Opposite effect of NF-kappa B and c-Jun N-terminal kinase on p53-independent GADD45 induction by arsenite

Arsenic trioxide induces cell cycle arrest and alters DNA methylation patterns of cell cycle regulatory genes in colorectal cancer cells

AIMS

Cell cycle dysregulation is important in tumorigenesis. Transcriptional silencing of cell cycle regulatory genes, due to DNA methylation, is a common epigenetic event in malignancies. As₂O₃ has been shown to induce cell cycle arrest and also to be a potential hypomethylating agent. Our study aimed to investigate DNA methylation patterns of cell cycle regulatory genes promoters, the effects of Arsenic trioxide (As₂O₃) on the methylated genes and cell cycle distribution in colorectal cancer (CRC) cell lines.

MAIN METHODS

The methylation-specific PCR (MSP) and/or restriction enzyme-based methods were used to study the promoter methylation patterns of 24 cell cycle regulatory genes in CRC cell lines. Gene expression level and cell cycle distribution were determined by Real-time PCR and flow cytometric analyses, respectively.

KEY FINDINGS

Our methylation analysis indicated that only promoters of RBL1 (p107), CHFR and p16 genes were aberrantly methylated in three cell lines. As₂O₃ significantly decreased DNA methylation in promoter regions of these genes and restored their expression. We found that As₂O₃ significantly reduced the expression of DNA methyltransferase 1 (DNMT1) and increased arsenic methyltransferase (AS3MT). Furthermore, As₂O₃ altered transcriptional activity of several unmethylated cell cycle regulatory genes including cyclin B1, E1, D1, GADD45A and p21. Cell cycle flow cytometry analysis showed As₂O₃ induced G2/M arrest in all three cell lines.

SIGNIFICANCE

These data suggest that demethylation and alteration in the expression level of the cell cycle-related genes may be possible mechanisms in As₂O₃-induced cell cycle arrest in colorectal cancer cells.

Arsenic acid inhibits proliferation of skin fibroblasts, and increases cellular senescence through ROS mediated MST1-FOXO signaling pathway

Arsenic exposure through drinking water is a major public health problem. It causes a number of toxic effects on skin. Arsenic has been reported to inhibit cell proliferation in in vitro conditions. However, reports about the molecular mechanisms are limited. Here, we investigated the mechanism involved in arsenic acid-mediated inhibition of cell proliferation using mouse skin fibroblast cell line. The present study found that 10 ppm arsenic acid inhibited cell proliferation, without any effect on cell death. Arsenic acid induced the generation of reactive oxygen species (ROS), resulting in oxidative stress to DNA. It also activated the mammalian Ste20-like protein kinase 1 (MST1); however the serine/threonine kinase Akt was downregulated. Forkhead box O (FOXO) transcription factors are activated through phosphorylation by MST1 under stress conditions. They are inhibited by phosphorylation by Akt through external and internal stimuli. Activation of FOXOs results in their nuclear localization, followed by an increase in transcriptional activity. Our results showed that arsenic induced the nuclear translocation of FOXO1 and FOXO3a, and altered the cell cycle, with cells accumulating at the G2/M phase. These effects caused cellular senescence. Taken together, our results indicate that arsenic acid inhibited cell proliferation through cellular senescence process regulated by MST1-FOXO signaling pathway.

Induction of G2/M phase arrest and apoptosis by ZGDHU-1 in A549 and RERF-LC-MA lung cancer cells

Lung cancer is a major public health issue worldwide and is associated with high mortality and poor prognosis. Chemotherapy has the potential to reduce tumor size, increase operability and eradicate micrometastases; therefore, novel chemicals to treat lung cancer are urgently required. In the present study, the effects of N, N'-di-(m-methylphenyi)-3,6-dimethyl-1,4-dihydro-1,2,4, 5-tetrazine-1,4-dicarboamide (ZGDHu-1), a novel tetrazine derivative, were investigated in A549 and RERF-LC-MA lung cancer cells, and the underlying molecular mechanism of ZGDHu in treating lung cancer was determined. Following incubation with different concentrations of ZGDHu-1, flow cytometry analysis results indicated that ZGDHu-1 could induce G₂/mitotic (M) cell cycle arrest and apoptosis in A549 and RERF-LC-MA cells in a dose-dependent manner. Furthermore, western blot analysis demonstrated that the expression levels of G₂/M regulatory molecules, including cyclin B1, Cdc2 and cell division cycle 25c, decreased following treatment with ZGDHu-1, whilst p53 expression increased. In addition, A549 and RERF-LC-MA cell apoptosis was induced by cell cycle arrest at the G₂/M phase and through the downregulation of nuclear factor-κB. These results suggest that ZGDHu-1 may induce G₂/M phase arrest and apoptosis of lung cancer cells, and may serve as a potential therapeutic drug for the treatment of lung cancer.

Caspase-9b Interacts Directly with cIAP1 to Drive Agonist-Independent Activation of NF-κB and Lung Tumorigenesis

Alternate RNA processing of caspase-9 generates the splice variants caspase 9a (C9a) and caspase 9b (C9b). C9b lacks a domain present in C9a, revealing a tumorigenic function that drives the phenotype of non-small cell lung cancer (NSCLC) cells. In this study, we elucidated the mechanistic underpinnings of the malignant character of this splice isoform. In NSCLC cells, C9b expression correlated with activation of the canonical arm of the NF-κB pathway, a major pathway linked to the NSCLC tumorigenesis. Mechanistic investigations revealed that C9b activates this pathway via direct interaction with cellular inhibitor of apoptosis 1 (cIAP1) and subsequent induction of the E3 ligase activity of this IAP family member. The C9b:cIAP1 interaction occurred via the BIR3 domain of cIAP1 and the IAP-binding motif of C9b, but did not require proteolytic cleavage of C9b. This protein:protein interaction was essential for C9b to promote viability and malignant growth of NSCLC cells in vitro and in vivo, broadly translating to diverse NSCLC oncogenotypes. Overall, our findings identified a novel point for therapeutic invention in NSCLC that may be tractable to small-molecule inhibitors, as a new point to broadly address this widespread deadly disease. Cancer Res; 76(10); 2977-89. ©2016 AACR.

Arsenic-induced sub-lethal stress reprograms human bronchial epithelial cells to CD61¯ cancer stem cells

In the present report, we demonstrate that sub-lethal stress induced by consecutive exposure to 0.25 μM arsenic (As³⁺) for six months can trigger reprogramming of the human bronchial epithelial cell (BEAS-2B) to form cancer stem cells (CSCs) without forced introduction of the stemness transcription factors. These CSCs formed from As³⁺-induced sub-lethal stress featured with an increased expression of the endogenous stemness genes, including Oct4, Sox2, Klf4, Myc, and others that are associated with the pluripotency and self-renewal of the CSCs. Flow cytometry analysis indicated that 90% of the CSC cells are CD61¯, whereas 100% of the parental cells are CD61⁺. These CD61¯ CSCs are highly tumorigenic and metastatic to the lung in xenotransplantation tests in NOD/SCID Il2rγ^−/− mice. Additional tests also revealed that the CD61¯ CSCs showed a significant decrease in the expression of the genes important for DNA repair and oxidative phosphorylation. To determine the clinical relevance of the above findings, we stratified human lung cancers based on the level of CD61 protein and found that CD61^low cancer correlates with poorer survival of the patients. Such a correlation was also observed in human breast cancer and ovarian cancer. Taken together, our findings suggest that in addition to the traditional approaches of enforced introduction of the exogenous stemness circuit transcription factors, sub-lethal stress induced by consecutive low dose As³⁺ is also able to convert non-stem cells to the CSCs.

Arsenic-induced abnormalities in glucose metabolism: Biochemical basis and potential therapeutic and nutritional interventions

Health hazards due to the consumption of heavy metals such as arsenic have become a worldwide problem. Metabolism of arsenic produces various intermediates which are more toxic and cause toxicity. Arsenic exposure results in impairment of glucose metabolism, insulin secretion in pancreatic β-cells, altered gene expressions and signal transduction, and affects insulin-stimulated glucose uptake in adipocytes or skeletal muscle cells. Arsenic toxicity causes abnormalities in glucose metabolism through an increase in oxidative stress. Arsenic interferes with the sulfhydryl groups and phosphate groups present in various enzymes involved in glucose metabolism including pyruvate dehydrogenase and α-ketoglutarate dehydrogenase, and contributes to their impairment. Arsenic inhibits glucose transporters present in the cell membrane, alters expression of genes involved in glucose metabolism, transcription factors and inflammatory cytokines which stimulate oxidative stress. Some theories suggest that arsenic exposure under diabetic conditions inhibits hyperglycemia. However, the exact mechanism behind the behavior of arsenic as an antagonist or synergist on glucose homeostasis and insulin secretion is not yet fully understood. The present review delineates the relationship between arsenic and the biochemical basis of its relationship to glucose metabolism. This review also addresses potential therapeutic and nutritional interventions for attenuating arsenic toxicity. Several other potential nutritional supplements are highlighted in the review that could be used to combat arsenic toxicity.

The two opposite facets of arsenic: toxic and anticancer drug

Arsenic compounds have been known and used for centuries but their effects in living organisms still represent a large unknown. Arsenic compounds have paradoxical effects: they are threatening to human health, especially upon long-term exposure that can induce the development of cancer; however, they are used as drugs against cancer. This review focuses on the effects shown by clinically and environmentally relevant arsenic compounds in living organisms with a focus on the calcium–apoptosis link.

JNK and STAT3 signaling pathways converge on Akt-mediated phosphorylation of EZH2 in bronchial epithelial cells induced by arsenic

The molecular mechanisms by which arsenic (As ( 3+) ) causes human cancers remain to be fully elucidated. Enhancer of zeste homolog 2 (EZH2) is the catalytic subunit of polycomb-repressive complexes 2 (PRC2) that promotes trimethylation of lysine 27 of histone H3, leading to altered expression of tumor suppressors or oncogenes. In the present study, we determined the effect of As ( 3+) on EZH2 phosphorylation and the signaling pathways important for As ( 3+) -induced EZH2 phosphorylation in human bronchial epithelial cell line BEAS-2B. The involvement of kinases in As ( 3+) -induced EZH2 phosphorylation was validated by siRNA-based gene silencing. The data showed that As ( 3+) can induce phosphorylation of EZH2 at serine 21 in human bronchial epithelial cells and that the phosphorylation of EZH2 requires an As ( 3+) -activated signaling cascade from JNK and STAT3 to Akt. Transfection of the cells with siRNA specific for JNK1 revealed that JNK silencing reduced serine727 phosphorylation of STAT3, Akt activation and EZH2 phosphorylation, suggesting that JNK is the upstream kinase involved in As ( 3+) -induced EZH2 phosphorylation. Because As ( 3+) is capable of inducing miRNA-21 (miR-21), a STAT3-regulated miRNA that represses protein translation of PTEN or Spry2, we also tested the role of STAT3 and miR-21 in As ( 3+) -induced EZH2 phosphorylation. Ectopic overexpression of miR-21 promoted Akt activation and phosphorylation of EZH2, whereas inhibiting miR-21 by transfecting the cells with anti-miR-21 inhibited Akt activation and EZH2 phosphorylation. Taken together, these results demonstrate a contribution of the JNK, STAT3 and Akt signaling axis to As ( 3+) -induced EZH2 phosphorylation. Importantly, these findings may reveal new molecular mechanisms underlying As ( 3+) -induced carcinogenesis.

New molecular insights into peripheral T cell lymphomas

Peripheral T cell lymphomas (PTCLs) are heterogeneous neoplasms and represent about 12% of all lymphoid malignancies. They are often regarded as "orphan diseases," a designation that does not reflect their real incidence but rather signifies the difficulties encountered in their classification, diagnosis, and treatment. Here we revise the current understanding of the pathobiological characteristics of the most common nodal PTCLs by focusing on the contribution given by high-throughput technologies and the identification of potential therapeutic targets proposed by translational studies.

JNK-dependent Stat3 phosphorylation contributes to Akt activation in response to arsenic exposure

Environmental exposure to arsenic, especially the trivalent inorganic form (As(3+)), has been linked to human cancers in addition to a number of other diseases including skin lesions, cardiovascular disorders, neuropathy, and internal organ injury. In the present study, we describe a novel signaling axis of the c-Jun NH2 kinase (JNK) and signal transducer and activator of transcription 3 (Stat3) and its involvement in As(3+)-induced Akt activation in human bronchial epithelial cells. As(3+) activates JNK and induces phosphorylation of the Stat3 at serine 727 (S727) in a dose- and time-dependent manner, which occurred concomitantly with Akt activation. Disruption of the JNK signaling pathway by treatment with the JNK inhibitor SP600125, siRNA knockdown of JNK, or genetic deficiency of the JNK1 or JNK2 gene abrogated As(3+)-induced S727 phosphorylation of Stat3, Akt activation, and the consequent release of vascular endothelial growth factor (VEGF) and migration of the cells. Similarly, pretreatment of the cells with Stat3 inhibitor or Stat3 siRNA prevented Akt activation and VEGF release from the cells in response to As(3+) treatment. Taken together, these data revealed a new signaling mechanism that might be pivotal in As(3+)-induced malignant transformation of the cells by linking the key stress signaling pathway, JNK, to the activation of Stat3 and the carcinogenic kinase, Akt.

Arsenic exposure and the induction of human cancers

Arsenic is a metalloid, that is, considered to be a human carcinogen. Millions of individuals worldwide are chronically exposed through drinking water, with consequences ranging from acute toxicities to development of malignancies, such as skin and lung cancer. Despite well-known arsenic-related health effects, the molecular mechanisms involved are not fully understood; however, the arsenic biotransformation process, which includes methylation changes, is thought to play a key role. This paper explores the relationship of arsenic exposure with cancer development and summarizes current knowledge of the potential mechanisms that may contribute to the neoplastic processes observed in arsenic exposed human populations.

NF-kappaB in lung cancer, a carcinogenesis mediator and a prevention and therapy target

Lung cancer ranks as the first malignant tumor killer worldwide. Despite the knowledge that carcinogens from tobacco smoke and the environment constitute the main causes of lung cancer, the mechanisms for lung carcinogenesis are still elusive. Cancer development and progression depend on the balance between cell survival and death signals. Common cell survival signaling pathways are activated by carcinogens as well as by inflammatory cytokines, which contribute substantially to cancer development. As a major cell survival signal, nuclear factor-kappaB (NF-kappaB) is involved in multiple steps in carcinogenesis and in cancer cell's resistance to chemo- and radio-therapy. Recent studies with animal models and cell culture systems have established the links between NF-kappaB and lung carcinogenesis, highlighting the significance of targeting NF-kappa signaling pathway for lung cancer treatment and chemoprevention. In this review, we summarize progresses in understanding the NF-kappaB pathway in lung cancer development as well as in modulating NF-kappaB for lung cancer prevention and therapy.

GADD45alpha mediates arsenite-induced cell apoptotic effect in human hepatoma cells via JNKs/AP-1-dependent pathway

Arsenite (As(III)), an effective chemotherapeutic agent for the acute promyelocytic leukemia (APL) and multiple myeloma (MM), might be also a promise for the therapy of other cancers, including the solid tumors. However, the molecular bases of arsenite-induced cytotoxicity in the tumor cells have not been fully defined. In this study, we have disclosed that arsenite effectively induces the apoptotic response in the HepG2 human hepatoma cells by triggering GADD45alpha induction and the subsequent activation of JNKs/AP-1 cell death pathway. However, signaling events relating to GADD45alpha/JNKs/AP-1 pathway activation have not been observed in HL7702 human diploid hepatic cells under the same arsenite exposure condition. Our results thus have illustrated the selective pro-apoptotic role of arsenite in the hepatoma cells by activating GADD45alpha-dependent cell death pathway whereas with little effect on the normal hepatic cells. The approaches to up-regulate GADD45alpha levels might be helpful in improving the chemotherapeutic action of arsenite on certain solid tumors including hepatoma.

TMS, a chemically modified herbal derivative of resveratrol, induces cell death by targeting Bax

Breast cancer recurrence after an initial favorable response to treatment is a major concern for patients who receive hormonal therapies. Additional therapies are necessary to extend the time of response, and ideally, these therapies should exhibit minimal toxicity. Our study described herein focuses on a non-toxic pro-apoptotic agent, TMS (2,4,3',5'-tetramethoxystilbene), which belongs to the Resveratrol family of stilbenes. Prior study demonstrated that TMS was more effective than Resveratrol for inducing apoptosis. Additionally, TMS was effective for invoking death of relapsing breast cancer cells. As TMS was effective for reducing tumor burden, we sought to determine the mechanism by which it achieved its effects. Microarray analysis demonstrated that TMS treatment increased tubulin genes as well as stress response and pro-apoptotic genes. Fractionation studies uncovered that TMS treatment causes cleavage of Bax from the p21 form to a truncated p18 form which is associated with the induction of potent apoptosis. Co-localization analysis of immunofluorescent studies showed that Bax moved from the cytosol to the mitochondria. In addition, the pro-apoptotic proteins Noxa and Bim (EL, L, and S) were increased upon TMS treatment. Cell lines reduced for Bax, Bim, and Noxa are compromised for TMS-mediated cell death. Electron microscopy revealed evidence of nuclear condensation, formation of apoptotic bodies and DAPI staining showed evidence of DNA fragmentation. TMS treatment was able to induce both caspase-independent and caspase-dependent death via the intrinsic death pathway.

Analysis of genomic dose-response information on arsenic to inform key events in a mode of action for carcinogenicity

A comprehensive literature search was conducted to identify information on gene expression changes following exposures to inorganic arsenic compounds. This information was organized by compound, exposure, dose/concentration, species, tissue, and cell type. A concentration-related hierarchy of responses was observed, beginning with changes in gene/protein expression associated with adaptive responses (e.g., preinflammatory responses, delay of apoptosis). Between 0.1 and 10 microM, additional gene/protein expression changes related to oxidative stress, proteotoxicity, inflammation, and proliferative signaling occur along with those related to DNA repair, cell cycle G2/M checkpoint control, and induction of apoptosis. At higher concentrations (10-100 microM), changes in apoptotic genes dominate. Comparisons of primary cell results with those obtained from immortalized or tumor-derived cell lines were also evaluated to determine the extent to which similar responses are observed across cell lines. Although immortalized cells appear to respond similarly to primary cells, caution must be exercised in using gene expression data from tumor-derived cell lines, where inactivation or overexpression of key genes (e.g., p53, Bcl-2) may lead to altered genomic responses. Data from acute in vivo exposures are of limited value for evaluating the dose-response for gene expression, because of the transient, variable, and uncertain nature of tissue exposure in these studies. The available in vitro gene expression data, together with information on the metabolism and protein binding of arsenic compounds, provide evidence of a mode of action for inorganic arsenic carcinogenicity involving interactions with critical proteins, such as those involved in DNA repair, overlaid against a background of chemical stress, including proteotoxicity and depletion of nonprotein sulfhydryls. The inhibition of DNA repair under conditions of toxicity and proliferative pressure may compromise the ability of cells to maintain the integrity of their DNA.

Identification of a small molecule inhibitor of serine 276 phosphorylation of the p65 subunit of NF-kappaB using in silico molecular docking

NF-kappaB is activated in many types of cancer. Phosphorylation of p65 at serine 276 is required for the expression of a subset of NF-kappaB regulated genes, including vascular cell adhesion molecule-1 (VCAM-1) and interleukin-8 (IL-8). Thus, inhibition of serine 276 phosphorylation may prevent metastasis and angiogenesis in certain tumor types. Using in silico molecular docking, small molecules that are predicted to bind to a structural pocket near serine 276 were identified. One compound, NSC-127102, hinders serine 276 phosphorylation and the expression of IL-8 and VCAM-1. Small molecules such as NSC-127102 may be optimized for the future treatment of cancer.

Characterization of an alternatively spliced GADD45alpha, GADD45alpha1 isoform, in arsenic-treated epithelial cells

A new GADD45alpha isoform, GADD45alpha1, was identified in the cellular response to arsenic. DNA sequencing and biochemical analyses suggested that GADD45alpha1 is derived from an alternative splicing of the GADD45alpha mRNA by skipping the region corresponding to exon2 of the gadd45alpha gene during mRNA maturation. In addition to the size difference due to the lack of 34 amino acids encoded by exon2, GADD45alpha1 and GADD45alpha proteins differ in their effects on cell proliferation and cell cycle transition. Unlike GADD45alpha, the GADD45alpha1 is unable to attenuate cell growth. In over-expression experiments, the full length GADD45alpha, but not the GADD45alpha1, sensitized cells to arsenic-induced prometaphase arrest of the cell cycle. Furthermore, GADD45alpha1 appears to be able to antagonize the function of the GADD45alpha on the G2/M phase cell cycle arrest as demonstrated in cotransfection experiment. Thus, these data suggest that the generation of the GADD45alpha1 isoform may not only offset but also antagonize the effects of arsenic and GADD45alpha on cell growth and cell cycle regulation.

Sustained JNK1 activation is associated with altered histone H3 methylations in human liver cancer

BACKGROUND/AIMS

Aberrant c-Jun N-terminal kinase (JNK) activation has been linked to hepatocellular carcinoma (HCC) in mouse models. It remains unclear whether JNK activation plays an important role in human HCC and, if so, how JNK signaling contributes to the initiation or progression of HCC.

METHODS

The JNK activation, global gene expression, and the status of histone H3 methylations were measured in 31 primary human hepatocellular carcinoma (HCC) samples paired with the adjacent non-cancerous (ANC) tissues.

RESULTS

Enhanced JNK1 activation was noted in 17 out of 31 HCC samples (55%) relative to the corresponding ANC tissues, whereas JNK2 activation was roughly equal between HCC and ANC tissues. This enhancement in JNK1 activation is associated with an increased tumor size and a lack of encapsulation of the tumors. In addition, an association of JNK1 activation with the histone H3 lysines 4 and 9 tri-methylation was observed in the HCC tissues, which leads to an elevated expression of genes regulating cell growth and a decreased expression of the genes for cell differentiation and the p450 family members in HCC.

CONCLUSIONS

These results, thus, suggest that JNK1 plays important roles in the development of human HCC partially through the epigenetic mechanisms.

Role of oxidative stress in pancreatic inflammation

Reactive oxygen and reactive nitrogen species (ROS/RNS) have been implicated in the pathogenesis of acute and chronic pancreatitis. Clinical and basic science studies have indicated that ROS/RNS formation processes are intimately linked to the development of the inflammatory disorders. The detrimental effects of highly reactive ROS/RNS are mediated by their direct actions on biomolecules (lipids, proteins, and nucleic acids) and activation of proinflammatory signal cascades, which subsequently lead to activation of immune responses. The present article summarizes the possible sources of ROS/RNS formation and the detailed signaling cascades implicated in the pathogenesis of pancreatic inflammation, as observed in acute and chronic pancreatitis. A therapeutic ROS/RNS-scavenging strategy has been advocated for decades; however, clinical studies examining such approaches have been inconsistent in their results. Emerging evidence indicates that pancreatitis-inducing ROS/RNS generation may be attenuated by targeting ROS/RNS-generating enzymes and upstream mediators.

Gene expression profiling analysis reveals arsenic-induced cell cycle arrest and apoptosis in p53-proficient and p53-deficient cells through differential gene pathways

Arsenic (As) is a well-known environmental toxicant and carcinogen as well as an effective chemotherapeutic agent. The underlying mechanism of this dual capability, however, is not fully understood. Tumor suppressor gene p53, a pivotal cell cycle checkpoint signaling protein, has been hypothesized to play a possible role in mediating As-induced toxicity and therapeutic efficiency. In this study, we found that arsenite (As(3+)) induced apoptosis and cell cycle arrest in a dose-dependent manner in both p53(+/+) and p53(-/-) mouse embryonic fibroblasts (MEFs). There was, however, a distinction between genotypes in the apoptotic response, with a more prominent induction of caspase-3 in the p53(-/-) cells than in the p53(+/+) cells. To examine this difference further, a systems-based genomic analysis was conducted comparing the critical molecular mechanisms between the p53 genotypes in response to As(3+). A significant alteration in the Nrf2-mediated oxidative stress response pathway was found in both genotypes. In p53(+/+) MEFs, As(3+) induced p53-dependent gene expression alterations in DNA damage and cell cycle regulation genes. However, in the p53(-/-) MEFs, As(3+) induced a significant up-regulation of pro-apoptotic genes (Noxa) and down-regulation of genes in immune modulation. Our findings demonstrate that As-induced cell death occurs through a p53-independent pathway in p53 deficient cells while apoptosis induction occurs through p53-dependent pathway in normal tissue. This difference in the mechanism of apoptotic responses between the genotypes provides important information regarding the apparent dichotomy of arsenic's dual mechanisms, and potentially leads to further advancement of its utility as a chemotherapeutic agent.

Peripheral T cell lymphoma, not otherwise specified: the stuff of genes, dreams and therapies

Peripheral T cell lymphomas (PTCL) account for about 12% of lymphoid tumours worldwide. Almost half show such morphological and molecular variability as to hamper any further classification, and to justify their inclusion in a waste-basket category termed “not otherwise specified (NOS)”. The latter term is used for neoplasms with aggressive presentation, poor response to therapy and dismal prognosis. In contrast to B cell lymphomas, PTCL have been the subject of only a limited number of studies to elucidate their pathobiology and identify novel pharmacological approaches. Herewith, the authors revise the most recent contributions on the subject based on the experience they have gained in the extensive application of microarray technologies. PTCL/NOS are characterised by erratic expression of T cell associated antigens, including CD4 and CD52, which have recently been proposed as targets for ad hoc immunotherapies. PTCL/NOS also show variable Ki-67 marking, with rates >80% heralding a worse prognosis. Gene expression profiling studies have revealed that PTCL/NOS derive from activated T lymphocytes, more often of the CD4+ type, and bear a signature composed of 155 genes and related products that play a pivotal role in cell signalling transduction, proliferation, apoptosis and matrix remodelling. This observation seems to pave the way for the use of innovative drugs such as tyrosine kinase and histone deacetylase inhibitors whose efficacy has been proven in PTCL primary cell cultures. Gene expression profiling also allows better distinction of PTCL/NOS from angioimmunoblastic T cell lymphoma, the latter being characterised by follicular T helper lymphocyte derivation and CXCL13, PD1 and vascular endothelial growth factor expression.

Arsenic trioxide in environmentally and clinically relevant concentrations interacts with calcium homeostasis and induces cell type specific cell death in tumor and non-tumor cells

While arsenic compounds are known as environmental toxicants (especially in drinking water) and as carcinogens, some arsenic compounds, like arsenic trioxide (As2O3), are clinically used in humans to treat some forms of cancer (e.g. leukemia). Although arsenic compounds have been studied intensively, their interactions with living cells are still not fully elucidated. We have previously proposed that modulation of intracellular calcium ([Ca2+]i) homeostasis induced by As2O3 could be an important mechanism to induce cytotoxicity. Here we demonstrate, using human cell models (neuroblastoma (SY-5Y) or embryonic kidney cells (HEK)) and confocal microscopy in combination with the calcium sensitive dye fluo 4-AM, that As2O3 interferes with calcium signaling at low (environmentally and clinically relevant concentrations of 100 pM to 1 microM). Within this concentration range, As2O3 had cell type specific cytotoxic effects, with neuroblastoma cells being more sensitive to As2O3 than HEK 293. In addition, by staining with Hoechst 33347 and counting micronucleated cells as well as apoptotic nuclei, As2O3 was found to increase the rate of apoptosis and DNA damage, which was also cell type specific. These results indicate that the As2O3-induced cell death could be triggered or mediated by [Ca2+]i signals and suggest that low concentrations of As2O3 are able to interfere with specific physiological processes in diverse cell models.

Sensitivity to sodium arsenite in human melanoma cells depends upon susceptibility to arsenite-induced mitotic arrest

Arsenic induces clinical remission in patients with acute promyelocytic leukemia and has potential for treatment of other cancers. The current study examines factors influencing sensitivity to arsenic using human malignant melanoma cell lines. A375 and SK-Mel-2 cells were sensitive to clinically achievable concentrations of arsenite, whereas SK-Mel-3 and SK-Mel-28 cells required supratherapeutic levels for toxicity. Inhibition of glutathione synthesis, glutathione S-transferase (GST) activity, and multidrug resistance protein (MRP) transporter function attenuated arsenite resistance, consistent with studies suggesting that arsenite is extruded from the cell as a glutathione conjugate by MRP-1. However, MRP-1 was not overexpressed in resistant lines and GST-pi was only slightly elevated. ICP-MS analysis indicated that arsenite-resistant SK-Mel-28 cells did not accumulate less arsenic than arsenite-sensitive A375 cells, suggesting that resistance was not attributable to reduced arsenic accumulation but rather to intrinsic properties of resistant cell lines. The mode of arsenite-induced cell death was apoptosis. Arsenite-induced apoptosis is associated with cell cycle alterations. Cell cycle analysis revealed arsenite-sensitive cells arrested in mitosis whereas arsenite-resistant cells did not, suggesting that induction of mitotic arrest occurs at lower intracellular arsenic concentrations. Higher intracellular arsenic levels induced cell cycle arrest in the S-phase and G(2)-phase in SK-Mel-3 and SK-Mel-28 cells, respectively. The lack of arsenite-induced mitotic arrest in resistant cell lines was associated with a weakened spindle checkpoint resulting from reduced expression of spindle checkpoint protein BUBR1. These data suggest that arsenite has potential for treatment of solid tumors but a functional spindle checkpoint is a prerequisite for a positive response to its clinical application.

Metals and apoptosis: recent developments

Apoptosis, also known as programmed cell death is a highly regulated and crucial process found in all multicellular organisms. It is not only implicated in regulatory mechanisms of cells, but has been attributed to a number of diseases, i.e. inflammation, malignancy, autoimmunity and neurodegeneration. A variety of toxins can induce apoptosis. Carcinogenic transition metals, viz. cadmium, chromium and nickel promote apoptosis along with DNA base modifications, strand breaks and rearrangements. Generation of reactive oxygen species, accumulation of Ca(2+), upregulation of caspase-3, down regulation of bcl-2, and deficiency of p-53 lead to arsenic-induced apoptosis. In the case of cadmium, metallothionein expression determines the choice between apoptosis and necrosis. Reactive oxygen species (ROS) and p53 contribute in apoptosis caused by chromium. Immuno suppressive mechanisms contribute in lead-induced apoptosis whereas in the case of mercury, p38 mediated caspase activation regulate apoptosis. Nickel kills the cells by apoptotic pathways. Copper induces apoptosis by p53 dependent and independent pathways. Beryllium stimulates the formation of ROS that play a role in Be-induced macrophage apoptosis. Selenium induces apoptosis by producing superoxide that activates p53. Thus, disorders of apoptosis may play a critical role in some of the most debilitating metal-induced afflictions including hepatotoxicity, renal toxicity, neurotoxicity, autoimmunity and carcinogenesis. An understanding of metal-induced apoptosis will be helpful in the development of preventive molecular strategies.

Regulation of heme oxygenase-1 mRNA deadenylation and turnover in NIH3T3 cells by nitrosative or alkylation stress

Background

Heme oxygenase-1 (HO-1) catalizes heme degradation, and is considered one of the most sensitive indicators of cellular stress. Previous work in human fibroblasts has shown that HO-1 expression is induced by NO, and that transcriptional induction is only partially responsible; instead, the HO-1 mRNA half-life is substantially increased in response to NO. The mechanism of this stabilization remains unknown.

Results

In NIH3T3 murine fibroblasts, NO exposure increased the half-life of the HO-1 transcript from ~1.6 h to 11 h, while treatments with CdCl₂, NaAsO₂ or H₂O₂ increased the half-life only up to 5 h. Although poly(A) tail shortening can be rate-limiting in mRNA degradation, the HO-1 mRNA deadenylation rate in NO-treated cells was ~65% of that in untreated controls. In untreated cells, HO-1 poly(A) removal proceeded until 30–50 nt remained, followed by rapid mRNA decay. In NO-treated cells, HO-1 deadenylation stopped with the mRNA retaining poly(A) tails 30–50 nt long. We hypothesize that NO treatment stops poly(A) tail shortening at the critical 30- to 50-nt length. This is not a general mechanism for the post-transcriptional regulation of HO-1 mRNA. Methyl methane sulfonate also stabilized HO-1 mRNA, but that was associated with an 8-fold decrease in the deadenylation rate compared to that of untreated cells. Another HO-1 inducer, CdCl₂, caused a strong increase in the mRNA level without affecting the HO-1 mRNA half-life.

Conclusion

The regulation of HO-1 mRNA levels in response to cellular stress can be induced by transcriptional and different post-transcriptional events that act independently, and vary depending on the stress inducer. While NO appears to stabilize HO-1 mRNA by preventing the final steps of deadenylation, methyl methane sulfonate achieves stabilization through the regulation of earlier stages of deadenylation.

Gene expression analysis of angioimmunoblastic lymphoma indicates derivation from T follicular helper cells and vascular endothelial growth factor deregulation

Angioimmunoblastic lymphoma (AILT) is the second most common subtype of peripheral T-cell lymphoma (PTCL) and is characterized by dismal prognosis. Thus far, only a few studies have dealt with its molecular pathogenesis. We performed gene expression profile (GEP) analysis of six AILT, six anaplastic large cell lymphomas (ALCL), 28 PTCL-unspecified (PTCL/U), and 20 samples of normal T lymphocytes (including CD4(+), CD8(+), and activated and resting subpopulations), aiming to (a) assess the relationship of AILT with other PTCLs, (b) establish the relationship between AILT and normal T-cell subsets, and (c) recognize the cellular programs deregulated in AILT possibly looking for novel potential therapeutic targets. First, we found that AILT and other PTCLs have rather similar GEP, possibly sharing common oncogenic pathways. Second, we found that AILTs are closer to activated CD4(+), rather than to resting or CD8(+) lymphocytes. Furthermore, we found that the molecular signature of follicular T helper cells was significantly overexpressed in AILT, reinforcing the idea that AILT may arise from such cellular counterpart. Finally, we identified several genes deregulated in AILT, including PDGFRA, REL, and VEGF. The expression of several molecules was then studied by immunohistochemistry on tissue microarrays containing 45 independent AILT cases. Notably, we found that the vascular endothelial growth factor (VEGF) was expressed not only by reactive cells, but also by neoplastic cells, and that nuclear factor-kappaB (NF-kappaB) activation is uncommon in AILT, as suggested by frequent exclusively cytoplasmic c-REL localization. Our study provides new relevant information on AILT biology and new candidates for possible therapeutic targets such as PDGFRA (platelet-derived growth factor alpha) and VEGF.

The role of Akt on arsenic trioxide suppression of 3T3-L1 preadipocyte differentiation

The present study investigates the molecular details of how arsenic trioxide inhibits preadipocyte differentiation and examines the role of Akt/PKB in regulation of differentiation and apoptosis. Continual exposure of arsenic trioxide, at the clinic achievable dosage that does not induce apoptosis, suppressed 3T3-L1 cell differentiation into fat cells by inhibiting the expression of PPARgamma and C/EBPalpha and disrupting the interaction between PPARgamma and RXRalpha, which determines the programming of the adipogenic genes. Interestingly, if we treated the cells for 12 or 24 h and then withdrew arsenic trioxide, the cells were able to differentiate to the comparable levels of untreated cells as assayed by the activity of GAPDH, the biochemical marker of preadipocyte differentiation. Long term treatment blocked the differentiation and the activity of GAPDH could not recover to the comparable levels of untreated cells. Continual exposure of arsenic trioxide caused accumulation in G2/M phase and the accumulation of p21. We found that arsenic trioxide induced the expression and the phosphorylation of Akt/PKB and it inhibited the interaction between Akt/PKB and PPARgamma . Akt/PKB inhibitor appears to block the arsenic trioxide suppression of differentiation. Our results suggested that Akt/PKB may play a role in suppression of apoptosis and negatively regulate preadipocyte differentiation.

Cyclin B1 proteolysis via p38 MAPK signaling participates in G2 checkpoint elicited by arsenite

Timely induction of cyclin B1 controls mitotic entry, whereas its proteolysis is essential for mitotic exit. By contrast, cyclin B1 transcription is repressed during G(2) arrest induced by DNA damage. The p38 mitogen-activated protein kinase is involved in the G(2) checkpoint; yet, its impact on cyclin B1 protein levels remains unclear. Here we show that untimely proteolysis of cyclin B1 following p38 activation contributes to G(2) checkpoint. Exposing early G(2) cells to arsenite impeded cyclin B1 protein accumulation, Cdk1 activation, and G(2)-to-M progression. Conversely, cyclin B1 was non-degradable in late G(2) and mitotic cells after arsenite. Cyclin B1 proteolysis was enhanced by arsenite in early G(2) and asynchronous cells. This rapid destruction of cyclin B1 was mediated via the ubiquitin-proteasome pathway probably in a Cdc20 and Cdh1 independent mechanism. Under arsenite, inhibition of p38 activation or depletion of p38alpha suppressed cyclin B1 ubiquitination and proteolysis, while forced expression of MKK6-p38 accelerated these events. Inactivation of p38 in arsenite-treated early G(2) cells allowed G(2)-to-M progression, blocked apoptosis, increased cell viability, and decreased micronucleus formation. Thus, p38 signaling pathway triggering cyclin B1 proteolysis after arsenite may play an important role in connecting G(2) arrest with apoptosis or genome instability.

Berberine induces apoptosis in SW620 human colonic carcinoma cells through generation of reactive oxygen species and activation of JNK/p38 MAPK and FasL

Berberine is the major constituent of Coptidis Rhizoma with multiple pharmacological activities, including anti-inflammation, promotion of apoptosis and anticancer potential effect. Mitogen-activated protein kinase (MAPK) and reactive oxygen species (ROS) may contribute to the causal relationship between tumorigenesis and pro-apoptotic function. Berberine is studied for the mechanism of its action in apoptotic pathway in human colonic carcinoma cell. Treatment of SW620 cells with 50 microM berberine resulted in activation of the caspase 3 and caspase 8, cleavage of poly ADP-ribose polymerase (PARP) and the release of cytochrome c; whereas, the expression of BID and anti-apoptosis factor c-IAP1, Bcl-2, and Bcl-(XL) were decreased markedly. Berberine-induced, dose-dependent induction of apoptosis was accompanied by sustained phosphorylation of JNK and p38 MAPK, as well as generation of the ROS. Furthermore, the induction of apoptosis was alleviated by inhibitors specific for JNK and p38. In addition, there was an increase in the cellular levels of phospho-c-Jun, FasL and t-BID in the berberine-induced apoptosis via the activation of JNK and p38 signaling modules. NAC administration, a scavenger of ROS, reversed berberine-induced apoptosis effects via inhibition of JNK, p38 and c-jun activation, and FasL and t-BID expression. These results leads us to speculate that berberine may play an apoptotic cascade in SW620 cells by activation of the JNK/p38 pathway and induction of ROS production, providing a new mechanism for berberine-induced cell death in human colon cancer cells.

Incorporation of an internal ribosome entry site-dependent mechanism in arsenic-induced GADD45 alpha expression

We have previously shown that trivalent arsenic (arsenite, As(3+)) is able to induce GADD45 alpha expression in human bronchial epithelial cells through activation of c-Jun NH(2)-terminal kinase and nucleolin-dependent mRNA stabilization. In the present report, we show that As(3+) is capable of inducing translation of the GADD45 alpha protein through a cap-independent, or rather, an internal ribosome entry site (IRES)-dependent mechanism. In growth-arrested cells, As(3+) elevated the GADD45 alpha protein level in a dose- and time-dependent manner which did not correlate with the GADD45 alpha mRNA expression. Pretreatment of the cells with rapamycin, an inhibitor for the cap-dependent translation machinery through the suppression of mTOR and p70S6 kinase, failed to affect the induction of the GADD45 alpha protein induced by As(3+). Sequence analysis revealed a potential IRES element in the 5'-untranslated region of the GADD45 alpha mRNA. This IRES element in the 5'-untranslated region of the GADD45 alpha mRNA is functional in mediating As(3+)-induced translation of the GADD45 alpha protein in a dicistronic reporter gene activity assay. Immunoprecipitation and proteomic studies suggest that As(3+) impairs the assembly of the cap-dependent initiating complex for general protein translation but increases the association of human elongation factor 2 and human heterogeneous nuclear ribonucleoprotin with this complex. Thus, these results suggest that in growth-arrested cells, As(3+) is still capable of inducing GADD45 alpha expression through an IRES-dependent translational regulation.

Low-dose arsenic trioxide sensitizes glucocorticoid-resistant acute lymphoblastic leukemia cells to dexamethasone via an Akt-dependent pathway

Incorporation of apoptosis-inducing agents into current therapeutic regimens is an attractive strategy to improve treatment for drug-resistant leukemia. We tested the potential of arsenic trioxide (ATO) to restore the response to dexamethasone in glucocorticoid (GC)-resistant acute lymphoblastic leukemia (ALL). Low-dose ATO markedly increased in vitro GC sensitivity of ALL cells from T-cell and precursor B-cell ALL patients with poor in vivo response to prednisone. In GC-resistant cell lines, this effect was mediated, at least in part, by inhibition of Akt and affecting downstream Akt targets such as Bad, a proapoptotic Bcl-2 family member, and the X-linked inhibitor of apoptosis protein (XIAP). Combination of ATO and dexamethasone resulted in increased Bad and rapid down-regulation of XIAP, while levels of the antiapoptotic regulator Mcl-1 remained unchanged. Expression of dominant-active Akt, reduction of Bad expression by RNA interference, or overexpression of XIAP abrogated the sensitizing effect of ATO. The inhibitory effect of XIAP overexpression was reduced when the Akt phosphorylation site was mutated (XIAP-S87A). These data suggest that the combination of ATO and glucocorticoids could be advantageous in GC-resistant ALL and reveal additional targets for the evaluation of new antileukemic agents.

Arsenic trioxide (As2O3) induced calcium signals and cytotoxicity in two human cell lines: SY-5Y neuroblastoma and 293 embryonic kidney (HEK)

Arsenic trioxide (As(2)O(3)) has anticancer properties; however, its use also leads to neuro-, hepato- or nephro-toxicity, and therefore, it is important to understand the mechanism of As(2)O(3) toxicity. We studied As(2)O(3) influence on intracellular calcium ([Ca(2+)](i)) homeostasis of human neuroblastoma SY-5Y and embryonic kidney cells (HEK 293). We also relate the As(2)O(3) induced [Ca(2+)](i) modifications with cytotoxicity. We used Ca(2+) sensitive dyes (fluo-4 and rhod-2) combined with laser scanning microscopy or fluorescence activated cell sorting to measure Ca(2+) changes during the application of As(2)O(3) and we approach evaluation of cytotoxicity. As(2)O(3) (1 microM) increased [Ca(2+)](i) in SY-5Y and HEK 293 cells. Three forms of [Ca(2+)](i)-elevations were found: (1) steady-state increases, (2) transient [Ca(2+)](i)-elevations and (3) Ca(2+)-spikes. [Ca(2+)](i) modifications were independent from extracellular Ca(2+) but dependent on internal calcium stores. The effect was not reversible. Inositol triphosphate (IP(3)) and ryanodine (Ry) receptors are involved in regulation of signals induced by As(2)O(3). 2-APB and dantrolene significantly reduced the [Ca(2+)](i)-rise (p<0.001, t-test) but did not completely abolish [Ca(2+)](i)-elevation or spiking. This indicates that other Ca(2+) regulating mechanisms are involved. In cytotoxicity tests As(2)O(3) significantly reduced cell viability in both cell types. Staining with Hoechst 33342 showed occurrence of apoptosis and DNA damage. Our data suggest that [Ca(2+)](i) is an important messenger in As(2)O(3) induced cell death.

Deficiency in Ikkbeta gene enhances arsenic-induced gadd45alpha expression

Chronic arsenic exposure is implicated in the pathophysiology of various human diseases, including cancer and diabetes. Using Ikkbeta gene knockout mouse embryonic fibroblast cells (Ikkbeta-/-), in the present study we demonstrated that NF-kappaB inhibition due to Ikkbeta deficiency up-regulated basal and arsenic-induced expression of gadd45alpha. In addition to gadd45alpha, the basal expression of other gadd family members including gadd45beta, gadd45gamma and gadd153 was substantially increased in Ikkbeta-/- cells. Ikkbeta deficiency prevented the induction of gadd45beta and gadd45gamma by arsenic, whereas the induction of gadd45alpha and gadd153 was appreciably enhanced in Ikkbeta-/- cells. Furthermore, a substantial decrease in the expression of c-myc, an established endogenous transcriptional repressor of gadd45alpha and gadd153 genes, was noted. Thus, these results uncover the molecular mechanism by which NF-kappaB signalling contributes to the regulation of gadd family gene expression induced by arsenic.

Gene expression analysis of peripheral T cell lymphoma, unspecified, reveals distinct profiles and new potential therapeutic targets

Peripheral T cell lymphoma, unspecified (PTCL/U), the most common form of PTCL, displays heterogeneous morphology and phenotype, poor response to treatment, and poor prognosis. We demonstrate that PTCL/U shows a gene expression profile clearly distinct from that of normal T cells. Comparison with the profiles of purified T cell subpopulations (CD4+, CD8+, resting [HLA-DR-], and activated [HLA-DR+]) reveals that PTCLs/U are most closely related to activated peripheral T lymphocytes, either CD4+ or CD8+. Interestingly, the global gene expression profile cannot be surrogated by routine CD4/CD8 immunohistochemistry. When compared with normal T cells, PTCLs/U display deregulation of functional programs often involved in tumorigenesis (e.g., apoptosis, proliferation, cell adhesion, and matrix remodeling). Products of deregulated genes can be detected in PTCLs/U by immunohistochemistry with an ectopic, paraphysiologic, or stromal location. PTCLs/U aberrantly express, among others, PDGFRalpha, a tyrosine-kinase receptor, whose deregulation is often related to a malignant phenotype. Notably, both phosphorylation of PDGFRalpha and sensitivity of cultured PTCL cells to imatinib (as well as to an inhibitor of histone deacetylase) were found. These results, which might be extended to other more rare PTCL categories, provide insight into tumor pathogenesis and clinical management of PTCL/U.

IKKbeta programs to turn on the GADD45alpha-MKK4-JNK apoptotic cascade specifically via p50 NF-kappaB in arsenite response

Cross talk between NF-κB and c-Jun N-terminal kinases (JNKs) has been implicated in the cell life and death decision under various stresses. Functional suppression of JNK activation by NF-κB has recently been proposed as a key cellular survival mechanism and contributes to cancer cells escaping from apoptosis. We provide a novel scenario of the proapoptotic role of IκB kinase β (IKKβ)–NF-κB, which can act as the activator of the JNK pathway through the induction of GADD45α for triggering MKK4/JNK activation, in response to the stimulation of arsenite, a cancer therapeutic reagent. This effect of IKKβ–NF-κB is dependent on p50 but not the p65/relA NF-κB subunit, which can increase the stability of GADD45α protein through suppressing its ubiquitination and proteasome-dependent degradation. IKKβ–NF-κB can therefore either activate or suppress the JNK cascade and consequently mediate pro- or antiapoptotic effects, depending on the manner of its induction. Furthermore, the NF-κB p50 subunit can exert a novel regulatory function on protein modification independent of the classical NF-κB transcriptional activity.

Arsenite inhibits p53 phosphorylation, DNA binding activity, and p53 target gene p21 expression in mouse epidermal JB6 cells

Epidemiologic investigations demonstrated that arsenite exposure increases the risk of various human cancers, including skin, lung, bladder, and kidney cancers. However, oral administration of arsenite alone has failed to induce tumors in animal models, suggesting that arsenic may act to enhance mutagenicity induced by other carcinogens. Arsenite may function as a co-carcinogen, acting by inhibiting repair of carcinogen-induced DNA damage mediated by p53 and p21, a p53 target gene. To elucidate the interaction between arsenite and p53 tumor suppressor protein, we studied the effect of arsenite on ultraviolet B (UVB)-induced p53 phosphorylation, p53 DNA binding activity, and p53-induced target gene transactivation in the JB6 Cl41 mouse epidermal skin cell model. Our results indicated that arsenite suppressed UVB-induced p53 phosphorylation and p53 DNA binding activity. Arsenite also inhibited casein kinase 2 (CK2) activity and decreased p53-regulated p21 protein expression. These data suggest that the direct inhibition of p53 functional activation is one of the mechanisms through which arsenite interferes with p53 function, and thus may be a significant mechanism for the co-carcinogenic effects of arsenite.

Coordination of JNK1 and JNK2 is critical for GADD45alpha induction and its mediated cell apoptosis in arsenite responses

Arsenite is a well documented environmental pathogen, whereas it has also been applied as medication to treat various neoplasmas. The pathogenic and therapeutic effects of arsenite are associated with cellular apoptotic responses. However, the molecular mechanisms of arsenite-induced apoptosis are not very well understood. Our previous study has shown that arsenite exposure is able to activate JNKs, which subsequently mediate the apoptotic outcome. The present study further revealed that the coordination of JNK1 and JNK2 was critical for the arsenite-induced expression of GADD45alpha (growth arrest and DNA damage 45alpha), which in turn mediated the cellular apoptosis. The arsenite-induced apoptosis and GADD45alpha expression were significantly impaired in mouse embryonic fibroblasts deficient in either jnk1 (JNK1-/-) or jnk2 (JNK2-/-). Knockdown of GADD45alpha by its specific small interfering RNA also dramatically reduced the apoptotic responses, and overexpression of GADD45alpha in either JNK1-/- or JNK2-/- mouse embryonic fibroblasts partially resensitized the cell death. Furthermore, it was found that the regulation of GADD45alpha by JNK1 and JNK2 was achieved through mediating the activation of c-Jun, since in the JNK1-/- and JNK2-/- cells the c-Jun activation was impaired, and overexpression of the dominant negative mutant of c-Jun (TAM67) in wild type cells could also block GADD45alpha induction as well as cellular apoptosis. Our results demonstrate that the coordination of JNK1 and JNK2 is critical for c-Jun/GADD45alpha-mediated cellular apoptosis induced by arsenite.

Loss of Ikkbeta promotes migration and proliferation of mouse embryo fibroblast cells

The IkappaB kinase complex (IKK) is central to the activation of NF-kappaB, a critical transcription factor governing expression of genes involved in cell proliferation and anti-apoptotic responses. Mice with genetic disruptions of the Ikkbeta or Ikkgamma gene loci die during embryogenesis because of severe hepatic apoptosis. We now show that Ikkbeta gene deficiency promotes migration and proliferation of mouse embryo fibroblast cells. Morphological analyses revealed an unusual protrusion of the cytoplasm in Ikkbeta(-/-) cells when cultured at a lower density. In a Boyden chamber assay, Ikkbeta(-/-) cells exhibited a high rate of invasion and migration. Enhanced formation of actin stress fibers was also observed in the Ikkbeta(-/-) cells. Mechanistic studies indicated that IKKbeta affects the expression of proteins involved in the assembly of cytoskeleton and cell movement. Furthermore, re-expression of Ikkbeta and antioxidant treatment in Ikkbeta(-/-) cells caused a reversal of protrusive phenotype and high motility, respectively. Furthermore, elimination of reactive oxygen species (ROS) blocked expression of snail and subsequently derepressed E-cadherin expression. Although the underlying mechanism is likely entangled and complicated, the data presented indicate that generation of ROS played a key role in the morphological and mobility changes in Ikkbeta(-/-) cells. These data thus suggest that IKKbeta provides inhibitory signals for cell mobility and growth. Deficiency in the Ikkbeta gene promotes cell mobilization, at least partially, through a ROS-dependent mechanism.

As(III) transcriptionally activates the gadd45a gene via the formation of H2O2

Arsenic is a ubiquitous environmental contaminant associated with increased risks of human cancers of the skin, lung, bladder, and prostate. Intriguingly, it is also used to treat certain types of leukemia. It has recently been suggested that these paradoxic effects may be mediated by arsenic's ability to simultaneously activate DNA damage and apoptotic and transformation pathways. Here, we investigate the effects of arsenic exposure on the induction of the growth arrest and DNA damage protein 45 alpha (GADD45 alpha), which is thought to play roles in apoptosis, DNA damage response, and cell cycle arrest. We found that arsenic transcriptionally activates the gadd45 alpha promoter located in a 153-bp region between -234 and -81, relative to the transcriptional start site. In addition, this transcriptional induction was abrogated in the presence of H2O2 scavengers, suggesting a role for H2O2 in the transcriptional control of the gadd45a gene through a Fenton-like free radical mechanism.

GADD45alpha is highly expressed in pancreatic ductal adenocarcinoma cells and required for tumor cell viability

Pancreatic ductal adenocarcinoma is one of the most common causes of cancer death in the western civilization. Recently, NF-kappaB has been shown to be activated in pancreatic ductal adenocarcinoma through constitutive activation of IkappaB kinase (IKK). Inhibition of NF-kappaB by a super-inhibitor of NF-kappaB--delta-N-IkappaBalpha--resulted in impaired proliferation and induction of apoptosis, suggesting an important role of NF-kappaB in pancreatic tumorigenesis. Downstream target genes of IkappaBalpha have not been elucidated in pancreatic ductal adenocarcinoma in detail. Using expression profiling by cDNA array analysis of pancreatic ductal adenocarcinoma cell lines stably transfected with super-IkappaBalpha, we identified GADD45alpha as a significant regulated gene. GADD45alpha is overexpressed in pancreatic ductal adenocarcinoma at the mRNA and protein level. Using RNAi we show that downregulation of GADD45alpha reduces proliferation and induces apoptosis in pancreatic cancer cells. These findings provide evidence that GADD45alpha contributes to pancreatic cancer cell proliferation and viability.

Arsenic trioxide inhibits cell growth in SH-SY5Y and SK-N-AS neuroblastoma cell lines by a different mechanism

Neuroblastoma, characterized by heterogeneous cell population, is a common solid tumor in childhood and some malignant neuroblastomas are refractory to conventional chemotherapy. Recently, treatment with arsenic trioxide (As2O3) was found effective in the treatment of acute promyelocytic leukemia as well as neuroblastoma cells by inducing apoptosis. To define the mechanism contributing to cell death in those heterogenous cell populations, the authors used two different types of neuroblastoma cells, SH-SY5Y and SK-N-AS, to compare the pathways that mediate death response to arsenic trioxide. With arsenic trioxide exposure, both cell lines were arrested at the S-G2/M phase with the increase of cyclin B expression and CDK1 activity. Although caspase 3 was activated in both cell lines, the NF-kappaB activity and the expression of cyclin D1, cyclin E, and p27 were different. Therefore, arsenic trioxide could be an effective cytotoxic drug for the treatment of heterogeneous cellular population of neuroblastoma.

Fibronectin induces cell proliferation and inhibits apoptosis in human bronchial epithelial cells: pro-oncogenic effects mediated by PI3-kinase and NF-κB

The extracellular matrix glycoprotein, fibronectin, influences a variety of cellular functions including adhesion, migration, survival, differentiation, and growth. Fibronectin has also been shown to increase the migration and proliferation of human lung carcinoma cells. However, the role of fibronectin in controlling lung airway epithelial cell phenotype remains unknown. Here, we demonstrate that fibronectin stimulates the proliferation of human bronchial epithelial cells (BEAS-2B and 16-HBE). Of note, fibronectin induced the mRNA and protein expression of c-Myc and cyclin D1, while it decreased the expressions of cyclin-dependent kinase inhibitor p21 (WAF-1/CIP1/MDA-6) (p21) and the tumor suppressor gene phosphatase and tensin homolog deleted on chromosome ten (PTEN). Fibronectin also stimulated the phosphorylation of the phosphatidylinositol 3 kinase (PI3-K) downstream signal Akt. The inhibitor of PI3-K, Wortmannin, and anti-alpha5beta1 integrin antibodies abrogated the effect of fibronectin on c-Myc, cyclin D1, p21, and PTEN expression. The stimulatory effect of fibronectin was mediated by nuclear factor kappaB (NF-kappaB) since fibronectin induced the expression of the p65 component of NF-kappaB and enhanced NF-kappaB DNA binding. Furthermore, we found that p65 small interfering RNA inhibited the effect of fibronectin on c-Myc, cyclin D1, p21, PTEN expression, and on fibronectin-induced cell proliferation. Finally, we found that fibronectin inhibits apoptosis by reducing DNA fragmentation and inhibiting the activities of caspases 3/7. Taken together, our findings demonstrate that fibronectin stimulates human bronchial epithelial cell growth and inhibits apoptosis through activation of NF-kappaB, which, in turn, increases the expression of c-Myc and cyclin D1 and decreases p21 and PTEN via alpha5beta1 integrin-dependent signals that include PI3-K/Akt. Therefore, alternations in the extracellular matrix composition of the lung, with increased fibronectin, might promote epithelial cell growth and thereby contribute to oncogenesis in certain settings.

Nucleolin links to arsenic-induced stabilization of GADD45alpha mRNA

The present study shows that arsenic induces GADD45alpha (growth arrest and DNA damage inducible gene 45alpha) mainly through post-transcriptional mechanism. Treatment of the human bronchial epithelial cell line, BEAS-2B, with arsenic(III) chloride (As3+) resulted in a significant increase in GADD45alpha protein and mRNA. However, As3+ only exhibited a marginal effect on the transcription of the GADD45alpha gene. The accumulation of GADD45alpha mRNA is largely achieved by the stabilization of GADD45alpha mRNA in the cellular response to As3+. As3+ is able to induce binding of mRNA stabilizing proteins, nucleolin and less potently, HuR, to the GADD45alpha mRNA. Although As3+ was unable to affect the expression of nucleolin, treatment of the cells with As3+ resulted in re-distribution of nucleolin from nucleoli to nucleoplasm. Silencing of the nucleolin mRNA by RNA interference reversed As3+-induced stabilization of the GADD45alpha mRNA and accumulation of the GADD45alpha protein. Stabilization of GADD45alpha mRNA, thus, represents a novel mechanism contributing to the production of GADD45alpha and cell cycle arrest in response to As3+.

Respiratory burst: role in signal transduction in alveolar macrophages

Alveolar macrophages play an important role in defense against airborne pathogens and particles. These macrophages respond through both the adaptive and acquired immune responses, and through the activation of a multitude of signaling pathways. One major macrophage defense mechanism is respiratory burst, the production of reactive oxygen species (ROS). While the ROS produced may act directly in pathogen killing, they may also be involved as secondary signaling messengers. This review focuses on the activation of four main signaling pathways following the production of reactive oxygen species. These pathways include the nuclear factor kappa beta (NFkB), activating protein-1 (AP-1), mitogen-activating protein kinase (MAPK), and phosphotidyl inositol-3 kinase (PI3K) pathways. This review also briefly examines the role of ROS in DNA damage, in particular looking at the base excision repair pathway (BER), the main pathway involved in repair of oxidative DNA damage. This review highlights many of the studies in the field of ROS, signal transduction, and DNA damage; however, work still remains to further elucidate the role of ROS in disease.

Heat shock protein 70 as an indicator of early lung injury caused by exposure to arsenic

Heat shock proteins (HSPs) are a family of highly conserved proteins that are induced by a number of stresses including toxic metals. Heat shock proteins expression has been reported to be an early and sensitive biomarker of cell stress. Arsenic is a naturally occurring metal that exists widely in the environment and is used in several industries. Exposure to arsenic is associated with the development of pulmonary cancers. We monitored changes in Hsp70 and markers of oxidative injury induced by arsenic in human pulmonary epithelial cells (BEAS-2B). Hsp70 protein, mRNA and reactive oxygen species (ROS) generation were measured after exposing cells to arsenic as markers of injury. Hsp70 protein expression showed significant 7.9-fold and 31.5-fold increase using Western blotting and ELISA assay, respectively, at a 50 microM As(III) with a 12 h exposure and an 12 h recovery time. Hsp70A and Hsp70B mRNA expression showed a two-fold increase and Hsp70C mRNA expression showed a six-fold increase. As(III)-induced Hsp70 protein expression was inhibited significantly by catalase and NAC, indicating mediation of ROS in Hsp70 expression. Intracellular glutathione (GSH) was significantly depleted by As(III) exposure. Lipid peroxidation by-product, 8-isoprostane, was increased six-fold at 24 h exposure to 20 microM As(III). Electron spin resonance and confocal microscope studies also showed As(III)-stimulated ROS generation. These results suggest that cellular injury by arsenic is mediated through ROS generation resulting in the expression of Hsp70. It is possible that Hsp70 may prove to be a sensitive biomarker for arsenic exposure with other markers of oxidative stress in human serum.