UV radiation-induced XPC translocation within chromatin is mediated by damaged-DNA binding protein, DDB2

The tumor suppressor p53 protein has been established as an important factor in modulating the efficiency of global genomic repair. Our recent repair studies in human cells reported that p53 regulates the recruitment of XPC and TFIIH proteins to specific DNA damage sites. Here, we have examined the influence of p53 and damaged-DNA binding complex (DDB2) proteins on the distribution of XPC within damaged chromatin in vivo and the recruitment of XPC to DNA damage sites in situ. The results show that UV irradiation causes the translocation of XPC from a loosely bound form into a tight association with chromatin in vivo. The UV radiation-induced redistribution of XPC was equally compromised in p53-deficient, as well as DDB2-deficient, human cells. Similarly, rapid recruitment of XPC to DNA damage in situ was also impaired in both cell lines. Ectopic expression of DDB2 in p53-deficient cells overcame the requirement of p53 function for UV-induced translocation of XPC in vivo. Restoration of DDB2 function also enhanced the recruitment of XPC to DNA damage sites in situ and increased the global repair of cyclobutane pyrimidine dimer from the genome. These results indicate that DDB2 is a key downstream factor of p53 for regulating the movement of XPC to DNA damage in irradiated cells.     

Ionizing radiation-induced micronucleus formation is mediated by reactive oxygen species that are produced in a manner dependent on mitochondria, Nox1, and JNK

Ionizing radiation (IR) is known to induce genotoxic damage to DNA, chromosomes, and the nucleus. However, the damage that IR causes to the nucleus has received much less attention. Given that reactive oxygen species (ROS) are involved in IR-induced DNA breaks and chromosomal aberrations, this study examined the role of ROS in IR-induced damage to the nucleus. Human Jurkat T cells were irradiated with gamma-rays at a dose of 2.5 Gy, which resulted in a dramatic increase in both the cellular ROS levels and the number of micronuclei. This latter event was attenuated when the IR-induced ROS were eliminated through the exogenous application of an antioxidant enzyme catalase. The ability of IR to induce the accumulation of ROS and micronucleus formation was also reduced either when the cells were irradiated in the presence of rotenone, a mitochondrial respiratory chain inhibitor, or when the cellular Nox1 levels were reduced by RNA interference. These results suggest that IR stimulates both the mitochondria and Nox1 to produce ROS, and that these ROS are involved in the IR-induced formation of micronuclei. IR also activated c-Jun N-terminal kinase (JNK), which was reversed by catalase, rotenone, or Nox1 RNA interference. SP600125, a JNK-specific inhibitor, suppressed the IR-induced accumulation of ROS. This inhibitor consistently attenuated the IR-induced formation of micronuclei. Therefore, ROS and JNK appear to act in a positive mutual manner in IR-induced signaling processes. Overall, IR appears to induce the formation of micronuclei by inducing ROS through mitochondria, Nox1, and JNK.     

Ionizing radiation-induced E-selectin gene expression and tumor cell adhesion is inhibited by lovastatin and all-trans retinoic acid

E-selectin mediated tumor cell adhesion plays an important role in metastasis. Here we show that ionizing radiation (IR) induces E-selectin gene and protein expression in human endothelial cells at therapeutically relevant dose level. E-selectin expression is accompanied by an increase in the adhesion of human colon carcinoma cells to primary human umbilical vein endothelial cells (HUVEC). The HMG-CoA reductase inhibitor lovastatin impairs IR-stimulated E-selectin expression as analyzed at the level of the protein, mRNA and promoter. Inactivation of Rho GTPases either by use of Clostridium difficile toxin A or by co-expression of dominant-negative Rho blocked IR-induced E-selectin gene induction, indicating Rho GTPases to be essential. Radiation-induced expression of E-selectin was also blocked by all-trans retinoic acid (at-RA), whereas 9-cis retinoic acid was ineffective. Abrogation of IR-stimulated E-selectin expression by lovastatin and at-RA reduced tumor cell adhesion in a dose-dependent manner. Combined treatment with lovastatin and at-RA exerted additive inhibitory effects on radiation-induced E-selectin expression and tumor cell adhesion. Therefore, application of statins and at-RA might have clinical impact in protecting against E-selectin-promoted metastasis, which might arise as an unwanted side effect from radiation treatment.     

Ionizing radiation-induced apoptosis via separate Pms2- and p53-dependent pathways

The cytotoxicity of ionizing radiation (IR) has been associated with both the p53 pathway and with DNA mismatch repair (MMR). p53 mediates cell cycle arrest and apoptosis in response to X-ray damage, whereas the MMR complex is thought to recognize damaged bases and initiate a signal transduction pathway that can include phosphorylation of p53. To determine whether p53 and MMR mediate X-ray cytotoxicity via the same pathway, mice with targeted disruptions in either the p53 gene or the MutL homologue MMR gene Pms2 were interbred and primary fibroblasts were established from the progeny with genotypes of either wild type, p53 null, Pms2 null, or double null. Cells with either p53 or Pms2 separately disrupted showed reduced levels of apoptosis after IR in comparison with wild type, but the double null cells showed even lower levels, consistent with nonoverlapping roles for p53 and PMS2 in the X-ray response. In transformed cell lines established from the primary cells at early passage, similar differences in the apoptotic response to IR were seen, and clonogenic survival assays following low dose rate IR further showed that nullizygosity for Pms2 confers increased survival on cells in both wild-type and p53 null backgrounds. These results indicate that both p53 and MMR contribute to X-ray-induced apoptosis and that the role of MMR in the cytotoxicity of IR does not depend on p53.     

骨形态发生蛋白2基因转染诱导异位成骨的机制研究

目的观察骨形态发生蛋白2基因直接及间接转染诱导异位成骨的效果和机制。方法1.将携带骨形态发生蛋白-2基因的腺病毒载体(Ad-BMP-2)直接注射到裸鼠肌内诱导成骨;2.Ad-BMP-2体外转染人骨髓间质干细胞(hBMSC)后种植异种骨支架(BCB)植入裸鼠皮下。实验分为5组:①BMP-2基因转染细胞 BCB;②对照基因转染细胞 BCB;③未转染细胞 重组BMP-2 BCB;④未转染细胞 BCB;⑤BCB。术后行X线、免疫组化及原位杂交染色观察BMP-2基因诱导下的成骨方式及成骨机制。结果1.裸鼠肌内注射后有异位成骨,其主要为软骨化骨。2.Y染色体探针荧光原位杂交法(FISH)示踪植入细胞命运,见部分转基因细胞直接参与成骨;骨钙素免疫组化检测见基因表达产生的BMP-2诱导宿主间质细胞向成骨细胞转化。结论BMP-2基因转染的hBMSC不仅作为运载生长因子的工具,而且直接参与成骨,但BMP-2的诱导趋化作用占主导地位。     

Ionizing radiation-induced metabolic oxidative stress and prolonged cell injury

Cellular exposure to ionizing radiation leads to oxidizing events that alter atomic structure through direct interactions of radiation with target macromolecules or via products of water radiolysis. Further, the oxidative damage may spread from the targeted to neighboring, non-targeted bystander cells through redox-modulated intercellular communication mechanisms. To cope with the induced stress and the changes in the redox environment, organisms elicit transient responses at the molecular, cellular and tissue levels to counteract toxic effects of radiation. Metabolic pathways are induced during and shortly after the exposure. Depending on radiation dose, dose-rate and quality, these protective mechanisms may or may not be sufficient to cope with the stress. When the harmful effects exceed those of homeostatic biochemical processes, induced biological changes persist and may be propagated to progeny cells. Physiological levels of reactive oxygen and nitrogen species play critical roles in many cellular functions. In irradiated cells, levels of these reactive species may be increased due to perturbations in oxidative metabolism and chronic inflammatory responses, thereby contributing to the long-term effects of exposure to ionizing radiation on genomic stability. Here, in addition to immediate biological effects of water radiolysis on DNA damage, we also discuss the role of mitochondria in the delayed outcomes of ionization radiation. Defects in mitochondrial functions lead to accelerated aging and numerous pathological conditions. Different types of radiation vary in their linear energy transfer (LET) properties, and we discuss their effects on various aspects of mitochondrial physiology. These include short and long-term in vitro and in vivo effects on mitochondrial DNA, mitochondrial protein import and metabolic and antioxidant enzymes.     

Ionizing radiation inhibition of distant untreated tumors (abscopal effect) is immune mediated

PURPOSE: Ionizing radiation can reduce tumor growth outside the field of radiation, known as the abscopal effect. Although it has been reported in multiple malignancies, the abscopal effect remains a rare and poorly understood event. Ionizing radiation generates inflammatory signals and, in principle, could provide both tumor-specific antigens from dying cells and maturation stimuli that are necessary for dendritic cells' activation of tumor-specific T cells. We therefore tested the hypothesis that the abscopal effect elicited by radiation is immune mediated. This was directly tested by enhancing the number of available dendritic cells using the growth factor Flt3-Ligand (Flt3-L). METHODS AND MATERIALS: Mice bearing a syngeneic mammary carcinoma, 67NR, in both flanks were treated with Flt3-L daily for 10 days after local radiation therapy (RT) to only 1 of the 2 tumors at a single dose of 2 or 6 Gy. The second nonirradiated tumor was used as indicator of the abscopal effect. Data were analyzed using repeated measures regression. RESULTS: RT alone led to growth delay exclusively of the irradiated 67NR tumor, as expected. Surprisingly, growth of the nonirradiated tumor was also impaired by the combination of RT and Flt3-L. As control, Flt3-L had no effect without RT. Importantly, the abscopal effect was shown to be tumor specific, because growth of a nonirradiated A20 lymphoma in the same mice containing a treated 67NR tumor was not affected. Moreover, no growth delay of nonirradiated 67NR tumors was observed when T cell deficient (nude) mice were treated with RT plus Flt3-L. CONCLUSIONS: These results demonstrate that the abscopal effect is in part immune mediated and that T cells are required to mediate distant tumor inhibition induced by radiation.     

Ionizing radiation-induced, mitochondria-dependent generation of reactive oxygen/nitrogen

Transient generation of reactive oxygen or nitrogen (ROS/RNS), detected with dihydrodichlorofluoroscein by fluorescence microscopy, occurs within minutes of exposing cells to ionizing radiation. In the 1-10 Gy dose range, the amount of ROS/RNS produced/cell is constant, but the percentage of producing cells increases with dose (20 to 80%). Reversible depolarization of the mitochondrial membrane potential () and decrease in fluorescence of a mitochondria-entrapped dye, calcein, are observed coincidentally. Radiation-induced ROS/RNS, depolarization, and calcein fluorescence decrease are inhibited by the mitochondrial permeability transition inhibitor, cyclosporin A, but not the structural analogue, cyclosporin H. Radiation-stimulated ROS/RNS is also inhibited by overexpressing the Ca(2+)-binding protein, calbindin 28K, or treating cells with an intracellular Ca(2+) chelator. Radiation-induced ROS/RNS is observed in several cell types with the exception of rho(o) cells deficient in mitochondrial electron transport. rho(o) cells show neither radiation-induced ROS/RNS production nor depolarization. We propose that radiation damage in a few mitochondria is transmitted via a reversible, Ca(2+)-dependent mitochondrial permeability transition to adjacent mitochondria with resulting enhanced ROS/RNS generation. Measurements of radiation-induced mitogen-activated protein kinase activity indicate that this sensing/amplification mechanism is necessary for activation of some cytoplasmic signaling pathways by low doses of radiation.     

Growth of chronic myeloid leukemia cells is inhibited by infection with Ad-SH2-HA adenovirus that disrupts Grb2-Bcr-Abl complexes

The persistence of Bcr-Abl-positive cells in patients on imatinib therapy indicates that inhibition of the Bcr-Abl kinase activity alone might not be sufficient to eradicate the leukemia cells. Many downstream effectors of Bcr-Abl have been described, including activation of both the Grb2-SoS-Ras-MAPK and Grb2-Gab2-PI3K-Akt pathways. The Bcr-Abl-Grb2 interaction, which is mediated by the direct interaction of the Grb2 SH2 domain with the phospho-Bcr-Abl Y177, is required for activation of these signaling pathways. Therefore, disrupting their interaction represents a potential therapeutic strategy for inhibiting the oncogenic downstream signals of Bcr-Abl. Adenovirus Ad-SH2-HA expressing the Grb2 SH2 domain was constructed and applied in this study. As expected, Ad-SH2-HA efficiently infected CML cells and functioned by binding to the phospho-Bcr-Abl Y177 site, competitively disrupting the Grb2 SH2-phospho-Bcr-Abl Y177 complex. They induced potent anti-proliferation and apoptosis-inducing effects in CML cell lines. Moreover, the Ras, MAPK and Akt activities were significantly reduced in the Ad-SH2-HA treated cells. These were not observed with the point-mutated control adenovirus Ad-Sm-HA with abolished phospho-Bcr-Abl Y177 binding sites. These data indicate that, in addition to the direct targeting of Bcr-Abl, selective inhibition of its downstream signaling pathways may be a therapeutic option for CML, and the Ad-SH2-HA-mediated killing strategy could be explored as a promising anti-leukemia agent in CML.     

Cancer angiogenesis induced by Kaposi sarcoma-associated herpesvirus is mediated by EZH2

EZH2 is a component of the epigenetic regulator PRC2 that suppresses gene expression. Elevated expression of EZH2 is common in human cancers and is associated with tumor progression and poor prognosis. In this study, we show that EZH2 elevation is associated with epigenetic modifications of Kaposi sarcoma-associated herpesvirus (KSHV), an oncogenic virus that promotes the development of Kaposi sarcoma and other malignancies that occur in patients with chronic HIV infections. KSHV induction of EZH2 expression was essential for KSHV-induced angiogenesis. High expression of EZH2 was observed in Kaposi sarcoma tumors. In cell culture, latent KSHV infection upregulated the expression of EZH2 in human endothelial cells through the expression of vFLIP and LANA, two KSHV-latent genes that activate the NF-κB pathway. KSHV-mediated upregulation of EZH2 was required for the induction of Ephrin-B2, an essential proangiogenic factor that drives endothelial cell tubule formation. Taken together, our findings indicate that KSHV regulates the host epigenetic modifier EZH2 to promote angiogenesis.     

Interleukin-2-induced lung permeability is mediated by leukotriene B4

Interleukin (IL)-2 therapy leads to respiratory dysfunction due to increased vascular permeability. This study examines the role of the chemoattractant, immunomodulator, and permeability-promoting agent leukotriene (LT) B4 in this setting. Sheep with chronic lung lymph fistulae were given IL-2, 10(5) U/kg as an IV bolus (n = 6). Within 2 hours this led to a significant increase in LTB4 levels in both plasma and lung lymph. The mean pulmonary artery pressure (MPAP) rose while the pulmonary artery wedge pressure was unchanged. Arterial oxygen tension (PaO2) fell. Lung lymph flow (QL) was tripled (P less than 0.05) at 3 hours, coinciding with an increase in the lymph/plasma (L/P) protein ratio (P less than 0.05) resulting in an increase in the lymph protein clearance (P less than 0.05), data documenting increased microvascular permeability to protein. Mild leukopenia and thrombocytopenia (P less than 0.05) occurred. Body temperature rose and shaking chills were common. Pretreatment with the lipoxygenase inhibitor diethylcarbamazine (DEC; n = 6) reduced baseline plasma LTB4 levels and prevented the IL-2-induced increases in LTB4 in plasma and lung lymph (P less than 0.05). In contrast to IL-2 treatment alone, DEC blunted the increase in MPAP and prevented the rises in QL (P less than 0.05), L/P protein ratio (P less than 0.05), and lymph protein clearance (P less than 0.05). DEC also prevented the IL-2-induced leukopenia, the fall in platelet count, and the rise in body temperature (P less than 0.05, respectively). Infusion of IL-2 excipient control (n = 5) did not affect plasma or lymph LTB4 levels but there were mild increases in MPAP (P less than 0.05). The QL also rose but this occurred while the L/P protein ratio fell (P less than 0.05). Body temperature rose moderately. The PaO2, leukocyte, and platelet counts were unaffected. These data indicate that IL-2 administration leads to pulmonary dysfunction manifest by pulmonary hypertension and increased vascular permeability, events associated with LTB4 synthesis and prevented by DEC. Leukotriene B4 appears therefore to mediate the IL-2-induced lung injury.     

内皮抑素基因治疗对小鼠肿瘤组织内新生血管形成抑制作用的实验研究

目的:研究腺病毒介导的内皮抑素基因治疗对小鼠肺肿瘤组织内部血管的抑制作用。方法:皮下注射2×106LLC细胞至C57BL/6小鼠背部建立小鼠肺癌种植瘤模型,2周后瘤内注射2×109pfu内皮抑素腺病毒载体治疗。免疫组化检测内皮抑素在肿瘤组织的原位表达,观察治疗对肿瘤生长的影响。免疫组化标记计数肿瘤内部血管密度,观察治疗对肿瘤血管的影响。结果:Admendostatin治疗从第2周起就可明显减缓肿瘤生长速度,P<0.05。免疫组化显示治疗组肿瘤组织内皮抑素蛋白强阳性表达,对照组阴性或痕量表达。Admendostatin治疗组、空载体对照组和阴性对照组肿瘤血管密度用CD31和CD105抗原标记分别为37.5±4.6、65.2±5.8、68.5±4.5和10.5±3.2、39.7±5.6、42.4±4.8。治疗组与两对照组相比差异有统计学意义,P<0.05;空载体对照与阴性对照相比差异无统计学意义,P>0.05。结论:腺病毒介导的内皮抑素基因治疗可抑制小鼠皮下种植瘤的生长,其作用机制是抑制肿瘤内部新生血管的生成,应用CD105抗原标记可准确反映新生血管的变化。     

联合IL-2基因和B7-1基因转染G422细胞体外生物学特性

目的　通过研究联合基因转染后胶质母细胞瘤G42 2细胞生物学特性的变化 ,探讨脑胶质瘤细胞因子基因治疗的新途径。方法　通过重组腺病毒作载体 ,将IL 2基因和B7 1基因转染至小鼠G42 2细胞 ,通过CTLL 2细胞增殖的MTT法检测IL 2的分泌水平 ,FACS检测B7 1和ICAM 1的表达 ,MTT法检测转基因后G42 2细胞的增殖活性 ,双层琼脂糖培养法检测其克隆形成能力。结果　IL 2基因转染 4小时后即可检测到IL 2的分泌 ,2 4小时达高峰 ( 4 83U/ml) ,一周时表达明显下降 ,B7 1高表达 ,ICAM 1表达增加 ,增殖能力和克隆形成能力无变化。结论　重组腺病毒作载体 ,IL 2基因及B7 1基因共转染G42 2细胞 ,能得到目的基因的高效表达 ,同时促进了粘附分子ICAM 1的表达 ,体外增殖活性不受影响。     

Rejection of RG-2 gliomas is mediated by microglia and T lymphocytes

Summary Immunotherapy holds great promise for the treatment of invasive brain tumors, and we are interested specifically in evaluating immune stimulation of microglial cells as one potential strategy. In order to better understand the tumor fighting capabilities of microglial cells, we have compared the responses of syngeneic (Fisher 344) and allogeneic (Wistar) rat strains after intracranial implantation of RG-2 gliomas. Animals were evaluated by clinical examination, magnetic resonance imaging (MRI) and immunohistochemistry for microglial and other immune cell antigens. While lethal RG-2 gliomas developed in all of the Fisher 344 rats, tumors grew variably in the Wistar strain, sometimes reaching considerable sizes, but eventually all of them regressed. Tumor regression was associated with greater numbers of T cells and CD8 positive cells and increases in MHC I and CD4 positive microglia. Our findings suggest that the combined mobilization of peripheral and CNS endogenous immune cells is required for eradicating large intracranial tumors.     

腺病毒介导Her2／neu siRNA对卵巢癌细胞的生长抑制作用

目的观察腺病毒介导的针对Her2／neu基因RNAi表达载体对Her2／neu的抑制及抑制后对卵巢癌SKOV-3细胞的生长的影响。方法通过构建的针对Her2neu的siRNA重组腺病毒（滴度为1．6×10^8PFU／mL）感染卵巢癌细胞SKOV-3后，采用Western—blot法观察Her2／neu基因的沉默效果，流式细胞仪分析细胞周期变化，cell Proliferation法检查细胞体外增殖能力。结果构建的重组腺病毒Adeno—Her2siRNA感染卵巢癌细胞SKOV-3后Her2／neu的蛋白表达降低；S期细胞较对照组未感染细胞比例增加；肿瘤细胞胞增殖速度缓慢（P〈0．05）。结论成功构建的重组腺病毒Adeno-Her2siRNA感染后可有效降低Her2／neu蛋白水平表达，阻滞细胞感染于S期，造成感染细胞生长速度减慢，有望为卵巢癌的基因治疗提供一种选择手段。     

The repression of the growth factor-inducible genes JE, c-myc and stromelysin by adenovirus E1A is mediated by conserved region 1

The growth factor-inducible cellular genes JE, c-myc and stromelysin (sml) are strongly repressed upon transformation by adenovirus E1A. As E1A proteins are multifunctional and apparently contain distinct domains (conserved regions 1, 2 and 3), each with a specific effect on gene regulation and cell-transformation, we have investigated which of the three conserved regions are responsible for the reduced expression of these genes. To this end, we monitored the expression of the JE, sml and c-myc genes in a panel of normal rat kidney (NRK) cells expressing different mutant E1A genes. Only CR1, and not CR2 or CR3 were found to be essential for the repression of the genes, indicating that CR1, one of the regions essential for cell transformation, represents an autonomous gene regulatory function that can operate in the absence of CR2. We also show that the association of E1A proteins to a 300 kD cellular protein in NRK cells coincides with the ability to repress these genes.