ATOX1 is a cytoplasmic copper chaperone that interacts with the copper-binding domain of the membrane copper transporters ATP7A and ATP7B. ATOX1 has also been suggested to have a potential anti-oxidant activity. As the trace element copper is essential, but extremely toxic in high concentrations, intracellular copper concentrations are tightly controlled. Once in the cell, copper is distributed by metallochaperones, including the small cytoplasmic protein ATOX1. ATOX1 plays an important role in the transfer of copper to the copper export P-type ATPases ATP7A and ATP7B to facilitate copper excretion. There is a novel function for Atox1 as a transcription factor (TF) regulating Ccnd1 was proposed. Antioxidant 1 (ATOX1) functions as an antioxidant against hydrogen peroxide and superoxide, and therefore may play a significant role in many human diseases, including diabetes mellitus (DM). The transduced Tat-ATOX1 protein protects pancreatic beta-cells by inhibiting STZ-induced cellular toxicity in vitro and in vivo. Thus Tat-ATOX1 protein has potential applications as a therapeutic agent for oxidative stress-induced diseases including DM.