SLC39A9 and prostate cancer: In human prostate cancer cells with overexpressed ZIP9 (PC-3-ZIP9) and breast cancer cells (MDA-MB-468), stimulation with testosterone leads to G proteins being activated, second messenger pathways, and elevation of intracellular free zinc, resulting in initiation of apoptosis and upregulation of pro-apoptotic genes such as BAX, p53, and Caspase-3 (36, 40).