Progesterone receptor membrane component 1 is phosphorylated upon progestin treatment in breast cancer cells

// Marina Willibald 1 , Giuliano Bayer 1 , Vanessa Stahlhut 1 , Gereon Poschmann 2 , Kai Stühler 2, 3 , Berthold Gierke 4 , Michael Pawlak 4 , Harald Seeger 5 , Alfred O. Mueck 5 , Dieter Niederacher 1 , Tanja Fehm 1 and Hans Neubauer 1 1 Department of Obstetrics and Gynecology, University Hospital and Medical Faculty of the Heinrich-Heine University Duesseldorf, Duesseldorf, Germany 2 Molecular Proteomics Laboratory, BMFZ, Heinrich Heine University Duesseldorf, Duesseldorf, Germany 4 Institute for Molecular Medicine, University Hospital Duesseldorf, Duesseldorf, Germany 3 NMI Natural and Medical Sciences Institute at the University of Tuebingen, Reutlingen, Germany 4 Department of Women’s Health, University Hospital and Faculty of Medicine of the Eberhard Karls University Tuebingen, Tuebingen, Germany Correspondence to: Marina Willibald, email: marina.willibald@med.uni-duesseldorf.de Keywords: breast cancer, PGRMC1, progestins, norethisterone, casein Kinase 2 Received: January 24, 2017    Accepted: June 27, 2017    Published: August 02, 2017 ABSTRACT Menopausal hormone therapy, using estrogen and synthetic progestins, is associated with an increased risk of developing breast cancer. The effect of progestins on breast cells is complex and not yet fully understood. In previous in vitro and in vivo studies, we found different progestins to increase the proliferation of Progesterone Receptor Membrane Component-1 (PGRMC1)-overexpressing MCF7 cells (MCF7/PGRMC1), suggesting a possible role of PGRMC1 in transducing membrane-initiated progestin signals. Understanding the activation mechanism of PGRMC1 by progestins will provide deeper insights into the mode of action of progestins on breast cells and the often-reported phenomenon of elevated breast cancer rates upon progestin-based hormone therapy. In the present study, we aimed to further investigate the effect of progestins on receptor activation in MCF7 and T47D breast cancer cell lines. We report that treatment of both breast cancer cell lines with the progestin norethisterone (NET) induces phosphorylation of PGRMC1 at the Casein Kinase 2 (CK2) phosphorylation site Ser181, which can be decreased by treatment with CK2 inhibitor quinalizarin. Point mutation of the Ser181 phosphorylation site in MCF7/PGRMC1 cells impaired proliferation upon NET treatment. This study gives further insights into the mechanism of differential phosphorylation of the receptor and confirms our earlier hypothesis that phosphorylation of the CK2-binding site is essential for activation of PGRMC1. It further suggests an important role of PGRMC1 in the tumorigenesis and progression of breast cancer in progestin-based hormone replacement therapy.