Variable NF-κB pathway responses in colon cancer cells treated with chemotherapeutic drugs
© Samuel et al.; licensee BioMed Central Ltd. 2014
Received: 1 April 2014
Accepted: 6 August 2014
Published: 18 August 2014
The nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway is activated in cells exposed to various stimuli, including those originating on the cell surface or in the nucleus. Activated NF-κB signaling is thought to enhance cell survival in response to these stimuli, which include chemotherapy and radiation. In the present effort, we determined which anticancer drugs preferentially activate NF-κB in colon cancer cells.
NF-κB reporter cells were established and treated with 5-fluorouracil (5-FU, DNA/RNA damaging), oxaliplatin (DNA damaging), camptothecin (CTP, topoisomerase inhibitor), phleomycin (radiomimetic), or erlotinib (EGFR inhibitor). The activation of NF-κB was assessed by immunofluorescence for p65 translocation, luciferase assays, and downstream targets of NF-κB activation (cIAP2, and Bcl-XL) were evaluated by immunoblotting, by ELISA (CXCL8 and IL-6 in culture supernatants), or by gene expression analysis.
Colon cancer cells responded variably to different classes of therapeutic agents, and these agents initiated variable responses among different cell types. CPT activated NF-κB in SW480 colon cancer cells in a dose-dependent manner, but not in HCT116 cells that were either wild-type or deficient for p53. In SW480 colon cancer cells, NF-κB activation by CPT was accompanied by secretion of the cytokine CXCL8, but not by up-regulation of the anti-apoptotic genes, cIAP2 or Bcl-XL. On the contrary, treatment of HCT116 cells with CPT resulted in up-regulation of CXCR2, a receptor for CXCL8, without an increase in cytokine levels. In SW480 cells, NF-κB reporter activity, but not cytokine secretion, was inhibited by SM-7368, an NF-κB inhibitor.
The results show that, in response to cancer therapeutic agents, NF-κB activation varies with the cellular make up and that drug-induced NF-κB activation may be functionally uncoupled from anti-apoptotic outcomes found for other stimuli. Some cancer cells in a heterogeneous tumor tissue may, under therapeutic pressure, release soluble factors that have paracrine activity on neighboring cells that express the cognate receptors.
KeywordsColon cancer NF-κB Camptothecin Drug response Cytokine Chemokine
The outcomes of cancer therapy depend on various determinants that include tumor-intrinsic factors and inter-individual variation in drug response and metabolism. It is still not possible to predict with certainty the response of a given tumor to a particular chemotherapeutic agent. The core tenet of personalized cancer medicine is to identify subsets of patients who will favorably respond to a given therapy and to avoid non-beneficial drug exposure for those who may not respond [1–4]. The efficacy of chemotherapy, especially that of non-targeted agents, is hindered by dose-limiting toxicity and by the development of non-responsiveness. Although targeted agents are designed to reduce the off-target effects of chemotherapy, the development of resistance has hindered progress in cancer therapy and management [2, 5–7]. In line with the potential of personalized medicine, it is essential to identify the genetic, epigenetic, and adaptive characteristics of cancer cells and other cells in the microenvironment that contribute to response to both targeted and broad-acting drugs.
The NF-κB pathway is now a target for therapeutic development, primarily because of its role in chronic inflammatory states, which promote oncogenesis [8–11]. Moreover, experimental and association studies indicate the benefits of suppressing chronic inflammation in reducing the incidence of various types of cancers [12–17]. Moreover, the risk of cancer is higher among colitis patients, and chronic bacterial infection by H. pylori is linked to gastric cancer [18–23].
Nevertheless, the NF-κB mechanism, which contributes to the initiation and progression of cancer, is activated by anticancer drugs and radiation [24–27]. Such activation is clinically undesirable because cells may emerge as resistant, once they are relieved of the drug pressure, or may carry mutations that drive their aggressiveness. Cancer stem-like cells, which utilize the NF-κB pathway, may be responsible for resistance and for re-seeding of the tumor mass after initially effective chemotherapy or radiation [28–31].
The mechanisms through which drugs induce NF-κB activation, and how NF-κB-driven gene expression contributes to drug resistance or other functions, are not fully understood. Drug-induced damage to cancer cell DNA is thought to activate NF-κB through the protein IKK-gamma. DNA-damage activates ATM kinase, which in turn activates NF-κB essential modifier (NEMO), a component of the IKK complex that induces nuclear translocation of the p65/p50 transcription factor complex [24, 32, 33]. The determinants for drug-induced NF-κB activation and the function of activated NF-κB in this context remain to be elucidated.
In the present investigation, reporter cells that carry NF-κB response elements linked to the luciferase gene were used to examine the response of colon cancer cells to drugs. Activation of NF-κB by chemotherapeutic drugs and the downstream effects of the activation varied among cell lines and drug types. Moreover, in the colon cancer cells, the cytokine response was apparently uncoupled from expression of anti-apoptotic genes.
Cell lines and culture
SW480 human colon cancer cells were from American Type Cell Culture (ATCC, Manassas, VA; CCL-228, and CRL-2577). Wild-type and p53-null (p53-/-) HCT116 colon cancer cells were generous gifts from Dr. Bert Vogelstein (Johns Hopkins, Baltimore, MD). Both cell lines were grown in McCoy’s 5A culture medium (ATCC® 30-2007) containing 10% fetal bovine serum, penicillin (10,000 U/ml) and streptomycin (10 mg/ml).
Drugs and reagents
TNFα, 5-FU, CPT, and phleomycin were purchased from Sigma Aldrich (St. Louis, MO); oxaliplatin and erlotinib were purchased from LC laboratories (Woburn, MA). Stock concentrations of the compounds were prepared in sterile water (TNFα and phleomycin) or in dimethylsulfoxide (DMSO) (5-FU, CPT, oxaliplatin, and erlotinib), and stored at -40°C, except TNFα, which was stored at -80°C. Antibodies against p65, NF-κB, cIAP2, and Bcl-XL were purchased from Cell Signaling Technology (Danvers, MA), and anti-tubulin (M2) antibody from Sigma Aldrich. SignalSilence® NF-κB p65 siRNA I (#6261) was purchased from Cell Signaling Technology and NF-κB inhibitor III (SM7368) from EMD Millipore (Billerica, MA). The Chk1/Chk2 specific inhibitor AZD-7762 was purchased from Sigma Aldrich (St. Louis, MO).
Generation and testing of NF-κB reporter SW480 and HCT116 cells
NF-κB reporter stable cells were established by transducing p53-mutant SW480 (ATCC), p53 wild-type HCT116, and p53-null HCT116 (both from Dr. Vogelstein) colon cancer cells with lentiviral constructs containing NF-κB transcriptional response elements (TREs) linked to the luciferase gene (Qiagen, Valencia, CA). In parallel, cells transduced with a construct that lacks the TREs, and which therefore do not respond to NF-κB activation, were used as negative controls to validate the specificity of reporter activity. A construct expressing GFP was used to assess transduction efficiency, which was 100 percent. Transduced cells were selected in a medium containing puromycin (2.5 μg/ml), a concentration established to kill 100% of the control cells within 3 days. To minimize any insertion site bias, pooled populations of transduced cells were used for the assays.
For luciferase assays, cells were seeded and treated in 96-well plates. Before reading the plates, the culture medium was removed by aspiration, and 50 μL of 1× luciferin-PBS substrate solution was added to each well. With a luminometer set at 37°C, plates were read immediately after addition of substrate solution and after 5 and 10 minutes. The time point at which peak readings for all the wells were obtained was taken for calculation of relative luciferase units (RLU). Luciferase expression was quantified as RLU, normalized to readings of control wells, and expressed as relative NF-κB reporter activity.
Colorimetric CXCL8 and IL-6 ELISA kits were purchased from R&D Systems, and the assays were performed according to the manufacturer’s instructions. Culture supernatants from equivalent numbers of cells seeded in multi-well plates were harvested 24 hours after the last treatment. Total protein in the supernatants was measured with DC Protein Assay (BioRad, Herculus, CA) and volume-adjusted with sterile PBS to the sample with the lowest protein content. Samples were diluted 1:3 in the assay diluent buffer. Color development at the end of ELISA assays was measured with a microplate reader (BioTek, Winooski, VT).
RT-PCR for cytokine and receptor gene expression analysis
Total RNA was extracted from cells by use of RNeasy extraction kits (Qiagen, Valencia, CA). QuantiTect cDNA synthesis kits (Qiagen) were used to reverse transcribe 100 ng of RNA in a final volume of 20 μL. RNA and cDNA were stored at -80°C until used. Primers suitable for RT-PCR were designed using the PrimerQuest designer tool (IDT DNA, Coralville, IA), ensuring exon spanning. Primer sequences in 5′ to 3′ orientation were: CXCL8 forward, CTTGGCAGCCTTCCTGATTT, reverse, GGGTGGAAAGGTTTGGAGTATG; CXCR1 forward, CAAGTGCCCTCTAGCTGTTAAG, reverse, CAGCAATGGTTTGATCTAACTGAAG; CXCR2 forward, CATCGTCAAGGTTGTTTCATCTT, reverse, AGCTGTGACCTGCTGTTATT; and IL6 forward, AAAGAGGCACTGGCAGAAA, reverse, CAGGCAAGTCTCCTCATTGAA. SYBR Green PCR was performed by use of Quantitect SYBR Green master mix (Qiagen) and run on a MX3005P or MX3000P thermocycler from Agilent Technologies/Stratagene (Santa Clara, CA). For each experiment, expression values were normalized against the control values.
CellMiner data mining and analysis
CellMiner tool (http://discover.nci.nih.gov/cellminer/home.do; version 1.5) was used to compare and plot the relative baseline expression of CXCR1 and CXCR2 mRNA among colon cancer cells included in the NCI-60 panel. The tool enables retrieval and integrated analysis of baseline and experimental data compiled from the 60 cell lines included in the panel [34, 35]. CellMiner gene transcript data was generated from five microarray platforms. To generate the transcript graph for colon cancer cells, we selected gene transcript level z-score for analysis type and CXCR1 and CXCR2 as gene identifier inputs.
Cells for immunofluorescent staining were grown and treated in chamber slides, and then fixed in 4% formaldehyde in PBS for 10 minutes, permeabilized for 10 minutes with 0.2% Triton X-100 in PBS, and blocked with 2% BSA for 1 hour. Rabbit primary antibody to p65 (Cell Signaling®) was diluted at 1:400 in PBS containing 1% BSA and incubated for 1 hour at room temperature. AF-488 anti-rabbit secondary antibody was from Life Technologies® (Grand Island, NY), and was diluted 1:250 in 1% BSA in PBS, and incubated for 1 hour. Images were captured using Olympus® BX53 optical microscope.
Signal-specific response of reporter cells
Drug- and cell type-dependent NF-κB responses in SW480 and HCT116 colon cancer cells
Having established the responsiveness of these cells to NF-κB pathway activation, the effects of four drugs currently in clinical use, 5-FU (10 μM), CPT (1 μm), oxaliplatin (10 μM), and erlotinib (20 μM), as well as phleomycin (100 μg/ml), a radiomimetic compound, were determined. Among these, only erlotinib (an EGFR inhibitor) is a receptor-targeted drug; the others are non-selective. The results (Figure 2A-C, lower panels) show that SW480 and HCT116 cells respond to these drugs differently. The radiomimetic drug phleomycin induced the highest activation of NF-κB reporter activity in the p53 mutant SW480 cells, but only erlotinib induced NF-κB in both wild-type and p53-null HCT116 cells. As in the previous results, there was no difference in the pattern of NF-κB activation between the p53-null and wild-type HCT116 cells. However, unlike in SW480 cells, CPT decreased the level of basal reporter activity in both types of HCT116 cells. In contrast, CPT treatment consistently increased the activation of NF-κB reporter activity in SW480 cells, albeit to a lower extent relative to phleomycin. 5-FU and oxaliplatin did not induce remarkable activity in these cell lines and therefore were not utilized further (Additional file 1: Figure S1).
Concentration-dependent NF-κB response in SW480 and HCT116 colon cancer cells
NF-κB activation by CPT is accompanied by p65 nuclear re-localization
NF-κB activation by CPT in SW480 cells is accompanied by up-regulation of CXCL8, but not of cIAP2 or Bcl-XL
Chemical and molecular inhibition of the NF-κB pathway suggests cytokine induction by CPT proceeds through alternative mechanisms
CPT treatment up-regulates the expression of CXCL8 receptors CXCR1 and CXCR2 in HCT116 colon cancer cells
The evidence presented here indicates that treatment of colon cancer cells with broad-acting and targeted chemotherapeutic drugs leads to heterogeneous responses that vary depending on the cellular make-up and the type of drug used. Adding to the complexity of such responses, no comparable NF-κB response was evident, even when drugs with similar known mechanisms of action (for example, DNA damage) were used on colon cancer cells, and neither did the same drug elicit similar responses in different types of cells. While the response of cells to a given drug could be dynamic, identification of the factors that determine which cells will respond to a given drug by activating the NF-κB pathway emerges as a new challenge. Moreover, given the heterogeneity of cells in tumor tissues and their microenvironments, the question of which of these cells exposed to chemotherapeutic drugs or radiation respond in a particular way needs to be addressed. Such responses include secretion of proteins that regulate motility, vasculature, drug resistance, cytokines, and growth factors as well as the receptors for those factors. Moreover, the functions of such predictable or dynamic responses to the outcomes of cancer treatment remain challenges to be addressed.
The activation of NF-κB in response to chemotherapy is established [25, 39, 40], although the mechanisms and the functions of such activation remain largely unknown. Inhibition of NF-κB activation may sensitize cells to CPT [41, 42]. NF-κB pathways could be activated through two mechanisms: signals that originate at cell receptors and signals that originate in the nucleus [10, 37]. The pathways that originate at the cell membrane involve the TNF receptor-family proteins as well as their downstream adaptor and signal transducer proteins [37, 43]. Nevertheless, the nuclear signaling of NF-κB activation is still largely unknown. Nuclear-mediated activation of NF-κB involves DNA-damage proteins, primarily the ATM/ATR kinase proteins, which transduce the signal to the cytoplasm through the adapter protein, NEMO [24, 25, 32]. It is perplexing that not all DNA-damaging drugs activate NF-κB in colon cancer cells, even under similar conditions. Since cell lines vary from one another, identification of key regulators for nuclear NF-κB activation and systematic examination of their functions could elucidate the mechanisms behind the activation. Moreover, the activation of NF-κB by receptor-acting erlotinib only in HCT116 cells raises another level of complexity, because both SW480 and HCT116 cells are wild-type for the erlotinib target, EGFR. It is possible that erlotinib has targets that are differentially expressed between SW480 and HCT116 cells, or that signaling intermediates downstream of EGFR may be divergent in cross-talk with the NF-κB pathway.
Perhaps activation of specific genes by NF-κB requires interactions with additional regulatory factors. For example, the CXCL8 promoter contains AP1 transcription factor binding sites that may co-regulate expression of the cytokine . Accordingly, cross-talk between the AP-1 and NF-κB pathways may explain the differential regulation of CXCL8 and anti-apoptotic proteins downstream of NF-κB activation. Further studies are needed to discern how this distinction is achieved in cells.
The up-regulation of CXCR2 and CXCR1 receptors by HCT116 cells, which do not activate NF-κB in response to CPT, raises the possibility that subgroups of cells in a heterogeneous tumor mass may, under chemotherapy, secrete or respond to soluble factors in the microenvironment. Although HCT116 and SW480 cells are more evolutionarily divergent from each other than cancer cells in a patient, the heterogeneity in solid tumors and their metastases does not preclude the existence of subsets of cells with different secretory and responsive characteristics. Therefore, it is rational to suggest that the combination of CPT therapy with antagonists of CXCR2 and CXCR1, especially in individuals who respond to CPT by activation of NF-κB, may improve the therapeutic efficacy. To enhance the efficacy of chemotherapy, further studies are needed to identify additional targets in the NF-κB – CXCR2/CXCR1 axis.
In response to cancer therapeutic agents, NF-κB activation varies with the cellular make up and that drug-induced NF-κB activation may be functionally uncoupled from anti-apoptotic outcomes found for other stimuli. Some cancer cells in a heterogeneous tumor tissue may, under therapeutic pressure, release soluble factors that have paracrine activity on neighboring cells that express the cognate receptors. The potential benefits of targeting these soluble factors and their receptors alongside mainstream chemotherapy need to be further studied.
Nuclear factor kappa-light-chain-enhancer of activated B cells
C-X-C chemokine receptor
Epidermal growth factor receptor
Cellular inhibitor of apoptosis 2.
This study was supported by NIH grants U54CA118948, SC3GM109314 and G12MD007585 (RCMI support to Tuskegee University shared instrumentation core facility). We thank Donald Hill for editorial assistance.
- Gonzalez de Castro D, Clarke PA, Al-Lazikani B, Workman P: Personalized cancer medicine: molecular diagnostics, predictive biomarkers, and drug resistance. Clin Pharmacol Ther. 2013, 93 (3): 252-259.View ArticlePubMedPubMed CentralGoogle Scholar
- Cirkel GA, Gadellaa-van Hooijdonk CG, Koudijs MJ, Willems SM, Voest EE: Tumor heterogeneity and personalized cancer medicine: are we being outnumbered?. Future Oncol. 2014, 10 (3): 417-428.View ArticlePubMedGoogle Scholar
- Burke W, Brown Trinidad S, Press NA: Essential elements of personalized medicine. Urol Oncol. 2014, 32 (2): 193-197.View ArticlePubMedGoogle Scholar
- Jiang Y, Wang M: Personalized medicine in oncology: tailoring the right drug to the right patient. Biomark Med. 2010, 4 (4): 523-533.View ArticlePubMedGoogle Scholar
- Stehle F, Schulz K, Seliger B: Towards defining biomarkers indicating resistances to targeted therapies. Biochim Biophys Acta. 2014, 1844 (5): 909-916.View ArticlePubMedGoogle Scholar
- Lackner MR, Wilson TR, Settleman J: Mechanisms of acquired resistance to targeted cancer therapies. Future Oncol. 2012, 8 (8): 999-1014.View ArticlePubMedGoogle Scholar
- Gentry LR, Martin TD, Der CJ: Mechanisms of targeted therapy resistance take a de-TOR. Cancer Cell. 2013, 24 (3): 284-286.View ArticlePubMedGoogle Scholar
- Takahashi H, Ogata H, Nishigaki R, Broide DH, Karin M: Tobacco smoke promotes lung tumorigenesis by triggering IKKbeta- and JNK1-dependent inflammation. Cancer Cell. 2010, 17 (1): 89-97.View ArticlePubMedPubMed CentralGoogle Scholar
- Meylan E, Dooley AL, Feldser DM, Shen L, Turk E, Ouyang C, Jacks T: Requirement for NF-kappaB signalling in a mouse model of lung adenocarcinoma. Nature. 2009, 462 (7269): 104-107.View ArticlePubMedPubMed CentralGoogle Scholar
- Karin M: Nuclear factor-kappaB in cancer development and progression. Nature. 2006, 441 (7092): 431-436.View ArticlePubMedGoogle Scholar
- Greten FR, Eckmann L, Greten TF, Park JM, Li ZW, Egan LJ, Kagnoff MF, Karin M: IKKbeta links inflammation and tumorigenesis in a mouse model of colitis-associated cancer. Cell. 2004, 118 (3): 285-296.View ArticlePubMedGoogle Scholar
- Wernli KJ, Newcomb PA, Hampton JM, Trentham-Dietz A, Egan KM: Inverse association of NSAID use and ovarian cancer in relation to oral contraceptive use and parity. Br J Cancer. 2008, 98 (11): 1781-1783.View ArticlePubMedPubMed CentralGoogle Scholar
- McCormack VA, Hung RJ, Brenner DR, Bickeboller H, Rosenberger A, Muscat JE, Lazarus P, Tjonneland A, Friis S, Christiani DC, Chun EM, Le Marchand L, Rennert G, Rennert HS, Andrew AS, Orlow I, Park B, Boffetta P, Duell EJ: Aspirin and NSAID use and lung cancer risk: a pooled analysis in the International Lung Cancer Consortium (ILCCO). Cancer Causes Control. 2011, 22 (12): 1709-1720.View ArticlePubMedGoogle Scholar
- Kune GA: Colorectal cancer chemoprevention: aspirin, other NSAID and COX-2 inhibitors. Aust N Z J Surg. 2000, 70 (6): 452-455.View ArticlePubMedGoogle Scholar
- Coghill AE, Phipps AI, Bavry AA, Wactawski-Wende J, Lane DS, Lacroix A, Newcomb PA: The association between NSAID use and colorectal cancer mortality: results from the women’s health initiative. Cancer Epidemiol Biomarkers Prev. 2012, 21 (11): 1966-1973.View ArticlePubMedPubMed CentralGoogle Scholar
- Chell S, Patsos HA, Qualtrough D, AM HZ, Hicks DJ, Kaidi A, Witherden IR, Williams AC, Paraskeva C: Prospects in NSAID-derived chemoprevention of colorectal cancer. Biochem Soc Trans. 2005, 33 (Pt 4): 667-671.View ArticlePubMedGoogle Scholar
- Altinoz MA, Korkmaz R: NF-kappaB, macrophage migration inhibitory factor and cyclooxygenase-inhibitions as likely mechanisms behind the acetaminophen- and NSAID-prevention of the ovarian cancer. Neoplasma. 2004, 51 (4): 239-247.PubMedGoogle Scholar
- Wang CY, Mayo MW, Korneluk RG, Goeddel DV, Baldwin AS: NF-kappaB antiapoptosis: induction of TRAF1 and TRAF2 and c-IAP1 and c-IAP2 to suppress caspase-8 activation. Science. 1998, 281 (5383): 1680-1683.View ArticlePubMedGoogle Scholar
- Lakatos L, Mester G, Erdelyi Z, David G, Pandur T, Balogh M, Fischer S, Vargha P, Lakatos PL: Risk factors for ulcerative colitis-associated colorectal cancer in a Hungarian cohort of patients with ulcerative colitis: results of a population-based study. Inflamm Bowel Dis. 2006, 12 (3): 205-211.View ArticlePubMedGoogle Scholar
- Kornfeld D, Ekbom A, Ihre T: Is there an excess risk for colorectal cancer in patients with ulcerative colitis and concomitant primary sclerosing cholangitis? A population based study. Gut. 1997, 41 (4): 522-525.View ArticlePubMedPubMed CentralGoogle Scholar
- Kanneganti M, Mino-Kenudson M, Mizoguchi E: Animal models of colitis-associated carcinogenesis. J Biomed Biotechnol. 2011, 2011: 342637-View ArticlePubMedPubMed CentralGoogle Scholar
- Eaden JA, Abrams KR, Mayberry JF: The risk of colorectal cancer in ulcerative colitis: a meta-analysis. Gut. 2001, 48 (4): 526-535.View ArticlePubMedPubMed CentralGoogle Scholar
- Danese S, Mantovani A: Inflammatory bowel disease and intestinal cancer: a paradigm of the Yin-Yang interplay between inflammation and cancer. Oncogene. 2010, 29 (23): 3313-3323.View ArticlePubMedGoogle Scholar
- McCool KW, Miyamoto S: DNA damage-dependent NF-kappaB activation: NEMO turns nuclear signaling inside out. Immunol Rev. 2012, 246 (1): 311-326.View ArticlePubMedPubMed CentralGoogle Scholar
- Huang TT, Wuerzberger-Davis SM, Seufzer BJ, Shumway SD, Kurama T, Boothman DA, Miyamoto S: NF-kappaB activation by camptothecin. A linkage between nuclear DNA damage and cytoplasmic signaling events. J Biol Chem. 2000, 275 (13): 9501-9509.View ArticlePubMedGoogle Scholar
- Enzler T, Sano Y, Choo MK, Cottam HB, Karin M, Tsao H, Park JM: Cell-selective inhibition of NF-kappaB signaling improves therapeutic index in a melanoma chemotherapy model. Cancer Discov. 2011, 1 (6): 496-507.View ArticlePubMedPubMed CentralGoogle Scholar
- Brea-Calvo G, Siendones E, Sanchez-Alcazar JA, de Cabo R, Navas P: Cell survival from chemotherapy depends on NF-kappaB transcriptional up-regulation of coenzyme Q biosynthesis. PLoS One. 2009, 4 (4): e5301-View ArticlePubMedPubMed CentralGoogle Scholar
- Perona R, Lopez-Ayllon BD, de Castro CJ, Belda-Iniesta C: A role for cancer stem cells in drug resistance and metastasis in non-small-cell lung cancer. Clin Transl Oncol. 2011, 13 (5): 289-293.View ArticlePubMedGoogle Scholar
- Houthuijzen JM, Daenen LG, Roodhart JM, Voest EE: The role of mesenchymal stem cells in anti-cancer drug resistance and tumour progression. Br J Cancer. 2012, 106 (12): 1901-1906.View ArticlePubMedPubMed CentralGoogle Scholar
- Gangemi R, Paleari L, Orengo AM, Cesario A, Chessa L, Ferrini S, Russo P: Cancer stem cells: a new paradigm for understanding tumor growth and progression and drug resistance. Curr Med Chem. 2009, 16 (14): 1688-1703.View ArticlePubMedGoogle Scholar
- Dean M, Fojo T, Bates S: Tumour stem cells and drug resistance. Nat Rev Cancer. 2005, 5 (4): 275-284.View ArticlePubMedGoogle Scholar
- Wu ZH, Shi Y, Tibbetts RS, Miyamoto S: Molecular linkage between the kinase ATM and NF-kappaB signaling in response to genotoxic stimuli. Science. 2006, 311 (5764): 1141-1146.View ArticlePubMedGoogle Scholar
- Huang TT, Wuerzberger-Davis SM, Wu ZH, Miyamoto S: Sequential modification of NEMO/IKKgamma by SUMO-1 and ubiquitin mediates NF-kappaB activation by genotoxic stress. Cell. 2003, 115 (5): 565-576.View ArticlePubMedGoogle Scholar
- Shankavaram UT, Varma S, Kane D, Sunshine M, Chary KK, Reinhold WC, Pommier Y, Weinstein JN: Cell Miner: a relational database and query tool for the NCI-60 cancer cell lines. BMC Genomics. 2009, 10: 277-View ArticlePubMedPubMed CentralGoogle Scholar
- Reinhold WC, Sunshine M, Liu H, Varma S, Kohn KW, Morris J, Doroshow J, Pommier Y: Cell Miner: a web-based suite of genomic and pharmacologic tools to explore transcript and drug patterns in the NCI-60 cell line set. Cancer Res. 2012, 72 (14): 3499-3511.View ArticlePubMedPubMed CentralGoogle Scholar
- Krasinskas AM: EGFR signaling in colorectal carcinoma. Patholog Res Int. 2011, 2011: 932932-PubMedPubMed CentralGoogle Scholar
- Hayden MS, Ghosh S: NF-kappaB, the first quarter-century: remarkable progress and outstanding questions. Genes Dev. 2012, 26 (3): 203-234.View ArticlePubMedPubMed CentralGoogle Scholar
- Gales D, Clark C, Manne U, Samuel T: The chemokine CXCL8 in carcinogenesis and drug response. ISRN Oncol. 2013, 2013: 859154-PubMedPubMed CentralGoogle Scholar
- Wang CY, Cusack JC, Liu R, Baldwin AS: Control of inducible chemoresistance: enhanced anti-tumor therapy through increased apoptosis by inhibition of NF-kappaB. Nat Med. 1999, 5 (4): 412-417.View ArticlePubMedGoogle Scholar
- Togano T, Sasaki M, Watanabe M, Nakashima M, Tsuruo T, Umezawa K, Higashihara M, Watanabe T, Horie R: Induction of oncogene addiction shift to NF-kappaB by camptothecin in solid tumor cells. Biochem Biophys Res Commun. 2009, 390 (1): 60-64.View ArticlePubMedGoogle Scholar
- He L, Kim BY, Kim KA, Kwon O, Kim SO, Bae EY, Lee MS, Kim MS, Jung M, Moon A, Bae K, Ahn JS: NF-kappaB inhibition enhances caspase-3 degradation of Akt1 and apoptosis in response to camptothecin. Cell Signal. 2007, 19 (8): 1713-1721.View ArticlePubMedGoogle Scholar
- Guo J, Verma UN, Gaynor RB, Frenkel EP, Becerra CR: Enhanced chemosensitivity to irinotecan by RNA interference-mediated down-regulation of the nuclear factor-kappaB p65 subunit. Clin Cancer Res. 2004, 10 (10): 3333-3341.View ArticlePubMedGoogle Scholar
- Hoesel B, Schmid JA: The complexity of NF-kappaB signaling in inflammation and cancer. Mol Cancer. 2013, 12: 86-View ArticlePubMedPubMed CentralGoogle Scholar
- Sankpal NV, Fleming TP, Gillanders WE: EpCAM modulates NF-kappaB signaling and interleukin-8 expression in breast cancer. Mol Cancer Res. 2013, 11 (4): 418-426.View ArticlePubMedPubMed CentralGoogle Scholar
- The pre-publication history for this paper can be accessed here:http://www.biomedcentral.com/1471-2407/14/599/prepub
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