On the use of Zn2+ to discriminate endonucleases activated during apoptosis

Cyanobacterial VOCs β-ionone and β-cyclocitral poisoning Lemna turionifera by triggering programmed cell death

β-Ionone and β-cyclocitral are two typical components in cyanobacterial volatiles, which can poison aquatic plants and even cause death. To reveal the toxic mechanisms of the two compounds on aquatic plants through programmed cell death (PCD), the photosynthetic capacities, caspase-3-like activity, DNA fragmentation and ladders, as well as expression of the genes associated with PCD in Lemna turionifera were investigated in exposure to β-ionone (0.2 mM) and β-cyclocitral (0.4 mM) at lethal concentration. With prolonging the treatment time, L. turionifera fronds gradually died, and photosynthetic capacities gradually reduced and even disappeared at the 96th h. This demonstrated that the death process might be a PCD rather than a necrosis, due to the gradual loss of physiological activities. When L. turionifera underwent the death, caspase-3-like was activated after 3 h, and reached to the strongest activity at the 24th h. TUNEL-positive nuclei were detected after 12 h, and appeared in large numbers at the 48th h. The DNA was cleaved by Ca2+-dependent endonucleases and showed obviously ladders. In addition, the expression of 5 genes (TSPO, ERN1, CTSB, CYC, and ATR) positively related with PCD initiation was up-regulated, while the expression of 2 genes (RRM2 and TUBA) negatively related with PCD initiation was down-regulated. Therefore, β-ionone and β-cyclocitral can poison L. turionifera by adjusting related gene expression to trigger PCD.

Toxic mechanism of eucalyptol and β-cyclocitral on Chlamydomonas reinhardtii by inducing programmed cell death

Eucalyptol and β-cyclocitral are 2 main compounds in cyanobacterial volatile organic compounds and can poison other algae. To uncover the toxic mechanism of the 2 compounds, the cell growth, photosynthetic abilities, H₂O₂ production, caspase-like activities, nuclear variation and DNA laddering were investigated in Chlamydomonas reinhardtii treated with eucalyptol and β-cyclocitral. Eucalyptol at ≥ 0.1 mM and β-cyclocitral at ≥ 0.05 mM showed toxic effects on C. reinhardtii cells, and 1.2 mM eucalyptol and 0.4 mM β-cyclocitral killed the whole of the cells during 24 h. During the death process, the photosynthetic pigment gradually degraded, and Fv/Fm gradually declined, indicating that the death is not a necrosis due to the gradual disappearance of the physiological process. In the treatments with 1.2 mM eucalyptol and 0.4 mM β-cyclocitral, H₂O₂ content burst at 10 min and 30 min, respectively. Caspase-9-like and caspase-3-like were activated, and cell nucleuses concentrated firstly and then broke with prolonging the treatment time. Meanwhile, DNA showed laddering after 1 h, and was gradually cleaved by Ca²⁺-dependent endonucleases to mainly about 100-250 bp fragments. These hallmarks indicated that eucalyptol and β-cyclocitral may poison other algal cells by inducing programmed cell death triggered by the increased H₂O₂.

Structure of acid deoxyribonuclease

Deoxyribonuclease II (DNase II) is also known as acid deoxyribonuclease because it has optimal activity at the low pH environment of lysosomes where it is typically found in higher eukaryotes. Interestingly, DNase II has also been identified in a few genera of bacteria and is believed to have arisen via horizontal transfer. Here, we demonstrate that recombinant Burkholderia thailandensis DNase II is highly active at low pH in the absence of divalent metal ions, similar to eukaryotic DNase II. The crystal structure of B. thailandensis DNase II shows a dimeric quaternary structure which appears capable of binding double-stranded DNA. Each monomer of B. thailandensis DNase II exhibits a similar overall fold as phospholipase D (PLD), phosphatidylserine synthase (PSS) and tyrosyl-DNA phosphodiesterase (TDP), and conserved catalytic residues imply a similar mechanism. The structural and biochemical data presented here provide insights into the atomic structure and catalytic mechanism of DNase II.

Acetic acid-induced programmed cell death and release of volatile organic compounds in Chlamydomonas reinhardtii

Acetic acid widely spreads in atmosphere, aquatic ecosystems containing residues and anoxic soil. It can inhibit aquatic plant germination and growth, and even cause programmed cell death (PCD) of yeast. In the present study, biochemical and physiological responses of the model unicellular green algae Chlamydomonas reinhardtii were examined after acetic acid stress. H(2)O(2) burst was found in C. reinhardtii after acetic acid stress at pH 5.0 for 10 min. The photosynthetic pigments were degraded, gross photosynthesis and respiration were disappeared gradually, and DNA fragmentation was also detected. Those results indicated that C. reinhardtii cells underwent a PCD but not a necrotic, accidental cell death event. It was noticed that C. reinhardtii cells in PCD released abundant volatile organic compounds (VOCs) upon acetic acid stress. Therefore, we analyzed the VOCs and tested their effects on other normal cells. The treatment of C. reinhardtii cultures with VOCs reduced the cell density and increased antioxidant enzyme activity. Therefore, a function of VOCs as infochemicals involved in cell-to-cell communication at the conditions of applied stress is suggested.

Erythropoietin: elucidating new cellular targets that broaden therapeutic strategies

Given that erythropoietin (EPO) is no longer believed to have exclusive biological activity in the hematopoietic system, EPO is now considered to have applicability in a variety of nervous system disorders that can overlap with vascular disease, metabolic impairments, and immune system function. As a result, EPO may offer efficacy for a broad number of disorders that involve Alzheimer's disease, cardiac insufficiency, stroke, trauma, and diabetic complications. During a number of clinical conditions, EPO is robust and can prevent metabolic compromise, neuronal and vascular degeneration, and inflammatory cell activation. Yet, use of EPO is not without its considerations especially in light of frequent concerns that may compromise clinical care. Recent work has elucidated a number of novel cellular pathways governed by EPO that can open new avenues to avert deleterious effects of this agent and offer previously unrecognized perspectives for therapeutic strategies. Obtaining greater insight into the role of EPO in the nervous system and elucidating its unique cellular pathways may provide greater cellular viability not only in the nervous system but also throughout the body.

Erythropoietin and oxidative stress

Unmitigated oxidative stress can lead to diminished cellular longevity, accelerated aging, and accumulated toxic effects for an organism. Current investigations further suggest the significant disadvantages that can occur with cellular oxidative stress that can lead to clinical disability in a number of disorders, such as myocardial infarction, dementia, stroke, and diabetes. New therapeutic strategies are therefore sought that can be directed toward ameliorating the toxic effects of oxidative stress. Here we discuss the exciting potential of the growth factor and cytokine erythropoietin for the treatment of diseases such as cardiac ischemia, vascular injury, neurodegeneration, and diabetes through the modulation of cellular oxidative stress. Erythropoietin controls a variety of signal transduction pathways during oxidative stress that can involve Janus-tyrosine kinase 2, protein kinase B, signal transducer and activator of transcription pathways, Wnt proteins, mammalian forkhead transcription factors, caspases, and nuclear factor kappaB. Yet, the biological effects of erythropoietin may not always be beneficial and may be poor tolerated in a number of clinical scenarios, necessitating further basic and clinical investigations that emphasize the elucidation of the signal transduction pathways controlled by erythropoietin to direct both successful and safe clinical care.

The Src homology 2 domain tyrosine phosphatases SHP-1 and SHP-2: diversified control of cell growth, inflammation, and injury

Interest in the diverse biology of protein tyrosine phosphatases that are encoded by more than 100 genes in the human genome continues to grow at an accelerated pace. In particular, two cytoplasmic protein tyrosine phosphatases composed of two Src homology 2 (SH2) NH2-terminal domains and a C-terminal protein-tyrosine phosphatase domain referred to as SHP-1 and SHP-2 are known to govern a host of cellular functions. SHP-1 and SHP-2 modulate progenitor cell development, cellular growth, tissue inflammation, and cellular chemotaxis, but more recently the role of SHP-1 and SHP-2 to directly control cell survival involving oxidative stress pathways has come to light. SHP-1 and SHP-2 are fundamental for the function of several growth factor and metabolic pathways yielding far reaching implications for disease pathways and disorders such as diabetes, neurodegeneration, and cancer. Although SHP-1 and SHP-2 can employ similar or parallel cellular pathways, these proteins also clearly exert opposing effects upon downstream cellular cascades that affect early and late apoptotic programs. SHP-1 and SHP-2 modulate cellular signals that involve phosphatidylinositol 3-kinase, Akt, Janus kinase 2, signal transducer and activator of transcription proteins, mitogen-activating protein kinases, extracellular signal-related kinases, c-Jun-amino terminal kinases, and nuclear factor-kappaB. Our progressive understanding of the impact of SHP-1 and SHP-2 upon multiple cellular environments and organ systems should continue to facilitate the targeted development of treatments for a variety of disease entities.

Mechanistic insights into diabetes mellitus and oxidative stress

Diabetes mellitus (DM) is a significant healthcare concern worldwide that affects more than 165 million individuals leading to cardiovascular disease, nephropathy, retinopathy, and widespread disease of both the peripheral and central nervous systems. The incidence of undiagnosed diabetes, impaired glucose tolerance, and impaired fasting glucose levels raises future concerns in regards to the financial and patient care resources that will be necessary to care for patients with DM. Interestingly, disease of the nervous system can become one of the most debilitating complications and affect sensitive cognitive regions of the brain, such as the hippocampus that modulates memory function, resulting in significant functional impairment and dementia. Oxidative stress forms the foundation for the induction of multiple cellular pathways that can ultimately lead to both the onset and subsequent complications of DM. In particular, novel pathways that involve metabotropic receptor signaling, protein-tyrosine phosphatases, Wnt proteins, Akt, GSK-3beta, and forkhead transcription factors may be responsible for the onset and progression of complications form DM. Further knowledge acquired in understanding the complexity of DM and its ability to impair cellular systems throughout the body will foster new strategies for the treatment of DM and its complications.

A systems view of haloarchaeal strategies to withstand stress from transition metals

Given that transition metals are essential cofactors in central biological processes, misallocation of the wrong metal ion to a metalloprotein can have resounding and often detrimental effects on diverse aspects of cellular physiology. Therefore, in an attempt to characterize unique and shared responses to chemically similar metals, we have reconstructed physiological behaviors of Halobacterium NRC-1, an archaeal halophile, in sublethal levels of Mn(II), Fe(II), Co(II), Ni(II), Cu(II), and Zn(II). Over 20% of all genes responded transiently within minutes of exposure to Fe(II), perhaps reflecting immediate large-scale physiological adjustments to maintain homeostasis. At steady state, each transition metal induced growth arrest, attempts to minimize oxidative stress, toxic ion scavenging, increased protein turnover and DNA repair, and modulation of active ion transport. While several of these constitute generalized stress responses, up-regulation of active efflux of Co(II), Ni(II), Cu(II), and Zn(II), down-regulation of Mn(II) uptake and up-regulation of Fe(II) chelation, confer resistance to the respective metals. We have synthesized all of these discoveries into a unified systems-level model to provide an integrated perspective of responses to six transition metals with emphasis on experimentally verified regulatory mechanisms. Finally, through comparisons across global transcriptional responses to different metals, we provide insights into putative in vivo metal selectivity of metalloregulatory proteins and demonstrate that a systems approach can help rapidly unravel novel metabolic potential and regulatory programs of poorly studied organisms.

Intracellular trafficking of nonviral vectors

Nonviral vectors continue to be attractive alternatives to viruses due to their low toxicity and immunogenicity, lack of pathogenicity, and ease of pharmacologic production. However, nonviral vectors also continue to suffer from relatively low levels of gene transfer compared to viruses, thus the drive to improve these vectors continues. Many studies on vector-cell interactions have reported that nonviral vectors bind and enter cells efficiently, but yield low gene expression, thus directing our attention to the intracellular trafficking of these vectors to understand where the obstacles occur. Here, we will review nonviral vector trafficking pathways, which will be considered here as the steps from cell binding to nuclear delivery. Studies on the intracellular trafficking of nonviral vectors has given us valuable insights into the barriers these vectors must overcome to mediate efficient gene transfer. Importantly, we will highlight the different approaches used by researchers to overcome certain trafficking barriers to gene transfer, many of which incorporate components from biological systems that have naturally evolved the capacity to overcome such obstacles. The tools used to study trafficking pathways will also be discussed.

Winding through the WNT pathway during cellular development and demise

In slightly over a period of twenty years, our comprehension of the cellular and molecular mechanisms that govern the Wnt signaling pathway continue to unfold. The Wnt proteins were initially implicated in viral carcinogenesis experiments associated with mammary tumors, but since this period investigations focusing on the Wnt pathways and their transmembrane receptors termed Frizzled have been advanced to demonstrate the critical nature of Wnt for the development of a variety of cell populations as well as the potential of the Wnt pathway to avert apoptotic injury. In particular, Wnt signaling plays a significant role in both the cardiovascular and nervous systems during embryonic cell patterning, proliferation, differentiation, and orientation. Furthermore, modulation of Wnt signaling under specific cellular influences can either promote or prevent the early and late stages of apoptotic cellular injury in neurons, endothelial cells, vascular smooth muscle cells, and cardiomyocytes. A number of downstream signal transduction pathways can mediate the biological response of the Wnt proteins that include Dishevelled, beta-catenin, intracellular calcium, protein kinase C, Akt, and glycogen synthase kinase-3beta. Interestingly, these cellular cascades of the Wnt-Frizzled pathways can participate in several neurodegenerative, vascular, and cardiac disorders and may be closely integrated with the function of trophic factors. Identification of the critical elements that modulate the Wnt-Frizzled signaling pathway should continue to unlock the potential of Wnt pathway for the development of new therapeutic options against neurodegenerative and vascular diseases.

Vital elements of the Wnt-Frizzled signaling pathway in the nervous system

Wnt proteins are cysteine-rich glycosylated proteins named after the Drosophilia Wingless (Wg) and the mouse Int-1 genes that play a role in embryonic cell patterning, proliferation, differentiation, orientation, adhesion, survival, and programmed cell death (PCD). Wnt proteins involve at least two intracellular signaling pathways. One pathway controls target gene transcription through beta-catenin, generally referred to as the canonical pathway and a second pathway pertains to intracellular calcium (Ca(2+)) release which is termed the non-canonical or Wnt/ Ca(2+) pathway. The majority of Wnt proteins activate gene transcription through the canonical signaling pathway regulated by pathways that include the Frizzled transmembrane receptor and the co-receptor LRP-5/6, Dishevelled, glycogen synthase kinase-3beta (GSK-3beta), adenomatous polyposis coli (APC), and beta-catenin. In contrast, the non-canonical Wnt signaling pathway has two intracellular signaling cascades that consist of the Wnt/ Ca(2+) pathway with protein kinase C (PKC) and the Wnt/PCP pathway involving Rho/Rac small GTPase and Jun N-terminal kinase (JNK). Through a series of signaling pathways, Wnt proteins modulate cell development, proliferation, and cell fate. In regards to cell survival and fate through PCD, Wnt may be critical for the prevention of tissue pathology that involves cytokine and growth factor control during disorders such as neuropsychiatric disease, retinal disease, and Alzheimer's disease. Elucidation of the vital elements that shape and control the Wnt-Frizzled signaling pathway may provide significant prospects for the treatment of disorders of the nervous system.

Driving cellular plasticity and survival through the signal transduction pathways of metabotropic glutamate receptors

Metabotropic glutamate receptors (mGluRs) share a common molecular morphology with other G protein-linked receptors, but there expression throughout the mammalian nervous system places these receptors as essential mediators not only for the initial development of an organism, but also for the vital determination of a cell's fate during many disorders in the nervous system that include amyotrophic lateral sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease, Multiple Sclerosis, epilepsy, trauma, and stroke. Given the ubiquitous distribution of these receptors, the mGluR system impacts upon neuronal, vascular, and glial cell function and is activated by a wide variety of stimuli that includes neurotransmitters, peptides, hormones, growth factors, ions, lipids, and light. Employing signal transduction pathways that can modulate both excitatory and inhibitory responses, the mGluR system drives a spectrum of cellular pathways that involve protein kinases, endonucleases, cellular acidity, energy metabolism, mitochondrial membrane potential, caspases, and specific mitogen-activated protein kinases. Ultimately these pathways can converge to regulate genomic DNA degradation, membrane phosphatidylserine (PS) residue exposure, and inflammatory microglial activation. As we continue to push the envelope for our understanding of this complex and critical family of metabotropic receptors, we should be able to reap enormous benefits for both clinical disease as well as our understanding of basic biology in the nervous system.

Oxidative stress in the brain: novel cellular targets that govern survival during neurodegenerative disease

Despite our present knowledge of some of the cellular pathways that modulate central nervous system injury, complete therapeutic prevention or reversal of acute or chronic neuronal injury has not been achieved. The cellular mechanisms that precipitate these diseases are more involved than initially believed. As a result, identification of novel therapeutic targets for the treatment of cellular injury would be extremely beneficial to reduce or eliminate disability from nervous system disorders. Current studies have begun to focus on pathways of oxidative stress that involve a variety of cellular pathways. Here we discuss novel pathways that involve the generation of reactive oxygen species and oxidative stress, apoptotic injury that leads to nuclear degradation in both neuronal and vascular populations, and the early loss of cellular membrane asymmetry that mitigates inflammation and vascular occlusion. Current work has identified exciting pathways, such as the Wnt pathway and the serine-threonine kinase Akt, as central modulators that oversee cellular apoptosis and their downstream substrates that include Forkhead transcription factors, glycogen synthase kinase-3beta, mitochondrial dysfunction, Bad, and Bcl-x(L). Other closely integrated pathways control microglial activation, release of inflammatory cytokines, and caspase and calpain activation. New therapeutic avenues that are just open to exploration, such as with brain temperature regulation, nicotinamide adenine dinucleotide modulation, metabotropic glutamate system modulation, and erythropoietin targeted expression, may provide both attractive and viable alternatives to treat a variety of disorders that include stroke, Alzheimer's disease, and traumatic brain injury.

Stress in the brain: novel cellular mechanisms of injury linked to Alzheimer's disease

More than a century has elapsed since the description of Alois Alzheimer's patient Auguste D. Yet, the well-documented generation of beta-amyloid aggregates and neurofibrillary tangles that define Alzheimer's disease is believed to represent only a portion of the cellular processes that can determine the course of Alzheimer's disease. Understanding of the complex nature of this disorder has evolved with an increased appreciation for pathways that involve the generation of reactive oxygen species and oxidative stress, apoptotic injury that leads to nuclear degradation in both neuronal and vascular populations, and the early loss of cellular membrane asymmetry that mitigates inflammation and vascular occlusion. Recent work has identified novel pathways, such as the Wnt pathway and the serine-threonine kinase Akt, as central modulators that oversee cellular apoptosis and the formation of neurofibrillary tangles through their downstream substrates that include glycogen synthase kinase-3beta, Bad, and Bcl-xL. Other closely integrated pathways control microglial activation, release of inflammatory cytokines, and caspase and calpain activation for the processing of amyloid precursor protein, tau protein cleavage, and presenilin disposal. New therapeutic avenues that are just open to exploration, such as with nicotinamide adenine dinucleotide modulation, cell cycle modulation, metabotropic glutamate system modulation, and erythropoietin targeted expression, may provide both attractive and viable alternatives to treat Alzheimer's disease.

Enhanced systemic transgene expression after nonviral salivary gland transfection using a novel endonuclease inhibitor/DNA formulation

Gene transfer to the major salivary glands is an attractive method for the systemic delivery of therapeutic proteins. To date, nonviral gene transfer to these glands has resulted in inadequate systemic protein concentrations. We believe that identification of the barriers responsible for this inefficient transfection will enable the development of enhanced nonviral gene transfer in salivary glands and other tissues. One potential barrier is the degradation of plasmid DNA by endonucleases. To test this hypothesis, we coadministered two endonuclease inhibitors ((zinc and aurintricarboxylic acid (ATA)) with plasmid DNA, containing the secreted alkaline phosphatase gene (SEAP), to the submandibular glands of rats. The effect of zinc and ATA on SEAP expression, tissue accumulation of plasmid DNA, and plasmid DNA stability was then characterized. We observed that mixtures containing zinc/DNA, ATA/DNA, and zinc/ATA/DNA significantly enhanced both systemic transgene expression and the amount of plasmid DNA associated with treated tissues. The relative endonuclease inhibitory activity of zinc, ATA, and zinc/ATA correlated with the observed effects on transfection efficacy. The use of zinc/ATA enhanced the efficacy of salivary gland transfection by at least 1000-fold versus DNA alone. Importantly, this improved performance resulted in robust systemic secretion of an exogenous protein (SEAP), thus demonstrating the potential this nonviral gene transfer technology has as a method to treat systemic protein deficiencies.

[Role of intracellular zinc in programmed cell death]

Apoptosis is a type of cell death involved in several biological events during tissue development, remodelling or involution. It could be induced by several extracellular or intracellular stimuli with an important role for metals like zinc or calcium. Cellular zinc is described as an inhibitor of apoptosis, while its depletion induces death in many cell lines. Using different chemical tools like specific zinc-chelators or ionophores, it is possible to study and understand the mechanisms of programmed cell death induction. The decrease in intracellular zinc concentration induces a characteristic apoptosis with apoptotic bodies formation and nuclear DNA condensation and fragmentation. This zinc depletion activates the caspases-3, -8 and -9, responsible for the proteolysis of several target proteins like poly(ADP-ribose) polymerase or transcription factors. Zinc addition in cell culture medium prevents the apparition of morphological and biochemical signs induced by intracellular zinc chelation, but also by other apoptosis inducers like etoposide or tumour necrosis factor alpha (TNF alpha). However, excess of zinc can also be cytotoxic. The balance between life and cell death is maintained by several zinc channels, controlling the intracellular zinc movements and the free amount of the metal.

Zinc resistance impairs sensitivity to oxidative stress in HeLa cells: protection through metallothioneins expression

To analyze the effects of high concentrations of zinc ions on oxidative stress protection, we developed an original model of zinc-resistant HeLa cells (HZR), by using a 200 microM zinc sulfate-supplemented medium. Resistant cells specifically accumulate high zinc levels in intracellular vesicles. These resistant cells also exhibit high expression of metallothioneins (MT), mainly located in the cytoplasm. Exposure of HZR to Zn-depleted medium for 3 or 7 d decreases the intracellular zinc content, but only slightly reduces MT levels of resistant cells. No changes of the intracellular redox status were detected, but zinc resistance enhanced H2O2-mediated cytotoxicity. Conversely, zinc-depleted resistant cells were protected against H2O2-induced cell death. Basal- and oxidant-induced DNA damage was increased in zinc resistant cells. Moreover, measurement of DNA damage on zinc-depleted resistant cells suggests that cytoplasmic metal-free MT ensures an efficient protection against oxidative DNA damage, while Zn-MT does not. This newly developed Zn-resistant HeLa model demonstrates that high intracellular concentrations of zinc enhance oxidative DNA damage and subsequent cell death. Effective protection against oxidative damage is provided by metallothionein under nonsaturating zinc conditions. Thus, induction of MT by zinc may mediate the main cellular protective effect of zinc against oxidative injury.

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.

High levels of zinc ions induce loss of mitochondrial potential and degradation of antiapoptotic Bcl-2 protein in in vitro cultivated human prostate epithelial cells

Prostate epithelial cells contain the highest levels of zinc among all organs and tissues in the human body. Zinc is accumulated primarily in the mitochondria, where it is responsible for inhibition of mitochondrial aconitase activity, thereby increasing citrate production. The present study was designed to clarify the role of zinc for human prostate epithelial cell growth and apoptosis. Apoptosis of in vitro cultivated human prostate epithelial cells exposed to ZnCl(2) was analyzed by determination of phospholipid membrane asymmetry, nuclear fragmentation, DNA strand breaks, changes of mitochondrial potential and cellular pro/antiapoptotic proteins. Zinc induced apoptosis without involvement of p53 by decreasing mitochondrial transmembrane potential (DeltaPsi(m)) and Bcl-2 protein levels in proliferating epithelial cells. Thus, the high local concentrations of zinc ions in the prostatic lumen seem to be necessary to regulate proliferative activities and to enforce epithelial differentiation processes.

The C. elegans apoptotic nuclease NUC-1 is related in sequence and activity to mammalian DNase II

The Caenorhabditis elegans nuc-1 gene has previously been implicated in programmed cell death due to the presence of persistent undegraded apoptotic DNA in nuc-1 mutant animals. In this report, we describe the cloning and characterization of nuc-1, which encodes an acidic nuclease with significant sequence similarity to mammalian DNase II. Database searches performed with human DNase II protein sequence revealed a significant similarity with the predicted C. elegans C07B5.5 ORF. Subsequent analysis of crude C. elegans protein extracts revealed that wild-type animals contained a potent endonuclease activity with a cleavage preference similar to DNase II, while nuc-1 mutant worms demonstrated a marked reduction in this nuclease activity. Sequence analysis of C07B5.5 DNA and mRNA also revealed that nuc-1(e1392), but not wild-type animals contained a nonsense mutation within the CO7B5.5 coding region. Furthermore, nuc-1 transgenic lines carrying the wild-type C07B5.5 locus demonstrated a complete complementation of the nuc-1 mutant phenotype. Our results therefore provide compelling evidence that the C07B5.5 gene encodes the NUC-1 apoptotic nuclease and that this nuclease is related in sequence and activity to DNase II.

DNases and apoptosis

Here we review the different apoptotic DNases. From a functional point of view, DNases implicated in apoptosis may be classified into three groups: the Ca2+/Mg2+endonucleases, the Mg2+-endonucleases, and the cation-independent endonucleases. The first group includes DNase I which has no specificity for the linker region, DNase gamma which has some homology with DNase I, and other DNases which cleave DNA in the linker region. Both DNase I and DNase gamma have been cloned. The other nucleases of this category have dispersed molecular weights. Their sequences are unknown and it is difficult to determine their role(s) in apoptosis. It seems that different pathways are present and that these nucleases may be activated either by caspases or serine proteases. The caspase 3 activated DNase (CAD, CPAN, or DFF40) belongs to the Mg2+-dependent endonucleases. DNase II belongs to the third group of acid endonucleases or cation-independent DNases. We have shown the involvement of DNase II in lens cell differentiation. Recently, the molecular structure of two different enzymes has been elucidated, one of which has a signal peptide and appears to be secreted. The other, called L-DNase II, is an intracellular protein having two enzymatic activities; in its native form, it is an anti-protease, and after posttranslational modification, it becomes a nuclease.Key words: endonucleases, apoptosis, caspases, serine proteases.

Nitric oxide induction of neuronal endonuclease activity in programmed cell death

Neuronal survival is intricately linked to the maintenance of intact DNA. In contrast, neuronal degeneration following nitric oxide (NO) exposure is dependent, in part, on the degradation of DNA through programmed cell death (PCD). We therefore investigated in primary rat hippocampal neurons the role of endogenous deoxyribonucleases, enzymes responsible for metabolically derived DNA cleavage, during NO-induced neurodegeneration. Twenty-four hours following exposure to the NO generators sodium nitroprusside (300 microM) and SIN-1 (300 microM), neuronal survival was reduced from approximately 88 to 23%. Treatment with aurintricarboxylic acid (1-100 microM), an endonuclease inhibitor, during NO exposure increased neuronal survival from 23 to 80% and decreased DNA fragmentation from 70 to 30% over a 24-h period. Enhancement of endonuclease activity alone with zinc chelation actively decreased neuronal survival from approximately 80% to approximately 34%. DNA digestion assays identified not only two constitutively active endonucleases, an acidic endonuclease (pH 4.0-7.0) and a calcium/magnesium-dependent endonuclease (pH 7.2-8.0), but also a NO-inducible magnesium-dependent endonuclease (pH 8.0). In the absence of endonuclease activity, DNA degradation did not occur during NO application, suggesting that endonuclease activity was a requisite pathway for NO-induced PCD. In addition, NO independently altered intracellular pH in ranges that were physiologically relevant for the activity of the endonucleases responsible for DNA degradation. Our identification and characterization of specific neuronal endonucleases suggest that the constitutive endonucleases may play a role in the initial stages of NO-induced PCD, but the subsequent "downstream" degradation of DNA may ultimately be dependent upon the NO-inducible endonuclease.