Huibo Wang

A novel T-77C polymorphism in DNA repair gene XRCC1 contributes to diminished promoter activity and increased risk of non-small cell lung cancer.

X-ray repair cross-complementing 1 (XRCC1) plays a key role in DNA base excision repair and cells lacking its activity are hypersensitive to DNA damage. Recently, we reported a SNP (rs3213245, −77T>C) in the XRCC1 gene 5′ untranslated region (UTR) was significantly associated with the risk of developing esophageal squamous-cell carcinoma. Computer analysis predicted that this SNP was in the core of Sp1-binding motif, which suggested its functional significance. Gel shift and super shift assays confirmed that −77T>C polymorphic site in the XRCC1 promoter was within the Sp1-binding motif and the T>C substitution greatly enhanced the binding affinity of Sp1 to this region. Luciferase assays indicated that the Sp1-high-affinity C-allelic XRCC1 promoter was associated with a reduced transcriptional activity. The association between −77T>C and three other amino-acid substitution-causing polymorphisms in XRCC1 and risk of lung cancer was examined in 1024 patients and 1118 controls and the results showed that only the −77T>C polymorphism was significantly associated with an increased risk of developing lung cancer. Multivariate logistic regression analysis found that an increased risk of lung cancer was associated with the variant XRCC1 −77 genotypes (TC and CC) compared with the TT genotype (OR=1.46, 95% CI=1.18–1.82; P=0.001) and the increased risk was more pronounced in smokers (OR=1.63, 95% CI=1.20–2.21) than in non-smokers (OR=1.28, 95% CI=0.94–1.76). Taken together, these results showed that the functional SNP −77T>C in XRCC1 5′UTR was associated with cancer development owing to the decreased transcriptional activity of C-allele-containing promoter with higher affinity to Sp1 binding.

Functional characterization of a promoter polymorphism in APE1/Ref-1 that contributes to reduced lung cancer susceptibility

Apurinic/apyrimidinic endonuclease 1/redox effector factor‐1 (APE1/Ref‐1) is a ubiquitous multifunctional protein that possesses both DNA‐repair and redox regulatory activities. Although it was originally identified as a DNA‐repair enzyme, accumulating evidence supports a role of APE1/Ref‐1 in tumor development. To investigate association between APE1/ Ref‐1 polymorphisms and lung cancer risk in Chinese populations, we first genotyped three variants of APE1/ Ref‐1 and found a ‐141 T‐to‐G variant (rs1760944) in the promoter associated with decreased risk of lung cancer [odds ratio (OR) = 0.62 for GG;P=0.043]. Similar results were obtained in a follow‐up replication study. Combined data from the two studies comprising a total of 1072 lung cancer patients and 1064 cancer‐free control participants generated a more significant association (P= 0.002). We observed lower APE1/Ref‐1 mRNA levels in the presence of the protective G allele in human peripheral blood mononuclear cells and normal lung tissues. The ‐ 141G‐allele‐promoter construct exhibited decreased luciferase reporter gene expression. Electrophoretic mobility shift assays and surface plasmon resonance analysis showed that the — 141G allele impaired the binding affinity of some transcription factor, accounting for lower APE1/Ref‐1‐promoter activity. Supershift assays further revealed that the protein of interest was octamer‐binding transcription factor‐1 (Oct‐1). Chromatin immunoprecipitation reconfirmed binding of Oct‐1 to the APE1/Ref‐1 — 141‐promoter region. We also found that Oct‐1 conferred attenuated transactivation capacity toward the — 141G variant by exogenously introducing Oct‐1. These data indicate that genetic variations in APE1/Ref‐1 may modify susceptibility to lung cancer and provide new insights into an unexpected effect of APE1/Ref‐1 on lung carcinogenesis.—Lu, J., Zhang, S., Chen, D., Wang, H., Wu, W., Wang, X., Lei, Y., Wang, J., Qian, J., Fan, W., Hu, Z., Jin, L., Shen, H., Huang, W., Wei, Q., Lu, D. Functional characterization of a promoter polymorphism in APE1/Ref‐1 that contributes to reduced lung cancer susceptibility. FASEB J. 23, 3459–3469 (2009). www.fasebj.org

REV3L confers chemoresistance to cisplatin in human gliomas: The potential of its RNAi for synergistic therapy

The REV3L gene, encoding the catalytic subunit of human polymerase zeta, plays a significant role in the cytotoxicity, mutagenicity, and chemoresistance of certain tumors. However, the role of REV3L in regulating the sensitivity of glioma cells to chemotherapy remains unknown. In this study, we investigated the expression of the REV3L gene in 10 normal brain specimens and 30 human glioma specimens and examined the value of REV3L as a potential modulator of cellular response to various DNA-damaging agents. Reverse transcriptase PCR/real-time PCR analysis revealed that REV3L was overexpressed in human gliomas compared with normal brain tissues. A glioma cell model with stable overexpression of REV3L was used to probe the role of REV3L in cisplatin treatment; upregulation of REV3L markedly attenuated cisplatin-induced apoptosis of the mitochondrial apoptotic pathway. We therefore assessed the REV3L-targeted treatment modality that combines suppression of REV3L expression using RNA interference (RNAi) with the cytotoxic effects of DNA-damaging agents. Downregulation of REV3L expression significantly enhanced the sensitivity of glioma cells to cisplatin, as evidenced by the increased apoptosis rate and marked alterations in the anti-apoptotic proteins B-cell lymphoma 2 (Bcl-2) and B-cell lymphoma-extra large (Bcl-xl) and proapoptotic Bcl-2-associated x protein (Bax) expression levels, and reduced mutation frequencies in surviving glioma cells. These results suggest that REV3L may potentially contribute to gliomagenesis and play a crucial role in regulating cellular response to the DNA cross-linking agent cisplatin. Our findings indicate that RNAi targeting REV3L combined with chemotherapy has synergistic therapeutic effects on glioma cells, which warrants further investigation as an effective novel therapeutic regimen for patients with this malignancy.

Analysis of specialized DNA polymerases expression in human gliomas: association with prognostic significance

Aberrant activation of the translesion DNA synthesis (TLS) pathway has been suggested to play a role in tumorigenesis by promoting genetic mutations. We therefore examined glioma specimens for the expression of specialized DNA polymerases involved in TLS and assessed their prognostic significance. The expression levels of DNA polymerase κ (Pol κ), Pol ι, and Pol η were assessed in 40 primary glioma samples and 10 normal brain samples using quantitative real-time PCR and Western blot analysis. Their prognostic significance was evaluated using a population-based tissue microarray derived from a cohort of 104 glioma patients. Overexpression of Pol κ and Pol ι was observed in 57.5% (23-40) and 27.5% (11-40) of patients, respectively, whereas no significant expression of Pol η was seen in the specimens. Immunohistochemical studies revealed positive Pol κ and Pol ι staining in 72 (69.2%) and 33 (31.7%) of the 104 glioma specimens, respectively. Pol κ expression was associated with advanced stages of the disease. Both Pol κ- and Pol ι-positive staining were associated with shorter survival in glioma patients (P < .001 and P = .014, respectively). A multivariate survival analysis identified Pol κ as an independent prognostic factor for glioma patients (P < .001). These findings demonstrate, for the first time, that the expression of Pol κ and Pol ι is deregulated in gliomas, and upregulation of Pol κ is associated with poorer prognosis in glioma patients.

Association of XPD Polymorphisms with Severe Toxicity in Non-Small Cell Lung Cancer Patients in a Chinese Population

Purpose: Platinum agents cause DNA cross-linking and adducts. Xeroderma pigmentosum group D (XPD) plays a key role in the nucleotide excision repair pathway of DNA repair. Genetic polymorphisms of XPD may affect the capacity to remove the deleterious DNA lesions in normal tissues and lead to greater treatment-related toxicity. This study aimed to investigate the association of three polymorphisms of XPD at codons 156, 312, and 711, with the occurrence of grade 3 or 4 toxicity in advanced non–small cell lung cancer patients. Experimental Design: We used matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to genotype the three polymorphisms in 209 stage III and IV non–small cell lung cancer patients treated with platinum-based chemotherapy. Results: The variant homozygotes of XPD p.Arg156Arg (rs238406) polymorphism were associated with a significantly increased risk of grade 3 or 4 hematologic toxicity (adjusted odds ratios, 3.24; 95% confidence interval, 1.35-7.78; P for trend = 0.009), and, more specifically, severe leukopenia toxicity (P for trend = 0.005). No statistically significant association was found for the three polymorphisms and grade 3 or 4 gastrointestinal toxicity. Consistent with these results of single-locus analysis, both the haplotype and the diplotype analyses revealed a protective effect of the haplotype “CG” (in the order of p.Arg156Arg-p.Asp312Asn) on the risk of grade 3 or 4 hematologic toxicity. Conclusions: This investigation, for the first time, provides suggestive evidence of an effect of XPD p.Arg156Arg polymorphism on severe toxicity variability among platinum-treated non–small cell lung cancer patients.

MicroRNA-377 inhibited proliferation and invasion of human glioblastoma cells by directly targeting specificity protein 1

BACKGROUND Increasing evidence has indicated that microRNAs (miRNAs) are strongly implicated in the initiation and progression of glioblastoma multiforme (GBM). Here, we identified a novel tumor suppressive miRNA, miR-377, and investigated its role and therapeutic effect for GBM. METHODS MiRNA global screening was performed on GBM patient samples and adjacent nontumor brain tissues. The expression of miR-377 was detected by real-time reverse-transcription PCR. The effects of miR-377 on GBM cell proliferation, cell cycle progression, invasion, and orthotopic tumorigenicity were investigated The therapeutic effect of miR-377 mimic was explored in a subcutaneous GBM model. Western blot and luciferase reporter assay were used to identify the direct and functional target of miR-377. RESULTS MiR-377 was markedly downregulated in human GBM tissues and cell lines. Overexpression of miR-377 dramatically inhibited cell growth both in culture and in orthotopic xenograft tumor models, blocked G1/S transition, and suppressed cell invasion in GBM cells. Importantly, introduction of miR-377 could strongly inhibit tumor growth in a subcutaneous GBM model. Subsequent investigation revealed that specificity protein 1 (Sp1) was a direct and functional target of miR-377 in GBM cells. Silencing of Sp1 recapitulated the antiproliferative and anti-invasive effects of miR-377, whereas restoring the Sp1 expression antagonized the tumor-suppressive function of miR-377. Finally, analysis of miR-377 and Sp1 levels in human GBM tissues revealed that miR-377 is inversely correlated with Sp1 expression. CONCLUSION These findings reveal that miR-377/Sp1 signaling that may be required for GBM development and may consequently serve as a therapeutic target for the treatment of GBM.

Effect of Polymorphisms in XPD on Clinical Outcomes of Platinum-Based Chemotherapy for Chinese Non-Small Cell Lung Cancer Patients

Purpose Xeroderma pigmentosum group D (XPD) codes for a DNA helicase involved in nucleotide excision repair that removes platinum-induced DNA damage. Genetic polymorphisms of XPD may affect DNA repair capacity and lead to individual differences in the outcome of patients after chemotherapy. This study aims to identify whether XPD polymorphisms affect clinical efficacy among advanced non-small cell lung cancer (NSCLC) patients treated with platinum-based chemotherapy. Experimental Design 353 stage III-IV NSCLC patients receiving platinum-based chemotherapy as the first-line treatment were enrolled in this study. Four potentially functional XPD polymorphisms (Arg156Arg, Asp312Asn, Asp711Asp and Lys751Gln) were genotyped by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry or PCR-based sequencing. Results Variant genotypes of XPD Asp312Asn, Asp711Asp and Lys751Gln were significantly associated with poorer NSCLC survival (P = 0.006, 0.006, 0.014, respectively, by log-rank test). The most common haplotype GCA (in order of Asp312Asn, Asp711Asp and Lys751Gln) also exhibited significant risk effect on NSCLC survival (log-rank P = 0.001). This effect was more predominant for patients with stage IIIB disease (P = 2.21×10−4, log-rank test). Increased risks for variant haplotypes of XPD were also observed among patients with performance status of 0–1 and patients with adenocarcinoma. However, no significant associations were found between these polymorphisms, chemotherapy response and PFS. Conclusions Our study provides evidence for the predictive role of XPD Asp312Asn, Asp711Asp and Lys751Gln polymorphisms/haplotype on NSCLC prognosis in inoperable advanced NSCLC patients treated with platinum-based chemotherapy.

VAMP8 facilitates cellular proliferation and temozolomide resistance in human glioma cells

BACKGROUND Malignant glioma is a common and lethal primary brain tumor in adults. Here we identified a novel oncoprotein, vesicle-associated membrane protein 8 (VAMP8), and investigated its roles in tumorigenisis and chemoresistance in glioma. METHODS The expression of gene and protein were determined by quantitative PCR and Western blot, respectively. Histological analysis of 282 glioma samples and 12 normal controls was performed by Pearsons chi-squared test. Survival analysis was performed using the log-rank test and Cox proportional hazards regression. Cell proliferation and cytotoxicity assay were conducted using Cell Counting Kit-8. Autophagy was detected by confocal microscopy and Western blot. RESULTS VAMP8 was significantly overexpressed in human glioma specimens and could become a potential novel prognostic and treatment-predictive marker for glioma patients. Overexpression of VAMP8 promoted cell proliferation in vitro and in vivo, whereas knockdown of VAMP8 attenuated glioma growth by arresting cell cycle in the G0/G1 phase. Moreover, VAMP8 contributed to temozolomide (TMZ) resistance by elevating the expression levels of autophagy proteins and the number of autophagosomes. Further inhibition of autophagy via siRNA-mediated knockdown of autophagy-related gene 5 (ATG5) or syntaxin 17 (STX17) reversed TMZ resistance in VAMP8-overexpressing cells, while silencing of VAMP8 impaired the autophagic flux and alleviated TMZ resistance in glioma cells. CONCLUSION Our findings identified VAMP8 as a novel oncogene by promoting cell proliferation and therapeutic resistance in glioma. Targeting VAMP8 may serve as a potential therapeutic regimen for the treatment of glioma.

A variant in the CHEK2 promoter at a methylation site relieves transcriptional repression and confers reduced risk of lung cancer

Checkpoint kinase (CHEK) 2, a tumor suppressor gene, plays an essential role in the DNA damage checkpoint response cascade. We first investigated two polymorphisms in the proximal promoter of the CHEK2 gene and evaluated their associations with the risk of lung cancer in a case-control study using 500 incident lung cancer cases and 517 cancer-free controls. We found that CHEK2 rs2236141 -48 G > A was significantly associated with lung cancer risk (P = 0.0018). Similar results were obtained in a follow-up replication study in 575 lung cancer patients and 589 controls (P = 0.042). Quantitative polymerase chain reaction showed that individuals with the G allele had lower levels of CHEK2 transcripts in peripheral blood mononuclear cells and normal lung tissues. The -48 G-->A variant eliminated a methylation site and thereby relieve the transcriptional repression of CHEK2. Therefore, this polymorphism affected downstream transcription through genetic and epigenetic modifications. Luciferase reporter assays demonstrated that the major G allele significantly attenuated reporter gene expression when methylated. Electrophoretic Mobility shift assays and surface plasmon resonance revealed that the methylated G allele increased transcription factor accessibility. We used in vivo chromatin immunoprecipitation to confirm that the relevant transcription factor was Sp1. Using lung tissue heterozygous for the G/A single-nucleotide polymorphism, we found that Sp1 acted as a repressor and had a stronger binding affinity for the G allele. These results support our hypothesis that the CHEK2 rs2236141 variant modifies lung cancer susceptibility in the Chinese population by affecting CHEK2 expression.