ZnR/GPR39 upregulation of K+/Cl−-cotransporter 3 in tamoxifen resistant breast cancer cells

Abstract Expression of the zinc receptor, ZnR/GPR39, is increased in higher grade breast cancer tumors and cells. Zinc, its ligand, is accumulated at larger concentrations in the tumor tissue and can therefore activate ZnR/GPR39-dependent Ca 2+ signaling leading to tumor progression. The K + /Cl − co-transporters (KCC), activated by intracellular signaling, enhance breast cancer cell migration and invasion. We asked if ZnR/GPR39 enhances breast cancer cell malignancy by activating KCC. Activation of ZnR/GPR39 by Zn 2+ upregulated K + /Cl − co-transport activity, measured using NH 4 + as a surrogate to K + while monitoring intracellular pH. Upregulation of NH 4 + transport was monitored in tamoxifen resistant cells with functional ZnR/GPR39-dependent Ca 2+ signaling but not in MCF-7 cells lacking this response. The NH 4 + transport was Na + -independent, and we therefore focused on KCC family members. Silencing of KCC3, but not KCC4, expression abolished Zn 2+ -dependent K + /Cl − co-transport, suggesting that KCC3 is mediating upregulated NH 4 + transport. The ZnR/GPR39-dependent KCC3 activation accelerated scratch closure rate, which was abolished by inhibiting KCC transport with [(DihydroIndenyl) Oxy] Alkanoic acid (DIOA). Importantly, silencing of either ZnR/GPR39 or KCC3 attenuated Zn 2+ -dependent scratch closure. Thus, a novel link between KCC3 and Zn 2+ , via ZnR/GPR39, promotes breast cancer cell migration and proliferation.