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.