Arsenite-induced apoptosis of human neuroblastoma cells requires p53 but occurs independently of c-Jun

Tyrosine hydroxylase gene promoter activity is upregulated in female catecholaminergic neuroblastoma cells following activation of a Gαq-coupled designer receptor

Tyrosine hydroxylase is the rate-limiting enzyme of catecholamine biosynthesis that catalyzes the conversion of L-tyrosine to L-3,4-dihydroxyphenylalanine. The tyrosine hydroxylase gene is regulated by extracellular signaling molecules such as epidermal growth factor, nerve growth factor and steroids. Here, we investigated whether the activity of the tyrosine hydroxylase gene promoter is upregulated by activation of G protein-coupled receptors, the largest group of plasma membrane receptors. We used catecholaminergic neuroblastoma cells as a cellular model and chromatin-integrated tyrosine hydroxylase promoter-luciferase reporter genes. The results show that stimulation of Rαq, a Gαq-coupled designer receptor, triggered transcription of a reporter gene driven by the tyrosine hydroxylase promoter. Transcription was attenuated by overexpression of regulator of G-protein signaling-2, which activates the GTPase activity of the G protein α-subunit, and by a truncated, dominant-negative mutant of phospholipase Cβ3. Extracellular signal-regulated protein kinase was identified as the signal transducer. At the transcriptional level, tyrosine hydroxylase promoter activity was found to be controlled by the transcription factor CREB. Expression experiments with the adenoviral regulator protein E1A, an inhibitor of CBP/p300 histone acetyltransferases, showed that transcription of the reporter gene controlled by the tyrosine hydroxylase is under epigenetic control. We identified the protein phosphatases MAP kinase phosphatase-1 and calcineurin as part of a shutdown device of the signaling cascade linking Rαq designer receptor activation to tyrosine hydroxylase gene transcription. We conclude that tyrosine hydroxylase promoter activity is controlled by Gαq-coupled receptors.

Arsenic trioxide increases apoptosis of SK-N-BE (2) cells partially by inducing GPX4-mediated ferroptosis

BACKGROUND

Neuroblastoma (NB) is the most common extracranial tumor in central nervous system threatening children's health with limited therapeutic options. Arsenic trioxide (ATO) has been identified the cytotoxicity in NB cells but the potential mechanism remains unclear. In this study, we attempted to obtain some insight into the mechanisms of cell death induced by ATO in NB cells.

METHODS AND RESULTS

Proteomic analyses found that ATO can affect the signaling pathway associated with ferroptosis, including the upregulation of iron absorption (FTL, FTH1, HO-1), ferritinophagy (LC3, P62, ATG7, NCOA4) and modifier of glutathione synthesis (GCLM); downregulation of glutamine synthetase (GS) and GPX4, which was the critical inhibitor of ferroptosis. Western blot analysis revealing GPX4 expression in SK-N-BE (2) cells decreased after treatment with ATO (7.3 µM), resulting in a loss of GPX4 activity. Furthermore, Ferroptosis inhibitor ferrostatin-1 partially blocked ATO-induced cell death.

CONCLUSIONS

Our study revealed that ATO may induce ferroptosis in neuroblastoma cell SK-N-BE (2) by facilitating the downregulation of GPX4, ultimately resulting in iron-dependent oxidative death.

Urolithin A attenuates arsenic-induced gut barrier dysfunction

Environmental chemicals such as inorganic arsenic (iAs) significantly contribute to redox toxicity in the human body by enhancing oxidative stress. Imbalanced oxidative stress rapidly interferes with gut homeostasis and affects variety of cellular processes such as proliferation, apoptosis, and maintenance of intestinal barrier integrity. It has been shown that gut microbiota are essential to protect against iAs3+-induced toxicity. However, the effect of microbial metabolites on iAs3+-induced toxicity and loss of gut barrier integrity has not been investigated. The objectives of the study are to investigate impact of iAs on gut barrier function and determine benefits of gut microbial metabolite, urolithin A (UroA) against iAs3+-induced adversaries on gut epithelium. We have utilized both colon epithelial cells and in a human intestinal 3D organoid model system to investigate iAs3+-induced cell toxicity, oxidative stress, and gut barrier dysfunction in the presence or absence of UroA. Here, we report that treatment with UroA attenuated iAs3+-induced cell toxicity, apoptosis, and oxidative stress in colon epithelial cells. Moreover, our data suggest that UroA significantly reduces iAs3+-induced gut barrier permeability and inflammatory markers in both colon epithelial cells and in a human intestinal 3D organoid model system. Mechanistically, UroA protected against iAs3+-induced disruption of tight junctional proteins in intestinal epithelial cells through blockade of oxidative stress and markers of inflammation. Taken together, our studies for the first time suggest that microbial metabolites such as UroA can potentially be used to protect against environmental hazards by reducing intestinal oxidative stress and by enhancing gut barrier function.

A Deletion of the Nuclear Localization Signal Domain in the Fus Protein Induces Stable Post-stress Cytoplasmic Inclusions in SH-SY5Y Cells

Mutations in Fused-in-Sarcoma (FUS) gene involving the nuclear localization signal (NLS) domain lead to juvenile-onset Amyotrophic Lateral Sclerosis (ALS). The mutant protein mislocalizes to the cytoplasm, incorporating it into Stress Granules (SG). Whether SGs are the first step to the formation of stable FUS-containing aggregates is still unclear. In this work, we used acute and chronic stress paradigms to study the SG dynamics in a human SH-SY5Y neuroblastoma cell line carrying a deletion of the NLS domain of the FUS protein (homozygous: ΔNLS^–/–; heterozygous: ΔNLS^+/–). Wild-type (WT) cells served as controls. We evaluated the subcellular localization of the mutant protein through immunoblot and immunofluorescence, in basal conditions and after acute stress and chronic stress with sodium arsenite (NaAsO₂). Cells were monitored for up to 24 h after rescue. FUS was expressed in both nucleus and cytoplasm in the ΔNLS^+/– cells, whereas it was primarily cytoplasmic in the ΔNLS^–/–. Acute NaAsO₂ exposure induced SGs: at rescue,>90% of ΔNLS cells showed abundant FUS-containing if compared to less than 5% of the WT cells. The proportion of FUS-positive SGs remained 15–20% at 24 h in mutant cells. Cycloheximide did not abolish the long-lasting SGs in mutant cells. Chronic exposure to NaAsO₂ did not induce significant SGs formation. A wealth of research has demonstrated that ALS-associated FUS mutations at the C-terminus facilitate the incorporation of the mutant protein into SGs. We have shown here that mutant FUS-containing SGs tend to fail to dissolve after stress, facilitating a liquid-to-solid phase transition. The FUS-containing inclusions seen in the dying motor neurons might therefore directly derive from SGs. This might represent an attractive target for future innovative therapies.

Ternary complex factor regulates pancreatic islet size and blood glucose homeostasis in transgenic mice

A hallmark of diabetes mellitus is the inability of pancreatic β-cells to secrete sufficient amounts of insulin for maintaining normoglycemia. The formation of smaller islets may underlie the development of a diabetic phenotype, as a decreased β-cell mass will produce an insufficient amount of insulin. For a pharmacological intervention it is crucial to identify the proteins determining β-cell mass. Here, we identified the ternary complex factor (TCF) Elk-1 as a regulator of the size of pancreatic islets. Elk-1 mediates, together with a dimer of the serum-response factor (SRF), serum response element-regulated gene transcription. Elk-1 is activated in glucose-treated pancreatic β-cells but the biological functions of this protein in β-cells are so far unknown. Elk-1 and homologous TCF proteins are expressed in islets and insulinoma cells. Gene targeting experiments revealed that the TCF proteins show redundant activities. To solve the problem of functional redundancy of these homologous proteins, we generated conditional transgenic mice expressing a dominant-negative mutant of Elk-1 in pancreatic β-cells. The mutant competes with the wild-type TCFs for DNA and SRF-binding. Expression of the Elk-1 mutant in pancreatic β-cells resulted in the generation of significantly smaller islets and increased caspase-3 activity, indicating that apoptosis was responsible for the reduction of the pancreatic islet size. Glucose tolerance tests revealed that transgenic mice expressing the dominant-negative mutant of Elk-1 in pancreatic β-cells displayed impaired glucose tolerance. Thus, we show here for the first time that TCF controls important functions of pancreatic β-cells in vivo. Elk-1 may be considered as a new therapeutic target for the treatment of diabetes.

Pharmacological inhibition of TRPM8-induced gene transcription

Transient receptor potential melastatin-8 (TRPM8) channels are activated by cold temperature, menthol and icilin, leading to cold sensation. TRPM8 activation is connected with various diseases, indicating that a specific pharmacological antagonist, allowing nongenetic channel suppression, would be a valuable tool for therapy and basic research. Here, we assessed the biological activity and specificity of various TRPM8 inhibitors following stimulation of TRPM8 channels with either icilin or menthol. Recently, we showed that icilin strikingly upregulates the transcriptional activity of AP-1. By measuring AP-1 activity, we assessed which compound interrupted the TRPM8-induced intracellular signaling cascade from the plasma membrane to the nucleus. We tested the specificity of various TRPM8 inhibitors by analyzing AP-1 activation following stimulation of TRPM3 and TRPV1 channels, L-type voltage-gated Ca²⁺ channels, and Gαq-coupled receptors, either in the presence or absence of a particular TRPM8 inhibitor. The results show that the TRPM8 inhibitors BCTC, RQ-00203078, TC-1 2014, 2-APB, and clotrimazole blocked TRPM8-mediated activation of AP-1. However, only the compound RQ-00203078 showed TRPM8-specificity, while the other compounds function as broad-spectrum Ca²⁺ channel inhibitors. In addition, we show that progesterone interfered with TRPM8-induced activation of AP-1, as previously shown for TRPM3 and TRPC6 channels. TRPM8-induced transcriptional activation of AP-1 was additionally blocked by the compound PD98059, indicating that extracellular signal-regulated protein kinase-1/2 is essential to couple TRPM8 stimulation with transcriptional activation of AP-1. Moreover, an influx of Ca²⁺-ions is essential to induce the intracellular signaling cascade leading to the activation of AP-1.

Novel Combination of Arsenic Trioxide (As2O3) Plus Resveratrol in Inducing Programmed Cell Death of Human Neuroblastoma SK-N-SH Cells

AIM

Arsenic trioxide (As₂O₃), known as pi-shuang and the most toxic compound in traditional Chinese medicine, has been used as an antitumor agent for thousands of years. Resveratrol (3,5,4'-trihydroxy-trans-stilbene) is a natural phenol that has significant anti-bacterial, anti-fungaI and antiaging activities. Our study aimed to examine the combined anticancer effects of As₂O₃ and resveratrol against human neuroblastoma SK-N-SH cells, and elucidate the underlying intracellular signaling.

MATERIALS AND METHODS

SK-N-SH cells were treated with an extremely low-dose (2-4 μM) of As₂O₃ alone or combined with 75 μg/ml resveratrol for further comparisons. Cell viability, apoptotic signaling as well as synergistic cytotoxic effects were estimated using the MTT assay, microscopy observation, flow cytometric analysis for loss of mitochondrial membrane potential (MMP) and reactive oxygen species (ROS), and typical quantitative western blotting analysis. Student's t-test, and one- and two-way analysis of variance (ANOVA) were used for examination of significant differences.

RESULTS

The combined treatment was more effective than single treatment of As₂O₃ or resveratrol alone in suppressing cell viability, which correlated with the elevation of ROS levels. The intracellular mechanisms of cytotoxicity of As₂O₃ plus resveratrol were revealed as ROS accumulation and relative decrease of MMP, leading to activation of caspase-3 and -9, but not of caspase-1, -7 and-8. Combination treatment reduced the expression of B-cell lymphoma 2 (BCL2), BH3 interacting domain death agonist (BID), and BCL-x/L.

CONCLUSION

Combined treatment at extremely low concentration of two agents from natural products, As₂O₃ and resveratrol, has high potential as a cocktail of anticancer drugs for neuroblastoma.

Stimulation of TRPV1 channels activates the AP-1 transcription factor

Transient receptor potential vanilloid 1 (TRPV1) channels were originally described as the receptors of capsaicin, the main constituent of hot chili pepper. The biological functions of TRPV1 channels include pain sensation and inflammatory thermal hyperalgesia. Here, we show that stimulation of HEK293 cells expressing TRPV1 channels (H2C1 cells) with capsaicin or the TRPV1 ligand resiniferatoxin activated transcription mediated by the transcription factor AP-1. No cell death was occurring under these experimental conditions. The AP-1 activity was not altered in capsaicin or resiniferatoxin-stimulated HEK293 cells lacking TRPV1. We identified the AP-1 DNA binding site as the capsaicin/resiniferatoxin-responsive element. Stimulation with the TRPV1 ligand N-arachidonoyldopamine increased AP-1 activity in a TRPV1-dependent and TRPV1-independent manner. Stimulation of TRPV1 channels induced an influx of Ca²⁺ into the cells and this rise in intracellular Ca²⁺ was essential for activating AP-1 in capsaicin or resiniferatoxin-stimulated cells. N-arachidonoyldopamine stimulation induced a rise in intracellular Ca²⁺ in a TRPV-1 dependent and independent manner. AP-1 is a dimeric transcription factor, composed of proteins of the c-Jun, c-Fos and ATF families. Stimulation of TRPV1 channels with capsaicin increased c-Jun and c-Fos biosynthesis in H2C1 cells. The signal transduction of capsaicin, leading to enhanced AP-1-mediated transcription, required extracellular signal-regulated protein kinase ERK1/2 as a signal transducer and the activation of the transcription factors c-Jun and ternary complex factor. Together, these data suggest that the intracellular functions of TRPV1 stimulation may rely on the activation of a stimulus-regulated protein kinase and stimulus-responsive transcription factors.

Stimulation of transient receptor potential M3 (TRPM3) channels increases interleukin-8 gene promoter activity involving AP-1 and extracellular signal-regulated protein kinase

Stimulation of Ca²⁺ permeable TRPM3 (transient receptor potential melastatin-3) channels with the steroid ligand pregnenolone sulfate activates stimulus-responsive transcription factors, including the transcription factor AP-1 (activator protein-1). As part of a search for AP-1-regulated target genes we analyzed the gene encoding interleukin-8 (IL-8) in HEK293 cells expressing TRPM3 channels. Here, we show that stimulation of TRPM3 channels activated transcription of an IL-8 promoter-controlled reporter gene that was embedded into the chromatin of the cells. Mutational analysis of the IL-8 promoter revealed that the AP-1 binding site of the IL-8 promoter was essential to connect TRPM3 stimulation with the transcription of the IL-8 gene. Genetic experiments revealed that the basic region leucine zipper proteins c-Jun and ATF2 and the ternary complex factor Elk-1 are essential to couple TRPM3 channel stimulation with the IL-8 gene. Moreover, we identified extracellular signal-regulated protein kinase (ERK1/2) as signal transducer connecting TRPM3 stimulation with enhanced transcription of the IL-8 gene. Furthermore, we show that stimulation of TRPC6 (transient receptor potential canonical-6) channels with its ligand hyperforin also increased IL-8 promoter activity, involving the AP-1 binding site within the IL-8 gene, suggesting that activation of IL-8 gene transcription may be a common theme following TRP channel stimulation.

Arsenite induces DNA damage via mitochondrial ROS and induction of mitochondrial permeability transition

Arsenite is an established DNA-damaging agent and human carcinogen. We initially selected conditions in which the metalloid causes DNA strand scission in the absence of detectable apoptotic DNA degradation in U937 cells. This response was suppressed by catalase and by treatments (rotenone and ascorbic acid), or manipulations (respiration-deficient phenotype), preventing the mitochondrial formation of O2-. ( mitoO2-.). MitoO2-., and its dismutation product, H₂ O₂ , are therefore critically involved in the arsenite-dependent DNA-damaging response. We then established a link between mitoO2-./H₂ O₂ and mitochondrial permeability transition (MPT), and found that this second event also promoted the formation of DNA-damaging species. As a consequence, the DNA damage induced by arsenite, in addition to being abolished by the aforementioned treatments/manipulations, was also significantly reduced by the MPT inhibitor cyclosporin A (CsA). A CsA-sensitive induction of p53 mRNA expression was also detected. Finally, evidence of CsA-sensitive DNA strand scission was also obtained in MCF-7, HT22, and NCTC-2544 cells. MitoO2-./H₂ O₂ therefore directly mediates DNA damage induced by arsenite and indirectly promotes the formation of additional DNA-damaging species via the induction of MPT. © 2017 BioFactors, 43(5):673-684, 2017.

Isolation and purification of novel peptides derived from Sepia ink: Effects on apoptosis of prostate cancer cell PC‑3

Novel prostate cancer therapeutics are in high demand. In order to identify potential therapeutic targets, protein from sepia ink was hydrolyzed by utilizing pepsin in an orthogonal array design. Pepsin hydrolysate (SH) obtained at optimal conditions exhibited the highest antitumor activity. Subsequently, a novel antitumor peptide, which was termed SHP, was isolated through ultrafiltration, gel filtration chromatography and reversed phase high‑performance liquid chromatography. The amino acid sequence of SHP was identified as Leu‑Lys‑Glu‑Glu‑Asn‑Arg‑Arg‑Arg‑Arg‑Asp with a molecular mass of 1371.53 Da. The results of the proliferation assay revealed that SHP significantly inhibited the proliferation of PC‑3 cells in a time‑ and dose‑dependent manner. Acridine orange/ethidium bromide staining indicated significant SHP‑induced apoptosis. Furthermore, Annexin V/PI double‑staining assays revealed that the percentage of early‑ stage apoptotic cells increased from 8.85 to 29% following PC‑3 exposure to 5, 10 and 15 mg/ml SHP for 24 h. SHP‑induced apoptosis was accompanied by the activation of cellular tumor antigen p53 and caspase‑3, the upregulation of apoptosis regulator BAX, and the downregulation of apoptosis regulator Bcl‑2. These findings suggest that SHP is a novel inducer of apoptosis in vitro and merits further investigation as a possible therapeutic agent for the treatment of cancer.

Arsenic Exposure Induces Unscheduled Mitotic S Phase Entry Coupled with Cell Death in Mouse Cortical Astrocytes

There is serious concern about arsenic in the natural environment, which exhibits neurotoxicity and increases the risk of neurodevelopmental disorders. Adverse effects of arsenic have been demonstrated in neurons, but it is not fully understood how arsenic affects other cell types in the brain. In the current study, we examined whether sodium arsenite (NaAsO₂) affects the cell cycle, viability, and apoptosis of in vitro-cultured astrocytes isolated from the cerebral cortex of mice. Cultured astrocytes from transgenic mice expressing fluorescent ubiquitination-based cell cycle indicator (Fucci) were subjected to live imaging analysis to assess the effects of NaAsO₂ (0, 1, 2, and 4 μM) on the cell cycle and number of cells. Fucci was designed to express monomeric Kusabira Orange2 (mKO2) fused with the ubiquitylation domain of hCdt1, a marker of G1 phase, and monomeric Azami Green (mAG) fused with the ubiquitylation domain of hGem, a marker of S, G2, and M phases. NaAsO₂ concentration-dependently decreased the peak levels of the mAG/mKO2 emission ratio when the ratio had reached a peak in astrocytes without NaAsO₂ exposure, which was due to attenuating the increase in the mAG-expressing cell number. In contrast, the mAG/mKO2 emission ratio and number of mAG-expressing cells were concentration-dependently increased by NaAsO₂ before their peak levels, indicating unscheduled S phase entry. We further examined the fate of cells forced to enter S phase by NaAsO₂. We found that most of these cells died up to the end of live imaging. In addition, quantification of the copy number of the glial fibrillary acidic protein gene expressed specifically in astrocytes revealed a concentration-dependent decrease caused by NaAsO₂. However, NaAsO₂ did not increase the amount of nucleosomes generated from DNA fragmentation and failed to alter the gene expression of molecules relevant to unscheduled S phase entry-coupled apoptosis (p21, p53, E2F1, E2F4, and Gm36566). These findings suggest that NaAsO₂ adversely affects the cell cycle and viability of astrocytes by inducing unscheduled S phase entry coupled with cell death that may be caused by mechanisms other than apoptosis.

Prenatal Exposure to Arsenic Impairs Behavioral Flexibility and Cortical Structure in Mice

Exposure to arsenic from well water in developing countries is suspected to cause developmental neurotoxicity. Although, it has been demonstrated that exposure to sodium arsenite (NaAsO₂) suppresses neurite outgrowth of cortical neurons in vitro, it is largely unknown how developmental exposure to NaAsO₂ impairs higher brain function and affects cortical histology. Here, we investigated the effect of prenatal NaAsO₂ exposure on the behavior of mice in adulthood, and evaluated histological changes in the prelimbic cortex (PrL), which is a part of the medial prefrontal cortex that is critically involved in cognition. Drinking water with or without NaAsO₂ (85 ppm) was provided to pregnant C3H mice from gestational days 8 to 18, and offspring of both sexes were subjected to cognitive behavioral analyses at 60 weeks of age. The brains of female offspring were subsequently harvested and used for morphometrical analyses. We found that both male and female mice prenatally exposed to NaAsO₂ displayed an impaired adaptation to repetitive reversal tasks. In morphometrical analyses of Nissl- or Golgi-stained tissue sections, we found that NaAsO₂ exposure was associated with a significant increase in the number of pyramidal neurons in layers V and VI of the PrL, but not other layers of the PrL. More strikingly, prenatal NaAsO₂ exposure was associated with a significant decrease in neurite length but not dendrite spine density in all layers of the PrL. Taken together, our results indicate that prenatal exposure to NaAsO₂ leads to behavioral inflexibility in adulthood and cortical disarrangement in the PrL might contribute to this behavioral impairment.

Roles of oxidative stress and the ERK1/2, PTEN and p70S6K signaling pathways in arsenite-induced autophagy

Studies show that arsenite induces oxidative stress and modifies cellular function via phosphorylation of proteins and inhibition of DNA repair enzymes. Autophagy, which has multiple physiological and pathological roles in cellular function, is initiated by oxidative stress and is regulated by the signaling pathways of phosphatidylinositol 3-phosphate kinase (PI3K)/mammalian target of rapamycin (mTOR)/p70S6 kinase (p70S6K) and extracellular signaling-regulated protein kinase 1/2 (ERK1/2) that play important roles in oncogenesis. However, the effects of arsenite-induced oxidative stress on autophagy and on expression of related proteins are not fully understood. This study found that cells treated with sodium arsenite had reduced 8-oxoguanine DNA glycosylase 1 (OGG1) and increased 8-hydroxy-2'-deoxyguanosine (8-OHdG) and activating transcription factor (ATF) 3 in SV-40 immortalized human uroepithelial (SV-HUC-1) cells. Arsenite also increased the number of autophagosomes and increased levels of the autophagy markers Beclin-1 and microtubule-associated protein 1 light chain 3B. Reactive oxygen species scavenger decreased arsenite-induced autophagy in SV-HUC-1 cells. Our previous work showed that arsenite induced phosphorylation of the ERK1/2 signaling pathway. The current study further showed that arsenite decreased phosphatase and tensin homologue (PTEN) levels and increased phospho-p70S6 kinase (p-p70S6K) in SV-HUC-1 cells. However, both kinase inhibitor U0126 and the DNA (cytosine-5-)-methyltransferase 1 (DNMT1) inhibitor 5-aza-deoxycytidine abolished the effect of arsenite on expressions of PTEN and p-p70S6K. These results show that autophagy induced by arsenite exposure is mediated by oxidative stress, which regulates activation of the PTEN, p70S6K and ERK1/2 signaling pathways. Thus, this study clarifies the role of autophagy in arsenite-induced urothelial carcinogenesis.

Prenatal sodium arsenite affects early development of serotonergic neurons in the fetal rat brain

Prenatal arsenite exposure has been associated with developmental disorders in children, including reduced IQ and language abnormalities. Animal experiments have also shown that exposure to arsenite during development induced developmental neurotoxicity after birth. However, the evidence is not enough, and the mechanism is poorly understood, especially on the exposure during early brain development. This study assessed effects of sodium (meta) arsenite shortly after exposure on early developing fetal rat brains. Pregnant rats were administered 50 mg/L arsenite in their drinking water or 20 mg/kg arsenite orally using a gastric tube, on gestational days (GD) 9-15. Fetal brains were examined on GD16. Pregnant rats administered 20 mg/kg arsenite showed reductions in maternal body weight gain and food consumption during treatment, but not with 50 mg/L arsenite. Arsenite did not affect fetal development, as determined by body weight, mortality and brain size. Arsenite also did not induce excessive cell death or affect neural cell division in any region of the fetal neuroepithelium. Thyrosine hydroxylase immunohistochemistry revealed no difference in the distribution of catecholaminergic neurons between fetuses of arsenite treated and control rats. However, reductions in the number of serotonin positive cells in the fetal median and dorsal raphe nuclei were observed following maternal treatment with 20mg/kg arsenite. Image analysis showed that the serotonin positive areas decreased in all fetal mid- and hind-brain areas without altering distribution patterns. Maternal stress induced by arsenite toxicity did not alter fetal development. These results suggest that arsenite-induced neurodevelopmental toxicity involves defects in the early development of the serotonin nervous system.

Resveratrol stimulates AP-1-regulated gene transcription

SCOPE

Many intracellular functions have been attributed to resveratrol, a polyphenolic phytoalexin found in grapes and in other plants, including the regulation of transcription. Here, we have analyzed the impact of resveratrol on the activity of the transcription factor activator protein-1 (AP-1).

METHODS AND RESULTS

Using a chromosomally embedded AP-1-responsive reporter gene, we show that the AP-1 activity was significantly elevated in resveratrol-treated 293 human embryonic kidney and HepG2 hepatoma cells. The 12-O-tetradecanoylphorbol-13-acetate-responsive element, a binding site for c-Jun and c-Fos, was identified as resveratrol-responsive element. Expression of c-Jun and c-Fos, two proteins that constitute AP-1, is upregulated in resveratrol-stimulated HEK293 cells. On the transcriptional level, c-Jun and the ternary complex factor Elk-1 are essential for the activation of AP-1 in resveratrol-treated cells. In addition, mitogen-activated protein kinases and protein kinase C are required to connect resveratrol stimulation with enhanced AP-1 controlled transcription. Finally, we show that resveratrol increased the activities of the AP-1 responsive cyclin D1 and tumor necrosis factor α promoters.

CONCLUSION

Resveratrol regulates gene transcription via activation of stimulus-regulated protein kinases and the stimulus-responsive AP-1 transcription factors. The fact that resveratrol regulates AP-1 activity may explain many of the pleiotropic intracellular alterations induced by resveratrol.

Arsenic trioxide induces apoptosis in B-cell chronic lymphocytic leukemic cells through down-regulation of survivin via the p53-dependent signaling pathway

Arsenic trioxide (As2O3) can induce apoptosis in many tumors. However, the associated mechanisms are not clearly understood. We found that As2O3 significantly inhibited the proliferation of WSU-CLL cells and induced apoptosis in dose- and time-dependent manners. WSU-CLL cells treated with 2μM As2O3 showed survivin down-regulation and p53 up-regulation. Survivin siRNA combined with As2O3 further inhibited the proliferation of WSU-CLL cells. p53 inhibition by siRNA prevented the down-regulation of survivin by As2O3 and prevented the As2O3-induced cytotoxicity of WSU-CLL cells. These results suggest that As2O3 may be of therapeutic value for chronic lymphocytic leukemia.

GADD45β mediates p53 protein degradation via Src/PP2A/MDM2 pathway upon arsenite treatment

Growth arrest and DNA-damage-inducible, beta (GADD45β) has been reported to inhibit apoptosis via attenuating c-Jun N-terminal kinase (JNK) activation. We demonstrated here that GADD45β mediated its anti-apoptotic effect via promoting p53 protein degradation following arsenite treatment. We found that p53 protein expression was upregulated in GADD45β−/− cells upon arsenite exposure as compared with those in GADD45β+/+ cells. Further studies showed that GADD45β attenuated p53 protein expression through Src/protein phosphatase 2A/murine double minute 2-dependent p53 protein-degradation pathway. Moreover, we identified that GADD45β-mediated p53 protein degradation was crucial for its anti-apoptotic effect due to arsenite exposure, whereas increased JNK activation was not involved in the increased cell apoptotic response in GADD45β−/− cells under same experimental conditions. Collectively, our results demonstrate a novel molecular mechanism responsible for GADD45β protection of arsenite-exposed cells from cell death, which provides insight into our understanding of GADD45β function and a unique compound arsenite as both a cancer therapeutic reagent and an environmental carcinogen. Those novel findings may also enable us to design more effective strategies for utilization of arsenite for the treatment of cancers.