Induction of stem cell factor/c-Kit/slug signal transduction in multidrug-resistant malignant mesothelioma cells

Enhancer remodeling activates NOTCH3 signaling to confer chemoresistance in advanced nasopharyngeal carcinoma

Acquired resistance to chemotherapy is one of the major causes of mortality in advanced nasopharyngeal carcinoma (NPC). However, effective strategies are limited and the underlying molecular mechanisms remain elusive. In this study, through transcriptomic profiling analysis of 23 tumor tissues, we found that NOTCH3 was aberrantly highly expressed in chemoresistance NPC patients, with NOTCH3 overexpression being positively associated with poor clinical outcome. Mechanistically, using an established NPC cellular model, we demonstrated that enhancer remodeling driven aberrant hyperactivation of NOTCH3 in chemoresistance NPC. We further showed that NOTCH3 upregulates SLUG to induce chemo-resistance of NPC cells and higher expression of SLUG have poorer prognosis. Genetic or pharmacological perturbation of NOTCH3 conferred chemosensitivity of NPC in vitro and overexpression of NOTCH3 enhanced chemoresistance of NPC in vivo. Together, these data indicated that genome-wide enhancer reprogramming activates NOTCH3 to confer chemoresistance of NPC, suggesting that targeting NOTCH3 may provide a potential therapeutic strategy to effectively treat advanced chemoresistant NPC.

Bufalin Inhibits Tumorigenesis, Stemness, and Epithelial-Mesenchymal Transition in Colorectal Cancer through a C-Kit/Slug Signaling Axis

Colorectal cancer (CRC) is a major source of morbidity and mortality, characterized by intratumoral heterogeneity and the presence of cancer stem cells (CSCs). Bufalin has potent activity against many tumors, but studies of its effect on CRC stemness are limited. We explored bufalin's function and mechanism using CRC patient-derived organoids (PDOs) and cell lines. In CRC cells, bufalin prevented nuclear translocation of β-catenin and down-regulated CSC markers (CD44, CD133, LGR5), pluripotency factors, and epithelial-mesenchymal transition (EMT) markers (N-Cadherin, Slug, ZEB1). Functionally, bufalin inhibited CRC spheroid formation, aldehyde dehydrogenase activity, migration, and invasion. Network analysis identified a C-Kit/Slug signaling axis accounting for bufalin's anti-stemness activity. Bufalin treatment significantly downregulated C-Kit, as predicted. Furthermore, overexpression of C-Kit induced Slug expression, spheroid formation, and bufalin resistance. Similarly, overexpression of Slug resulted in increased expression of C-Kit and identical functional effects, demonstrating a pro-stemness feedback loop. For further study, we established PDOs from diagnostic colonoscopy. Bufalin differentially inhibited PDO growth and proliferation, induced apoptosis, restored E-cadherin, and downregulated CSC markers CD133 and C-Myc, dependent on C-Kit/Slug. These findings suggest that the C-Kit/Slug axis plays a pivotal role in regulating CRC stemness, and reveal that targeting this axis can inhibit CRC growth and progression.

Snail-Family Proteins: Role in Carcinogenesis and Prospects for Antitumor Therapy

The review analyzes Snail family proteins, which are transcription factors involved in the regulation of the epithelial-mesenchymal transition (EMT) of tumor cells. We describe the structure of these proteins, their post-translational modification, and the mechanisms of Snail-dependent regulation of genes. The role of Snail proteins in carcinogenesis, invasion, and metastasis is analyzed. Furthermore, we focus on EMT signaling mechanisms involving Snail proteins. Next, we dissect Snail signaling in hypoxia, a condition that complicates anticancer treatment. Finally, we offer classes of chemical compounds capable of down-regulating the transcriptional activity of Snails. Given the important role of Snail proteins in cancer biology and the potential for pharmacological inhibition, Snail family proteins may be considered promising as therapeutic targets.

The Experimental Pathology at Ancona: 50 Years of Exciting and Pioneering Research on Human Pathology

Half century ago, a few academic pioneers founded the laboratories of experimental and ultrastructural pathology in Ancona. From this origin, a new phase of experimental studies developed aimed at translational and clinical research up to the present, when our group is internationally recognized for its fundamental contributions in gerontological research and molecular diagnostic pathology. Since the desire of immortality and of eternal youth seems to be as old as mankind, in the future we plan to focus our scientific research on Regenerative Medicine and Rejuvenation strategies. This is the most ambitious aim in the framework of the world aging population. We do not know whether we would achieve these results by ourselves. We are confident that, as in the past, new generations of scientist of the school of experimental pathology at Ancona will get the baton by the older one and lead the future with the same enthusiasm, love and commitment.

Epithelial-mesenchymal-transition-inducing transcription factors: new targets for tackling chemoresistance in cancer?

Chemoresistance remains a major complication of cancer treatments. Recent data provide strong evidence that chemoresistance is linked to epithelial-mesenchymal transition (EMT), a latent developmental process, which is re-activated during cancer progression. EMT involves transcriptional reprogramming and is driven by specific EMT transcription factors (EMT-TFs). In this review, we provide support for the idea that EMT-TFs contribute to the development of resistance against cancer therapy and discuss how EMT-TFs might be targeted to advance novel therapeutic approaches to the treatment of cancer.

SLUG transcription factor: a pro-survival and prognostic factor in gastrointestinal stromal tumour

BACKGROUND

The SLUG transcription factor has been linked with the KIT signalling pathway that is important for gastrointestinal stromal tumour (GIST) tumourigenesis. Its clinical significance in GIST is unknown.

METHODS

Influence of SLUG expression on cell proliferation and viability were investigated in GIST48 and GIST882 cell lines. The association between tumour SLUG expression in immunohistochemistry and recurrence-free survival (RFS) was studied in two clinical GIST series, one with 187 patients treated with surgery alone, and another one with 313 patients treated with surgery and adjuvant imatinib.

RESULTS

SLUG downregulation inhibited cell proliferation, induced cell death in both cell lines, and sensitised GIST882 cells to lower imatinib concentrations. SLUG was expressed in 125 (25.0%) of the 500 clinical GISTs evaluated, and expression was associated with several factors linked with unfavourable prognosis. SLUG expression was associated with unfavourable RFS both when patients were treated with surgery alone (HR=3.40, 95% CI=1.67-6.89, P=0.001) and when treated with surgery plus adjuvant imatinib (HR=1.83, 95% CI=1.29-2.60, P=0.001).

CONCLUSIONS

GIST patients with high tumour SLUG expression have unfavourable RFS. SLUG may mediate pro-survival signalling in GISTs.

A novel slug-containing negative-feedback loop regulates SCF/c-Kit-mediated hematopoietic stem cell self-renewal

The stem cell factor (SCF)/c-Kit pathway has crucial roles in controlling hematopoietic stem cell (HSC) renewal. However, little is known about the intracellular regulation of the SCF/c-Kit pathway in HSCs. We report here that Slug, a zinc-finger transcription repressor, functions as a direct transcriptional repressor of c-Kit in HSCs. Conversely, SCF/c-Kit signaling positively regulates Slug through downstream c-Myc and FoxM1 transcription factors. Intriguingly, c-Kit expression is induced by SCF/c-Kit signaling in Slug-deficient HSCs. The balance between Slug and c-Kit is critical for maintaining HSC repopulating potential in vivo. Together, our studies demonstrate that Slug functions in a novel negative-feedback regulatory loop in the SCF/c-Kit signaling pathway in HSCs.

Receptor tyrosine kinase (c-Kit) inhibitors: a potential therapeutic target in cancer cells

c-Kit, a receptor tyrosine kinase, is involved in intracellular signaling, and the mutated form of c-Kit plays a crucial role in occurrence of some cancers. The function of c-Kit has led to the concept that inhibiting c-Kit kinase activity can be a target for cancer therapy. The promising results of inhibition of c-Kit for treatment of cancers have been observed in some cancers such as gastrointestinal stromal tumor, acute myeloid leukemia, melanoma, and other tumors, and these results have encouraged attempts toward improvement of using c-Kit as a capable target for cancer therapy. This paper presents the findings of previous studies regarding c-Kit as a receptor tyrosine kinase and an oncogene, as well as its gene targets and signaling pathways in normal and cancer cells. The c-Kit gene location, protein structure, and the role of c-Kit in normal cell have been discussed. Comprehending the molecular mechanism underlying c-Kit-mediated tumorogenesis is consequently essential and may lead to the identification of future novel drug targets. The potential mechanisms by which c-Kit induces cellular transformation have been described. This study aims to elucidate the function of c-Kit for future cancer therapy. In addition, it has c-Kit inhibitor drug properties and their functions have been listed in tables and demonstrated in schematic pictures. This review also has collected previous studies that targeted c-Kit as a novel strategy for cancer therapy. This paper further emphasizes the advantages of this approach, as well as the limitations that must be addressed in the future. Finally, although c-Kit is an attractive target for cancer therapy, based on the outcomes of treatment of patients with c-Kit inhibitors, it is unlikely that Kit inhibitors alone can lead to cure. It seems that c-Kit mutations alone are not sufficient for tumorogenesis, but do play a crucial role in cancer occurrence.

Silencing stem cell factor attenuates stemness and inhibits migration of cancer stem cells derived from Lewis lung carcinoma cells

Stem cell factor (SCF) plays an important role in tumor growth and metastasis. However, the function of SCF in regulating stemness and migration of cancer stem cells (CSCs) remains largely undefined. Here, we report that non-adhesive culture system can enrich and expand CSCs derived from Lewis lung carcinoma (LLC) cells and that the expression level of SCF in CSCs was higher than those in LLC cells. Silencing SCF via short hairpin (sh) RNA lentivirus transduction attenuated sphere formation and inhibited expressions of stemness genes, ALDH1, Sox2, and Oct4 of CSCs in vitro and in vivo. Moreover, SCF-silenced CSCs inhibited the migration and epithelial-mesenchymal transition, with decreased expression of N-cadherin, Vimentin, and increased expression of E-cadherin in vitro and in vivo. Finally, SCF-short hairpin RNA (shRNA) lentivirus transduction suppressed tumorigenicity of CSCs. Taken together, our findings unraveled an important role of SCF in CSCs derived from LLC cells. SCF might serve as a novel target for lung cancer therapy.

Sustained proliferation in cancer: Mechanisms and novel therapeutic targets

Proliferation is an important part of cancer development and progression. This is manifest by altered expression and/or activity of cell cycle related proteins. Constitutive activation of many signal transduction pathways also stimulates cell growth. Early steps in tumor development are associated with a fibrogenic response and the development of a hypoxic environment which favors the survival and proliferation of cancer stem cells. Part of the survival strategy of cancer stem cells may manifested by alterations in cell metabolism. Once tumors appear, growth and metastasis may be supported by overproduction of appropriate hormones (in hormonally dependent cancers), by promoting angiogenesis, by undergoing epithelial to mesenchymal transition, by triggering autophagy, and by taking cues from surrounding stromal cells. A number of natural compounds (e.g., curcumin, resveratrol, indole-3-carbinol, brassinin, sulforaphane, epigallocatechin-3-gallate, genistein, ellagitannins, lycopene and quercetin) have been found to inhibit one or more pathways that contribute to proliferation (e.g., hypoxia inducible factor 1, nuclear factor kappa B, phosphoinositide 3 kinase/Akt, insulin-like growth factor receptor 1, Wnt, cell cycle associated proteins, as well as androgen and estrogen receptor signaling). These data, in combination with bioinformatics analyses, will be very important for identifying signaling pathways and molecular targets that may provide early diagnostic markers and/or critical targets for the development of new drugs or drug combinations that block tumor formation and progression.

Gain-of-function p53 mutant with 21-bp deletion confers susceptibility to multidrug resistance in MCF-7 cells

The majority of p53 mutations, which are responsible for gain of oncogenic function, are missense mutations in hotspot codons. However, in our previous study, we demonstrated that a deletion spanning codons 127-133 in the p53 gene (designated as del p53) was detected in doxorubicin-resistant MCF-7 cell lines following various induction processes. In the present study, we aimed to investigate the role of del p53 and its association with the proliferation, metastasis and drug resistance of MCF-7 cells. The MCF-7/del p53 cell line is a representative of the del p53 stably expressed clones which were constructed by transfection of the del p53-containing construct into MCF-7/wt cells. Markers of multidrug resistance (MDR), epithelial-mesenchymal transition (EMT) and stem cell-like properties were examined in the MCF-7/del p53 cells. The results revealed that the MCF-7/del p53 cells expressed full-length p53 and del p53 mRNA and protein, as well as P-glycoprotein (P-gp). The MCF-7/del p53 cells acquired resistance to doxorubicin with increased P-gp efflux function. Using a transient expression assay, the mdr1 promoter was found to be significantly activated by external or integrated del p53 (P<0.001). The inhibition of nuclear factor (NF)-κB by cyclosporine sensitized the MCF-7/del p53 cells to doxorubicin toxicity. In addition, the morphological characteristics of the MCF-7/del p53 and MCF-7/adr were similar. EMT was observed in the MCF-7/del p53 cells as demonstrated by the presence of the mesenchymal markers, Slug and vimentin, and the decrease in the epithelial marker, cadherin 1, type 1, E-cadherin (CDH1), as well as an enhanced migration ability (P<0.001). Furthermore, the number of cells expressing the cancer stem cell-like marker, CD44, increased, accompanied by mammosphere formation. Taken together, these findings indicate that the expression of del p53 in MCF-7/del p53 cells enables the cells to partially acquire doxorubicin resistance characteristics of the MCF-7/adr cells. Thus, del p53 may be an important factor in non-invasive MCF-7 cells, activating NF-κB signaling and the mdr1 promoter and partially attributing to EMT; the cells thus acquire stem cell‑like properties, which facilitates drug resistance. Therefore, the 21-bp deletion of p53 may prove to be a therapeutic strategy with which to prevent cancer cells from acquiring resistance to drugs.

Suppression of invasion and metastasis of triple-negative breast cancer lines by pharmacological or genetic inhibition of slug activity

Most triple-negative breast cancers (TNBCs) exhibit gene expression patterns associated with epithelial-to-mesenchymal transition (EMT), a feature that correlates with a propensity for metastatic spread. Overexpression of the EMT regulator Slug is detected in basal and mesenchymal-type TNBCs and is associated with reduced E-cadherin expression and aggressive disease. The effects of Slug depend, in part, on the interaction of its N-terminal SNAG repressor domain with the chromatin-modifying protein lysine demethylase 1 (LSD1); thus, we investigated whether tranylcypromine [also known as trans-2-phenylcyclopropylamine hydrochloride (PCPA) or Parnate], an inhibitor of LSD1 that blocks its interaction with Slug, suppresses the migration, invasion, and metastatic spread of TNBC cell lines. We show here that PCPA treatment induces the expression of E-cadherin and other epithelial markers and markedly suppresses migration and invasion of TNBC cell lines MDA-MB-231 and BT-549. These effects were phenocopied by Slug or LSD1 silencing. In two models of orthotopic breast cancer, PCPA treatment reduced local tumor growth and the number of lung metastases. In mice injected directly in the blood circulation with MDA-MB-231 cells, PCPA treatment or Slug silencing markedly inhibited bone metastases but had no effect on lung infiltration. Thus, blocking Slug activity may suppress the metastatic spread of TNBC and, perhaps, specifically inhibit homing/colonization to the bone.

C-kit induces epithelial-mesenchymal transition and contributes to salivary adenoid cystic cancer progression

Epithelial-mesenchymal transition (EMT) is associated with salivary adenoid cystic cancer (ACC) progression and metastasis. Here, we report that ectopic overexpression of c-kit in ACC cell lines is sufficient for acquisition of mesenchymal traits, enhanced cell invasion, along with stem cell properties defined by the presence of a CD133+/CD44+ cell subpopulation. c-kit positively regulated expression of known EMT inducers, also activating TGF-β to contribute to EMT. c-kit itself was induced by TGF-β in ACC cell lines and required for TGF-β-induced EMT. Xenograft experiments showed that c-kit cooperated with oncogenic Ras to promote tumorigenesis in vivo. Finally, in human specimens of ACC, we found that c-kit was abnormally overexpressed and correlated with the prognosis of ACC. Our findings define an important function for c-kit in ACC progression by orchestrating EMT, and they implicate this gene product as a marker of poor prognosis in this disease.

CK2α, over-expressed in human malignant pleural mesothelioma, regulates the Hedgehog signaling pathway in mesothelioma cells

Background

The Hedgehog (Hh) signaling pathway has been implicated in stem cell maintenance and its activation is aberrant in several types of cancer including mesothelioma. Protein kinase CK2 affects several cell signaling pathways through the mechanism of phosphorylation.

Methods

Protein and mRNA levels of CK2α and Gli1 were tested by quantitative RT-PCR and immunohistochemistry staining in mesothelioma samples and cell lines. Down-regulated Gli1 expression and transcriptional activity were demonstrated by RT-PCR, Western blot and luciferase reporter assay.

Results

In this study, we show that CK2α is over-expressed and a positive regulator of Hegdehog/Gli1 signaling in human malignant pleural mesothelioma. First of all, we found that the mRNA levels of CK2α and Gli1 were broadly elevated and correlated (n = 52, r = 0.401, P < 0.05), compared with LP9 (a normal mesothelial cell line). We then investigated their expression at the protein level, and found that all the 7 mesothelioma cell lines tested showed positive staining in CK2α and Gli1 immunohistochemistry. Correlation analysis by Pearson test for CK2α and Gli1 expression in the 75 mesothelioma tumors and the 7 mesothelioma cell lines showed that the two protein expression was significantly correlated (n = 82, r = 0.554, P < 0.01). Furthermore, we demonstrated that Gli1 expression and transcriptional activity were down-regulated after CK2α was silenced in two mesothelioma cell lines (H28 and H2052). CK2α siRNA also down-regulated the expression of Hh target genes in these cell lines. Moreover, treatment with a small-molecule CK2α inhibitor CX-4945 led to dose-dependent inhibition of Gli1 expression and transcriptional activity. Conversely, forced over-expression of CK2α resulted in an increase in Gli1 transcriptional activity in H28 cells.

Conclusions

Thus, we report for the first time that over-expressed CK2α positively regulate Hh/Gli1 signaling in human mesothelioma.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-014-0093-6) contains supplementary material, which is available to authorized users.

Expression of acidosis-dependent genes in human cancer nests

Previous studies investigating cancer cells cultured at acidic pH have shown that the expression level of ~700 genes were more than two-fold higher than those of the cells cultured in alkaline medium at pH 7.5. The aim of the present study was to confirm whether these acidosis-induced genes are expressed in human cancer tissues. Therefore, 7 genes were selected from our previous study, which encoded interleukin 32 (IL-32), lysosomal H⁺ transporting ATPase, V0 subunit d2 (ATP6V0D2), tumor necrosis factor receptor superfamily, member 9 (TNFRSF9), amphiregulin, schwannoma-derived growth factor (AREG), v-erb-b2 erythroblastic leukemia viral oncogene homolog 3 (ErbB3), PRR5-ARHGAP8 (LOC553158) and dimethylglycine dehydrogenase (DMGDH), and their expression was examined in human clinical specimens from patients with cancer. In addition, the expression of the gene encoding manganese superoxide dismutase (MnSOD) was examined. The specimens from patients with colon, stomach and renal cancer showed increased MnSOD, IL-32, and TNFRSF9 transcripts compared to those from non-tumorous regions of the same patients. Notably, an elevated expression of ATP6V0D2 was found in the specimens from patients with stomach cancer, whereas the expression was decreased in those from patients with colon and renal cancer. The expression of LOC553158 was upregulated in colon and stomach cancer specimens. These results indicate that the investigation of gene expression under acidic conditions is useful for the development of novel cancer markers and/or chemotherapeutic targets.

Repression of c-Kit by p53 is mediated by miR-34 and is associated with reduced chemoresistance, migration and stemness

The c-Kit receptor tyrosine kinase is commonly over-expressed in different types of cancer. p53 activation is known to result in the down-regulation of c-Kit. However, the underlying mechanism has remained unknown. Here, we show that the p53-induced miR-34 microRNA family mediates repression of c-Kit by p53 via a conserved seed-matching sequence in the c-Kit 3'-UTR. Ectopic miR-34a resulted in a decrease in Erk signaling and transformation, which was dependent on the down-regulation of c-Kit expression. Furthermore, ectopic expression of c-Kit conferred resistance of colorectal cancer (CRC) cells to treatment with 5-fluorouracil (5-FU), whereas ectopic miR-34a sensitized the cells to 5-FU. After stimulation with c-Kit ligand/stem cell factor (SCF) Colo320 CRC cells displayed increased migration/invasion, whereas ectopic miR-34a inhibited SCF-induced migration/invasion. Activation of a conditional c-Kit allele induced several stemness markers in DLD-1 CRC cells. In primary CRC samples elevated c-Kit expression also showed a positive correlation with markers of stemness, such as Lgr5, CD44, OLFM4, BMI-1 and β-catenin. On the contrary, activation of a conditional miR-34a allele in DLD-1 cells diminished the expression of c-Kit and several stemness markers (CD44, Lgr5 and BMI-1) and suppressed sphere formation. MiR-34a also suppressed enhanced sphere-formation after exposure to SCF. Taken together, our data establish c-Kit as a new direct target of miR-34 and demonstrate that this regulation interferes with several c-Kit-mediated effects on cancer cells. Therefore, this regulation may be potentially relevant for future diagnostic and therapeutic approaches.

Synergistic inhibition of lung cancer cell invasion, tumor growth and angiogenesis using aptamer-siRNA chimeras

Early metastasis is one of the major causes of mortality among patient with lung cancer. The process of tumor metastasis involves a cascade of events, including epithelial-mesenchymal transition, tumor cell migration and invasion, and angiogenesis. To specifically suppress tumor invasion and angiogenesis, two nucleolin aptamer-siRNA chimeras (aptNCL-SLUGsiR and aptNCL-NRP1siR) were used to block key signaling pathways involved in lung cancer metastasis that are pivotal to metastatic tumor cells but not to normal cells under ordinary physiologic conditions. Through nucleolin-mediated endocytosis, the aptNCL-siRNA chimeras specifically and significantly knocked down the expressions of SLUG and NRP1 in nucleolin-expressing cancer cells. Furthermore, simultaneous suppression of SLUG and NRP1 expressions by the chimeras synergistically retarded cancer cell motility and invasive ability. The synergistic effect was also observed in a xenograft mouse model, wherein the combined treatment using two chimeras suppressed tumor growth, the invasiveness, circulating tumor cell amount, and angiogenesis in tumor tissue without affecting liver and kidney functions. This study demonstrates that combined treatment of aptNCL-SLUGsiR and aptNCL-NRP1siR can synergistically suppress lung cancer cell invasion, tumor growth and angiogenesis by cancer-specific targeting combined with gene-specific silencing.

Increased expression of Slug and Vimentin as novel predictive biomarkers for lymph node metastasis and poor prognosis in colorectal cancer

Slug and Vimentin genes play a critical role in regulating epithelial-mesenchymal transition (EMT) via downregulation of epithelial markers and upregulation of mesenchymal markers. The present study evaluated the clinical significance of Slug and Vimentin expression as potential disease biomarkers in colorectal cancer (CRC). At first, the biological role of Slug in CRC was assessed by RNA interference in CRC cell lines to assess tumor progression, invasion and migration. Next, we analyzed Slug and Vimentin expression in surgical tissue specimens from 181 CRC patients (Cohort 1) by quantitative real-time reverse transcription-PCR and 208 patients (Cohort 2) by immunohistochemistry. Knockdown of Slug using small interfering RNA in CRC cell lines resulted in inhibition of EMT, reduced cell proliferation, invasion and migration in CRC cells. Interestingly, Slug and Vimentin expression in cancer tissues was significantly higher in patients with higher T stage, lymph node involvement, liver metastasis and advanced tumor node metastasis stages. A significant correlation was observed between Slug and Vimentin expression in CRC (messenger RNA: ρ = 0.546, protein: ρ = 0.405), and increased expression of Slug and Vimentin was significantly associated with poor prognosis. Furthermore, increased expression of Slug emerged as an independent prognostic factor and a predictive marker of lymph node metastasis in CRC patients. Our data provide novel evidence for the biological and clinical significance of Slug and Vimentin expression as potential predictive biomarkers for identifying patients with lymph node metastasis or poor prognosis in CRC.

Gremlin-1 associates with fibrillin microfibrils in vivo and regulates mesothelioma cell survival through transcription factor slug

Malignant mesothelioma is a form of cancer that is highly resistant to conventional cancer therapy for which no major therapeutic advances have been introduced. Here, we identify gremlin-1, a known bone morphogenetic protein inhibitor crucial for embryonic development, as a potential therapeutic target for mesothelioma. We found high expression levels of gremlin-1 in the mesothelioma tumor tissue, as well as in primary mesothelioma cells cultured from pleural effusion samples. Downregulation of gremlin-1 expression by siRNA-mediated silencing in a mesothelioma cell line inhibited cell proliferation. This was associated with downregulation of the transcription factor slug as well as mesenchymal proteins linked to cancer epithelial-to-mesenchymal transition. Further, resistance to paclitaxel-induced cell death was associated with high gremlin-1 and slug expression. Treatment of gremlin-1-silenced mesothelioma cells with paclitaxel or pemetrexed resulted in efficient loss of cell survival. Finally, our data suggest that concomitant upregulation of fibrillin-2 in mesothelioma provides a mechanism for extracellular localization of gremlin-1 to the tumor microenvironment. This was supported by the demonstration of interactions between gremlin-1, and fibrillin-1 and -2 peptides as well as by colocalization of gremlin-1 to fibrillin microfibrils in cells and tumor tissue samples. Our data suggest that gremlin-1 is also a potential target for overcoming drug resistance in mesothelioma.

KISS1R induces invasiveness of estrogen receptor-negative human mammary epithelial and breast cancer cells

Kisspeptins (KPs), peptide products of the KISS1 metastasis-suppressor gene, are endogenous ligands for a G protein-coupled receptor (KISS1R). KISS1 acts as a metastasis suppressor in numerous human cancers. However, recent studies have demonstrated that an increase in KISS1 and KISS1R expression in patient breast tumors correlates with higher tumor grade and metastatic potential. We have shown that KP-10 stimulates invasion of estrogen receptor α (ERα)-negative MDA-MB-231 breast cancer cells via transactivation of the epidermal growth factor receptor (EGFR). Here, we report that either KP-10 treatment of ERα-negative nonmalignant mammary epithelial MCF10A cells or expression of KISS1R in MCF10A cells induced a mesenchymal phenotype and stimulated invasiveness. Similarly, exogenous expression of KISS1R in ERα-negative SKBR3 breast cancer cells was sufficient to trigger invasion and induced extravasation in vivo. In contrast, KP-10 failed to transactivate EGFR or stimulate invasiveness in the ERα-positive MCF7 and T47D breast cancer cells. This suggested that ERα negatively regulates KISS1R-dependent breast cancer cell migration, invasion, and EGFR transactivation. In support of this, we found that these KP-10-induced effects were ablated upon exogenous expression of ERα in the MDA-MB-231 cells, by down-regulating KISS1R expression. Lastly, we have identified IQGAP1, an actin cytoskeletal binding protein as a novel binding partner of KISS1R, and have shown that KISS1R regulates EGFR transactivation in breast cancer cells in an IQGAP1-dependent manner. Overall, our data strongly suggest that the ERα status of mammary cells dictates whether KISS1R may be a novel clinical target for treating breast cancer metastasis.

The role of aldehyde dehydrogenase (ALDH) in cancer drug resistance

Chemotherapy in cancer patients is still not satisfactory because of drug resistance. The main mechanism of drug resistance results from the ability of cancer cells to actively expel therapeutic agents via transport proteins of the ABC family. ABCB1 and ABCG2 are the two main proteins responsible for drug resistance in cancers. Recent investigations indicate that aldehyde dehydrogenase (ALDH) can also be involved in drug resistance. Expression of the ABC transporters and ALDH enzymes is observed in normal stem cells, cancer stem cells and drug resistant cancers. Current chemotherapy regimens remove the bulk of the tumour but are usually not effective against cancer stem cells (CSCs) expressing ALDH. As a result, the number of ALDH positive drug resistant CSCs increases after chemotherapy. This indicates that therapies targeting drug resistant CSCs should be developed. A number of therapies targeting CSCs are currently under investigation. These therapies include differentiation therapy using different retinoic acids (RA) as simple agents or in combination with DNA methyltransferase inhibitors (DNMTi) and/or histone deacetylase inhibitors (HDACi). Therapies that target cancer stem cell signaling pathways are also under investigation. A number of natural compounds are effective against cancer stem cells and lead to decreasing numbers of ALDH positive cells and downregulation of the ABC proteins. Combinations of differentiation therapies or therapies targeting CSC signaling pathways with classical cytostatics seem promising. This review discusses the role of ALDH and ABC proteins in the development of drug resistance in cancer and current therapies designed to target CSCs.

CD117 expression in operable oesophageal squamous cell carcinomas predicts worse clinical outcome

Aims

To investigate the aberrant expression of CD117 in oesophageal squamous cell carcinoma (SCC) and its prognostic significance.

Methods and results

Immunohistochemical staining for CD117 was performed on tissue microarray and routine tissue sections from 157 oesophageal SCC patients and 10 normal oesophageal epithelia adjacent to tumour. The positive rate of CD117 expression was 29.9% in oesophageal SCC tissues, whereas no CD117 expression was detected in the 10 normal oesophageal epithelia. CD117 expression was significantly associated with T stage (P < 0.001), distant metastasis (P = 0.015), lymph node metastasis (P = 0.019), and clinical stage (P = 0.021). Progression-free survival in the patients with CD117-positive tumours was shorter than that in the patients with CD117-negative tumours (P = 0.010). In univariate analyses, CD117 expression was the most significant factor for overall survival of oesophageal SCC patients (P < 0.001), followed by lymph node metastasis (P = 0.001), T stage (P = 0.002), clinical stage (P = 0.006), distant metastasis (P = 0.020), and histological grade (P = 0.027). Multivariate analyses verified that CD117 expression was an independent prognostic marker for oesophageal SCC patients (P = 0.002). In addition, CD117 expression predicted poorer survival in patients without distant metastases.

Conclusions

CD117 expression in operable oesophageal SCC may be a valuable prognostic marker, and detection of its expression in clinical samples may be useful in defining a subclass of oesophageal SCCs with extremely poor clinical outcome, which may require a specially targeted treatment modality.

SLUG is activated by nuclear factor kappa B and confers human alveolar epithelial A549 cells resistance to tumor necrosis factor-alpha-induced apoptosis

BACKGROUND

The role of tumor necrosis factor alpha (TNF-α) in cancer is complex with both apoptotic and anti-apoptotic roles proposed. However the mechanism is not clear. In the study, we designed to investigate the effect of TNF-α on the activation and expression of nuclear factor kappa B (NF-κB)/p65/SLUG/PUMA/Bcl-2 levels in human lung cancer A549 cell line, and in conditions of TNF-α-induced apoptosis.

METHODS

We have engineered three A549 cell lines that were transiently transfected with PUMA siRNA, SLUG siRNA and Bcl-2 siRNA, respectively. We have measured the in vitro effects of siRNA on apoptosis, and sensitivity to 20 ng/ml of TNF-α treatment for 24-48 h.

RESULTS

We found the NF-κB activity and PUMA mRNA/protein was significantly increased after treatment of TNF-α for 24 h in untreated A549 cells, and led to a significant increase in TNF-α-induced apoptosis, no significant increase of SLUG and Bcl-2 level was shown. However, after treatment of TNF-α for 48 h in untreated A549 cells, SLUG and Bcl-2 level was significant increased, and PUMA level was significant decreased, and TNF-α-induced apoptosis was significantly decreased compared to the apoptosis level after treatment of TNF-α for 24 h. Inhibition of the NF-κB activity could effectively decrease the PUMA level and increase the SLUG and Bcl-2 level. PUMA silencing by siRNA led to a significant decrease in TNF-α-induced apoptosis after treatment of TNF-α for 24 h. Bcl-2 and SLUG silencing by siRNA led to a significant increase in TNF-α-induced apoptosis for 48 h. Furthermore, SLUG silencing increased PUMA level and decreased Bcl-2 level.

CONCLUSIONS

The findings suggested that TNF-α treatment promoted apoptosis via the NF-κB-dependent PUMA pathway. The anti-apoptotic role of TNF-α was via NF-κB-dependent SLUG and Bcl-2 pathway at a later time.

Epithelial mesenchymal transition is required for acquisition of anoikis resistance and metastatic potential in adenoid cystic carcinoma

Human adenoid cystic carcinoma (ACC) is characterized by diffused invasion of the tumor into adjacent organs and early distant metastasis. Anoikis resistance and epithelial mesenchymal transition (EMT) are considered prerequisites for cancer cells to metastasize. Exploring the relationship between these processes and their underlying mechanism of action is a promising way to better understand ACC tumors. We initially established anoikis-resistant sublines of ACC cells; the variant cells revealed a mesenchymal phenotype through Slug-mediated EMT-like transformation and displayed enhanced metastatic potential both in vitro and in vivo. Suppression of EMT by knockdown of Slug significantly impaired anoikis resistance, migration, and invasion of the variant cells. With overexpression of Slug and Twist, we determined that induction of EMT in normal ACC cells could prevent anoikis, albeit partially. These findings strongly suggest that EMT is indispensable in anoikis resistance, at least in ACC cells. Furthermore, we found that the EGFR/PI3K/Akt pathway acts as the common regulator for EMT-like transformation and anoikis resistance, as confirmed by their specific inhibitors. Gefitinib and LY294003 restored the sensibilities of anoikis-resistant cells to anoikis and simultaneously impaired their metastatic potential. In addition, the results from our in vivo model of metastasis suggest that pretreatment with gefitinib promotes mouse survival by alleviating pulmonary metastasis. Most importantly, immunohistochemistry of human ACC specimens showed a correlation between the overexpression of Slug and EGFR staining. This study has demonstrated that Slug-mediated EMT-like transformation is required by human ACC cells to achieve anoikis resistance and their metastatic potential. Targeting the EGFR/PI3K/Akt pathway holds potential as a preventive strategy against distant metastasis of ACC.

Inhibiting interactions of lysine demethylase LSD1 with snail/slug blocks cancer cell invasion

The process of epithelial-mesenchymal transition (EMT) which is required for cancer cell invasion is regulated by a family of E-box-binding transcription repressors, which include Snail (SNAIL1) and Slug (SNAI2). Snail appears to repress the expression of the EMT marker E-cadherin by epigenetic mechanisms dependent on the interaction of its N-terminal SNAG domain with chromatin-modifying proteins including lysine-specific demethylase 1 (LSD1/KDM1A). We assessed whether blocking Snail/Slug-LSD1 interaction by treatment with Parnate, an enzymatic inhibitor of LSD1, or TAT-SNAG, a cell-permeable peptide corresponding to the SNAG domain of Slug, suppresses the motility and invasiveness of cancer cells of different origin and genetic background. We show here that either treatment blocked Slug-dependent repression of the E-cadherin promoter and inhibited the motility and invasion of tumor cell lines without any effect on their proliferation. These effects correlated with induction of epithelial and repression of mesenchymal markers and were phenocopied by LSD1 or Slug downregulation. Parnate treatment also inhibited bone marrow homing/engraftment of Slug-expressing K562 cells. Together, these studies support the concept that targeting Snail/Slug-dependent transcription repression complexes may lead to the development of novel drugs selectively inhibiting the invasive potential of cancer cells.

EMT-activating transcription factors in cancer: beyond EMT and tumor invasiveness

Cancer is a complex multistep process involving genetic and epigenetic changes that eventually result in the activation of oncogenic pathways and/or inactivation of tumor suppressor signals. During cancer progression, cancer cells acquire a number of hallmarks that promote tumor growth and invasion. A crucial mechanism by which carcinoma cells enhance their invasive capacity is the dissolution of intercellular adhesions and the acquisition of a more motile mesenchymal phenotype as part of an epithelial-to-mesenchymal transition (EMT). Although many transcription factors can trigger it, the full molecular reprogramming occurring during an EMT is mainly orchestrated by three major groups of transcription factors: the ZEB, Snail and Twist families. Upregulated expression of these EMT-activating transcription factors (EMT-ATFs) promotes tumor invasiveness in cell lines and xenograft mice models and has been associated with poor clinical prognosis in human cancers. Evidence accumulated in the last few years indicates that EMT-ATFs also regulate an expanding set of cancer cell capabilities beyond tumor invasion. Thus, EMT-ATFs have been shown to cooperate in oncogenic transformation, regulate cancer cell stemness, override safeguard programs against cancer like apoptosis and senescence, determine resistance to chemotherapy and promote tumor angiogenesis. This article reviews the expanding portfolio of functions played by EMT-ATFs in cancer progression.

Functional regulation of Slug/Snail2 is dependent on GSK-3β-mediated phosphorylation

Snail family proteins regulate transcription of molecules for cell-cell adhesion during epithelial-mesenchymal transition (EMT). Based on putative glycogen synthase kinase 3β (GSK-3β) phosphorylation sites within the Slug/Snail2, we explored the significance of GSK-3β-mediated phosphorylation in Slug/Snail2 expression during EMT. Mutation of the putative GSK-3β phosphorylation sites (S92/96A or S100/104A) enhanced the Slug/Snail2-mediated EMT properties of E-cadherin repression and vimentin induction, compared with wild-type Slug/Snail2. S92/96A mutation inhibited degradation of Slug/Snail2 and S100/104A mutation extended nuclear stabilization. Inhibition of GSK-3β activity caused similar effects, as did the phosphorylation mutations. Thus, our study suggests that GSK-3β-mediated phosphorylation of Slug/Snail2 controls its turnover and localization during EMT.

Ovarian cancer cells with the CD117 phenotype are highly tumorigenic and are related to chemotherapy outcome

Cancer stem cells (CSCs) play an important role in the recurrence and drug resistance of cancer. Isolation and characterization of CSCs from ovarian cancer samples may help to provide novel diagnostic and therapeutic targets in the management of recurrent disease and drug resistance in ovarian cancer. Here, we developed a xenograft model in which cells from 14 samples of human ovarian serous adenocarcinoma tissue or ascites were implanted in immunodeficient mice to test the tumorigenic potential of different populations of ovarian cancer cells. We identified and isolated the tumorigenic cells as CD117(+)Lineage(-) from three different xenografts. As few as 10(3) cells with the CD117(+)Lineage(-) phenotype, which comprise <2% of the xenograft tumor cells, were able to regenerate tumors in a mouse model, a 100-fold increase in tumorigenic potential compared to CD117(-)Lineage(-) cells. The tumors that arose from purified CD117(+)Lineage(-) cells reproduced the original tumor heterogeneity and could be serially generated, demonstrating the ability to self-renew and to differentiate, two defining properties of stem cells. Furthermore, immunohistochemistry analysis of 25 patients with advanced ovarian serous adenocarcinoma revealed positive immunostaining for CD117 in 40% (10 of 25) of patients. CD117 expression was statistically correlated with resistance to conventional chemotherapy (P=0.027). In conclusion, our study demonstrates that human ovarian cancer cells with the CD117(+) phenotype possess the unique properties of CSCs, including self-renewal, differentiation, a high tumorigenic potential, and chemoresistance. Future studies designed to target CD117(+) cancer cells may identify more attractive and effective therapies for treatment of ovarian cancer.

RNA interference targeting slug increases cholangiocarcinoma cell sensitivity to cisplatin via upregulating PUMA

Slug is an E-cadherin repressor and a suppressor of PUMA (p53 upregulated modulator of apoptosis) and it has recently been demonstrated that Slug plays an important role in controlling apoptosis. In this study, we examined whether Slug's ability to silence expression suppresses the growth of cholangiocarcinoma cells and/or sensitizes cholangiocarcinoma cells to chemotherapeutic agents through induction of apoptosis. We targeted the Slug gene using siRNA (Slug siRNA) via full Slug cDNA plasmid (Slug cDNA) transfection of cholangiocarcinoma cells. Slug siRNA, cisplatin, or Slug siRNA in combination with cisplatin, were used to treat cholangiocarcinoma cells in vitro. Western blot was used to detect the expression of Slug, PUMA, and E-cadherin protein. TUNEL, Annexin V Staining, and cell cycle analysis were used to detect apoptosis. A nude mice subcutaneous xenograft model of QBC939 cells was used to assess the effect of Slug silencing and/or cisplatin on tumor growth. Immunohistochemical staining was used to analyze the expression of Slug and PUMA. TUNEL was used to detect apoptosis in vivo. The results showed that PUMA and E-cadherin expression in cholangiocarcinoma cells is Slug dependent. We demonstrated that Slug silencing and cisplatin both promote apoptosis by upregulation of PUMA, not by upregulation of E-cadherin. Slug silencing significantly sensitized cholangiocarcinoma cells to cisplatin through upregulation of PUMA. Finally, we showed that Slug silencing suppressed the growth of QBC939 xenograft tumors and sensitized the tumor cells to cisplatin through PUMA upregulation and induction of apoptosis. Our findings indicate that Slug is an important modulator of the therapeutic response of cholangiocarcinoma cells and is potentially useful as a sensitizer in cholangiocarcinoma therapy. One of the mechanisms is the regulation of PUMA by Slug.

Inhibition of KIT RNAi mediated with adenovirus in gastrointestinal stromal tumor xenograft

AIM: To investigate a therapeutic method for gastrointestinal stromal tumor (GIST) based on KIT RNA interference (RNAi) with AdMax adenovirus.

METHODS: KIT short hairpin RNA (shRNA), whose lateral sides were decorated with restriction endonuclease sequences, was designed. T₄ DNA ligase catalyzed the joint of the KIT shRNA and the green fluorescent protein-containing PDC316-EGFP-U6 to form PDC316-EGFP-U6-KIT. Homologous recombination of AdEGFP-U6-KIT was performed with the AdMax system. Heterotopically transplanted GISTs were established in nude mice. AdEGFP-U6-KIT was intratumorally injected. The volume, inhibition ratio of tumor and CD117 expression of GIST graft tumor in nude mice were compared between test and control groups.

RESULTS: The length of KIT shRNA was determined to be about 50bp by agarose electrophoresis. Gene sequencing detected the designed KIT RNAi sequence in PDC316-EGFP-U6-KIT. After transfection with AdEGFP-U6-KIT, 293 cells displayed green fluorescence. The physical and infective titers of AdEGFP-U6-KIT were 5 × 10¹¹ viral particles/mL and 5.67 × 10⁷ plaque forming units/mL, respectively. The mean volume of the grafted tumor was significantly smaller in test mice than in control mice (75.3 ± 22.9 mm³vs 988.6 ± 30.5 mm³, t = -18.132, P < 0.05). The inhibition ratio of the tumors was 59.6% in the test group. CD117 positive expression was evident in two cases (20%) in the test group and 10 cases (100%) in the control group (χ² = 10.2083, P < 0.005).

CONCLUSION: AdEGFP-U6-KIT is successfully constructed, and KIT RNAi mediated with Admax vector system can effectively inhibit the expression of the KIT gene and the growth of GIST in nude mice.

Expression of Slug is regulated by c-Myb and is required for invasion and bone marrow homing of cancer cells of different origin

In metastatic cancer cells, the process of invasion is regulated by several transcription factors that induce changes required for migration and resistance to apoptosis. Slug (SNAI2, Snail2) is involved in epithelial mesenchymal transition in physiological and in pathological contexts. We show here that in embryonic kidney, colon carcinoma, chronic myeloid leukemia-blast crisis, and in neuroblastoma cells, expression of Slug is transcriptionally regulated by c-Myb via Myb binding sites in the 5'-flanking region and in the first intron of the slug gene. In embryonic kidney and neuroblastoma cells, c-Myb induced vimentin, fibronectin, and N-cadherin expression and membrane ruffling via actin polymerization consistent with the acquisition of a mesenchymal-like phenotype. Furthermore, down-regulation of endogenous c-Myb levels in colon carcinoma cells led to increased expression of E-cadherin and reduced levels of vimentin. Some of these changes are predominantly Slug-dependent as Slug silencing via RNA interference (RNAi) reverts the cells to a quasi-parental condition. Changes in gene expression and morphology induced by c-Myb-activated Slug correlated with increased ability to migrate (embryonic kidney) and to invade through a Matrigel membrane (embryonic kidney, colon carcinoma, neuroblastoma). c-Myb-dependent Slug expression was also essential for the homing of chronic myeloid leukemia K562 cells to the bone marrow. In summary, we show here that the proto-oncogene c-Myb controls Slug transcription in tumor cells of different origin. Such a regulatory pathway contributes to the acquisition of invasive properties that are important for the metastatic process.

Slug suppression induces apoptosis via Puma transactivation in rheumatoid arthritis fibroblast-like synoviocytes treated with hydrogen peroxide

Inadequate apoptosis contributes to synovial hyperplasia in rheumatoid arthritis (RA). Recent study shows that low expression of Puma might be partially responsible for the decreased apoptosis of fibroblast-like synoviocytes (FLS). Slug, a highly conserved zinc finger transcriptional repressor, is known to antagonize apoptosis of hematopoietic progenitor cells by repressing Puma transactivation. In this study, we examined the expression and function of Slug in RA FLS. Slug mRNA expression was measured in the synovial tissue (ST) and FLS obtained from RA and osteoarthritis patients. Slug and Puma mRNA expression in FLS by apoptotic stimuli were measured by real-time PCR analysis. FLS were transfected with control siRNA or Slug siRNA. Apoptosis was quantified by trypan blue exclusion, DNA fragmentation and caspase-3 assay. RA ST expressed higher level of Slug mRNA compared with osteoarthritis ST. Slug was significantly induced by hydrogen peroxide (H2O2) but not by exogenous p53 in RA FLS. Puma induction by H2O2 stimulation was significantly higher in Slug siRNA-transfected FLS compared with control siRNA-transfected FLS. After H2O2 stimulation, viable cell number was significantly lower in Slug siRNA-transfected FLS compared with control siRNA-transfected FLS. Apoptosis enhancing effect of Slug siRNA was further confirmed by ELISA that detects cytoplasmic histone-associated DNA fragments and caspase-3 assay. These data demonstrate that Slug is overexpressed in RA ST and that suppression of Slug gene facilitates apoptosis of FLS by increasing Puma transactivation. Slug may therefore represent a potential therapeutic target in RA.

Zinc-finger transcription factor slug contributes to the survival advantage of chronic myeloid leukemia cells

Slug, a Snail-related zinc-finger transcription factor implicated in the increased motility of mesenchymal cells during embryonic development and progression of cancer cells towards an invasive phenotype, plays a specific and critical role in the pathogenesis of Bcr-Abl-associated leukemias. Here we report that Slug over-expression associated with Bcr-Abl is conditional upon the tyrosine kinase (TK) activity of 210 fusion protein. Slug over-expression is driven by transcriptional events eventually integrated by post-transcriptional mechanisms leading to protein stabilization and is at least partly regulated by the ERK1/2 mitogen-activated protein kinase (MAPK). It contributes to apoptosis resistance of leukemic progenitors through the repression of pro-apoptotic Puma. Moreover, Slug is a component of leukemic progenitor resistance to imatinib mesylate (IM) driven by Bcr-Abl point mutations and, in particular, by T315I. Slug over-expression associated with p210 Bcr-Abl TK either in the wild type (wt) or mutated conformation results in a significant reduction of E-cadherin, the substrate of Beta catenin at cell membranes. In conclusion, our results suggest that Slug has a central role in a complex network involved in prolonged survival and IM resistance of CML progenitors.

ERalpha signaling through slug regulates E-cadherin and EMT

The ERalpha signaling pathway is one of the most important and most studied pathways in human breast cancer, yet numerous questions still exist such as how hormonally responsive cancers progress to a more aggressive and hormonally independent phenotype. We have noted that human breast cancers exhibit a strong direct correlation between ERalpha and E-cadherin expression by immunohistochemistry, suggesting that ERalpha signaling might regulate E-cadherin and implying that this regulation might influence epithelial-mesenchymal transition (EMT) and tumor progression. To investigate this hypothesis and the mechanisms behind it, we studied the effects of ERalpha signaling in ERalpha-transfected ERalpha-negative breast carcinoma cell lines, the MDA-MB-468 and the MDA-MB-231 and the effects of ERalpha knockdown in naturally expressing ERalpha-positive lines, MCF-7 and T47D. When ERalpha was overexpressed in the ERalpha-negative lines, 17beta-estradiol (E2) decreased slug and increased E-cadherin. Clones maximally exhibiting these changes grew more in clumps and became less invasive in Matrigel. When ERalpha was knocked down in the ERalpha-positive lines, slug increased, E-cadherin decreased, cells became spindly and exhibited increased Matrigel invasion. ERalpha signaling decreased slug expression by two different mechanisms: directly, by repression of slug transcription by the formation of a corepressor complex of ligand-activated ERalpha, HDAC inhibitor (HDAC1), and nuclear receptor corepressor (N-CoR) that bound the slug promoter in three half-site estrogen response elements (EREs); indirectly by phosphorylation and inactivation of GSK-3beta through phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt). The GSK-3beta inactivation, in turn, repressed slug expression and increased E-cadherin. In human breast cancer cases, there was a strong inverse correlation between slug and ERalpha and E-cadherin immunoreactivity. Our findings indicate that ERalpha signaling through slug regulates E-cadherin and EMT.

Extracellular signal-regulated kinase signaling pathway regulates breast cancer cell migration by maintaining slug expression

Cell migration is a critical step in cancer cell invasion. Recent studies have implicated the importance of the extracellular signal-regulated kinase (ERK) signaling pathway in cancer cell migration. However, the mechanism associated with ERK-regulated cell migration is poorly understood. Using a panel of breast cancer cell lines, we detected an excellent correlation between ERK activity and cell migration. Interestingly, we noticed that a 48-hour treatment with U0126 [specific mitogen-activated protein/ERK kinase (MEK)-1/2 inhibitor] was needed to significantly inhibit breast cancer cell migration, whereas this inhibitor blocked ERK activity within 1 hour. This observation suggests that ERK-dependent gene expression, rather than direct ERK signaling, is essential for cell migration. With further study, we found that ERK activity promoted the expression of the activator protein-1 (AP1) components Fra-1 and c-Jun, both of which were necessary for cell migration. Combination of U0126 treatment and Fra-1/c-Jun knockdown did not yield further reduction in cell migration than either alone, indicating that ERKs and Fra-1/c-Jun act by the same mechanism to facilitate cell migration. In an attempt to investigate the role of Fra-1/c-Jun in cell migration, we found that the ERK-Fra-1/c-Jun axis regulated slug expression in an AP1-dependent manner. Moreover, the occurrence of U0126-induced migratory inhibition coincided with slug reduction, and silencing slug expression abrogated breast cancer cell migration. These results suggest an association between ERK-regulated cell migration and slug expression. Indeed, cell migration was not significantly inhibited by U0126 treatment or Fra-1/c-Jun silencing in cells expressing slug transgene. Our study suggests that the ERK pathway regulates breast cancer cell migration by maintaining slug expression.

Effect of PTTG on endogenous gene expression in HEK 293 cells

Background

Pituitary tumor transforming gene (PTTG), also known as securin, is highly expressed in various tumors including pituitary, thyroid, colon, ovary, testis, lung, and breast. An overexpression of PTTG enhances cell proliferation, induces cellular transformation in vitro, and promotes tumor development in nude mice. PTTG also inhibits separation of sister chromatids leading to aneuploidy and genetic instability. A great amount of work has been undertaken to understand the biology of PTTG and its expression in various tumors. However, mechanisms by which PTTG mediates its tumorigenic function are not fully understood. To utilize this gene for cancer therapy, identification of the downstream signaling genes regulated by PTTG in mediation of its tumorigenic function is necessary. For this purpose, we expressed PTTG in human embryonic kidney (HEK293) cells that do not express PTTG and analyzed the downstream genes using microarray analysis.

Results

A total of 22,277 genes printed on an Affymetrix HG-U133A 2.0 GeneChip™ array were screened with labeled cRNA prepared from HEK293 cells infected with adenovirus vector expressing PTTG cDNA (AdPTTG cDNA) and compared with labeled cRNA prepared from HEK293 cells infected with control adenovirus (control Ad) or adenovirus vector expressing GFP (AdGFP). Out of 22,277 genes, 71 genes were down-regulated and 35 genes were up-regulated with an FDR corrected p-value of ≤ 0.05 and a fold change of ≥2. Most of the altered genes identified are involved in the cell cycle and cell apoptosis; a few are involved in mRNA processing and nitrogen metabolism. Most of the up-regulated genes belong to the histone protein family.

Conclusion

PTTG is a well-studied oncogene for its role in tumorigenesis. In addition to its importance in regulation of the cell cycle, this gene has also been recently shown to play a role in the induction of cell apoptosis. The microarray analysis in the present study demonstrated that PTTG may induce apoptosis by down-regulation of oncogenes such as v-Jun and v-maf and up-regulation of the histone family of genes.

Sorafenib inhibits ERK1/2 and MCL-1(L) phosphorylation levels resulting in caspase-independent cell death in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive, rapidly progressive malignancy without effective therapy. We evaluate sorafenib efficacy and impact on the cellular pro-survival machinery in vitro, efficacy of sorafenib as monotherapy and in combination with the naturally occurring death receptor agonist, TRAIL using human MPM cell lines, MSTO-211H, M30, REN, H28, H2052 and H2452. In vitro studies of the six MPM lines demonstrated single agent sensitivity to the multikinase inhibitor sorafenib and resistance to TRAIL. H28 and H2452 demonstrated augmented apoptosis with the addition of TRAIL to sorafenib in vitro. Treated cell lines demonstrated sorafenib-induced rapid dephosphorylation of AKT followed shortly by near complete dephosphorylation of the constitutively phosphorylated ERK1/2. Sorafenib therapy also decreased phosphorylation of B-Raf and mTOR in several cell lines. Within 3 h of sorafenib treatment, a number of known pro-survival molecules were dephosphorylated and/or downregulated in expression including MCL-1(L), c-FLIP(L), survivin and cIAP(1). These changes and eventual cell death did not elicit significant caspase-3 activation or PARP cleavage and pretreatment with the pan-caspase inhibitor, Z-VAD-FMK, did not block sorafenib efficacy but did block the effect of TRAIL monotherapy. Pre-treatment with Z-VAD-FMK did not block the synergistic effect of TRAIL and sorafenib in H28. In summary, single agent treatment with sorafenib results in widespread inhibition of the pro-survival machinery in vitro leading to cell death via a primarily caspase-independent mechanism. Combining sorafenib therapy with TRAIL, may be useful in order to provide a more efficient death signal and this synergistic effect appears to be caspase-independent. Pilot in vivo data demonstrates promising evidence of therapeutic efficacy in human tumor bearing xenograft nu/nu mice. We document single agent activity of sorafenib against MPM, unravel novel effects of sorafenib on anti-apoptotic signaling mediators, and suggest the combination of sorafenib plus TRAIL as possible therapy for clinical testing in MPM.

Malignant pleural mesothelioma cells resist anoikis as quiescent pluricellular aggregates

Pleural fluid accumulation is a frequent clinical observation in diffuse malignant pleural mesothelioma (MPM). The cytological analysis of pleural fluid often reveals the presence of free spheroid aggregates of malignant cells, giving rise to the question of the ability of non-adherent tumor cells to resist the loss of anchorage-induced apoptosis (termed as anoikis), and to develop new tumor foci in the pleural cavity. Here, we show that MPM cells cultured under non-adherent conditions form well-organized aggregates composed of viable cells, which progressively enter in G(0). Although the PI3K/Akt, ERK and SAPK/JNK signaling pathways are activated in adherent MPM cells, loss of anchorage results in the inactivation of these pathways. By comparison, we show that the non-tumoral mesothelial cells MeT-5A enter anoikis in an SAPK/JNK-, Bim- and caspase-9-dependent pathway. The survival of MPM cells can be reversed by activating SAPK/JNK with anisomycin, according to a Bim-dependent mitochondrial pathway. Finally, our findings show that impairment of cell aggregation activates SAPK/JNK and Bim and induces anoikis. Our results underline the importance of intercellular contacts in the anoikis resistance of MPM cells.

The plexin-A1 receptor activates vascular endothelial growth factor-receptor 2 and nuclear factor-kappaB to mediate survival and anchorage-independent growth of malignant mesothelioma cells

The semaphorins and their receptors, the neuropilins and the plexins, are constituents of a complex regulatory system that controls axonal guidance. Moreover, many types of tumor cells express various members of semaphorins and receptors, but the biological activities within tumor mass and the signal transduction mechanism(s) they use are largely unknown. Here, we show that in asbestos-related malignant pleural mesothelioma (MPM), Semaphorin-6D (Sema6D) and its receptor plexin-A1 are frequently expressed and trigger a prosurvival program that promotes anchorage-independent growth of MPM cells. Interestingly, the same response is also controlled by the tyrosine kinase receptors of vascular endothelial growth factor (VEGF) through a nuclear factor-kappaB (NF-kappaB)-dependent pathway. We found that in MPM cells, plexin-A1 and VEGF-receptor 2 (VEGF-R2) are associated in a complex. Moreover, the presence of Sema6D promotes the tyrosine phosphorylation of VEGF-R2 in a plexin-A1-dependent manner. This is necessary for basal and Sema6D-induced NF-kappaB transcriptional activity, and NF-kappaB mediates tumor cell survival. Expression of Sema6D and plexin-A1 is induced by asbestos fibers and overexpression of plexin-A1 in nonmalignant mesothelial cells inhibits cell death after asbestos exposure. This work identifies a new biological function of semaphorins in cancer cells and suggests the involvement of an undescribed survival pathway during MPM tumorigenesis.

Clusterin silencing in human lung adenocarcinoma cells induces a mesenchymal-to-epithelial transition through modulating the ERK/Slug pathway

The ubiquitously expressed glycoprotein Clusterin (CLU) is implicated in diverse cellular processes, yet its genuine molecular function remains undefined. CLU expression has been associated with various human malignancies, yet the mechanisms by which CLU promotes cancer progression and metastasis are not elucidated. In this study, using human lung adenocarcinoma cell lines as a model, we explored the involvement of CLU in modulating invasiveness of cancer cells. We discovered that CLU levels positively correlated with the degree of invasiveness in human lung adenocarcinoma cell lines. The observation that CLU-rich cells displayed a spindle-shape morphology while those with low CLU levels were cuboidal in shape prompted us to investigate if CLU modulates epithelial-to-mesenchymal transitions (EMT). CLU silencing by siRNA in a highly invasive, CLU-rich lung adenocarcinoma cell line induced a mesenchymal-to-epithelial transition (MET) evidenced by the spindle-to-cuboidal morphological change, increased E-cadherin expression, and decreased fibronectin expression. Compared with the vector-transfected cells, CLU-knocked-down (CLUi) cells showed reduced migration and invasion in vitro, as well as decreased metastatic potential in experimental metastasis. Re-expression of CLU in CLUi cells reversed the MET and restored the mesenchymal and invasive phenotypes. We found that Slug, a zinc-finger-containing transcriptional repressor of E-cadherin, was downregulated in CLUi cells. We also discovered that levels of activated ERK correlated with those of CLU and Slug. Taken together, our data suggest that CLU may regulate EMT and aggressive behaviour of human lung adenocarcinoma cells through modulating ERK signalling and Slug expression.

ERalpha suppresses slug expression directly by transcriptional repression

Two of the most common signalling pathways in breast cancer are the ER (oestrogen receptor) ligand activation pathway and the E-cadherin snai1 slug EMT (epithelial-mesenchymal transition) pathway. Although these pathways have been thought to interact indirectly, the present study is the first to observe direct interactions between these pathways that involves the regulation of slug expression. Specifically we report that ligand-activated ERalpha suppressed slug expression directly by repression of transcription and that knockdown of ERalpha with RNA interference increased slug expression. More specifically, slug expression was down-regulated in ERalpha-negative MDA-MB-468 cells transfected with ERalpha after treatment with E2 (17beta-oestradiol). The down-regulation of slug in the ERalpha-positive MCF-7 cell line was mediated by direct repression of slug transcription by the formation of a co-repressor complex involving ligand-activated ERalpha protein, HDAC1 (histone deacetylase 1) and N-CoR (nuclear receptor co-repressor). This finding was confirmed by sequential ChIP (chromatin immunoprecipitation) studies. In the MCF-7 cell line, slug expression normally was low. In addition, knockdown of ERalpha with RNA interference in this cell line increased slug expression. This effect could be partially reversed by treatment of the cells with E2. The efficacy of the effect of ERalpha on slug repression was dependent on the overall level of ERalpha. These observations confirmed that slug was an E2-responsive gene.

Enhanced antitumor therapy by inhibition of p21waf1 in human malignant mesothelioma

PURPOSE

The p21 cyclin-dependent kinase inhibitor was frequently expressed in human malignant pleural mesothelioma (MPM) tissues as well as cell lines. Recent data indicate that p21 keeps tumor cells alive after DNA damage, favoring a survival advantage. In this study, we assessed the possibility of p21 suppression as a therapeutic target for MPM.

EXPERIMENTAL DESIGN

We established two different MPM-derived (from H28 and H2052 cells) subclones using vector-based short hairpin RNA (shRNA). Then, chemosensitivity against low doses of antineoplastic DNA-damaging agents was investigated by colony formation assays, and furthermore, the type of cell response induced by these drugs was analyzed. To examine the effect of p21 shRNA on chemosensitivity in vivo, tumor formation assays in nude mice were done.

RESULTS

In colony formation assay, the IC50 of doxorubicin was 33 +/- 3.0 nmol/L in p21 shRNA-transfected cells with respect to 125 +/- 10 nmol/L of control vector-transfected cells. This enhancement of growth inhibition was achieved by converting a senescence-like growth arrest to apoptosis in response to doxorubicin, etoposide, and CPT11. In the in vivo assays, CPT11 and loss-of-expression of p21 in combination led to considerable suppression of tumor growth associated with a substantially enhanced apoptotic response, whereas CPT11 alone was ineffective at inducing these responses.

CONCLUSIONS

These results indicated that p21 might play an important role in chemosensitivity to anticancer agents, and the suppression of its expression might be a potential therapeutic target for MPM.

Slug (SNAI2) down-regulation by RNA interference facilitates apoptosis and inhibits invasive growth in neuroblastoma preclinical models

PURPOSE

We assessed the relevance of Slug (SNAI2) for apoptosis resistance and invasion potential of neuroblastoma cells in vitro and in vivo.

EXPERIMENTAL DESIGN

We evaluated the effect of imatinib mesylate on invasion and analyzed the genes modulated by imatinib mesylate treatment in neuroblastoma cells. Slug expression, inhibited by imatinib mesylate treatment, was knocked down in neuroblastoma cells by RNA interference, and the effects on invasion and apoptosis were evaluated in vitro. A pseudometastatic model of neuroblastoma in severe combined immunodeficient mice was used to assess the effects of Slug silencing alone or in combination with imatinib mesylate treatment on metastasis development.

RESULTS

Microarray analysis revealed that several genes, including Slug, were down-regulated by imatinib mesylate. Slug expression was detectable in 8 of 10 human neuroblastoma cell lines. Two Slug-expressing cell lines were infected with a vector encoding a microRNA to Slug mRNA. Infected cells with reduced levels of Slug were tested for the expression of apoptosis-related genes (p53, Bax, and Bcl-2) identified previously as Slug targets. Bcl-2 was down-regulated in Slug-interfered cells. Slug down-regulation increased sensitivity to apoptosis induced by imatinib mesylate, etoposide, or doxorubicin. Invasion of Slug-silenced cells was reduced in vitro. Animals injected with Slug-silenced cells had fewer tumors than controls and the inhibition of tumor growth was even higher in animals treated with imatinib mesylate.

CONCLUSIONS

Slug down-regulation facilitates apoptosis induced by proapoptotic drugs in neuroblastoma cells and decreases their invasion capability in vitro and in vivo. Slug inhibition, possibly combined with imatinib mesylate, may represent a novel strategy for treatment of metastatic neuroblastoma.

c-Kit expression in human normal and malignant stem cells prognostic and therapeutic implications

The human stem cell factor/c-Kit signaling pathway is pivotal for the survival of embryonic, foetal and adult stem cells and for their fundamental role in generating healthy functioning cell and tissue types during embryonic, foetal and adult life. Common biological features between human stem cells and cancer cells include (A) self-renewal, (B) extensive capacity of proliferation, (C) migration to and homing at distant sites and (D) resistance to toxic agents. Given these shared attributes, cancer was proposed to originate from transforming mutation(s) in normal stem cells that dysregulate their physiological programs. This theory has been recently supported by the findings that among all malignant cells within a particular tumour, only cell fraction expressing stem cell markers such as c-Kit named 'cancer stem cells' has the exclusive potential to generate tumour cell population. The involvement of c-Kit and its mutation in various haematological malignancies and solid tumours are reviewed. The impacts of dysregulated c-Kit as oncogenic tyrosine kinase on autocrine stimulation and resistance to chemotherapy of cancer stem cells are evaluated. The significance and efficacy of molecular therapeutic targeting of c-Kit signaling pathway in the management of patients with c-Kit-positive malignancies are appraised.

Evidence of a novel docetaxel sensitizer, garlic-derived S-allylmercaptocysteine, as a treatment option for hormone refractory prostate cancer

The recent introduction of docetaxel in the treatment of hormone refractory prostate cancer (HRPC) has made a small but significant impact on patient survival. However, its effect is limited by intolerance and resistance. The aim of our study was to investigate if the garlic-derived compound, S-allylmercaptocysteine (SAMC), was able to act as a docetaxel sensitizing agent. First, the effect of SAMC on docetaxel sensitivity was examined on 3 HRPC cell lines by colony forming assay. We found that SAMC increased the efficacy of docetaxel on colony forming inhibition by 9-50% compared to single agent treatment. Second, using the HRPC CWR22R nude mice model, we found that the combination of SAMC and docetaxel was 53% more potent than docetaxel alone (p = 0.037). In addition, there was no additive toxicity in the mice treated with the combination therapy evidenced by histological and functional analysis of liver, kidney and bone marrow. These results suggest that SAMC is able to increase the anticancer effect of docetaxel without causing additional toxic effect in vivo. Third, flow cytometry and Western blotting analysis on HRPC cell lines demonstrated that SAMC promoted docetaxel-induced G2/M phase cell cycle arrest and apoptotic induction. In addition, immunohistochemistry on CWR22R xenograft revealed a suppression of Bcl-2 expression and upregulation of E-cadherin in the SAMC and docetaxel treated animals. These results suggest that SAMC may promote docetaxel-induced cell death through promoting G2/M cell cycle arrest and apoptosis. Our study implies a potential role for SAMC in improving docetaxel based chemotherapy for the treatment of HRPC.