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Published online: 9 December 2009 | doi:10.1038/nchina.2009.233

Oncology: Prepare for an invasion

Felix Cheung

Introduction

Polycomb-group proteins are gene-silencing proteins with important roles in embryonic development and oncogenesis. Previous studies have found that the upregulation of the polycomb-group protein Bmi-1 enhances the invasiveness of nasopharyngeal cancer, but the underlying mechanism is unknown. Musheng Zeng at Sun Yat-sen University in Guangzhou and co-workers¹ have now uncovered the functional role of Bmi-1 in promoting nasopharyngeal cancer invasion.

The researchers studied the effects of Bmi-1 on human nasopharyngeal epithelial cells (NPECs). They found that the overexpression of Bmi-1 triggers epithelial mesenchymal transition (EMT) — a key cellular program responsible for cancer invasion — and enhances the motility of NPECs. Conversely, the knockdown of endogenous Bmi-1 expression reverses EMT and reduces the motility of NPECs.

Further studies revealed that the upregulation of Bmi-1 leads to the stabilization of Snail — a transcriptional repressor associated with EMT — and the downregulation of the tumour suppressor PTEN. This result helps explain why there was a significant correlation between Bmi-1 expression and local nasopharyngeal cancer invasion — but not metastasis — in a previous cohort study².

Interestingly, the researchers found that the ablation of PTEN expression partially inhibits nasopharyngeal cancer invasion. The finding suggests that PTEN might be a major mediator of Bmi-1-induced EMT.

The authors of this work are from:
State Key Laboratory of Oncology in South China and Department of Experimental Research, Cancer Center, Sun Yat-sen University, Guangzhou, China; Department of Biochemistry, School of Medicine, Sun Yat-sen University, Guangzhou, China; Department of Anatomy and Center for Cancer Research, University of Hong Kong, Hong Kong, China; Department of Genetics, Cell Biology, and Anatomy and Eppley Institute for Research in Cancer and Allied Disease, Medical Center, University of Nebraska, Omaha, Nebraska, USA; School of Life Sciences, University of Science and Technology of China, Hefei, China.

References

1. Song, L. B. et al. The polycomb group protein Bmi-1 represses the tumor suppressor PTEN and induces epithelial-mesenchymal transition in human nasopharyngeal epithelial cells. J. Clin. Invest. doi:10.1172/JCI39374 (2009). | Article | OpenURL
2. Song, L. B. et al. Bmi-1 is a novel molecular marker of nasopharyngeal carcinoma progression and immortalizes primary human nasopharyngeal epithelial cells. Cancer Res. 66, 6225–6232 (2006).  | Article | PubMed | OpenURL | | ChemPort |