Copper is an essential transition metal but is toxic in excess; therefore, its metabolism needs to be tightly regulated. Defects in the regulation of copper can lead to various disorders characterized by copper deficiency or copper excess. Recently, we characterized the COMMD1 (previously MURR1) gene as the defective gene in canine copper toxicosis. The molecular functions of COMMD1 remain unknown, but significant progress has been made in identifying the cellular processes in which COMMD1 participates, through the identification of proteins interacting with COMMD1. This review discusses how COMMD1 functions as a regulator of not only copper homeostasis but also sodium transport and the NF-κB signaling pathway. We outline the possible mechanisms through which COMMD1 exerts these newly identified functions.