Arsenic trioxide induces abnormal mitotic spindles through a PIP4KIIγ/Rho pathway

Gene expression analyses reveal potential mechanism of inorganic arsenic-induced apoptosis in zebrafish

Our previous study showed that sodium arsenite (200 mg/L) affected the nervous system and induced motor neuron development via the Sonic hedgehog pathway in zebrafish larvae. To gain more insight into the effects of arsenite on other signaling pathways, including apoptosis, we have performed quantitative polymerase chain reaction array-based gene expression analyses. The 96-well array plates contained primers for 84 genes representing 10 signaling pathways that regulate several biological functions, including apoptosis. We exposed eggs at 5 h postfertilization until the 72 h postfertilization larval stage to 200 mg/L sodium arsenite. In the Janus kinase/signal transducers and activators of transcription, nuclear factor κ-light-chain-enhancer of activated B cells, and Wingless/Int-1 signaling pathways, the expression of only one gene in each pathway was significantly altered. The expression of multiple genes was altered in the p53 and oxidative stress pathways. Sodium arsenite induced excessive apoptosis in the larvae. This compelled us to analyze specific genes in the p53 pathway, including cdkn1a, gadd45aa, and gadd45ba. Our data suggest that the p53 pathway is likely responsible for sodium arsenite-induced apoptosis. In addition, sodium arsenite significantly reduced global DNA methylation in the zebrafish larvae, which may indicate that epigenetic factors could be dysregulated after arsenic exposure. Together, these data elucidate potential mechanisms of arsenic toxicity that could improve understanding of arsenic's effects on human health.

Sodium arsenite and dimethylarsenic acid induces apoptosis in OC3 oral cavity cancer cells

Although arsenic is an environmental toxicant, arsenic trioxide (ATO) is used to treat acute promyelocytic leukemia (APL) with anticancer effects. Studies have demonstrated oral cancer is in the top 10 cancers in Taiwan. High rate of oral cancers is linked to various behaviors, such as excessive alcohol consumption and tobacco use. Similarly, betel chewing is a strong risk factor in oral cancer. In the present study, oral squamous carcinoma OC3 cells were investigated with the treatments of sodium arsenite (NaAsO2) and dimethylarsenic acid (DMA), respectively, to examine if arsenic compounds have anti‑cancer efforts. It was found that 1 µM NaAsO2 and 1 mM DMA for 24 h induced rounded contours with membrane blebbing phenomena in OC3 cells, revealing cell apoptotic characteristics. In addition, NaAsO2 (10‑100 µM) and DMA (1‑100 mM) significantly decreased OC3 cell survival. In cell cycle regulation detected by flow cytometry, NaAsO2 and DMA significantly augmented percentage of subG1 and G2/M phases in OC3 cells, respectively. Annexin V/PI double staining assay was further used to confirm NaAsO2 and DMA did induce OC3 cell apoptosis. In mechanism investigation, western blotting assay was applied and the results showed that NaAsO2 and DMA significantly induced phosphorylation of JNK, ERK1/2 and p38 and then the cleavages of caspase‑8, ‑9, ‑3 and poly ADP‑ribose polymerase (PARP) in OC3 cells, dynamically. In conclusion, NaAsO2 and DMA activated MAPK pathways and then apoptotic pathways to induce OC3 oral cancer cell apoptosis.

The Development and Clinical Applications of Oral Arsenic Trioxide for Acute Promyelocytic Leukaemia and Other Diseases

Appreciation of the properties of arsenic trioxide (ATO) has redefined the treatment landscape for acute promyelocytic leukaemia (APL) and offers promise as a treatment for numerous other diseases. The benefits of ATO in patients with APL is related to its ability to counteract the effects of PML::RARA, an oncoprotein that is invariably detected in the blood or bone marrow of affected individuals. The PML::RARA oncoprotein is degraded specifically by binding to ATO. Thus ATO, in combination with all-trans retinoic acid, has become the curative treatment for ATO. The multiple mechanisms of action of ATO has also paved the way for application in various condition encompassing autoimmune or inflammatory disorders, solid organ tumours, lymphomas and other subtypes of AML. The development of oral formulation of ATO (oral ATO) has reduced costs of treatment and improved treatment convenience allowing widespread applicability. In this review, we discuss the mechanisms of action of ATO, the development of oral ATO, and the applications of oral ATO in APL and other diseases.

Arsenic compounds induce apoptosis by activating the MAPK and caspase pathways in FaDu oral squamous carcinoma cells

For a number of years, oral cancer has remained in the top ten most common types of cancer, with an incidence rate that is steadily increasing. In total, ~75% oral cancer cases are associated with lifestyle factors, including uncontrolled alcohol consumption, betel and tobacco chewing, and the excessive use of tobacco. Notably, betel chewing is highly associated with oral cancer in Southeast Asia. Arsenic is a key environmental toxicant; however, arsenic trioxide has been used as a medicine for the treatment of acute promyelocytic leukemia, highlighting its anticancer properties. The present study aimed to investigate the role of arsenic compounds in the treatment of cancer, using FaDu oral squamous carcinoma cells treated with sodium arsenite (NaAsO₂) and dimethyl arsenic acid (DMA). The results demonstrated that FaDu cells exhibited membrane blebbing phenomena and high levels of apoptosis following treatment with 10 µM NaAsO₂ and 1 mM DMA for 24 h. The results of cell viability assay demonstrated that the rate of FaDu cell survival was markedly reduced as the concentration of arsenic compounds increased from 10 to 100 µM NaAsO₂, and 1 to 100 mM DMA. Moreover, flow cytometry was carried out to further examine the effects of arsenic compounds on FaDu cell cycle regulation; the results revealed that treatment with NaAsO₂ and DMA led to a significant increase in the percentage of FaDu cells in the sub‑G1 and G2/M phases of the cell cycle. An Annexin V/PI double staining assay was subsequently performed to verify the levels of FaDu cell apoptosis following treatment with arsenic compounds. Furthermore, the results of the western blot analyses revealed that the expression levels of caspase‑8, ‑9 and ‑3, and poly ADP‑ribose polymerase, as well the levels of phosphorylated JNK and ERK1/2 were increased following treatment with NaAsO₂ and DMA in the FaDu cells. On the whole, the results of the present study revealed that treatment with NaAsO₂ and DMA promoted the apoptosis of FaDu oral cancer cells, by activating MAPK pathways, as well as the extrinsic and intrinsic apoptotic pathways.

Mdivi-1 induces spindle abnormalities and augments taxol cytotoxicity in MDA-MB-231 cells

Taxol is a first-line chemotherapeutic for numerous cancers, including the highly refractory triple-negative breast cancer (TNBC). However, it is often associated with toxic side effects and chemoresistance in breast cancer patients, which greatly limits the clinical utility of the drug. Hence, compounds that act in concert with taxol to promote cytotoxicity may be useful to improve the efficacy of taxol-based chemotherapy. In this study, we demonstrated that mdivi-1, a putative inhibitor of mitochondrial fission protein Drp1, enhances the anticancer effects of taxol and overcomes taxol resistance in a TNBC cell line (MDA-MB-231). Not only did mdivi-1 induce mitotic spindle abnormalities and mitotic arrest when used alone, but it also enhanced taxol-induced antimitotic effects when applied in combination. In addition, mdivi-1 induced pronounced spindle abnormalities and cytotoxicity in a taxol-resistant cell line, indicating that it can overcome taxol resistance. Notably, the antimitotic effects of mdivi-1 were not accompanied by prominent morphological or functional alterations in mitochondria and were Drp1-independent. Instead, mdivi-1 exhibited affinity to tubulin at μM level, inhibited tubulin polymerization, and immediately disrupted spindle assembly when cells entered mitosis. Together, our results show that mdivi-1 associates with tubulin and impedes tubulin polymerization, actions which may underlie its antimitotic activity and its ability to enhance taxol cytotoxicity and overcome taxol resistance in MDA-MB-231 cells. Furthermore, our data imply a possibility that mdivi-1 could be useful to improve the therapeutic efficacy of taxol in breast cancer.

Arsenic Exposure and Compromised Protein Quality Control

Exposure to arsenic in contaminated drinking water is a worldwide public health problem that affects more than 200 million people. Protein quality control constitutes an evolutionarily conserved mechanism for promoting proper folding of proteins, refolding of misfolded proteins, and removal of aggregated proteins, thereby maintaining homeostasis of the proteome (i.e., proteostasis). Accumulating lines of evidence from epidemiological and laboratory studies revealed that chronic exposure to inorganic arsenic species can elicit proteinopathies that contribute to neurodegenerative disorders, cancer, and type II diabetes. Here, we review the effects of arsenic exposure on perturbing various elements of the proteostasis network, including mitochondrial homeostasis, molecular chaperones, inflammatory response, ubiquitin-proteasome system, autophagy, as well as asymmetric segregation and axonal transport of misfolded proteins. We also discuss arsenic-induced disruptions of post-translational modifications of proteins, for example, ubiquitination, and their implications in proteostasis. Together, studies in the past few decades support that disruption of protein quality control may constitute an important mechanism underlying the arsenic-induced toxicity.

First evaluation of novel potential synergistic effects of glyphosate and arsenic mixture on Rhinella arenarum (Anura: Bufonidae) tadpoles

The toxicity of glyphosate-based herbicide (GBH) and arsenite (As(III)) as individual toxicants and in mixture (50:50 v/v, GBH-As(III)) was determined in Rhinella arenarum tadpoles during acute (48 h) and chronic assays (22 days). In both types of assays, the levels of enzymatic activity [Acetylcholinesterase (AChE), Carboxylesterase (CbE), and Glutathione S-transferase (GST)] and the levels of thyroid hormones (triiodothyronine; T3 and thyroxine; T4) were examined. Additionally, the mitotic index (MI) of red blood cells (RBCs) and DNA damage index were calculated for the chronic assay. The results showed that the LC50 values at 48 h were 45.95 mg/L for GBH, 37.32 mg/L for As(III), and 30.31 mg/L for GBH-As(III) (with similar NOEC = 10 mg/L and LOEC = 20 mg/L between the three treatments). In the acute assay, Marking's additive index (S = 2.72) indicated synergistic toxicity for GBH-As(III). In larvae treated with GBH and As(III) at the NOEC-48h (10 mg/L), AChE activity increased by 36.25% and 33.05% respectively, CbE activity increased by 22.25% and 39.05 % respectively, and GST activity increased by 46.75% with the individual treatment with GBH and by 131.65 % with the GBH-As(III) mixture. Larvae exposed to the GBH-As(III) mixture also showed increased levels of T4 (25.67 %). In the chronic assay at NOEC-48h/8 (1.25 mg/L), As(III) and GBH-As(III) inhibited AChE activity (by 39.46 % and 35.65%, respectively), but did not alter CbE activity. In addition, As(III) highly increased (93.7 %) GST activity. GBH-As(III) increased T3 (97.34%) and T4 (540.93%) levels. Finally, GBH-As(III) increased the MI of RBCs and DNA damage. This study demonstrated strong synergistic toxicity of the GBH-As(III) mixture, negatively altering antioxidant systems and thyroid hormone levels, with consequences on RBC proliferation and DNA damage in treated R. arenarum tadpoles.

Phosphatidylinositol-5-phosphate 4-kinase gamma accumulates at the spindle pole and prevents microtubule depolymerization

Background

A previous screen of a human kinase and phosphatase shRNA library to select genes that mediate arsenite induction of spindle abnormalities resulted in the identification of phosphatidylinositol-5-phosphate 4-kinase type-2 gamma (PIP4KIIγ), a phosphatidylinositol 4,5-bisphosphate (PIP2)-synthesizing enzyme. In this study, we explored how PIP4KIIγ regulates the assembly of mitotic spindles.

Results

PIP4KIIγ accumulates at the spindle pole before anaphase, and is required for the assembly of functional bipolar spindles. Depletion of PIP4KIIγ enhanced the spindle pole accumulation of mitotic centromere-associated kinesin (MCAK), a microtubule (MT)-depolymerizing kinesin, and resulted in a less stable spindle pole-associated MT. Depletion of MCAK can ameliorate PIP4KIIγ depletion-induced spindle abnormalities. In addition, PIP2 binds to polo-like kinase (PLK1) and reduces PLK1-mediated phosphorylation of MCAK. These results indicate that PIP4KIIγ and PIP2 may negatively regulate the MT depolymerization activity of MCAK by reducing PLK1-mediated phosphorylation of MCAK. Consequently, depletion of PLK1 has been shown to counteract the PIP4KIIγ depletion-induced instability of spindle pole-associated MT and cell resistance to arsenite.

Conclusions

Our current results imply that PIP4KIIγ may restrain MT depolymerization at the spindle pole through attenuating PLK1-mediated activation of MCAK before anaphase onset.

HSP70 regulates the function of mitotic centrosomes

To establish a functional bipolar mitotic spindle, the centrosome expands and matures, acquiring enhanced activities for microtubule (MT) nucleation and assembly at the onset of mitosis. However, the regulatory mechanisms of centrosome maturation and MT assembly from the matured centrosome are largely unknown. In this study, we showed that heat shock protein (HSP) 70 considerably accumulates at the mitotic centrosome during prometaphase to metaphase and is required for bipolar spindle assembly. Inhibition or depletion of HSP70 impaired the function of mitotic centrosome and disrupted MT nucleation and polymerization from the spindle pole, and may thus result in formation of abnormal mitotic spindles. In addition, HSP70 may associate with NEDD1 and γ-tubulin, two pericentriolar material (PCM) components essential for centrosome maturation and MT nucleation. Loss of HSP70 function disrupted the interaction between NEDD1 and γ-tubulin, and reduced their accumulation at the mitotic centrosome. Our results thus demonstrate a role for HSP70 in regulating centrosome integrity during mitosis, and indicate that HSP70 is required for the maintenance of a functional mitotic centrosome that supports the assembly of a bipolar mitotic spindle.

Rac1 and Cdc42 Play Important Roles in Arsenic Neurotoxicity in Primary Cultured Rat Cerebellar Astrocytes

This study aimed to explore whether Rac1 and Cdc42, representative members of Ras homologue guanosine triphosphatases (Rho GTPases), are involved in neurotoxicity induced by arsenic exposure in rat nervous system. Expressions of Rac1 and Cdc42 in rat cerebellum and cerebrum exposed to different doses of NaAsO2 (Wistar rats drank 0, 2, 10, and 50 mg/L NaAsO2 water for 3 months) were examined. Both Rac1 and Cdc42 expressions increased significantly in a dose-dependent manner in cerebellum (P < 0.01) by Western blot and immunohistochemistry assay, but in cerebrum, Rac1 and Cdc42 expressions only in 2 mg/L exposure groups were significantly higher than those in control groups (P < 0.01). Five to 50 μM NaAsO2 decreased cell viability in a dose-dependent manner in primary cultured rat astrocytes, whereas 1 μM NaAsO2 increased the cell viability in these cells. Rac1 inhibitor, NSC23766, decreased NaAsO2-induced apoptosis and increased the cell viability in primary cultured rat cerebellar astrocytes exposed to 30 μM NaAsO2. Cdc42 inhibitor, ZCL278, increased cell viability in the cells exposed to 30 μM NaAsO2. Taken together, our current studies in vivo and in vitro indicate that activations of Rac1 and Cdc42 play a very important role in arsenic neurotoxicity in rat cerebellum, providing a new insight into arsenic neurotoxicity.

Phosphatidylinositol 5-phosphate 4-kinase γ (PI5P4Kγ), a lipid signalling enigma

The phosphatidylinositol 5-phosphate 4-kinases (PI5P4Ks) are an important family of enzymes, whose physiological roles are being teased out by a variety of means. Phosphatidylinositol-5-phosphate 4-kinase γ (PI5P4Kγ) is especially intriguing as its in vitro activity is very low. Here we review what is known about this enzyme and discuss some recent advances towards an understanding of its physiology. Additionally, the effects of the ATP-competitive inhibitor I-OMe Tyrphostin AG-538 on all three mammalian PI5P4Ks was explored, including two PI5P4Kγ mutants with altered ATP- or PI5P-binding sites. The results suggest a strategy for targeting non-ATP binding sites on inositol lipid kinases.

Disruption of Mitotic Progression by Arsenic

Arsenic is an enigmatic xenobiotic that causes a multitude of chronic diseases including cancer and also is a therapeutic with promise in cancer treatment. Arsenic causes mitotic delay and induces aneuploidy in diploid human cells. In contrast, arsenic causes mitotic arrest followed by an apoptotic death in a multitude of virally transformed cells and cancer cells. We have explored the hypothesis that these differential effects of arsenic exposure are related by arsenic disruption of mitosis and are differentiated by the target cell's ability to regulate or modify cell cycle checkpoints. Functional p53/CDKN1A axis has been shown to mitigate the mitotic block and to be essential to induction of aneuploidy. More recent preliminary data suggest that microRNA modulation of chromatid cohesion also may play a role in escape from mitotic block and in generation of chromosomal instability. Other recent studies suggest that arsenic may be useful in treatment of solid tumors when used in combination with other cytotoxic agents such as cisplatin.

The function of phosphatidylinositol 5-phosphate 4-kinase γ (PI5P4Kγ) explored using a specific inhibitor that targets the PI5P-binding site

NIH-12848 (NCGC00012848-02), a putative phosphatidylinositol 5-phosphate 4-kinase γ (PI5P4Kγ) inhibitor, was explored as a tool for investigating this enigmatic, low activity, lipid kinase. PI5P4K assays in vitro showed that NIH-12848 inhibited PI5P4Kγ with an IC₅₀ of approximately 1 μM but did not inhibit the α and β PI5P4K isoforms at concentrations up to 100 μM. A lack of inhibition of PI5P4Kγ ATPase activity suggested that NIH-12848 does not interact with the enzyme's ATP-binding site and direct exploration of binding using hydrogen–deuterium exchange (HDX)-MS (HDX-MS) revealed the putative PI5P-binding site of PI5P4Kγ to be the likely region of interaction. This was confirmed by a series of mutation experiments which led to the identification of a single PI5P4Kγ amino acid residue that can be mutated to its PI5P4Ks α and β homologue to render PI5P4Kγ resistant NIH-12848 inhibition. NIH-12848 (10 μM) was applied to cultured mouse principal kidney cortical collecting duct (mpkCCD) cells which, we show, express PI5P4Kγ that increases when the cells grow to confluence and polarize. NIH-12848 inhibited the translocation of Na⁺/K⁺-ATPase to the plasma membrane that occurs when mpkCCD cells grow to confluence and also prevented reversibly their forming of ‘domes’ on the culture dish. Both these NIH-12848-induced effects were mimicked by specific RNAi knockdown of PI5P4Kγ, but not that of PI5P4Ks α or β. Overall, the data reveal a probable contribution of PI5P4Kγ to the development and maintenance of epithelial cell functional polarity and show that NIH-12848 is a potentially powerful tool for exploring the cell physiology of PI5P4Ks.

We have characterised a specific inhibitor of the enzyme Phosphatidylinositol 5-phosphate 4-kinase γ, including establishing where on the enzyme the inhibitor binds, and then applied this inhibitor to a kidney cell line to elucidate the intracellular functions of the enzyme.

Sodium arsenite and arsenic trioxide differently affect the oxidative stress, genotoxicity and apoptosis in A549 cells: an implication for the paradoxical mechanism

Although arsenic toxicity greatly depends on its chemical forms, few studies have taken into account the paradoxical phenomenon which is manifested by that sodium arsenite (NaAsO₂) acts as a potent carcinogen but arsenic trioxide (As₂O₃) serves as an effective therapeutic agent. In this study, we compared the in vitro effects of NaAsO₂ and As₂O₃ on cell viability, colony formation, cell cycle progression, apoptosis, genotoxicity and oxidative stress in human lung adenocarcinoma A549 cells. Our results demonstrated that both NaAsO₂ and As₂O₃ caused oxidative stress, genotoxicity, cytotoxicity, cell cycle arrest as well as apoptosis, while As₂O₃ induced higher production of reactive oxygen species (ROS) with a more remarkable decrease in superoxide dismutase (SOD) activities and intracellular levels of glutathione (GSH) than NaAsO₂. Moreover, the degree of DNA damage, chromosomal breakage, cell cycle arrest and apoptosis in As₂O₃-treated cells were more severe than those in NaAsO₂-treated cells. These findings suggest that differential effects and mechanisms of NaAsO₂ and As₂O₃ may responsible for the paradoxical effects of arsenic on the carcinogenesis and anticancer function.

Inhibition of AKT enhances mitotic cell apoptosis induced by arsenic trioxide

Accumulated evidence has revealed a tight link between arsenic trioxide (ATO)-induced apoptosis and mitotic arrest in cancer cells. AKT, a serine/threonine kinase frequently over-activated in diverse tumors, plays critical roles in stimulating cell cycle progression, abrogating cell cycle checkpoints, suppressing apoptosis, and regulating mitotic spindle assembly. Inhibition of AKT may therefore enhance ATO cytotoxicity and thus its clinical utility. We show that AKT was activated by ATO in HeLa-S3 cells. Inhibition of AKT by inhibitors of the phosphatidyl inositol 3-kinase/AKT pathway significantly enhanced cell sensitivity to ATO by elevating mitotic cell apoptosis. Ectopic expression of the constitutively active AKT1 had no effect on ATO-induced spindle abnormalities but reduced kinetochore localization of BUBR1 and MAD2 and accelerated mitosis exit, prevented mitotic cell apoptosis, and enhanced the formation of micro- or multi-nuclei in ATO-treated cells. These results indicate that AKT1 activation may prevent apoptosis of ATO-arrested mitotic cells by attenuating the function of the spindle checkpoint and therefore allowing the formation of micro- or multi-nuclei in surviving daughter cells. In addition, AKT1 activation upregulated the expression of aurora kinase B (AURKB) and survivin, and depletion of AURKB or survivin reversed the resistance of AKT1-activated cells to ATO-induced apoptosis. Thus, AKT1 activation suppresses ATO-induced mitotic cell apoptosis, despite the presence of numerous spindle abnormalities, probably by upregulating AURKB and survivin and attenuating spindle checkpoint function. Inhibition of AKT therefore effectively sensitizes cancer cells to ATO by enhancing mitotic cell apoptosis.