De-Bing Xiang

APE1 overexpression is associated with cisplatin resistance in non-small cell lung cancer and targeted inhibition of APE1 enhances the activity of cisplatin in A549 cells

PURPOSE Apurinic/apyrimidinic endonuclease (APE1), a bifunctional AP endonuclease/redox factor, is important in DNA repair and redox signaling, may be associated with chemoresistance. In this study, we first investigated APE1 expression and its correlation with cisplatin resistance and prognosis in non-small cell lung cancer (NSCLC) patients. Then, we investigated the effect of chimeric adenoviral vector Ad5/F35 carrying human APE1 siRNA (Ad5/F35-APE1 siRNA) on the sensitivity of cisplatin in A549 human lung adenocarcinoma cells. METHODS Tumor specimens from 103 patients with operable NSCLC were obtained from 1999 to 2001. Among these patients, 72 patients have been treated with at least three cycles of cisplatin-based chemotherapy. APE1 protein expression was examined by immunohistochemistry and Western blot on the tumor samples and a cultured A549 cell line, respectively. Cell survival and apoptosis were determined by MTT and TUNEL, respectively. RESULTS 83.3% (20/24) cisplatin-resistant tumors showed high APE1 expression levels, while 8.3% (4/48) cisplatin-sensitive tumors showed high APE1 expression levels (p<0.01). Univariate analysis indicated that overall survival and disease-free survival were significantly better in NSCLC patients with low vs those with high APE1 expression levels (p<0.01). Treatment with cisplatin resulted in a dose-dependent increase in APE1 protein expression in A549 cells, and Ad5/F35-APE1 siRNA effectively inhibited APE1 expression. Ad5/F35-APE1 siRNA significantly enhanced sensitivity of A549 cells to cisplatin, associated with increased cell apoptosis. CONCLUSIONS Our results indicate that APE1 is a new promising target for the combination of cisplatin-based chemotherapy in NCSLC patients.

Signal amplification of electrochemical immunosensor for the detection of human serum IgG using double-codified nanosilica particles as labels

A simple and sensitive method for in situ amplified electrochemical immunoassay of human serum IgG has been developed by using double-codified nanosilica particles as labels based on horseradish peroxidase-doped nanosilica particles (HRP-SiO(2)) with the conjugation of anti-IgG antibodies (anti-IgG-SiO(2)-HRP). With the sandwich-type immunoassay format, the linear range of the developed immunosensor by using anti-IgG-SiO(2)-HRP as tracer and hydrogen peroxide (H(2)O(2)) as enzyme substrate is 0.01-15 nmol/L IgG with a detection limit of 5.0 pmol/L, while the assay sensitivity by directly using HRP-labeled anti-IgG as secondary antibodies is 1.0-10 nmol/L with a detection limit of 0.1 nmol/L IgG. The reproducibility, stability and specificity of the proposed immunoassay method were acceptable. The IgG concentrations of the clinical serum specimens assayed by the developed immunosensor show consistent results in comparison with those obtained by commercially available enzyme-linked immunosorbent assay (ELISA) method.

Identification and characterization of mitochondrial targeting sequence of human apurinic/apyrimidinic endonuclease 1.

Dually targeted mitochondrial proteins usually possess an unconventional mitochondrial targeting sequence (MTS), which makes them difficult to predict by current bioinformatics approaches. Human apurinic/apyrimidinic endonuclease (APE1) plays a central role in the cellular response to oxidative stress. It is a dually targeted protein preferentially residing in the nucleus with conditional distribution in the mitochondria. However, the mitochondrial translocation mechanism of APE1 is not well characterized because it harbors an unconventional MTS that is difficult to predict by bioinformatics analysis. Two experimental approaches were combined in this study to identify the MTS of APE1. First, the interactions between the peptides from APE1 and the three purified translocase receptors of the outer mitochondrial membrane (Tom) were evaluated using a peptide array screen. Consequently, the intracellular distribution of green fluorescent protein-tagged, truncated, or mutated APE1 proteins was traced by tag detection. The results demonstrated that the only MTS of APE1 is harbored within residues 289–318 in the C terminus, which is normally masked by the intact N-terminal structure. As a dually targeted mitochondrial protein, APE1 possesses a special distribution pattern of different subcellular targeting signals, the identification of which sheds light on future prediction of MTSs.

Targeting truncated APE1 in mitochondria enhances cell survival after oxidative stress

The high steady-state level of mitochondrial DNA (mtDNA) oxidative lesions is assumed to be the result of high susceptibility to DNA damage attack and limited DNA repair capacity in mitochondria. As a key enzyme of base excision repair (BER), human apurinic/apyrimidinic endonuclease (APE1) is often scarce in mitochondria, and mitochondria-targeted APE1 with robust repair activity represents a promising therapeutic candidate. In this study, overexpression vectors of mitochondria-targeted truncated APE1 (mtAPE1) and that of full-length APE1 (flAPE1) were constructed and transfected to human umbilical vein endothelial cells to test their protective effects after hydrogen peroxide-induced oxidative stress. The overexpression of truncated APE1 was achieved at protein and enzyme activity levels in mitochondria of mtAPE1-transfected cells. In parallel, enhanced mtDNA repair capacity and increased cell survival were observed. MtAPE1 transfection also prevented apoptosis by blocking mitochondria-dependent pathways. In contrast, flAPE1 transfection rendered slight elevation of nuclear APE1 protein level and nuclear APE activity but no benefits for cell resistance to oxidative stress. The present results suggest that overexpression of the truncated APE1 in mitochondria appears to be a viable approach to protecting healthy cells from some deleterious effects of oxidative stress.

Vector-based Ape1 small interfering RNA enhances the sensitivity of human osteosarcoma cells to endostatin in vivo

Osteosarcoma is a highly vascular and extremely destructive malignancy, and the survival of patients with osteosarcoma has not improved significantly in recent years. Antiangiogenic therapy currently holds great potential in conjunction with conventional treatment modalities for osteosarcoma. However, there are examples of gradual loss of response, and perhaps acquired resistance to antiangiogenic drugs. The acquired resistance of antiangiogenesis may be associated with a lot of hypoxia‐response genes. The human apurinic/apyrimidinic endonuclease (Ape1) protein, a bifunctional redox factor and apurinic/apyrimidinic (AP) endonuclease, plays a crucial role in protecting against cell death due to hypoxia. We therefore hypothesized that Ape1 may contribute to the resistance of antiangiogenic therapy. To investigate the effect of Ape1 on the sensitivity of human osteosarcoma cells to endostatin, we constructed an Ape1 small interfering RNA expression vector, pSilenceApe1. Transfection of human osteosarcoma 9901 and HOS cells with pSilenceApe1 resulted in a dose‐dependent loss of Ape1 protein. pSilenceApe1 also significantly suppressed the expression of vascular endothelial growth factor (VEGF) protein in the 9901 cells. Combined treatment with pSilenceApe1 and recombinant human endostatin (rhES) showed potent antiangiogenic effects in the transwell chamber invasion assay. Then, 20 nude mice bearing 9901 xenografts were divided into four groups: the phosphate‐buffered saline treatment control group; the rhES treatment group (1.5 mg/kg, daily); the pSilenceApe1 treatment group (20 µg, once every 3 days); and the combination of rhES and pSilenceApe1 treatment group. pSilenceApe1 significantly suppressed the expression of Ape1 and VEGF protein in the 9901 xenografts. The tumor‐inhibition rate of the pSilenceApe1, rhES, and combination of rhES and pSilenceApe1 treatment groups was 38.23, 35.29, and 62.18%, respectively. Furthermore, a significant decrease in microvessel density with an increase in apoptosis was observed following combined treatment with pSilenceApe1 and rhES, compared with control and either agent alone in 9901 xenografts. These results indicate that Ape1 small interfering RNA could enhance the sensitivity of osteosarcoma cells to endostatin. (Cancer Sci 2007; 98: 1993–2001)

Elevated Expression of APE1/Ref-1 and its Regulation on IL-6 and IL-8 in Bone Marrow Stromal Cells of Multiple Myeloma

A number of growth factors secreted by bone marrow stromal cells (BMSCs), including interleukin-6 and -8 (IL-6/8), are important for the initiation and progression of multiple myeloma (MM). However, the mechanisms that regulate the production of IL-6/8 by BMSC have not yet been well characterized. Human dual functional protein apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE1/Ref-1) is essential for cell survival and proliferation. Previous studies showed that APE1/Ref-1 was overexpressed in tumor cells, but few studies showed its expression in supportive cells in the tumor microenvironment. We first detected APE1/Ref-1 expression in BMSCs of normal, initial, and recurrent MM patients, and then explore the correlation between APE1/Ref-1 level and IL-6/8 secretion of BMSCs. A marked increase of APE1/Ref-1 expression and abnormal subcellular distribution were observed in MM BMSCs. APE1/Ref-1 overexpression was related to higher secretary level of IL-6/8 by MM BMSCs and the IL-6/8 secretion was blocked significantly by adenovirus-mediated APE1/Ref-1-specific (small interfering RNA) siRNA. Our results also demonstrated that APE1/Ref-1-specific siRNA significantly inhibited DNA binding activity of AP-1 and nuclear factor-κB (NF-κB), 2 important transcription factors in the regulation IL-6/8 secretion in MM BMSCs. The results provided by the present study indicate APE1/Ref-1, which plays a regulatory role in IL-6/8 production by BMSCs, may be a potential therapeutic target of MM.

Knock down of the dual functional protein apurinic /apyrimidinic endonuclease 1 enhances the killing effect of hematoporphrphyrin derivative‐mediated photodynamic therapy on non‐small cell lung cancer cells in vitro and in a xenograft model

Photodynamic therapy (PDT) is considered to be effective treatment for many cancers including lung cancer, head and neck cancers, and prostate cancer. It uses the combination of nontoxic photosensitizers and harmless visible light to generate reactive oxygen species and kill cells. However, DNA repair and reactive oxygen species‐induced signaling pathway activation play crucial roles in cellular response to PDT and may also result in therapeutic limitation of PDT. To improve the cancer therapeutic efficacy of PDT, we targeted apurinic/apyrimidinic endonuclease (APE1), which is essential for both DNA repair and redox regulation of gene transcription, as a potential candidate for PDT combined gene therapy. In our study, an adenovirus‐mediated APE1 silencing strategy was introduced to test its therapeutic enhancement for the non‐small cell lung cancer cell line A549 both in vitro and in vivo after hematoporphrphyrin derivative (HpD)‐mediated PDT. The adenovirus vector Ad5/F35‐shAPE1 was validated to significantly suppress the protein expression of APE1 in cultured A549 cell and in its xenograft of nude mice. Ad5/F35‐shAPE1 effectively inhibited APE1 protein upregulation induced by PDT and resulted in an increase in A549 cell killing by photoirradiation compared with the hematoporphrphyrin derivative‐PDT alone group. Ad5/F35‐shAPE1 suppressed the DNA repair capacity for single‐strand breaks and abolished the activation of some stress‐related transcription factors such as hypoxia‐induced factor (HIF)‐1 that consequently lead to increased cell apoptosis after PDT. Additionally, knock down of APE1 enhanced the tumor suppression efficacy of PDT on the A549 xenograft. Our study indicated that APE1‐targeted gene therapy combined with PDT is a promising strategy for enhancement of the efficacy of PDT in treatment of non‐small cell lung cancer. (Cancer Sci 2009)

Nm23-H1 Protein Binds to APE1 at AP Sites and Stimulates AP Endonuclease Activity Following Ionizing Radiation of the Human Lung Cancer A549 Cells

Non-metastatic protein-23 homolog-1 (Nm23-H1) is a multifunctional protein with DNase and histidine protein kinase activities. Human apurinic endonuclease-1 (APE1) is the AP endonuclease DNA base excision repair (BER) enzyme involved in several important cellular functions. Since the relationship between Nm23-H1 and APE1 proteins is unclear, we evaluated their interaction at different time points after irradiating human lung cancer A549 cells with X-rays. We found that Nm23-H1 and APE1 overexpression was induced by irradiation in a dose- and time-dependent manner. Subcellular distribution pattern of both proteins was reversed after irradiation. After irradiation, APE1 that initially showed nuclear localization was gradually increased in the cytoplasm, whereas Nm23-H1 that mainly showed cytoplasmic localization was gradually increased in the nuclei of A549 cells. Nm23-H1 and APE1 interaction was demonstrated by His-pull-down and co-immunoprecipitation assays. The presence of Nm23-H1/APE1 complex in X-ray-irradiated A549 cells was also detected by DNA affinity precipitation analysis of a DNA fragment containing an AP site. Although the AP endonuclease activity of Nm23-H1 was too weak to be detected, the AP endonuclease activity of APE1 was increased with the enhanced Nm23-H1 expression. In conclusion, our data point to a mechanism by which Nm23-H1 protects cells against oxidative stress through the engagement of DNA BER enzyme APE1.