Sai Wah Tsao

The University of Hong Kong, Hong Kong, Hong Kong

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Publications (218)1065.94 Total impact

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    ABSTRACT: CRISPR/Cas9 system is a highly efficient and powerful tool for RNA-guided editing of cellular genome. Whether CRISPR/Cas9 can also cleave the genome of DNA viruses such as Epstein-Barr virus (EBV), which undergo episomal replication in human cells, remains to be established. Here we reported on CRISPR/Cas9-mediated editing of EBV genome in human cells. Two guide RNAs were used to direct a targeted deletion of 558 bp in the promoter region of BART transcript which encodes viral microRNAs. Targeted editing was achieved in several human epithelial cell lines latently infected with EBV, including nasopharyngeal carcinoma C666-1 cells. CRISPR/Cas9-mediated editing of EBV genome was efficient. A recombinant virus with the desired deletion was obtained after puromycin selection of cells expressing Cas9 and guide RNAs. No off-target cleavage was found by deep sequencing. The loss of BART microRNA expression and activity was verified, supporting that the BART promoter is the major promoter of BART RNA. Although CRISPR/Cas9-mediated editing of the multicopy episome of EBV in infected HEK293 cells was mostly incomplete, viruses can be recovered and introduced into other cells at low multiplicity of infection. Recombinant viruses with an edited genome can be further isolated through single-cell sorting. Finally, a DsRed selectable marker was successfully introduced into the EBV genome during the course of CRISPR/Cas9-mediated editing. Taken together, our work provides not only the first genetic evidence that the BART promoter drives the expression of BART transcript, but also a new and efficient method for targeted editing of EBV genome in human cells.
    Journal of General Virology 12/2014; · 3.13 Impact Factor
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    ABSTRACT: Hepatocellular carcinoma (HCC) is an invasive cancer with a high rate of recurrence and metastasis. Agents with anti-proliferative as well as anti-metastatic activity will be ideal for effective treatment. Here, we demonstrated that berberine, an isoquinoline alkaloid, harbored potent anti-metastatic and anti-proliferative activities in vivo. Using an orthotopic model of HCC (MHCC-97L), which spontaneously develops lung metastases (one of the most common sites of HCC metastasis), we found that berberine treatment (10mg/kg/2days) significantly reduced lung metastasis from the liver tumors by ~85% (quantitated by bioluminescence emitted from lung metastases). Histological examination also confirmed the reduced incidence and number of lung metastases in berberine-treated mice. Furthermore, berberine effectively suppressed extra-tumor invasion of the primary HCC implant into the surrounding normal liver tissue, illustrating its potent anti-metastatic action in vivo. Consistent with previous reports in other cancer, berberine's anti-tumor activity was accompanied by suppression of cellular proliferation, invasiveness and HIF-1α/VEGF signaling. Strikingly, further mechanistic investigation revealed that berberine exerted profound inhibitory effect on the expression of Id-1, which is a key regulator for HCC development and metastasis. Bereberine could suppress the transcription level of Id-1 through inhibiting its promotor activity. Specific downregulation of Id-1 by knocking down its RNA transcripts in HCC cells inhibited cellular growth, invasion and VEGF secretion, demonstrating the functional relevance of Id-1 downregulation induced by berberine. Lastly, berberine's anti-proliferative and anti-invasive activities could be partially rescued by Id-1 overexpression in HCC models, revealing a novel anti-cancer/anti-invasive mechanism of berberine via Id-1 suppression. Copyright © 2014. Published by Elsevier B.V.
    Biochimica et biophysica acta. 12/2014;
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    ABSTRACT: Aims: Nasopharyngeal carcinoma (NPC) is a common tumor consistently associated with Epstein-Barr virus infection and prevalent in South China, including Hong Kong, and southeast Asia. Current genomic sequencing studies found only rare mutations in NPC, indicating its critical epigenetic etiology, while no epigenome exists for NPC as yet. Materials & methods: We profiled the methylomes of NPC cell lines and primary tumors, together with normal nasopharyngeal epithelial cells, using methylated DNA immunoprecipitation (MeDIP). Results: We observed extensive, genome-wide methylation of cellular genes. Epigenetic disruption of Wnt, MAPK, TGF-β and Hedgehog signaling pathways was detected. Methylation of Wnt signaling regulators (SFRP1, 2, 4 and 5, DACT2, DKK2 and DKK3) was frequently detected in tumor and nasal swab samples from NPC patients. Functional studies showed that these genes are bona fide tumor-suppressor genes for NPC. Conclusion: The NPC methylome shows a special high-degree CpG methylation epigenotype, similar to the Epstein-Barr virus-infected gastric cancer, indicating a critical epigenetic etiology for NPC pathogenesis.
    Epigenomics 12/2014; · 2.43 Impact Factor
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    ABSTRACT: Epstein-Barr virus (EBV), a type of oncogenic herpesvirus, is associated with human malignancies. Previous studies have shown that lytic reactivation of EBV in latently-infected cells induces ATM-dependent DNA damage response (DDR). The involvement of ATM activation has been implicated in inducing viral lytic genes transcription to promote lytic reactivation. Its contribution to the formation of replication compartment during lytic reactivation of EBV remains poorly defined. In this study, the role of ATM in viral DNA replication was investigated in EBV-infected nasopharyngeal epithelial cells. We observed that induction of lytic infection of EBV triggers ATM activation and localization of DDR proteins at the viral replication compartments. Suppression of ATM activity using siRNA approach or specific chemical inhibitor profoundly suppressed replication of EBV DNA and production of infectious virion in EBV-infected cells induced to undergo lytic reactivation. We further showed that phosphorylation of Sp1 at Serine-101 residue is essential in promoting the accretion of EBV replication proteins at the replication compartment which is crucial for replication of viral DNA. Knockdown of Sp1 expression by siRNA effectively suppressed replication of viral DNA and localization of EBV replication proteins to the replication compartments. Our study supports an important role of ATM activation in lytic reactivation of EBV in epithelial cells and phosphorylation of Sp1 is an essential process downstream of ATM activation involved in the formation of viral replication compartments. Our study revealed an essential role of ATM-dependent DDR pathway in lytic reactivation of EBV suggesting a potential anti-viral replication strategy using specific DDR inhibitors.
    Journal of virology. 10/2014;
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    ABSTRACT: Esophageal cancer is the sixth most common cause of cancer-related deaths worldwide. Novel therapeutic intervention is urgently needed for this deadly disease. The functional role of PI3K/AKT pathway in esophageal cancer is little known. In this study, our results from 49 pairs of human esophageal tumor and normal specimens demonstrated that AKT was constitutively active in the majority (75.5%) of esophageal tumors compared with corresponding normal tissues. Inhibition of the PI3K/AKT pathway with specific inhibitors, wortmannin and LY294002, significantly reduced Bcl-xL expression, induced caspase-3-dependent apoptosis, and repressed cell proliferation and tumor growth in vitro and in vivo without obvious toxic effects. Moreover, significantly higher expression level of p-AKT was observed in fluorouracil (5-FU)-resistant esophageal cancer cells. Inactivation of PI3K/AKT pathway markedly increased the sensitivity and even reversed acquired resistance of esophageal cancer cells to chemotherapeutic drugs in vitro. More importantly, the resistance of tumor xenografts derived from esophageal cancer cells with acquired 5-FU resistance to chemotherapeutic drugs was significantly abrogated by wortmannin treatment in animals. In summary, our data support PI3K/AKT as a valid therapeutic target and strongly suggest that PI3K/AKT inhibitors used in conjunction with conventional chemotherapy may be a potentially useful therapeutic strategy in treating esophageal cancer patients.
    Oncotarget 10/2014; · 6.64 Impact Factor
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    ABSTRACT: Undifferentiated nasopharyngeal carcinoma (NPC) is a highly metastatic disease that is consistently associated with the Epstein-Barr virus (EBV) infection. In this study, we have investigated the contribution of lysophosphatidic acid (LPA) signalling to the pathogenesis of NPC. Here we demonstrate two distinct functional roles for LPA in NPC. First, we show that LPA enhances the migration of NPC cells and secondly that it can inhibit the activity of EBV-specific cytotoxic T cells. Focussing on the first of these phenotypes, we show that one of the LPA receptors, LPA receptor 5 (LPAR5), is down-regulated in primary NPC tissues and that this down-regulation promotes the LPA-induced migration of NPC cell lines. Furthermore, we found that EBV infection or ectopic expression of the EBV-encoded LMP2A gene was sufficient to down-regulate LPAR5 in NPC cell lines. Our data point to a central role for EBV in mediating the oncogenic effects of LPA in NPC and identify LPA signalling as a potential therapeutic target in this disease.
    The Journal of Pathology 10/2014; · 7.59 Impact Factor
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    ABSTRACT: Epstein-Barr virus (EBV) infection is closely associated with undifferentiated nasopharyngeal carcinoma (NPC), strongly implicating a role for EBV in NPC pathogenesis; conversely, EBV infection is rarely detected in normal nasopharyngeal epithelial tissues. In general, EBV does not show a strong tropism for infecting human epithelial cells, and EBV infection in oropharyngeal epithelial cells is believed to be lytic in nature. To establish lifelong infection in humans, EBV has evolved efficient strategies to infect B cells and hijack their cellular machinery for latent infection. Lytic EBV infection in pharyngeal epithelial cells, though an infrequent event, is believed to be a major source of infectious EBV particles for salivary transmission. The biological events associated with nasopharyngeal epithelial cells are only beginning to be understood with the advancement of EBV infection methods and the availability of nasopharyngeal epithelial cell models for EBV infection studies. EBV infection in human epithelial cells is a highly inefficient process compared to that in B cells, which express the complement receptor type 2 (CR2) to mediate EBV infection. Although receptor(s) on the epithelial cell surface for EBV infection remain(s) to be identified, EBV infection in epithelial cells could be achieved via the interaction of glycoproteins on the viral envelope with surface integrins on epithelial cells, which might trigger membrane fusion to internalize EBV into cells. Normal nasopharyngeal epithelial cells are not permissive for latent EBV infection, and EBV infection in normal nasopharyngeal epithelial cells usually results in growth arrest. However, genetic alterations in premalignant nasopharyngeal epithelial cells, including p16 deletion and cyclin D1 overexpression, could override the growth inhibitory effect of EBV infection to support stable and latent EBV infection in nasopharyngeal epithelial cells. The EBV episome in NPC is clonal in nature, suggesting that NPC develops from a single EBV-infected nasopharyngeal epithelial cell, and the establishment of persistent and latent EBV infection in premalignant nasopharyngeal epithelium may represent an early and critical event for NPC development.
    Chinese journal of cancer. 09/2014;
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    ABSTRACT: Over 75% of nasopharyngeal carcinoma (NPC) patients have already developed local or regional spread at diagnosis, which hampers effective treatment and results in a poor prognosis. It is essential to characterize more sensitive and specific biomarkers for screening of high risk individuals and assessment of NPC treatment effectiveness. NPC is an EBV associated tumor in which only a few viral proteins but more than 20 BART microRNAs are detected, at abundant levels. We hypothesized that these BART microRNAs may be novel biomarkers for NPC. Systematic analysis of EBV BART microRNA expression profiles in EBV latently infected MutuI and Mutu III cell lines, EBV-harboring NPC and non-cancerous nasopharyngeal cells found that miR-BART3, miR-BART7 and miR-BART13 microRNAs are highly expressed and regularly secreted into the extracellular environment of NPC cells. These BART microRNAs were evaluated for used as potential NPC biomarkers. Analysis of plasma specimens obtained from NPC patients (n=89), and healthy (n=28) and non-NPC tumor patient controls (n=18) found levels of both miR-BART7 and miR-BART13, but not miR-BART3, to be distinctly presence among NPC patients, with elevated levels being particularly apparent among patients with advanced disease. ROC curve analysis combining miR-BART7 and miR-BART13 levels produces a 90% predictive value for the presence of NPC. Analysis of 41 NPC patients before and after radiotherapy showed that miR-BART7 and miR-BART13, but not miR-BART3, were diminished after treatment. These results indicate That EBV microRNAs, miR-BART7 and miR-BART13, may constitute useful new serological biomarkers for diagnosis of NPC and prediction of treatment efficacy. © 2014 Wiley Periodicals, Inc.
    International Journal of Cancer 09/2014; · 6.20 Impact Factor
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    ABSTRACT: Apart from regulating stem cell self-renewal, embryonic development and proliferation, Bmi-1 has been recently reported to be critical in the maintenance of genome integrity. In searching for novel mechanisms underlying the anticlastogenic function of Bmi-1, we observed, for the first time, that Bmi-1 positively regulates p21 expression. We extended the finding that Bmi-1 deficiency induced chromosome breaks in multiple cancer cell models. Interestingly, we further demonstrated that knockdown of cyclin E or ectopic overexpression of p21 rescued Bmi-1 deficiency-induced chromosome breaks. We therefore conclude that p21/cyclin E pathway is crucial in modulating the anticlastogenic function of Bmi-1. Because it is well-established that the overexpression of cyclin E potently induces genome instability and p21 suppresses the function of cyclin E, the novel and important implication from our findings is that Bmi-1 plays an important role in limiting genomic instability in cylin E-overexpressing cancer cells by positive regulation of p21. © 2014 Wiley Periodicals, Inc.
    International Journal of Cancer 08/2014; · 6.20 Impact Factor
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    ABSTRACT: The p38 mitogen-activated protein (MAP) kinase signal transduction pathway plays an important role in inflammatory and stress responses. MAP Kinase Kinase 6 (MKK6), a dual specificity protein kinase, is a p38 activator. Activation of the MKK6-p38 pathway is kept in check by multiple layers of regulations, including autoinhibition, dimerization, scaffold proteins and lysine 63 (K63)-linked polyubiquitination. However, the mechanisms underlying deactivation of MKK6-p38, which is crucial for maintaining magnitude and duration of signal transduction, are not well understood. Lysine 48 (K48)-linked ubiquitination, which marks substrates for proteasomal degradation, is an important negative post-translational regulatory machinery for signal pathway transduction. Here we report that the accumulation of F-box only protein 31 (FBXO31), a component of Skp1-Cul1-F-box protein (SCF) E3 ligase, negatively regulated p38 activation in cancer cells upon genotoxic stresses. Our results showed that FBXO31 binds to MKK6 and mediates its K48-linked polyubiquitination and degradation, thereby functioning as a negative regulator of MKK6-p38 signaling and protecting cells from stress-induced cell apoptosis. Taken together, our findings uncover a new mechanism of deactivation of MKK6/p38, and substantiate a novel regulatory role of FBXO31 in stress response.
    The Journal of biological chemistry. 06/2014;
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    ABSTRACT: To investigate the autocrine/endocrine role of Id1-induced insulin-like growth factor 2 (IGF2) in esophageal cancer, and evaluate the potential of IGF2- and IGF type 1 receptor (IGF1R)-targeted therapies. Antibody array-based screening was used to identify differentially secreted growth factors from Id1-overexpressing esophageal cancer cells. In vitro and in vivo assays were performed to confirm the induction of IGF2 by Id1, and to study the autocrine and endocrine effects of IGF2 in promoting esophageal cancer progression. Human esophageal cancer tissue microarray was analyzed for overexpression of IGF2 and its correlation with that of Id1 and phosphorylated AKT (p-AKT). The efficacy of intratumorally injected IGF2 antibody and intraperitoneally injected cixutumumab (fully human monoclonal IGF1R antibody) was evaluated using in vivo tumor xenograft and experimental metastasis models. Id1 overexpression induced IGF2 secretion which promoted cancer cell proliferation, survival and invasion by activating AKT in an autocrine manner. Overexpression of IGF2 was found in 21/35 (60%) esophageal cancer tissues and was associated with upregulation of Id1 and p-AKT. IGF2 secreted by Id1-overexpressing esophageal cancer xenograft could instigate the growth of distant esophageal tumors, as well as promote metastasis of circulating cancer cells. Targeting IGF2 and IGF1R had significant suppressive effects on tumor growth and metastasis in mice. Cixutumumab treatment enhanced the chemosensitivity of tumor xenografts to fluorouracil and cisplatin. The Id1-IGF2-IGF1R-AKT signaling cascade plays an important role in esophageal cancer progression. Blockade of IGF2/IGF1R signaling has therapeutic potential in the management of esophageal cancer.
    Clinical Cancer Research 03/2014; · 7.84 Impact Factor
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    ABSTRACT: Nasopharyngeal carcinoma (NPC) is a common disease among southern Chinese. The major etiological factors proposed for NPC pathogenesis include genetic susceptibility, environment factors and EBV infection. In the high risk population, genetic susceptibility to NPC has been mapped to the HLA loci and adjacent genes in MHC region on chromosome 6p21. Consumption of preserved food including salted fish has been implicated in its etiology in earlier studies. Its contribution to pathogenesis of NPC remains to be determined. A decreasing trend of NPC incidence was observed in Hong Kong, Taiwan and Singapore in recent years which may be accounted by a change of dietary habits. A comprehensive epidemiological study will help to elucidate the relative importance of various risk factors in the pathogenesis of NPC. Despite the close association of EBV infection with NPC, the etiological role of EBV in NPC pathogenesis remains enigmatic. EBV infection in primary nasopharyngeal epithelial cells is uncommon and difficult to achieve. EBV does not transform primary nasopharyngeal epithelial cells into proliferative clones, which contrasts greatly with the well-documented ability of EBV to transform and immortalize primary B cells. Genetic alterations identified in premalignant nasopharyngeal epithelium may play crucial roles to support stable EBV infection. Subsequently, latent and lytic EBV gene products may drive clonal expansion and transformation of premalignant nasopharyngeal epithelial cells into cancer cells. Stromal inflammation in nasopharyngeal mucosa is believed to play an important role in modulating the growth and possibly drive the malignant transformation of EBV-infected nasopharyngeal epithelial cells. Furthermore, there are increasing evidences supporting a role of EBV infection to evade host immune surveillance. EBV-infected cells may have selective growth advantages in vivo by acquiring a stress–resistance phenotype. Understanding the etiological factors and pathogenesis of NPC will contribute effectively to the prevention and treatment of this disease.
    Oral Oncology 01/2014; · 2.70 Impact Factor
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    ABSTRACT: Cortidis rhizoma (Huanglian) and its major therapeutic component, berberine, have drawn extensive attention in recent years for their anti-cancer properties. Growth inhibitory effects of berberine on multiple types of human cancer cells have been reported. Berberine inhibits invasion, induces cell cycle arrest and apoptosis in human cancer cells. The anti-inflammatory property of berberine, involving inhibition of Signal Transducer and Activator of Transcription 3 (STAT3) activation, has also been documented. In this study, we have examined the effects of berberine on tumorigenicity and growth of nasopharyngeal carcinoma (NPC) cells and their relationship to STAT3 signaling using both in vivo and in vitro models. Berberine effectively inhibited the tumorigenicity and growth of an EBV-positive NPC cell line (C666-1) in athymic nude mice. Inhibition of tumorigenic growth of NPC cells in vivo was correlated with effective inhibition of STAT3 activation in NPC cells inside the tumor xenografts grown in nude mice. In vitro, berberine inhibited both constitutive and IL-6-induced STAT3 activation in NPC cells. Inhibition of STAT3 activation by berberine induced growth inhibition and apoptotic response in NPC cells. Tumor-associated fibroblasts were found to secret IL-6 and the conditioned medium harvested from the fibroblasts also induced STAT3 activation in NPC cells. Furthermore, STAT3 activation by conditioned medium of tumor-associated fibroblasts could be blocked by berberine or antibodies against IL-6 and IL-6R. Our observation that berberine effectively inhibited activation of STAT3 induced by tumor-associated fibroblasts suggests a role of berberine in modulating the effects of tumor stroma on the growth of NPC cells. The effective inhibition of STAT3 activation in NPC cells by berberine supports its potential use in the treatment of NPC.
    BMC Cancer 12/2013; 13(1):619. · 3.33 Impact Factor
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    ABSTRACT: The humanized anti-HER2 monoclonal antibody (mAb) Herceptin (trastuzumab) effectively inhibits HER2-positive breast tumors. However, many patients responding to treatment often develop resistance. Crosstalk between IGF-IR and HER2 and elevated IGF-IR signaling have been implicated in tumor cell resistance to Herceptin therapy. Previously, we reported that the anti-IGF-IR mAb m590 inhibits proliferation and migration of breast cancer MCF-7 cells in vitro. Here, we generated a "knobs-into-holes" bispecific antibody (Bi-Ab) against HER2 and IGF-IR by engineering Herceptin and m590. We compared the effects of Bi-Ab treatment in vitro and in SKOV-3 HER2- and IGF-IR-overexpressing cancer xenograft mouse model with those of m590 and Herceptin treatment alone or in combination (Comb). Bi-Ab effectively inhibited proliferation of HER2- and IGF-IR-overexpressing ovarian cancer SKOV-3 cells in vitro by ablating receptor phosphorylation and downstream PI3K/Akt and MAPK signaling. Bi-Ab more effectively inhibited cancer growth in SKOV-3 HER2- and IGF-IR-overexpressing cancer xenograft mouse model than m590 and Herceptin alone or in combination. Mice bearing SKOV-3 HER2- and IGF-IR-overexpressing xenografts showed extensive and sustainable tumor regression when treated with Bi-Ab. Our results suggest that Bi-Ab has superior antitumor activity compared with monospecific antibodies, and co-targeting HER2 and IGF-IR may be clinically beneficial in minimizing the acquired resistance to Herceptin therapy.
    Molecular Cancer Therapeutics 11/2013; · 5.60 Impact Factor
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    ABSTRACT: Disintegrins and metalloproteinases with thrombospondin motifs (ADAMTSs) have been reported dysregulated in various cancers. Through refining a loss of heterozygosity locus at 11q25 by array-CGH, we identified ADAMTS8 as a novel candidate tumor suppressor gene. Although ADAMTS8 downregulation has been reported in several tumors, its biological function and underlying mechanism remain largely unknown. Here, we found that ADAMTS8 is broadly expressed in normal tissues but frequently downregulated or silenced by promoter methylation in common carcinoma cell lines, including nasopharyngeal, esophageal squamous cell, gastric and colorectal carcinomas. Pharmacological or genetic demethylation restored ADAMTS8 expression, indicating that promoter methylation mediates its silencing. Aberrant methylation of ADAMTS8 was also detected in several types of primary tumors but rarely in normal tissues. Further functional studies showed that restoring ADAMTS8 expression suppressed tumor cell clonogenicity through inducing apoptosis. ADAMTS8 as a secreted protease inhibited EGFR signaling along with decreased levels of phosphorylated MEK and ERK. We further found that ADAMTS8 disrupted actin stress fiber organization and inhibited tumor cell motility. Thus, our data demonstrate that ADAMTS8 metalloprotease acts as a functional tumor suppressor through antagonizing EGFR-MEK-ERK signaling, in addition to its previously reported anti-angiogenesis function, and is frequently methylated in common tumors. Implications: This study uncovers the tumor suppressive funciton of ADAMTS8, one of the ADAMTS8 family memebers,and its frequent methylation in certain tumors could be developed as a potential biomarker.
    Molecular Cancer Research 11/2013; · 4.35 Impact Factor
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    ABSTRACT: Epstein-Barr virus (EBV) encodes at least 44 mature microRNAs (miRNAs), some of which are abundantly expressed in nasopharyngeal carcinoma cells. EBV-encoded miR-BART6 miRNA is known to undergo A-to-I RNA editing that impacts processing and function. Whether additional EBV miRNAs might be A-to-I edited remains to be determined. In this study we reported on A-to-I editing of EBV miR-BART3. The A-to-I editing enzyme was abundantly expressed in EBV-infected epithelial carcinoma cells. pri-miR-BART3 was found to be edited at four sites in these cells and in nasopharyngeal carcinoma samples. Whereas editing of the second site located within the seed region abrogated the targeting of DICE1 mRNA, editing of the third site effectively cripples the biogenesis of mature miR-BART3. Thus, A-to-I editing perturbs biogenesis and targeting of miR-BART3 and might contribute to its differential expression and function in EBV-infected epithelial cells.
    Journal of General Virology 09/2013; · 3.13 Impact Factor
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    ABSTRACT: The dual PI3K-mTOR inhibitor BEZ235 was evaluated in preclinical models of nasopharyngeal carcinoma (NPC). The IC50 value of BEZ235 for growth was in the nanomolar range in vitro, induce G1 cycle arrest and apoptosis, and inhibited AKT and mTOR signaling in most NPC cell lines. No synergistic effect was observed when BEZ235 was combined with chemotherapy. BEZ235 increased MAPK activation in vitro but not in vivo. A daily schedule was more effective than a weekly schedule on tumor growth and inhibition of downstream mTOR signaling in vivo. The activity of BEZ235 maybe independent of the PIK3CA amplification and mutation status.
    Cancer letters 09/2013; · 5.02 Impact Factor
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    ABSTRACT: Nasopharyngeal carcinoma (NPC) is a rare but highly invasive cancer. As options of agents for effective combination chemoradiotherapy of advanced NPC are limited, novel therapeutic approaches are desperately needed. The ubiquitin ligase CHFR is known to target poly(ADP-ribose) polymerase 1 (PARP1) for degradation and is epigenetically inactivated in NPC. We present evidence that PARP1 protein is indeed overexpressed in NPC cells in comparison to immortalized normal nasopharyngeal epithelial cells. Tissue microarray analysis also indicated that PARP1 protein is significantly elevated in primary NPC tissues, with strong correlation with all stages of NPC development. We found that the PARP inhibitor AZD2281 (Olaparib) increased DNA damage, cell cycle arrest, and apoptosis in NPC cells challenged with ionizing radiation or temozolomide. Isobologram analysis confirmed that the cytotoxicity triggered by AZD2281 and DNA damaging agents was synergistic. Finally, AZD2281 also enhanced the tumor-inhibitory effects of ionizing radiation in animal xenograft models. These observations implicate that PARP1 overexpression is an early event in NPC development and provide a molecular basis of using PARP inhibitors to potentiate treatment of NPC with radiotherapy and chemotherapy.
    Molecular Cancer Therapeutics 08/2013; · 5.60 Impact Factor
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    ABSTRACT: Nasopharyngeal carcinoma (NPC) is a cancer with its highest prevalence among the southern Chinese and is rare elsewhere in the world. The main treatment modalities include chemotherapy and radiotherapy. However, tumor chemoresistance often limits the efficacy of NPC treatment and reduces survival rates. Thus, identifying new selective chemotherapeutic drugs for NPC treatment is needed. In this current study, the anti-tumor efficacy of a polo-like kinase inhibitor, Ro5203280, was investigated. Ro5203280 induces tumor suppression both in vitro and in vivo. An inhibitory effect was observed with the highly proliferating cancer cell lines tested, but not with the non-tumorigenic cell line. Real-time cell proliferation and FACS analysis, together with immunohistochemical (IHC), immunofluorescence (IF), and Annexin V staining assays were used to evaluate the impact of drug treatment on cell cycle and apoptosis. Ro5203280 induces G2/M cell cycle arrest and apoptosis. Western blotting shows it inhibits PLK1 phosphorylation and down-regulates the downstream signaling molecule, Cdc25c, and up-regulates two important mitosis regulators, Wee1 and Securin, as well as the DNA damage-related factor Chk2 in vitro and in vivo. In vivo tumorigenicity assays with Ro5203280 intravenous injection demonstrated its potent ability to inhibit tumor growth in mice, with no observable signs of toxicity. These findings suggest the potential usefulness of Ro5203280 as a chemotherapeutic targeting drug for NPC treatment.
    Molecular Cancer Therapeutics 05/2013; · 5.60 Impact Factor
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    ABSTRACT: Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus (EBV)-associated tumor prevalent in Southern China and Southeast Asia, with the 3p14-12 locus reported as a critical tumor suppressor gene (TSG) region during its pathogenesis. We identified a novel 3p14.2 TSG, FEZF2 (FEZ family zinc finger 2), for NPC. FEZF2 is readily expressed in normal tissues including upper respiratory epithelium, testis, brain and ovary tissues as well as immortalized nasopharyngeal epithelial cell line NP69, but completely silenced in NPC cell lines due to CpG methylation of its promoter, although no homozygous deletion of FEZF2 was detected. Aza treatment restored FEZF2 expression in NPC cell lines along with its promoter demethylation. FEZF2 was frequently downregulated in NPC tumors, with promoter methylation detected in 75.5% of tumors, but only in 7.1% of normal nasopharyngeal tissues. Restored FEZF2 expression suppressed NPC cell clonogenicity through inducing G2/M cell cycle arrest and apoptosis, and also inhibited NPC cell migration and stemness. FEZF2 acted as a HDAC-associated repressor downregulating multiple oncogenes including EZH2 and MDM2, through direct binding to their promoters. Concomitantly, overexpression of EZH2 was frequently detected in NPC tumors. Thus, we have identified FEZF2 as a novel 3p14.2 TSG frequently inactivated by promoter methylation in NPC, which functions as a repressor downregulating multiple oncogene expression.
    Carcinogenesis 05/2013; · 5.64 Impact Factor

Publication Stats

5k Citations
1,065.94 Total Impact Points

Institutions

  • 1998–2014
    • The University of Hong Kong
      • • Centre for Cancer Research
      • • Department of Surgery
      • • Department of Anatomy
      • • Department of Clinical Oncology
      • • Department of Pathology
      Hong Kong, Hong Kong
  • 2013
    • Capital Medical University
      Peping, Beijing, China
  • 2012–2013
    • Xi'an Jiaotong University
      Ch’ang-an, Shaanxi, China
  • 2005–2013
    • Lands Department of The Government of the Hong Kong Special Administrative Region
      Hong Kong, Hong Kong
  • 1991–2013
    • The Chinese University of Hong Kong
      • • Department of Clinical Oncology
      • • Prince of Wales Hospital
      • • Department of Anatomical and Cellular Pathology
      Hong Kong, Hong Kong
  • 2005–2012
    • The Hong Kong University of Science and Technology
      • Division of Life Science
      Kowloon, Hong Kong
  • 2008–2010
    • Institut de Cancérologie Gustave Roussy
      • Department of Radiotherapy
      Île-de-France, France
    • University of Massachusetts Medical School
      Worcester, Massachusetts, United States
  • 2007–2008
    • Central South University
      • Cancer Research Institute
      Changsha, Hunan, China
  • 2003–2008
    • Queen Mary Hospital
      Hong Kong, Hong Kong
    • Linyi People's Hospital
      Yichow, Shandong Sheng, China
  • 2004
    • Harbin Medical University
      • Laboratory of Medical Genetics
      Charbin, Heilongjiang Sheng, China
  • 1997
    • Prince of Wales Hospital, Hong Kong
      Chiu-lung, Kowloon City, Hong Kong
  • 1991–1995
    • Brigham and Women's Hospital
      • • Department of Medicine
      • • Center for Brain Mind Medicine
      • • Department of Obstetrics and Gynecology
      Boston, MA, United States
  • 1990
    • Dana-Farber Cancer Institute
      Boston, Massachusetts, United States