HIF2α contributes to antiestrogen resistance via positive bilateral crosstalk with EGFR in breast cancer cells
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Muhammad Wasi Alam1, Camilla Ulrika Persson1, Susann Reinbothe1, Julhash U. Kazi1, Lars Rönnstrand1, Caroline Wigerup1, Henrik Jorn Ditzel2, Anne E. Lykkesfeldt3, Sven Påhlman1, Annika Jögi1
1Department of Laboratory Medicine, Translational Cancer Research, Lund University Cancer Center at Medicon Village, Lund University, Sweden
2Department of Cancer and Inflammation Research, University of Southern Denmark, and Department of Oncology, Odense University Hospital, Odense, Denmark
3Breast Cancer Group, Cell Death and Metabolism, Danish Cancer Society Research Center, Copenhagen, Denmark
Annika Jögi, e-mail: Annika.email@example.com
Keywords: breast cancer, antiestrogen, endocrine therapy, hypoxia, hypoxia inducible factor
Received: July 07, 2015 Accepted: January 22, 2016 Published: February 03, 2016
The majority of breast cancers express estrogen receptor α (ERα), and most patients with ERα-positive breast cancer benefit from antiestrogen therapy. The ERα-modulator tamoxifen and ERα-downregulator fulvestrant are commonly employed antiestrogens. Antiestrogen resistance remains a clinical challenge, with few effective treatments available for patients with antiestrogen-resistant breast cancer. Hypoxia, which is intrinsic to most tumors, promotes aggressive disease, with the hypoxia-inducible transcription factors HIF1 and HIF2 regulating cellular responses to hypoxia. Here, we show that the ERα-expressing breast cancer cells MCF-7, CAMA-1, and T47D are less sensitive to antiestrogens when hypoxic. Furthermore, protein and mRNA levels of HIF2α/HIF2A were increased in a panel of antiestrogen-resistant cells, and antiestrogen-exposure further increased HIF2α expression. Ectopic expression of HIF2α in MCF-7 cells significantly decreased sensitivity to antiestrogens, further implicating HIF2α in antiestrogen resistance. EGFR is known to contribute to antiestrogen resistance: we further show that HIF2α drives hypoxic induction of EGFR and that EGFR induces HIF2α expression. Downregulation or inhibition of EGFR led to decreased HIF2α levels. This positive and bilateral HIF2-EGFR regulatory crosstalk promotes antiestrogen resistance and, where intrinsic hypoxic resistance exists, therapy itself may exacerbate the problem. Finally, inhibition of HIFs by FM19G11 restores antiestrogen sensitivity in resistant cells. Targeting HIF2 may be useful for counteracting antiestrogen resistance in the clinic.
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