Implication of calcium activated RasGRF2 in Annexin A6-mediated breast tumor cell growth and motility
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Diva S. Whalen1,*, Sarrah E. Widatalla1,*, Olga Y. Korolkova1, Gladys S. Nangami1, Heather K. Beasley1, Stephen D. Williams1, Carlos Virgous2, Brian D. Lehmann3, Josiah Ochieng1 and Amos M. Sakwe1
1Department of Biochemistry and Cancer Biology, School of Graduate Studies and Research, Meharry Medical College, Nashville, TN, USA
2Animal Care Facility, Meharry Medical College, Nashville, TN, USA
3Department of Biochemistry, Vanderbilt University, Nashville, TN, USA
*These authors contributed equally to this work
Amos M. Sakwe, email: firstname.lastname@example.org
Keywords: annexin A6; breast cancer; RasGRF2; calcium; EGFR
Received: July 25, 2015 Accepted: December 16, 2018 Published: January 04, 2019
The role of AnxA6 in breast cancer and in particular, the mechanisms underlying its contribution to tumor cell growth and/or motility remain poorly understood. In this study, we established the tumor suppressor function of AnxA6 in triple negative breast cancer (TNBC) cells by showing that loss of AnxA6 is associated with early onset and rapid growth of xenograft TNBC tumors in mice. We also identified the Ca2+ activated RasGRF2 as an effector of AnxA6 mediated TNBC cell growth and motility. Activation of Ca2+ mobilizing oncogenic receptors such as epidermal growth factor receptor (EGFR) in TNBC cells or pharmacological stimulation of Ca2+ influx led to activation, subsequent degradation and altered effector functions of RasGRF2. Inhibition of Ca2+ influx or overexpression of AnxA6 blocked the activation/degradation of RasGRF2. We also show that AnxA6 acts as a scaffold for RasGRF2 and Ras proteins and that its interaction with RasGRF2 is modulated by GTP and/or activation of Ras proteins. Meanwhile, down-regulation of RasGRF2 and treatment of cells with the EGFR-targeted tyrosine kinase inhibitor (TKI) lapatinib strongly attenuated the growth of otherwise EGFR-TKI resistant AnxA6 high TNBC cells. These data not only suggest that AnxA6 modulated Ca2+ influx and effector functions of RasGRF2 underlie at least in part, the AnxA6 mediated TNBC cell growth and/or motility, but also provide a rationale to target Ras-driven TNBC with EGFR targeted therapies in combination with inhibition of RasGRF2.
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