Ginkgetin induces cell death in breast cancer cells via downregulation of the estrogen receptor.

Ginkgetin is a natural biflavonoid isolated from the leaves of Ginkgo biloba, and is characterized by its anti-inflammatory and anti-viral activities. Although numerous studies state that it has also antitumor activity, the anti-proliferative effect of ginkgetin and the underlying mechanism in breast cancer cells have not yet been investigated. In the present study, ginkgetin inhibited the cell viability of MCF-7 and T-47D cells dose-dependently, and suppressed the expression of the estrogen receptor (ER) at the mRNA and protein levels. Among the targets of the ER, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase 3 (PFKFB3), cyclin D1 and survivin were also downregulated by ginkgetin treatment. The anti-proliferative effects of ginkgetin were sufficient to suppress the growth by estradiol stimulation. However, ginkgetin did not significantly affect the viability of MDA-MB-231 cells, which are ER-negative cells. Furthermore, the knockdown of the ER and an inhibitor of PFKFB3 significantly sensitized MCF-7 and T-47D cells to ginkgetin. These findings suggest that ginkgetin induces cell death in ER-positive breast cancer cells via the inhibition of ER expression and that it is a promising agent for breast cancer treatment.

Melatonin enhances arsenic trioxide-induced cell death via sustained upregulation of Redd1 expression in breast cancer cells.

Melatonin is implicated in various physiological functions, including anticancer activity. However, the mechanism(s) of its anticancer activity is not well understood. In the present study, we investigated the combined effects of melatonin and arsenic trioxide (ATO) on cell death in human breast cancer cells. Melatonin enhanced the ATO-induced apoptotic cell death via changes in the protein levels of Survivin, Bcl-2, and Bax, thus affecting cytochrome c release from the mitochondria to the cytosol. Interestingly, we found that the cell death induced by co-treatment with melatonin and ATO was mediated by sustained upregulation of Redd1, which was associated with increased production of reactive oxygen species (ROS). Combined treatment with melatonin and ATO induced the phosphorylation of JNK and p38 MAP kinase downstream from Redd1 expression. Rapamycin and S6K1 siRNA enhanced, while activation of mTORC1 by transfection with TSC2 siRNA suppressed the cell death induced by melatonin and ATO treatment. Taken together, our findings suggest that melatonin enhances ATO-induced apoptotic cell death via sustained upregulation of Redd1 expression and inhibition of mTORC1 upstream of the activation of the p38/JNK pathways in human breast cancer cells.

Targeting HIF-1α is a prerequisite for cell sensitivity to dichloroacetate (DCA) and metformin.

Recently, targeting deregulated energy metabolism is an emerging strategy for cancer therapy. In the present study, combination of DCA and metformin markedly induced cell death, compared with each drug alone. Furthermore, the expression levels of glycolytic enzymes including HK2, LDHA and ENO1 were downregulated by two drugs. Interestingly, HIF-1α activation markedly suppressed DCA/metformin-induced cell death and recovered the expressions of glycolytic enzymes that were decreased by two drugs. Based on these findings, we propose that targeting HIF-1α is necessary for cancer metabolism targeted therapy.

Selective inhibition of histone deacetylase 2 induces p53-dependent survivin downregulation through MDM2 proteasomal degradation.

In the present study, we found that selective inhibition of histone deacetylase 2 (HDAC2) with small inhibitory RNA (siRNA) induced survivin downregulation in a p53-dependent manner. Interestingly, suberoylanilide hydroxamic acid (SAHA) or knockdown of HDAC2 induced downregulation of Mdm2, a negative regulator of p53, at the protein level. SAHA and/or HDAC2 siRNA increased Mdm2 ubiquitination, and MG132, an inhibitor of proteosome function, prevented HDAC2 inhibition-induced degradation of Mdm2. Clinically, the mRNA levels of HDAC2 and survivin were prominently overexpressed in lung cancer patients compared to normal lung tissues. Silencing of HDAC2 enhanced the cell death caused by ionizing radiation in lung cancer cells. Collectively, our results indicate that selective inhibition of HDAC2 causes survivin downregulation through activation of p53, which is mediated by downregulation of Mdm2. They further suggest that HDAC2 may exert a dominant effect on lung cancer cell survival by sustaining Mdm2-survivin levels.

Identification of cornifelin and early growth response-1 gene as novel biomarkers for in vitro eye irritation using a 3D reconstructed human cornea model MCTT HCE™.

Evaluation of the eye irritation is essential in the development of new cosmetic products. Draize rabbit eye irritation test has been widely used in which chemicals are directly applied to rabbit eye, and the symptoms and signs of eyes are scored. However, due to the invasive procedure, it causes substantial pain and discomfort to animals. Recently, we reported in vitro eye irritation test method using a 3D human corneal epithelial model (MCTT HCE™) which is reconstructed from remaining human tissues after a corneal transplantation. This model exhibited an excellent predictive capacity for 25 reference chemicals (sensitivity 100%, specificity 77% and accuracy 88% vs. GHS). To improve the test performance, we explored new biomarkers for the eye irritation through transcriptomic approach. Three surfactants were selected as model eye irritants that include sodium lauryl sulfate, benzalkonium chloride and triton X-100. After test chemicals were treated, we investigated differentially expressed genes through a whole-gene microarray (Affymetrix GeneChip(®) Human Gene 2.0 ST Array, 48,000 probes). As a result, we identified that mRNAs of cornifelin (CNFN), a constituent of the insoluble cornified cell envelope of stratified squamous epithelia, and early growth response-1 (EGR1), a nuclear transcriptional regulator, were significantly up-regulated by all three irritants. Up-regulation of CNFN and EGR1 was further confirmed by Q-RT-PCR, and immunohistochemistry revealed increased level of CNFN in irritant-treated tissues, supporting the relevance of CNFN and EGR1 as new biomarkers for eye irritation.

Inhibition of S6K1 enhances dichloroacetate-induced cell death.

PURPOSE: The unique metabolic profile of cancer (aerobic glycolysis) is an attractive therapeutic target for cancer. Dichloroacetate (DCA), an inhibitor of pyruvate dehydrogenase kinase, has been shown to reverse glycolytic phenotype and induce mitochondrion-dependent apoptosis. In the present study, we investigated the effects of S6 kinase 1 (S6K1) inhibition on DCA-induced cell death and the underlying mechanisms in breast cancer cells. METHODS: Cell death was evaluated by annexin V and PI staining. The synergistic effects of DCA and PF4708671 were assessed by isobologram analysis. Small interfering RNA (siRNA) was used for suppressing gene expression. The mRNA and protein levels were measured by RT-PCR and Western blot analysis, respectively. RESULTS: PF4708671, a selective inhibitor of S6K1, and knockdown of S6K1 with specific siRNA enhanced DCA-induced cell death. Interestingly, a combination of DCA/PF4708671 markedly reduced protein expression of a glycolytic enzyme, hexokinase 2 (HK2). Suppression of HK2 activity using specific siRNA and 2-deoxyglucose (2-DG) further enhanced cell sensitivity to DCA/PF4708671. Overexpression of Myc-tagged HK2 rescued cell death induced by DCA/PF4708671. CONCLUSIONS: Based on these findings, we propose that inhibition of S6K1, in combination with the glycolytic inhibitor, DCA, provides effective cancer therapy.

Implications of caspase-dependent proteolytic cleavage of cyclin A1 in DNA damage-induced cell death.

Cyclin A1 is an A-type cyclin that directly binds to CDK2 to regulate cell-cycle progression. In the present study, we found that doxorubicin decreased the expression of cyclin A1 at the protein level in A549 lung cancer cells, while markedly downregulating its mRNA levels. Interestingly, doxorubicin upregulated caspase-1 in a concentration-dependent manner, and z-YAVD-fmk, a specific inhibitor of caspase-1, reversed the doxorubicin-induced decrease in cyclin A1 in A549 lung cancer and MCF7 breast cancer cells. Active caspase-1 effectively cleaved cyclin A1 at D165 into two fragments, which in vitro cleavage assays showed were further cleaved by caspase-3. Finally, we found that overexpression of cyclin A1 significantly reduced the cytotoxicity of doxorubicin, and knockdown of cyclin A1 by RNA interference enhanced the sensitivity of cells to ionizing radiation. Our data suggest a new mechanism for the downregulation of cyclin A1 by DNA-damaging stimuli that could be intimately involved in the cell death induced by DNA damage-inducing stimuli, including doxorubicin and ionizing radiation.

Knockdown of TWIST1 enhances arsenic trioxide- and ionizing radiation-induced cell death in lung cancer cells by promoting mitochondrial dysfunction.

TWIST1 is implicated in the process of epithelial mesenchymal transition, metastasis, stemness, and drug resistance in cancer cells, and therefore is a potential target for cancer therapy. In the present study, we found that knockdown of TWIST1 by small interfering RNA (siRNA) enhanced arsenic trioxide (ATO)- and ionizing radiation (IR)-induced cell death in non-small-cell lung cancer cells. Interestingly, intracellular reactive oxygen species levels were increased in cells treated with TWIST1 siRNA and further increased by co-treatment with ATO or IR. Pretreatment of lung cancer cells with the antioxidant N-acetyl-cysteine markedly suppressed the cell death induced by combined treatment with TWIST1 siRNA and ATO or IR. Moreover, treatment of cells with TWIST1 siRNA induced mitochondrial membrane depolarization and significantly increased mitochondrial fragmentation (fission) and upregulated the fission-related proteins FIS1 and DRP1. Collectively, our results demonstrate that siRNA-mediated TWIST1 knockdown induces mitochondrial dysfunction and enhances IR- and ATO-induced cell death in lung cancer cells.

Sustained overexpression of Redd1 leads to Akt activation involved in cell survival.

Herein, we show that the constitutive overexpression of Redd1, a negative regulator of mTORC1, induces Akt activation in lung cancer cells. Akt phosphorylation was reduced to basal levels by Rictor siRNA, suggesting the involvement of mTORC2 in this process. Perifosine and PP242, selective inhibitors of Akt and mTORC1/2, respectively, efficiently suppressed the Akt phosphorylation that was induced by the sustained overexpression of Redd1 and increased the sensitivity of the cells to cisplatin. Therefore, the sustained overexpression of Redd1 leads to mTORC1 inhibition and to consequent Akt activation that is involved in cell survival. This finding highlights the importance of Akt activation as a therapeutic target to overcome resistance to chemotherapy.

Titrated extract of Centella asiatica provides a UVB protective effect by altering microRNA expression profiles in human dermal fibroblasts.

The titrated extract of Centella asiatica (TECA) is a reconstituted mixture comprising of asiatic acid, madecassic acid, asiaticoside and madecassoside, and is used as a therapeutic agent in wound healing and also as an anti-microbial, anticancer and anti-aging agent. Although these properties and the associated cell signaling pathways have been elucidated, the cellular mechanism of anti-photoaging upon ultraviolet (UV) exposure in normal human dermal fibroblasts (NHDFs) remains unknown. In this study, we investigated the photoprotective role of TECA via microRNA (miRNA) expression profiling analysis. Low dose of TECA did not exhibit toxicity and showed a protective effect against UVB irradiation in NDHFs. miRNA microarray experiments revealed that specific miRNAs were altered by TECA stimulation in UVB-irradiated NHDFs. Functional bioinformatic analysis showed that the putative target genes of the altered miRNAs were associated with the positive regulation of cell proliferation, anti-apoptosis, small GTPase- and Ras-mediated signal transduction and activation of MAPKK. Therefore, these results suggest that TECA may serve as a potential natural chemoprotective agent against UVB-mediated damage in NHDFs through changes in the expression of specific miRNAs.

Histone deacetylase inhibitors sensitize human non-small cell lung cancer cells to ionizing radiation through acetyl p53-mediated c-myc down-regulation.

INTRODUCTION: Histone deacetylase inhibitors (HDACIs) induce growth arrest and apoptosis in cancer cells. In addition to their intrinsic anticancer properties, HDACIs modulate cellular responses to ionizing radiation (IR). We examined the molecular mechanism(s) associated with the radiosensitizing effects of HDACIs in human lung cancer cells. METHODS: Lung cancer cells were pretreated with the appropriate concentrations of suberoylanilide hydroxamic acid or trichostatin A. After 2 hours, cells were irradiated with various doses of γ-IR, and then we performed 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, fluorescence-activated cell sorting analysis, clonogenic assay, and Western blotting to detect cell viability or apoptosis and changes of specific proteins expression levels. RESULTS: In this study, we showed that HDACIs (including suberoylanilide hydroxamic acid and trichostatin A) and IR synergistically trigger cell death in human non-small cell lung cancer cells. Cell viability and clonogenic survival were markedly decreased in cultures cotreated with HDACIs and IR. Interestingly, p53 acetylation at lysine 382 was significantly increased, and c-myc expression simultaneously down-regulated in cotreated cells. Radiosensitization by HDACIs was inhibited on transfection with small interfering RNA against p53 and c-myc overexpression, supporting the involvement of p53 and c-myc in this process. Furthermore, c-myc down-regulation and apoptotic cell death coinduced by IR and HDACI were suppressed in cells transfected with mutant K382R p53 and C135Y p53 displaying loss of acetylation at lysine 382 and DNA-binding activity, respectively. CONCLUSIONS: Our results collectively demonstrate that the degree of radiosensitization by HDACIs is influenced by acetyl p53-mediated c-myc down-regulation.

Sorafenib induces apoptotic cell death in human non-small cell lung cancer cells by down-regulating mammalian target of rapamycin (mTOR)-dependent survivin expression.

Sorafenib, a multikinase inhibitor, is emerging as a promising targeted agent that may possess antitumor activity against a broad range of cancers. The mechanism by which sorafenib induces lung cancer cell death and apoptosis, however, is not understood. In the present study, we provide evidence that sorafenib acts through inhibition of mammalian target of rapamycin (mTOR) to down-regulate survivin and promote apoptotic cell death in human non-small cell lung cancer (NSCLC) cells. Sorafenib induced ATF4-mediated Redd1 expression, leading to mTOR inhibition-the upstream signal for down-regulation of survivin. Overexpression of survivin reduced sorafenib-induced apoptosis, whereas silencing survivin using small interfering RNA (siRNA) enhanced it, supporting the interpretation that down-regulation of survivin is involved in sorafenib-induced cell death in human NSCLC cells. Furthermore, sorafenib abolished the induction of survivin that normally accompanies IGF-1-stimulated mTOR activation. We further found that Redd1-induced mTOR down-regulation and ATF4/CHOP-induced expression of the TRAIL receptor DR5 associated with sorafenib treatment helped sensitize cells to TRAIL-induced apoptosis. Our study suggests that sorafenib mediates apoptotic cell death in human NSCLC cells through Redd1-induced inhibition of mTOR and subsequent down-regulation of survivin, events that are associated with sensitization to TRAIL-induced apoptotic cell death.

Redd1 inhibits the invasiveness of non-small cell lung cancer cells.

Redd1 acts as a negative regulator of mTOR in response to various stress conditions, but its specific physiological role is currently unclear. In the present study, we showed that Redd1 inhibits the invasive activity of non-small cell lung cancer (NSCLC) cells. Interestingly, expression of Redd1 was extremely low in H1299 cells displaying high invasiveness, compared with that in H460 cells with lower invasive activity. Overexpression of Redd1 inhibited the invasive activity of H1299 cells, while suppression with specific siRNAs enhanced the invasiveness of H460 cells. Knockdown of the mTOR downstream substrate, S6K, resulted in a decrease in the invasive property of H1299 cells. Our results provide preliminary evidence that Redd1 inhibits the invasive activity of NSCLC cells via suppression of the mTOR downstream pathway.

Nuclear protein 1 induced by ATF4 in response to various stressors acts as a positive regulator on the transcriptional activation of ATF4.

Nuclear protein 1 (NUPR1) was originally identified as p8, a member of the family of HMG-I/Y transcription factors induced in response to various cellular stressors. However, the signaling pathway underlying NUPR1 induction by cellular stresses remains to be established. In this study, we found that the expression of NUPR1 by various stresses induced by activating transcription factor 4 (ATF4). Loss of ATF4 using siRNA significantly diminished NUPR1 expression. Overexpression of ATF4 caused NUPR1 levels to rise. NUPR1 expression was associated with enhanced transcriptional activation of genes of ATF4 downstream, suggesting that the protein promoted the transcription of stress-regulated genes via positive feedback on the ATF4 pathway.

Activating transcription factor 4 and CCAAT/enhancer-binding protein-beta negatively regulate the mammalian target of rapamycin via Redd1 expression in response to oxidative and endoplasmic reticulum stress.

Regulation of mRNA translation in mammalian cells involves the coordinated control of mammalian target of rapamycin (mTOR) signaling. At present, limited information is available on the potential relevance of mTOR regulation, although translation inhibition during oxidative and endoplasmic reticulum (ER) stress is clearly important. In this study, we show that activating transcription factor 4 (ATF4) and CCAAT/enhancer-binding protein-beta (C/EBP-beta) negatively regulate mTOR via Redd1 expression in response to oxidative and ER stress. Oxidative and ER stress conditions induce rapid and significant activation of ATF4 downstream of eIF2alpha phosphorylation, which is responsible for Redd1 expression. In our experiment, overexpression of ATF4 was associated with reduced mTOR activity via Redd1 expression, whereas suppression of ATF4 levels with small interfering RNA led to the recovery of decreased mTOR activity mediated by downregulation of Redd1 during oxidative and ER stress. We additionally identified Redd1 as a downstream effector of C/EBP-beta stimulated by ATF4 activated under the stress conditions examined. RNA interference studies provided further evidence of the requirement of C/EBP-beta for Redd1 expression. We conclude that the Redd1 gene is transactivated by the ATF4 and C/EBP family of transcription factors, leading to mTOR inhibition in response to oxidative and ER stress.

SP600125 negatively regulates the mammalian target of rapamycin via ATF4-induced Redd1 expression.

SP600125 (SAPK Inhibitor II) is reported to function as a reversible ATP competitive inhibitor of c-Jun N-terminal kinase (JNK). In the present study, we show that SP600125 induces a dose-dependent decrease in mTOR activity, as assessed by reduced phosphorylation of the downstream targets S6K1 and S6, and a significant increase in the expression of Redd1. Knockdown of Redd1 expression by siRNA resulted in a recovery of decreased S6 phosphorylation by SP600125. Overexpression of ATF4 upregulated the expression of Redd1, while suppression of ATF4 expression by siRNA enhanced the level of S6 phosphorylation by downregulating the SP600125-induced increase in Redd1 expression. Together, these results indicate that SP600125 inhibits mTOR activity via an ATF4-induced increase in Redd1 expression.

Activation of epidermal growth factor receptor and its downstream signaling pathway by nitric oxide in response to ionizing radiation.

Epidermal growth factor receptor (EGFR) is activated by ionizing radiation (IR), but the molecular mechanism for this effect is unknown. We have found that intracellular generation of nitric oxide (NO) by NO synthase (NOS) is required for the rapid activation of EGFR phosphorylation by IR. Treatment of A549 lung cancer cells with IR increased NOS activity within minutes, accompanied by an increase of NO. 2-Phenyl-4,4,5,5,-tetramethylimidazolline-1-oxyl-3-oxide, an NO scavenger, and NG-monomethyl-l-arginine, an NOS inhibitor, abolished the increase in intracellular NO and activation of EGFR by IR. In addition, an NO donor alone induced EGFR phosphorylation. Transient transfection with small interfering RNA for endothelial NOS reduced IR-induced NO production and suppressed IR-induced EGFR activation. Overexpression of endothelial NOS increased IR-induced NO generation and EGFR activation. These results indicate a novel molecular mechanism for EGFR activation by IR-induced NO production via NOS.

A combination of sulindac and arsenic trioxide synergistically induces apoptosis in human lung cancer H1299 cells via c-Jun NH2-terminal kinase-dependent Bcl-xL phosphorylation.

SUMMARY: In the present study, we show that a combination of sulindac and arsenic trioxide (ATO) induces more extensive apoptosis than either drug alone in H1299 human non-small cell lung carcinoma (NSCLC) cells. Treatment with sulindac/ATO triggered three major apoptotic signaling events, namely, collapse of the mitochondrial membrane potential, release of cytochrome c, and activation of caspases. Furthermore, the sulindac/ATO combination induced reactive oxygen species (ROS) generation, and the antioxidant, N-acetyl-L-cysteine, blocked this apoptotic signaling. The c-Jun NH(2)-terminal kinase (JNK) was activated downstream of ROS production in H1299 cells. Blockage of JNK by pretreatment with SP600125, a pharmacological inhibitor, or transfection with dominant-negative (DN) JNK1 vectors abrogated sulindac/ATO-induced apoptosis, as evident from the disruption of caspase activation. Interestingly, a slower migrating Bcl-xL band was observed on immunoblots after treatment of cells with sulindac/ATO. The band was absent upon the treatment of cell lysates with lambda protein phosphatase. Moreover, confocal microscopy findings disclose that active JNK translocates to mitochondria. Treatment with SP600125 and transfection with DN-JNK blocked Bcl-xL phosphorylation, suggesting that JNK plays an important role in sulindac/ATO-induced Bcl-xL phosphorylation. In conclusion, in H1299 human NSCLC cells, sulindac and ATO synergistically induce a high degree of apoptosis, which is mediated by the ROS-dependent JNK activation pathway via Bcl-xL phosphorylation.

Genome-wide screening and identification of novel proteolytic cleavage targets of caspase-8 and -10 in vitro.

Apoptosis executed by the mammalian caspase family plays a fundamental role in cellular homeostasis. Deregulation of this process is associated with several human diseases. The multimerization of ligand-induced death receptors results in the recruitment of the death inducing signaling complex and autocatalytic activation of initiator caspases, including caspase-8 and -10. However, it is still unclear how initiator caspases trigger and control the early apoptotic signaling pathways, partly because the downstream proteolytic cleavage targets of the initiator caspases are not completely known. Although it is known that a number of proteins are cleaved by various members of the caspase family, the identification of specific cleavage substrates of the initiator caspases 8 and 10, has been hindered by a lack of systematic and broadly applicable strategies for substrate identification. In the present study we constructed a mouse cDNA library and used it to perform a systematic, genome-wide screen for novel in vitro substrates of caspase-8 and -10. From this, we successfully identified six putative caspase substrates, including five novel proteins (ABCF1, AKAP1, CPE, DOPEY1 and GOPC1) that may be targeted specifically by the initiator caspases 8 and 10 during the early stages of apoptosis. These findings may provide useful information for elucidating the apoptotic signaling pathways downstream of the death receptors.

Combined effects of sulindac and suberoylanilide hydroxamic acid on apoptosis induction in human lung cancer cells.

Histone deacetylase (HDAC) inhibitors represent a promising group of anticancer agents. Treatment of cancer cells with HDAC blockers, such as suberoylanilide hydroxamic acid (SAHA), leads to the activation of apoptosis-promoting genes. To enhance proapoptotic efficiency, SAHA has been used in conjunction with radiation, kinase inhibitors, and cytotoxic drugs. In the present study, we show that at the suboptimal dose of 250 muM, sulindac [2-[6-fluoro-2-methyl-3-[(4-methylsulfinylphenyl)methylidene]inden-1-yl]-acetic acid] significantly enhances SAHA-induced growth suppression and apoptosis of A549 human non-small cell lung cancer cells, primarily via enhanced collapse of the mitochondrial membrane potential, release of cytochrome c, and caspase activation. Furthermore, sulindac/SAHA cotreatment induced marked down-regulation of survivin at both the mRNA and protein levels and stimulated the production of reactive oxygen species (ROS), which were blocked by the antioxidant N-acetyl-l-cysteine. Overexpression of survivin was associated with reduced sulindac/SAHA-induced apoptosis of A549 cells, whereas suppression of survivin levels with antisense oligonucleotides or small interfering RNA further sensitized cells to sulindac/SAHA-induced cell death. Our results collectively demonstrate that sulindac/SAHA-induced apoptosis is mediated by ROS-dependent down-regulation of survivin in lung cancer cells.