IR-induced Apoptosis Research Articles

MiR-449a Suppresses LDHA-Mediated Glycolysis to Enhance the Sensitivity of Non-Small Cell Lung Cancer Cells to Ionizing Radiation.

MicroRNA dysregulation contributes to malignant progression, dissemination, and profound treatment resistance in multiple cancers. miR-449a is recognized as a tumor suppresser. However, the roles of miR-449a in lung cancer initiation and progression are largely unknown. Our study aims to investigate the roles and underlying mechanism of miR-449a in modulating sensitivity to ionizing radiation (IR) in non-small cell lung cancer (NSCLC). Lung cancer cells were transfected with miR-449a mimics or negative control and exposed to IR; the levels of target protein, glycolysis, cell viability, apoptosis, and DNA damage were examined. miR-449a was suppressed in lung cancer tissues and cancer cells (A549 and H1299). IR exposure significantly increased the expression of miR-449a in A549 cells at doses ranging from 4 to 8 Gy at 24 h, whereas no significant change in miR-449a was found in H1299 cells after IR. When A549 cells were exposed to IR at a dose of 8 Gy, the miR-449a level only had an acute increase within 12 h. miR-449a restoration dramatically suppressed IR-induced cell apoptosis and DNA damage in both A549 and H1299 cells. Bioinformatics analysis indicated that lactate dehydrogenase A (LDHA) was a potential target of miR-449a. miR-449a mimic transfection substantially suppressed the LDHA expression and production of lactate catalyzed by LDHA as well as glucose uptake. We confirmed that miR-449a could bind to the 3′-UTR of LDHA mRNA using luciferase reporter assay. LDHA siRNA-transfected cells showed enhanced cell apoptosis and DNA damage in response to IR exposure. miR-449a upregulation enhanced IR sensitivity of lung cancer cells by suppressing LDHA and the subsequent glycolysis.

Abstract 235: Ionizing Radiation Induces Endothelial Inflammation and Apoptosis via P90rsk-mediated Erk5 S496 Phosphorylation

Background: Adverse cardiovascular events are a leading nonmalignant cause of morbidity and mortality among cancer survivors who have been exposed to ionizing radiation (IR), but the exact mechanism of the cardiovascular complications induced by IR remains unclear. In this study we investigated the potential role of the p90RSK-ERK5 module in regulating IR-induced endothelial cell inflammation and apoptosis. Methods and Results: Whole body radiation of mice with 2 Gy γ-ray significantly increased endothelial VCAM-1 expression; especially in the disturbed flow area in vivo . In vitro studies showed that IR increased p90RSK activation as well as subsequent ERK5 S496 phosphorylation in cultured human endothelial cells (ECs). A specific p90RSK inhibitor, FMK-MEA, significantly inhibited both p90RSK activation and ERK5 S496 phosphorylation, but it had no effect on IR-induced ERK5 TEY motif phosphorylation, suggesting that p90RSK regulates ERK5 transcriptional activity, but not its kinase activity. In fact, we found that IR-induced NF-kB activation and VCAM-1 expression in ECs were significantly inhibited by the over-expression of S496 phosphorylation site mutant of ERK5 (ERK5 S496A) compared to overexpression of wild type ERK5. Furthermore, when ECs were exposed to IR, the number of annexin V positive cells increased, and overexpression of ERK5 S496A, but not wild type ERK5, significantly inhibited this increase. Conclusions: Our results demonstrate that IR augmented disturbed flow-induced VCAM-1 expression in vivo. Endothelial p90RSK was robustly activated by IR and subsequently up-regulated ERK5 S496 phosphorylation, inflammation, and apoptosis in ECs. The EC p90RSK-ERK5 signaling axis can be a good target to prevent cardiovascular events after radiation therapy in cancer patients.

DRm217 attenuates myocardial ischemia-reperfusion injury via stabilizing plasma membrane Na+-K+-ATPase, inhibiting Na+-K+-ATPase/ROS pathway and activating PI3K/Akt and ERK1/2

Na+-K+-ATPase has close relationship with myocardial ischemia/reperfusion (IR) injury. Activation of Na+-K+-ATPase with its DR region specific antibody produces cardioprotective effect. In this study, we aimed to explore whether DRm217, a proved DR region specific antibody, could protect myocardial cells against IR injury and uncover the mechanisms under it. By employing H9c2 myocardial cell and SD rat, we found that DRm217 protected cardiac cells against IR-induced cell injury and apoptosis. DRm217 produced protective effect via stabilizing Na+-K+-ATPase membrane expression and inhibiting Na+-K+-ATPase/Src/NADPH oxidase dependent ROS accumulation. PI3K/Akt and ERK1/2 participated in DRm217-induced cardiomyocyte survival, but not in DRm217-related ROS reduction. Therefore, DRm217 can be used as a potential cardioprotective adjuvant in myocardial IR therapy and interference of Na+-K+-ATPase/ROS pathway will be a promising modality for clinical myocardial IR therapy.

Radiosensitization by Marine Sponge Agelas sp. Extracts in Hepatocellular Carcinoma Cells with Autophagy Induction

Although radiation therapy is an effective treatment modality in many cancers, there is an urgent need to develop therapeutic drugs capable of overcoming radioresistance or minimizing normal tissue toxicity. A wide variety of marine-derived bioactive compounds have been screened for anti-cancer drug discovery, but little is known regarding radiation therapy applications. In this study, six different extracts of marine sponges collected from the Micronesian sea were screened for anti-cancer and radiosensitizing activity. Two extracts derived from Agelas sponges collected off the coast of Kosrae and Chuuk, the Federated States of Micronesia significantly decreased clonogenic survival of hepatocellular carcinoma (HCC) cells after exposure to ionizing radiation (IR). The Agelas extracts augmented IR-induced apoptosis and accumulation of reactive oxygen species (ROS). Endoplasmic reticulum (ER) stress was increased via unfolded protein response stimulation, which induced autophagy. N-acetylcysteine, a ROS scavenger, diminished ER stress and autophagy induction effects. This result indicated that Agelas extracts may sensitize HCC cells to IR via ROS overproduction in vitro. Our findings suggest that the Agelas sp. may have potential utility in radiosensitizer development.

Hypoxia-Activated Adipose Mesenchymal Stem Cells Prevents Irradiation-Induced Salivary Hypofunction by Enhanced Paracrine Effect Through Fibroblast Growth Factor 10.

To explore the effects and mechanisms of paracrine factors secreted from human adipose mesenchymal stem cell (hAdMSCs) that are activated by hypoxia on radioprotection against irradiation-induced salivary hypofunction in subjects undergoing radiotherapy for head and neck cancers. An organotypic spheroid coculture model to mimic irradiation (IR)-induced salivary hypofunction was set up for in vitro experiments. Human parotid gland epithelial cells were organized to form three-dimensional (3D) acinus-like spheroids on growth factor reduced -Matrigel. Cellular, structural, and functional damage following IR were examined after cells were cocultured with hAdMSCs preconditioned with either normoxia (hAdMSCNMX ) or hypoxia (hAdMSCHPX ). A key paracrine factor secreted by hAdMSCsHPX was identified by high-throughput microarray-based enzyme-linked immunosorbent assay. Molecular mechanisms and signaling pathways on radioprotection were explored. Therapeutic effects of hAdMSCsHPX were evaluated after in vivo transplant into mice with IR-induced salivary hypofunction. In our 3D coculture experiment, hAdMSCsHPX significantly enhanced radioresistance of spheroidal human parotid epithelial cells, and led to greater preservation of salivary epithelial integrity and acinar secretory function relative to hAdMSCsNMX . Coculture with hAdMSCsHPX promoted FGFR expression and suppressed FGFR diminished antiapoptotic activity of hAdMSCsHPX . Among FGFR-binding secreted factors, we found that fibroblast growth factor 10 (FGF10) contributed to therapeutic effects of hAdMSCsHPX by enhancing antiapoptotic effect, which was dependent on FGFR-PI3K signaling. An in vivo transplant of hAdMSCsHPX into irradiated salivary glands of mice reversed IR-induced salivary hypofunction where hAdMSC-released FGF10 contributed to tissue remodeling. Our results suggest that hAdMSCsHPX protect salivary glands from IR-induced apoptosis and preserve acinar structure and functions by activation of FGFR-PI3K signaling via actions of hAdMSC-secreted factors, including FGF10. Stem Cells 2018;36:1020-1032.

Deoxycytidine kinase participates in the regulation of radiation-induced autophagy and apoptosis in breast cancer cells

Deoxycytidine kinase (dCK) is a rate limiting enzyme critical for the phosphorylation of endogenous deoxynucleosides and for the anti‑tumor activity of many nucleoside analogs. dCK is activated in response to ionizing radiation(IR) and it is required for the G2/M checkpoint induced by IR. However, whether dCK plays a role in radiation-induced autophagy and apoptosis is less clear. In this study, we reported that dCK decreased IR-induced total cell death and apoptosis, and increased IR-induced autophagy in SKBR3 and MDA‑MB‑231 breast cancer cell lines. A molecular switch exists between apoptosis and autophagy. We further demonstrated that serine74 phosphorylation was required for the regulation of autophagy. In dCK wild‑type(WT) or dCKS74E (mutant) MDA‑MB‑231 cell models, the expression levels of phospho-Akt, phospho-mammalian target of rapamycin (mTOR) and phospho-P70S6K significantly decreased following exposure to IR. Moreover, the ratio of Bcl‑2/Beclin1 (BECN1) significantly decreased in the S74E mutant cells; however, no change was observed in the ratio of Bcl‑2/BAX. Taken together, our findings indicate that phosphorylated and activated dCK inhibits IR-induced total cell death and apoptosis, and promotes IR-induced autophagy through the mTOR pathway and by inhibiting the binding of Bcl‑2 protein to BECN1.

Genistein promotes ionizing radiation-induced cell death by reducing cytoplasmic Bcl-xL levels in non-small cell lung cancer

Genistein (GEN) has been previously reported to enhance the radiosensitivity of cancer cells; however, the detailed mechanisms remain unclear. Here, we report that GEN treatment inhibits the cytoplasmic distribution of Bcl-xL and increases nuclear Bcl-xL in non-small cell lung cancer (NSCLC). Interestingly, our in vitro data show that ionizing radiation IR treatment significantly increases IR-induced DNA damage and apoptosis in a low cytoplasmic Bcl-xL NSCLC cell line compared to that of high cytoplasmic Bcl-xL cell lines. In addition, clinical data also show that the level of cytoplasmic Bcl-xL was negatively associated with radiosensitivity in NSCLC. Furthermore, we demonstrated that GEN treatment enhanced the radiosensitivity of NSCLC cells partially due to increases in Beclin-1-mediated autophagy by promoting the dissociation of Bcl-xL and Beclin-1. Taken together, these findings suggest that GEN can significantly enhance radiosensitivity by increasing apoptosis and autophagy due to inhibition of cytoplasmic Bcl-xL distribution and the interaction of Bcl-xL and Beclin-1 in NSCLC cells, respectively.

Choline Inhibits Ischemia-Reperfusion-Induced Cardiomyocyte Autophagy in Rat Myocardium by Activating Akt/mTOR Signaling

Backgroud/Aims: Growing evidence suggests that both cardiomyocyte apoptosis and excessive autophagy exacerbates cardiac dysfunction during myocardial ischemia-reperfusion (IR). As a precursor of acetylcholine, choline has been found to protect the heart by repressing ischemic cardiomyocyte apoptosis. However, the relationship between choline and cardiomyocyte autophagy is unclear. The present study aimed to investigate whether autophagy was involved in the cardioprotection of choline during IR. Methods: Rats were subjected to 30 min reversible ischemia by ligation of left anterior descending coronary artery followed by reperfusion for 2 h. Choline (5 mg/kg, i.v.) alone or along with rapamycin (5 mg/ kg, i.p.) were injected 30 min before ischemia. Transmission electron microscopy, hematoxylin and eosin (HE) and TUNEL staining were conducted to evaluate the effect of choline on cardiac apoptosis and autophagy. Protein levels of autophagic markers including LC3, beclin-1 and p62 as well as Akt and mammalian target of rapamycin (mTOR) were examined by Western blotting. Results: Myocardial IR-induced cardiac apoptosis and accumulation of autophagosomes was attenuated by choline. Choline treatment significantly ameliorated myocardial IR-induced autophagic activity characterized by repression of beclin-1 over-activation, the reduction of autophagosomes, the LC3-II/LC3-I ratio, and p62 protein abundance. In addition, IR-induced downregulation of p-Akt/mTOR cascade was increased by choline. However, the above functions of choline were abolished by rapamycin. Conclusion: These findings suggest that choline plays a protective role against myocardial IR injury by inhibiting excessive autophagy, which might be associated with the activation of Akt/mTOR pathway. This study provides new mechanistic understanding of cardioprotective effect of choline and suggests novel potential therapeutic targets for cardiac IR injury.

Tyrosine Kinase Inhibitors Protect the Salivary Gland from Radiation Damage by Inhibiting Activation of Protein Kinase C-δ.

In patients undergoing irradiation (IR) therapy, injury to nontumor tissues can result in debilitating, and sometimes permanent, side effects. We have defined protein kinase C-δ (PKCδ) as a regulator of DNA damage-induced apoptosis and have shown that phosphorylation of PKCδ by c-Abl and c-Src activates its proapoptotic function. Here, we have explored the use of tyrosine kinase inhibitors (TKI) of c-Src and c-Abl to block activation of PKCδ for radioprotection of the salivary gland. Dasatinib, imatinib, and bosutinib all suppressed tyrosine phosphorylation of PKCδ and inhibited IR-induced apoptosis in vitro To determine whether TKIs can provide radioprotection of salivary gland function in vivo, mice were treated with TKIs and a single or fractionated doses of irradiation. Delivery of dasatinib or imatinib within 3 hours of a single or fractionated dose of irradiation resulted in >75% protection of salivary gland function at 60 days. Continuous dosing with dasatinib extended protection to at least 5 months and correlated with histologic evidence of salivary gland acinar cell regeneration. Pretreatment with TKIs had no impact on clonogenic survival of head and neck squamous cell carcinoma (HNSCC) cells, and in mice harboring HNSCC cell-derived xenografts, combining dasatinib or imatinib with fractionated irradiation did not enhance tumor growth. Our studies indicate that TKIs may be useful clinically to protect nontumor tissue in HNC patients undergoing radiotherapy, without negatively impacting cancer treatment. Mol Cancer Ther; 16(9); 1989-98. ©2017 AACR.

Rho inhibition by lovastatin affects apoptosis and DSB repair of primary human lung cells in vitro and lung tissue in vivo following fractionated irradiation

Thoracic radiotherapy causes damage of normal lung tissue, which limits the cumulative radiation dose and, hence, confines the anticancer efficacy of radiotherapy and impacts the quality of life of tumor patients. Ras-homologous (Rho) small GTPases regulate multiple stress responses and cell death. Therefore, we investigated whether pharmacological targeting of Rho signaling by the HMG-CoA-reductase inhibitor lovastatin influences ionizing radiation (IR)-induced toxicity in primary human lung fibroblasts, lung epithelial and lung microvascular endothelial cells in vitro and subchronic mouse lung tissue damage following hypo-fractionated irradiation (4x4 Gy). The statin improved the repair of radiation-induced DNA double-strand breaks (DSBs) in all cell types and, moreover, protected lung endothelial cells from IR-induced caspase-dependent apoptosis, likely involving p53-regulated mechanisms. Under the in vivo situation, treatment with lovastatin or the Rac1-specific small molecule inhibitor EHT1864 attenuated the IR-induced increase in breathing frequency and reduced the percentage of γH2AX and 53BP1-positive cells. This indicates that inhibition of Rac1 signaling lowers IR-induced residual DNA damage by promoting DNA repair. Moreover, lovastatin and EHT1864 protected lung tissue from IR-triggered apoptosis and mitigated the IR-stimulated increase in regenerative proliferation. Our data document beneficial anti-apoptotic and genoprotective effects of pharmacological targeting of Rho signaling following hypo-fractionated irradiation of lung cells in vitro and in vivo. Rac1-targeting drugs might be particular useful for supportive care in radiation oncology and, moreover, applicable to improve the anticancer efficacy of radiotherapy by widening the therapeutic window of thoracic radiation exposure.

Synergy between Prkdc and Trp53 regulates stem cell proliferation and GI-ARS after irradiation.

Ionizing radiation (IR) is one of the most widely used treatments for cancer. However, acute damage to the gastrointestinal tract or gastrointestinal acute radiation syndrome (GI-ARS) is a major dose-limiting side effect, and the mechanisms that underlie this remain unclear. Here we use mouse models to explore the relative roles of DNA repair, apoptosis, and cell cycle arrest in radiation response. IR induces DNA double strand breaks and DNA-PK mutant Prkdcscid/scid mice are sensitive to GI-ARS due to an inability to repair these breaks. IR also activates the tumor suppressor p53 to trigger apoptotic cell death within intestinal crypt cells and p53 deficient mice are resistant to apoptosis. To determine if DNA-PK and p53 interact to govern radiosensitivity, we compared the response of single and compound mutant mice to 8 Gy IR. Compound mutant Prkdcscid/scid/Trp53-/-mice died earliest due to severe GI-ARS. While both Prkdcscid/scid and Prkdcscid/scid/Trp53-/-mutant mice had higher levels of IR-induced DNA damage, particularly within the stem cell compartment of the intestinal crypt, in Prkdcscid/scid/Trp53-/-mice these damaged cells abnormally progressed through the cell cycle resulting in mitotic cell death. This led to a loss of Paneth cells and a failure to regenerate the differentiated epithelial cells required for intestinal function. IR-induced apoptosis did not correlate with radiosensitivity. Overall, these data reveal that DNA repair, mediated by DNA-PK, and cell cycle arrest, mediated by p53, cooperate to protect the stem cell niche after DNA damage, suggesting combination approaches to modulate both pathways may be beneficial to reduce GI-ARS. As many cancers harbor p53 mutations, this also suggests targeting DNA-PK may be effective to enhance sensitivity of p53 mutant tumors to radiation.

The efficacy of human placenta-derived mesenchymal stem cells on radiation enteropathy along with proteomic biomarkers predicting a favorable response

BackgroundRadiation enteropathy is a common complication in patients with abdominopelvic cancer, but no treatment has yet been established. Stem cell therapy may be a viable therapeutic option because intestinal stem cells are highly vulnerable to ionizing radiation (IR) and stem cell loss explains its intractability to general treatment. Here, we investigated either prophylactic or therapeutic efficacy of human placenta-derived mesenchymal stem cells (hPDSCs) against radiation enteropathy and could identify biomarkers predicting a favorable response to stem cell therapy.MethodsWe challenged a radiation-induced enteropathy model with hPDSCs. After sacrifice, we checked the gross anatomy of small intestine, histology gross, and analyzed that, accompanied with molecular changes implicated in this model.ResultshPDSCs significantly improved the outcome of mice induced with either radiation enteropathy or lethal radiation syndrome (P < 0.01). hPDSCs exerted inhibitory actions on inflammatory cytokines, the re-establishment of epithelium homeostasis was completed with increasing endogenous restorative processes as assessed with increased levels of proliferative markers in the hPDSCs group, and a significant inhibition of IR-induced apoptosis. The preservation of cells expressing lysozyme, and Musashi-1 were significantly increased in the hPDSC treatment group. Both preventive and therapeutic efficacies of hPDSCs were noted against IR-induced enteropathy. Label-free quantification was used to identify biomarkers which predict favorable responses after hPDSC treatment, and finally glutathione S-transferase-mu type, interleukin-10, and peroxiredoxin-2 were validated as proteomic biomarkers predicting a favorable response to hPDSCs in radiation enteropathy.ConclusionshPDSCs may be a useful prophylactic and therapeutic cell therapy for radiation enteropathy.

Ionizing radiation induces long-term senescence in endothelial cells through mitochondrial respiratory complex II dysfunction and superoxide generation

Ionizing radiation causes oxidative stress, leading to acute and late cellular responses. We previously demonstrated that irradiation of non-proliferating endothelial cells, as observed in normal tissues, induces early apoptosis, which can be inhibited by pretreatment with Sphingosine-1-Phosphate. We now propose to better characterize the long-term radiation response of endothelial cells by studying the molecular pathways associated with senescence and its link with acute apoptosis. First, senescence was validated in irradiated quiescent microvascular HMVEC-L in a dose- and time-dependent manner by SA β-galactosidase staining, p16Ink4a and p21Waf1 expression, pro-inflammatory IL-8 secretion and DNA damage response activation. This premature aging was induced independently of Sphingosine 1-Phosphate treatment, supporting its non-connection with acute IR-induced apoptosis. Then, senescence under these conditions showed persistent activation of p53 pathway and mitochondrial dysfunctions, characterized by O2·- generation, inhibition of respiratory complex II activity and over-expression of SOD2 and GPX1 detoxification enzymes. Senescence was significantly inhibited by treatment with pifithrin–α, a p53 inhibitor, or by MnTBAP, a superoxide dismutase mimetic, validating those molecular actors in IR-induced endothelial cell aging. However, MnTBAP, but not pifithrin–α, was able to limit superoxide generation and to rescue the respiratory complex II activity. Furthermore, MnTBAP was not modulating p53 up-regulation, suggesting that IR-induced senescence in quiescent endothelial cells is provided by at least 2 different pathways dependent of the mitochondrial oxidative stress response and the p53 activation. Further characterization of the actors involved in the respiratory complex II dysfunction will open new pharmacological strategies to modulate late radiation toxicity.

Mechanism of the Antitumor and Radiosensitizing Effects of a Manganese Porphyrin, MnHex-2-PyP.

Cationic manganese (Mn)-substituted N-pyridylporphyrin-based potent mimics of the family of superoxide dismutases (SODs) protect normal tissues from injury related to ionizing radiation (IR) by reducing levels of reactive oxygen and nitrogen species (ROS/RNS). Furthermore, Mn-porphyrins have demonstrated antitumor and radiosensitizing effects on cancer cells by promoting IR-induced tumor vasculature damage and apoptotic processes. In this study, we explored the underlying mechanisms of Mn-porphyrin-mediated tumor radiosensitization using murine mammary carcinoma 4T1 and melanoma B16 cells in vitro and in vivo. Combination treatment with MnTnHex-2-PyP and IR substantially reduced cell viability, clonogenic cell survival, and DNA damage repair and synergistically increased IR-induced apoptosis of 4T1 and B16 cells. MnTnHex-2-PyP in combination with IR caused a significant delay in growth of 4T1 and B16 xenograft tumors. MnTnHex-2-PyP dose-dependently enhanced IR-mediated production of H2O2-derived species, but not superoxide. Catalase overexpression reversed MnTnHex-2-PyP-enhanced ROS production and apoptosis. Demonstrated suppression of phosphorylation of several mitogen-activated protein (MAP) kinases and activation of NF-κB by MnTnHex-2-PyP/IR, which presumably inhibited activation of the antiapoptotic pathway, are in agreement with our other data on the apoptosis of cancer cells. Innovation and Conclusions: MnTnHex-2-PyP exerted a radiosensitizing effect on 4T1 and B16 tumor models in vitro and in vivo via pro-oxidative actions and therefore bears a large therapeutic potential. When combined with IR, it attenuated DNA damage repair and triggered a shift from prosurvival pathways to apoptotic cell death, likely due to increased ROS production and disturbed cellular redox balance, acting at the level of nuclear factor κB (NF-κB). Antioxid. Redox Signal. 27, 1067-1082.

MiR-185 enhances the inhibition of proliferation and migration induced by ionizing radiation in melanoma

Melanoma is an aggressive malignancy that is increasingly common and exhibits a poor patient survival rate. Radiotherapy is the primary option for patients with melanoma, particularly those who are not candidates for surgery; however, the therapeutic effect is limited due to the relative radioresistance of melanoma to ionizing radiation (IR). It has been reported that microRNAs (miRNAs) serve a vital role in determining the radiosensitivity of tumors; however, little is known concerning the radiosensitization of melanoma using miRNA. In the present study, the radiosensitization effect of miRNA 185 (miR-185), which has been demonstrated to reduce renal cancer radioresistance, was investigated in B16 cells, a skin melanoma cell line derived from C57/BL mice, was investigated. Cell proliferation and scratch wound healing assays were used to determine the proliferative and migratory abilities of B16 cells. Annexin V/propidium iodide double staining was used to determine the apoptosis induced by IR. A tumor formation assay was performed to determine the radiosensitization effect of miR-185 on melanoma cells in vivo. Proliferation marker protein Ki-67, and hematoxylin and eosin staining were used to assess the proliferative activity and histological changes, respectively. The results of the present study demonstrated that miR-185 suppresses cellular proliferation and migration, and enhances IR-induced apoptosis, and the inhibition of proliferation and migration, in vitro and in vivo, which provides an insight into understanding the radiosensitization of melanoma using miRNA.

The Impact of DIDS-Induced Inhibition of Voltage-Dependent Anion Channels (VDAC) on Cellular Response of Lymphoblastoid Cells to Ionizing Radiation.

The voltage-dependent anion channels (VDAC) play an essential role in the cross talk between mitochondria and the rest of the cell. Their implication in cell life and cell death has been studied extensively in recent years. In this work we studied the impact of mitochondrial membrane (VDACs) on cell survival and response to X-ionizing radiation (IR) of human lymphoblastoid K562 cells. The inhibition of VDACs was achieved by 4,4`-diisothiocyanostilbene-2,2`-disulfonic acid (DIDS) inhibitor and in vitro experiments including clonogenity assay, UV-visible spectrophotometry, comet assay and FACS analysis were implemented. Inhibition of VDAC led to augmentation of IR-induced apoptosis and ROS production. Additionally, DIDS affected repair of IR-induced DNA strand breaks and was in line with both induction of apoptosis and caspase activity. The IR-induced NO production was potently reduced by inhibition of VDAC. Our results suggest that VDAC control cellular response to ionizing radiation through modulation of the ROS- and NO-dependent signaling pathways. Inhibition of VDAC with DIDS induced apoptosis in irradiated K562 lymphoblastoid cells points at DIDS, as a promising agent to enhance the effectiveness of radiotherapy.

Abstract B05: Ecto-5’-nucleotidase (CD73) confers radioresistance in pancreatic cancer

Abstract Pancreatic cancer is an exceptional aggressive cancer, and acquired radiation resistance in this type of cancer is common. The objective of this study was to use a comparative proteomic method to identify the proteins that are responsible for acquired radioresistance in pancreatic cancer cells. In order to eliminate the complications caused by genetic background variations, we first generated a pancreatic cancer isogenic stable cell line that differs in radioresistance. The isogenic stable cell line was generated by exposing the pancreatic cancer MIA PaCa-2 cells (an undifferentiated pancreatic cancer cell line) to a total dose of 60 Gy of ionizing radiation (IR; gamma radiation) in 30 fractions over a period of 6 weeks, a protocol that is commonly used in clinical radiotherapy. The clones that survived from the fractionated exposures showed strong radioresistance, which could be demonstrated by both cell apoptotic assays and the long-term clonogenic survival assays. We then used a mass spectrometry-based quantitative proteomic method to systematically compare the expression of proteins between the radiosensitive parental cells and the selected radioresistant cells. One protein identified to be substantially upregulated in the radioresistant cells was ecto-5’-nucleotidase (CD73), a cell surface enzyme that converts adenosine monophosphate (AMP) into adenosine and is known to play important roles in cell-cell/cell-matrix interactions and immune suppression. To examine whether the upregulated CD73 was functionally related to the acquired radioresistance of pancreatic cancer cells, we silenced or ectopically overexpressed CD73 gene in the cells and examined the effect of the expression manipulations on long-term survival and apoptosis of the cells in response to IR exposure. The results demonstrated that knockdown of CD73 in the radioresistant cells significantly decreased the long-term survival rates, and resensitized the cells to apoptosis after the cells were exposed to IR. Concomitantly, stable overexpression of CD73 in the radiosensitive parental cells significantly increased the long-term survival rates, and enhanced resistance of the cells to apoptosis upon exposure of the cells to IR. To determine if the enzyme activity of CD73 is important for its effect on radioresistance, we generated an enzyme-dead mutant CD73 and overexpressed the mutant CD73 in the parental cells. Functional assays demonstrated that the mutant CD73 affected radioresistance of pancreatic cancer cells in a similar way as wild-type CD73, suggesting that the enzyme activity is not related to its effect on radioresistance. In summary, our results suggest that upregulation of CD73 expression is an important mechanism by which pancreatic cancer cells acquire resistance to IR, and the effect of CD73 on radioresistance in pancreatic cancer cells is enzyme-independent and at least partially through affecting the sensitivity of the cells to IR-induced apoptosis. Citation Format: Anna M. Nguyen, Jianhong Zhou, Yuchun Du.{Authors}. Ecto-5’-nucleotidase (CD73) confers radioresistance in pancreatic cancer. [abstract]. In: Proceedings of the AACR Special Conference on Pancreatic Cancer: Advances in Science and Clinical Care; 2016 May 12-15; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2016;76(24 Suppl):Abstract nr B05.

Distinct Roles of CHK2 and Cell Death in Suppressing Oncogenic Potential of Tandem DNA Breaks in Human Hematopoietic Stem Cells

DNA double strand breaks (DSBs) are the most dangerous genomic lesions that can be induced by endogenous and exogenous sources. DNA damage response determines cellular fate decisions following DSBs and can lead to cell death or cell survival. Incorrect DSB repair via canonical Non-Homologous End Joining (cNHEJ) or Alternative NHEJ (Alt-NHEJ) is the main source of oncogenic aberrations, including leukemogenic translocations, DNA sequence deletions and insertions. The long life span of Hematopoietic Stem Cells (HSC) and their practically unlimited potential for self-renewal requires efficient strategies to cope with DNA damage to eliminate erroneous genetic information inheritance to daughter cells.Although the critical importance of maintaining genome integrity for normal hematopoiesis and prevention of leukemogenesis has been established, definitive analysis of DNA damage response and its mutagenic outcomes in human HSC and Progenitors in response to DSBs is missing.Here we repot that human cord blood purified HSC (defined as CD34+CD38-CD45RA-) are exquisitely sensitive to irradiation (IR)-induced apoptosis in contrast to committed progenitors (defined as CD34+CD38+) as validated by PARP cleavage induction. Interestingly, pan-caspase inhibitor Z-VAD-FMK prevented, whereas CHK2 inhibitor (PV1019) failed in altering apoptosis onset of irradiated HSC. Strikingly, CHK2 inhibitor blocked IR-induced apoptosis in cycling HSC, suggesting differential wiring of DNA damage induced apoptosis in quiescent versus mitogenically stimulated HSC.To characterize cNHEJ repair pathway and its mutagenic potential in live primitive hematopoietic cells we analyzed I-SceI endonuclease induced tandem DSBs joining capacity using DNA repair reporter assay. We found that HSC exhibit inferior cNHEJ capacity as compared with committed progenitors. By decreasing DSBs persistence we revealed that progenitors utilize to the higher degree than HSC the mutagenic component of cNHEJ pathway that results in DNA deletions. We identified HSC-specific contribution of CHK2 kinase activity in limiting incorrect DNA ends joining. Blockade of apoptosis induction also led to the selective increase in mutagenic NHEJ in HSC. On the other hand, inhibition of DNA-PK led to increased oncogenic repair in progenitors only. Importantly, we revealed that HSC utilized mutagenic Alt-NHEJ pathway that depends on microhomologies search and extensive DNA ends processing less efficiently than Progenitors. Thus, our results indicate that oncogenic consequences of DSBs repair in HSC are distinctly minimized by the non-redundant cell death and CHK2 dependent mechanisms. More broadly, these findings will help to elucidate additional repair modifiers and the mechanism by which HSC contend with genotoxic stress. DisclosuresNo relevant conflicts of interest to declare.

The Role of Deoxycytidine Kinase (dCK) in Radiation-Induced Cell Death.

Deoxycytidine kinase (dCK) is a key enzyme in deoxyribonucleoside salvage and the anti-tumor activity for many nucleoside analogs. dCK is activated in response to ionizing radiation (IR)-induced DNA damage and it is phosphorylated on Serine 74 by the Ataxia-Telangiectasia Mutated (ATM) kinase in order to activate the cell cycle G2/M checkpoint. However, whether dCK plays a role in radiation-induced cell death is less clear. In this study, we genetically modified dCK expression by knocking down or expressing a WT (wild-type), S74A (abrogates phosphorylation) and S74E (mimics phosphorylation) of dCK. We found that dCK could decrease IR-induced total cell death and apoptosis. Moreover, dCK increased IR-induced autophagy and dCK-S74 is required for it. Western blotting showed that the ratio of phospho-Akt/Akt, phospho-mTOR/mTOR, phospho-P70S6K/P70S6K significantly decreased in dCK-WT and dCK-S74E cells than that in dCK-S74A cells following IR treatment. Reciprocal experiment by co-immunoprecipitation showed that mTOR can interact with wild-type dCK. IR increased polyploidy and decreased G2/M arrest in dCK knock-down cells as compared with control cells. Taken together, phosphorylated and activated dCK can inhibit IR-induced cell death including apoptosis and mitotic catastrophe, and promote IR-induced autophagy through PI3K/Akt/mTOR pathway.

Downregulation of Annexin A1 is correlated with radioresistance in nasopharyngeal carcinoma.

Radiotherapy is the primary treatment for nasopharyngeal carcinoma (NPC), but radioresistance often remains an obstacle to successful treatment. In our previous study, it was demonstrated that Annexin A1 (ANXA1) was involved in the p53-mediated radioresponse in NPC cells, which suggested that it may be associated with radioresistance in NPC; however, the role of ANXA1 in NPC radioresistance is unknown. In the present study, CNE2 cells were stably transfected with pLKO.1-ANXA1-small hairpin (sh)RNAs to investigate the effects of ANXA1 on the radiosensitivity of NPC. CNE2 cells transfected with pLKO.1 were used as the control. The radiosensitivities of the cells in vitro were analyzed using the clonogenic survival assay, cell growth analysis, flow cytometry and Hoechst 33258 staining. ANXA1 downregulation significantly enhanced clonogenic survival and cell growth following treatment of CNE2 cells with ionizing radiation (IR), increased the number of cells in the S phase and decreased IR-induced apoptosis. These results suggested that the radiosensitivity of CNE2 cells transfected with ANXA1-specific shRNA was significantly lower compared with the control cells. Therefore, ANXA1 downregulation may be involved in the radioresistance of NPC, and ANXA1 may be considered a novel biomarker for predicting NPC response to radiotherapy.