Phenotypic and molecular characterization of novel pulmonary adenocarcinoma cell lines established from a dog

Canine pulmonary adenocarcinoma (PAC) resembles human lung tumors in never-smokers, but it is rarer than human pulmonary adenocarcinoma. Therefore, research on canine PAC is challenging. In the present study, we successfully established various novel canine PAC cell lines from a single lesion in a dog, including two parent cell lines and fourteen cloned cell lines, and characterized their cellular properties in vitro. Several of these cell lines showed epithelial-mesenchymal transition (EMT)-like and/or cancer stem cell (CSCs)-like phenotypes. We additionally assessed the sensitivity of the cells to vinorelbine in vitro. Three clonal lines, two of which showed EMT- and CSC-like phenotypes, were resistant to vinorelbine. Furthermore, we evaluated the expression and activation status of EGFR, HER2, and Ras signaling factors. The findings indicated that the cell lines we established preserved the expression and activation of these factors to varying extents. These novel canine PAC cell lines can be utilized in future research for understanding the pathogenesis and development of treatments for canine PAC.

mTOR pathway as a potential therapeutic target for cancer stem cells in canine mammary carcinoma

Mammary adenocarcinoma, the most common cancer in female dogs, often exhibits the lymph node and lung metastases and has a higher mortality rate. However, mammary adenocarcinoma has no established treatment, except early surgical excision. Canine mammary carcinoma has many common features with human mammary carcinoma, including clinical characteristics, heterogeneity, and genetic aberrations, making it an excellent spontaneous tumor model for human breast cancer. Diverse cancers comprised heterogeneous cell populations originating from cancer stem cells (CSCs) with self-renewal ability. Therefore, in addition to conventional therapy, therapeutic strategies targeting CSCs are essential for cancer eradication. The present study aimed to extract inhibitors of canine mammary CSCs that suppress their self-renewal ability. Sphere-formation assay, which evaluates self-renewal ability, was performed for the canine mammary cancer cell lines CTBp and CNMp. The spheres formed in this assay were used in inhibitor library screening, which identified various signaling pathways such as proteosome, stress inducer, and mammalian target of rapamycin (mTOR). The present study focused on the mTOR signaling pathway. Western blotting showed higher levels of phosphorylated mTOR in sphere-forming CTBp and CNMp cells than in adherent cells. Drug sensitivity examination using the mTOR inhibitors everolimus and temsirolimus revealed dose-dependent reductions in viability among both sphere-forming cells and adherent cells. Expression of phosphorylated mTOR in adherent and sphere-forming cells decreased by everolimus and temsirolimus treatment. In mice transplanted with CTBp-derived spheres, everolimus treatment significantly decreased tumor volume compared to control. These results reveal that the mTOR signaling pathway may be a potential to be a therapeutic target in both cancer cells and CSCs. Novel therapeutic strategies for canine mammary carcinoma are expected to benefit to human breast carcinoma as well.

Sprouty 1 is associated with stemness and cancer progression in glioblastoma

Glioblastoma multiforme (GBM) is the most severe type of human brain tumor, with a poor prognosis and a low survival rate. GBM is composed of a variety of cell types, including glioma stem-like cells (GSCs), which attribute to its therapeutic resistance (Boyd et al., 2020). Sprouty1 (SPRY1) was first identified as a receptor tyrosine kinases (RTK) signaling mediator in a mammalian cell (Christofori, 2003), however, its role in GBM is unknown. Therefore, the goal of this study was to investigate the role of SPRY1 in the stemness and aggressiveness of GSCs. The mRNA expression levels of SPRY1 were confirmed using quantitative reverse transcription PCR (RT-qPCR) in normal human astrocytes (NHA), glioma cells, and glioma stem cells. SPRY1 expression was inhibited in glioma stem cells using small interference RNA (siRNAs) to examine its role in cell proliferation and tumorsphere formation. Bioinformatics analyses were also employed to investigate the association of SPRY1 expression with patient survival, tumor grade, and subtypes publicly available datasets. We demonstrated that SPRY1 is highly expressed in glioma stem cells than in NHA, glioma cells, and differentiated glioma stem cells. siRNA-mediated downregulation of SPRY1 expression decreased the stemness and self-renewal ability in GSC11. Bioinformatics results showed that high SPRY1 expression correlates with poor overall survival in glioma patients. Our findings suggest that SPRY1 contributes to the stemness and aggressiveness of GBM.

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Glioblastoma (GBM) is the most aggressive cancer type in human brain.

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Glioma stem cell (GSC) is a small population in GBM, associated therapy resistance and recurrence.

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Sprouty1 expression associated with GBM grade and patient survival.

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Sprouty1 highly expressed in GBM cell lines and GSC.

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Suppression of SPRY1 expression downregulated GSC proliferation and tumorsphere formation.

Antitumor activity of the dual PI3K/mTOR inhibitor gedatolisib and the involvement of ABCB1 in gedatolisib resistance in canine tumor cells

The phosphatidylinositol 3-kinase/mammalian target of rapamycin (PI3K/mTOR) signaling pathway is a therapeutic target for various types of human tumors, and dual PI3K/mTOR inhibitors demonstrate antitumor activities in both preclinical and clinical studies. However, resistance mechanisms limit their abilities. As the molecular mechanisms involved in the cellular resistance are not clear in any canine tumors, an understanding of resistance mechanisms would support the potential use of dual PI3K/mTOR inhibitors in canine tumors. The antitumor activity of gedatolisib on cell viability, protein phosphorylation, and cell cycle distribution was assessed using 12 canine tumor cell lines from 6 types of tumors. In addition, the molecular determinants involved in the cellular sensitivity to gedatolisib were explored by investigating the involvement of serum-and-glucocorticoid-induced kinase 1 (SGK1), PIK3CA, and ATP-binding cassette, subfamily B, member 1 (ABCB1). The results demonstrated that gedatolisib decreased cell viability in all cell lines, with IC₅₀ values <1 µM in 10 of the 12 lines. Gedatolisib inhibited Akt and mTOR complex 1 substrate phosphorylation and induced G₀/G₁ cell cycle arrest. However, certain cell lines with higher IC₅₀ values were more resistant to these effects. These cell lines exhibited higher ABCB1 activity and the ABCB1 inhibitor cyclosporin A enhanced the decrease of cell viability caused by gedatolisib. SGK1 overexpression did not confer resistance to gedatolisib. The mutations of E545K and H1047R in PIK3CA were not observed. The present results indicated that gedatolisib decreased cell viability in canine tumor cell lines and ABCB1 played an important role in gedatolisib resistance, supporting the potential use of gedatolisib for canine tumors.

Visualizing the cancer stem-like properties of canine tumour cells with low proteasome activity

Cancer stem-like cells (CSCs) cause treatment failure in various tumours; however, establishing CSC-targeted therapies has been hampered by difficulties in the identification and isolation of this small sub-population of cells. Recent studies have revealed that tumour cells with low proteasome activity display a CSC phenotype that can be utilized to image CSCs in canines. This study visualizes and reveals the CSC-like properties of tumour cells with low proteasome activity in HMPOS (osteosarcoma) and MegTCC (transitional cell carcinoma), which are canine cell lines. The parent cells were genetically engineered to express ZsGreen1, a fluorescent protein connected to the carboxyl-terminal degron of canine ornithine decarboxylase that accumulates with low proteasome activity (ZsG⁺ cells). ZsG⁺ cells were imaged and the mode of action of this system was confirmed using a proteasome inhibitor (MG-132), which increased the ZsGreen1 fluorescence intensity. The CSC-like properties of ZsG⁺ cells were evaluated on the basis of cell divisions, cell cycle, the expression of CSC markers and tumourigenicity. ZsG⁺ cells underwent asymmetric divisions and had a low percentage of G0/G1 phase cells; moreover, ZsG⁺ cells expressed CSC markers such as CD133 and showed a large tumourigenic capability. In histopathological analysis, ZsG⁺ cells were widely distributed in the tumour samples derived from ZsG⁺ cells and in the proliferative regions of the tumours. The results of this study indicate that visualized canine tumour cells with low proteasome activity have a CSC-like phenotype and that this visualization system can be utilized to identify and isolate canine CSCs.

Functional analysis of CD44 variants and xCT in canine tumours

The cell surface glycoprotein CD44 has various types of splicing variants, which contribute to its multiple distinct cellular functions. Recently, it was reported that the CD44v8‐10 isoform interacts with the system Xc(‐) transporter‐related protein (xCT), and inhibits the accumulation of reactive oxygen species by promoting the synthesis of the antioxidant glutathione in human tumour cells. In this study, we investigated the expression and function of CD44 variants and xCT in canine tumours. From semi‐quantitative reverse transcription polymerase chain reaction analysis, the mRNA expression of the CD44v8‐10 isoform was observed in canine tumour tissues as well as human cases. The overexpression of CD44v8‐10 may promote the synthesis of glutathione and enhance the resistance to radiation of canine breast tumour cells. Furthermore, canine xCT mRNA expression was significantly upregulated in the canine breast tumour tissues as compared to the normal tissues surrounding the tumours. To investigate the function of canine xCT, we treated canine tumour cells with the xCT inhibitor sulfasalazine. Consequently, the sulfasalazine‐treated cells were more sensitive to oxidative stress than the non‐treated cells. Taken together, these results suggested that CD44v8‐10 and xCT play important roles in the therapy resistance of canine tumours as well as human tumours.

Understanding of tumourigenesis in canine mammary tumours based on cancer stem cell research

Mammary tumours occur frequently in female dogs, where such tumours exhibit complexity when examined histologically. These tumours are composed not only of proliferative luminal epithelial cells, but also of myoepithelial cells and/or mesenchymal cells with cartilage and osseous tissues in a solitary mass. The origin of this complexed histogenesis remains speculative, but cancer stem cells (CSCs) are likely involved. CSCs possess self-renewing capacity, differentiation potential, high tumourigenicity in immunodeficient mice, and resistance to chemotherapy and radiation. These cells are at the apex of a hierarchy in cancer tissues and are involved in tumour initiation, recurrence, and metastasis. For these reasons, understanding the properties of CSCs is of paramount importance. Analysis of the characteristics of CSCs may contribute to the elucidation of the histogenesis underlying canine mammary tumours, formulation of novel CSC-targeted therapeutic strategies, and development of biomarkers for early diagnostic and prognostic applications. Here, we review research on CSCs in canine mammary tumours, focusing on: (1) identification and properties of CSCs; (2) hypotheses regarding hierarchal structures in simple type, complex type and mixed tumours of the canine mammary gland; and (3) current and prospective studies of CSC metabolism.

Size of canine hepatocellular carcinoma as an adverse prognostic factor for surgery

Objective

Liver neoplasms are problematic among small domestic animals. The etiological cause of hepatocellular carcinomas in domestic animals is still unknown although it is believed that chronic infections and toxic substances can affect the development of this type of tumor. This study aimed to analyze the clinical and morphological characteristics of canine hepatocellular carcinoma.

Materials and methods

In total, 6,958 cancer operations were performed in the clinic. Liver tumors were detected in 123 dogs in vivo and 375 dogs postmortem. All animals with suspected liver neoplasm were assessed, including history, clinical examination, complete blood count, biochemical blood tests, radiographic examination, and ultrasound with a biopsy for performing cytological and histological analyses.

Results

Hepatocellular carcinomas have nonspecific clinical manifestations, also a characteristic aspect of other tumors of the hepatobiliary system. The hematological changes have an impact on the prognosis, and biochemical abnormalities reflect the changes in liver activity. The cytological diagnosis of hepatocellular tumors is difficult because of hepatocyte atypia in highly differentiated carcinomas. Finally, a histological examination was performed in all the dogs diagnosed with hepatocellular carcinoma.

Conclusion

Hematological changes in dogs with hepatocellular carcinoma affect their prognosis. Biochemical abnormalities of this pathology reflect the changes in liver activity, not indicating a specific pathology. However, an increase in the activity of aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase is an unfavorable prognostic sign. In this study, five of seven dogs with a tumor size of more than 5.0 cm had a life expectancy of 30, 51, and 91 days, suggesting that the size of the tumor is an adverse prognostic factor.

Analysis of radiosensitivity of cancer stem-like cells derived from canine cancer cell lines

Cancer stem-like cells (CSCs) are self-renewing cells comprising a small subpopulation in tumours, and generate differentiated progeny through asymmetric division. It has been shown that CSCs are resistant to ionizing radiation, and this feature could be one of the mechanisms of tumour recurrence after radiation therapy. Much attention has been focused on to target CSCs; however, difficult of isolating CSCs and lack of knowledge on their radiosensitivity have limited this kind of research in veterinary medicine. In the present study, sphere-forming cells (SC), cultured using sphere formation method, were isolated from four type of canine tumour cell lines and evaluated if they have CSCs-like properties by expression of CSCs markers (real-time polymerase chain reaction) and capacity of tumorigenesis (xenograft transplantation in nude mice), and were assessed radiosensitivity (clonogenic survival assay) and DNA repair kinetics (immunofluorescence staining for p53-binding protein 1) after X-ray irradiation in comparison with the corresponding normal adherent culture cells (AC). All SCs were isolated using sphere formation and showed high gene expression of CD133 and tumorigenic ability as compared with AC. All SCs were significantly resistant against X-ray irradiation as compared with AC. In addition, the amount of DNA double-strand breaks after X-ray irradiation were significantly lower in SC compared with the corresponding AC. These results indicate that SC isolated through sphere formation possess CSCs-like characteristics and CSCs are important factor that affect radiosensitivity in canine tumours. In addition, radioresistance of CSCs may depend on reaction of DNA double-strand break after X-ray exposure.

Circ008913,viamiR-889 regulation of DAB2IP/ZEB1, is involved in the arsenite-induced acquisition of CSC-like properties by human keratinocytes in carcinogenesis

Circ008913,viamiR-889 regulation of DAB2IP/ZEB1, is involved in the arsenite-induced acquisition of CSC-like properties and the neoplastic transformation.

Human Genetic Relevance and Potent Antitumor Activity of Heat Shock Protein 90 Inhibition in Canine Lung Adenocarcinoma Cell Lines

Background

It has been an open question how similar human and canine lung cancers are. This has major implications in availability of human treatments for dogs and in establishing translational models to test new therapies in pet dogs. The prognosis for canine advanced lung cancer is poor and new treatments are needed. Heat shock protein 90 (HSP90) is an ATPase-dependent molecular chaperone ubiquitously expressed in eukaryotic cells. HSP90 is essential for posttranslational conformational maturation and stability of client proteins including protein kinases and transcription factors, many of which are important for the proliferation and survival of cancer cells. We investigated the activity of STA-1474, a HSP90 inhibitor, in two canine lung cancer cell lines, BACA and CLAC.

Results

Comparative genomic hybridization analysis of both cell lines revealed genetic relevance to human non-small cell lung cancer. STA-1474 inhibited growth and induced apoptosis of both cell lines in a dose- and time-dependent manner. The ICs₅₀ after 72 h treatment with STA-1474 were 0.08 and 0.11 μM for BACA and CLAC, respectively. When grown as spheroids, the IC₅₀ of STA-1474 for BACA cells was approximately two-fold higher than when grown as a monolayer (0.348 μM vs. 0.168 μM), whereas CLAC spheroids were relatively drug resistant. Treatment of tumor-stromal fibroblasts with STA-1474 resulted in a dose-dependent decrease in their relative cell viability with a low IC₅₀ of 0.28 μM.

Conclusions

Here we first established that lung adenocarcinoma in people and dogs are genetically and biochemically similar. STA1474 demonstrated biological activity in both canine lung cancer cell lines and tumor-stromal fibroblasts. As significant decreases in relative cell viability can be achieved with nanomolar concentrations of STA-1474, investigation into the clinical efficacy of this drug in canine lung cancer patients is warranted.

Presence of neural progenitors in spontaneous canine gliomas: A histopathological and immunohistochemical study of 20 cases

Gliomas are the most common primary brain tumours in humans and are associated with a poor prognosis. An accurate animal model of human glioma tumorigenesis is needed to test new treatment strategies. Dogs represent a promising model because they develop spontaneous diffusely-infiltrating gliomas. This study investigated whether spontaneous canine gliomas contain cancer stem cells previously identified in all grades of human gliomas. Twenty spontaneous cases of canine gliomas were graded according to the human WHO classification. The expression of different markers of lineage differentiation was evaluated with immunohistochemistry as follows: nestin and CD133 for neural stem cells, doublecortin for neuronal progenitor cells, Olig2 for glial progenitor cells, glial fibrillary acidic protein, vimentin and S-100 for mature glial cells, and NeuN and βIII-tubulin for mature neurons. Gliomas were characterised as follows: five grade II (oligodendrogliomas); nine grade III (seven anaplastic oligodendrogliomas, one anaplastic astrocytoma, one anaplastic oligoastrocytoma); six grade IV (glioblastomas). Immunohistochemical evaluation revealed that (1) nestin and CD133 were expressed in all grades of gliomas with a higher proportion of positive cells in high-grade gliomas; (2) the expression of S-100 protein and Olig2 did not differ substantially between astrocytic and oligodendroglial tumours, and (3) all gliomas were negative for mature neuron markers. The results demonstrated the presence of undifferentiated neural progenitors in all grades of spontaneous canine gliomas, confirming the relevance of this animal model for further studies on cancer stem cells.

The acquisition of cancer stem cell-like properties and neoplastic transformation of human keratinocytes induced by arsenite involves epigenetic silencing of let-7c via Ras/NF-κB

Exposure of humans to inorganic arsenic can cause skin cancer. The acquisition of cancer stem cell-like properties is involved in the initiation of some cancers, and there are changes in let-7 levels in some tumors. The mechanisms of action, however, remain obscure. Here, we report that there are decreased levels of let-7a, let-7b, and let-7c in human keratinocyte HaCaT cells during malignant transformation induced by a low concentration (1.0μM) of arsenite. The process by which arsenite reduces the level of let-7c apparently involves methylation, for 5-aza-2'-deoxycytidine, an inhibitor of methyltransferases, prevents arsenite-induced hypermethylation, decreases the level of let-7c, and thereby blocks arsenite-induced activation of the Ras/NF-κB signal pathway. Let-7c is an up-stream regulator of the Ras/NF-κB signal pathway and down-regulates activation of this pathway. In arsenite-transformed HaCaT cells, the acquisition of cancer stem cell-like properties is prevented by over-expression of let-7c, and over-expression of let-7c decreases the malignancy of transformed HaCaT cells. Thus, we conclude that epigenetic silencing of let-7c via Ras/NF-κB is involved in the acquisition of cancer stem cell-like properties and neoplastic transformation of HaCaT cells induced by arsenite, which contribute to the tumorigenesis of arsenite.

Identification of tumor-initiating cells in a canine hepatocellular carcinoma cell line

Tumor-initiating cells (TICs) or cancer stem cells (CSCs), a small subset of tumor cells, are involved in tumor initiation, progression, recurrence and metastasis. In human hepatocellular carcinoma (HCC), TICs are enriched with cell surface markers and have the ability to self-renew and differentiate tumors at a high frequency. We established a canine HCC cell line, HCC930599, and analyzed it for stem and progenitor cell marker expression using flow cytometry. HCC930599 showed high CD44 and CD29, moderate CD90, and low CD133, CD34, CD24, CD117, and CD13 expression. CD90(+)CD44(+) and CD90(-)CD44(+) cells were characterized using the in vitro sphere assay and an in vivo transplant model. CD90(+)CD44(+) cells acquired enhanced self-renewal capacity, proliferative activity and tumourigenicity compared with CD90(-)CD44(+) cells, suggesting that TICs exist in the HCC930599 cell line and that CD90 is a marker for enriched TICs. Understanding TIC characteristics may help elucidate hepatic carcinogenesis and HCC therapy development.

Inhibitions of epithelial to mesenchymal transition and cancer stem cells-like properties are involved in miR-148a-mediated anti-metastasis of hepatocellular carcinoma

The epithelial-mesenchymal transition (EMT) and acquisition of cancer stem cells (CSCs)-like properties are essential steps in the metastasis and postsurgical recurrence of hepatocellular carcinomas (HCCs). The molecular mechanisms involved, however, remain obscure. As determined by an miRNA microarray analysis, there was lower expression of miR-148a in poorly differentiated HCC tissues relative to well-differentiated HCC tissues. MHCC97H and MHCC97L (HCC cells with migratory capacity) and HCC tissues with various differentiation status were selected for further investigation. The results showed that miR-148a levels inversely correlated with the differentiation status of HCC tissues. In MHCC97H and MHCC97L cells, over-expression of miR-148a blocked the EMT process, attenuated the expression of CD90 and CD44 (biomarkers for liver cancer stem cells), and inhibited their migratory capacity. Via TargetScan and microRNA.org algorithms, miR-148a was predicted to bind to the Wnt1 mRNA 3'-UTR. Wnt1 was confirmed as a target gene of miR-148a in HCC cells, and the Wnt signal pathway was determined to be involved in the miR-148a-mediated inhibition of EMT and CSCs-like properties of MHCC97H cells. Moreover, the expression of miR-148a in nonmetastatic HCC tissues was higher than that in metastatic HCC tissues. The results suggest that miR-148a inhibits the metastasis of HCCs by blocking EMT and CSCs-like properties through effects on the Wnt signaling pathway.

P38/NF-κB/snail pathway is involved in caffeic acid-induced inhibition of cancer stem cells-like properties and migratory capacity in malignant human keratinocyte

Background

Skin cancer is the most common cancer throughout the world. The epithelial-mesenchymal transition (EMT) and the acquisition of cancer stem cells (CSCs)-like properties emerge as critical steps in the metastasis of human skin cancers. Caffeic acid (CaA) exerts anticarcinogenic effects. However, the effects of CaA on the migratory capability and on the CSCs-like properties of skin cancer cells, and the molecular mechanisms underlying it are not fully understood.

Methods

Malignant HaCaT cells were treated by CaA. Transwell assay was performed to determine that CaA attenuated the migratory capability; Spheroid formation assay was performed to confirm that CaA decreased the CSCs-like phenotype; Treated malignant HaCaT cells were molecularly characterized by RT-PCR, Western blots, Southwestern blot, and immunoprecipitation.

Results

In CaA-treated malignant human keratinocyte (malignant HaCaT cells), inhibition of the migratory capability and CSCs-like phenotype were observed. CaA up-regulated the phosphorylation of p38, and down-regulated the activation of nuclear factor κB (NF-κB)/snail signal pathway. Indeed, p38 decreased the DNA-binding activity of NF-κB to the promoter of snail gene, which resulted in the transcriptional inactivation of snail. Blockage of p38 attenuated the CaA-induced inhibition of migratory capability and CSCs-like phenotype in malignant HaCaT cells.

Conclusions

CaA attenuates the migratory capability and CSCs-like Properties of malignant human keratinocyte, in which, p38-mediated down-regulation of NF-κB/snail signal pathway is involved.

Regulation of expression of ABCB1 and LRP genes by mitogen-activated protein kinase/extracellular signal-regulated kinase pathway and its role in generation of side population cells in canine lymphoma cell lines

The concept of the cancer stem cell (CSC) has been recognized as key for elucidation of the mechanisms that confer the multidrug resistance (MDR) phenotype to tumor cells, and the side population (SP) fraction has been shown to be enriched by cells with the CSC phenotype. The purpose of the present study was to identify the mechanism that induces a difference of phenotype between the SP and the remaining major population (MP) using two canine lymphoma cell lines. Expression levels of ABCB1 and LRP genes, which encode efflux pumps, were significantly higher in the SP than in the MP. Microarray analysis revealed up-regulation of the expression of transforming growth factor-β (TGF-β) type II receptor in SP compared with MP, and the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) pathway was more up-regulated in the SP than in the MP. Stimulation of the MAPK/ERK pathway significantly increased the mRNA expression of both ABCB1 and LRP genes. These results indicate increased expression of the efflux pumps through the MAPK/ERK pathway in SP cells.

EMT and CSC-like properties mediated by the IKKβ/IκBα/RelA signal pathway via the transcriptional regulator, Snail, are involved in the arsenite-induced neoplastic transformation of human keratinocytes

Exposure of humans to inorganic arsenic can cause skin cancer. The epithelial-mesenchymal transition (EMT) and acquisition of cancer stem cell (CSC)-like properties are essential steps in the initiation of human skin cancers; however, the mechanisms of action remain obscure. We have found that, during the neoplastic transformation induced by a low concentration (1.0 μM) of arsenite in human keratinocyte HaCaT cells, the cells undergo an EMT and then acquire a malignant CSC-like phenotype. With longer times for transformation of HaCaT cells, there were increased activations of IκB kinase β (IKKβ), inhibitor nuclear factor-kappa B alpha (IκBα), and nuclear factor κB (NF-κB) RelA and increases in the level of Snail. Further, during the transformation of HaCaT cells, the activation of NF-κB RelA up-regulated Snail levels. Inhibition of NF-κB RelA blocked the arsenite-induced EMT, acquisition of a CSC-like phenotype, and neoplastic transformation. These observations show that EMT, along with acquisition of a CSC-like phenotype mediated by IKKβ/IκBα/RelA signal pathway via Snail, contributes to a low concentration of arsenite-induced tumorigenesis.