Cancer Cell Radioresistance Research Articles

HLF/miR-132/TTK axis regulates cell proliferation, metastasis and radiosensitivity of glioma cells.

Glioma is a malignant cancer with high mortality. A key prognostic factor of glioma is radiosensitivity. It has also been known that microRNAs (miR) significantly contribute to the development of glioma. miR-132 has been previously reported to inhibit tumor growth in some cancers, but not well studied in glioma. It is necessary to understand the association between miR-132 and glioma, including miR-132 expression in glioma, effects of miR-132 on cancer metastasis and radiosensitivity, and the involved molecular mechanism. We first explored the expression levels of miR-132 in human normal and glioma tissues, then correlated the expression levels with different stages of glioma. Utilizing human glioma U87 cells, lentiviral transduction technique, luciferase reporter assay, wound healing assay, transwell invasion assay and clonogenic assay, we investigated the effects of hepatic leukemia factor (HLF), miR-132 and TTK protein kinase (TTK) on cancer cell viability, proliferation, migration, invasion and radiosensitivity. The expression of miR-132 was low in human glioma tissues, and the downregulated expression was associated with advanced glioma grades. HLF directly bound to the BS1 site of miR-132 promoter to enhance the expression of miR-132. HLF-mediated miR-132 was able to directly target and inhibit a downstream factor TTK, which had an oncogenic role. Overexpression of TTK could reverse the inhibitory effects of either miR-132 or HLF on cancer cell proliferation, metastasis and radioresistance. TTK acts as an oncogene in glioma. HLF-mediated miR-132 directly suppresses TTK expression, thus exerting inhibitory effects on cancer cell proliferation, metastasis and radioresistance.

Downregulation of AATK mediates microRNA-558-induced resistance of A549 cells to radiotherapy.

The deregulation of microRNAs (miRNAs) is often implicated in the control of sensitivity to radiotherapy. The objective of the present study was to identify the association between miR‑558 and apoptosis‑associated tyrosine kinase (AATK), and their importance in regulating the development of resistance to radiotherapy. The current study demonstrated that AATK, a radiosensitization-associated gene, is a target of miR‑558 in lung cancer cells, using insilico analysis and a luciferase reporter system. Furthermore, it was determined that transfection of 30 or 50nM miR‑558 mimics and AATK specific siRNA markedly suppressed the mRNA and protein expression of AATK. To determine whether miR‑558 was required for lung cancer cell radioresistance, A549 cells were treated with different doses of ionizing radiation, from 0to 10Gy, following transfection with miR‑558 mimics or AATK specific siRNA. It was determined that the administration of miR‑558 mimics or AATK specific siRNA alone did not significantly alter the survival rate of the cells. By contrast, in the cells exposed to 4, 6or8Gy, the administration of miR‑558 mimics or AATK specific siRNA significantly promoted cell survival rate and overexpression of AATK reversed this effect. In conclusion, these data demonstrate that the miR‑558/AATK cascade is important for the radiosensitization of lung cancer cells and may be a potential radiotherapy target.

The Involvement of Mitochondrial Membrane Potential in Cross-Resistance Between Radiation and Docetaxel

To understand the molecular mechanisms underlying cancer cell radioresistance, clinically relevant radioresistant (CRR) cells that continue to proliferate during exposure to 2Gy/day X-rays for more than 30days were established. A modified high-density survival assay for anticancer drug screening revealed that CRR cells were resistant to an antimicrotubule agent, docetaxel (DTX). The involvement of reactive oxygen species (ROS) from mitochondria (mtROS) in the cross-resistance to X-rays and DTX was studied. Sensitivity to anticancer agents was determined by a modified high-density cell survival or water-soluble tetrazolium salt assay. DTX-induced mtROS generation was determined by MitoSOX red staining. JC-1 staining was used to visualize mitochondrial membrane potential. DTX-induced DNA double-strand breaks were determined by γ-H2AX staining. To obtain mitochondrial DNA-lacking (ρ(0)) cells, the cells were cultured for 3 to 4weeks in medium containing ethidium bromide. Treatment with DTX increased mtROS in parental cells but not in CRR cells. DTX induced DNA double-strand breaks in parental cells. The mitochondrial membrane potential of CRR cells was lower in CRR cells than in parental cells. Depletion of mtDNA induced DTX resistance in parental cells. Treatment with dimethyl sulfoxide also induced DTX resistance in parental cells. The mitochondrial dysfunction observed in CRR cells contributes to X-ray and DTX cross-resistance. The activation of oxidative phosphorylation in CRR cells may represent an effective approach to overcome radioresistant cancers. In general, the overexpression of β-tubulin or multidrug efflux pumps is thought to be involved in DTX resistance. In the present study, we discovered another DTX resistant mechanism by investigating CRR cells.

Ganetespib radiosensitization for liver cancer therapy

ABSTRACTTherapies for liver cancer particularly those including radiation are still inadequate. Inhibiting the stress response machinery is an appealing anti-cancer and radiosensitizing therapeutic strategy. Heat-shock-protein-90 (HSP90) is a molecular chaperone that is a prominent effector of the stress response machinery and is overexpressed in liver cancer cells. HSP90 client proteins include critical components of pathways implicated in liver cancer cell survival and radioresistance. The effects of a novel non-geldanamycin HSP90 inhibitor, ganetespib, combined with radiation were examined on 3 liver cancer cell lines, Hep3b, HepG2 and HUH7, using in vitro assays for clonogenic survival, apoptosis, cell cycle distribution, γH2AX foci kinetics and client protein expression in pathways important for liver cancer survival and radioresistance. We then evaluated tumor growth delay and effects of the combined ganetespib-radiation treatment on tumor cell proliferation in a HepG2 hind-flank tumor graft model. Nanomolar levels of ganetespib alone exhibited liver cancer cell anti-cancer activity in vitro as shown by decreased clonogenic survival that was associated with increased apoptotic cell death, prominent G2-M arrest and marked changes in PI3K/AKT/mTOR and RAS/MAPK client protein activity. Ganetespib caused a supra-additive radiosensitization in all liver cancer cell lines at low nanomolar doses with enhancement ratios between 1.33–1.78. These results were confirmed in vivo, where the ganetespib-radiation combination therapy produced supra-additive tumor growth delay compared with either therapy by itself in HepG2 tumor grafts. Our data suggest that combined ganetespib-radiation therapy exhibits promising activity against liver cancer cells, which should be investigated in clinical studies.

Role of Natural Radiosensitizers and Cancer Cell Radioresistance: An Update.

Cancer originates from genetic mutations accumulation. Cancer stem cells have been depicted as tumorigenic cells that can differentiate and self-renew. Cancer stem cells are thought to be resistant to conventional therapy like chemotherapy and radiation therapy. Radiation therapy and chemotherapy damage carcinomic DNA cells. Because of the ability of cancer stem cells to self-renew and reproduce malignant tumors, they are the subject of intensive research. In this review, CSCs radioresistant mechanisms which include DNA damage response and natural radiosensitizers have been summed up. Reactive oxygen species play an important role in different physiological processes. ROS scavenging is responsible for regulation of reactive oxygen species generation. A researcher has proved that microRNAs regulate tumor radiation resistance. Ionizing radiation does not kill the cancer cells; rather, IR just slows down the signs and symptoms. Ionizing radiation damages DNA directly/indirectly. IR is given mostly in combination with other chemo/radiotherapies. We briefly described here the behavior of cancer stem cells and radioresistance therapies in cancer treatment. To overcome radioresistance in treatment of cancer, strategies like fractionation modification, treatment in combination, inflammation modification, and overcoming hypoxic tumor have been practiced. Natural radiosensitizers, for example, curcumin, genistein, and quercetin, are more beneficial than synthetic compounds.

Double-negative feedback loop between long non-coding RNA TUG1 and miR-145 promotes epithelial to mesenchymal transition and radioresistance in human bladder cancer cells

LncRNAs have a critical role in the regulation of cellular processes such as cancer progression and metastasis. In the present study, we confirmed that TUG1 was overexpressed in bladder cancer tissues and established cell lines. Knockdown of TUG1 inhibited bladder cancer cell metastasis both in vitro and in vivo. Furthermore, we found that TUG1 promoted cancer cell invasion and radioresistance through inducing epithelial-to-mesenchymal transition (EMT). Interestingly, TUG1 decreased the expression of miR-145 and there was a reciprocal repression between TUG1 and miR-145 in an Argonaute2-dependent manner. ZEB2 was identified as a down-stream target of miR-145 and TUG1 exerted its function through the miR-145/ZEB2 axis. In summary, our data indicated that blocking TUG1 function may be an effective anti-cancer therapy.

Guanine nucleotide-binding protein 1 is one of the key molecules contributing to cancer cell radioresistance.

Standard fractionated radiotherapy for the treatment of cancer consists of daily irradiation of 2-Gy X-rays, 5 days a week for 5–8 weeks. To understand the characteristics of radioresistant cancer cells and to develop more effective radiotherapy, we established a series of novel, clinically relevant radioresistant (CRR) cells that continue to proliferate with 2-Gy X-ray exposure every 24 h for more than 30 days in vitro. We studied three human and one murine cell line, and their CRR derivatives. Guanine nucleotide-binding protein 1 (GBP1) gene expression was higher in all CRR cells than their corresponding parental cells. GBP1 knockdown by siRNA cancelled radioresistance of CRR cells in vitro and in xenotransplanted tumor tissues in nude mice. The clinical relevance of GBP1 was immunohistochemically assessed in 45 cases of head and neck cancer tissues. Patients with GBP1-positive cancer tended to show poorer response to radiotherapy. We recently reported that low dose long-term fractionated radiation concentrates cancer stem cells (CSCs). Immunofluorescence staining of GBP1 was stronger in CRR cells than in corresponding parental cells. The frequency of Oct4-positive CSCs was higher in CRR cells than in parental cells, however, was not as common as GBP1-positive cells. GBP1-positive cells were radioresistant, but radioresistant cells were not necessarily CSCs. We concluded that GBP1 overexpression is necessary for the radioresistant phenotype in CRR cells, and that targeting GBP1-positive cancer cells is a more efficient method in conquering cancer than targeting CSCs.

Effects of dna-dependent protein kinase inhibition by NU7026 on dna repair and cell survival in irradiated gastric cancer cell line N87.

Repair of radiation-induced dna double-strand breaks is a key mechanism in cancer cell radio-resistance. The synthesized compound NU7026 specifically inhibits dna-dependent protein kinase (dna-pk) within the non-homologous end-joining repair mechanism. Earlier studies demonstrated increased radiosensitivity in dna-pk deficient cells compared with wild-type cells. In chronic leukemia cells, NU7026 appears to enhance the cytotoxic effect of chlorambucil. The radio-modifying effects of NU7026 on cell survival, cell cycle, apoptosis, and dna double-strand break repair have yet to be studied in gastric cancer cells. The gastric cancer cell line N87 was treated with 0 Gy or 4 Gy in the presence of NU7026 at a dose range of 0-20 μmol/L. Clonogenic assays were used to assess cell survival after treatment. Cell-cycle distribution was analyzed using propidium iodide with fluorescence-activated cell sorting. Apoptosis was detected using annexin-V and propidium iodide with fluorescence-activated cell sorting. The γH2AX assay was used to measure dna double-strand breaks. Statistically significant increases in G2/M arrest were observed in N87 cells treated with radiation and NU7026 compared with those treated with radiation alone (p = 0.0004). Combined treatment also led to an increase in apoptosis (p = 0.01). At 24 hours, the γH2AX analysis revealed more dna double-strand breaks in N87 cells treated with radiation and NU7026 than in those treated with radiation alone (p = 0.04). Clonogenic assays demonstrated declining cell survival as both the radiation and the NU7026 dose increased. The dose enhancement factor at 0.1 survival fraction was 1.28 when N87 cells were treated with 4 Gy radiation and 5 μmol/L NU7026. In gastric cancer cells, NU7026 appears to enhance the cytotoxic effect of irradiation as assessed by clonogenic assays. This increased cytotoxicity might be the result of an increase in dna double-strand breaks resulting in G2/M cell arrest and possibly higher levels of apoptosis.

Sphingosine analog fingolimod (FTY720) increases radiation sensitivity of human breast cancer cells in vitro

Radiotherapy is one of the most effective therapeutic strategies for breast cancer patients, although its efficacy may be reduced by intrinsic radiation resistance of cancer cells. Recent investigations demonstrate a link between cancer cell radio-resistance and activation of sphingosine kinase (SphK1), which plays a key role in the balance of lipid signaling molecules. Sphingosine kinase (SphK1) activity can alter the sphingosine-1-phosphate (S1P)/ceramide ratio leading to an imbalance in the sphingolipid rheostat. Fingolimod (FTY720) is a novel sphingosine analog and a potent immunosuppressive drug that acts as a SphK1 antagonist, inhibits the growth, and induces apoptosis in different human cancer cell lines. We sought to investigate the in vitro radiosensitizing effects of FTY720 on the MDA-MB-361 breast cancer cell line and to assess the effects elicited by radiation and FTY720 combined treatments. We found that FTY720 significantly increased anti-proliferative and pro-apoptotic effects induced by a single dose of ionizing radiation while causing autophagosome accumulation. At the molecular level, FTY720 significantly potentiated radiation effects on perturbation of signaling pathways involved in regulation of cell cycle and apoptosis, such as PI3K/AKT and MAPK. In conclusion, our data highlight a potent radiosensitizing effect of FTY720 on breast cancer cells and provide the basis of novel therapeutic strategies for breast cancer treatment.

Using NBN to predict biochemical relapse following image-guided radiotherapy (IGRT) for intermediate-risk prostate cancer (IR-PCa).

26 Background: Despite the use of clinical prognostic factors, 20 to 40% of patients with intermediate-risk prostate cancer (IR-PCa) fail local treatment for unexplained reasons. Given that an accurate DNA damage response (DDR) may be associated with genetic instability and radioresponse, we investigated whether copy number alterations (CNAs) in DDR genes are predictive or prognostic following local treatment. Methods: Using array comparative genomic hybridization (aCGH), we characterized CNAs in biopsies derived from 126 IR-PCa pts. who underwent image-guided radiotherapy (IGRT). We studied the DDR-sensing genes: MRE11A, RAD50, NBN, ATM, and ATR. The IGRT cohort (median dose: 76.4Gy; median follow-up: 7.8yrs) was compared to a radical prostatectomy (RP) cohort (154 pts. from Memorial Sloan-Kettering Cancer Center database; median follow-up: 4.8yrs). CNAs were then tested for their independent prognostic capability using Kaplan-Meir method and Cox proportional hazard models. Results: In our IGRT cohort, m,ost frequent DDR gene CNAs were: NBN 20 of 126 (15.9%), ATR 11of 126 (8.7%), and ATM 7 of 126 (5.5%). NBN CNAs were mainly gains (19/20) and strongly correlated with increased NBN-mRNA abundance compared to NBN-neutral cases (p=0.016). CNAs in DDR genes were not associated with GS, prostate-specific antigen, or T-stage. Importantly, NBN gain ranked among the top 3.3% of all genes in terms of its strength of association with the percent of the genome altered (PGA). After adjusting for clinical factors in a multivariate model, NBN gain was a significant independent predictor of 5 years-biochemical relapse-free rate (bRFR) following IGRT (48.6% versus 78.8%; HR = 3.14, 95% CI: 1.42-6.94, p=0.004). No DDR CNA was prognostic in the RP cohort. Increased NBN mRNA expression correlated to radioresistance in vitro (i.e. clonogenic surviving fraction after 3Gy) in five prostate cancer cell lines (R2= 0.665). This relationship was not observed for any of the other DDR genes. Conclusions: NBN copy number gain or increased expression correlates with tumor genomic instability, decreased bRFR (IGRT- but not surgery-treated pts.) and intrinsic prostate cancer cell radioresistance. If validated in independent IGRT cohorts, NBN gain could be the first PCa predictive biomarker to facilitate local treatment decisions using precision medicine approaches.

COX-2 promotes breast cancer cell radioresistance via p38/MAPK-mediated cellular anti-apoptosis and invasiveness

Radioresistance is one of the major barriers to improve the survival rate of breast cancer patients. Cyclooxygenase 2 (COX-2) is usually overexpressed in highly invasive and metastatic breast cancer, which may indicate an association with breast cancer radioresistance. The function role of COX-2 was investigated by using a radioresistant breast cancer cell line MDA-MB-231/RR10 and its parental cell line MDA-MB-231 cells before or after COX-2 was silenced by a specific small hairpin RNA (shRNA). The cell proliferation, migration, invasion, colony formation, and apoptosis were measured by CCK-8, scratch-wound, transwell, clone formation assay, and flow cytometry. Protein and mRNA expression were analyzed by Western blot and quantitative reverse transcriptase-polymerase chain reaction. COX-2 is upregulated in MDA-MB-231/RR10 cells compared with in MDA-MB-231 cells, and silencing of COX-2 expression by shRNA in MDA-MB-231/RR10 cells decreases the expression of Bcl-2 and Bcl-XL, but increases the proapoptotic protein BAK, leading to the increased apoptosis following treatment with γ-irradiation in comparison with those in control cells. Silencing of COX-2 also increases the expression of β-catenin and E-cadherin, two anti-invasion proteins, resulting in reduced cell migration and invasion tested by transwell chambers and wound-healing assays. Further study demonstrated that COX-2-induced radioresistance is negatively regulated through the phosphorylation of p38 at Tyr182, and that the phosphorylation of p38 induced by TNF-alpha reduces the expression of Bcl-2, BCL-XL, but increases β-catenin and E-cadherin, leading to the decreased invasiveness of cells. Our data suggest that COX-2, p38, Bcl-2, Bcl-XL, β-catenin, and E-cadherin may be considered as potential therapeutic targets against radioresistant breast cancer.

Novel Hsp90 inhibitor NVP-AUY922 radiosensitizes prostate cancer cells

Outcomes for poor-risk localized prostate cancers treated with radiation are still insufficient. Targeting the “non-oncogene” addiction or stress response machinery is an appealing strategy for cancer therapeutics. Heat-shock-protein-90 (Hsp90), an integral member of this machinery, is a molecular chaperone required for energy-driven stabilization and selective degradation of misfolded “client” proteins, that is commonly overexpressed in tumor cells. Hsp90 client proteins include critical components of pathways implicated in prostate cancer cell survival and radioresistance, such as androgen receptor signaling and the PI3K-Akt-mTOR pathway. We examined the effects of a novel non-geldanamycin Hsp90 inhibitor, AUY922, combined with radiation (RT) on two prostate cancer cell lines, Myc-CaP and PC3, using in vitro assays for clonogenic survival, apoptosis, cell cycle distribution, γ-H2AX foci kinetics and client protein expression in pathways important for prostate cancer survival and radioresistance. We then evaluated tumor growth delay and effects of the combined treatment (RT-AUY922) on the PI3K-Akt-mTOR and AR pathways in a hind-flank tumor graft model. We observed that AUY922 caused supra-additive radiosensitization in both cell lines at low nanomolar doses with enhancement ratios between 1.4–1.7 (p < 0.01). RT-AUY922 increased apoptotic cell death compared with either therapy alone, induced G2-M arrest and produced marked changes in client protein expression. These results were confirmed in vivo, where RT-AUY922 combination therapy produced supra-additive tumor growth delay compared with either therapy by itself in Myc-CaP and PC3 tumor grafts (both p < 0.0001). Our data suggest that combined RT-AUY922 therapy exhibits promising activity against prostate cancer cells, which should be investigated in clinical studies.

DNA Double-Strand Break Repair as Determinant of Cellular Radiosensitivity to Killing and Target in Radiation Therapy

Radiation therapy plays an important role in the management of a wide range of cancers. Besides innovations in the physical application of radiation dose, radiation therapy is likely to benefit from novel approaches exploiting differences in radiation response between normal and tumor cells. While ionizing radiation induces a variety of DNA lesions, including base damages and single-strand breaks, the DNA double-strand break (DSB) is widely considered as the lesion responsible not only for the aimed cell killing of tumor cells, but also for the general genomic instability that leads to the development of secondary cancers among normal cells. Homologous recombination repair (HRR), non-homologous end-joining (NHEJ), and alternative NHEJ, operating as a backup, are the major pathways utilized by cells for the processing of DSBs. Therefore, their function represents a major mechanism of radiation resistance in tumor cells. HRR is also required to overcome replication stress – a potent contributor to genomic instability that fuels cancer development. HRR and alternative NHEJ show strong cell-cycle dependency and are likely to benefit from radiation therapy mediated redistribution of tumor cells throughout the cell-cycle. Moreover, the synthetic lethality phenotype documented between HRR deficiency and PARP inhibition has opened new avenues for targeted therapies. These observations make HRR a particularly intriguing target for treatments aiming to improve the efficacy of radiation therapy. Here, we briefly describe the major pathways of DSB repair and review their possible contribution to cancer cell radioresistance. Finally, we discuss promising alternatives for targeting DSB repair to improve radiation therapy and cancer treatment.

Abstract LB-211: beta1 integrin targeting results in radiosensitization by controlling DNA repair mechanisms and chromatin organization

Abstract Integrin-mediated cell-extracellular matrix (ECM) interactions confer cancer cell resistance to therapy. Our own data and data of others generated in three-dimensional (3D) ECM-based cell cultures and in vivo provided evidence that particularly beta1 integrin targeting potently reduces this resistance involving downstream integrin signaling mediators like focal adhesion kinase, cortactin and JNK1. However, it remains unknown whether beta1 integrin inhibition affects the repair of radiation-induced DNA double strand breaks (DSB) and their distribution in eu- and heterochromatic DNA regions. Here, we show that 3D growth (cell culture, xenograft models) increased the amount of heterochromatin in human head and neck squamous cell (HNSCC) and lung carcinoma cell lines relative to 2D, induced higher radioresistance, reduced the number of chromosomal aberrations and gammaH2AX/53BP1-positive foci, which was accompanied by a shift of the euchromatin-to-heterochromatin DSB distribution from a 2:1 (2D) to a 1:1 (3D). Upon beta1 integrin inhibition using the inhibitory monoclonal antibody AIIB2 or siRNA, cells grown in 3D or as xenografts in nude mice were radiosensitized or showed a significant growth delay, respectively. The disruption of beta1 integrin-mediated cell-ECM interactions induced an increase in heterochromatin levels indicated by HP1alpha and H3K9me3 elevation. In line with these findings was a strong impairment of both ATM and DNA-PK and their associated downstream signaling pathways (e.g. Chk2, Mre11, Nbs1, Rad50) in beta1 integrin inhibited, irradiated cells relative to IgG isotype controls. In contrast to unchanged number of heterochromatic foci identified in stably transfected HP1alpha cells, kinetic DSB measurements revealed an increased number of euchromatic foci upon beta1 integrin blocking, which evidently showed strongly perturbed DSB repair. In conclusion, our data generated in 3D cell culture and tumor xenograft models suggest a regulatory function of beta1 integrin signaling in the repair of radiogenic DSBs and the organization of chromatin. In addition to our understanding of the initial steps deactivated upon beta1 integrin blocking, these findings bridge membrane bound integrin function to nuclear DNA repair processes, thus providing further insights into how integrins confer cancer cell radioresistance and why integrin targeting is potentially useful as adjuvant to conventional radio- and radiochemotherapy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-211. doi:1538-7445.AM2012-LB-211

Abstract 2497: Induction of AP-1 activity by ceramide results in ASAH1 upregulation: A mechanism of prostate cancer cell radioresistance

Abstract Background: Although radiation therapy is a mainstay of treatment for localized prostatic disease, the escape of a subset of tumor cells from ionizing radiation (IR)-induced killing may lead to disease relapse and progression. The metabolic balance between the pro-apoptotic sphingolipid, ceramide, and its anti-apoptotic metabolites has been characterized as a critical mediator of cell death under conditions of cell stress, including IR exposure. While the lysosomal ceramide-metabolizing enzyme, acid ceramidase (ASAH1), is constitutively expressed in all human tissues, ASAH1 has been found to be over-expressed in cancer cells exposed to IR. The goal of this study was to examine the biological impact of and possible mechanism for altered ASAH1 expression observed in irradiated prostate cancer cells. Methods: Sphingolipid expression was measured by LC-MS. Ceramidase activities were assessed by thin layer chromatography. ASAH1 mRNA and protein expression in cell lines were measured by qPCR and western blot, respectively. Transcription activity was assessed using a luciferase reporter driven by the 1.5kb proximal promoter region of ASAH1. AP-1 promoter occupancy was determined by chromatin immunoprecipitation (ChIP)-qPCR. Post-irradiative cell growth was determined by clonogenic survival assay. Results: IR induced nearly two-fold expression of ceramide, and between three- and four-fold expression of its metabolites, sphingosine and sphingosine-1-phosphate. Enzyme activity assays demonstrated specific increase of acid, but not neutral or alkaline, ceramidase in the irradiated prostate cancer cells, suggesting a prominent role for ASAH1 in IR-induced sphingolipid metabolism. Consistent with increased mRNA and protein levels, luciferase-promoter-reporter assay confirmed that ASAH1 regulation occurs at least in part at the transcriptional level. Interestingly, inhibition of de novo and salvage pathways of ceramide biogenesis abrogated IR-induced ASAH1 upregulation, implicating the involvement of ceramide in IR-induced ASAH1 overexpression. Through studies using protein-DNA binding arrays and ChIP-qPCR, we identified AP-1 as a direct, ceramide-sensitive transcription factor of ASAH1 in irradiated cells. Expression of a dominant negative mutant of c-Jun, a central component of the AP-1 complex, was able to abrogate IR-induced ASAH1 overexpression. Since ASAH1 silencing by shRNA sensitized prostate cancer cells to IR-induced cell killing, here we also observed radiosensitization by expression of the c-Jun dominant negative construct, which was rescued in part by forced overexpression of an ASAH1 transgene. Conclusion: The reported studies demonstrate that IR programs an unexpected phenotype of radiation resistance through ASAH1 upregulation mediated by ceramide-sensitive AP-1 activation. This study was supported in part by NIH/NCI P01 CA097132. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2497. doi:10.1158/1538-7445.AM2011-2497

Identification of differentially expressed genes related to radioresistance of human esophageal cancer cells

Radioresistant cells in esophageal cancer is one of the important reasons for the local failure of radiotherapy. In recent years, some researchers used gene chip technology to screen the differentially expressed genes between parental and radioresistant human esophageal cancer cells. But there were some problems in these studies, for example comparing cells at only one time interval, and genetic background not matching. In this study, we selected 3 different pairs of parental and radioresistant human esophageal cancer cells, and compared the gene expression profiles by cDNA microarray at 3 time intervals to identify and analyze the differentially expressed genes between parental and radioresistant human esophageal cancer cells. We compared the gene expression profiles between parental cells (TE13, Seg-1, Kyse170) and radioresistant cells (TE13R, Seg-1R, Kyse170R) before, and at 8 h and 24 h after irradiation with a cDNA microarray consisting of 48 000 genes (Human Genome). We identified differentially expressed genes by Pathway and GO analyses, and verified the differentially expressed genes LEF1 and CTNNB1 by RT-PCR. A total of 460, 451, and 397 differentially expressed genes were found before, and at 8 h and 24 h after irradiation. After Pathway and GO analyses, 14 differentially expressed genes, participating in cell growth, apoptosis, cell cycle regulation, gene repair and signal transmission, were selected to further research. LEF1 and CTNNB1 were verified by RT-PCR, and the results were consistent with those of cDNA microarray. The WNT signal pathway may be an important pathway participating in the formation of radioresistance of esophageal cancer cells. LEF1 and CTNNB1 may be the important genes causing the esophageal cancer cell radioresistance.