-1 (PARP-1). The role of the cleavage and consequent inactivation of PARP-1 by caspase-3 in the activation of DNAS1L3 has now been investigated further both in vitro and in vivo. In an in vitro system based on purified recombinant proteins and NAD, caspase-3 prevented the inhibition of DNAS1L3 endonuclease activity by wild-type PARP-1 but not that induced by a caspase-3-resistant PARP-1 mutant. The induction by etoposide of apoptosis in human osteosarcoma cells (which were shown not to express endogenous DNAS1L3) was accompanied by internucleosomal DNA fragmentation only after transfection of the cells with a plasmid encoding DNAS1L3. This DNA fragmentation in etoposide-treated cells was blocked by 1,2-bis(2-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid, an inhibitor of intracellular Ca2+ release. Expression of the endonuclease subunit of DNA fragmentation factor (DFF40) and cleavage of its inhibitor, DFF45, were not sufficient to cause internucleosomal DNA fragmentation in osteosarcoma cells during etoposide-induced apoptosis. Coexpression of caspase-3-resistant PARP-1 mutant with DNAS1L3 in osteosarcoma cells blocked etoposide-induced internucleosomal DNA fragmentation and resulted in persistent poly(ADP-ribosyl)ation of DNAS1L3; it did not, however, prevent the activation of caspase-3 and the consequent cleavage of endogenous PARP-1. These results indicate that PARP-1 cleavage during apoptosis is not simply required to prevent excessive depletion of NAD and ATP but is also necessary to release DNAS1L3 from poly(ADP-ribosyl)ation-mediated inhibition.

Cytochrome c release into cytosol with subsequent caspase activation during warm ischemia in rat liver

Apoptosis plays an important role in liver ischemia and reperfusion (I/R) injury. However, the molecular basis of apoptosis in I/R injury is poorly understood. The aims of this study were to ascertain when and how apoptotic signal transduction occurs in I/R injury. The apoptotic pathway in rats undergoing 90 min of warm ischemia with reperfusion was compared with that of rats undergoing prolonged ischemia alone. During ischemia, mitochondrial cytochrome c was released into the cytosol in a time-dependent manner in hepatocytes and sinusoidal endothelial cells, and caspase-3 and an inhibitor of caspase-activated DNase were cleaved. However, apoptotic manifestation and DNA fragmentation were not observed. After reperfusion, nuclear condensation, cells positive for terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling, and DNA fragmentation were observed and caspase-8 and Bid cleavage occurred. In contrast, prolonged ischemia alone induced necrosis rather than apoptosis. In summary, our results show that release of mitochondrial cytochrome c and caspase activation proceed during ischemia, although apoptosis is manifested after reperfusion.