Human Colon Cancer Stem Cells Research Articles

Long intergenic non-protein-coding RNA 1567 (LINC01567) acts as a \u201csponge\u201d against microRNA-93 in regulating the proliferation and tumorigenesis of human colon cancer stem cells

BackgroundCancer stem cells (CSCs) are considered to be the major factor in tumor initiation, progression, metastasis, recurrence and chemoresistance. Maintaining the stemness and promoting differentiation of these cells involve various factors. Recently, long non-coding RNAs (lncRNAs) have been identified as new regulatory factors in human cancer cells. However, the function of lncRNAs in colon CSCs is still unknown.MethodsPrimary colon cancer cells were maintained in serum-free medium to form spheres and CD133+/CD166+/CD44+ spheroid cells were selected using FACS technique. Then we detected growth curve, colony formation, invasion and migration ability, and tumorigenicity of CD133+/CD166+/CD44+ cells. LOCCS-siRNA and pcDNA-LOCCS plasmid vectors were constructed and transfected to evaluate impact of the lncRNA. We also performed dual luciferase reporter assay to verify the interaction of LOCCS and miR-93.ResultsThe research explored lncRNA expression and the regulatory role of novel lncRNAs in colon CSCs. Using the stem cell markers CD133, CD166 and CD44, we found a subpopulation of highly tumorigenic human colon cancer cells. They displayed some characteristics of stem cells, including the ability to proliferate and form colonies, to resist chemotherapeutic drugs, and to produce xenografts in nude mice. We also found an lncRNA, LOCCS, with obviously upregulated expression in colon CSCs. Knockdown of LOCCS reduced cell proliferation, invasion, migration, and generation of tumor xenografts. Furthermore, microRNA-93 (miR-93) and Musashi-1 mediated the tumor suppression of LOCCS knockdown.ConclusionsThere was reciprocal repression between LOCCS and miR-93. Research on mechanisms suggested direct binding, as a predicted miR-93 binding site was identified in LOCCS. This comprehensive analysis of LOCCS in colon CSCs provides insight for elucidating important roles of the lncRNA–microRNA functional network in human colon cancer.

Abstract 3901: Therapeutic targeting of C-terminal binding protein: a key dependency for polyposis and cancer stem cell activity in APC mutant neoplasia

Abstract The C terminal binding proteins (CtBP) 1 and 2 are a family of transcriptional co-repressors overexpressed in a variety of cancers, and are frequently associated with poor prognosis and chemoresistance. CtBP has also been characterized in cell culture models as drivers of migration/invasion and epithelial-mesenchymal transition. CtBP mediates its transcriptional corepressor activity via its dehydrogenase domain, and inhibition of this domain interferes with CtBP oncogenic functions. The role of CtBP in APC mutant neoplasia remains obscure even though APC is responsible for degradation of both β-catenin and CtBP in suppressing colorectal tumorigenesis. Our prior work demonstrates that CtBP proteins can be effectively therapeutically targeted with substrate analogues of their intrinsic dehydrogenase domains. We now observe that pharmacologic inhibition of CtBP using either the 1st generation inhibitor 2-keto-4-methylthiobutyrate (MTOB) or the 2nd generation inhibitor hydroxyimino-3-phenylpropanoic acid (HIPP) significantly reduces the burden of intestinal polyps in the Apcmin mouse model of the human cancer predisposition syndrome Familial Adenomatous Polyposis. The number of intestinal polyps in mice with CtBP2 inhibitors were significantly lower (21 polyps/mouse for MTOB, 15 polyps/mouse for HIPP) as compared with vehicle treated mice (45 polyps/mouse) with a P value <0.0001. Pointing to the anti-neoplastic mechanism of MTOB and HIPP, polyps that did grow in MTOB or HIPP treated mice demonstrated robust downregulation of β catenin and Ctbp2 proteins. This observation points to the role of Ctbp2 as a putative driver oncogene that can be therapeutically targeted in vivo. In addition, CtBP2 has been reported to play an important role in human colon cancer stem cells via its interaction with the transcription factor TCF4 on chromatin. We now show that inhibiting CtBP with HIPP or HIPP analogues attenuates CtBP2 protein levels in colon cancer stem cells with resultant decreased expression of CtBP transcriptional target genes, such as the motility/invasion regulator TIAM1, and c-MYC, a known driver of the cancer stem cell phenotype. Moreover, colonospheres treated with CtBP inhibitor showed downregulation of cancer stem cell markers CD133 and c-MYC, as compared with vehicle treatment. Flow cytometry analysis of intestinal epithelium from Apcmin mice treated with CtBP inhibitor vs. vehicle indicated a significant reduction in CD133+/CXCR4+ cells that are associated with a tumor initiating cell phenotype. Our data demonstrate that CtBP inhibition may reduce colon neoplasia via downregulation of c-MYC and the cancer stem cell/tumor initiating cell compartment, and that CtBP is a promising and novel target for therapy in colon cancer. Citation Format: Ayesha T. Chawla, Agnes Cororaton, Rashmi Seth, Barbara Szomju, Evan T. Sumner, Steven R. Grossman. Therapeutic targeting of C-terminal binding protein: a key dependency for polyposis and cancer stem cell activity in APC mutant neoplasia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3901. doi:10.1158/1538-7445.AM2017-3901

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

Visualization and targeting of LGR5+ human colon cancer stem cells.

The cancer stem cell (CSC) theory highlights a self-renewing subpopulation of cancer cells that fuels tumour growth. The existence of human CSCs is mainly supported by xenotransplantation of prospectively isolated cells, but their clonal dynamics and plasticity remain unclear. Here, we show that human LGR5+ colorectal cancer cells serve as CSCs in growing cancer tissues. Lineage-tracing experiments with a tamoxifen-inducible Cre knock-in allele of LGR5 reveal the self-renewal and differentiation capacity of LGR5+ tumour cells. Selective ablation of LGR5+ CSCs in LGR5-iCaspase9 knock-in organoids leads to tumour regression, followed by tumour regrowth driven by re-emerging LGR5+ CSCs. KRT20 knock-in reporter marks differentiated cancer cells that constantly diminish in tumour tissues, while reverting to LGR5+ CSCs and contributing to tumour regrowth after LGR5+ CSC ablation. We also show that combined chemotherapy potentiates targeting of LGR5+ CSCs. These data provide insights into the plasticity of CSCs and their potential as a therapeutic target in human colorectal cancer.

O-Linked N-Acetylglucosamine (O-GlcNAc) Expression Levels Epigenetically Regulate Colon Cancer Tumorigenesis by Affecting the Cancer Stem Cell Compartment via Modulating Expression of Transcriptional Factor MYBL1

To study the regulation of colorectal adenocarcinoma progression by O-GlcNAc, we have focused on the O-GlcNAc-mediated epigenetic regulation of human colon cancer stem cells (CCSC). Xenograft tumors from colon tumor cells with O-linked N-acetylglucosamine transferase (OGT) knockdown grew significantly slower than those formed from control cells, indicating a reduced proliferation of tumor cells due to inhibition of OGT expression. Significant reduction of the CCSC population was observed in the tumor cells after OGT knockdown, whereas tumor cells treated with the O-GlcNAcase inhibitor showed an increased CCSC population, indicating that O-GlcNAc levels regulated the CCSC compartment. When grown in suspension, tumor cells with OGT knockdown showed a reduced ability to form tumorspheres, indicating a reduced self-renewal of CCSC due to reduced levels of O-GlcNAc. ChIP-sequencing experiments using an anti-O-GlcNAc antibody revealed significant chromatin enrichment of O-GlcNAc-modified proteins at the promoter of the transcription factor MYBL1, which was also characterized by the presence of H3K27me3. RNA-sequencing analysis showed an increased expression of MYBL1 in tumor cells with OGT knockdown. Forced overexpression of MYBL1 led to a reduced population of CCSC and tumor growth in vivo, similar to the effects of OGT silencing. Moreover, two CpG islands near the transcription start site of MYBL1 were identified, and O-GlcNAc levels regulated their methylation status. These results strongly argue that O-GlcNAc epigenetically regulates MYBL1, functioning similarly to H3K27me3. The aberrant CCSC compartment observed after modulating O-GlcNAc levels is therefore likely to result, at least in part, from the epigenetic regulation of MYBL1 expression by O-GlcNAc, thereby significantly affecting tumor progression.

Peroxiredoxin 2 is essential for maintaining cancer stem cell-like phenotype through activation of Hedgehog signaling pathway in colon cancer.

Cancer stem cells (CSCs) are a key target for reducing tumor growth, metastasis, and recurrence. Redox status is a critical factor in the maintenance of CSCs, and the antioxidant enzyme Peroxiredoxin 2 (Prdx2) plays an important role in the development of colon cancer. Therefore, we investigated the contribution of Prdx2 to the maintenance of stemness of colon CSCs. Here, we used short-hairpin RNAs and a Prdx2-overexpression vector to determine the effects of Prdx2. We demonstrated that knockdown of Prdx2 reduced the self-renewal and sphere formation and resulted in increased 5-FU-induced apoptosis in human colon CSCs. Prdx2 overexpression induced reversion of the self-renewal and sphere formation. Furthermore, the effects of Prdx2 resulted in an altered expression of stemness associated with the Hh/Gli1 signaling pathway. Finally, knockdown of Prdx2 in CD133+ cells reduced the volume of xenograft tumors in BALB/c-nu mice. Taken together, colon CSCs overexpress Prdx2, which promotes their stem cell properties via the Hh/Gli1 signaling pathway. The results suggest that Prdx2 may be an effective therapeutic target for the elimination of CSCs in colorectal cancer.

MiniSY-5-2 - Upregulation of Oncogenic miR-221 in Human Colon Cancer Stem Cells

MiniSY-5-2 - Upregulation of Oncogenic miR-221 in Human Colon Cancer Stem Cells

Abstract 1714: The role of Hedgehog signaling in the regulation of human colon cancer stem cells

Abstract Recent data support a hierarchical model of colon cancer in which tumor growth is driven by a subpopulation of cancer stem cells (CSCs) that may also be the source of relapse following treatment. Elucidation of the cellular heterogeneity within a tumor would therefore facilitate better characterization of patient subtypes and lead to more personalized and effective treatments. Here, as part of the OncoTrack* consortium, we report the use of Matrigel-based 3D in vitro models of patient-derived colon cancer for the characterization of molecular pathways important in the regulation of CSC self-renewal and survival. Cellular subpopulations were isolated from patient-derived 3D-culture models based on expression of the CSC marker aldehyde dehydrogenase (ALDH) and then functionally tested for tumor initiation and self-renewal capacity by limiting dilution serial xenotransplantation. These studies demonstrate CSCs to be ALDH+. ALDH+ and ALDH- cells from 3D-culture and xenograft models were then subjected to RNA sequencing for whole transcriptome analysis. These analyses demonstrated ALDH+ CSCs cells to be enriched for stem cell associated genes (ALDH1A1, LGR5, BMI1, CD44, CD166), developmental processes (embryonic, tissue development, EMT) and signaling pathways (Wnt signaling). In particular, the Hedgehog signaling pathway was found to be enriched in both 3D in vitro and xenograft models. The role of Hedgehog signaling in colon cancer remains controversial. It has been reported as a negative regulator of Wnt signaling and to be inactive in colon cancer cells lines. Here, using small molecule inhibitors and lentivirus mediated gene knockdown, we report on the role of Hedgehog signaling in the regulation of colon CSC self-renewal and identify non-canonical Hedgehog signaling as a positive regulator of Wnt signaling. *The research leading to these results has received funding from the European Union's Seventh Framework Program (FP7/2007-2013) for the Innovative Medicine Initiative under grant agreement n°115234. Citation Format: Joseph L. Regan, Stephanie Staudte, Dirk Schumacher, Ulrich Keilholz, Johannes Haybaeck, Hans Lehrach, Marie-Laure Yaspo, David Henderson, Andreas Steffen, Joern Toedling, Ralf Lesche, Reinhold Schaefer, Christian R. Regenbrecht, Dominik Mumberg, Martin Lange. The role of Hedgehog signaling in the regulation of human colon cancer stem cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1714.

Abstract 3839: Vitamin E delta-tocotrienol targets human colon cancer stem cells and inhibits colon cancer metastasis and induces apoptosis

Abstract Background: Colon cancer is the most commonly diagnosed cancer both in men and women and cause of cancer related deaths worldwide. Treatment for the recurrent and metastatic colon cancer remains a center of clinical attention. Cancer stem cells (CSCs) are suggested to be the only cells within tumor with tumorigenic capacity and implicated in metastasis. We have shown that vitamin E delta-tocotrienol (VEDT) is the most bioactive tocotrienols against cancers. This study aimed to evaluate the effect of VEDT on colon cancer growth, metastatic epithelial to mesenchymal transition (EMT), migration/ invasion/angiogenesis and colon CSCs growth and apoptosis. Methods: Human colon cancer cells HCT-116 and metastatic colon cancer cells SW-620 and colon CSCs were treated with VEDT (10-100 μM) for 72 h and cell viability recorded. VEDT (50 μM) was used for malignant transformation; migration/invasion, CSCs spheroid formation, and pluripotency were determined. Azoxymethane treated Fisher 344 rats were used as colon carcinogenesis model. They were treated with 1) vehicle control and 2) VEDT (200 mg/kg, orally twice a day) for 20 weeks. After 20 weeks the polyps and tumor formation were recorded. Results: VEDT significantly inhibited the anchorage-dependent and independent cancer cell growth, migration/invasion and induced apoptosis compared to control. VEDT inhibited the CSC spheroid formation EMT (E-cadherin to vimentin), metastasis (MMP9), angiogenesis (VEGF), CSCs transcription factors (Nanog, Oct4, Sox2 and KLF4) compared to control. Conclusion: Vitamin E delta-tocotrienol inhibited colon cancer growth and metastasis through inhibition of cancer stem cell pluripotency, EMT, migration, invasion, angiogenesis and induction of apoptosis. Citation Format: Kazim Husain, Domenico Coppola, Said M. Sebti, Mokenge P. Malafa. Vitamin E delta-tocotrienol targets human colon cancer stem cells and inhibits colon cancer metastasis and induces apoptosis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3839.

Indian gooseberry (Emblica officinalis Gaertn.) suppresses cell proliferation and induces apoptosis in human colon cancer stem cells independent of p53 status via suppression of c-Myc and cyclin D1

Indian gooseberry, also known as amla, a widely consumed fruit in South Asia, was evaluated for its anti-proliferative and pro-apoptotic mechanisms on human colon cancer stem cells (HCCSC). Amla extracts suppressed proliferation and induced apoptosis independent of p53, a tumour suppressor gene, in HCCSCs. Further, amla extracts suppressed cell proliferation by targeting the Wnt/β-catenin signalling pathway as seen by decreased nuclear translocation of β-catenin. Additionally, this led to suppressed expression of c-Myc and cyclin D1, key proteins involved in cell proliferation. Inhibition of stem-ness of HCCSCs by amla may be due to its effect on the Wnt/β-catenin signalling. These results indicate that amla suppresses HCCSC proliferation and induces apoptosis independent of p53 status via potentially targeting Wnt/β-catenin signalling pathway. Amla is therefore a promising functional food for preventing colon cancer and might be a novel resource for the food industry.

Inhibition of c-Yes induces differentiation of HT-29 human colon cancer stem cells through midbody elongation.

Recent research suggests that a small group of cells, named cancer stem cells (CSCs), is responsible for initiating tumor formation, recurrence, and metastasis. c-Yes, a proto-oncogene that is a subfamily of Src family kinase, is often activated in human colon cancer; this implicates c-Yes in the onset and progression of the disease. The objective of this study was to investigate the correlation between c-Yes and CSCs. We performed a sphere formation assay and reverse transcription-polymerase chain reaction for studying the differentiation of HT-29 human colon CSCs. To demonstrate the specific role of c-Yes in CSCs, we performed live cell microscopy and a cell cycle assay. These study shows, for the first time, that c-Yes is enriched in CD133+ CSCs, compared to their CD133- counterparts, and that c-Yes depletion in CD133+ cells induces cell differentiation. Moreover, c-Yes depletion was found to elongate the midbody and increase the proliferation doubling time. This also suggested that the misregulation of microtubules during chromosomal separation causes aneuploidy. Our results suggest that c-Yes may play a crucial role in initiating, maintaining, and driving the tumorigenic property of colon cancer.

Pro-apoptotic activity against cancer stem cells differs between different parts of sweet sorghum

The extracts from sweet sorghum stalk were previously shown to eliminate human colon cancer stem cells (CCSC) in a partial p53-dependent fashion. However, the underlying mechanisms remain unknown. In this study, we transfected CCSC with shRNA against p53 and treated with sweet sorghum phenolics extracted from different plant components. While all sweet sorghum components demonstrated anti-proliferative and pro-apoptotic effects in CCSC, phenolics extracted from the dermal layer and seed head were more potent in eliminating CCSC by elevating caspase 3/7 activity, poly ADP-ribose polymerase cleavage, and DNA fragmentation in a p53-dependent and partial p53-dependent manner, respectively. These effects were associated with decreases in β-catenin, cyclin D1, cMyc, and survivin protein levels. These results suggest that the anti-proliferative and pro-apoptotic effects of sweet sorghum extracts against CCSC are potentially via suppression of Wnt/β-catenin signalling in a p53-dependent (dermal layer) and partial p53-dependent (seed head) manner.

Eugenia jambolana (Java Plum) Fruit Extract Exhibits Anti-Cancer Activity against Early Stage Human HCT-116 Colon Cancer Cells and Colon Cancer Stem Cells.

The World Health Organization predicts over a 70% increase in cancer incidents in developing nations over the next decade. Although these nations have limited access to novel therapeutics, they do have access to foods that contain chemopreventive bioactive compounds such as anthocyanins, and as such, consumption of these foods can be encouraged to combat cancer. We and others have previously characterized the anti-colon cancer properties of dietary anthocyanins from different sources. Eugenia jambolana (Java plum) is a tropical medicinal fruit rich in anthocyanins, however, its anti-colon cancer properties are not well characterized. Furthermore, recent evidence suggests that colon cancer stem cells (colon CSCs) promote resistance to chemotherapy, relapse of tumors and contribute to poor prognosis. The objectives of this study were to 1) characterize the anthocyanin profile of Java plum using HPLC-MS; and 2) determine the anti-proliferative (cell counting and MTT) and pro-apoptotic (TUNEL and caspase 3/7 glo assay) properties of Java plum fruit extract (JPE) using HCT-116 colon cancer cell line and colon CSCs (positive for CD 44, CD 133 and ALDH1b1 markers). HPLC-MS analysis showed that JPE contains a variety of anthocyanins including glucosides of delphinidin, cyanidin, petunidin, peonidin and malvidin. JPE anthocyanins suppressed (p < 0.05) proliferation in HCT-116 cells and elevated (p < 0.05) apoptosis in both HCT-116 cells and colon CSCs. JPE also suppressed the stemness in colon CSCs as evaluated using colony formation assay. These results warrant further assessment of the anti-cancer activity of JPE, and its molecular mechanisms using pre-clinical models of colon cancer.

Identification of thiostrepton as a novel therapeutic agent that targets human colon cancer stem cells.

Accumulating evidence shows that colorectal cancer stem cells (CRSCs) are largely responsible for the metastasis and relapse of colorectal cancer (CRC) after therapy. Hence, identifying new agents that specifically target CRSCs would help improve the effectiveness of current CRC therapies. To accelerate identification of agents targeting CRSCs, the Connectivity Map (CMap) approach was used. Among the top-ranked candidates, thiostrepton, a thiazole antibiotic, was selected for further investigation because of its known tumoricidal activity. Thiostrepton could selectively induce apoptosis in CRSC subpopulations in both parental HCT-15 and HT-29 human CRC lines as well as in EMT and chemoresistant clones derived from them. Further, we investigated its inhibitory effects on the sphere- and colony-forming capabilities of the aforementioned CRC lines. The in vitro inhibition of sphere and colony formation was associated with downregulation of various modulators of the stem cell phenotype. The combination of thiostrepton and oxaliplatin eradicated both CD44+ HCT-15 and HT-29 cells more efficiently than either drug alone. FoxM1, an oncogenic transcription factor, was identified as a critical positive modulator of stemness and as the main target of thiostrepton in the CRC lines. This is the first report showing the selective killing of CRSCs by thiostrepton, which has been proposed to be a promising anti-neoplastic agent. On the basis of its synergism with oxaliplatin in killing CRSCs in vitro, if this activity is confirmed in vivo, thiostrepton may be a promising agent to be used clinically in combination with current chemotherapies to improve the efficacy of these regimens.

FOXM1-Induced PRX3 Regulates Stemness and Survival of Colon Cancer Cells via Maintenance of Mitochondrial Function

Reagents designed to target cancer stem cells (CSCs) could reduce tumor growth, recurrence, and metastasis. We investigated the mitochondrial features of CSCs. Colon adenocarcinoma fragments were obtained from 8 patients during surgery at Busan Paik Hospital in Korea. We used immunohistochemistry and quantitative polymerase chain reaction to compare expression of mitochondrial peroxiredoxin 3 (PRX3) in CD133(+)CD44(+) Lgr5(+)cells (CSCs) vs CD133(-)CD44(-)Lgr5(-) colon tumor cells (non-CSCs). Cell survival and expression of mitochondrial-related genes were analyzed in the presence of 5-fluorouracil and/or antimycin A. We used small-interfering and short-hairpin RNAs and an overexpression vector to study PRX3, which functions in the mitochondria. CD133(+) cells with PRX3 knockdown or overexpressing PRX3 were grown as xenograft tumors in immunocompromised mice. Metastasis was studied after injection of tumor cells in spleens of mice. We used chromatin immunoprecipitation and reporter assays to characterize transcriptional regulation of PRX3 by forkhead box protein1. CSCs had a higher mitochondrial membrane potential and increased levels of adenosine triphosphate, Ca(2+), reactive oxygen species, and oxygen consumption than non-CSCs. Levels of PRX3 were increased in colon CSCs compared with non-CSCs. PRX3 knockdown reduced the viability of CSCs, but non non-CSCs, by inducing mitochondrial dysfunction. PRX3 knockdown reduced growth of CSCs as xenograft tumors or metastases in mice. The expression of FOXM1 activated transcription of PRX3 and expression of CD133 in colon CSCs. Human colon CSCs have increased mitochondrial function compared with colon tumor cells without stem cell properties. Colon CSCs overexpress the mitochondrial gene PRX3, which is required for maintenance of mitochondrial function and tumorigenesis, and is regulated by forkhead box protein 1, which also regulates expression of CD133 in these cells. These proteins might be therapeutic targets for colorectal cancer.

Triphala Extract Suppresses Proliferation and Induces Apoptosis in Human Colon Cancer Stem Cells via Suppressing c-Myc/Cyclin D1 and Elevation of Bax/Bcl-2 Ratio.

Colon cancer is the second leading cause of cancer related deaths in the USA. Cancer stem cells (CSCs) have the ability to drive continued expansion of the population of malignant cells. Therefore, strategies that target CSCs could be effective against colon cancer and in reducing the risk of relapse and metastasis. In this study, we evaluated the antiproliferative and proapoptotic effects of triphala, a widely used formulation in Indian traditional medicine, on HCT116 colon cancer cells and human colon cancer stem cells (HCCSCs). The total phenolic content, antioxidant activity, and phytochemical composition (LC-MS-MS) of methanol extract of triphala (MET) were also measured. We observed that MET contains a variety of phenolics including naringin, quercetin, homoorientin, and isorhamnetin. MET suppressed proliferation independent of p53 status in HCT116 and in HCCSCs. MET also induced p53-independent apoptosis in HCCSCs as indicated by elevated levels of cleaved PARP. Western blotting data suggested that MET suppressed protein levels of c-Myc and cyclin D1, key proteins involved in proliferation, and induced apoptosis through elevation of Bax/Bcl-2 ratio. Furthermore, MET inhibited HCCSCs colony formation, a measure of CSCs self-renewal ability. Anticancer effects of triphala observed in our study warrant future studies to determine its efficacy in vivo.

Detachment of Mesenchymal Stem Cells with Trypsin/EDTA Has No Effect on Apoptosis Detection

Hui and colleagues have raised the concern that the detection of cell surface Annexin V staining on mesenchymal stem cells (MSC) following treatment with the enhancer of Zeste homology 2 (EZH2) inhibitor, DZNep (Sequoia Research, Pangbourne, United States, http:// www.seqchem.com/) may have been compromised due to the use of Trypsin/EDTA to detach the adherent cells in our recent publication “EZH2 and KDM6A Act as an Epigenetic Switch to Regulate MSC lineage specification” [1]. Specifically, it is proposed that EDTA could affect the structure of the plasma membrane and chelate Ca preventing the binding of Annexin V protein to the phosphatidylserine [2–4]. However, different manufacturers specify the use of Trypsin/EDTA, and not EDTA-free trypsin for detaching adherent cells prior to staining for Annexin V, where Trypsin/EDTA has been used by various studies for a wide range of adherent cell types [5–12]. While the Letter to the Editor by Hui and colleagues, published in this article, use the example that DZNep has been previously shown to induced apoptosis in human colon cancer stem cells [13], our study [1] found that DZNep had no effect on the apoptosis status of human bone marrow-derived MSC, in accord with other studies reporting that DZNeP is not harmful for nontransformed cells at tumor-inhibiting doses [14]. The discrepancy in DZNep sensitivity between normal stem cells and cancer stem cells may be due to aberrant levels of EZH2 in cancer cells required for survival [15, 16]. In order to determine whether EDTA influences Annexin V binding on MSC, we performed the Annexin V protocol with either Trypsin/EDTA (Sigma Aldrich, NSW, Australia, http://www.sigmaaldrich.com/australia.html) as described in our published study [1], or with EDTA-free Collagenase I (2 mg/ml Worthington Biochemical Corporation, NJ, United States of America, http://www.worthington-biochem. com/default.html). Two different human MSC cultures were treated with 5 mM of the potent apoptotic drug, doxorubicin (Sapphire Biosciences, NSW, Australia, http://www.sapphirebiosci ence.com/) for 24 hours prior to Annexin V staining. Single-cell suspensions were harvested by either Trypsin/EDTA or Collagenase I treatment then washed with Hanks Balanced Salt Solution (Sigma Aldrich, NSW, Australia, http://www.sigmaaldrich.com/australia.html) supplemented with 5% fetal calf serum (FCS; SAFC Biosciences, Sydney, NSW, Australia, http://www.safcglobal.com/safc-global/en-us/ home.html). The cells were further washed twice with cold phosphate buffered saline prior to cell staining for Annexin V as specified in the manufacturer’s protocol (Annexin V conjugates Alexa Fluro 488, for apoptosis detection, Life Technologies, VIC, Australia, http:// www.lifetechnologies.com/au/). Flow cytometry was used to determine the levels of Annexin V staining under each condition. Cells treated with doxorubicin without Annexin V Figure 1. Comparable expression of Annexin V on doxorubicin treated MSC detached by Trypsin/EDTA or Collagenase I. Two different human bone marrow-derived MSC cultures were treated with 5 mM doxorubicin for 24 hours. Single-cell suspensions were harvested by either Trypsin/EDTA or Collagenase I treatment then stained for Annexin V. Assessment of Annexin V levels was performed by flow cytometric analysis. Data represent mean fluorescence intensity from three replicate experiments. Abbreviation: MSC, mesenchymal stem cells. Mesechymal Stem Cell Laboratory, School of Health Sciences, Faculty of Health Sciences and Centre for Stem Cell Research, University of Adelaide, South Australia, Australia

Inhibitory effects of epoxy metabolites of docosahexaenoic acid on human colon cancer stem cells (261.3)

Epidemiological and preclinical evidence supports that omega‐3 dietary fatty acids such as DHA reduce the risks of cancers, but the underlying mechanisms are poorly understood. Epoxydocosapentaenoic acids (EDPs) are the cytochrome P450 epoxygenases (CYP450) metabolites of DHA, and have been reported to mediate some of the health‐promoting effects of DHA. Increasing evidence suggests that cancer stem cells (CSCs) may be responsible for occurrence of malignant tumors. Herein we investigated the inhibitory effect of EDPs on human colon CSCs. CSC‐ associated tumor spheres were obtained from human cancer stem cells. The inhibitory effect of 19, 20‐EDP and a mixture of six different EDPs (i.e. 7‐, 8‐, 10, 11‐, 13, 14‐, 16, 17‐ and 19, 20‐EDP) were determined on both HT29 and HCT116 colon cancer cells. The results showed that both 19, 20‐EDP and EDPs mix showed a dose‐dependent inhibition on human colon CSCs. For example, treatment with 19, 20‐EDP at 1µM for 10 days caused 55% inhibition on tumor spheres derived from HT29 cells, while EDPs mix at same total concentration caused 71% inhibition. Most interestingly, 19, 20‐EDP and EDPs mix at a very low concentration of 0.1 µM still resulted in significant inhibition (33% and 55%, respectively) on tumor spheres derived from HT29 cell line. Overall, our study for the first time demonstrated the inhibitory effects of EDPs on human colon CSCs.Grant Funding Source: Supported by funding from NIH, AICR and USDA

Nodal Promotes the Self-Renewal of Human Colon Cancer Stem Cells via an Autocrine Manner through Smad2/3 Signaling Pathway

Colorectal cancer is one of the most common and fatal tumors. However, molecular mechanisms underlying carcinogenesis of colorectal cancer remain largely undefined. Here, we explored the expression and function of Nodal in colon cancer stem cells (CCSCs). Nodal and its receptors were present in numerous human colorectal cancer cell lines. NODAL and ALK-4 were coexpressed in human colon cancerous tissues, and NODAL, CD24, and CD44, markers for CCSCs, were expressed at higher levels in human colon cancerous tissues than adjacent noncancerous colon tissues. Human CCSCs were isolated by magnetic activated cell sorting using anti-CD24 and anti-CD44. Nodal transcript and protein were hardly detectable in CD44- or CD24-negative human colorectal cancer cell lines, whereas Nodal and its receptors were present in CCSCs. Notably, Nodal facilitated spheroid formation of human CCSCs, and phosphorylation of Smad2 and Smad3 was activated by Nodal in cells of spheres derived from human CCSCs. Collectively, these results suggest that Nodal promotes the self-renewal of human CCSCs and mediate carcinogenesis of human colorectal cancer via an autocrine manner through Smad2/3 pathway. This study provides a novel insight into molecular mechanisms controlling fate of human CCSCs and offers new targets for gene therapy of human colorectal cancer.

Evidence for Two Modes of Synergistic Induction of Apoptosis by Mapatumumab and Oxaliplatin in Combination with Hyperthermia in Human Colon Cancer Cells

Colorectal cancer is the third leading cause of cancer-related mortality in the world-- the main cause of death from colorectal cancer is hepatic metastases, which can be treated with isolated hepatic perfusion (IHP). Searching for the most clinically relevant approaches for treating colorectal metastatic disease by isolated hepatic perfusion (IHP), we developed the application of oxaliplatin concomitantly with hyperthermia and humanized death receptor 4 (DR4) antibody mapatumumab (Mapa), and investigated the molecular mechanisms of this multimodality treatment in human colon cancer cell lines CX-1 and HCT116 as well as human colon cancer stem cells Tu-12, Tu-21 and Tu-22. We showed here, in this study, that the synergistic effect of the multimodality treatment-induced apoptosis was caspase dependent and activated death signaling via both the extrinsic apoptotic pathway and the intrinsic pathway. Death signaling was activated by c-Jun N-terminal kinase (JNK) signaling which led to Bcl-xL phosphorylation at serine 62, decreasing the anti-apoptotic activity of Bcl-xL, which contributed to the intrinsic pathway. The downregulation of cellular FLICE inhibitory protein long isoform (c-FLIPL) in the extrinsic pathway was accomplished through ubiquitination at lysine residue (K) 195 and protein synthesis inhibition. Overexpression of c-FLIPL mutant (K195R) and Bcl-xL mutant (S62A) completely abrogated the synergistic effect. The successful outcome of this study supports the application of multimodality strategy to patients with colorectal hepatic metastases who fail to respond to standard chemoradiotherapy that predominantly targets the mitochondrial apoptotic pathway.