Professional Education

  • Doctor of Philosophy, University Of Hong Kong (2008)

Stanford Advisors


Journal Articles

  • Id-1 Induces Cell Invasiveness in Immortalized Epithelial Cells by Regulating Cadherin Switching and Rho GTPases JOURNAL OF CELLULAR BIOCHEMISTRY Cheung, P. Y., Yip, Y. L., Tsao, S. W., Ching, Y. P., Cheung, A. L. 2011; 112 (1): 157-168


    Epithelial-mesenchymal transition (EMT), characterized by cadherin switching, contributes to cancer metastasis. Our recent study showed that Id-1 (inhibitor of differentiation-1) promotes metastasis in esophageal cancer cells, but whether the invasive and metastatic dynamics can be induced early in the carcinogenesis process is still unclear. Immortalization is regarded as the initial stage in the malignant transformation of normal cells. In this study, we investigated the role and mechanisms of Id-1 in inducing EMT and cell invasiveness in immortalized esophageal epithelial cells. We found that immortalized epithelial cells expressed higher endogenous levels of Id-1 compared with normal cells. Ectopic Id-1 expression inhibited the differentiation of immortalized esophageal epithelial cells and promoted cadherin switching, which was accompanied by increased adhesiveness to extracellular matrix, cell motility, migratory potential and matrix metalloproteinase-dependent invasiveness. GTPase activity assays showed that over-expression or short-hairpin RNA knockdown of Id-1 led to corresponding changes in Rac1 activity, whereas RhoA activity was significantly decreased with Id-1 depletion. Inhibitors targeting Rac1, RhoA, and Rho kinase suppressed the invasiveness of Id-1-expressing NE2-hTERT cells. Knockdown of N-cadherin in Id-1-over-expressing cells inhibited cell invasiveness and down-regulated RhoA activity. These data suggest that the Id-1-induced invasive potential may be regulated through the N-cadherin-RhoA axis and Rac1 activation.

    View details for DOI 10.1002/jcb.22911

    View details for Web of Science ID 000287216200016

    View details for PubMedID 21053361

  • Expression of Epstein-Barr Virus-Encoded LMP1 and hTERT Extends the Life Span and Immortalizes Primary Cultures of Nasopharyngeal Epithelial Cells JOURNAL OF MEDICAL VIROLOGY Yip, Y., Tsang, C., Deng, W., Cheung, P., Jin, Y., Cheung, A. L., Lung, M. L., Tsao, S. 2010; 82 (10): 1711-1723


    Cell immortalization is regarded as an early and pre-requisite step in tumor development. Defining the specific genetic events involved in cell immortalization may provide insights into the early events of carcinogenesis. Nasopharyngeal carcinoma is common among the Southern Chinese population. Epstein-Barr virus (EBV) infection is associated closely with nasopharyngeal carcinoma. The involvement of LMP1 (an EBV-encoded oncogene) has been implicated in the pathogenesis of nasopharyngeal carcinoma. In this study, LMP1 expression, in combination with ectopic expression of hTERT (catalytic unit of human telomerase), was shown to extend the life span of primary cultures of nasopharyngeal epithelial cells and facilitate the immortalization of one of the cell lines (NP446). This is the first report on the successful immortalization of nasopharyngeal epithelial cells involving LMP1. The events associated with the immortalization of nasopharyngeal epithelial cells by LMP1/hTERT were characterized. Expression of c-Myc, Bmi-1, and Id-1 were upregulated at an early stage of immortalization. At a later stage of immortalization, downregulation of p21 and p16 expression were observed. Upregulation of EGFR expression and activation of MAPK signaling pathway were observed in LMP1/hTERT-immortalized nasopharyngeal epithelial cells. The LMP1/hTERT-immortalized NP446 cells were non-tumorigenic in immunosuppressed nude mice and retained anchorage-dependent growth, suggesting that additional events are required for tumorigenic transformation. The ability of the EBV-encoded LMP1, in the presence of hTERT expression, to extend the life span and immortalize primary cultures of nasopharyngeal epithelial cells supports the involvement of EBV infection and its viral products in the early stage of pathogenesis of nasopharyngeal carcinoma.

    View details for DOI 10.1002/jmv.21875

    View details for Web of Science ID 000281081000013

    View details for PubMedID 20827769

  • Genetic alterations in a telomerase-immortalized human esophageal epithelial cell line: Implications for carcinogenesis CANCER LETTERS Cheung, P. Y., Deng, W., Man, C., Tse, W. W., Srivastava, G., Law, S., Tsao, S. W., Cheung, A. L. 2010; 293 (1): 41-51


    Ectopic expression of viral oncoproteins disrupts cellular functions and limits the value of many existing immortalization models as models for carcinogenesis, especially for cancers without definitive viral etiology. Our newly established telomerase-immortalized human esophageal epithelial cell line, NE2-hTERT, retained nearly-diploid and non-tumorigenic characteristics, but exhibited genetic and genomic alterations commonly found in esophageal cancer, including progressive loss of the p16(INK4a) alleles, upregulation of anti-apoptotic proteins, epithelial-mesenchymal transition, whole-chromosome 7 gain and duplicated 5q arm. Our data also revealed a novel positive regulation of p16(INK4a) on cyclin D1. These findings probably represent early crucial events and mechanisms in esophageal carcinogenesis.

    View details for DOI 10.1016/j.canlet.2009.12.015

    View details for Web of Science ID 000278155900005

    View details for PubMedID 20092939

  • Id-1 induces cell invasiveness in immortalized epithelial cells by regulating cadherin switching and Rho GTPases J Cell Biochem. Cheung PY, Yip YL, Tsao SW, Ching YP, Cheung AL 2010
  • Berberine inhibits Rho GTPases and cell migration at low doses but induces G2 arrest and apoptosis at high doses in human cancer cells INTERNATIONAL JOURNAL OF MOLECULAR MEDICINE Tsang, C. M., Lau, E. P., Di, K., Cheung, P. Y., Hau, P. M., Ching, Y. P., Wong, Y. C., Cheung, A. L., Wan, T. S., Tong, Y., Tsao, S. W., Feng, Y. 2009; 24 (1): 131-138


    Berberine is an active ingredient extracted from Coptidis rhizoma which has been used for centuries as a traditional Chinese medicine for treatment of inflammatory diseases. Recent studies have indicated that berberine has anticancer properties. Berberine arrested cell growth and inhibited cell migration in various cancer cell lines. In this study, we examined the effects of berberine on HONE1 cells, which have been commonly used as a cell model for nasopharyngeal carcinoma. We observed the inhibitory effects of berberine on HONE1 cells at a high dosage (>150 microM). Berberine effectively induced the mitotic arrest of HONE1 cells at 300 microM which was associated with apoptosis. Berberine had differential intracellular localization at low and high doses. At a low dose (50 microM), berberine was localized in the mitochondria while at a high dose (300 microM), berberine was localized in the nucleus which may have induced mitotic arrest. Berberine effectively inhibited cell migration and invasion at low doses. Using a specific GST pull-down assay of activated Rho GTPases, we demonstrated that berberine suppressed the activation of Rho GTPases including RhoA, Cdc42 and Rac1. This indicates a novel function of berberine in the suppression of Rho GTPase signaling to mediate its inhibitory action on cell migration and motility. The potential of berberine to inhibit cancer metastasis in cancer warrants further investigation.

    View details for DOI 10.3892/ijmm_00000216

    View details for Web of Science ID 000267230900019

    View details for PubMedID 19513545

  • Id-1 activation of PI3K/Akt/NF kappa B signaling pathway and its significance in promoting survival of esophageal cancer cells CARCINOGENESIS Li, B., Cheung, P. Y., Wang, X., Tsao, S. W., Ling, M. T., Wong, Y. C., Cheung, A. L. 2007; 28 (11): 2313-2320


    Inhibitor of differentiation or DNA binding (Id-1) is a helix-loop-helix protein that is over-expressed in many types of cancer including esophageal cancer. This study aims to investigate its effects on the phosphatidylinositol-3-kinase (PI3K)/Akt/ nuclear factor kappa B (NFkappaB) signaling pathway and the significance in protecting esophageal cancer cells against apoptosis. We found elevated expression of phosphorylated forms of Akt, glycogen synthase kinase 3beta and inhibitor of kappa B, as well as increased nuclear translocation of NFkappaB subunit p65 and NFkappaB DNA-binding activity, in esophageal cancer cells with stable ectopic Id-1 expression. Transient transfection of Id-1 into HEK293 cells confirmed activation of PI3K/Akt/NFkappaB signaling and the effects were counteracted by the PI3K inhibitor LY294002. Treatment with tumor necrosis factor-alpha (TNF-alpha) elicited a significantly weaker apoptotic response, following a marked and sustained activation of Akt and NFkappaB in the Id-1-over-expressing cells, compared with the vector control. The effects of Id-1 on the PI3K/Akt/NFkappaB signaling pathway and apoptosis were reversed in esophageal cancer cells transfected with siRNA against Id-1. In addition, inhibition of PI3K or NFkappaB signaling using the PI3K inhibitor LY294002 or the NFkappaB inhibitor Bay11-7082 increased the sensitivity of Id-1-over-expressing esophageal cancer cells to TNF-alpha-induced apoptosis. Our results provide the first evidence that Id-1 induces the activation of PI3K/Akt/NFkappaB signaling pathway, and protects esophageal cancer cells from TNF-alpha-induced apoptosis in vitro. Inactivation of Id-1 may provide us with a novel strategy to improve the treatment and survival of patients with esophageal cancer.

    View details for DOI 10.1093/carcin/bgm152

    View details for Web of Science ID 000250826400009

    View details for PubMedID 17638919

  • Id-1 promotes proliferation of p53-deficient esophageal cancer cells INTERNATIONAL JOURNAL OF CANCER Hui, C. M., Cheung, P. Y., Ling, M. T., Tsao, S. W., Wang, X., Wong, Y. C., Cheung, A. L. 2006; 119 (3): 508-514


    The helix-loop-helix protein inhibitor of differentiation and DNA binding (Id-1) is known to promote cellular proliferation in several types of human cancer. Although it has been reported that Id-1 is over-expressed in esophageal squamous cell carcinoma (ESCC), its function and signaling pathways in esophageal cancer are unknown. In our study, we investigated the direct effects of Id-1 on esophageal cancer cell growth by transfecting an Id-1 expression vector into an ESCC cell line (HKESC-3), which showed serum-dependent Id-1 expression. Ectopic Id-1 expression resulted in increased serum-independent cell growth and G1-S phase transition, as well as up-regulation of mouse double minute 2 (MDM2) and down-regulation of p21Waf1/Cip1 protein expressions in the transfectant clones in a p53-independent manner. However, overexpression of Id-1 had no effect on the pRB, CDK4 and p16INK4A expressions. Stable transfection of Id-1 antisense expression vector to inhibit the expression of endogenous Id-1 in another ESCC cell line (HKESC-1) reversed the effects on MDM2 and p21Waf1/Cip1. In addition, Id-1 expression protected ESCC cells from Tumor Necrosis Factor (TNF)-alpha-induced apoptosis by up-regulating and activating Bcl-2. In conclusion, our study provides evidence for the first time that Id-1 plays a role in both proliferation and survival of esophageal cancer cells. Our findings also suggest that unlike prostate, hepatocellular and nasopharyngeal carcinomas in which Id-1 induces cell proliferation through inactivation of p16INK4A/RB pathway, the increased cell proliferation observed in ESCC cells may be mediated through a different mechanism.

    View details for DOI 10.1002/ijc.21874

    View details for Web of Science ID 000238476800005

    View details for PubMedID 16506209

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