The ZnR/GPR39 interacts with the CaSR to enhance signaling in prostate and salivary epithelia

Zinc signaling is mediated by the zinc sensing receptor, ZnR, recently suggested to be the same receptor as G-protein coupled receptor 39, GPR39. However, it is unknown if GPR39 is mediating Zn²⁺-dependent signaling in prostate and salivary tissue where changes in zinc concentrations are frequent and of physiological significance. Here, we show that GPR39 is mediating Zn²⁺-dependent Ca²⁺ responses and is regulating activity of MAP and PI3 pathways in prostate cancer cells, PC3, and ductal salivary gland cells, HSY. We next ask whether ZnR/GPR39 interacts with other GPCR family members. We find that endogenous ZnR/GPR39 activity is regulated by the expression and activity of another cation sensing GPCR, the Ca²⁺-sensing receptor (CaSR). Although CaSR is not activated by Zn²⁺, co-expression of CaSR and ZnR/GPR39 synergistically enhances Ca²⁺ responses in PC3 and HSY cells. Silencing of the CaSR using siRNA or a dominant negative construct reduces the Zn²⁺-dependent signaling. Importantly, overexpression of GPR39 in HEK293 cells is sufficient to trigger Zn²⁺-dependent responses. Nevertheless, application of the CaSR agonist spermine, at concentration below its threshold, enhanced Zn²⁺-dependent Ca²⁺ response. Our results suggest that the CaSR interacts with ZnR/GPR39 and thereby regulates its activity. Finally, we show that in PC3 cells ZnR/GPR39 is required for mediating the Zn²⁺-dependent activation of MAPK and PI3K, pathways leading to enhanced cell growth. Importantly, Zn²⁺-dependent activation of ZnR/GPR39 also enhances the expression of the Ca²⁺-binding protein S100A4 that is linked to invasion of prostate cancer cells. J. Cell. Physiol. 229: 868-877, 2014.