Reversal of multidrug resistance in gastric cancer cells by E2F-1 downregulation in vitro and in vivo

E2F2 enhances the chemoresistance of pancreatic cancer to gemcitabine by regulating the cell cycle and upregulating the expression of RRM2

Both pro-oncogenic and anti-oncogenic effects of E2F2 have been revealed in different malignancies. However, the precise role of E2F2 in pancreatic cancer, in particular in relation to therapeutic intervention with gemcitabine, remains unclear. In this study, the effect of E2F2 on the proliferation and cell cycle modulation of pancreatic cancer cells, and whether E2F2 plays a role in the treatment of pancreatic cancer cells by gemcitabine, were investigated. The expression of E2F2 in pancreatic cancer was assessed by various methods including bioinformatics prediction, Western blotting, and real-time PCR. The effect of E2F2 on the proliferation and cell cycling of pancreatic cancer cells was analyzed by tissue culture and flow cytometry. In addition, the effect of E2F2 on the intervention of pancreatic cancer by gemcitabine was investigated using both in vitro and in vivo approaches. The expression of E2F2 was found to be significantly increased in pancreatic cancer tissues and cell lines. The pathogenic capacity of E2F2 lied in the fact that this transcription factor promoted the transformation of pancreatic cancer cell cycle from G1-phase to S-phase, thus enhancing the proliferation of pancreatic cancer cells. Furthermore, the expression of E2F2 was increased in pancreatic cancer cells in the presence of gemcitabine, and the augmented expression of E2F2 upregulated the gemcitabine resistance-related gene RRM2 and its downstream signaling molecule deoxycytidine kinase (DCK). The resistance of pancreatic cancer cells to gemcitabine was confirmed using both in vitro and in vivo models. In this study, E2F2 has been demonstrated for the first time to play a pro-oncogenic role in pancreatic cancer by promoting the transition of the cell cycle from G1-phase to S-phase and, therefore, enhancing the proliferation of pancreatic cancer cells. E2F2 has also been demonstrated to enhance the chemotherapy resistance of pancreatic cancer cells to gemcitabine by upregulating the expression of RRM2 and DCK that is downstream of RRM2.

Positive regulation of ataxia-telangiectasia-mutated protein (ATM) by E2F transcription Factor 1 (E2F-1) in cisplatin-resistant nasopharyngeal carcinoma cells

Objective

To explore the mechanism of E2F transcription Factor 1 (E2F-1)-mediated ataxia-telangiectasia-mutated protein (ATM) in cisplatin (DDP)-resistant nasopharyngeal carcinoma (NPC).

Methods

E2F-1 and ATM expression was assessed in DDP-resistant NPC cell lines (CNE2/DDP and HNE1/DDP) and parental cells. Then, DDP-resistant NPC cells were transfected with control shRNA (short hairpin RNA) or E2F-1 shRNAs with or without ATM lentiviral activation particles. The half maximal inhibitory concentration (IC50) was evaluated by 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) assay, and the cell cycle and cell proliferation were measured by flow cytometry and EdU staining, respectively. In addition, the expression of genes and proteins was quantified by quantitative reverse-transcription polymerase chain reaction (qRT–PCR) and western blotting, respectively.

Results

Both E2F-1 and ATM expression in DDP-resistant NPC cells was much higher than that in parental cells. E2F-1 shRNA reduced ATM expression in DDP-resistant NPC cells, but ATM overexpression had no significant effect on E2F-1. ATM overexpression enhanced DDP resistance in DDP-resistant NPC cells with increased IC50 values, which was reversed by E2F-1 inhibition. Meanwhile, ATM overexpression resulted in upregulation of ABCA2 and ABCA5 in DDP-resistant NPC cells, induced elevations in the transition of the cells into S-phase, and increased cell proliferation with enhanced expression of cyclin E1, CDK2, and Ki67, which was reversed by E2F-1 shRNAs.

Conclusion

Downregulation of E2F-1, possibly by regulating ATM, could block the cell cycle in the G1 phase and reduce the proliferation of CNE2/DDP cells, thereby reversing the resistance of human NPC cells to DDP.

Impact of Cancer Stem Cells on Therapy Resistance in Gastric Cancer

Gastric cancer (GC) is the fourth leading cause of cancer death worldwide, with an average 5-year survival rate of 32%, being of 6% for patients presenting distant metastasis. Despite the advances made in the treatment of GC, chemoresistance phenomena arise and promote recurrence, dissemination and dismal prognosis. In this context, gastric cancer stem cells (gCSCs), a small subset of cancer cells that exhibit unique characteristics, are decisive in therapy failure. gCSCs develop different protective mechanisms, such as the maintenance in a quiescent state as well as enhanced detoxification procedures and drug efflux activity, that make them insusceptible to current treatments. This, together with their self-renewal capacity and differentiation ability, represents major obstacles for the eradication of this disease. Different gCSC regulators have been described and used to isolate and characterize these cell populations. However, at the moment, no therapeutic strategy has achieved the effective targeting of gCSCs. This review will focus on the properties of cancer stem cells in the context of therapy resistance and will summarize current knowledge regarding the impact of the gCSC regulators that have been associated with GC chemoradioresistance.

The Role and Clinical Implications of the Retinoblastoma (RB)-E2F Pathway in Gastric Cancer

Gastric cancer is the most common malignant tumor in the digestive tract, with very high morbidity and mortality in developing countries. The pathogenesis of gastric cancer is a complex biological process mediated by abnormal regulation of proto-oncogenes and tumor suppressor genes. Although there have been some in-depth studies on gastric cancer at the molecular level, the specific mechanism has not been fully elucidated. RB family proteins (including RB, p130, and p107) are involved in cell cycle regulation, a process that largely depends on members of the E2F gene family that encode transcriptional activators and repressors. In gastric cancer, inactivation of the RB-E2F pathway serves as a core transcriptional mechanism that drives cell cycle progression, and is regulated by cyclins, cyclin-dependent kinases, cyclin-dependent kinase inhibitors, p53, Helicobacter pylori and some other upstream molecules. The E2F proteins are encoded by eight genes (i.e. E2F1 to E2F8), each of which may play a specific role in gastric cancer. Interestingly, a single E2F such as E2F1 can activate or repress transcription, and enhance or inhibit cell proliferation, depending on the cell environment. Thus, the function of the E2F transcription factor family is very complex and needs further exploration. Importantly, the presence of H. pylori in stomach mucosa may affect the RB and p53 tumor suppressor systems, thereby promoting the occurrence of gastric cancer. This review aims to summarize recent research progress on important roles of the complex RB-E2F signaling network in the development and effective treatment of gastric cancer.

E2F1 Maintains Gastric Cancer Stemness Properties by Regulating Stemness-Associated Genes

Purpose

To determine the regulatory role of E2F1 in maintaining gastric cancer stemness properties and the clinical significance of E2F1 in gastric cancer.

Materials and Methods

We conducted a tumor spheroid formation assay to enrich gastric cancer stem-like cells. The protein and mRNA expression levels of genes were measured using Western Blot and qRT-PCR. Lentivirus-mediated overexpression and downregulation of E2F1 were performed to evaluate the effect of E2F1 on the stemness properties of gastric cancer cells. The effect of E2F1 on gastric cancer cell sensitivity of 5-Fu was evaluated using cell viability assay and TdT-mediated dUTP Nick-End Labeling staining. We also analyzed the association between E2F1 expression and clinical characteristics in gastric cancer patients. The KM plotter database was used to analyze the relationship between E2F1 and overall survival in GC patients.

Results

We found that E2F1 expression was significantly higher in gastric cancer tissues than in the paired adjacent normal tissues (p < 0.05) and was positively correlated with tumor size (p < 0.05), T stage (p < 0.05), and differentiation degree (p < 0.05). KM plotter database demonstrated a close association between higher E2F1 expression level and worse overall survival of gastric cancer patients (p < 0.05). In vitro assay illustrated that E2F1 could regulate the expression of stemness-associated genes, such as BMI1, OCT4, Nanog, and CD44, and maintain the tumor spheroid formation ability of gastric cancer cells. E2F1 enhanced 5-Fu resistance in gastric cancer cells, and the E2F1 expression level was correlated with the prognosis of gastric cancer patients receiving 5-Fu therapy. The expression levels of stemness-associated genes were also significantly higher in gastric cancer tissues than the paired adjacent normal tissues (p < 0.05). A positive correlation was observed between E2F1 and BMI1 (r = 0.422, p < 0.05), CD44 (r = 0.634, p < 0.05), OCT4 (r = 0.456, p < 0.05), and Nanog (r = 0.337, p < 0.05) in gastric cancer tissues. The co-overexpression of E2F1 and stemness-associated genes was associated with worse overall survival.

Conclusion

E2F1 plays a significant role in gastric cancer progression by maintaining gastric cancer stemness properties through the regulation of stemness-associated genes. The close association between E2F1 and poor prognosis of patients suggests that E2F1 could serve as a prognostic biomarker and a therapeutic target in gastric cancer patients.

Clinicopathological factors affecting the effect of neoadjuvant chemotherapy in patients with gastric cancer

BACKGROUND

Neoadjuvant chemotherapy is an important part of the comprehensive treatment of advanced gastric cancer (GC). The effect of neoadjuvant chemotherapy plays a key role in the prognosis of GC patients. Pathological response can represent the effect of neoadjuvant chemotherapy. However, evidence focused on pathological response and associated clinicopathological factors in GC patients is quite little. In this retrospective study, the clinicopathological factors affecting the effect of neoadjuvant chemotherapy in GC patients were investigated, and suggestions were proposed to improve the effect of neoadjuvant chemotherapy on GC.

METHODS

Retrospective analysis was performed on GC patients who received radical surgery after neoadjuvant chemotherapy from February 2016 to December 2019 at Peking Union Medical College Hospital. Relevant clinicopathological data was collected to analyze the factors influencing the effect of neoadjuvant chemotherapy. Chi-square test was used for univariate analysis. Logistic regression was used for multivariate analysis. Receiver operating characteristic curve (ROC) was used to determine the cutoff value of variables which significantly influenced the effect of neoadjuvant chemotherapy.

RESULTS

A total of 203 GC patients were included in the study. Analyses showed that patients < 60 years old (OR = 1.840 [1.016-3.332], P = 0.044), histological type of poor differentiation or signet-ring cell carcinoma (OR = 2.606 [1.321-5.140], P = 0.006), and weight loss during neoadjuvant chemotherapy (OR = 2.110 [1.161-3.834], P = 0.014) were independent risk factors for neoadjuvant chemotherapy effect. In ROC analysis of weight change and neoadjuvant chemotherapy effect, area under the curve (AUC) was 0.593 (P = 0.024) and cutoff value of weight change was - 2.95%. Chi-square test showed that patients without weight loss during neoadjuvant chemotherapy had a higher rate of oral nutritional supplement (ONS) than patients with weight loss (P = 0.039).

CONCLUSIONS

Patients <60 years old, histological type of poor differentiation or signet-ring cell carcinoma, and weight loss during neoadjuvant chemotherapy were independent risk factors for neoadjuvant chemotherapy effect in GC patients. Patients with weight loss > 2.95% during neoadjuvant may have a worse chemotherapy effect. Timely nutritional support such as ONS to maintain patients' body weight is crucial for improving the effect of neoadjuvant chemotherapy.

Cancer-testis specific gene OIP5: a downstream gene of E2F1 that promotes tumorigenesis and metastasis in glioblastoma by stabilizing E2F1 signaling

Background

The cancer-testis specific gene Opa interacting protein 5 (OIP5) is reactivated in many human cancers, but its functions in glioblastoma remain unclear. Here, we assessed the significance of OIP5 in the tumorigenesis and metastasis of glioblastoma for the first time.

Methods

An immunohistochemistry assay was performed to detect OIP5 expression changes in glioblastoma patients. Overall survival analysis was performed to evaluate the prognostic significance of OIP5. Growth curve, colony formation, and transwell assays were used to analyze cell proliferation and metastasis. Tumorigenicity potential was investigated in orthotopic tumor models, and immunoprecipitation, chromatin immunoprecipitation, and luciferase assays were employed to explore the mechanisms underlying the activation of OIP5 expression by E2F transcription factor 1 (E2F1) to stabilize and maintain E2F1 signaling.

Results

OIP5 was found to be upregulated in glioblastoma patients and to impair patient survival, and the increased expression of OIP5 was positively correlated with tumor stage. Compared with short hairpin green fluorescent protein cells, cells in which OIP5 was knocked down exhibited significantly reduced proliferation, metastasis, colony formation, and tumorigenicity abilities, whereas OIP5 recovery enhanced these abilities. OIP5 was highly correlated with cell cycle progression but had no obvious effects on apoptosis. Notably, we demonstrated a feedback loop in which E2F1 activates the expression of OIP5 to stabilize and maintain E2F1 signaling and promote the E2F1-regulated gene expression that is required for aggressive tumor biology.

Conclusions

Collectively, our findings demonstrate that OIP5 promotes glioblastoma progression and metastasis, suggesting that OIP5 is a potential target for anticancer therapy.

miR-135a promotes gastric cancer progression and resistance to oxaliplatin

Resistance to oxaliplatin (OXA)-based chemotherapy regimens continues to be a major cause of gastric cancer (GC) recurrence and metastasis. We analyzed GC samples and matched non-tumorous control stomach tissues from 280 patients and found that miR-135a was overexpressed in GC samples relative to control tissues. Tumors with high miR-135a expression were more likely to have aggressive characteristics (high levels of carcino-embryonic antigen, vascular invasion, lymphatic metastasis, and poor differentiation) than those with low levels. Patients with greater tumoral expression of miR-135a had shorter overall survival times and times to disease recurrence. Furthermore, miR-135a, which promotes the proliferation and invasion of OXA-resistant GC cells, inhibited E2F transcription factor 1 (E2F1)-induced apoptosis by downregulating E2F1 and Death-associated protein kinase 2 (DAPK2) expression. Our results indicate that higher levels of miR-135a in GC are associated with shorter survival times and reduced times to disease recurrence. The mechanism whereby miR-135a promotes GC pathogenesis appears to be the suppression of E2F1 expression and Sp1/DAPK2 pathway signaling.

Transcription activated p73-modulated cyclin D1 expression leads to doxorubicin resistance in gastric cancer

Gastric cancer (GC) is one of the leading types of cancer in terms of mortality cases worldwide. Doxorubicin (Dox), a common chemotherapy drug, is frequently used to treat GC; however, acquired resistance to Dox hinders the chemotherapeutic outcome and causes shorter survival in GC patients. Several Dox-resistant GC cell lines, including SGC7901, SNU-1 and SNU-5 were generated to investigate the mechanism of Dox resistance in GC. Various methods were used to test the response of Dox-resistant GC cells and parental cells, including flow cytometry, Cell Counting kit-8 assay, reverse transcription polymerase chain reaction and western blot analysis. In the present study, various Dox-resistant cells presented reduced apoptosis and cell cycle arrest in response to Dox treatment. Western blot results revealed that cyclin D1 was upregulated in Dox-resistant cells, whereas inhibition or depletion of cyclin D1 re-sensitized the resistant cells to Dox treatment, which indicated that the induction of cyclin D1 expression was a result of the Dox resistance in GC cells. Furthermore, it was observed that a transcription activated form of p73 (TAp73), is the upstream modulator of cyclin D1, manipulating the cyclin D1 transcription with the assistance of activator protein 1 (AP-1). Overall, the present study data provided a rational strategy to overcome the Dox resistance in GC treatment by inhibiting cyclin D1 expression.

Gastrin induces multidrug resistance via the degradation of p27Kip1 in the gastric carcinoma cell line SGC7901

Multidrug resistance (MDR) is one of the major reasons for the failure of chemotherapy-based gastric carcinoma (GC) treatments, hence, biologically based therapies are urgently needed. Gastrin (GAS), a key gastrointestinal (GI) hormone, was found to be involved in tumor formation, progression, and metastasis. In this study, quantitative real-time polymerase chain reaction (qRT-PCR) and immunohistochemical staining analysis revealed a high level of expression of GAS in drug-insensitive GC tissues (P<0.01) and similar results were revealed in GC cell lines SGC7901 and its multidrug-resistant variants SGC7901/VCR and SGC7901/ADR. We constructed a eukaryotic expression vector pCDNA3.1(+)/GAS for GAS overexpression and recombinant lentiviral vectors for specific siRNA (siGAS). Transfection of pCDNA3.1(+)/GAS increased (P<0.05) while transfection of siGAS (P<0.05) and co-treated with paclitaxel (TAX) and vincristine (VCR) combination (TAX-VCR) decreased (P<0.01) the cell viability of SGC7901, SGC7901/VCR and SGC7901/ADR. Apoptosis rates of SGC7901/VCR and SGC7901/ADR were reduced by pCDNA3.1(+)/GAS and increased by siGAS (P<0.05). The apoptosis rates of SGC7901/VCR, SGC7901/ADR and SGC7901 were all upregulated (P<0.01) when cells were co-treated with a combination of siGAS and TAX-VCR. Additionally, siGAS significantly downregulated the expression of Bcl-2 and multidrug-resistant associate protein (MRP1) and P-glycoprotein (Pgp) (P<0.05) in SGC7901/VCR and SGC7901/ADR cells. Moreover, GAS overexpression in SGC7901 cells significantly inhibited p27Kip1 expression but increased phosphorylation levels of p27Kip1 on Thr (187) and Ser (10) sites (P<0.05), as well as increasing nuclear accumulation of S-phase kinase-associated protein 2 (Skp2) and cytoplasmic accumulation of the Kip1 ubiquitination-promoting complex (KPC) (P<0.05). Silencing of Skp2 blocked the promoting effects of pCDNA3.1(+)/GAS on viability, the expression of MRP1 and Pgp and the inhibitory effects of pCDNA3.1(+)/GAS on apoptosis. In conclusion, we suggest that GAS contributes to the emergence of MDR of SGC7901 cells via the degradation of p27Kip1.

Zoledronic acid reverses cisplatin resistance in nasopharyngeal carcinoma cells by activating the mitochondrial apoptotic pathway

Despite improvements to radiotherapeutic strategies, resistance to adjuvant chemotherapy remains the main problem underlying the low 5-year survival rate in patients with nasopharyngeal carcinoma (NPC). In the present study, the human NPC cell line HNE1 was exposed to gradually increasing concentrations of cisplatin (CDDP) in order to establish a drug-resistant sub-cell line, HNE1/CDDP. HNE1/CDDP cells exhibited multidrug resistance and a prolonged doubling time, as compared with the parent HNE1 cells. Furthermore, pretreatment with zoledronic acid (ZOL) appeared to resensitize the CDDP-resistant cells by inducing S-phase cell cycle arrest and the mitochondrial apoptotic pathway by upregulating the expression of B-cell lymphoma-2 (BCL-2)-associated X protein and caspase-9 and downregulating the expression of BCL-2. The results of the present study suggested that HNE1/CDDP cells are a stable, multidrug-resistant NPC cell line that may serve as an important tool for research in drug resistance. In addition, the application of ZOL may hold clinical therapeutic potential for the treatment of drug resistance in NPC.

Enhancement of Drug Sensitivity by Knockdown of HIF-1α in Gastric Carcinoma Cells

In this study, the effects of hypoxia-inducible factor-1α (HIF-1α) on gastric carcinoma (GC) drug resistance through apoptosis-related genes are investigated. First, HIF-1α-specific siRNA was synthetized and transfected into drug-resistant GC cell line OCUM-2MD3/L-OHP. Then MTT assay was applied to test the inhibition rate of GC cells by 5-fluorouracil (5-FU) and oxaliplatin (L-OHP). After that, flow cytometry (FCM) was applied to measure apoptosis rate. qPCR and Western blot assay were employed to detect HIF-1α and apoptosis-related genes. Results showed that HIF-1α in OCUM-2MD3/L-OHP cells was higher than that in OCUM-2MD3 and gastric epithelial cells. After HIF-1α-siRNA transfection, inhibition rates of 5-FU and L-OHP to tumor cells increased significantly. FCM results showed that apoptosis rate of OCUM-2MD3/L-OHP cells increased significantly. After HIF-1α-siRNA transfection, survivin and Bcl-2 decreased, whereas Bax, caspase 3, and caspase 8 increased significantly. Results from this study seem to confirm that HIF-1α getting involved in GC drug resistance is possibly due to its regulation of some apoptosis-related genes. HIF-1α may be a potential target to reverse drug resistance of GC.

E2F-1 promotes DAPK2-induced anti-tumor immunity of gastric cancer cells by targeting miR-34a

Activation of the transcription factor E2F-1 gene is a negative event in dendritic cell (DC) maturation process. Down-regulation of E2F1 causes immaturity of DC thereby stopping antigen production which in turn leads to inhibition of immune responses. E2F-1-free stimulates the NF-kB signaling pathway, leading to activation of monocytes and several other transcription factor genes. In the study, we report that down-regulation of E2F-1 in DCs promote anti-tumor immune response in gastric cancer (GC) cells through a novel mechanism. DCs were isolated from peripheral blood mononuclear cells. E2F-1 small interfering RNA (E2F-1-shRNA) induced down-regulation of E2F-1 mRNA and protein expression in DCs. Furthermore, we identified the E2F-1-shRNA targeted the CD80, CD83, CD86, and MHC II molecules, promoted their expression, and induced T lymphocytes proliferation activity and up-regulation of IFN-Ī³ production and GC cell killing effect, which significantly correlated with the cytotoxic T lymphocytes activated by E2F-1-shRNA DCs. The higher expression of miR-34a was found which was significantly correlated with the DC enhancing anti-tumor immunity against gastric cancer cell, and miR-34a potently targeted DAPK2 and Sp1, both of which were involved in the deactivation of E2F-1. Moreover, in E2F-1-DC-down-regulation in mice, GC transplantation tumors displayed down-regulation of Sp1, DAPK2, Caspase3, and Caspase7 and progressed to anti-tumor immunity. Collectively, our data uncover an E2F-1-mediated mechanism for the control of DC anti-tumor immunity via miR-34a-dependent down-regulation of E2F-1 expression and suggest its contribution to GC immunotherapy.

Hurdles in selection process of nanodelivery systems for multidrug-resistant cancer

PURPOSE

Most of the nanomedicines for treatment of multidrug-resistant cancer do not reach Phase III trials and many are terminated or withdrawn or are in an indeterminate state since long without any study results being presented. Extensive perusal of nanomedicine development research revealed that one of the critical aspects influencing clinical outcomes and which requires diligent scrutiny is selection process of nanodelivery system.

METHODS

Research papers and articles published on development of nanodelivery systems for treatment of multidrug-resistant cancer were analyzed. Observations and conclusions noted by these researchers which might shed some light on poor clinical performance of nanocarriers were collated and summarized under observation section. Further research articles were studied to find possible solutions which may be applied to these particular problems for resolving them. The inferences of these findings were composed in Result section.

RESULT

Plausible solutions for the observed obstacles were noted as examples of novel formulations that can yield the following: better in vivo imaging, precise targeting and dosing of a specific site and specific cell type in a particular cancer, modulation of tumor surroundings, intonation of systemic effects and high reproducibility.

CONCLUSION

The angle of approach to the development of best nanosystem for a specific type of tumor needs to be spun around. Some of these changes can be brought about by individual scientists, some need to be established by collated efforts of scientists globally and some await advent of better technologies. Regardless of the stratagem, it can be said decisively that the schematics of development phase need rethinking.

Interrupted E2F1-miR-34c-SCF negative feedback loop by hyper-methylation promotes colorectal cancer cell proliferation

E2F1 promoted miR-34c transcription which reduced its target stem cell factor (SCF) and inhibited colorectal cancer (CRC) cell proliferation. While, SCF increased E2F1 production, suggesting an existence of E2F1-miR-34c-SCF negative feedback loop, which was interrupted by hyper-methylation of miR-34c promoter in CRC cells.

Tumour suppressor miR-34c deficiency resulted from hyper-methylation in its promoter is believed to be one of the main causes of colorectal cancer (CRC). Till date, miR-34c has been validated as a direct target of p53; but previous evidence suggested other transcription factor(s) must be involved in miR-34c transcription. In the present study, we in the first place identified a core promoter region (−1118 to −883 bp) of pre-miR-34c which was embedded within a hyper-methylated CpG island. Secondly, E2F1 promoted miR-34c transcription by physical interaction with the miR-34c promoter at site −897 to −889 bp. The transcriptional activating effect of E2F1 on miR-34c was in a p53 independent manner but profoundly promoted in the presence of p53 with exposure to 5-aza-2′-deoxycytidine (DAC). Thirdly, stem cell factor (SCF), a miR-34c target, was specifically reduced upon an introduction of E2F1 which lead to suppression of CRC cell proliferation. The E2F1-suppressed cell proliferation was partially abrogated by additional miR-34c inhibitor, indicating that the anti-proliferation effect of E2F1 was probably through activating miR-34c-SCF axis. Finally, SCF/KIT signalling increased E2F1 production by reducing its proteosomal degradation dependent on PI3K/Akt-GSK3β pathway. In conclusion, our results suggested the existence of E2F1-miR-34c-SCF negative feedback loop which was interrupted by the hyper-methylation of miR-34c promoter in CRC cells and increased cell proliferation.

miR-16 induction after CDK4 knockdown is mediated by c-Myc suppression and inhibits cell growth as well as sensitizes nasopharyngeal carcinoma cells to chemotherapy

Cyclin-dependent kinase 4 (CDK4) is a member of cyclin-dependent kinase family which regulates G1 to S cell cycle transition. CDK4 activity is increased in many tumor types. Here, we report a negative automodulatory feedback loop between CDK4 and miR-16 that regulates cell cycle progression in nasopharyngeal carcinoma (NPC). By miRNA array and real-time PCR, we identified upregulation of tumor suppressor miR-16a, which inhibited cell cycle progression and sensitized NPC cells to chemotherapy. CDK4 knockdown reduced the expression of c-Myc, the latter of which directly suppresses the miR-16 expression by directly binding to the miR-16 promoter. Moreover, we found that miR-16 upregulation could reduce CDK4 expression by repressing CCND1 and thus forms a feedback loop via the CDK4/c-Myc/miR-16/CCND1 pathway. Finally, miR-16 was negatively correlated with CDK4 expression in NPC biopsies. In summary, our results define a double-negative feedback loop involving CDK4 and miR-16 mediated by c-Myc that modulates NPC cell growth and chemotherapy sensitivity.

Integrative analysis of the microRNA-mRNA response to radiochemotherapy in primary head and neck squamous cell carcinoma cells

Background

Head and neck squamous cell carcinoma (HNSCC) is a very heterogeneous disease resulting in huge differences in the treatment response. New individualized therapy strategies including molecular targeting might help to improve treatment success. In order to identify potential targets, we developed a HNSCC radiochemotherapy cell culture model of primary HNSCC cells derived from two different patients (HN1957 and HN2092) and applied an integrative microRNA (miRNA) and mRNA analysis in order to gain information on the biological networks and processes of the cellular therapy response. We further identified potential target genes of four therapy-responsive miRNAs detected previously in the circulation of HNSCC patients by pathway enrichment analysis.

Results

The two primary cell cultures differ in global copy number alterations and P53 mutational status, thus reflecting heterogeneity of HNSCC. However, they also share many copy number alterations and chromosomal rearrangements as well as deregulated therapy-responsive miRNAs and mRNAs. Accordingly, six common therapy-responsive pathways (direct P53 effectors, apoptotic execution phase, DNA damage/telomere stress induced senescence, cholesterol biosynthesis, unfolded protein response, dissolution of fibrin clot) were identified in both cell cultures based on deregulated mRNAs. However, inflammatory pathways represented an important part of the treatment response only in HN1957, pointing to differences in the treatment responses of the two primary cultures. Focused analysis of target genes of four therapy-responsive circulating miRNAs, identified in a previous study on HNSCC patients, revealed a major impact on the pathways direct P53 effectors, the E2F transcription factor network and pathways in cancer (mainly represented by the PTEN/AKT signaling pathway).

Conclusions

The integrative analysis combining miRNA expression, mRNA expression and the related cellular pathways revealed that the majority of radiochemotherapy-responsive pathways in primary HNSCC cells are related to cell cycle, proliferation, cell death and stress response (including inflammation). Despite the heterogeneity of HNSCC, the two primary cell cultures exhibited strong similarities in the treatment response. The findings of our study suggest potential therapeutic targets in the E2F transcription factor network and the PTEN/AKT signaling pathway.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1865-x) contains supplementary material, which is available to authorized users.

Genome-wide analysis of the oxyntic proliferative isthmus zone reveals ASPM as a possible gastric stem/progenitor cell marker over-expressed in cancer

The oxyntic proliferative isthmus zone contains the main stem/progenitor cells that provide for physiological renewal of the distinct mature cell lineages in the oxyntic epithelium of the stomach. These cells are also proposed to be the potential cells-of-origin of gastric cancer, although little is known about their molecular characteristics and specific biological markers are lacking. In this study, we developed a method for serial section-navigated laser microdissection to isolate cells from the proliferative isthmus zone of rat gastric oxyntic mucosa for genome-wide microarray gene expression analysis. Enrichment analysis showed a distinct gene expression profile for the isthmus zone, with genes regulating intracellular processes such as the cell cycle and ribosomal activity. The profile was also related to stem cell transcriptional networks and stomach neoplasia. Genes expressed uniquely in the isthmus zone were associated with E2F transcription factor 1 (E2F1), which participates in the self-renewal of stem cells and in gastric carcinogenesis. One of the unique genes was Aspm [Asp (abnormal spindle) homologue, microcephaly-associated (Drosophila)]. Here we show ASPM in single scattered epithelial cells located in the proliferative isthmus zone of rat, mouse and human oxyntic mucosa, which do not seem to be actively dividing. The ASPM-expressing cells are mainly mature cell marker-deficient, except for a limited overlap with cells with neuroendocrine and tuft cell features. Further, both ASPM and E2F1 were expressed in human gastric cancer cell lines and increased and correlated in human gastric adenocarcinomas compared to non-tumour mucosa, as shown by expression profile analyses and immunohistochemistry. The association between ASPM and the transcription factor E2F1 in gastric tissue is relevant, due to their common involvement in crucial cell fate-regulatory mechanisms. Our results thus introduce ASPM as a novel possible oxyntic stem/progenitor cell marker that may be involved in both normal gastric physiology and gastric carcinogenesis.

Sunitinib dose escalation overcomes transient resistance in clear cell renal cell carcinoma and is associated with epigenetic modifications

Sunitinib is considered a first-line therapeutic option for patients with advanced clear cell renal cell carcinoma (ccRCC). Despite sunitinib's clinical efficacy, patients eventually develop drug resistance and disease progression. Herein, we tested the hypothesis whether initial sunitinib resistance may be transient and could be overcome by dose increase. In selected patients initially treated with 50 mg sunitinib and presenting with minimal toxicities, sunitinib dose was escalated to 62.5 mg and/or 75 mg at the time of tumor progression. Mice bearing two different patient-derived ccRCC xenografts (PDX) were treated 5 days per week with a dose-escalation schema (40-60-80 mg/kg sunitinib). Tumor tissues were collected before dose increments for immunohistochemistry analyses and drug levels. Selected intrapatient sunitinib dose escalation was safe and several patients had added progression-free survival. In parallel, our preclinical results showed that PDXs, although initially responsive to sunitinib at 40 mg/kg, eventually developed resistance. When the dose was incrementally increased, again we observed tumor response to sunitinib. A resistant phenotype was associated with transient increase of tumor vasculature despite intratumor sunitinib accumulation at higher dose. In addition, we observed associated changes in the expression of the methyltransferase EZH2 and histone marks at the time of resistance. Furthermore, specific EZH2 inhibition resulted in increased in vitro antitumor effect of sunitinib. Overall, our results suggest that initial sunitinib-induced resistance may be overcome, in part, by increasing the dose, and highlight the potential role of epigenetic changes associated with sunitinib resistance that can represent new targets for therapeutic intervention.

Overexpression of E2F1 in human gastric carcinoma is involved in anti-cancer drug resistance

Background

Routine chemotherapy often cannot achieve good therapeutic effects because of multidrug resistance (MDR). MDR is frequently caused by the elevated expression of the MDR1 gene encoding P-glycoprotein (P-gp). E2F1 is a frequently overexpressed protein in human tumor cells that increases the activity of the MDR1 promoter, resulting in higher P-gp levels. The upregulation of P-gp might contribute to the survival of tumor cells during chemotherapy. E2F1 confers anticancer drug resistance; however, we speculate whether E2F1 affects MDR through other pathways. This study investigated the possible involvement of E2F1 in anticancer drug resistance of gastric carcinoma in vitro and in vivo.

Methods

A cisplatin-resistant SGC7901/DDP gastric cancer cell line with stable overexpression of E2F1 was established. Protein expression levels of E2F1, MDR1, MRP, TAp73, GAX, ZEB1, and ZEB2 were detected by western blotting. The influence of overexpression of E2F1 on anticancer drug resistance was assessed by measuring IC50 of SGC7901/DDP cells to cisplatin, doxorubicin, and 5-fluorouracil, as well as the rate of doxorubicin efflux, apoptosis, and cell cycle progression detected by flow cytometry. We determined the in vivo effects of E2F1-overexpression on tumor size in nude mice, and apoptotic cells in tumor tissues were detected by deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling and hematoxylin and eosin staining.

Results

The SGC7901/DDP gastric cancer cell line stably overexpressing E2F1 exhibited significantly inhibited sensitivity to cisplatin, doxorubicin, and 5-fluorouracil. Flow cytometry confirmed that the percentage of apoptotic cells decreased after E2F1 upregulation, and that upregulation of E2F1 potentiated S phase arrest of the cell cycle. Furthermore, upregulation of E2F1 significantly decreased intracellular accumulation of doxorubicin. Western blot revealed that E2F1 upregulation suppressed expression of GAX, and increased the expression of MDR1, MRP, ZEB1, TAp73, and ZEB2.

Conclusions

Overexpression of E2F1 promotes the development of MDR in gastric carcinoma, suggesting that E2F1 may represent an efficacious target for gastric cancer therapy.

Relationship between Survivin and gastric cancer

Survivin is a member of the apoptosis inhibitory protein family [inhibitor of apoptosis proteins (IAPs)] found in recent years. It is expressed in tumors and fetal tissue and closely related to tumor cell differentiation, proliferation, invasion and metastasis. Currently, functional studies reveal that survivin is directly related to invasion, metastasis, resistance to chemotherapy, angiogenesis, diagnosis and prognosis in gastric cancer. Survivin may provide a new target for early diagnosis, gene therapy and prognosis evaluation in gastric cancer. This paper reviews the structure and biological characteristics of Survivin and discuss its relationship with tumor susceptibility, treatment, diagnosis and prognosis in gastric cancer.

Helicobacter pylori modulates cisplatin sensitivity in gastric cancer by down-regulating miR-141 expression

BACKGROUND

Recent studies found that gastric cancer patients with Helicobacter pylori infection had a better response to chemotherapy and had an improved overall prognosis compared with those without. However, the underlying mechanism remains unknown.

METHODS

Quantitative real-time PCR (qRT-PCR) was utilized to determine the expression profile of miR-141 in H. pylori infected cells and tissues and their respective controls. qRT-PCR and Western blot were used to determine the expression level of KEAP-1. Luciferase reporter assays were used to determine whether KEAP-1 was a direct target of miR-141 in the gastric cancer cells. MTT and apoptosis assay were performed to detect the survival of cells under cisplatin treatment.

RESULT

We found that H. pylori infection can significantly down-regulate miR-141 expression. Knockdown miR-141 expression in 7901/DDP and 7901 cells could significantly improve cisplatin sensitivity. Over-expression of miR-141 resulted in enhanced resistance to cisplatin in both gastric cancer cells. We also demonstrated that miR-141 directly targets KEAP1 by luciferase reporter assay, and that down-regulation of KEAP1 induces cisplatin resistance. Conversely, over-expression of KEAP1 significantly enhanced cisplatin sensitivity. Our 75 pairs of tissues also showed that KEAP1 was significantly up-regulated in H. pylori-positive tissues.

CONCLUSION

Altogether, these findings demonstrated that the H. pylori infection could modulate cisplatin sensitivity through miR-141-mediated regulation of KEAP1.