Enhancer of zeste homolog 2 (EZH2)-dependent sirtuin-3 determines sensitivity to glucose starvation in radioresistant head and neck cancer cells

Sirtuin 3 (SIRT3) regulates mitochondrial function as a mitochondrial deacetylase during oxidative stress. However, the specific regulatory mechanism and function of SIRT3 in radioresistant cancer cells are unclear. In this study, we aim to investigate how SIRT3 determines the susceptibility to glucose deprivation and its regulation in p53-based radioresistant head and neck cancer cells. We observed mitochondrial function using two established isogenic radioresistant subclones (HN3R-A [p53 null] and HN3R-B [p53 R282W]) with intratumoral p53 heterogeneity. Cell counting analysis was performed to evaluate cell proliferation and cell death. The correlation between the regulation of SIRT3 and enhancer of zeste homolog 2 (EZH2) was confirmed by immunoblotting and chromatin immunoprecipitation assay. p53-deficient radioresistant cells (HN3R-A) expression reduced SIRT3 levels and increased sensitivity to glucose deprivation due to mitochondrial dysfunction compared to other cells. In these cells, activation of SIRT3 significantly prevented glucose deprivation-induced cell death, whereas the loss of SIRT3 increased the susceptibility to glucose deficiency. We discovered that radiation-induced EZH2 directly binds to the SIRT3 promoter and represses the expression. Conversely, inhibiting EZH2 increased the expression of SIRT3 through epigenetic changes. Our findings indicate that p53-deficient radioresistant cells with enhanced EZH2 exhibit increased sensitivity to glucose deprivation due to SIRT3 suppression. The regulation of SIRT3 by EZH2 plays a critical role in determining the cell response to glucose deficiency in radioresistant cancer cells. Therefore, EZH2-dependent SIRT3 could be used as a predictive biomarker to select treatment options for patients with radiation-resistance.

ZBTB7A suppresses glioblastoma tumorigenesis through the transcriptional repression of EPB41L5

Glioblastoma multiforme (GBM), the most aggressive and malignant glioma, has a poor prognosis. Although patients with GBM are treated with surgery, chemotherapy, and radiation therapy, GBM is highly resistant to treatment, making it difficult and expensive to treat. In this study, we analyzed the Gene Expression Profiling Interactive Analysis dataset, the Cancer Genome Atlas dataset, and Gene Expression Omnibus array data. ZBTB7A (also called FBI1/POKEMON/LRF) was found to be highly expressed in low-grade glioma but significantly downregulated in patients with GBM. ZBTB7A is a transcription factor that plays an important role in many developmental stages, including cell proliferation. The activation of epithelial-mesenchymal transition (EMT) is a key process in cancer progression and metastasis. Erythrocyte membrane protein band 4.1 like 5 (EPB41L5) is an essential protein for EMT progression and metastasis in various types of cancer. We found that ZBTB7A depletion in U87 cells induced GBM progression and metastasis. Based on RNA sequencing data, ZBTB7A directly binds to the promoter of the EPB41L5 gene, reducing its expression and inhibiting GBM progression. We demonstrated that ZBTB7A dramatically inhibits GBM tumor growth through transcriptional repression of EPB41L5. Thus, both ZBTB7A and EPB41L5 may be potential biomarkers and novel therapeutic targets for GBM treatment. Overall, we discovered the role of a novel tumor suppressor that directly inhibits GBM progression (ZBTB7A) and identified EPB41L5 as a therapeutic target protein for patients with GBM.

Epigenetic regulation of p62/SQSTM1 overcomes the radioresistance of head and neck cancer cells via autophagy-dependent senescence induction

Tumors are composed of subpopulations of cancer cells with functionally distinct features. Intratumoral heterogeneity limits the therapeutic effectiveness of cancer drugs. To address this issue, it is important to understand the regulatory mechanisms driving a subclonal variety within a therapy-resistant tumor. We identified tumor subclones of HN9 head and neck cancer cells showing distinct responses to radiation with different levels of p62 expression. Genetically identical grounds but epigenetic heterogeneity of the p62 promoter regions revealed that radioresistant HN9-R clones displayed low p62 expression via the creation of repressive chromatin architecture, in which cooperation between DNMT1 (DNA methyltransferases 1) and HDAC1 (histone deacetylases 1) resulted in DNA methylation and repressive H3K9me3 and H3K27me3 marks in the p62 promoter. Combined inhibition of DNMT1 and HDAC1 by genetic depletion or inhibitors enhanced the suppressive effects on proliferative capacity and in vivo tumorigenesis following irradiation. Importantly, ectopically p62-overexpressed HN9-R clones increased the induction of senescence along with p62-dependent autophagy activation. These results demonstrate the heterogeneous expression of p62 as the key component of clonal variation within a tumor against irradiation. Understanding the epigenetic diversity of p62 heterogeneity among subclones allows for improved identification of the functional state of subclones and provides a novel treatment option to resolve resistance to current therapies.

p53-dependent glutamine usage determines susceptibility to oxidative stress in radioresistant head and neck cancer cells

The manner in which p53 maintains redox homeostasis and the means by which two key metabolic elements, glucose and glutamine, contribute to p53-dependent redox stability remain unclear. To elucidate the manner in which p53 deals with glucose-deprived, reactive oxygen species (ROS)-prone conditions in this regard, two isogenic cancer subclones (HN3R-A and HN3R-B) bearing distinct p53 mutations as an in vitro model of intratumoral p53 heterogeneity were identified. Following cumulative irradiation, the subclones showed a similar metabolic shift to aerobic glycolysis and increasing NADPH biogenesis for cellular defense against oxidative damage irrespective of p53 status. The radioresistant cancer cells became more sensitive to glycolysis-targeting drugs. However, in glucose-deprived and ROS-prone conditions, HN3R-B, the subclone with the original p53 increased the utilization of glutamine by GLS2, thereby maintaining redox homeostasis and ATP. Conversely, HN3R-A, the p53-deficient radioresistant subclone displayed an impairment in glutamine usage and high susceptibility to metabolic stresses as well as ROS-inducing agents despite the increased ROS scavenging system. Collectively, our findings suggest that p53 governs the alternative utilization of metabolic ingredients, such as glucose and glutamine, in ROS-prone conditions. Thus, p53 status may be an important biomarker for selecting cancer treatment strategies, including metabolic drugs and ROS-inducing agents, for recurrent cancers after radiotherapy.

Branched-chain amino acids sustain pancreatic cancer growth by regulating lipid metabolism

Branched-chain amino acid (BCAA) catabolism and high levels of enzymes in the BCAA metabolic pathway have recently been shown to be associated with cancer growth and survival. However, the precise roles of BCAA metabolism in cancer growth and survival remain largely unclear. Here, we found that BCAA metabolism has an important role in human pancreatic ductal adenocarcinoma (PDAC) growth by regulating lipogenesis. Compared with nontransformed human pancreatic ductal (HPDE) cells, PDAC cells exhibited significantly elevated BCAA uptake through solute carrier transporters, which were highly upregulated in pancreatic tumor tissues compared with normal tissues. Branched-chain amino-acid transaminase 2 (BCAT2) knockdown markedly impaired PDAC cell proliferation, but not HPDE cell proliferation, without significant alterations in glutamate or reactive oxygen species levels. Furthermore, PDAC cell proliferation, but not HPDE cell proliferation, was substantially inhibited upon knockdown of branched-chain α-keto acid dehydrogenase a (BCKDHA). Interestingly, BCKDHA knockdown had no significant effect on mitochondrial metabolism; that is, neither the level of tricarboxylic acid cycle intermediates nor the oxygen consumption rate was affected. However, BCKDHA knockdown significantly inhibited fatty-acid synthesis, indicating that PDAC cells may utilize BCAAs as a carbon source for fatty-acid biosynthesis. Overall, our findings show that the BCAA metabolic pathway may provide a novel therapeutic target for pancreatic cancer.

Essential nutrient molecules called branched-chain amino acids (BCAAs) sustain pancreatic cancer by supporting the formation of fatty ‘lipid’ compounds, offering possible new approaches for treatment. Jaekyoung Son and colleagues at the University of Ulsan College of Medicine in Seoul, South Korea, explored the role of BCAAs in the most common form of pancreatic cancer, pancreatic ductal adenocarcinoma. Effective treatments are urgently required as the disease is generally diagnosed too late for surgery, the most effective treatment, to be successful. The researchers found that human cancer cells exploit increased uptake of BCAAs as a source of carbon to build lipids. Disabling the genes for enzymes that convert BCAAs into lipids significantly and selectively reduced cancer cell growth. Drugs that interfere with key points in the over-active uptake of BCAA and conversion to lipids could be developed into new therapies.

Population genetic structure and putative migration pathway of Sogatella furcifera (Horváth) (Hemiptera, Delphacidae) in Asia

The white-backed planthopper, Sogatella furcifera (Horváth) (Hemiptera, Delphacidae), has emerged as a serious rice pest in Asia. In the present study, 12 microsatellite markers were employed to investigate the genetic structure, diversity and migration route of 43 populations sampled from seven Asian countries (Bangladesh, China, Korea, Laos, Nepal, Thailand, and Vietnam). According to the isolation by distance analysis, a significant positive correlation was observed between genetic and geographic distances by the Mantel test (r2 = 0.4585, P = 0.01), indicating the role of geographic isolation in the genetic structure of S. furcifera. A population assignment test using the first-generation migrants detection method (thresholds a = 0.01) revealed southern China and northern Vietnam as the main sources of S. furcifera in Korea. Nepal and Bangladesh might be additional potential sources via interconnection with Vietnam populations. This paper provides useful data for the migration route and origin of S. furcifera in Korea and will contribute to planthopper resistance management.

Abstract 2405: P53-dependent mitophagy controls glycolytic shift in radioresistant head and neck cancer cells

P53 is an important biomarker in response to genotoxic stress, but it is also known to plays a key role in the regulation of metabolic homeostasis. The loss of p53 is a well-established contributor to the malignant transformation and glycolytic phenotype acquisition of cells during cancer development. However, the role of p53 in genotoxic therapy-induced metabolic shift in cancers remains unclear. Here, we attempted to elucidate how p53 participates in the glycolytic shift of head and neck cancer cell lines following irradiation. We established a stable radioresistant head and neck cancer cells (HN30-R; p53 wild type and UMSCC1-R; p53 null type) through cumulative irradiation and then analyzed their glucose metabolic profiles and mitochondria respiration. As a result, the metabolic analysis revealed no changes glycolysis of HN30-R cells, but UMSCC1-R cells exhibited increased glycolysis through increased glucose uptake and lactate production and glycolytic intermediates as well as related glycolytic enzymes, compared to UMSCC1 cells. Also, we confirmed that the mitochondrial respiration was reduced by the maximal respiration parameters of oxygen consumption rate (OCR) and that abnormal mitochondria were accumulated by electron microscopy in UMSCC1-R cells. Thus, UMSCC1-R cells exhibited an increased sensitivity to glycolysis-targeting drugs such a hexokinases inhibitor (2-deoxy-D-glucoes; 2-DG) and a lactate dehydrogenase-A inhibitor (AT101), but HN30-R cells did not shown any changes. Moreover, we identified that mitophagy limits glycolytic shift through the p53-dependent clearance of abnormal mitochondria. Taken together, these results suggest that p53 null type cells increased aerobic glycolysis to overcome the accumulation of abnormal mitochondria in radioresistnat cells. Conversely, p53 wild type cells inhibited the glycolytic shift by regulating a integrity through p53-dependent mitophagy. Thus, glycolysis-targeted drugs could be an alternative strategy for overcoming recurrent cancers after radiotherapy, and p53 status could be a biomarker for selecting participants for clinical trials.

Citation Format: Hyo Won Chang, Ji Won Kim, Mi Ra Kim, Hae Yun Nam, Myungjin Lee, Won Hyeok Lee, Song Hee Kim, Da Seul Seong, Myung Woul Han, Jong Cheol Lee, Jung Je Park, Ji-hyun Seo, Seong Who Kim, Sang Yoon Kim. P53-dependent mitophagy controls glycolytic shift in radioresistant head and neck cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2405.

Abstract 144: Src leads to a novel mechanism of resistance to PI3K inhibitors through regulation of PI3K/p85 activation

Activation of the PI3K pathway is commonly observed and is correlated with tumor development, progression, poor prognosis, and resistance to cancer therapies, such as radiotherapy, in most cancers. As a central node of this pathway, PI3K is an attractive target for PI3K-addicted cancer therapy and PI3K inhibitors may thus restore sensitivity to other treatments when administered as part of combination regimens. Here, we found that PI3K/p85 was expressed predominantly in the radioresistant head and neck cancer cell line (HN31 cell line). And then, we investigated whether PI3K modulation was crucial for the development of novel treatment strategies for radioresistant cancer cell line. Interestingly, we found that head and neck cancer cell lines with PI3K/p85 activation showed the resistance to PI3K inhibitors and the resistance mechanism was associated with Src activation which is a member of a superfamily of membrane-associated nonreceptor protein tyrosine kinases. Src inhibitor improves the efficacy of PI3K inhibitor treatment through suppression of Src and PI3K/p85 activation in HN31 cell line. Collectively, our study highlights the role of p85 and Src activation in the resistance for PI3K inhibition and the potential clinical application of combination regimens of Src and PI3K inhibitors in head and neck cancers. This is the first investigation to analyze the role of Src in resistance to the PI3K inhibitors of head and neck cancer. As a consequence, a greater understanding of resistance mechanisms through our results will enable the rational design of combination regimens and sequential treatment algorithms to improve clinical outcomes.

Citation Format: Gui Chul Kim, Hae Yun Nam, Hyang Ju Lee, Min Kyung Kim, Geun Hee Lee, Myung Woul Han, Seong Who KIM, Sang Yoon Kim. Src leads to a novel mechanism of resistance to PI3K inhibitors through regulation of PI3K/p85 activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 144. doi:10.1158/1538-7445.AM2017-144

Angiotensin II Causes Apoptosis of Adult Hippocampal Neural Stem Cells and Memory Impairment Through the Action on AMPK-PGC1α Signaling in Heart Failure

Data are limited on the mechanisms underlying memory impairment in heart failure (HF). We hypothesized that angiotensin II (Ang II) may determine the fate of adult hippocampal neural stem cells (HCNs), a cause of memory impairment in HF. HCNs with neurogenesis potential were isolated and cultured from adult rat hippocampi. Ang II decreased HCN proliferation in dose- and time-dependent manners. Moreover, Ang II treatment (1 µM) for 48 hours induced apoptotic death, which was attenuated by pretreatment with Ang II receptor blockers (ARBs). Ang II increased mitochondrial reactive oxygen species (ROS) levels, which was related to mitochondrial morphological changes and functional impairment. Moreover, ROS activated the AMP-activated protein kinase (AMPK) and consequent peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC1α) expression, causing cell apoptosis. In the HF rat model induced by left anterior descending artery ligation, ARB ameliorated the spatial memory ability which decreased 10 weeks after ischemia. In addition, neuronal cell death, especially of newly born mature neurons, was observed in HF rat hippocampi. ARB decreased cell death and promoted the survival of newly born neural precursor cells and mature neurons. In conclusion, Ang II caused HCN apoptosis through mitochondrial ROS formation and subsequent AMPK-PGC1α signaling. ARB improved learning and memory behaviors impaired by neuronal cell death in the HF animal model. These findings suggest that HCN is one treatment target for memory impairment in HF and that ARBs have additional benefits in HF combined with memory impairment. Stem Cells Translational Medicine 2017;6:1491-1503.

Abstract 1170: EphA3 maintains radioresistance in head and neck cancers

Radiotherapy is a well-established therapeutic modality used in treatment of many cancers. However, radioresistance remains a serious obstacle to successful treatment. Radioresistance can cause local recurrence and distant metastases in some patients after treatment by radiation. Thus, special emphasis has been given to the discovery of effective radiosensitizers. EphA3 receptors functions contribute to tumor development, modulating cell-cell adhesion, invasion, neo-angiogenesis, tumor growth and metastasis. However, the role of EphA3 in radioresistance remains to be elucidated. Here, we established the stable radioresistant head and neck cancer cell line (AMC HN3R cell line) and identified that EphA3 was overexpressed predominantly in the AMC HN3R cancer cell line through DNA microarray, real time PCR and Western blotting. Additionally, we identified that EphA3 was overexpressed in recurred laryngeal cancer specimen after radiation therapy. And we found that EphA3 mediated the tumor invasiveness and migration and EMT (epithelial mesenchymal transition) related protein expression in AMC HN3R cancer cell line. To investigate the role of EphA3 in modulating the radiosensitivity, we observed the change of survival fraction after transfection EphA3 siRNA. And we found that inhibition of EphA3 enhances radiosensitivity in AMC HN 3R cell line. In conclusion, these results suggest that EphA3 is overexpressed in radioresistant head and neck cancer and can play a crucial role in development radioresistance in head and neck cancers through regulation of EMT pathway.

Citation Format: Myung Woul Han, Song Hee Kim, Hyo Won Chang, Hae Yun Nam, Myungjin Lee, Gui Chul Kim, Yoon sun Lee, Mi Ra Kim. EphA3 maintains radioresistance in head and neck cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1170.

Senescence-Associated MCP-1 Secretion Is Dependent on a Decline in BMI1 in Human Mesenchymal Stromal Cells

AIMS

Cellular senescence and its secretory phenotype (senescence-associated secretory phenotype [SASP]) develop after long-term expansion of mesenchymal stromal cells (MSCs). Further investigation of this phenotype is required to improve the therapeutic efficacy of MSC-based cell therapies. In this study, we show that positive feedback between SASP and inherent senescence processes plays a crucial role in the senescence of umbilical cord blood-derived MSCs (UCB-MSCs).

RESULTS

We found that monocyte chemoattractant protein-1 (MCP-1) was secreted as a dominant component of the SASP during expansion of UCB-MSCs and reinforced senescence via its cognate receptor chemokine (c-c motif) receptor 2 (CCR2) by activating the ROS-p38-MAPK-p53/p21 signaling cascade in both an autocrine and paracrine manner. The activated p53 in turn increased MCP-1 secretion, completing a feed-forward loop that triggered the senescence program in UCB-MSCs. Accordingly, knockdown of CCR2 in UCB-MSCs significantly improved their therapeutic ability to alleviate airway inflammation in an experimental allergic asthma model. Moreover, BMI1, a polycomb protein, repressed the expression of MCP-1 by binding to its regulatory elements. The reduction in BMI1 levels during UCB-MSC senescence altered the epigenetic status of MCP-1, including the loss of H2AK119Ub, and resulted in derepression of MCP-1.

INNOVATION

Our results provide the first evidence supporting the existence of the SASP as a causative contributor to UCB-MSC senescence and reveal a so far unappreciated link between epigenetic regulation and SASP for maintaining a stable senescent phenotype.

CONCLUSION

Senescence of UCB-MSCs is orchestrated by MCP-1, which is secreted as a major component of the SASP and is epigenetically regulated by BMI1.

Effect of β-catenin silencing in overcoming radioresistance of head and neck cancer cells by antagonizing the effects of AMPK on Ku70/Ku80

BACKGROUND

We attempted to elucidate the mechanism of cell death after radiation by studying how β-catenin silencing controls the radiation sensitivity of radioresistant head and neck cancer cells.

METHODS

The most radioresistant cancer cell line (AMC-HN-9) was selected for study. Targeted silencing of β-catenin was used on siRNAs. Sensitivity to radiation was examined using clonogenic and methylthiazol tetrazolium (MTT) assays.

RESULTS

A combination of irradiation plus β-catenin silencing led to a significant reduction in the inherent radioresistance of AMC-HN-9 cells. Although expression of Ku70/80 was upregulated in AMC-HN-9 cells after irradiation, Ku70/80 was dramatically decreased in a combination of irradiation and β-catenin silencing. Interestingly, irradiation-induced Ku70/80 was completely prevented by β-catenin silencing-induced LKB1/AMP-activated protein kinase (LKB1/AMPK) signal.

CONCLUSION

The LKB1/AMPK pathway might relay the signal between the Wnt/β-catenin pathway and the Ku70/Ku80 DNA repair machinery, and play a decisive role in fine-tuning the responses of cancer cells to irradiation. © 2015 Wiley Periodicals, Inc. Head Neck 38: E1909-E1917, 2016.

Design of a platform technology for systemic delivery of siRNA to tumours using rolling circle transcription

For therapeutic applications of siRNA, there are technical challenges with respect to targeted and systemic delivery. We here report a new siRNA carrier, RNAtr NPs, in a way that multiple tandem copies of RNA hairpins as a result of rolling circle transcription (RCT) can be readily adapted in tumour-targeted and systemic siRNA delivery. RNAtr NPs provide a means of condensing large amounts of multimeric RNA transcripts into the compact nanoparticles, especially without the aid of polycationic agents, and thus reduce the risk of immunogenicity and cytotoxicity by avoiding the use of synthetic polycationic reagents. This strategy allows the design of a platform technology for systemic delivery of siRNA to tumour sites, because RCT reaction, which enzymatically generates RNA polymers in multiple copy numbers at low cost, can lead to directly accessible routes to targeted and systemic delivery. Therefore, RNAtr NPs suggest great potentials as the siRNA therapeutics for cancer treatment.

RNA interference has provided a promising tool to suppress the expression of specific genes associated with human diseases. Here, the authors present a platform technology for the systemic delivery of siRNA to tumour sites using rolling circle transcription.

A decline in Wnt3a signaling is necessary for mesenchymal stem cells to proceed to replicative senescence

Umbilical cord blood-derived mesenchymal stem cells are a promising source of cells for regeneration therapy due to their multipotency, high proliferative capacity, relatively noninvasive collection, and ready availability. However, extended cell culture inevitably triggers cellular senescence-the irreversible arrest of cell division-thereby limiting the proliferative lifespan of adult stem cells. Wnt/β-catenin signaling plays a functional role as a key regulator of self-renewal and differentiation in mesenchymal stem cells (MSCs), and thus Wnt/β-catenin signaling and cellular senescence might be closely connected. Here, we show that the expression levels of canonical Wnt families decrease as MSCs age during subculture. Activation of the Wnt pathway by treatment with Wnt3a-conditioned medium or glycogen synthase kinase 3β inhibitors, such as SB-216763 and 6-bromoindirubin-3'-oxime, delays the progression of cellular senescence as shown by the decrease in the senescence effectors p53 and pRb, lowered senescence-associated β-galactosidase activity, and increased telomerase activity. In contrast, suppression of the Wnt pathway by treatment with dickkopf-1 (an antagonist of the Wnt coreceptor) and β-catenin siRNA transfection promotes senescence in MSCs. Interestingly, the magnitude of the response to enhanced Wnt3a/β-catenin signaling appears to depend on the senescent state during extended culture, particularly after multiple passages. These results suggest that Wnt3a signaling might be a predominant factor that could be used to overcome senescence in long-term cultured MSCs by directly intervening in the proliferative capacity and MSC senescence. The functional role of Wnt3a/β-catenin signaling in hedging cellular senescence may allow the development of new approaches for stem cell-based therapies.

Abstract 4904: β-catenin silencing enhances radiation sensitivity through antagonizing effect of AMPK against Ku70/80 in head and neck cancer cells

The Wnt/β-catenin pathway regulates the cell growth and survival following radiation in various types of cancer cells. Our previous report show that activation of the Wnt/β-catenin signaling pathway is a key radioprotective mechanism in irradiated head and neck cancer (HNC) cells. However, the molecular mechanisms by which β-catenin regulates radiation sensitivity are not clear. Here we attempted to elucidate the mechanism of cell death following radiation by studying how β-catenin silencing controls the radiation sensitivity of radioresistant HNC cells.

Of nine cell lines examined, the most radioresistant cell line (AMC-HN-9) were selected for this experiments. β-catenin silencing using small interfering RNA(siRNA) down-regulated β-catenin expression up to 72 h, which was confirmed by western blot analysis. The sensitivity to radiation was anlayzed by clonogenic analysis and MTT assay. As a result, β-catenin silencing remarkably decreased the survival of irradiated AMC-HN-9 cells and the cell viability also significantly reduced more by the combination treatment with β-catenin siRNA and radiation (0.37±0.034 fold) than when treated with β-catenin siRNA or radiation alone (0.68±0.055 fold and 0.90±0.043 fold, respectively). Interestingly, whereas expression of Ku70/80 was up regulated in AMC-HN-9 cells following irradiation (4Gy), in the cells treated with combination of radiation and β-catenin siRNA, Ku70/80 expression was dramatically decreased. In additionally, when exposed to radiation after β-catenin silencing, the up-regulation of irradiation-induced Ku80 completely was prevented by β-catenin silencing-induced AMPK.

Taken together, these results suggest that suppression of Ku70/80 expression through β-catenin silencing-induced AMPK is associated with its radio-sentitizing effect in AMC-HN-9 cells, thus supporting a novel radiosensitive mechanism of radioresistant HNC cells.

Citation Format: Hyo Won Chang, Hae Yun Nam, Mi Ra Kim, Hyang Ju Lee, Ji Hyun Seo, So Yeon Lee, Seong Who Kim, Sang Yoon Kim. β-catenin silencing enhances radiation sensitivity through antagonizing effect of AMPK against Ku70/80 in head and neck cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4904. doi:10.1158/1538-7445.AM2014-4904

Autophagy inhibition can overcome radioresistance in breast cancer cells through suppression of TAK1 activation

BACKGROUND/AIM

Autophagy is frequently activated in radioresistant cancer cells. In the present study, we evaluated the role of autophagy and transforming growth factor-activated kinase 1 (TAK1) in radioresistance.

MATERIALS AND METHODS

TAK1 phosphorylation in MDA-MB231 breast cancer cells was evaluated by western blotting. The regulatory effects of the TAK1 inhibitor and autophagy inhibitor were assessed by cell morphology, cell survival and induction of apoptosis.

RESULTS

Radiation induced the phosphorylation of TAK1, whereas the inhibition of TAK1 activity enhanced the cytotoxicity of radiation in MDA-MB231 cells. Autophagy inhibitors significantly enhanced radiation-induced apoptosis of MDA-MB231 cells. This augmentation in radiosensitivity seemed to result from the suppression of TAK1 activation.

CONCLUSION

Inhibition of autophagy enhanced radiosensitivity through suppression of radiation-induced TAK1 activation, suggesting that the modulation of TAK1-induced autophagy may be a good therapeutic strategy to treat radioresistant breast cancer.

Comparison of in vitro developmental competence of cloned caprine embryos using donor karyoplasts from adult bone marrow mesenchymal stem cells vs ear fibroblast cells

The aim of this study was to produce cloned caprine embryos using either caprine bone marrow-derived mesenchymal stem cells (MSCs) or ear fibroblast cells (EFCs) as donor karyoplasts. Caprine MSCs were isolated from male Boer goats of an average age of 1.5 years. To determine the pluripotency of MSCs, the cells were induced to differentiate into osteocytes, chondrocytes and adipocytes. Subsequently, MSCs were characterized through cell surface antigen profiles using specific markers, prior to their use as donor karyoplasts for nuclear transfer. No significant difference (p > 0.05) in fusion rates was observed between MSCs (87.7%) and EFCs (91.3%) used as donor karyoplasts. The cleavage rate of cloned embryos derived with MSCs (87.0%) was similar (p > 0.05) to those cloned using EFCs (84.4%). However, the in vitro development of MSCs-derived cloned embryos (25.3%) to the blastocyst stage was significantly higher (p < 0.05) than those derived with EFCs (20.6%). In conclusion, MSCs could be reprogrammed by caprine oocytes, and production of cloned caprine embryos with MSCs improved their in vitro developmental competence, but not in their fusion and cleavage rate as compared to cloning using somatic cells such as EFCs.

Prolonged autophagy by MTOR inhibitor leads radioresistant cancer cells into senescence

Radiotherapy is one of the well-established therapeutic modalities for cancer treatment. However, the emergence of cells refractory to radiation is a major obstacle to successful treatment with radiotherapy. Many reports suggest that inhibitors targeting the mechanistic target of rapamycin (MTOR) can sensitize cancer cells to the effect of radiation, although by which mechanism MTOR inhibitors enhance the efficacy of radiation toward cancer cells remains to be elucidated. Our studies indicate that a potent and persistent activation of autophagy via inhibition of the MTOR pathway, even in cancer cells where autophagy is occurring, can trigger premature senescence, cellular proliferation arrest. Combined treatment of MTOR inhibitor and radiation induce heterochromatin formation, an irreversible growth arrest and an increase of senescence-associated GLB1 (β-galactosidase) activity, which appear to result from a constant activation of TP53 and a restoration in the activity of retinoblastoma 1 protein (RB1)-E2F1. Thus, this study provides evidence that promoting cellular senescence via inhibition of the MTOR pathway may serve as an avenue to augment radiosensitivity in cancer cells that initiate an autophagy-survival mode to radiotherapy.

Radioresistant cancer cells can be conditioned to enter senescence by mTOR inhibition

Autophagy is frequently activated in radioresistant cancer cells where it provides a cell survival strategy. The mTOR inhibitor rapamycin activates autophagy but paradoxically it also enhances radiosensitivity. In this study, we investigated the mechanisms of these opposing actions in radiation-resistant glioma or parotid carcinoma cells. Radiation treatment transiently enhanced autophagic flux for a period of 72 hours in these cells and treatment with rapamycin or the mTOR inhibitor PP242 potentiated this effect. However, these treatments also increased heterochromatin formation, irreversible growth arrest, and premature senescence, as defined by expression of senescence-associated β-galactosidase activity. This augmentation in radiosensitivity seemed to result from a restoration in the activity of the tumor suppressor RB and a suppression of RB-mediated E2F target genes. In tumor xenografts, we showed that administering rapamycin delayed tumor regrowth after irradiation and increased senescence-associated β-galactosidase staining in the tumor. Our findings suggest that a potent and persistent activation of autophagy by mTOR inhibitors, even in cancer cells where autophagy is occurring, can trigger premature senescence as a method to restore radiosensitivity.

Knockdown of β-catenin controls both apoptotic and autophagic cell death through LKB1/AMPK signaling in head and neck squamous cell carcinoma cell lines

The Wnt/β-catenin pathway regulates the viability and radiosensitivity of head and neck squamous cancer cells (HNSCC). Increased β-catenin predisposes HNSCC patients to poor prognosis and survival. This study was conducted to determine the mechanism by which β-catenin regulates the viability of HNSCC. AMC-HN-3, -HN-8, UM-SCC-38, and -SCC-47 cells, which were established from human head and neck cancer specimens, and underwent cell death following β-catenin silencing. β-Catenin silencing significantly induced G1 arrest and increased the expression of Bax and active caspase-3, which demonstrates the sequential activation of apoptotic cascades following treatment of HNSCC with targeted siRNA. Intriguingly, β-catenin silencing also induced autophagy. Here, we confirm that the number of autophagic vacuoles and the expression of type II light chain 3 were increased in cells that were treated with β-catenin siRNA. These cell death modes are most likely due to the activation of LKB1-dependent AMPK following β-catenin silencing. The activated LKB1/AMPK pathway in AMC-HN-3 cells caused G1 arrest by phosphorylating p53 and suppressing mTOR signaling. In addition, treating AMC-HN-3 cells with LKB1 siRNA preserved cell viability against β-catenin silencing-induced cytotoxicity. Taken together, these results imply that following β-catenin silencing, HNSCC undergo both apoptotic and autophagic cell death that are under the control of LKB1/AMPK. To the best of our knowledge, these results suggest for the first time that novel crosstalk between β-catenin and the LKB1/AMPK pathway regulates the viability of HNSCC. This study thus presents new insights into our understanding of the cellular and molecular mechanisms involved in β-catenin silencing-induced cell death.

Abstract 3954: mTOR inhibitor increases radiation sensitivity in a radiation-resistance cancer cells through induction of cellular senescence

Autophagy is frequently activated in cancer cells resistant to ionizing radiation and is considered to limit the efficacy of radiotherapy as a prosurvival mechanism. In autophagy signaling, mTOR is an important target for enhancing the therapeutic effect of radiation since inhibiting mTOR limits cell growth and decreases cell proliferation, while increasing autophagy. However, the mode of these actions has remained poorly understood. Here, using radioresistant carcinoma cells, we investigated the mechanism by which the enhanced autophagy flux through the mTOR inhibition overcomes radioresistance of cancer cells subjected to irradiation. AMC-HN-9 cells triggered robust cellular proliferation, and induced cell arrest and autophagy activation in an irradiation dose-dependent manner, showing that adoption of an autophagy mode serves as a survival strategy against radiation. Interestingly, however, the potentiation of radiation-induced autophagy by concomitant inhibition of mTOR activity with mTOR inhibitors (rapamycin or PP242) reduced rather than enhanced cell survival and cell proliferation. Notably, mTOR inhibition in radiation-exposed cells was accompanied by senescence features, including the increased senescence-associated β-galactosidase (SA α-gal) activity and heterochromatin formation and irreversible growth arrest. Stress-induced senescence was associated with suppression of Rb-mediated E2F target genes. The results of this study show that the mTOR-dependent induction of autophagy can maintain a growth-arrested state in radioresistant cancer cells and increase radiosensitivity. It indicates that cellular senescence induced by mTOR inhibitor is a promising interventional strategy for enhancing the therapeutic efficacy in cancer cells refractory to irradiation

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3954. doi:1538-7445.AM2012-3954

Activation of p53-p21 is closely associated with the acquisition of resistance to apoptosis caused by β1-integrin silencing in head and neck cancer cells

The issue of whether aberrant expression of β1-integrin is associated with cancer progression and development of resistance to cytotoxic therapy is of considerable interest. Studies to date have shown that the anchorage-independent survival of cancer is attributed, in part, to epithelial-to-mesenchymal transition (EMT). Here, we have reported a novel alternative mechanism of anchorage-independent survival of cancer cells. Cell lines derived from head and neck cancer patients (AMC-HN-3 and AMC-HN-9) and the well-known EMT cancer cell line, MDA-MB231, were examined. The EMT features of AMC-HN-9 cells were comparable to those of MDA-MB231, whereas AMC-HN-3 cells showed no EMT characteristics. Although the pattern and degree of β1-integrin expression were similar in all three cell lines, sensitivities of the cells to β1-integrin knockdown with small interfering RNA (siRNA) were different. Cancer cells with no EMT features underwent cell death to a more significant extent following β1-integrin silencing than those with EMT. Intriguingly, we observed reactive activation of the p53-p21 pathway after β1-integrin silencing in AMC-HN-9 cells lacking an apparent cell death response. Simultaneous knockdown of wild-type p53 and β1-integrin in this cell line promoted cell death. Our data collectively indicate that β1-integrin-related cell death is closely associated with EMT phenotypes and activation of the p53-p21 pathway is partly involved in the acquisition of resistance to apoptosis induced by β1-integrin silencing. Further clarification of the mechanisms underlying p53 integration with β1-integrin signaling may facilitate the development of novel anti-cancer strategies.

A monitoring method for Atg4 activation in living cells using peptide-conjugated polymeric nanoparticles

To date, several principal methods are presently used to monitor the autophagic process, but they have some potential experimental pitfalls or limitations that make them not applicable to living cells. In order to improve on the currently developed detection methods for autophagy, we report here fluorescent peptide-conjugated polymeric nanoparticles loaded with a lysosome staining dye in their core. The fluorescent peptide is designed to be specifically cleaved by the Atg4 cysteine protease, which plays a crucial role in autophagy activation. In this study, we demonstrate that peptide-conjugated polymeric nanoparticles can be used to visualize Atg4 activity in both cell-free and cell culture systems. The fluorescence imaging of cells incubated with nanoparticles demonstrates that Atg4 activity is activated in the autophagy-induced conditions, but suppressed in the autophagy-inhibited conditions. These results indicate that Atg4 activity is correlated with autophagic flux through its own regulatory pathway. Therefore, our strategy provides an alternative detection method that can clearly distinguish between an "autophagy active" and "autophagy inactive" state in cultured cells. As our nanoparticles are highly cell-permeable and biocompatible, this detection system has general applicability to living cells and can be extended to cell-based screening to evaluate newly developed compounds.

Clinical implication of (18)F-FDG PET/CT in carcinoma of unknown primary

The value of (18)F-Fluorodeoxyglucose positron emission tomography/computed tomography (FDG PET/CT) in the detection of carcinoma of unknown primary (CUP) differs among the studies. This study aimed to evaluate the role of (18)F-FDG PET/CT in CUP. Fifty-one patients (19 women, 32 men) with metastasis confirmed by histopathology from an unknown primary tumor were included in this study. Patients received 370 MBq of (18)F-FDG intravenously, and PET/CT was performed at 60 minutes after injection. Primary tumor sites were detected in 5 of 51 patients (9.6%): in 2 patients with carcinoma of the lung, in 1 patient with carcinoma of the gallbladder, in 1 patient with carcinoma of the esophagus, and in 1 patient with carcinoma of the stomach. No primary tumor was discovered in the remaining 46 patients (90.4%) during the follow-up. The sensitivity, specificity, and accuracy of (18)F-FDG PET/CT were 100%, 80.4%, and 82.4%. The positive and negative predictive values were 35.7 and 100%, respectively. Based on the data presented, (18)F-FDG PET/CT has a clinical implicative value in detecting the primary tumor of CUP. PET/CT can be useful to rule out the possibility of detecting the primary tumor during the follow-up.

Abstract 3789: Induction of autophagy increases the radiation sensitivity of head and neck cancer cells via growth arrest

Autophagy is frequently activated in cancer cells resistant to various apoptotic stimuli such as ionizing radiation, which supports the premise of enhancing the efficiency of radiotherapy by interventional means of autophagy regulation. In this study, we investigated whether autophagy pathway mediates the radio-sensitizing effect in head and neck cancer cells, and how the mechanism underlying the enhanced sensitivity works in cancer cells.

The cellular responses following the ionizing radiation were examined by cell morphologic change, cell proliferation, clonogenic survival, cell cycle distribution, and expression level of several corresponding marker proteins in head and neck cancer HN-9 cells. Induction of autophagy was performed by down-regulating the mTOR signaling pathway using mTOR inhibitors such as rapamycin and PP242. Also, autophagy was inhibited by blocking the formation of autophagic vacuole (3-MA) or by disturbing the autophagosome maturation (bafilomycin A1, pepstatin A/E-46d). The change of autophagic flux was evidenced by the level of autophagy-related proteins and the morphological manifestation of autophagy. Upon exposure to radiation, the number of autophagic vacuoles was increased greatly in radiation dose- and time-dependent manners; however, the increase of apoptotic cells was not observed even in cells exposed to 12 Gy. In the meanwhile, the initial inhibition of cell cycle was maintained at slightly enhanced G1 phase. In some of the cases, it was restored to normal states, which implied that HN-9 cells adopted the mode of autophagy as a survival strategy against radiation. However, unexpectedly, further augmentation of autophagy pathway through the combination of either rapamycin or PP242 and radiation toward HN-9 cells hindered rather than enhanced clonogenic survival and cell proliferation, accompanying prolonged G1 arrest. Taken together, these results suggest that either induction of autophagy could serve as a therapeutic strategy to enhance radio-sensitivity, which is possibly due to irreversible cell cycle arrest following the excessive activation of autophagy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3789. doi:10.1158/1538-7445.AM2011-3789

Abstract 2278: Tumor microenvironment might be more important than pro-angiogenic chemotactic factors for tumor angiogenesis

During angiogenesis, many different tumor cytokines have been known to be involved in the regulation of chemotactic endothelial cell migration. Among those, a vascular endothelial growth factor (VEGF) is one of the most essential pro-angiogenic factors and the blockage of VEGF action through competitive inhibition on its receptor or by using of neutralizing antibody such as avastin has been considered as a promising anti-cancer approach to treat several solid tumors. However, despite their ability of releasing VEGF, some cancers show scarce angiogenesis and resistance to avastin treatment.

To explore key factors deciding tumor angiogenesis apart from well-known pro-angiogenic cytokines, we compared the pro-angiogenic capability of the AMC-HN9 head and neck cancer cell line (HN9) which has a low degree of angiogenesis in vivo and are reluctant to avastin treatment with that of the highly angiogenic AMC-HN3 cancer cell line (HN3). Of interest, in vitro cytokine assay of HN9 culture media revealed no difference in the secretion profile of pro-angiogenic cytokines such as VEGF, PlGF, FGF2 and PDGF compared with those of HN3. In addition, HN9 media could strongly promoted tubular formation of HUVECs and migration of fibroblasts in vitro as much as HN3 could. Next, we proceeded to HN9 xenograft co-injected with ECM molecules including fibronectin, collagen III or matrigel. In the co-injected xenografts, density of CD34 positivity significantly increased and the tumor growth exceeded that of HN9 alone-injected ones. Moreover, prominent fibroblast infiltration adjacent to tumor vessels was detected in the co-injected xenografts.

Taken together, these results imply that the formation of extracellular matrix surrounding tumor cells and the presence of activated fibroblasts are pre-requisites and more decisive in angiogenesis than tumor secreted pro-angiogenic cytokine per se.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2278.

GD2 expression is closely associated with neuronal differentiation of human umbilical cord blood-derived mesenchymal stem cells

GD2 ganglioside has been identified as a key determinant of bone marrow-derived mesenchymal stem cells (BM-MSCs). Here, we characterized GD2 ganglioside expression and its implications in umbilical cord blood-derived MSCs (UCB-MSCs). Using immune-selection analysis, we showed that both GD2-positive and GD2-negative UCB-MSCs expressed general stem cell markers and possessed mesodermal lineage differentiation potential. Although the fraction of GD2-expressing cells was lower in UCB-MSC than in BM-MSC populations, inhibition of GD2 synthesis in UCB-MSCs suppressed neuronal differentiation and down-regulated basic helix-loop-helix (bHLH) transcription factors, which are involved in early stage neuronal differentiation. In addition, the levels of bHLH factors in neuronally induced UCB-MSCs were significantly higher in GD2-positive than GD2-negative cells. Our data demonstrate that GD2 ganglioside expression is associated with regulation of bHLH factors and identify neurogenic-capable UCB-MSCs, providing new insights into the potential clinical applications of MSC-based therapy.

Cellular uptake mechanism and intracellular fate of hydrophobically modified glycol chitosan nanoparticles

Polymeric nanoparticle-based carriers are promising agents for the targeted delivery of therapeutics to the intracellular site of action. To optimize the efficacy in delivery, often the tuning of physicochemical properties (i.e., particle size, shape, surface charge, lipophilicity, etc.) is necessary, in a manner specific to each type of nanoparticle. Recent studies showed an efficient tumor targeting by hydrophobically modified glycol chitosan (HGC) nanoparticles through the enhanced permeability and retention (EPR) effect. As a continued effort, here the investigations on the cellular uptake mechanism and the intracellular fate of the HGC nanoparticles are reported. The HGC nanoparticle, prepared by a partial derivatization of the free amino groups of glycol chitosan (GC) with 5beta-cholanic acid, had a globular shape with the average diameter of 359 nm and the zeta potential of ca. 22 mV. Interestingly, these nanoparticles showed an enhanced distribution in the whole cells, compared to the parent hydrophilic GC polymers. In vitro experiments with endocytic inhibitors suggested that several distinct uptake pathways (e.g., clathrin-mediated endocytosis, caveolae-mediated endocytosis, and macropinocytosis) are involved in the internalization of HGC. Some HGC nanoparticles were found entrapped in the lysosomes upon entry, as determined by TEM and colocalization studies. Given such favorable properties including low toxicity, biocompatibility, and fast uptake by several nondestructive endocytic pathways, our HGC nanoparticles may serve as a versatile carrier for the intracellular delivery of therapeutic agents.

Outpatient pre-operative assessment in joint replacement surgery

An anaesthetist-led outpatient pre-operative assessment (OPA) clinic was introduced in our unit in an effort to improve patient care and cost-effectiveness. To assess the efficiency of the clinic, 112 patients who attended the OPA clinic (attendance rate 98%) during the first year were assessed prospectively and compared with 118 patients who did not undergo OPA the year before. There were fewer cancellations among those who attended the OPA clinic (13.6% compared to 3.6%), and the hospital stay was shortened from an average of 10.7 days to 7.0 days. This has resulted in more efficient utilization of operating theatre, reduced hospital costs and improved patient satisfaction. More extensive use of the pre-admission clinic is recommended and should be explored in other clinical settings.

Effect of polymer molecular weight on the tumor targeting characteristics of self-assembled glycol chitosan nanoparticles

To improve the in vivo tumor targeting characteristics of polymeric nanoparticles, three glycol chitosan (GC-20 kDa, GC-100 kDa, and GC-250 kDa) derivatives with different molecular weights were modified with cholanic acid at the same molar ratio. The resulting amphiphilic glycol chitosan-cholanic acid conjugates self-assembled to form glycol chitosan nanoparticles (GC-20 kDa-NP, GC-100 kDa-NP, and GC-250 kDa-NP) under aqueous conditions. The physicochemical properties of all three glycol chitosan nanoparticles, including degree of substitution with cholanic acid, surface charge, particle size and in vitro stability, were similar regardless of molecular weight. In vivo tissue distribution, time-dependent excretion, and tumor accumulation of glycol chitosan nanoparticles labeled with the near-infrared (NIR) fluorophore, Cy5.5, were monitored in SCC7 tumor-bearing mice, using NIR fluorescence imaging systems. Glycol chitosan nanoparticles displayed prolonged blood circulation time, decreased time-dependent excretion from the body, and elevated tumor accumulation with increasing polymer molecular weight. The results collectively suggest that high molecular weight glycol chitosan nanoparticles remain for longer periods in the blood circulation, leading to increased accumulation at the tumor site. Accordingly, we propose that enhanced tumor targeting by high molecular weight glycol chitosan nanoparticles is related to better in vivo stability, based on a pharmacokinetic improvement in blood circulation time.

Diesel exhaust particles increase IL-1beta-induced human beta-defensin expression via NF-kappaB-mediated pathway in human lung epithelial cells

Background

Human β-defensin (hBD)-2, antimicrobial peptide primarily induced in epithelial cells, is a key factor in the innate immune response of the respiratory tract. Several studies showed increased defensin levels in both inflammatory lung diseases, such as cystic fibrosis, diffuse panbronchiolitis, idiopathic pulmonary fibrosis and acute respiratory distress syndrome, and infectious diseases. Recently, epidemiologic studies have demonstrated acute and serious adverse effects of particulate air pollution on respiratory health, especially in people with pre-existing inflammatory lung disease. To elucidate the effect of diesel exhaust particles (DEP) on pulmonary innate immune response, we investigated the hBD-2 and interleukin-8 (IL-8) expression to DEP exposure in interleukin-1 beta (IL-1β)-stimulated A549 cells.

Results

IL-1β markedly up-regulated the hBD-2 promoter activity, and the subsequent DEP exposure increased dose-dependently the expression of hBD-2 and inflammatory cytokine IL-8 at the transcriptional level. In addition, DEP further induced the NF-κB activation in IL-1β-stimulated A549 cells more rapidly than in unstimulated control cells, which was showed by nuclear translocation of p65 NF-κB and degradation of IκB-α. The experiment using two NF-κB inhibitors, PDTC and MG132, confirmed that this increase of hBD-2 expression following DEP exposure was regulated through NF-κB-mediated pathway.

Conclusion

These results demonstrated that DEP exposure increases the expression of antimicrobial peptide and inflammatory cytokine at the transcriptional level in IL-1β-primed A549 epithelial cells and suggested that the increase is mediated at least partially through NF-κB activation. Therefore, DEP exposure may contribute to enhance the airway-responsiveness especially on the patients suffering from chronic respiratory disease.

Evaluation of cellular toxicity of TAFMAG, a natural substitute for asbestos from China

Asbestos is a very important material for industrial use. However, the need for a substitute for asbestos fiber is currently on the rise due to its high disease causing potential. This study evaluated the potential bio-hazardous effects of TAFMAG, a natural fibrous silicate produced in China, in comparison with chrysotile, a typical toxic asbestos. The physicochemical properties of TAFMAG were very similar to those of chrysotile when it was examined by a scanning electron microscope (SEM) and X-ray diffraction (XRD) analyses. Both of TAFMAG and chrysotile showed high content of magnetite and Fenton activity when compared with wollastonite, a non-asbestos fiber with a known low toxicity. When their cellular toxicity was assessed, TAFMAG showed no or less comparable to that of chrysotile in the hemolysis and lipid peroxidation of erythrocytes, and also on a MTT assay in RLE-6TN, a rat alveolar epithelial cell line. Pre-treatment of fibers with desferrioxamine, an iron chelator, showed that iron content of TAFMAG and chrysotile might be important in their cellular toxicity. These results suggest that TAFMAG is potentially toxic when inhaled into the lung and appropriate laws and regulations should be established for its use.

The role of nitric oxide in the particulate matter (PM2.5)-induced NFκB activation in lung epithelial cells

NFkappaB is one of key transcription factors that are involved in the inflammatory responses to the particulate matter (PM) in the lungs. In order to further understand the molecular mechanism, the effects of antioxidants and an inducible nitric oxide synthase (iNOS) inhibitor on PM-induced NFkappaB activation were examined in A549 lung epithelial cells. NFkappaB activation by 2.5 microm particulates (PM2.5) was evident from the degradation of an NFkappaB inhibitory protein, IkappaBalpha, and a luciferase reporter assay for NFkappaB activity. In these experiments, a pre-treatment of the cells with antioxidants N-acetyl-l-cysteine (NAC) and dimethylthiourea (DMTU) or an iNOS inhibitor l-N6-1-iminoethyl-lysine (L-NIL) clearly inhibited the NFkappaB activation by PM2.5. The inhibitory effect of L-NIL was also observed on the PM2.5-induced interleukin-8 (IL-8) gene expression both at the transcriptional and protein levels. These results suggest that PM2.5 induces NFkappaB activity via the pathways involving ROS and/or RNS generation. Considering the fact that NFkappaB also induces NO generation via iNOS expression, they might make a positive feedback loop that amplifies the downstream responses.