The Polycomb protein BMI1 induces an invasive gene expression signature in melanoma that promotes metastasis and chemoresistance.

The epigenetic regulator BMI1 is upregulated in many human malignancies and has been implicated in cell migration, but the impact on autochthonous tumor progression is unexplored. Our analyses of human expression data show that BMI1 levels increase with progression in melanoma. We find that BMI1 expression in melanoma cells does not influence cell proliferation or primary tumor growth. In contrast, BMI1 levels are a key determinant of melanoma metastasis, whereby deletion impairs and overexpression enhances dissemination. Remarkably, BMI1’s pro-metastatic effect reflects enhancement of all stages of the metastatic cascade including invasion, migration, extravasation, adhesion and survival. Additionally, downregulation or upregulation of BMI1 induces sensitivity or resistance to BRAF inhibitor. Consistent with these pleiotropic effects, we find that BMI1 promotes widespread gene expression changes that encompass key hallmarks of the melanoma invasive signature, including activation of TGFß, non-canonical Wnt, EMT and EGF/PDGF pathways. Importantly, for both primary and metastatic melanoma samples, this BMI1-induced signature identifies invasive subclasses of human melanoma and predicts poor patient outcome. Our data yield key insights into melanoma biology and establish BMI1 as a compelling drug target whose inhibition would suppress both metastasis and chemoresistance. Overall design: Three replicates of A375 BMI1 or GFP overexpressing cells.

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Ferretti R, Bhutkar A, McNamara MC, Lees JA