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The polycomb group protein Bmi-1 represses the tumor suppressor PTEN and induces epithelial-mesenchymal transition in human nasopharyngeal epithelial cells.

ABSTRACT: The polycomb group protein B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1) is dysregulated in various cancers, and its upregulation strongly correlates with an invasive phenotype and poor prognosis in patients with nasopharyngeal carcinomas. However, the underlying mechanism of Bmi-1-mediated invasiveness remains unknown. In the current study, we found that upregulation of Bmi-1 induced epithelial-mesenchymal transition (EMT) and enhanced the motility and invasiveness of human nasopharyngeal epithelial cells, whereas silencing endogenous Bmi-1 expression reversed EMT and reduced motility. Furthermore, upregulation of Bmi-1 led to the stabilization of Snail, a transcriptional repressor associated with EMT, via modulation of PI3K/Akt/GSK-3beta signaling. Chromatin immunoprecipitation assays revealed that Bmi-1 transcriptionally downregulated expression of the tumor suppressor PTEN in tumor cells through direct association with the PTEN locus. This in vitro analysis was consistent with the statistical inverse correlation detected between Bmi-1 and PTEN expression in a cohort of human nasopharyngeal carcinoma biopsies. Moreover, ablation of PTEN expression partially rescued the migratory/invasive phenotype of Bmi-1-silenced cells, indicating that PTEN might be a major mediator of Bmi-1-induced EMT. Our results provide functional and mechanistic links between the oncoprotein Bmi-1 and the tumor suppressor PTEN in the development and progression of cancer.

SUBMITTER: Song LB

PROVIDER: S-EPMC2786794 | biostudies-literature | 2009 Dec

REPOSITORIES: biostudies-literature

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The polycomb group protein Bmi-1 represses the tumor suppressor PTEN and induces epithelial-mesenchymal transition in human nasopharyngeal epithelial cells.

Song Li-Bing LB Li Jun J Liao Wen-Ting WT Feng Yan Y Yu Chun-Ping CP Hu Li-Juan LJ Kong Qing-Li QL Xu Li-Hua LH Zhang Xing X Liu Wan-Li WL Li Man-Zhi MZ Zhang Ling L Kang Tie-Bang TB Fu Li-Wu LW Huang Wen-Lin WL Xia Yun-Fei YF Tsao Sai Wah SW Li Mengfeng M Band Vimla V Band Hamid H Shi Qing-Hua QH Zeng Yi-Xin YX Zeng Mu-Sheng MS

The Journal of clinical investigation 20091102 12

The polycomb group protein B lymphoma Mo-MLV insertion region 1 homolog (Bmi-1) is dysregulated in various cancers, and its upregulation strongly correlates with an invasive phenotype and poor prognosis in patients with nasopharyngeal carcinomas. However, the underlying mechanism of Bmi-1-mediated invasiveness remains unknown. In the current study, we found that upregulation of Bmi-1 induced epithelial-mesenchymal transition (EMT) and enhanced the motility and invasiveness of human nasopharyngea ...[more]

PMID: 19884659

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Project description:Epithelial to mesenchymal transition (EMT) is associated with the basal-like breast cancer phenotypes. 60% of basal-like cancers have been shown to express wild-type estrogen receptor beta (ERbeta1). However, it is still unclear whether the ERbeta expression is related to EMT, invasion and metastasis in breast cancer. In the present study, we examined whether ERbeta1 through regulating EMT can influence invasion and metastasis in basal-like cancers.Basal-like breast cancer cells (MDA-MB-231 and Hs578T) in which ERbeta1 was either overexpressed or downregulated were analyzed for their ability to migrate and invade (wound-healing assay, matrigel-coated Transwell assay) as well as for the expression of EMT markers and components of the EGFR pathway (immunoblotting, RT-PCR). Coimmunoprecipitation and ubiquitylation assays were employed to examine whether ERbeta1 alters EGFR protein degradation and the interaction between EGFR and the ubiquitin ligase c-Cbl. The metastatic potential of the ERbeta1-expressing MDA-MB-231 cells was evaluated in vivo in a zebrafish xenotransplantation model and the correlation between ERbeta1 and E-cadherin expression was examined in 208 clinical breast cancer specimens by immunohistochemistry.Here we show that ERbeta1 inhibits EMT and invasion in basal-like breast cancer cells when they grow either in vitro or in vivo in zebrafish. The inhibition of EMT correlates with an ERbeta1-mediated upregulation of miR-200a/b/429 and the subsequent repression of ZEB1 and SIP1, which results in increased expression of E-cadherin. The positive correlation of ERbeta1 and E-cadherin expression was additionally observed in breast tumor samples. Downregulation of the basal marker EGFR through stabilization of the ubiquitin ligase c-Cbl complexes and subsequent ubiquitylation and degradation of the activated receptor is involved in the ERbeta1-mediated repression of EMT and induction of EGFR signaling abolished the ability of ERbeta1 to sustain the epithelial phenotype.Taken together, the results of our study strengthen the association of ERbeta1 with the regulation of EMT and propose the receptor as a potential crucial marker in predicting metastasis in breast cancer.

Dataset Information

The polycomb group protein Bmi-1 represses the tumor suppressor PTEN and induces epithelial-mesenchymal transition in human nasopharyngeal epithelial cells.

Publications

The polycomb group protein Bmi-1 represses the tumor suppressor PTEN and induces epithelial-mesenchymal transition in human nasopharyngeal epithelial cells.

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