Hypoxia-mediated translational activation of ITGB3 in breast cancer cells enhances TGF-β signaling and malignant features in vitro and in vivo

Abstract

Breast cancer is the most prevalent malignancy in women and there is an urgent need for new therapeutic drugs targeting aggressive and metastatic subtypes, such as hormone-refractory triple-negative breast cancer (TNBC). Control of protein synthesis is vital to cell growth and tumour progression and permits increased resistance to therapy and cellular stress. Hypoxic cancer cells attain invasive and metastatic properties and chemotherapy resistance, but the regulation and role of protein synthesis in this setting is poorly understood. We performed a polysomal RNA-Seq screen in non-malignant breast epithelial (MCF10A) and TNBC (MDA-MB-231) cells exposed to normoxic or hypoxic conditions and/or treated with an mTOR pathway inhibitor. Analysis of both the transcriptome and the translatome identified mRNA transcripts translationally activated or repressed by hypoxia in an mTOR-dependent or -independent manner. Integrin beta 3 (ITGB3) was translationally activated in hypoxia and its knockdown increased apoptosis and reduced survival and migration, particularly under hypoxic conditions. Moreover, ITGB3 was required for sustained TGF-β pathway activation and for the induction of Snail and associated epithelial-mesenchymal transition markers. ITGB3 downregulation significantly reduced lung metastasis and improved overall survival in mice. Collectively, these data suggest that ITGB3 is translationally activated in hypoxia and regulates malignant features, including epithelial-mesenchymal transition and cell migration, through the TGF-β pathway, revealing a novel angle for the treatment of therapy-resistant hypoxic tumours.