Ca2+ signal blockers can inhibit M/A transition in mammalian cells by interfering with the spindle checkpoint

Mechanisms Underlying Influence of Bioelectricity in Development

To execute the intricate process of development, cells coordinate across tissues and organs to determine where each cell divides and differentiates. This coordination requires complex communication between cells. Growing evidence suggests that bioelectrical signals controlled via ion channels contribute to cell communication during development. Ion channels collectively regulate the transmembrane potential of cells, and their function plays a conserved role in the development of organisms from flies to humans. Spontaneous calcium oscillations can be found in nearly every cell type and tissue, and disruption of these oscillations leads to defects in development. However, the mechanism by which bioelectricity regulates development is still unclear. Ion channels play essential roles in the processes of cell death, proliferation, migration, and in each of the major canonical developmental signaling pathways. Previous reviews focus on evidence for one potential mechanism by which bioelectricity affects morphogenesis, but there is evidence that supports multiple different mechanisms which are not mutually exclusive. Evidence supports bioelectricity contributing to development through multiple different mechanisms. Here, we review evidence for the importance of bioelectricity in morphogenesis and provide a comprehensive review of the evidence for several potential mechanisms by which ion channels may act in developmental processes.

Kv10.1 Regulates Microtubule Dynamics during Mitosis

Kv10.1 (potassium voltage-gated channel subfamily H member 1, known as EAG1 or Ether-à-go-go 1), is a voltage-gated potassium channel, prevailingly expressed in the central nervous system. The aberrant expression of Kv10.1 is detected in over 70% of all human tumor tissues and correlates with poorer prognosis. In peripheral tissues, Kv10.1 is expressed almost exclusively during the G2/M phase of the cell cycle and regulates its progression-downregulation of Kv10.1 extends the duration of the G2/M phase both in cancer and healthy cells. Here, using biochemical and imaging techniques, such as live-cell measurements of microtubule growth and of cytosolic calcium, we elucidate the mechanisms of Kv10.1-mediated regulation at the G2/M phase. We show that Kv10.1 has a dual effect on mitotic microtubule dynamics. Through the functional interaction with ORAI1 (calcium release-activated calcium channel protein 1), it modulates cytosolic calcium oscillations, thereby changing microtubule behavior. The inhibition of either Kv10.1 or ORAI1 stabilizes the microtubules. In contrast, the knockdown of Kv10.1 increases the dynamicity of mitotic microtubules, resulting in a stronger spindle assembly checkpoint, greater mitotic spindle angle, and a decrease in lagging chromosomes. Understanding of Kv10.1-mediated modulation of the microtubule architecture will help to comprehend how cancer tissue benefits from the presence of Kv10.1, and thereby increase the efficacy and safety of Kv10.1-directed therapeutic strategies.

Pretreatment with nimodipine reduces incidence of POCD by decreasing calcineurin mediated hippocampal neuroapoptosis in aged rats

Background

Calcineurin (CaN) having a high expression in hippocampal neurons is closely related to apoptosis. Pretreatment with nimodipine can lower the apoptosis rate of hippocampal neuron to reduce the incidence of postoperative cognitive dysfunction (POCD). However, the relationship between cerebral protective effect of pretreatment with nimodipine and CaN is controversial in the literature. The aim of this study is to evaluate the relationship between neuroprotective effect of nimodipine and CaN on POCD in aged rats.

Methods

Ninety-six 18-month-old male Sprague-Dawley rats were randomly assigned into 4 groups (n = 24 each): control group (Group C), nimodipine group (Group N), surgery group (Group S) and nimodipine + surgery group (Group N + S). In Group N and Group N + S, nimodipine 1 mg/kg was intraperitoneally injected, while the equal volume of normal saline was given instead in Group S. 30 min later, Group N and Group C inhaled pure oxygen for 2 h, and Group S and N + S inhaled 3% sevoflurane for 2 h when exploratory laparotomy was performed. Morris water maze test was performed on 1 day before operation and 1, 3 and 7 days after operation. After the end of Morris water maze test at 1 day before operation and 1 and 7 days after operation, 8 rats were sacrificed, brains were removed and hippocampal tissues were obtained for detection of apoptosis in hippocampal neurons, cytoplasmic calcium ([Ca²⁺]_i), and hippocampal CaN and caspase-3 expression.

Results

Compared with the 1st day before operation, the escape latency, apoptosis rate, [Ca²⁺]_i, expression of CaN and caspase-3 increased significantly, but the frequency of crossing the original platform decreased dramatically in Group S and N + S(P<0.05). In addition, the escape latency, apoptosis rate, [Ca²⁺]_i, and expression of CaN and caspase-3 decreased markedly, but the frequency of crossing the original platform increased significantly in Group N + S as compared with Group S (P<0.05).

Conclusions

Pretreatment with nimodipine reduces the incidence of POCD by decreasing CaN mediated hippocampal neuroapoptosis in aged rats.

Calcium depletion destabilises kinetochore fibres by the removal of CENP-F from the kinetochore

The attachment of spindle fibres to the kinetochore is an important process that ensures successful completion of the cell division. The Ca²⁺ concentration increases during the mitotic phase and contributes microtubule stability. However, its role in the spindle organisation in mitotic cells remains controversial. Here, we investigated the role of Ca²⁺ on kinetochore fibres in living cells. We found that depletion of Ca²⁺ during mitosis reduced kinetochore fibre stability. Reduction of kinetochore fibre stability was not due to direct inhibition of microtubule polymerisation by Ca²⁺-depletion but due to elimination of one dynamic component of kinetochore, CENP-F from the kinetochore. This compromised the attachment of kinetochore fibres to the kinetochore which possibly causes mitotic defects induced by the depletion of Ca²⁺.

Calcium signaling and cell cycle: Progression or death

Cytosolic Ca²⁺ concentration levels fluctuate in an ordered manner along the cell cycle, in line with the fact that Ca²⁺ is involved in the regulation of cell proliferation. Cell proliferation should be an error-free process, yet is endangered by mistakes. In fact, a complex network of proteins ensures that cell cycle does not progress until the previous phase has been successfully completed. Occasionally, errors occur during the cell cycle leading to cell cycle arrest. If the error is severe, and the cell cycle checkpoints work perfectly, this results into cellular demise by activation of apoptotic or non-apoptotic cell death programs. Cancer is characterized by deregulated proliferation and resistance against cell death. Ca²⁺ is a central key to these phenomena as it modulates signaling pathways that control oncogenesis and cancer progression. Here, we discuss how Ca²⁺ participates in the exogenous and endogenous signals controlling cell proliferation, as well as in the mechanisms by which cells die if irreparable cell cycle damage occurs. Moreover, we summarize how Ca²⁺ homeostasis remodeling observed in cancer cells contributes to deregulated cell proliferation and resistance to cell death. Finally, we discuss the possibility to target specific components of Ca²⁺ signal pathways to obtain cytostatic or cytotoxic effects.

Calcium ions function as a booster of chromosome condensation

Chromosome condensation is essential for the faithful transmission of genetic information to daughter cells during cell division. The depletion of chromosome scaffold proteins does not prevent chromosome condensation despite structural defects. This suggests that other factors contribute to condensation. Here we investigated the contribution of divalent cations, particularly Ca2+, to chromosome condensation in vitro and in vivo. Ca2+ depletion caused defects in proper mitotic progression, particularly in chromosome condensation after the breakdown of the nuclear envelope. Fluorescence lifetime imaging microscopy-Förster resonance energy transfer and electron microscopy demonstrated that chromosome condensation is influenced by Ca2+. Chromosomes had compact globular structures when exposed to Ca2+ and expanded fibrous structures without Ca2+. Therefore, we have clearly demonstrated a role for Ca2+ in the compaction of chromatin fibres.

Insecticide cytotoxicology in China: Current status and challenges

The insecticide cytotoxicology, as a new branch of toxicology, has rapidly developed in China. During the past twenty years, thousands of investigations have sprung up to evaluate the damages and clarify the mechanisms of insecticidal chemical substances to insect cells in vivo or in vitro. The mechanisms of necrosis, apoptosis or autophagy induced by synthetic or biogenic pesticides and virus infections have been systematically illuminated in many important models, including S2, BmN, SL-1, Sf21 and Sf9 cell lines. In addition, a variety of methods have also been applied to examine the effects of insecticides and elaborate the modes of action. As a result, many vital factors and pathways, such as cytochrome c, the Bcl-2 family and caspases, in mitochondrial signaling pathways, intracellular free calcium and lysosome signal pathways have been illuminated and drawn much attention. Benefiting from the application of insecticide cytotoxicology, natural products purifications, biological activities assessments of synthetic compounds and high throughput screening models have been accelerated in China. However, many questions remained, and there exist great challenges, especially in theory system, evaluation criterion, evaluation model, relationship between activity in vitro and effectiveness in vivo, and the toxicological mechanism. Fortunately, the generation of "omics" could bring opportunities for the development of insecticide cytotoxicology.

Effects of soybean agglutinin on mechanical barrier function and tight junction protein expression in intestinal epithelial cells from piglets

In this study, we sought to investigate the role of soybean agglutinin (SBA) in mediating membrane permeability and the mechanical barrier function of intestinal epithelial cells. The IPEC-J2 cells were cultured and treated with 0, 0.5, 1.0, 1.5, 2.0, 2.5, or 3.0 mg/mL SBA. Transepithelial electrical resistance (TEER) and alkaline phosphatase (AP) activity were measured to evaluate membrane permeability. The results showed a significant decrease in TEER values (p < 0.05) in a time- and dose-dependent manner, and a pronounced increase in AP activity (p < 0.05). Cell growth and cell morphology were used to evaluate the cell viability. A significant cell growth inhibition (p < 0.05) and alteration of morphology were observed when the concentration of SBA was increased. The results of western blotting showed that the expression levels of occludin and claudin-3 were decreased by 31% and 64% compared to those of the control, respectively (p < 0.05). In addition, immunofluorescence labeling indicated an obvious decrease in staining of these targets and changes in their localizations. In conclusion, SBA increased the membrane permeability, inhibited the cell viability and reduced the levels of tight junction proteins (occludin and claudin-3), leading to a decrease in mechanical barrier function in intestinal epithelial cells.

Calmodulin activation of Aurora-A kinase (AURKA) is required during ciliary disassembly and in mitosis

This study demonstrates for the first time that binding of calcium-activated calmodulin to a minimal interaction site within the disordered N-terminal domain is required for the essential Aurora-A activity in mitosis and in regulation of ciliary disassembly.

The centrosomal Aurora-A kinase (AURKA) regulates mitotic progression, and overexpression and hyperactivation of AURKA commonly promotes genomic instability in many tumors. Although most studies of AURKA focus on its role in mitosis, some recent work identified unexpected nonmitotic activities of AURKA. Among these, a role for basal body–localized AURKA in regulating ciliary disassembly in interphase cells has highlighted a role in regulating cellular responsiveness to growth factors and mechanical cues. The mechanism of AURKA activation involves interactions with multiple partner proteins and is not well understood, particularly in interphase cells. We show here that AURKA activation at the basal body in ciliary disassembly requires interactions with Ca²⁺ and calmodulin (CaM) and that Ca²⁺/CaM are important mediators of the ciliary disassembly process. We also show that Ca²⁺/CaM binding is required for AURKA activation in mitosis and that inhibition of CaM activity reduces interaction between AURKA and its activator, NEDD9. Finally, mutated derivatives of AURKA impaired for CaM binding and/or CaM-dependent activation cause defects in mitotic progression, cytokinesis, and ciliary resorption. These results define Ca²⁺/CaM as important regulators of AURKA activation in mitotic and nonmitotic signaling.

Aldosterone increases kidney tubule cell oxidants through calcium-mediated activation of NADPH oxidase and nitric oxide synthase

Chronic hyperaldosteronism has been associated with an increased cancer risk. We recently showed that aldosterone causes an increase in cell oxidants, DNA damage, and NF-κB activation. This study investigated the mechanisms underlying aldosterone-induced increase in cell oxidants in kidney tubule cells. Aldosterone caused an increase in both reactive oxygen and reactive nitrogen (RNS) species. The involvement of the activation of NADPH oxidase in the increase in cellular oxidants was demonstrated by the inhibitory action of the NADPH oxidase inhibitors DPI, apocynin, and VAS2870 and by the migration of the p47 subunit to the membrane. NADPH oxidase activation occurred as a consequence of an increase in cellular calcium levels and was mediated by protein kinase C. The prevention of RNS increase by BAPTA-AM, W-7, and L-NAME indicates a calcium-calmodulin activation of NOS. A similar pattern of effects of the NADPH oxidase and NOS inhibitors was observed for aldosterone-induced DNA damage and NF-κB activation, both central to the pathogenesis of chronic aldosteronism. In summary, this paper demonstrates that aldosterone, via the mineralocorticoid receptor, causes an increase in kidney cell oxidants, DNA damage, and NF-κB activation through a calcium-mediated activation of NADPH oxidase and NOS. Therapies targeting calcium, NOS, and NADPH oxidase could prevent the adverse effects of hyperaldosteronism on kidney function as well as its potential oncogenic action.

Rhythmic actomyosin-driven contractions induced by sperm entry predict mammalian embryo viability

Fertilization-induced cytoplasmic flows are a conserved feature of eggs in many species. However, until now the importance of cytoplasmic flows for the development of mammalian embryos has been unknown. Here, by combining a rapid imaging of the freshly fertilized mouse egg with advanced image analysis based on particle image velocimetry, we show that fertilization induces rhythmical cytoplasmic movements that coincide with pulsations of the protrusion forming above the sperm head. We find that these movements are caused by contractions of the actomyosin cytoskeleton triggered by Ca²⁺ oscillations induced by fertilization. Most importantly, the relationship between the movements and the events of egg activation makes it possible to use the movements alone to predict developmental potential of the zygote. In conclusion, this method offers, thus far, the earliest and fastest, non-invasive way to predict the viability of eggs fertilized in vitro and therefore can potentially improve greatly the prospects for IVF treatment.

Cytoplasmic flows—the movement of cytoplasmic material—can be detected following the fertilization of an egg by a sperm in many species. In this study, rhythmic cytoplasmic flows are shown to be induced in mice by calcium-induced cytoskeleton contractions which could be used to predict the successful outcome of fertilization.

Dietary reference values of individual micronutrients and nutriomes for genome damage prevention: current status and a road map to the future

Damage to the genome is recognized as a fundamental cause of developmental and degenerative diseases. Several micronutrients play an important role in protecting against DNA damage events generated through endogenous and exogenous factors by acting as cofactors or substrates for enzymes that detoxify genotoxins as well as enzymes involved in DNA repair, methylation, and synthesis. In addition, it is evident that either micronutrient deficiency or micronutrient excess can modify genome stability and that these effects may also depend on nutrient-nutrient and nutrient-gene interaction, which is affected by genotype. These observations have led to the emerging science of genome health nutrigenomics, which is based on the principle that DNA damage is a fundamental cause of disease that can be diagnosed and nutritionally prevented on an individual, genetic subgroup, or population basis. In this article, the following topics are discussed: 1) biomarkers used to study genome damage in humans and their validation, 2) evidence for the association of genome damage with developmental and degenerative disease, 3) current knowledge of micronutrients required for the maintenance of genome stability in humans, 4) the effect of nutrient-nutrient and nutrient-genotype interaction on DNA damage, and 5) strategies to determine dietary reference values of single micronutrients and micronutrient combinations (nutriomes) on the basis of DNA damage prevention. This article also identifies important knowledge gaps and future research directions required to shed light on these issues. The ultimate goal is to match the nutriome to the genome to optimize genome maintenance and to prevent pathologic amounts of DNA damage.

Global Gene Expression Profiling of Hyperkeratotic Skin Lesions from Inner Mongolians Chronically Exposed to Arsenic

The skin is an organ that is highly sensitive to chronic arsenic (As) exposure. Skin lesions such as hyperkeratoses (HKs) are common early manifestations of arsenicosis in humans. HKs can be precursor lesions of nonmelanoma skin cancers (NMSCs), but the driving forces behind their formation and how they may ultimately progress to NMSCs are unknown. The goal of this study was to examine the global gene expression profiles of As-related HKs in an effort to better understand gene expression changes that are potentially associated with early stages of As carcinogenesis. HK biopsies were removed from individuals living in an arsenicosis-endemic region in Inner Mongolia who had been exposed to high As levels in their drinking water for >20 years. Gene expression profiling was performed on RNA isolated from 7 individuals in this group and from 4 lesion-free skin samples from healthy individuals. Consistent with the pathological characteristics of the HK lesions, major functional categories and known canonical pathways represented by altered transcripts include those involved in development, differentiation, apoptosis, proliferation, and stress response. The results of this study may help define a signature profile of gene expression changes associated with long-term As exposure in the skin.

Transient receptor potential channel C3 contributes to the progression of human ovarian cancer

Ovarian cancer (OC) is the leading cause of death from gynecological malignancy. However, the mechanism by which OC develops remains largely unknown. Increases in cytosolic free Ca(2+) ([Ca(2+)](i)) can result in different physiological changes including cell growth, differentiation and death. The transient receptor potential (TRP) C channels are nonselective cation channels with permeability to Ca(2+). Here we report that TRPC3 channels promote human OC growth. The TRPC3 protein levels in human OC specimens were greatly increased than those in normal ovarian specimens. Downregulating TRPC3 expression in SKOV3 cells, a human OC cell line, led to reduction of proliferation, suppression in epidermal growth factor-induced Ca(2+) influx, dephosphorylation of Cdc2 and CaMKIIalpha and prolonged progression through M phase of these cells. Further, decreased the expression of TRPC3 suppressed the tumor formation generated by injecting SKOV3 cells in nude mice. Together, our results suggest that increased activity of TRPC3 channels is necessary for the development of OCs.

Boric acid inhibits stored Ca2+ release in DU-145 prostate cancer cells

Boron (B) is a developmental and reproductive toxin. It is also essential for some organisms. Plants use uptake and efflux transport proteins to maintain homeostasis, and in humans, boron has been reported to reduce prostate cancer. Ca2+ signaling is one of the primary mechanisms used by cells to respond to their environment. In this paper, we report that boric acid (BA) inhibits NAD+ and NADP+ as well as mechanically induced release of stored Ca2+ in growing DU-145 prostate cancer cells. Cell proliferation was inhibited by 30% at 100 microM, 60% at 250 microM, and 97% at 1,000 microM BA. NAD+-induced Ca2+ transients were partly inhibited at 250 microM BA and completely at 1,000 microM BA, whereas both NADP+ and mechanically induced transients were inhibited by 1,000 microM BA. Expression of CD38 protein increased in proportion to BA exposure (0-1,000 microM). In vitro mass spectrometry analysis showed that BA formed adducts with the CD38 products and Ca2+ channel agonists cyclic adenosine diphosphate ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP). Vesicles positive for the Ca2+ fluorophore fluo-3 acetoxymethyl ester accumulated in cells exposed to 250 and 1,000 microM BA. The BA analog, methylboronic acid (MBA; 250 and 1,000 microM), did not inhibit cell proliferation or NAD+, NADP+, or mechanically stimulated Ca2+ store release. Nor did MBA increase CD38 expression or cause the formation of intracellular vesicles. Thus, mammalian cells can distinguish between BA and its synthetic analog MBA and exhibit graded concentration-dependent responses. Based on these observations, we hypothesize that toxicity of BA stems from the ability of high concentrations to impair Ca2+ signaling.

Genome-health nutrigenomics and nutrigenetics: nutritional requirements or ‘nutriomes’ for chromosomal stability and telomere maintenance at the individual level

It is becoming increasingly evident that (a) risk for developmental and degenerative disease increases with more DNA damage, which in turn is dependent on nutritional status, and (b) the optimal concentration of micronutrients for prevention of genome damage is also dependent on genetic polymorphisms that alter the function of genes involved directly or indirectly in the uptake and metabolism of micronutrients required for DNA repair and DNA replication. The development of dietary patterns, functional foods and supplements that are designed to improve genome-health maintenance in individuals with specific genetic backgrounds may provide an important contribution to an optimum health strategy based on the diagnosis and individualised nutritional prevention of genome damage, i.e. genome health clinics. The present review summarises some of the recent knowledge relating to micronutrients that are associated with chromosomal stability and provides some initial insights into the likely nutritional factors that may be expected to have an impact on the maintenance of telomeres. It is evident that developing effective strategies for defining nutrient doses and combinations or ‘nutriomes’ for genome-health maintenance at the individual level is essential for further progress in this research field.

Quantitative imaging of subcellular calcium stores in mammalian LLC-PK1 epithelial cells undergoing mitosis by SIMS ion microscopy

Quantitative 3-D total calcium gradients, representing subcellular stored calcium, were imaged with a CAMECA IMS-3f SIMS ion microscope in cryogenically prepared frozen freeze-dried LLC-PK1 cells captured in interphase and various stages of mitosis. 39K and 23Na concentrations were also measured in the same cells. Correlative optical (or SEM) and SIMS analysis of cells revealed a redistribution of the interphase Golgi calcium store in prophase and prometaphase cells. In metaphase cells, simultaneous SIMS imaging of total calcium in both the spindle and the non-spindle cytoplasm of individual cells revealed a gradual and dynamic alignment of calcium stores in both half-spindles prior to the onset of anaphase. The anaphase cells revealed the highest local total calcium concentrations in the spindle regions behind the daughter chromosomes and the lowest in the central spindle region. The pericentriolar material in telophase cells contained calcium stores. Quantitatively, a typical metaphase cell with well-aligned calcium stores in the spindle region contained 1.1 mM total calcium in each half-spindle, 0.8 mM total calcium in the non-spindle cytoplasm, and 0.5mM total calcium in the chromosomes. At the submicron scale, the distribution of total calcium was heterogeneous in the chromosomes, metaphase spindle, and non-spindle cytoplasm. An increased binding of calcium to chromosomes is not a physiological requirement for chromosomal condensation in mitosis, since interphase nuclei and mitotic chromosomes contained comparable total calcium concentrations measured per unit volume. A significant reduction of total calcium in the non-spindle cytoplasm was observed in the metaphase, anaphase, and telophase cells, which is indicative of the limited storage of the releasable calcium pool in these specific stages of mitosis. Direct total calcium measurements in subcellular regions confirmed that both the spindle and the non-spindle cytoplasm of metaphase cells contained inositol 1,4,5-trisphosphate (IP3)-sensitive calcium stores sensitive to arginine vasopressin, thapsigargin, and calcium ionophore A23187. The dynamic alignment of calcium stores in both half-spindles may be an integral part of the time-dependent process of a cell's overall preparation for exiting the metaphase stage in mammalian LLC-PK1 cells.

Strontium promotes calcium oscillations in mouse meiotic oocytes and early embryos through InsP3 receptors, and requires activation of phospholipase and the synergistic action of InsP3

BACKGROUND

Sr2+ is the most efficient agent for mouse oocyte activation and functions by inducing Ca2+ oscillations. However, its specific mechanism of action remains unknown. Here we investigated the specificity and possible mechanism of Sr2+-induced Ca2+ oscillations in mouse oocytes and early embryos.

METHODS

Ca2+ oscillations in oocytes and embryos were measured by ratiometric fluorescence imaging using fura-2AM. The role of phospholipase C (PLC) and inositol trisphosphate (InsP3) receptors in Sr2+-induced Ca2+ oscillations was examined by selective inhibitors.

RESULTS

Sr2+ can induce Ca2+ oscillations in both immature and mature oocytes, and in early embryos. A cell cycle stage-dependent phenomenon to Sr2+ stimulation was observed in 1-cell embryos. By using a low molecular weight heparin to antagonize the function of InsP3 receptors, we were able to show that InsP3 receptors are essential for Sr2+-induced Ca2+ oscillations. Treating metaphase II (MII) oocytes with the PLC inhibitor, U73122, abolished Sr2+-induced increases in Ca2+. This inhibitory effect of U73122 could be rescued by microinjection of InsP3, indicating that Sr2+-induced Ca2+ oscillations require the synergistic action of InsP3.

CONCLUSIONS

Sr2+-induced calcium oscillations in mouse oocytes and early embryos are mediated through InsP3 receptors, and require PLC activation and the synergistic action of InsP3.

Intracellular calcium disturbances induced by arsenic and its methylated derivatives in relation to genomic damage and apoptosis induction

Arsenic and its methylated derivatives are contaminants of air, water, and food and are known as toxicants and carcinogens. Arsenic compounds are also being used as cancer chemotherapeutic agents. In humans, inorganic arsenic is metabolically methylated to mono-, di-, and trimethylated forms. Recent findings suggest that the methylation reactions represent a toxification rather than a detoxification pathway. In recent years, the correlation between arsenic exposure, cytotoxicity and genotoxicity, mutagenicity, and tumor promotion has been established, as well as the association of arsenic exposure with perturbation of physiologic processes, generation of reactive oxygen species, DNA damage, and apoptosis induction. Trivalent forms of arsenic have been found to induce apoptosis in several cellular systems with involvement of membrane-bound cell death receptors, activation of caspases, release of calcium stores, and changes of the intracellular glutathione level. It is well known that calcium ion deregulation plays a critical role in apoptotic cell death. A calcium increase in the nuclei might lead to toxic effects in the cell. In this review, we highlight the relationship between induced disturbances of calcium homeostasis, genomic damage, and apoptotic cell death caused by arsenic and its organic derivatives.

Low intake of calcium, folate, nicotinic acid, vitamin E, retinol, beta-carotene and high intake of pantothenic acid, biotin and riboflavin are significantly associated with increased genome instability--results from a dietary intake and micronucleus index survey in South Australia

The aim of this study was to determine the association between dietary intake, determined using a food frequency questionnaire, and genome damage in lymphocytes measured using the micronucleus (MN) assay. The study, performed on 190 healthy individuals (mean age 47.8 years, 46% males), also examined whether a supplementation with beta-carotene, vitamins C and E along with zinc (ACEZn), in a randomized trial for 6 months, improves genome stability. Multivariate analysis of baseline data showed that (1) the highest tertile of intake of vitamin E, retinol, folic acid, nicotinic acid (preformed) and calcium is associated with significant reductions in MN frequency, i.e. -28, -31, -33, -46 and -49%, respectively (P < 0.005) relative to the lowest tertile of intake and (2) the highest tertile of intake of riboflavin, pantothenic acid and biotin was associated with significant increases in MN frequency, i.e. +36% (P = 0.054), +51% (P = 0.021), and +65% (P = 0.001), respectively, relative to the lowest tertile of intake. Mid-tertile beta-carotene intake was associated with an 18% reduction in MN frequency (P = 0.038); however, the highest tertile of intake (>6400 microg/day) resulted in an 18% increment in MN frequency. Supplementation with ACEZn significantly reduced the MN index by 13% (P = 0.038). The study also showed interactive additive effects such as the protective effect of increased calcium intake (-46%) and the exacerbating effect of riboflavin (+42%) on increased genome damage caused by low folate intake. The results from this study illustrate the strong impact of a wide variety of micronutrients and their interactions on genome health, depending on the level of intake.

Fertilization and InsP3-induced Ca2+ release stimulate a persistent increase in the rate of degradation of cyclin B1 specifically in mature mouse oocytes

Vertebrate oocytes proceed through meiosis I before undergoing a cytostatic factor (CSF)-mediated arrest at metaphase of meiosis II. Exit from MII arrest is stimulated by a sperm-induced increase in intracellular Ca2+. This increase in Ca2+ results in the destruction of cyclin B1, the regulatory subunit of cdk1 that leads to inactivation of maturation promoting factor (MPF) and egg activation. Progression through meiosis I also involves cyclin B1 destruction, but it is not known whether Ca2+ can activate the destruction machinery during MI. We have investigated Ca2+ -induced cyclin destruction in MI and MII by using a cyclin B1-GFP fusion protein and measurement of intracellular Ca2+. We find no evidence for a role for Ca2+ in MI since oocytes progress through MI in the absence of detectable Ca2+ transients. Furthermore, Ca2+ increases induced by photorelease of InsP3 stimulate a persistent destruction of cyclin B1-GFP in MII but not MI stage oocytes. In addition to a steady decrease in cyclin B1-GFP fluorescence, the increase in Ca2+ stimulated a transient decrease in fluorescence in both MI and MII stage oocytes. Similar transient decreases in fluorescence imposed on a more persistent fluorescence decrease were detected in cyclin-GFP-injected eggs undergoing fertilization-induced Ca2+ oscillations. The transient decreases in fluorescence were not a result of cyclin B1 destruction since transients persisted in the presence of a proteasome inhibitor and were detected in controls injected with eGFP and in untreated oocytes. We conclude that increases in cytosolic Ca2+ induce transient changes in autofluorescence and that the pattern of cyclin B1 degradation at fertilization is not stepwise but exponential. Furthermore, this Ca2+ -induced increase in degradation of cyclin B1 requires factors specific to mature oocytes, and that to overcome arrest at MII, Ca2+ acts to release the CSF-mediated brake on cyclin B1 destruction.