PI-3K/Akt pathway-dependent cyclin D1 expression is responsible for arsenite-induced human keratinocyte transformation

Role of the USP7/FOXO3A axis in environmentally relevant doses of arsenic-induced lung carcinogenesis: Insights from bioinformatics analysis and model of human epithelial cell malignant transformation

Arsenic (As) is classified as a Group 1 carcinogen by the International Agency for Research on Cancer (IARC). Exposure to As has been associated with an increased risk of various cancers, particularly lung cancer. However, the precise molecular mechanisms contributing to this carcinogenesis are not well understood. In our study, we analyzed transcriptomic data from the GEO database (GSE36684), identifying 764 differentially expressed genes (DEGs) in BEAS-2B cells treated with environmentally relevant doses of As for 8 weeks. A KEGG pathway enrichment analysis suggested that the FoxO pathway activation might be a novel key signaling event in As-induced carcinogenesis. We further analyzed the expression of 11 DEGs involved in the FoxO pathway using the TCGA-LUSC dataset. The findings revealed that four genes displayed expression patterns in tumor tissues consistent with those observed after As treatment in GEO dataset. Among them, USP7 was upregulated, while ATM, S1PR1, and PLK2 were downregulated in cancer tissues. High USP7 expression was specifically linked to a poor prognosis in lung squamous cell carcinoma (LUSC). To explore the role of USP7 in As-induced malignant transformation, BEAS-2B cells were exposed to NaAsO2 concentrations of 0.2 μM and 2 μM for up to 20 weeks. Experimental results confirmed that NaAsO2 treatment suppressed the FoxO transcriptional activity by upregulating USP7 expression, subsequently downregulating ATM and PLK2 expression, which led to abnormalities in cell cycle regulation and apoptosis. Notably, knocking down USP7 in As-transformed cells resulted in significant reductions in cell proliferation, colony formation, and tumor formation ability in nude mice, indicating the USP7-regulated FOXO3A pathway could be central to As-induced lung carcinogenesis. Moreover, our research demonstrated that USP7 inhibited FOXO3A's ability to translocate from the cytoplasm to the nucleus by affecting its monoubiquitination status. Additionally, we speculated that As-induced the elevation of USP7 expression due to the excessive inflammatory cytokines secretion and the activation of mTORC1/WTAP pathway. These findings offer novel insights into the molecular mechanisms underlying As-mediated lung cancer.

Evaluation the role of insulin signaling pathway in reproductive toxicity of dispersed diesel particulate extract under environmental conditions

Diesel particulate extract (DPE), which is a significant constituent of airborne particle pollution, has a strong association with the development of cancer and respiratory diseases. Fulvic acid (FA), a plentiful organic macromolecule found in water, has the capability to modify particle surface charge and adsorption capacity when combined with minerals. Nevertheless, there is a scarcity of data regarding the influence of their interaction on DPE toxicity. To examine the impact of environmental factor on the toxic effects of DPE, we used the Caenorhabditis elegans (C. elegans) model to investigate the reproductive toxicity of DPE and FA on insulin signaling pathway. C. elegans were subjected to a semi-fluid medium (NGG) containing different concentrations of DPE or DPE + FA in order to assess germline apoptosis and the expression of important genes in the insulin signaling pathway. Through several mutant strains, we found that daf-2, age-1, pdk-1, akt-1 and daf-16 were involved in DPE-induced apoptosis. Furthermore, and the expression levels of these genes significantly altered. The ratio of daf-16 translocation to nucleation, as well as the amount of reactive oxygen species (ROS), exhibited a dose-response relationship, however, the presence of FA could altered these effects. The results revealed that the insulin signaling pathway plays a vital role in mediating the harmful effects caused by DPE, whereas environmental factors have a substantial impact on its toxicity. Moreover, it was noted that semi-fluid medium could effectively replicate three-dimensional exposure circumstances closely resembling those observed in actual situations.

Protective effects of baicalin against phenylarsine oxide-induced cytotoxicity in human skin keratinocytes

Phenylarsine oxide (PAO) is a known environmental pollutant and skin keratinocytes are most seriously affected. Baicalin (BCN) was reported to have antioxidant and anti-inflammatory effects, but its protective effect against PAO toxicity is unknown. This study aimed at exploring whether baicalin can reverse the toxicity of human epidermal keratinocytes that are subjected to PAO exposure and underlying mechanisms. In silico analysis from a publicly accessible HaCaT cell transcriptome dataset exposed to chronic Arsenic showed significant differential expression of several genes, including the genes related to DNA replication. Later, we performed in vitro experiments, in which HaCaT cells were exposed to PAO (500 nM) in the existence of BCN (10-50 µM). Treatment of PAO alone induces the JNK, p38 and caspase-3 activation, which were engaged in the apoptosis induction, while the activity of AKT was significantly inhibited, which was engaged in the suppression of apoptosis. PAO suppressed SIRT3 expression and induced intracellular reactive oxygen species (ROS), causing a marked reduce in cell viability and apoptosis. However, BCN treatment restored the PAO-induced suppression of SIRT3 and AKT expression, reduced intracellular ROS generation, and markedly suppressed both caspase-3 activation and apoptosis induction. However, the protective effect of BCN was significantly attenuated after pretreatment with nicotinamide, an inhibitor of SIRT3. These findings indicate that BCN protects against cell death induced by PAO via inhibiting excessive intracellular ROS generation via restoring SIRT3 activity and reactivating downstream AKT pathway. In this study, we firstly shown that BCN is an efficient drug to prevent PAO-induced skin cytotoxicity, and these findings need to be confirmed by in vivo and clinical investigations.

MicroRNA-451a inhibits gemcitabine-refractory biliary tract cancer progression by suppressing the MIF-mediated PI3K/AKT pathway

Gemcitabine is an effective chemotherapeutic agent for biliary tract cancers (BTCs), including gallbladder cancer (GBC) and cholangiocarcinoma (CCA). However, few other effective agents are currently available, particularly for GEM-refractory BTCs. We previously identified microRNA-451a (miR-451a) as a potential therapeutic target in GBC. To elucidate the antineoplastic effects of miR-451a and its underlying mechanisms, we transfected miR-451a into GBC, gemcitabine-resistant GBC (GR-GBC), and gemcitabine-resistant CCA (GR-CCA) cell lines. Furthermore, mimicking in vivo conditions, tumorigenic GBC organoids and three-dimensional (3D) cell culture systems were employed to investigate the anti-proliferative effects of miR-451a on BTCs, and its effect on stem cell properties. We found that miR-451a significantly inhibited cell proliferation, induced apoptosis, and reduced chemoresistant phenotypes, such as epithelial-mesenchymal transition, in both GBC and GR-GBC. The principal mechanism is probably the negative regulation of the phosphatidylinositol 3-kinase/AKT pathway, partially accomplished by directly downregulating macrophage migration inhibitory factor. The Gene Expression Omnibus database revealed that miR-451a was the most significantly downregulated microRNA in CCA tissues. The introduction of miR-451a resulted in similar antineoplastic effects in GR-CCA. Furthermore, miR-451a reduced cell viability in 3D spheroid models and tumorigenic GBC organoids. These findings suggest that the supplementation of miR-451a is a potential treatment strategy for GEM-refractory BTCs.

The Hyperproliferation Mechanism of Cholesteatoma Based on Proteomics: SNCA Promotes Autophagy-Mediated Cell Proliferation Through the PI3K/AKT/CyclinD1 Signaling Pathway

Cholesteatoma is a chronic inflammatory ear disease with abnormal keratinized epithelium proliferation and tissue damage. However, the mechanism of keratinized epithelium hyperproliferation in cholesteatoma remains unknown. Hence, our study sought to shed light on mechanisms affecting the pathology and development of cholesteatoma, which could help develop adjunctive treatments. To investigate molecular changes in cholesteatoma pathogenesis, we analyzed clinical cholesteatoma specimens and paired ear canal skin with mass spectrometry-based proteomics and bioinformatics. From our screen, alpha-synuclein (SNCA) was overexpressed in middle ear cholesteatoma and might be a key hub protein associated with inflammation, proliferation, and autophagy in cholesteatoma. SNCA was more sensitive to lipopolysaccharide-induced inflammation, and autophagy marker increase was accompanied by autophagy activation in middle ear cholesteatoma tissues. Overexpression of SNCA activated autophagy and promoted cell proliferation and migration, especially under lipopolysaccharide inflammatory stimulation. Moreover, inhibiting autophagy impaired SNCA-mediated keratinocyte proliferation and corresponded with inhibition of the PI3K/AKT/CyclinD1 pathways. Also, 740Y-P, a PI3K activator reversed the suppression of autophagy and PI3K signaling by siATG5 in SNCA-overexpressing cells, which restored proliferative activity. Besides, knockdown of SNCA in RHEK-1 and HaCaT cells or knockdown of PI3K in RHEK-1 and HaCaT cells overexpressing SNCA both resulted in attenuated cell proliferation. Our studies indicated that SNCA overexpression in cholesteatoma might maintain the proliferative ability of cholesteatoma keratinocytes by promoting autophagy under inflammatory conditions. This suggests that dual inhibition of SNCA and autophagy may be a promising new target for treating cholesteatoma.

Transcriptomics reveals key regulatory pathways and genes associated with skin diseases induced by face paint usage

The use of face paint cosmetics can cause skin diseases in opera performers due to the presence of heavy metals and other toxic ingredients in the cosmetics. However, the underlying molecular mechanism for these diseases remains unknown. Here we examined the transcriptome gene profile of human skin keratinocytes exposed to artificial sweat extracts of face paints, and identified the key regulatory pathways and genes, using RNA sequencing technique. Bioinformatics analyses suggested that the face paint exposure induced the differentially expression of 1531 genes and enriched inflammation-relevant TNF and IL-17 signaling pathways after just 4 h of exposure. Inflammation-relevant genes CREB3L3, FOS, FOSB, JUN, TNF, and NFKBIA were identified as the potential regulatory genes, and SOCS3 capable to prevent inflammation-induced carcinogenesis as the hub-bottleneck gene. Long-term exposure (24 h) could exacerbate inflammation, accompanied by interference in cellular metabolism pathways, and the potential regulatory genes (ATP1A1, ATP1B1, ATP1B2, FXYD2, IL6, and TNF) and hub-bottleneck genes (JUNB and TNFAIP3) were all related to inflammation induction and other adverse responses. We proposed that the exposure to face paint might cause the inflammatory factors TNF and IL-17, which are encoded by the genes TNF and IL17, to bind to receptors and activate TNF and IL-17 signaling pathways, leading to the expression of cell proliferation factors (CREB and AP-1) and proinflammatory mediators including transcription factors (FOS, JUN, and JUNB), inflammatory factors (TNF-α and IL6), and intracellular signaling factors (TNFAIP3). This finally resulted in cell inflammation, apoptosis, and other skin diseases. TNF was identified as the key regulator and connector in all the enriched signaling pathways. Our study provides the first insights into the cytotoxicity mechanism of face paints to skin cells and highlights the need for stricter regulations in face paint safety.

N6-methyladenosine plays a dual role in arsenic carcinogenesis by temporal-specific control of core target AKT1

High-profile RNA epigenetic modification N⁶-methyladenosine (m⁶A), as a double-edged sword for cancer, can either promote or inhibit arsenic-induced skin carcinogenesis. However, the core m⁶A-target gene determining the duality of m⁶A and the regulatory mechanism of m⁶A on the core gene are still poorly understood. Based on m⁶A microarray detection, integrated multi-omics analysis, and further experiments in vitro and in vivo, we explored the molecular basis for the dual role of m⁶A in cancer induced by environmental pollutants using models in different stages of arsenic carcinogenesis, including As-treated, As-transformed, and As-tumorigenic cell models. We found that the key proliferative signaling node AKT1 is in the center of the m⁶A-regulatory network in arsenic carcinogenicity. The m⁶A level on AKT1 mRNA (3'UTR, CDS, and 5'UTR) dynamically changed in different stages of arsenic carcinogenesis. The m⁶A writer METTL3-catalyzed upregulation of m⁶A promotes AKT1 expression by elevating m⁶A reader YTHDF1-mediated AKT1 mRNA stability in As-treated and As-transformed cells, while the m⁶A eraser FTO-catalyzed downregulation of m⁶A promotes AKT1 expression mainly by inhibiting m⁶A reader YTHDF2-mediated AKT1 mRNA degradation in As-tumorigenic cells. Furthermore, upregulation of m⁶A inhibits the expression of AKT1 negative regulator PHLPP2 and promotes the expression of AKT1 positive regulator PDK1. These changes in AKT1 regulators result in AKT1 activation by upregulating AKT1 phosphorylation at S473 and T308. Interestingly, the FTO-catalyzed decrease in m⁶A prevents AKT upregulation in As-treated cells but promotes AKT upregulation in As-tumorigenic cells. Both inhibitors targeting the m⁶A writer and eraser can inhibit the AKT1-mediated proliferation of As-tumorigenic cells by breaking the balance of m⁶A regulators. Our results demonstrated that AKT1 is the core hub determining m⁶A as a double-edged sword. Changed m⁶A dynamically upregulates the expression and activity of AKT1 in different stages of arsenic carcinogenesis. This study can advance our understanding of the dual role and precise time-specific mechanism of RNA epigenetics involved in the carcinogenesis of hazardous materials.

Malignant growth of arsenic-transformed cells depends on activated Akt induced by reactive oxygen species

Arsenic is an identified carcinogen for humans.In this study, chronic exposure of human hepatocyte L-02 to low-doses of inorganic arsenic caused cell malignant proliferation. Meanwhile, compared with normal L-02 cells, arsenic-transformed malignant cells, L-02-As displayed more ROS and significantly higher Cyclin D1 expression as well as aerobic glycolysis. Moreover, Akt activation is followed by the upregulation of Cyclin D1 and HK2 expression in L-02-As cells, since inhibition of Akt activity by Ly294002 attenuated the colony formation in soft agar and decreased the levels of Cyclin D1 and HK2. In addition, scavenging of ROS by NAC resulted in a decreased expression of phospho-Akt, HK2 and Cyclin D1, and attenuates the ability of anchorage-independent growth ofL-02-As cells, suggested that ROS mediated the Akt activation in L-02-As cells. In summary, our results demonstrated that ROS contributes to the malignant phenotype of arsenic-transformed human hepatocyte L-02-As via the activation of Akt pathway.

Role of insulin signaling pathway in apoptosis induced by food chain delivery of nano-silver under the action of environmental factors

OBJECTIVE

To investigate how the environmental factor affects the delivery of nano silver through food chain, we set up a two-stage food delivery chain model of Escherichia coli and Caenorhabditis elegans system.

METHODS

Through a two-stage food delivery chain model of E. coli and C. elegans, the mRNA expression levels of DAF-2, age-1, PDK-1, Akt-1 and DAF-16 in the insulin growth factor 1 signaling pathway in nematode gonad cells which occurs AgNPs induced apoptosis were evaluated and the apoptosis of gonad cells in the mutant strains of the above key genes were detected.

RESULTS

DAF-2, age-1, PDK-1 and Akt-1 could significantly negatively regulate the apoptosis of nematode cells induced by AgNPs, while DAF-16 could significantly promote the apoptosis induced by AgNPs. The DAF-16 up-regulated expression was a protective effect on the body and the phenomenon of DNA double-strand breaks was significantly increased. The damage effect induced by AgNPs was significantly enhanced in the presence of the environmental factor fulvic acid.

CONCLUSION

The damage effect induced by AgNPs after food delivery involves the regulation of the insulin growth factor 1 signaling pathway and environmental factors have a significant impact on the biological effects.

Linc-ROR promotes arsenite-transformed keratinocyte proliferation by inhibiting P53 activity

Linc-ROR is an oncogenic long non-coding RNA over-expressed in many kinds of cancer that promotes cancer cell proliferation. Arsenite is a determined carcinogen that increases the risk of skin cancer, but the carcinogenic mechanism of arsenite remains unclear. To explore whether and how linc-ROR plays a role in arsenite-induced carcinogenesis of skin cancer, we established arsenite-transformed keratinocyte HaCaT cells by exposing them to 1 μM arsenite for 50 passages. Then we examined the linc-ROR expression during the transformation and explored the effect of linc-ROR on the cell proliferation of arsenite-transformed HaCaT cells. We found that the linc-ROR level in HaCaT cells was gradually increased during arsenite-induced malignant transformation, and the activity of P53 was decreased, but the P53 expression was not significantly altered, indicating that linc-ROR may play a role in arsenite-induced HaCaT cell transformation that is associated with P53 activity but not P53 expression. We further demonstrated that linc-ROR down-regulation by siRNA significantly inhibited the cellular proliferation and restored P53 activity in arsenite-transformed HaCaT cells, suggesting that linc-ROR promotes proliferation of arsenite-transformed HaCaT cells by inhibiting P53 activity. Moreover, linc-ROR siRNA also down-regulated the PI3K/AKT pathway in arsenite-transformed HaCaT cells, and treatment with AKT inhibitor wortmannin restored P53 activity, implying that linc-ROR inhibits P53 activity by activating the PI3K/AKT pathway. Taken together, the present study shows that linc-ROR promotes arsenite-transformed keratinocyte proliferation by inhibiting P53 activity through activating PI3K/AKT, providing a novel carcinogenic mechanism of arsenite-induced skin cancer.

Inorganic arsenic induces sex-dependent pathological hypertrophy in the heart

Arsenic exposure though drinking water is widespread and well associated with adverse cardiovascular outcomes, yet the pathophysiological mechanisms by which iAS induces these effects are largely unknown. Recently, an epidemiological study in an American population with a low burden of cardiovascular risk factors found that iAS exposure was associated with altered left ventricular geometry. Considering the possibility that iAS directly induces cardiac remodeling independently of hypertension, we investigated the impact of an environmentally relevant iAS exposure on the structure and function of male and female hearts. Adult male and female C56BL/6J mice were exposed to 615 μg/L iAS for 8 wk. Males exhibited increased systolic blood pressure via tail cuff photoplethysmography, left ventricular wall thickening via transthoracic echocardiography, and increased plasma atrial natriuretic peptide via enzyme immunoassay. RT-qPCR revealed increased myocardial RNA transcripts of Acta1, Myh7, and Nppa and decreased Myh6, providing evidence of pathological hypertrophy in the male heart. Similar changes were not detected in females, and nitric oxide-dependent mechanisms of cardioprotection in the heart appeared to remain intact. Further investigation found that Rcan1 was upregulated in male hearts and that iAS activated NFAT in HEK-293 cells via luciferase assay. Interestingly, iAS induced similar hypertrophic gene expression changes in neonatal rat ventricular myocytes, which were blocked by calcineurin inhibition, suggesting that iAS may induce pathological cardiac hypertrophy in part by targeting the calcineurin-NFAT pathway. As such, these results highlight iAS exposure as an independent cardiovascular risk factor and provide biological impetus for its removal from human consumption.NEW & NOTEWORTHY This investigation provides the first mechanistic link between an environmentally relevant dose of inorganic arsenic (iAS) and pathological hypertrophy in the heart. By demonstrating that iAS exposure may cause pathological cardiac hypertrophy not only by increasing systolic blood pressure but also by potentially activating calcineurin-nuclear factor of activated T cells and inducing fetal gene expression, these results provide novel mechanistic insight into the theat of iAS exposure to the heart, which is necessary to identify targets for medical and public health intervention.

Akt Regulated Phosphorylation of GSK-3β/Cyclin D1, p21 and p27 Contributes to Cell Proliferation Through Cell Cycle Progression From G1 to S/G2M Phase in Low-Dose Arsenite Exposed HaCat Cells

Arsenic is a toxic environmental contaminant. Long-term exposure to arsenic through drinking water induces human cancers. However, it is as yet uncertain about the mechanisms of arsenic induced carcinogenesis. Although the effects of low-dose arsenicals on proliferation and cell cycle have been revealed by short time exposure, the evidences for long-term exposure were seldom reported. The detailed mechanism has been unclear and supplemented constantly. In the present study, we used normal human keratinocytes (HaCat) to study the effects of long-term, low-dose sodium arsenite (NaAsO₂) exposure on cell proliferation with emphasis on the Akt regulated cell cycle signaling pathways. Treatment of NaAsO₂ resulted in increased cell proliferation and promotion of cell cycle progression from G1 to S/G2M phase, both of which could be attenuated by MK2206, a highly selective inhibitor of Akt. Along with the increased expression of phospho-Akt (p-Akt, Ser 473), increased expression of p-GSK-3β (Ser 9), p-p21 (Thr 145), p-p27 (Thr 157) and total cyclin D1, and decreased expression of p-cyclin D1 (Thr 286), p21 and p27 were also found in the NaAsO₂ exposed cells. Treatment of MK2206 markedly reversed the expression of all of the above proteins. Our findings indicated that the phosphorylated activation of Akt played a role in the proliferation of HaCat cells upon long-term, low-dose NaAsO₂ exposure through the phosphorylative regulation of its downstream cell cycle regulating factors of GSK-3β/cyclin D1, p21 and p27, which could induce the promotion of cell cycle progression from G1 to S/G2M phase.

An Air-Liquid Interface Organ-Level Lung Microfluidics Platform for Analysis on Molecular Mechanisms of Cytotoxicity Induced by Cancer-Causing Fine Particles

Fine particulate matter less than 2.5 μm in diameter (PM_2.5) is regarded as a carcinogenic factor, but the mechanism has been left unexplored. Our goal was to reveal the carcinogenic mechanism at the gene and protein level under the inhalational air-liquid interface (ALI) condition. Herein, we developed an ALI organ-level lung microfluidic platform (ALI-OLMP) carrying lung epithelial cell line BEAS-2B and human pulmonary microvascular endothelial cells (HPMEC); the cell viability was above 98% within 14 days on this system, which was used to mimic the practical alveolar microenvironment for the multiomics analysis, to identify the global gene and protein expression after exposure to PM_2.5 in Shanghai, China from 2014 to 2015. The combined RNA-Seq and iTRAQ analysis indicated that the unique set was 2532 genes at 10 μg/cm² of PM_2.5, and there were also at least 25 identical activated signal transduction cascades including bladder cancer, transcriptional dysregulation in cancer, the TP53 (p53) signaling pathway, Jak-STAT signaling pathway, and PI3K-Akt signaling pathway, which could lead to blocking of differentiation, cell proliferation and survival, and sustained angiogenesis. The images obtained by the transmission electron microscopy (TEM) showed that the particles could enter the mitochondria, and even get into the nucleus. The Pearson's correlation coefficient test elucidated that inorganics (EC), organics (OC, PAHs, and alkane), and metals (Cr, Mn, and Sb) were significantly correlated to the dysregulated oncoproteins (VEGF, IL6, MDM2, AKT1, STAT, and P53). The findings may to some extent explain the molecular mechanism of carcinogenicity caused by fine-particle exposure.

XIAP RING domain mediates miR-4295 expression and subsequently inhibiting p63α protein translation and promoting transformation of bladder epithelial cells

The X-linked inhibitor of apoptosis protein (XIAP) contains three N-terminal BIR domains that mediate anti-apoptosis and one C-terminal RING finger domain whose function(s) are not fully defined. Here we show that the RING domain of XIAP strongly inhibits the expression of p63α, a known tumor suppressor. XIAP knockdown in urothelial cells or RING deletion in knockin mice markedly upregulates p63α expression. This RING-mediated p63α downregulation is critical for the malignant transformation of normal urothelial cells following EGF treatment. We further show that the RING domain promotes Sp1-mediated transcription of miR-4295 which targets the 3′UTR of p63α mRNA and consequently inhibits p63α translation. Our results reveal a previously unknown function of the RING of XIAP in promoting miR-4295 transcription, thereby reducing p63α translation and enhancing urothelial transformation. Our data offer novel insights into the multifunctional effects of the XIAP RING domain on urothelial tumorigenesis and the potential for targeting this frequently overexpressed protein as a therapeutic alternative.

Red Ginseng Oil Inhibits TPA-Induced Transformation of Skin Epidermal JB6 Cells

Red ginseng oil (RGO) has been shown to possess anti-inflammatory and hepatoprotective activity. In this study, we evaluated the inhibitory effect of RGO on 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated neoplastic transformation of JB6 P+ cells. RGO pretreatment abolished the transformation of JB6 P+ cells challenged by TPA. RGO suppressed the transactivation of activator protein-1 (AP-1) and nuclear factor kappa B (NF-κB) transcription factors as well as protein levels of cyclooxygenase-2, cyclin D1, cyclin E, and Bcl-2 in the TPA-treated cells. Additionally, TPA-induced phosphorylations of extracellular signal-regulated kinases, 90 kDa ribosomal S6 kinase 2, c-Jun N-terminal kinases, and glycogen synthase kinase 3β were downregulated in the presence of RGO. Furthermore, RGO induced the nuclear factor erythroid 2-related factor 2 (Nrf2)-mediated antioxidant enzyme heme oxygenase-1 (HO-1) expression, and effectively blocked the overproduction of TPA-induced reactive oxygen species. These results suggest that RGO exerts a potent chemopreventive activity in skin cell model.

Mitochondrial catalase induces cells transformation through nucleolin-dependent Cox-2 mRNA stabilization

It's well documented that over-production of reactive oxygen species (ROS) causes detrimental damages to cells. While a low level of ROS, such as H2O2, functions as signaling transducer and motivates cell proliferation in both cancer and non-transformed stem cells. As a double-edged sword, the direct evidence for demonstrating the function of H2O2 in the cause of tumor is barely characterized in intact cells. In our current study, we found that targeted expression of mitochondrial catalase (mCAT), but not catalase, could significantly reduce the accumulation of H2O2 in mouse epithelial JB6 Cl41 cells, consequently led to the cell malignant transformation and anchorage-independent cell growth. Further study revealed that this reduction of H2O2 resulted in the translocation of nucleolin from the cytoplasm to nuclear, and maintaining the nucleolin nuclear location status, and in turn stabilizing the cox-2 mRNA and consequently leading to a COX-2 protein upregulation, as well as malignant transforming mCAT-overexpressed Cl41 cells. Collectively, our studies here provide direct experimental evidence demonstrating a novel function and molecular mechanisms of mCAT in transforming mouse Cl41 cells, and high significance insight into understanding the beneficial aspect of H2O2 in circumventing tumor promotion and the theoretical basis for the management of H2O2 in the clinic implementation as a chemotherapeutic strategy.

MicroRNA-155 regulates arsenite-induced malignant transformation by targeting Nrf2-mediated oxidative damage in human bronchial epithelial cells

Arsenite is a well-documented human lung carcinogen but the detailed mechanisms of carcinogenesis remain unclear. In this study, human bronchial epithelial (16-HBE) cells were continuously exposed to 2.5μM arsenite for about 13 weeks to induce the phenotypes of malignant transformation. Our results showed that Nrf2 expression was gradually decreased whereas no significant change was observed on NF-κB activation with increased time of arsenite exposure. To test the roles of Nrf2-meidtaed oxidative damage in the arsenite-induced malignant transformation, we compared the levels of cGMP, PKG and oxidative damage-related indicators between arsenic-transformed cells and control cells. Our data demonstrated there were no significantly differences on the contents of cGMP, PKG, MDA and the production of ROS, but the levels of GSH and NO, the activities of SOD, tNOS and iNOS were significantly enhanced in the arsenic-transformed cells. Importantly, Nrf2 inactivation could be modulated by miR-155, and inhibition of miR-155 remarkably attenuated the malignant phenotypes and promoted apoptotic cell death in the arsenic-transformed cells. Together, our findings provide the novel mechanism that miR-155 may regulate arsenite-induced cell malignant transformation by targeting Nrf2-mediated oxidative damage, indicating that inhibition of miR-155 may be a potential strategy against lung carcinogenesis of arsenite.

Preventive effects of butyric acid, nicotinamide, calcium glucarate alone or in combination during the 7, 12-dimethylbenz (a) anthracene induced mouse skin tumorigenesis via modulation of K-Ras-PI3K-AKTpathway and associated micro RNAs

Skin cancer is among the most common cancers worldwide and identifiable molecular changes for early and late stage of skin tumorigenesis can suggest the better targets for its control. In this study, we investigated the status of K-Ras-PI3K-AKTpathway followed by NF-κB, cyclin D1, MMP-9 and regulatory micro RNA during 7, 12-dimethylbenz[a]anthracene (DMBA) induced mouse skin tumorigenesis and its prevention by butyric acid (BA), nicotinamide (NA) and calcium glucarate (CAG), individually or in combination with respect to time. DMBA upregulated the K-Ras, PI3K, Akt, NF-κB, cyclin D1 and MMP-9, but downregulated the PTEN in a time dependent manner. DMBA also reduced the levels of micoRNA let-7a but induced the levels of miR-21 and miR-20a as a function of time. BA, NA and CAG were found to prevent DMBA induced changes, but they were most effective when used together in a combination. Reduced let-7a and miR-211 were correlated with the overexpression of K-Ras and MMP-9. Overexpression of miR-21 and miR-20a was correlated with the down regulation of PTEN and overexpression of Cyclin D1. Collectively, the enhanced chemopreventive potential of natural compound in combination via regulation of K-Ras-PI3K-AKTpathway along with regulatory micro RNAs provide a newer and effective mean for cancer management.

Isorhapontigenin (ISO) inhibited cell transformation by inducing G0/G1 phase arrest via increasing MKP-1 mRNA Stability

The cancer chemopreventive property of Chinese herb new isolate isorhapontigenin (ISO) and mechanisms underlying its activity have never been explored. Here we demonstrated that ISO treatment with various concentrations for 3 weeks could dramatically inhibit TPA/EGF-induced cell transformation of Cl41 cells in Soft Agar assay, whereas co-incubation of cells with ISO at the same concentrations could elicit G0/G1 cell-cycle arrest without redundant cytotoxic effects on non-transformed cells. Further studies showed that ISO treatment resulted in cyclin D1 downregulation in dose- and time-dependent manner. Our results indicated that ISO regulated cyclin D1 at transcription level via targeting JNK/C-Jun/AP-1 activation. Moreover, we found that ISO-inhibited JNK/C-Jun/AP-1 activation was mediated by both upregulation of MKP-1 expression through increasing its mRNA stability and deactivating MKK7. Most importantly, MKP-1 knockdown could attenuate ISO-mediated suppression of JNK/C-Jun activation and cyclin D1 expression, as well as G0/G1 cell cycle arrest and cell transformation inhibition, while ectopic expression of FLAG-cyclin D1 T286A mutant also reversed ISO-induced G0/G1 cell-cycle arrest and inhibition of cell transformation. Our results demonstrated that ISO is a promising chemopreventive agent via upregulating mkp-1 mRNA stability, which is distinct from its cancer therapeutic effect with downregulation of XIAP and cyclin D1 expression.

NF-κB1 inhibits c-Myc protein degradation through suppression of FBW7 expression

NF-κB is a well-known transcription factor in regulation of multiple gene transcription and biological processes, and most of them are relied on its transcriptional activity of the p65/RelA subunit, while biological function of another ubiquitously expressed subunit NF-κB1 (p50) remains largely unknown due to lack transcriptional activation domain. Here we discovered a novel biological function of p50 as a regulator of oncogenic c-Myc protein degradation upon arsenite treatment in a NF-κB transcriptional-independent mechanism. Our results found that p50 was crucial for c-Myc protein induction following arsenite treatment by using specific knockdown and deletion of p50 in its normal expressed cells as well as reconstituting expression of p50 in its deficient cells. Subsequently we showed that p50 upregulated c-Myc protein expression mainly through inhibiting its degradation. We also identified that p50 exhibited this novel property by suppression of FBW7 expression. FBW7 was profoundly upregulated in p50-defecient cells in comparison to that in p50 intact cells, whereas knockdown of FBW7 in p50-/- cells restored arsenite-induced c-Myc protein accumulation, assuring that FBW7 up-regulation was responsible for defect of c-Myc protein expression in p50-/- cells. In addition, we discovered that p50 suppressed fbw7 gene transcription via inhibiting transcription factor E2F1 transactivation. Collectively, our studies demonstrated a novel function of p50 as a regulator of c-Myc protein degradation, contributing to our notion that p50-regulated protein expression through multiple levels at protein translation and degradation, further providing a significant insight into the understanding of biomedical significance of p50 protein.

The N-terminal region of p27 inhibits HIF-1α protein translation in ribosomal protein S6-dependent manner by regulating PHLPP-Ras-ERK-p90RSK axis

P27 was identified as a tumor suppressor nearly two decades, being implicated in cell-cycle control, differentiation, senescence, apoptosis and motility. Our present study, for the first time to the best of our knowledge, revealed a potential role of p27 in inhibiting S6-mediated hypoxia-inducible factor-1α (HIF-1α) protein translation, which contributed to the protection from environmental carcinogen (sodium arsenite)-induced cell transformation. Our findings showed that depletion of p27 expression by knockout and knockdown approaches efficiently enhanced S6 phosphorylation in arsenite response via overactivating Ras/Raf/MEK/ERK pathway, which consequently resulted in the stimulation of p90RSK (90 kDa ribosomal S6 kinase), a direct kinase for S6 phosphorylation. Although PI3K/AKT pathway was also involved in S6 activation, blocking AKT and p70S6K activation did not attenuate arsenite-induced S6 activation in p27−/− cells, suggesting p27 specifically targeted Ras/ERK pathway rather than PI3K/AKT pathway for inhibition of S6 activation in response to arsenite exposure. Further functional studies found that p27 had a negative role in cell transformation induced by chronic low-dose arsentie exposure. Mechanistic investigations showed that HIF-1α translation was upregulated in p27-deficient cells in an S6 phosphorylation-dependent manner and functioned as a driving force in arsenite-induced cell transformation. Knockdown of HIF-1α efficiently reversed arsenite-induced cell transformation in p27-depleted cells. Taken together, our findings provided strong evidence showing that by targeting Ras/ERK pathway, p27 provided a negative control over HIF-1α protein synthesis in an S6-dependent manner, and abrogated arsenite-induced cell transformation via downregulation of HIF-1α translation.

Crucial role of c-Jun phosphorylation at Ser63/73 mediated by PHLPP protein degradation in the cheliensisin a inhibition of cell transformation

Cheliensisin A (Chel A), as a novel styryl-lactone isolated from Goniothalamus cheliensis Hu, has been demonstrated to have an inhibition of EGF-induced Cl41 cell transformation via stabilizing p53 protein in a Chk1-dependent manner, suggesting its chemopreventive activity in our previous studies. However, its underlying molecular mechanisms have not been fully characterized yet. In the current study, we found that Chel A treatment could increase c-Jun protein phosphorylation and activation, whereas the inhibition of c-Jun phosphorylation, by ectopic expression of a dominant-negative mutant of c-Jun, TAM67, reversed the Chel A inhibition of EGF-induced cell transformation and impaired Chel A induction of p53 protein and apoptosis. Moreover, our results indicated that Chel A treatment led to a PHLPP downregulation by promoting PHLPP protein degradation. We also found that PHLPP could interact with and bind to c-Jun protein, whereas ectopic PHLPP expression blocked c-Jun activation, p53 protein and apoptotic induction by Chel A, and further reversed the Chel A inhibition of EGF-induced cell transformation. With the findings, we have demonstrated that Chel A treatment promotes a PHLPP protein degradation, which can bind to c-Jun and mediates c-Jun phosphorylation, and further leading to p53 protein induction, apoptotic responses, subsequently resulting in cell transformation inhibition and chemopreventive activity of Chel A.

Molecular control of arsenite-induced apoptosis in Caenorhabditis elegans: roles of insulin-like growth factor-1 signaling pathway

Apoptosis is one of the main cellular processes in responses to arsenic, the well known environmental carcinogen. By using the nematode Caenorhabditis elegans as an in vivo model, we found that insulin-like growth factor-1 networks and their target protein DAF-16/FOXO, known as key regulators of energy metabolism and growth, played important roles in arsenite-induced apoptosis. Inactivation of DAF-2, AGE-1 and AKT-1 caused worms more susceptible to arsenite-induced apoptosis, which could be attenuated by DAF-16 knockout. Worms with inactivated AKT-2 and SGK-1 or with constitutively activated PDK-1 and AKT-1 showed low levels of apoptosis, which could be elevated by DAF-16 mutation. Our results demonstrated that DAF-2/IGF-1R, AGE-1/PI3K, PDK-1/PDK1 and AKT-1/PKB negatively regulated the arsenite-induced apoptosis, whereas AKT-2 and SGK-1 acted proapoptotically. DAF-16/FOXO antagonized IGF-1 signals in signaling the arsenite-induced apoptosis, and apoptosis promoted by DAF-16 inactivation was attributed to its higher sensitivity to oxidative stress.

SUMOylation of RhoGDIα is required for its repression of cyclin D1 expression and anchorage-independent growth of cancer cells

Selective activation of Rho GTPase cascade requires the release of Rho from RhoGDI (GDP-dissociation inhibitors) complexes. Our previous studies identified RhoGDIα SUMOylation at Lys-138 and its function in the regulation of cancer cell invasion. In the current study, we demonstrate that RhoGDIα SUMOylation has a crucial role in the suppression of cancer cell anchorage-independent growth as well as the molecular mechanisms underlying this suppression. We found that ectopic expression of RhoGDIα resulted in marked inhibition of an anchorage-independent growth with induction of G0/G1 cell cycle arrest, while point mutation of RhoGDIα SUMOylation at residue Lys-138 (K138R) abrogated this growth suppression and G0/G1 cell cycle arrest in cancer cells. Further studies showed that SUMOylation at Lys-138 was critical for RhoGDIα down-regulation of cyclin D1 protein expression and that MEK1/2-Erk was a specific downstream target of SUMOylated RhoGDIα for its inhibition of C-Jun/AP-1 cascade, cyclin d1 transcription, and cell cycle progression. These results strongly demonstrate that SUMOylated RhoGDIα suppressed C-Jun/AP-1-dependent transactivation specifically via targeting MEK1/2-Erk, subsequently leading to the down-regulation of cyclin D1 expression and anti-cancer activity. Our results provide new mechanistic insights into the understanding of essential role of SUMOylation at Lys-138 in RhoGDIα's biological function.

The role of EGFR/PI3K/Akt/cyclinD1 signaling pathway in acquired middle ear cholesteatoma

Cholesteatoma is a benign keratinizing and hyper proliferative squamous epithelial lesion of the temporal bone. Epidermal growth factor (EGF) is one of the most important cytokines which has been shown to play a critical role in cholesteatoma. In this investigation, we studied the effects of EGF on the proliferation of keratinocytes and EGF-mediated signaling pathways underlying the pathogenesis of cholesteatoma. We examined the expressions of phosphorylated EGF receptor (p-EGFR), phosphorylated Akt (p-Akt), cyclinD1, and proliferating cell nuclear antigen (PCNA) in 40 cholesteatoma samples and 20 samples of normal external auditory canal (EAC) epithelium by immunohistochemical method. Furthermore, in vitro studies were performed to investigate EGF-induced downstream signaling pathways in primary external auditory canal keratinocytes (EACKs). The expressions of p-EGFR, p-Akt, cyclinD1, and PCNA in cholesteatoma epithelium were significantly increased when compared with those of control subjects. We also demonstrated that EGF led to the activation of the EGFR/PI3K/Akt/cyclinD1 signaling pathway, which played a critical role in EGF-induced cell proliferation and cell cycle progression of EACKs. Both EGFR inhibitor AG1478 and PI3K inhibitor wortmannin inhibited the EGF-induced EGFR/PI3K/Akt/cyclinD1 signaling pathway concomitantly with inhibition of cell proliferation and cell cycle progression of EACKs. Taken together, our data suggest that the EGFR/PI3K/Akt/cyclinD1 signaling pathway is active in cholesteatoma and may play a crucial role in cholesteatoma epithelial hyper-proliferation. This study will facilitate the development of potential therapeutic targets for intratympanic drug therapy for cholesteatoma.

Cyclin d1 downregulation contributes to anticancer effect of isorhapontigenin on human bladder cancer cells

Isorhapontigenin (ISO) is a new derivative of stilbene compound that was isolated from the Chinese herb Gnetum Cleistostachyum and has been used for treatment of bladder cancers for centuries. In our current studies, we have explored the potential inhibitory effect and molecular mechanisms underlying isorhapontigenin anticancer effects on anchorage-independent growth of human bladder cancer cell lines. We found that isorhapontigenin showed a significant inhibitory effect on human bladder cancer cell growth and was accompanied with related cell cycle G(0)-G(1) arrest as well as downregulation of cyclin D1 expression at the transcriptional level in UMUC3 and RT112 cells. Further studies identified that isorhapontigenin downregulated cyclin D1 gene transcription via inhibition of specific protein 1 (SP1) transactivation. Moreover, ectopic expression of GFP-cyclin D1 rendered UMUC3 cells resistant to induction of cell-cycle G(0)-G(1) arrest and inhibition of cancer cell anchorage-independent growth by isorhapontigenin treatment. Together, our studies show that isorhapontigenin is an active compound that mediates Gnetum Cleistostachyum's induction of cell-cycle G(0)-G(1) arrest and inhibition of cancer cell anchorage-independent growth through downregulating SP1/cyclin D1 axis in bladder cancer cells. Our studies provide a novel insight into understanding the anticancer activity of the Chinese herb Gnetum Cleistostachyum and its isolate isorhapontigenin.

X-linked inhibitor of apoptosis protein (XIAP) regulation of cyclin D1 protein expression and cancer cell anchorage-independent growth via its E3 ligase-mediated protein phosphatase 2A/c-Jun axis

The X-linked inhibitor of apoptosis protein (XIAP) is a well known potent inhibitor of apoptosis; however, it is also involved in other cancer cell biological behavior. In the current study, we discovered that XIAP and its E3 ligase played a crucial role in regulation of cyclin D1 expression in cancer cells. We found that deficiency of XIAP expression resulted in a marked reduction in cyclin D1 expression. Consistently, cell cycle transition and anchorage-independent cell growth were also attenuated in XIAP-deficient cancer cells compared with those of the parental wild-type cells. Subsequent studies demonstrated that E3 ligase activity within the RING domain of XIAP is crucial for its ability to regulate cyclin D1 transcription, cell cycle transition, and anchorage-independent cell growth by up-regulating transactivation of c-Jun/AP-1. Moreover, we found that E3 ligase within RING domain was required for XIAP inhibition of phosphatase PP2A activity by up-regulation of PP2A phosphorylation at Tyr-307 in its catalytic subunit. Such PP2A phosphorylation and inactivation resulted in phosphorylation and activation of its downstream target c-Jun in turn leading to cyclin D1 expression. Collectively, our studies uncovered a novel function of E3 ligase activity of XIAP in the up-regulation of cyclin D1 expression, providing significant insight into the understanding of the biomedical significance of overexpressed XIAP in cancer development, further offering a new molecular basis for utilizing XIAP E3 ligase as a cancer therapeutic target.

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

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

Cyclooxygenase-2 (COX-2) mediates arsenite inhibition of UVB-induced cellular apoptosis in mouse epidermal Cl41 cells

Inorganic arsenic is an environmental human carcinogen, and has been shown to act as a co-carcinogen with solar ultraviolet (UV) radiation in mouse skin tumor induction even at low concentrations. However, the precise mechanism of its co-carcinogenic action is largely unknown. Apoptosis plays an essential role as a protective mechanism against neoplastic development in the organism by eliminating genetically damaged cells. Thus, suppression of apoptosis is thought to contribute to carcinogenesis. It is known that cyclooxygenase-2 (COX-2) can promote carcinogenesis by inhibiting cell apoptosis under stress conditions; and our current studies investigated the potential contribution of COX-2 to the inhibitory effect of arsenite in UV-induced cell apoptosis in mouse epidermal Cl41 cells. We found that treatment of cells with low concentration (5 μM) arsenite attenuated cellular apoptosis upon UVB radiation accompanied with a coinductive effect on COX-2 expression and nuclear factor-κB (NFκB) transactivation. Our results also showed that the COX-2 induction by arsenite and UVB depended on an NFκB pathway because COX-2 co-induction could be attenuated in either p65-deficient or p50-deficient cells. Moreover, UVB-induced cell apoptosis could be dramatically reduced by the introduction of exogenous COX-2 expression, whereas the inhibitory effect of arsenite on UVB-induced cell apoptosis could be impaired in COX-2 knockdown C141 cells. Our results indicated that COX-2 mediated the anti-apoptotic effect of arsenite in UVB radiation through an NFκB-dependent pathway. Given the importance of apoptosis evasion during carcinogenesis, we anticipated that COX-2 induction might be at least partially responsible for the co-carcinogenic effect of arsenite on UVB-induced skin carcinogenesis.

Ceftriaxone, an FDA-approved cephalosporin antibiotic, suppresses lung cancer growth by targeting Aurora B

Ceftriaxone, an FDA-approved third-generation cephalosporin antibiotic, has antimicrobial activity against both gram-positive and gram-negative organisms. Generally, ceftriaxone is used for a variety of infections such as community-acquired pneumonia, meningitis and gonorrhea. Its primary molecular targets are the penicillin-binding proteins. However, other activities of ceftriaxone remain unknown. Herein, we report for the first time that ceftriaxone has antitumor activity in vitro and in vivo. Kinase profiling results predicted that Aurora B might be a potential 'off' target of ceftriaxone. Pull-down assay data confirmed that ceftriaxone could bind with Aurora B in vitro and in A549 cells. Furthermore, ceftriaxone (500 µM) suppressed anchorage-independent cell growth by targeting Aurora B in A549, H520 and H1650 lung cancer cells. Importantly, in vivo xenograft animal model results showed that ceftriaxone effectively suppressed A549 and H520 lung tumor growth by inhibiting Aurora B. These data suggest the anticancer efficacy of ceftriaxone for the treatment of lung cancers through its inhibition of Aurora B.

Polycomb (PcG) proteins, BMI1 and SUZ12, regulate arsenic-induced cell transformation

Inorganic arsenic is a well-documented human carcinogen associated with cancers of the skin, lung, liver, and bladder. However, the underlying mechanisms explaining the tumorigenic role of arsenic are not well understood. The present study explored a potential mechanism of cell transformation induced by arsenic exposure. Exposure to a low dose (0.5 μm) of arsenic trioxide (As(2)O(3)) caused transformation of BALB/c 3T3 cells. In addition, in a xenograft mouse model, tumor growth of the arsenic-induced transformed cells was dramatically increased. In arsenic-induced transformed cells, polycomb group (PcG) proteins, including BMI1 and SUZ12, were activated resulting in enhanced histone H3K27 tri-methylation levels. On the other hand, tumor suppressor p16(INK4a) and p19(ARF) mRNA and protein expression were dramatically suppressed. Introduction of small hairpin (sh) RNA-BMI1 or -SUZ12 into BALB/c 3T3 cells resulted in suppression of arsenic-induced transformation. Histone H3K27 tri-methylation returned to normal in BMI1- or SUZ12-knockdown BALB/c 3T3 cells compared with BMI1- or SUZ12-wildtype cells after arsenic exposure. As a consequence, the expression of p16(INK4a) and p19(ARF) was recovered in arsenic-treated BMI1- or SUZ12-knockdown cells. Thus, arsenic-induced cell transformation was blocked by inhibition of PcG function. Taken together, these results strongly suggest that the polycomb proteins, BMI1 and SUZ12 are required for cell transformation induced by organic arsenic exposure.

Suberoylanilide hydroxamic acid (SAHA) inhibits EGF-induced cell transformation via reduction of cyclin D1 mRNA stability

Suberoylanilide hydroxamic acid (SAHA) inhibiting cancer cell growth has been associated with its downregulation of cyclin D1 protein expression at transcription level or translation level. Here, we have demonstrated that SAHA inhibited EGF-induced Cl41 cell transformation via the decrease of cyclin D1 mRNA stability and induction of G0/G1 growth arrest. We found that SAHA treatment resulted in the dramatic inhibition of EGF-induced cell transformation, cyclin D1 protein expression and induction of G0/G1 growth arrest. Further studies showed that SAHA downregulation of cyclin D1 was only observed with endogenous cyclin D1, but not with reconstitutionally expressed cyclin D1 in the same cells, excluding the possibility of SAHA regulating cyclin D1 at level of protein degradation. Moreover, SAHA inhibited EGF-induced cyclin d1 mRNA level, whereas it did not show any inhibitory effect on cyclin D1 promoter-driven luciferase reporter activity under the same experimental conditions, suggesting that SAHA may decrease cyclin D1 mRNA stability. This notion was supported by the results that treatment of cells with SAHA decreased the half-life of cyclin D1 mRNA from 6.95 h to 2.57 h. Consistent with downregulation of cyclin D1 mRNA stability, SAHA treatment also attenuated HuR expression, which has been well-characterized as a positive regulator of cyclin D1 mRNA stability. Thus, our study identifies a novel mechanism responsible for SAHA inhibiting cell transformation via decreasing cyclin D1 mRNA stability and induction of G0/G1 growth arrest in Cl41 cells.

Phosphorylation of histone H3 at serine 10 has an essential role in arsenite-induced expression of FOS, EGR1 and IL8 mRNA in cultured human cell lines

Trivalent inorganic arsenite [iAs(III)] is known to alter the expression of a number of genes associated with transcription and cell proliferation, which was thought to be one of the possible mechanisms of arsenical carcinogenesis. However, the detailed mechanisms underlying iAs(III) induction of changes in gene expression are not fully understood. Here we examine the role of histone H3 phosphorylation at serine 10 (Ser(10) ) in gene regulation when the cells were treated with iAs(III). Among the 34 genes tested, iAs(III) induced mRNA expression of JUN, FOS, EGR1, HMOX1, HSPA1A, IL8, GADD45A, GADD45B and GADD153. Phosphorylation of histone H3 Ser(10) was induced by iAs(III) in interphase cells, and was effectively blocked by the ERKs pathway inhibitor (U0126). U0126 treatment significantly reduced constitutive mRNA expression of FOS and EGR1, and dramatically suppressed the induction of FOS, EGR1 and IL8 mRNA in iAs(III)-treated cells. The other genes, which were induced by iAs(III), were not affected by U0126 treatment. When the histone H3 nonphosphorylatable mutant of serine 10 (S10A) was overexpressed in cells, iAs(III) induction of FOS, EGR1and IL8 expression was significantly decreased as compared with wild-type cells. The other genes induced by iAs(III) were not changed in S10A cells nor by U0126 treatment. In addition, S10A cells were more resistant to iAs(III) cytotoxicity. These results indicated that the phosphorylation of histone H3 at Ser(10) through the ERKs pathway in interphase cells is an important regulatory event for iAs(III)-mediated gene expression. Aberrant gene expression seems to be an important cause of cytotoxicity and may have some relation to iAs(III) carcinogenicity.

Akt activation is responsible for enhanced migratory and invasive behavior of arsenic-transformed human bronchial epithelial cells

BACKGROUND

Arsenic is one of the most common environmental contaminants. Long-term exposure to arsenic causes human bronchial epithelial cell (HBEC) malignant transformation and lung cancer. However, the mechanism of arsenic lung carcinogenesis is not clear, and the migratory and invasive properties of arsenic-transformed cells (As-transformed cells) have rarely been studied.

OBJECTIVES

This study was designed to investigate the migratory and invasive behavior of As-transformed HBECs and the underlying mechanism.

METHODS

As-transformed p53lowHBECs were generated by exposing p53-knockdown HBECs to sodium arsenite (2.5 μM) for 16 weeks. Cell migration was assessed by transwell migration and wound-healing assay. Cell invasion was evaluated using Matrigel-coated transwell chambers. Gene overexpression, small interfering RNA (siRNA) knockdowns, and pharmacological inhibitors were used to determine the potential mechanism responsible for enhanced cell migration and invasion.

RESULTS

Transwell migration and invasion assays revealed that As-transformed p53lowHBECs were highly migratory and invasive. Akt (also known as protein kinase B) and extracellular signal-regulated protein kinase 1/2 (Erk1/2) were strongly activated in As-transformed p53lowHBECs. Stable expression of microRNA 200b in As-transformed p53lowHBECs abolished Akt and Erk1/2 activation and completely suppressed cell migration and invasion. Pharmacological inactivation of Akt but not Erk1/2 significantly decreased cell migration and invasion. Inhibition of Akt reduced the expression of epithelial-to-mesenchymal transition-inducing transcription factors zinc-finger E-box-binding homeobox factor 1 (ZEB1) and ZEB2. siRNA knockdown of ZEB1 and ZEB2 impaired As-transformed p53lowHBEC migration and invasion.

CONCLUSIONS

Akt activation plays a critical role in enabling As-transformed HBEC migration and invasion by promoting ZEB1 and ZEB2 expression.

Arsenite induces cell transformation by reactive oxygen species, AKT, ERK1/2, and p70S6K1

Arsenic is naturally occurring element that exists in both organic and inorganic formulations. The inorganic form arsenite has a positive association with development of multiple cancer types. There are significant populations throughout the world with high exposure to arsenite via drinking water. Thus, human exposure to arsenic has become a significant public health problem. Recent evidence suggests that reactive oxygen species (ROS) mediate multiple changes to cell behavior after acute arsenic exposure, including activation of proliferative signaling and angiogenesis. However, the role of ROS in mediating cell transformation by chronic arsenic exposure is unknown. We found that cells chronically exposed to sodium arsenite increased proliferation and gained anchorage-independent growth. This cell transformation phenotype required constitutive activation of AKT, ERK1/2, mTOR, and p70S6K1. We also observed these cells constitutively produce ROS, which was required for the constitutive activation of AKT, ERK1/2, mTOR, and p70S6K1. Suppression of ROS levels by forced expression of catalase also reduced cell proliferation and anchorage-independent growth. These results indicate cell transformation induced by chronic arsenic exposure is mediated by increased cellular levels of ROS, which mediates activation of AKT, ERK1/2, and p70S6K1.

Activation and up-regulation of translation initiation factor 4B contribute to arsenic-induced transformation

Arsenic is a known human carcinogen. However, the mechanism of how arsenic induces cell transformation remains unclear. In this study, we demonstrated that long-term exposure to sodium arsenite at low-dose (2 µM) increases cell proliferation and neoplastic transformation in a mouse epidermal cell model, JB6 promotion-susceptible cells. The phosphorylation of AKT and its downstream targets, 70-kDa ribosomal protein S6 kinase (p70S6K) and translation initiation factor 4B (eIF4B), are increased in the arsenite treated cells, indicating that long-term arsenite treatment activates AKT-p70S6K signaling pathway. In addition, long-term exposure to arsenite up-regulates eIF4B expression and increases the rate of translation. Knockdown of eIF4B expression resulted in inhibition of arsenic-induced cell proliferation, transformation, and translation. Moreover, the expression of c-Myc which is up-regulated by long-term arsenite treatment is inhibited by eIF4B knockdown. Taken together, these results indicate that activation and up-regulation of eIF4B contributes to arsenic-induced transformation in JB6 cells.

p27 suppresses arsenite-induced Hsp27/Hsp70 expression through inhibiting JNK2/c-Jun- and HSF-1-dependent pathways

p27 is an atypical tumor suppressor that can regulate the activity of cyclin-dependent kinases and G(0)-to-S phase transitions. More recent studies reveal that p27 may also exhibit its tumor-suppressive function through regulating many other essential cellular events. However, the molecular mechanisms underlying these anticancer effects of p27 are largely unknown. In this study, we found that depletion of p27 expression by either gene knock-out or knockdown approaches resulted in up-regulation of both Hsp27 and Hsp70 expression at mRNA- and promoter-derived transcription as well as protein levels upon arsenite exposure, indicating that p27 provides a negative signal for regulating the expression of Hsp27 and Hsp70. Consistently, arsenite-induced activation of JNK2/c-Jun and HSF-1 pathways was also markedly elevated in p27 knock-out (p27(-/-)) and knockdown (p27 shRNA) cells. Moreover, interference with the expression or function of JNK2, c-Jun, and HSF-1, but not JNK1, led to dramatic inhibition of arsenite-induced Hsp27 and Hsp70 expression. Collectively, our results demonstrate that p27 suppresses Hsp27 and Hsp70 expression at the transcriptional level specifically through JNK2/c-Jun- and HSF-1-dependent pathways upon arsenite exposure, which provides additional important molecular mechanisms for the tumor-suppressive function of p27.

Cyclin D1 induction by benzo[a]pyrene-7,8-diol-9,10-epoxide via the phosphatidylinositol 3-kinase/Akt/MAPK- and p70s6k-dependent pathway promotes cell transformation and tumorigenesis

Benzo[a]pyrene-7,8-diol-9,10-epoxide (B[a]PDE), the major metabolite of B[a]P, has been well recognized as one ubiquitous carcinogen, but the molecular mechanism involved in its carcinogenic effect remains obscure. In the present study, we found that bronchial epithelial cells (Beas-2B) and hepatocytes treated with B[a]PDE presented a significant increase of cyclin D1 expression. Moreover, Akt, p70(s6k), and MAPKs including JNK, Erks, and p38 were notably activated in B[a]PDE-treated Beas-2B cells, whereas NF-kappaB, NFAT, and Egr-1 were not. Our results demonstrated that JNK and Erks were required in B[a]PDE-induced cyclin D1 expression because the inhibition of JNK or Erks by a selective chemical inhibitor or dominant negative mutant robustly impaired the cyclin D1 induction by B[a]PDE. Furthermore, we found that overexpression of the dominant negative mutant of p85 (regulatory subunit of phosphatidylinositol 3-kinase) or Akt dramatically suppressed B[a]PDE-induced JNK and Erk activation as well as cyclin D1 expression, suggesting that cyclin D1 induction by B[a]PDE is via the phosphatidylinositol 3-kinase/Akt/MAPK-dependent pathway. In addition, we clarified that p70(s6k) is also involved in B[a]PDE-induced cyclin D1 expression because rampamycin pretreatment dramatically reduced cyclin D1 induction by B[a]PDE. More importantly, we demonstrated that up-regulated cyclin D1 by B[a]PDE plays a critical role in oncogenic transformation and tumorigenesis of Beas-2B cells. These results not only broaden our knowledge of the molecular mechanism of B[a]PDE carcinogenicity but also lead to the further study of chemoprevention of B[a]PDE-associated human cancers.

PI3K/Akt/JNK/c-Jun signaling pathway is a mediator for arsenite-induced cyclin D1 expression and cell growth in human bronchial epithelial cells

Arsenite exposure is associated with an increased risk of human lung cancer. However, the molecular mechanisms underlying the arsenite-induced human lung carcinogenesis remain elusive. In this study, we demonstrated that arsenite upregulates cyclin D1 expression/activity to promote the growth of human bronchial epithelial Beas-2B cells. In this process, the JNKs (c-Jun N-terminal kinases)/c-Jun cascade is elicited. The inhibition of JNKs or c-Jun by chemical or genetic inhibitors blocks the cyclin D1 induction mediated by arsenite. Furthermore, using a loss of function mutant of p85 (Deltap85, a subunit of PI3K) or dominant-negative Akt (DN-Akt), we showed that PI3K and Akt act as the upstream regulators of JNKs and c-Jun in arsenite-mediated growth promotion. Overall, our data suggest a pathway of PI-3K/Akt/JNK/c-Jun/cylin D1 signaling in response to arsenite in human bronchial epithelial cells.

Induction of neoplastic transformation by ectopic expression of human aldo-keto reductase 1C isoforms in NIH3T3 cells

We have shown previously that chronic low-dose arsenic exposure induces malignant transformation of human skin keratinocyte HaCaT cells. In this study, we found that several isoforms of aldo-keto reductase 1C (AKR1C) were overexpressed in arsenic-exposed HaCaT cells. The AKR1C family of proteins are phase I drug-metabolizing enzymes involved in maintenance of steroid homeostasis, prostaglandin metabolism and metabolic activation of polycyclic aromatic hydrocarbons. To explore the oncogenic potential of AKR1C isoforms, we established mouse NIH3T3 cell lines ectopically and stably expressing human AKR1C1, AKR1C2 or AKR1C3. Our results showed that ectopic expression of human AKR1C1 and AKR1C2, but not AKR1C3, significantly enhanced foci formation. Following subcutaneous injection of these stable cell lines into nude mice, fibrosarcoma were formed from all three cell lines. However, the number and size of tumors formed by the AKR1C3-expressing cell line was fewer and smaller, respectively, than those formed by AKR1C1- and AKR1C2-expressing cells. Inhibitors of AKR1C, genistein and ursodeoxycholic acid, decreased foci formation in AKR1C1- and AKR1C2-expressing NIH3T3 cells in a dose-dependent manner, implying the association of enzymatic activity and oncogenic potential of AKR1C. The requirement of enzymatic ability for neoplastic transformation was confirmed by establishing a NIH3T3 cell line stably expressing a mutant AKR1C1 lacking enzymatic activity, which did not form foci in culture or tumors in nude mice. Our present study reveals that AKR1C enzymatic activity plays crucial roles on induction of neoplastic transformation of mouse NIH3T3 cells.

Role of cell signaling in poxvirus-mediated foreign gene expression in mammalian cells

Poxviruses have been extensively used as a promising vehicle to efficiently deliver a variety of antigens in mammalian hosts to induce immune responses against infectious diseases and cancer. Using recombinant vaccinia virus (VV) and canarypox virus (ALVAC) expressing enhanced green fluorescent protein (EGFP) or multiple HIV-1 gene products, we studied the role of four cellular signaling pathways, the phosphoinositide-3-OH kinase (PI3K), extracellular signal-regulated kinase (ERK), p38 mitogen-activated protein kinase (p38 MAPK), and c-Jun N-terminal kinase (JNK), in poxvirus-mediated foreign gene expression in mammalian cells. In nonpermissive infection (human monocytes), activation of PI3K, ERK, p38 MAPK, and JNK was observed in both VV and ALVAC and blocking PI3K, p38 MAKP, and JNK pathways with their specific inhibitors significantly reduced viral and vaccine antigen gene expression. Whereas, blocking the ERK pathway had no significant effect. Among these cellular signaling pathways studied, PI3K was the most critical pathway involved in gene expression by VV- or ALVAC-infected monocytes. The important role of PI3K in poxvirus-mediated gene expression was further confirmed in mouse epidermal cells stably transfected with dominant-negative PI3K mutant, as poxvirus-mediated targeted gene expression was significantly decreased in these cells when compared with their parental cells. Signaling pathway activation influenced gene expression at the mRNA level rather than virus binding. In permissive mammalian cells, however, VV DNA copies were also significantly decreased in the absence of normal function of the PI3K pathway. Poxvirus-triggered activation of PI3K pathway could be completely abolished by atazanavir, a new generation of antiretroviral protease inhibitors (PIs). As a consequence, ALVAC-mediated EGFP or HIV-1 gag gene expression in infected primary human monocytes was significantly reduced in the presence of atazanavir. These findings implicate that antiretroviral therapy (ART), also known as highly active antiretroviral therapy (HAART), may negatively impact the efficacy of live poxvirus vector-based vaccines and should be carefully considered when administering such live vaccines to individuals on ART.

c-Jun/AP-1 pathway-mediated cyclin D1 expression participates in low dose arsenite-induced transformation in mouse epidermal JB6 Cl41 cells

Arsenic is a well-documented human carcinogen associated with skin carcinogenesis. Our previous work reveals that arsenite exposure is able to induce cell transformation in mouse epidermal cell JB6 Cl41 through the activation of ERK, rather than JNK pathway. Our current studies further evaluate downstream pathway in low dose arsenite-induced cell transformation in JB6 Cl41 cells. Our results showed that treatment of cells with low dose arsenite induced activation of c-Jun/AP-1 pathway, and ectopic expression of dominant negative mutant of c-Jun (TAM67) blocked arsenite-induced transformation. Furthermore, our data indicated that cyclin D1 was an important downstream molecule involved in c-Jun/AP-1-mediated cell transformation upon low dose arsenite exposure, because inhibition of cyclin D1 expression by its specific siRNA in the JB6 Cl41 cells resulted in impairment of anchorage-independent growth of cells induced by low dose arsenite. Collectively, our results demonstrate that c-Jun/AP-1-mediated cyclin D1 expression is at least one of the key events implicated in cell transformation upon low dose arsenite exposure.