Soluble and insoluble nickel compounds exert a differential inhibitory effect on cell growth through IKKalpha-dependent cyclin D1 down-regulation

Contaminant Metals and Cardiovascular Health

A growing body of research has begun to link exposure to environmental contaminants, such as heavy metals, with a variety of negative health outcomes. In this paper, we sought to review the current research describing the impact of certain common contaminant metals on cardiovascular (CV) health. We reviewed ten metals: lead, barium, nickel, chromium, cadmium, arsenic, mercury, selenium, zinc, and copper. After a literature review, we briefly summarized the routes of environmental exposure, pathophysiological mechanisms, CV health impacts, and exposure prevention and/or mitigation strategies for each metal. The resulting article discloses a broad spectrum of pathological significance, from relatively benign substances with little to no described effects on CV health, such as chromium and selenium, to substances with a wide-ranging and relatively severe spectrum of CV pathologies, such as arsenic, cadmium, and lead. It is our hope that this article will provide clinicians with a practical overview of the impact of these common environmental contaminants on CV health as well as highlight areas that require further investigation to better understand how these metals impact the incidence and progression of CV diseases.

Among Gerontogens, Heavy Metals Are a Class of Their Own: A Review of the Evidence for Cellular Senescence

Advancements in modern medicine have improved the quality of life across the globe and increased the average lifespan of our population by multiple decades. Current estimates predict by 2030, 12% of the global population will reach a geriatric age and live another 3-4 decades. This swelling geriatric population will place critical stress on healthcare infrastructures due to accompanying increases in age-related diseases and comorbidities. While much research focused on long-lived individuals seeks to answer questions regarding how to age healthier, there is a deficit in research investigating what aspects of our lives accelerate or exacerbate aging. In particular, heavy metals are recognized as a significant threat to human health with links to a plethora of age-related diseases, and have widespread human exposures from occupational, medical, or environmental settings. We believe heavy metals ought to be classified as a class of gerontogens (i.e., chemicals that accelerate biological aging in cells and tissues). Gerontogens may be best studied through their effects on the "Hallmarks of Aging", nine physiological hallmarks demonstrated to occur in aged cells, tissues, and bodies. Evidence suggests that cellular senescence-a permanent growth arrest in cells-is one of the most pertinent hallmarks of aging and is a useful indicator of aging in tissues. Here, we discuss the roles of heavy metals in brain aging. We briefly discuss brain aging in general, then expand upon observations for heavy metals contributing to age-related neurodegenerative disorders. We particularly emphasize the roles and observations of cellular senescence in neurodegenerative diseases. Finally, we discuss the observations for heavy metals inducing cellular senescence. The glaring lack of knowledge about gerontogens and gerontogenic mechanisms necessitates greater research in the field, especially in the context of the global aging crisis.

Chronic nickel (II) exposure induces the stemness properties of cancer cells through repressing isocitrate dehydrogenase (IDH1)

BACKGROUND

Nickel is a component of biomedical alloys that is released during corrosion or friction and causes cytotoxicity, mutation, differentiation or even carcinogenesis in tissues. However, the mechanisms underlying the potential hazards of Nickel-containing alloys implanted in the human body by surgery remain uncertain.

OBJECTIVE

To study the effect of Ni(II) (NiCl_2•6H₂O) on cancer cells.

METHODS

A549 and RKO cells were treated with various concentrations of Ni(II) to determine the effect of Ni(II) on cellular viability using a CCK8 assay. Flow cytometry was performed to analyze the effect of Ni(II) on apoptosis and the cell cycle. Sphere-forming assays were conducted to examine the stemness properties of A549 and RKO cells. Western blotting was to evaluate the expression levels of SOX2, IDH1, HIF-1ɑ and β-catenin. The expression of isocitrate dehydrogenase (IDH1) in rectum adenocarcinoma (READ) was analyzed by Gene Expression Profiling Interactive Analysis (GEPIA). Kaplan-Meier analysis was used to calculate the correlation between survival and IDH1 expression.

RESULTS

Long-term exposure (120 days) to 100 µM Ni(II) significantly repressed cell proliferation, decreased colony formation and arrested the cell cycle at the G₀/G₁ phase. In addition, the stem-like traits of A549 and RKO cells were significantly augmented. Ni(II) also significantly decreased the protein expression of IDH1 and the synthesis rate of NAPDH, which competitively inhibited α-ketoglutarate (α-KG) generation. The downregulation of IDH1 not only promoted β-catenin accumulation in the cell nucleus in a HIF-1ɑ signaling-dependent manner but also induced the expression of the transcription factor SOX2 to maintain the stemness properties of cancer cells. Moreover, IDH1 expression negatively correlated with the clinicopathologic characteristics of READ.

CONCLUSION

These findings demonstrate that chronic and continuous release of Ni(II) to the microenvironment suppresses IDH1 expression and augments the stemness properties of cancer cells via the activation HIF-1ɑ/β-catenin/SOX2 pathway to enhance local tumor recurrence in patients with implanted Nickel-containing alloys at surgical sites.

PKCα/ERK/C7ORF41 axis regulates epidermal keratinocyte differentiation through the IKKα nuclear translocation

Aberrant differentiation of keratinocytes disrupts the skin barrier and causes a series of skin diseases. However, the molecular basis of keratinocyte differentiation is still poorly understood. In the present study, we examined the expression of C7ORF41 using tissue microarrays by immunohistochemistry and found that C7ORF41 is specifically expressed in the basal layers of skin epithelium and its expression is gradually decreased during keratinocytes differentiation. Importantly, we corroborated the pivotal role of C7ORF41 during keratinocyte differentiation by C7ORF41 knockdown or overexpression in TPA-induced Hacat keratinocytes. Mechanismly, we first demonstrated that C7ORF41 inhibited keratinocyte differentiation mainly through formatting a complex with IKKα in the cytoplasm, which thus blocked the nuclear translocation of IKKα. Furthermore, we also demonstrated that inhibiting the PKCα/ERK signaling pathway reversed the reduction in C7ORF41 in TPA-induced keratinocytes, indicating that C7ORF41 expression could be regulated by upstream PKCα/ERK signaling pathway during keratinocyte differentiation. Collectively, our study uncovers a novel regulatory network PKCα/ERK/C7ORF41/IKKα during keratinocyte differentiation, which provides potential therapeutic targets for skin diseases.

Nickel carcinogenesis mechanism: cell cycle dysregulation

Nickel (Ni) is a widely distributed metal in the environment and an important pollutant due to its widespread industrial applications. Ni has various toxicity in humans and experimental animals, including carcinogenicity. However, the carcinogenic effects of Ni remain troublesome. Cell cycle dysregulation may be an important carcinogenic mechanism and is also a potential molecular mechanism for Ni complexes anti-cancerous effects. Therefore, we conducted a literature review to summarize the effects of Ni on cell cycle. Up to now, there were three different reports on Ni-induced cell cycle arrest: (i) Ni can induce cell cycle arrest in G0/G1 phase, phosphorylation and degradation of IkappaB kinase-alpha (IKKα)-dependent cyclin D1 and phosphoinositide-3-kinase (PI3K)/serine-threonine kinase (Akt) pathway-mediated down-regulation of expressions of cyclin-dependent kinases 4 (CDK4) play important role in it; (ii) Ni can induce cell cycle arrest in S phase, but the molecular mechanism is not known; (iii) G2/M phase is the target of Ni toxicity, and Ni compounds cause G2/M cell cycle phase arrest by reducing cyclinB1/Cdc2 interaction through the activation of the ataxia telangiectasia mutated (ATM)-p53-p21 and ATM-checkpoint kinase inhibitor 1 (Chk1)/Chk2-cell division cycle 25 (Cdc25) pathways. Revealing the mechanisms of cell cycle dysregulation associated with Ni exposure may help in the prevention and treatment of Ni-related carcinogenicity and toxicology.

Intracellular nickel accumulation induces apoptosis and cell cycle arrest in human astrocytic cells

Nickel, a heavy metal found in electronic wastes and fume from electronic cigarettes, induces neuronal cell death and is associated with neurocognitive impairment. Astrocytes are the first line of defense against nickel after entering the brain; however, the effects of nickel on astrocytes remain unknown. Herein, we investigated the effect of nickel exposure on cell survival and proliferation and the underlying mechanisms in U-87 MG human astrocytoma cells and primary human astrocytes. Intracellular nickel levels were elevated in U-87 MG cells in a dose- and time-dependent manner after exposure to nickel chloride. The median toxic concentrations of nickel in astrocytoma cells and primary human astrocytes were 600.60 and >1000 µM at 48 h post-exposure, respectively. Nickel exposure triggered apoptosis in concomitant with the decreased expression of anti-apoptotic B-cell lymphoma protein (Bcl-2) and increased caspase-3/7 activity. Nickel induced reactive oxygen species formation. Additionally, nickel suppressed astrocyte proliferation in a dose- and time-dependent manner by delaying G2 to M phase transition through the upregulation of cyclin B1 and p27 protein expression. These results indicate that nickel-induced cytotoxicity of astrocytes is mediated by the activation of apoptotic pathway and disruption of cell cycle regulation.

Metal nickel exposure increase the risk of congenital heart defects occurrence in offspring: A case-control study in China

BACKGROUND

Previous studies have investigated heavy metal exposure could increase the occurrence of congenital heart defects (CHDs). However, there are limited data regarding the relationship between exposure to nickel and CHDs occurrence in offspring. The aim of this study was to analyze the association between nickel exposure in mothers and the risk of CHDs in offspring.

MATERIALS AND METHODS

To explore the association of nickel exposure and occurrence of CHD, a case-control study with 490 controls and 399 cases with CHDs in China were developed. The concentrations of nickel in hair of pregnant woman and fetal placental tissue were measured and used a logistic regression analysis to explore the relationship between nickel exposure and risk of CHD.

RESULTS

The median concentrations of nickel were 0.629 ng/mg, P < .05 (adjusted odds ratio [aOR], 1.326; 95% CI, 1.003-1.757) and 0.178 ng/mg, P < .05 (aOR, 2.204; 95% CI, 0.783-6.206), in maternal hair and in fetal placental tissue in the CHD group, respectively. Significant differences in the level of nickel in hair were also found in the different CHD subtypes including septal defects (P < .05), conotruncal defects (P < .05), right ventricular outflow tract obstruction (P < .01), and left ventricular outflow tract obstruction (P < .05). Dramatically different nickel concentrations in fetal placenta tissue were found in cases with other heart defects (P < .05).

CONCLUSIONS

The finding suggested that the occurrence of CHDs may be associated with nickel exposure.

Decreased c-Myc mRNA Stability via the MicroRNA 141-3p/AUF1 Axis Is Crucial for p63α Inhibition of Cyclin D1 Gene Transcription and Bladder Cancer Cell Tumorigenicity

Bladder cancer (BC) ranks as the sixth most common cancer in the United States and is the leading cause of death in patients with urinary malignancies. p63 is a member of the p53 family and is believed to function as a tumor suppressor in human BCs. Our most recent studies revealed a previously unknown function of the RING of XIAP in promoting microRNA 4295 (miR-4295) transcription, thereby reducing p63α protein translation and enhancing normal urothelial transformation, whereas p63α upregulates hsp70 transcription, subsequently activating the HSP70/Wasf3/Wave3/matrix metalloproteinase 9 (MMP-9) axis and promoting BC cell invasion via initiating the transcription factor E2F1. In this study, we found that p63α inhibited cyclin D1 protein expression, subsequently decreasing the ability of BC cell anchorage-independent growth in vitro and tumorigenicity in vivo Mechanistic studies demonstrated that p63α expression is able to downregulate cyclin D1 gene transcription through attenuation of c-Myc mRNA stability. We further show that the reduction of miR-141-3p expression by p63α directly releases its inhibition of 3' untranslated region (UTR) activity of AU-rich element RNA-binding factor 1 (AUF1) mRNA, thereby increasing AUF1 protein translation and further resulting in degradation of c-Myc mRNA, which, in turn, reduces cyclin D1 gene transcription and BC cell anchorage-independent growth. Collectively, our results demonstrate that p63α is a negative regulator of BC cell tumorigenic growth, a distinctly different function than its promotion of BC invasion, thus providing further new insight into the "two faces" of p63α in regulation of BC cell tumorigenic growth and progression/invasion.

LncRNA MEG3 downregulation mediated by DNMT3b contributes to nickel malignant transformation of human bronchial epithelial cells via modulating PHLPP1 transcription and HIF-1α translation

Long noncoding RNAs (lncRNAs) are emerging as key factors in various fundamental cellular biological processes, and many of them are likely to have functional roles in tumorigenesis. Maternally expressed gene 3 (MEG3) is an imprinted gene located at 14q32 that encodes a lncRNA, and the decreased MEG3 expression has been reported in multiple cancer tissues. However, nothing is known about the alteration and role of MEG3 in environmental carcinogen-induced lung tumorigenesis. Our present study, for the first time to the best of our knowledge, discovered that environmental carcinogen nickel exposure led to MEG3 downregulation, consequently initiating c-Jun-mediated PHLPP1 transcriptional inhibition and hypoxia-inducible factor-1α (HIF-1α) protein translation upregulation, in turn resulting in malignant transformation of human bronchial epithelial cells. Mechanistically, MEG3 downregulation was attributed to nickel-induced promoter hypermethylation via elevating DNMT3b expression, whereas PHLPP1 transcriptional inhibition was due to the decreasing interaction of MEG3 with its inhibitory transcription factor c-Jun. Moreover, HIF-1α protein translation was upregulated via activating the Akt/p70S6K/S6 axis resultant from PHLPP1 inhibition in nickel responses. Collectively, we uncover that nickel exposure results in DNMT3b induction and MEG3 promoter hypermethylation and expression inhibition, further reduces its binding to c-Jun and in turn increasing c-Jun inhibition of PHLPP1 transcription, leading to the Akt/p70S6K/S6 axis activation, and HIF-1α protein translation, as well as malignant transformation of human bronchial epithelial cells. Our studies provide a significant insight into understanding the alteration and role of MEG3 in nickel-induced lung tumorigenesis.

A new tumour suppression mechanism by p27Kip1: EGFR down-regulation mediated by JNK/c-Jun pathway inhibition

p27^Kip1 is a potent inhibitor of cyclin-dependent kinases that drive G₁-to-S cell-cycle transition. Reduced p27^Kip1 expression is prevalent in a wide range of human tumours; however, the exact mechanism(s) of p27^Kip1-mediated tumour suppression remains obscure. In the present study, we identified a close inverse relationship between p27^Kip1 and EGFR (epidermal growth factor receptor) expression: the parental T24 human bladder cancer cells had high p27^Kip1 expression but low EGFR expression and, in striking contrast, the metastatic derivative of T24 (T24T) had low p27^Kip1 expression but high EGFR expression. This relationship was also found in various human cancer tissues, and was not only just correlative but also causal; depletion of p27^Kip1 in MEF (mouse embryonic fibroblast) cells resulted in markedly elevated EGFR expression, a result reproducible with an Egfr promoter-luciferase reporter in both T24 and MEF cells, suggesting transcriptional repression of EGFR by p27^Kip1. Indeed, p27^Kip1 was found to regulate EGFR expression via the JNK (c-Jun N-terminal kinase)/c-Jun transcription factor: p27^Kip1 deficiency activated JNK/c-Jun, whereas inhibition of JNK/c-Jun by dominant-negative mutants dramatically repressed Egfr transcription. Furthermore, the proximal promoter of the Egfr gene was crucial for its transcription, where the recruiting activity of c-Jun was much greater in p27^Kip1−/− cells than in p27^Kip1+/+ cells. Introduction of GFP–p27^Kip1 into T24T cells suppressed JNK/c-Jun activation, EGFR expression and anchorage-independent growth. The results of the present study demonstrate that p27^Kip1 suppresses JNK/c-Jun activation and EGFR expression in MEFs and human bladder cancer cells, and the results obtained are consistent with those from human cancer specimens. The present study provides new insights into p27^Kip1 suppression of cancer cell growth, migration and metastasis.

An inverse relationship between p27^Kip1 and EGFR expression in parental T24 human bladder cancer cells and various human cancer tissues was found. Depletion of p27^Kip1 in cells markedly elevated EGFR expression through transcriptional repression of Egfr by p27^Kip1 via the JNK/c-Jun cascade.

10th NTES Conference: Nickel and Arsenic Compounds Alter the Epigenome of Peripheral Blood Mononuclear Cells

The mechanisms that underlie metal carcinogenesis are the subject of intense investigation; however, data from in vitro and in vivo studies are starting to piece together a story that implicates epigenetics as a key player. Data from our lab has shown that nickel compounds inhibit dioxygenase enzymes by displacing iron in the active site. Arsenic is hypothesized to inhibit these enzymes by diminishing ascorbate levels--an important co-factor for dioxygenases. Inhibition of histone demethylase dioxygenases can increase histone methylation levels, which also may affect gene expression. Recently, our lab conducted a series of investigations in human subjects exposed to high levels of nickel or arsenic compounds. Global levels of histone modifications in peripheral blood mononuclear cells (PBMCs) from exposed subjects were compared to low environmentally exposed controls. Results showed that nickel increased H3K4me3 and decreased H3K9me2 globally. Arsenic increased H3K9me2 and decreased H3K9ac globally. Other histone modifications affected by arsenic were sex-dependent. Nickel affected the expression of 2756 genes in human PBMCs and many of the genes were involved in immune and carcinogenic pathways. This review will describe data from our lab that demonstrates for the first time that nickel and arsenic compounds affect global levels of histone modifications and gene expression in exposed human populations.

Effect of nickel chloride on cell proliferation

Objective:

Metal alloys used in dentistry and in other biomedical fields may release nickel ions in the oral environment. The release of nickel might influence the normal biological and physiological processes, including tissue wound healing, cell growth and proliferation. The aim of this study was to evaluate in vitro the effects of nickel ions on cell cycle, viability and proliferation.

Materials and Methods:

Human osteosarcoma cells (U2OS) and human keratinocytes (HaCat) were exposed to different nickel chloride (NiCl₂) concentrations (0 - 5mM) for various periods exposure. The viability of cultured cells was estimated by flow cytometry using Annexin V-FITC and Propidium Iodide (PI). Cell proliferation was evaluated by using carboxyfluorescein diacetate succinimidyl ester (CFDA-SE) and flow cytometry. Finally, the effects of NiCl₂ on cell cycle were assessed and quantified by flow cytometry. Statistical analysis was performed by means of ANOVA followed by Tukey’s test.

Results:

NiCl₂ induced a dose and time dependent decrease in cell viability. After 24h, 1mM NiCl₂ caused a similar and significant reduction of viability in U2OS and HaCat cells, while higher NiCl₂ concentrations and longer exposure times showed a reduced cytotoxic effect in HaCat as compared to U2OS cells.

Exposure to NiCl₂ caused a dose- and time-dependent inhibition of cell proliferation in both cell lines tested, with a prominent effect on U2OS cells. Furthermore, both cell lines exposed to NiCl₂ exhibited significant changes in cell cycle distribution after 24h exposure 2mM NiCl2, as compared to untreated cells (p<0.05).

Conclusion:

Our results indicate that release of nickel ions may affect cell proliferation. The inhibition of cell growth by NiCl2 is mediated by both cell cycle arrest and by induction of cell death.

E3 ligase activity of XIAP RING domain is required for XIAP-mediated cancer cell migration, but not for its RhoGDI binding activity

Although an increased expression level of XIAP is associated with cancer cell metastasis, the underlying molecular mechanisms remain largely unexplored. To verify the specific structural basis of XIAP for regulation of cancer cell migration, we introduced different XIAP domains into XIAP^−/− HCT116 cells, and found that reconstitutive expression of full length HA-XIAP and HA-XIAP ΔBIR, both of which have intact RING domain, restored β-Actin expression, actin polymerization and cancer cell motility. Whereas introduction of HA-XIAP ΔRING or H467A mutant, which abolished its E3 ligase function, did not show obvious restoration, demonstrating that E3 ligase activity of XIAP RING domain played a crucial role of XIAP in regulation of cancer cell motility. Moreover, RING domain rather than BIR domain was required for interaction with RhoGDI independent on its E3 ligase activity. To sum up, our present studies found that role of XIAP in regulating cellular motility was uncoupled from its caspase-inhibitory properties, but related to physical interaction between RhoGDI and its RING domain. Although E3 ligase activity of RING domain contributed to cell migration, it was not involved in RhoGDI binding nor its ubiquitinational modification.

The role of cadmium and nickel in estrogen receptor signaling and breast cancer: metalloestrogens or not?

During the past half-century, incidences of breast cancer have increased globally. Various factors--genetic and environmental--have been implicated in the initiation and progression of this disease. One potential environmental risk factor that has not received a lot of attention is the exposure to heavy metals. While several mechanisms have been put forth describing how high concentrations of heavy metals play a role in carcinogenesis, it is unclear whether chronic, low-level exposure to certain heavy metals (i.e., cadmium and nickel) can directly result in the development and progression of cancer. Cadmium and nickel have been hypothesized to play a role in breast cancer development by acting as metalloestrogens--metals that bind to estrogen receptors and mimic the actions of estrogen. Since the lifetime exposure to estrogen is a well-established risk factor for breast cancer, anything that mimics its activity will likely contribute to the etiology of the disease. However, heavy metals, depending on their concentration, are capable of binding to a variety of proteins and may exert their toxicities by disrupting multiple cellular functions, complicating the analysis of whether heavy metal-induced carcinogenesis is mediated by the estrogen receptor. The purpose of this review is to discuss the various epidemiological, in vivo, and in vitro studies that show a link between the heavy metals, cadmium and nickel, and breast cancer development. We will particularly focus on the studies that test whether these two metals act as metalloestrogens in order to assess the strength of the data supporting this hypothesis.

A cross-talk between NFAT and NF-κB pathways is crucial for nickel-induced COX-2 expression in Beas-2B cells

Cyclooxygenase-2 (COX-2) is a critical enzyme implicated in chronic inflammation-associated cancer development. Our studies have shown that the exposure of Beas-2B cells, a human bronchial epithelial cell line, to lung carcinogenic nickel compounds results in increased COX-2 expression. However, the signaling pathways leading to nickel-induced COX-2 expression are not well understood. In the current study, we found that the exposure of Beas-2B cells to nickel compounds resulted in the activation of both nuclear factor of activated T cell (NFAT) and nuclear factor-κB (NF-κB). The expression of COX-2 induced upon nickel exposure was inhibited by either a NFAT pharmacological inhibitor or the knockdown of NFAT3 by specific siRNA. We further found that the activation of NFAT and NF-κB was dependent on each other. Since our previous studies have shown that NF-κB activation is critical for nickel-induced COX-2 expression in Beas-2B cells exposed to nickel compounds under same experimental condition, we anticipate that there might be a cross-talk between the activation of NFAT and NF-κB for the COX-2 induction due to nickel exposure in Beas-2B cells. Furthermore, we showed that the scavenging of reactive oxygen species (ROS) by introduction of mitochondrial catalase inhibited the activation of both NFAT and NF-κB, and the induction of COX-2 due to nickel exposure. Taken together, our results defining the evidence showing a key role of the cross-talk between NFAT and NF-κB pathways in regulating nickel-induced COX-2 expression, further provide insight into the understanding of the molecular mechanisms linking nickel exposure to its lung carcinogenic effects.

Nickel-induced down-regulation of ΔNp63 and its role in the proliferation of keratinocytes

Epidemiological, animal, and cell studies have demonstrated that nickel compounds are human carcinogens. The mechanisms of their carcinogenic actions remain to be investigated. p63, a close homologue of the p53 tumor suppressor protein, has been linked to cell fate determination and/or maintenance of self-renewing populations in several epithelial tissues, including skin, mammary gland, and prostate. ΔNp63, a dominant negative isoform of p63, is amplified in a variety of epithelial tumors including squamous cell carcinomas and carcinomas of the prostate and mammary glands. The present study shows that nickel suppressed ΔNp63 expression in a short-time treatment (up to 48 h). Nickel treatment caused activation of NF-κB. Blockage of NF-κB partially reversed nickel-induced ΔNp63 suppression. Nickel decreased interferon regulatory factor (IRF) 3 and IRF7, IKKε, and Sp100. Over-expression of IRF3 increased ΔNp63 expression suppressed by nickel. Nickel was able to activate p21, and its activation was offset by the over-expression of ΔNp63. In turn, elevated p63 expression counteracted the ability of nickel to restrict cell growth. The present study demonstrated that nickel decreased interferon regulatory proteins IRF3 and IRF7, and activated NF-κB, resulting in ΔNp63 suppression and then p21 up-regulation. ΔNp63 plays an important role in nickel-induced cell proliferation.

X-linked inhibitor of apoptosis protein (XIAP) mediates cancer cell motility via Rho GDP dissociation inhibitor (RhoGDI)-dependent regulation of the cytoskeleton

X-linked inhibitor of apoptosis protein (XIAP) overexpression has been found to be associated with malignant cancer progression and aggression in individuals with many types of cancers. However, the molecular basis of XIAP in the regulation of cancer cell biological behavior remains largely unknown. In this study, we found that a deficiency of XIAP expression in human cancer cells by either knock-out or knockdown leads to a marked reduction in β-actin polymerization and cytoskeleton formation. Consistently, cell migration and invasion were also decreased in XIAP-deficient cells compared with parental wild-type cells. Subsequent studies demonstrated that the regulation of cell motility by XIAP depends on its interaction with the Rho GDP dissociation inhibitor (RhoGDI) via the XIAP RING domain. Furthermore, XIAP was found to negatively regulate RhoGDI SUMOylation, which might affect its activity in controlling cell motility. Collectively, our studies provide novel insights into the molecular mechanisms by which XIAP regulates cancer invasion and offer a further theoretical basis for setting XIAP as a potential prognostic marker and specific target for treatment of cancers with metastatic properties.

Reactive oxygen species-activated Akt/ASK1/p38 signaling pathway in nickel compound-induced apoptosis in BEAS 2B cells

Nickel compounds are carcinogenic to humans, possibly through induction of reactive oxygen species (ROS) that damage macromolecules including DNA and proteins. The aim of the present study is to elucidate the role of the ROS-mediated Akt/apoptosis-regulating signal kinase (ASK) 1/p38 pathway in nickel-induced apoptosis. Exposure of human bronchial epithelial cells (BEAS-2B) to nickel compounds induced the generation of ROS and activation of Akt that is associated with the activation of ASK1 and p38 mitogen-activated protein kinase. Immunoblotting suggested a down-regulation of several antiapoptotic proteins, including Bcl-2 and Bcl-xL in the nickel compound-treated cells. Indeed, a notable cell apoptosis following nickel compound treatment is evident as revealed by flow cytometry analysis. N-Acetyl-l-cysteine (NAC, a general antioxidant) and vitamin E or catalase (a specific H₂O₂ inhibitor) all decreased nickel-induced ROS generation. Scavenging of nickel-induced ROS by NAC or catalase attenuated Akt, ASK1, and p38 MAPK activation and apoptosis, which implies involvement of ROS in the Akt/ASK1/p38 pathway. In addition, nickel-induced activation of p38 MAPK was attenuated by a small interference of RNA specific to ASK1 (siRNA ASK1), implying that p38 MAPK was downstream of ASK1, while ASK1 activation was not reversely regulated by the inhibition of p38 MAPK by SB203580, a widely used p38 MAPK inhibitor. Silencing Akt by siRNA reduced the activation of ASK1 and p38 MAPK and cell apoptosis, whereas without nickel stimulation, siRNA Akt had no effect on the activation of ASK1 and p38 MAPK. Thus, these results suggest that the ROS-dependent Akt-ASK1-p38 axis is important for nickel-induced apoptosis.

A novel role of IKKalpha in the mediation of UVB-induced G0/G1 cell cycle arrest response by suppressing Cyclin D1 expression

Exposure to ultraviolet B (UVB) irradiation (290-320nm wavelength) from sunlight induces a variety of medical problems, including sunburn, immunosuppression and skin cancers. However, the molecular mechanisms related to UVB-induced cell damage and/or mutagenic effects have not been fully defined. Here, we demonstrate that one of the catalytic subunits of the IkappaB kinase complex (IKK), IKKalpha, plays a critical role in mediation of the UVB-induced G0/G1 cell cycle arrest response by suppressing Cyclin D1 expression. Notably, IKKa-dependent Cyclin D1 regulation is unrelated to IKKbeta/NF-kappaB activity. We further show that IKKalpha-dependent downregulation of Cyclin D1 expression in the UVB response results from the reduction of ERK1/2-dependent Cyclin D1 transcription coupled with an increase of p38 kinase-dependent Cyclin D1 proteolysis. Thus, our results have identified the novel role of IKKalpha in regulating cell cycle progression during the cellular UVB response. Targeting IKKalpha might be promising for the prevention of UVB-induced cell damage and tumorigenic effects.

A genome-wide deletion mutant screen identifies pathways affected by nickel sulfate in Saccharomyces cerevisiae

Background

The understanding of the biological function, regulation, and cellular interactions of the yeast genome and proteome, along with the high conservation in gene function found between yeast genes and their human homologues, has allowed for Saccharomyces cerevisiae to be used as a model organism to deduce biological processes in human cells. Here, we have completed a systematic screen of the entire set of 4,733 haploid S. cerevisiae gene deletion strains (the entire set of nonessential genes for this organism) to identify gene products that modulate cellular toxicity to nickel sulfate (NiSO₄).

Results

We have identified 149 genes whose gene deletion causes sensitivity to NiSO₄ and 119 genes whose gene deletion confers resistance. Pathways analysis with proteins whose absence renders cells sensitive and resistant to nickel identified a wide range of cellular processes engaged in the toxicity of S. cerevisiae to NiSO₄. Functional categories overrepresented with proteins whose absence renders cells sensitive to NiSO₄ include homeostasis of protons, cation transport, transport ATPases, endocytosis, siderophore-iron transport, homeostasis of metal ions, and the diphthamide biosynthesis pathway. Functional categories overrepresented with proteins whose absence renders cells resistant to nickel include functioning and transport of the vacuole and lysosome, protein targeting, sorting, and translocation, intra-Golgi transport, regulation of C-compound and carbohydrate metabolism, transcriptional repression, and chromosome segregation/division. Interactome analysis mapped seven nickel toxicity modulating and ten nickel-resistance networks. Additionally, we studied the degree of sensitivity or resistance of the 111 nickel-sensitive and 72 -resistant strains whose gene deletion product has a similar protein in human cells.

Conclusion

We have undertaken a whole genome approach in order to further understand the mechanism(s) regulating the cell's toxicity to nickel compounds. We have used computational methods to integrate the data and generate global models of the yeast's cellular response to NiSO₄. The results of our study shed light on molecular pathways associated with the cellular response of eukaryotic cells to nickel compounds and provide potential implications for further understanding the toxic effects of nickel compounds to human cells.

Effects of nickel on cyclin expression, cell cycle progression and cell proliferation in human pulmonary cells

Frequent exposure to nickel compounds has been considered as one of the potential causes of human lung cancer. However, the molecular mechanism of nickel-induced lung carcinogenesis remains obscure. In the current study, slight S-phase increase, significant G(2)/M cell cycle arrest, and proliferation blockage were observed in human bronchial epithelial cells (Beas-2B) upon nickel exposure. Moreover, the induction of cyclin D1 and cyclin E by nickel was shown for the first time in human pulmonary cells, which may be involved in nickel-triggered G(1)/S transition and cell transformation. In addition, we verified that hypoxia-inducible factor-1alpha, an important transcription factor of nickel response, was not required for the cyclin D1 or cyclin E induction. The role of p53 in nickel-induced G(2)/M arrest was excluded, respecting that its protein level, ser(15) phosphorylation, and transcriptional activity were not changed in nickel response. Further study revealed that cyclin A was not activated in nickel response, and cyclin B1, which not only promotes G(2)/M transition but also prevents M-phase exit of cells if not degraded in time, was up-regulated by nickel through a manner independent of hypoxia-inducible factor. More importantly, our results verified that overexpressed cyclin B1, veiling the effect of cyclin D1 or cyclin E, mediated nickel-caused M-phase blockage and cell growth inhibition, which may render pulmonary cells more sensitive to DNA damage and facilitates cancer initiation. These results will not only deepen our understanding of the molecular mechanism involved in nickel carcinogenecity, but also lead to the further study on chemoprevention of nickel-associated human cancer.