Mel-18 acts as a tumor suppressor by repressing Bmi-1 expression and down-regulating Akt activity in breast cancer cells

Wei Jian Guo, Mu Sheng Zeng, Ajay Yadav, Li Bing Song, Bao Hong Guo, Vimla Band, Goberdhan P. Dimri

Research output: Contribution to journalArticle

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Abstract

The Bmi-1 oncogene is overexpressed in a number of malignancies including breast cancer. In addition to Bmi-1, mammalian cells also express four other polycomb group (PcG) proteins that are closely related to Bmi-1. Virtually nothing is known about the role of these PcG proteins in oncogenesis. We have recently reported that Mel-18, a Bmi-1-related PcG protein, negatively regulates Bmi-1 expression, and that its expression negatively correlates with Bmi-1 in proliferating and senescing human fibroblasts. Here, we report that the expression of Bmi-1 and Mel-18 inversely correlates in a number of breast cancer cell lines and in a significant number of breast tumor samples. Overexpression of Mel-18 results in repression of Bmi-1 and reduction of the transformed phenotype in malignant breast cancer cells. Furthermore, the repression of Bmi-1 by Mel-18 is accompanied by the reduction of Akt/protein kinase B (PKB) activity in breast cancer cells. Similarly, Bmi-1 knockdown using RNA interference approach results in down-regulation of Akt/PKB activity and reduction in transformed phenotype of MCF7 cells. Importantly, we show that overexpression of constitutively active Akt overrides tumor-suppressive effect of Mel-18 overexpression and the knockdown of Bmi-1 expression. Thus, our studies suggest that Mel-18 and Bmi-1 may regulate the Akt pathway in breast cancer cells, and that Mel-18 functions as a tumor suppressor by repressing the expression of Bmi-1 and consequently down-regulating Akt activity.

Original languageEnglish (US)
Pages (from-to)5083-5089
Number of pages7
JournalCancer Research
Volume67
Issue number11
DOIs
StatePublished - Jun 1 2007

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Polycomb-Group Proteins
Breast Neoplasms
Neoplasms
Proto-Oncogene Proteins c-akt
Phenotype
MCF-7 Cells
RNA Interference
Oncogenes
Carcinogenesis
Down-Regulation
Fibroblasts
Cell Line

ASJC Scopus subject areas

  • Oncology
  • Cancer Research

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Mel-18 acts as a tumor suppressor by repressing Bmi-1 expression and down-regulating Akt activity in breast cancer cells. / Guo, Wei Jian; Zeng, Mu Sheng; Yadav, Ajay; Song, Li Bing; Guo, Bao Hong; Band, Vimla; Dimri, Goberdhan P.

In: Cancer Research, Vol. 67, No. 11, 01.06.2007, p. 5083-5089.

Research output: Contribution to journalArticle

Guo, Wei Jian ; Zeng, Mu Sheng ; Yadav, Ajay ; Song, Li Bing ; Guo, Bao Hong ; Band, Vimla ; Dimri, Goberdhan P. / Mel-18 acts as a tumor suppressor by repressing Bmi-1 expression and down-regulating Akt activity in breast cancer cells. In: Cancer Research. 2007 ; Vol. 67, No. 11. pp. 5083-5089.
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