Loss of p53, rather than beta-catenin overexpression, induces survivin-mediated resistance to apoptosis in an esophageal cancer cell line

Potentiation of novel porphyrin based photodynamic therapy against colon cancer with low dose doxorubicin and elucidating the molecular signalling pathways responsible for relapse

Photodynamic therapy (PDT) is a promising non-invasive treatment modality for cancer and can be potentiated by combination with chemotherapy. Here, we combined PDT of novel porphyrin-based photosensitizers with low dose doxorubicin (Dox) to get maximum outcome. Dox potentiated and showed synergism with PDT under in vitro conditions on CT26.WT cells. The current colon cancer treatment strategies assure partial or even complete tumour regression but loco-regional relapse or distant metastasis is the major cause of death despite combination therapy. The spared cells after the treatment contribute to relapse and it is important to study their behaviour in host environment. Hence, we developed relapse models for PDT, Dox and combination treatments by transplanting respectively treated equal number of live cells to mice (n = 5) for tumour formation. Most of the treated cells lost tumour forming ability, but some treatment resistant cells developed tumours in few mice. These tumours served as relapse models and Western blot analysis of tumour samples provided clinically relevant information to delineate resistance strategies of individual as well as combination therapies at molecular level. Our results showed that low dose Dox helped in increasing the tumour inhibiting effect of PDT in combination therapy, but still there are indeed possibilities of relapse at later stages due to chemoresistance and immune suppression that may occur post-treatment. We observed that the combination therapy may also lead to the development of multidrug resistant (MDR) phenotype during relapse. Thus, this study provided clinically relevant information to further strengthen and improve PDT-drug combination therapy in order to avoid relapse and to treat cancer more effectively.

Synergy between histone deacetylase inhibitors and DNA-damaging agents is mediated by histone deacetylase 2 in colorectal cancer

Previous studies have associated the overexpression of histone deacetylase 2 (HDAC2) and the presence of TP53 mutations with the progression to advanced stage drug resistant colorectal cancer (CRC). However, the mechanistic link between HDAC2 expression and the TP53 mutational status has remained unexplored. Here, we investigated the function of HDAC2 in drug resistance by assessing the synergistic effects of DNA-targeted chemotherapeutic agents and HDAC inhibitors (HDACis) on two TP53-mutated colorectal adenocarcinoma CRC cell lines (SW480 and HT-29) and on the TP53-wild type carcinoma cell line (HCT116 p53+/+) and its TP53 deficient sub-line (HCT116 p53−/−). We showed that in the untreated SW480 and HT-29 cells the steady-state level of HDAC2 was low compared to a TP53-wild type carcinoma cell line (HCT116 p53+/+). Increased expression of HDAC2 correlated with drug resistance, and depletion by shRNA sensitised the multi-drug resistance cell line HT-29 to CRC chemotherapeutic drugs such as 5-fluorouracil (5-FU) and oxaliplatin (Oxa). Combined treatment with the HDACi suberoylanilide hydroxamic acid plus 5-FU or Oxa reduced the level of HDAC2 expression, modified chromatin structure and induced mitotic cell death in HT-29 cells. Non-invasive bioluminescence imaging revealed significant reductions in xenograft tumour growth with HDAC2 expression level reduced to <50% in treated animals. Elevated levels of histone acetylation on residues H3K9, H4K12 and H4K16 were also found to be associated with resistance to VPA/Dox or SAHA/Dox treatment. Our results suggest that HDAC2 expression rather than the p53 mutation status influences the outcome of combined treatment with a HDACi and DNA-damaging agents in CRC.

Radiation-resistant cancer stem-like cell properties are regulated by PTEN through the activity of nuclear β-catenin in nasopharyngeal carcinoma

Radiotherapy is the primary and most important treatment for nasopharyngeal carcinoma (NPC). Cancer stem-like cells (CSCs) have been shown to be resistant to radiation. The phosphatase and tensin homolog deleted on chromosome 10 (PTEN) tumor suppressor gene has been suggested to play a role in stem cell self-renewal. In the present study, we sorted PTEN−/+ cells using a flow cytometer. The clone formation assay showed that PTEN− cells were more radioresistant than PTEN+ NPC cells. We found that PTEN− cells demonstrated a significant increase in tumorsphere formation and CSCs markers compared with PTEN+ cells. Silencing the expression of PTEN with siRNA resulted in increased expression of p-AKT, active β-catenin and Nanog. siPTEN cells irradiated showed more radioresistant and DNA damage than parental cells. We also confirmed that down-regulation of β-catenin expression with shRNA resulted in a reduced percentage of side population cells and expression of Nanog. shβ-catenin cells significantly decreased survivin expression at 4 Gy irradiation in PTEN− cells compared with PTEN+ cells. In siPTEN cells, β-catenin staining shifted from the cytoplasmic membrane to the nucleus. Furthermore, immunofluorescence showed that following irradiation of PTEN− cells, at 4 Gy, active β-catenin was mainly found in the nucleus. Immunohistochemistry analysis also demonstrated that the PTEN−/p-AKT+/β-catenin+/Nanog+ axis may indicate poor prognosis and radioresistance in clinical NPC specimens. Thus, our findings strongly suggest that PTEN− cells have CSCs properties that are resistant to radiation in NPC. PTEN exerts these effects through the downstream effector PI3K/AKT/β-catenin/Nanog axis which depends on nuclear β-catenin accumulation.

Prognostic significance of survivin, β-catenin and p53 expression in urothelial carcinoma

Survivin, β-catenin, and p53 are well-known cell-cycle and apoptosis regulators of tumorigenesis. Urothelial carcinomas (UCs) are the most common of the human cancers. Compared to superficial tumors (Ta, CIS, or T1), invasive UCs are important with regard to recurrence, progression, and mortality. Therefore, we examined whether survivin, β-catenin, and p53 could be used as the biomarkers for the early prediction of the invasiveness of UCs and the overall survival of the patients. We investigated the prognostic expressions of those biomarkers in UC (n=147) and in non-muscle invasive UC (NMI-UC) (n=113), using tissue microarray and immunohistochemistry. Spearman's correlation analysis and multivariate Cox regression analyses were used for statistical interpretation. High expressions of β-catenin, survivin, and p53 were associated with a high T stage, recurrence, progression, mortality, low recurrence-free survival, low progression-free survival and low overall survival (p <0.01). Similar findings were achieved for recurrence and progression in the NMI-UC group, except for mortality. Moreover, a positive correlation was shown between p53 and β-catenin and between p53 and survivin (r=0.221, p <0.01; r=0.236, p <0.01, respectively). Survivin, p53, and β-catenin overexpression, as prognostic markers, might suggest that the UCs are biologically aggressive with the poor prognosis. Thus, dysregulation of those these cell-cycle and apoptosis regulators in bladder carcinoma could be used as a molecular marker to determine the best treatment strategy and could contribute to the development of targeted therapies.

Overexpression of miR-214-3p in esophageal squamous cancer cells enhances sensitivity to cisplatin by targeting survivin directly and indirectly through CUG-BP1

Based on its marked overexpression in multiple malignancies and its roles in promoting cell survival and proliferation, survivin is an attractive candidate for targeted therapy. Towards this end, a detailed understanding of the mechanisms regulating survivin expression in different cancer cells will be critical. We have previously shown that the RNA-binding protein (RBP) CUG-BP1 is overexpressed in esophageal cancer cells and post-transcriptionally regulates survivin in these cells. The objective of this study was to investigate the role of microRNAs (miRs) in regulating survivin expression in esophageal cancer cells. Using miR expression profiling analysis, we found that miR-214-3p is one of the most markedly downregulated miRs in two esophageal squamous cancer cell lines compared to esophageal epithelial cells. Interestingly, using miR target prediction programs, both survivin and CUG-BP1 mRNA were found to contain potential binding sites for miR-214-3p. Forced expression of miR-214-3p in esophageal cancer cells leads to a decrease in the mRNA and protein levels of both survivin and CUG-BP1. This effect is due to decreased mRNA stability of both targets. By contrast, silencing miR-214-3p in esophageal epithelial cells leads to an increase in both survivin and CUG-BP1 mRNA and protein. To determine whether the observed effect of miR-214-3p on survivin expression was direct, mediated through CUG-BP1, or both, binding studies utilizing biotin pull-down assays and heterologous luciferase reporter constructs were performed. These demonstrated that the mRNA of survivin and CUG-BP1 each contain two functional miR-214-3p binding sites as confirmed by mutational analysis. Finally, forced expression of miR-214-3p enhances the sensitivity of esophageal cancer cells to Cisplatin-induced apoptosis. This effect is abrogated with rescue expression of survivin or CUG-BP1. These findings suggest that miR-214-3p acts as a tumor suppressor and that its downregulation contributes to chemoresistance in esophageal cancer cells by targeting both survivin and CUG-BP1.

Correlation of STAT1 with apoptosis and cell-cycle markers in esophageal squamous cell carcinoma

We recently found evidence that STAT1 in esophageal squamous carcinoma (ESCC) cells exerts tumor suppressor function, and it regulates five key regulators of apoptosis or cell-cycle progression, including Bcl-2, Bcl-xL, survivin, cyclin D1 and p21. In this study, we confirmed these findings in four ESCC cell lines. Using immunohistochemistry, we also assessed the expression of these proteins in 62 primary tumors. The expression of these markers was heterogeneous, ranging 39 to 69% of the cohort. Significant correlation was found between STAT1 and three proteins (p21, Bcl-xL and survivin), whereas only a trend was identified for cyclin D1 and Bcl-2. We then correlated the expression of these proteins with several clinicopathologic parameters including lymph node metastasis, depth of invasion, clinical stage and overall survival. Significant correlations were found between Bcl-2 and deep invasion (p = 0.033), survivin and lymph node metastasis (p = 0.006), as well as cyclin D1 and clinical stage (p = 0.014). Patients with p21-positive tumors had a significantly longer survival compared to those with p21-negative tumors (p = 0.031). To conclude, our findings support the concept that STAT1 exerts its tumor suppressor effects in ESCC via modulating the expression of key regulators of apoptosis and cell-cycle progression.

Prognostic value and targeted inhibition of survivin expression in esophageal adenocarcinoma and cancer-adjacent squamous epithelium

BACKGROUND

Survivin is an inhibitor of apoptosis and its over expression is associated with poor prognosis in several malignancies. While several studies have analyzed survivin expression in esophageal squamous cell carcinoma, few have focused on esophageal adenocarcinoma (EAC) and/or cancer-adjacent squamous epithelium (CASE). The purpose of this study was 1) to determine the degree of survivin up regulation in samples of EAC and CASE, 2) to evaluate if survivin expression in EAC and CASE correlates with recurrence and/or death, and 3) to examine the effect of survivin inhibition on apoptosis in EAC cells.

METHODS

Fresh frozen samples of EAC and CASE from the same patient were used for qRT-PCR and Western blot analysis, and formalin-fixed, paraffin-embedded tissue was used for immunohistochemistry. EAC cell lines, OE19 and OE33, were transfected with small interfering RNAs (siRNAs) to knockdown survivin expression. This was confirmed by qRT-PCR for survivin expression and Western blot analysis of cleaved PARP, cleaved caspase 3 and survivin. Survivin expression data was correlated with clinical outcome.

RESULTS

Survivin expression was significantly higher in EAC tumor samples compared to the CASE from the same patient. Patients with high expression of survivin in EAC tumor had an increased risk of death. Survivin expression was also noted in CASE and correlated with increased risk of distant recurrence. Cell line evaluation demonstrated that inhibition of survivin resulted in an increase in apoptosis.

CONCLUSION

Higher expression of survivin in tumor tissue was associated with increased risk of death; while survivin expression in CASE was a superior predictor of recurrence. Inhibition of survivin in EAC cell lines further showed increased apoptosis, supporting the potential benefits of therapeutic strategies targeted to this marker.

ATF2 knockdown reinforces oxidative stress-induced apoptosis in TE7 cancer cells

Cancer cells showing low apoptotic effects following oxidative stress-induced DNA damage are mainly affected by growth arrest. Thus, recent studies focus on improving anti-cancer therapies by increasing apoptosis sensitivity. We aimed at identifying a universal molecule as potential target to enhance oxidative stress-based anti-cancer therapy through a switch from cell cycle arrest to apoptosis. A cDNA microarray was performed with hydrogen peroxide-treated oesophageal squamous epithelial cancer cells TE7. This cell line showed checkpoint activation via p21^WAF1, but low apoptotic response following DNA damage. The potential target molecule was chosen depended on the following demands: it should regulate DNA damage response, cell cycle and apoptosis. As the transcription factor ATF2 is implicated in all these processes, we focused on this protein. We investigated checkpoint activation via ATF2. Indeed, ATF2 knockdown revealed ATF2-triggered p21^WAF1 protein expression, suggesting p21^WAF1 transactivation through ATF2. Using chromatin immunoprecipitation (ChIP), we identified a hitherto unknown ATF2-binding sequence in the p21^WAF1 promoter. p-ATF2 was found to interact with p-c-Jun, creating the AP-1 complex. Moreover, ATF2 knockdown led to c-Jun downregulation. This suggests ATF2-driven induction of c-Jun expression, thereby enhancing ATF2 transcriptional activity via c-Jun-ATF2 heterodimerization. Notably, downregulation of ATF2 caused a switch from cell cycle arrest to reinforced apoptosis, presumably via p21^WAF1 downregulation, confirming the importance of ATF2 in the establishment of cell cycle arrest. 1-Chloro-2,4-dinitrobenzene also led to ATF2-dependent G2/M arrest, suggesting that this is a general feature induced by oxidative stress. As ATF2 knockdown also increased apoptosis, we propose ATF2 as a target for combined oxidative stress-based anti-cancer therapies.

Overexpression of cyclin B1 antagonizes chemotherapeutic-induced apoptosis through PTEN/Akt pathway in human esophageal squamous cell carcinoma cells

The role of cyclin B1 in the clinical therapeutic sensitivity of human esophageal squamous cell carcinoma (ESCC) remains to be defined. In this study, we found that elevated cyclin B1 expression attenuated the apoptosis induced by cisplatin or paclitaxel, while knockdown of cyclin B1 enhanced cisplatin or paclitaxel sensitivity in ESCC cells. Cyclin B1-mediated apoptosis may rely on the Bcl-2-dependent mitochondria-regulated intrinsic death pathway, and the antagonizing effect of cyclin B1 on chemotherapeutic agent-induced apoptosis was through PTEN/Akt pathway. Therefore, cyclin B1 might be a therapeutic target for the development of specific and efficient approaches in the treatment of ESCC.

The RNA-binding protein CUG-BP1 increases survivin expression in oesophageal cancer cells through enhanced mRNA stability

Survivin, a member of the IAP (inhibitor of apoptosis protein) family, plays important roles in maintaining cellular homoeostasis and regulating cell-cycle progression. This IAP is overexpressed in oesophageal cancer cells, leading to uncontrolled cell growth and resistance to apoptosis. CUG-BP1 (CUG-binding protein 1) is an RNA-binding protein that regulates the stability and translational efficiency of target mRNAs. In the present paper, we report that CUG-BP1 is overexpressed in oesophageal cancer cell lines and human oesophageal cancer specimens. CUG-BP1 associates with the 3'-untranslated region of survivin mRNA, thereby stabilizing the transcript and elevating its expression in oesophageal cancer cells. Our results show that overexpression of CUG-BP1 in oesophageal epithelial cells results in increased survivin mRNA stability and consequently survivin protein expression. Conversely, silencing CUG-BP1 in oesophageal cancer cells destabilizes survivin mRNA, lowering the level of survivin protein. In addition, we have found that altering CUG-BP1 expression modulates susceptibility to chemotherapy-induced apoptosis. Overexpression of CUG-BP1 in oesophageal epithelial cells increases resistance to apoptosis, whereas silencing CUG-BP1 makes oesophageal cancer cells more susceptible to chemotherapy-induced apoptosis. Co-transfection experiments with small interfering RNA directed against survivin suggest that the anti-apoptotic role for CUG-BP1 is not entirely dependent on its effect on survivin expression.

The RNA-binding protein HuR stabilizes survivin mRNA in human oesophageal epithelial cells

Overexpression of survivin, a member of the IAP (inhibitor of apoptosis) family, has been correlated with poorer outcomes in multiple malignancies, including oesophageal cancer. The regulatory mechanisms, particularly at the post-transcriptional level, involved in survivin overexpression are not well understood. Previous work from our group has shown that the RNA-binding protein HuR (Hu antigen R), which is also overexpressed in several malignancies, stabilizes the mRNA of XIAP (X-linked IAP), another IAP family member. In the present study, we demonstrate the binding of HuR to a 288 bp fragment in the 3'-UTR (untranslated region) of survivin mRNA in human oesophageal epithelial cells. Unexpectedly, overexpression of HuR led to a decrease in survivin expression. This was associated with decreased survivin mRNA and promoter activity, suggesting a decrease in transcription. Levels of p53, a negative transcriptional regulator of survivin, increased following HuR overexpression, in conjunction with enhanced p53 mRNA stability. Silencing p53 prior to HuR overexpression resulted in increased survivin protein and mRNA stability. These results demonstrate that, in the absence of p53, HuR overexpression results in increased survivin mRNA stability and protein expression. This provides an additional explanation for the increased survivin expression observed in oesophageal cancer cells that have lost p53.

Epstein-Barr Virus nuclear antigen 1 (EBNA1) confers resistance to apoptosis in EBV-positive B-lymphoma cells through up-regulation of survivin

Resistance to apoptosis is an important component of the overall mechanism which drives the tumorigenic process. EBV is a ubiquitous human gamma-herpesvirus which preferentially establishes latent infection in viral infected B-lymphocytes. EBNA1 is typically expressed in most forms of EBV-positive malignancies and is important for replication of the latent episome in concert with replication of the host cells. Here, we investigate the effects of EBNA1 on survivin up-regulation in EBV-infected human B-lymphoma cells. We present evidence which demonstrates that EBNA1 forms a complex with Sp1 or Sp1-like proteins bound to their cis-element at the survivin promoter. This enhances the activity of the complex and up-regulates survivin. Knockdown of survivin and EBNA1 showed enhanced apoptosis in infected cells and thus supports a role for EBNA1 in suppressing apoptosis in EBV-infected cells. Here, we suggest that EBV encoded EBNA1 can contribute to the oncogenic process by up-regulating the apoptosis suppressor protein, survivin in EBV-associated B-lymphoma cells.