Efflux function, tissue-specific expression and intracellular trafficking of the Zn transporter ZnT10 indicate roles in adult Zn homeostasis

Zn is essential to the structure and function of numerous proteins and enzymes so requires tight homeostatic control at both the systemic and cellular level. Two families of Zn transporters - ZIP (SLC39) and ZnT (SLC30) - contribute to Zn homeostasis. There are at least 10 members of the human ZnT family, and the expression profile and regulation of each varies depending on tissue type. Little is known about the role and expression pattern of ZnT10; however in silico data predict restricted expression to foetal tissue. We show a differential expression profile for ZnT10 in adult human tissue by RT-qPCR and detect highest levels of expression in small intestine, liver and brain tissues. We present data revealing the functional activity of ZnT10 to be in the efflux direction. Using a plasmid construct to express ZnT10 with an N-terminal FLAG-epitope tag, we reveal subcellular localisation in a neuroblastoma cell line (SH-SY5Y) to be at the Golgi apparatus under standard conditions of culture, with trafficking to the plasma membrane observed at higher extracellular Zn concentrations. We demonstrate down-regulation by Zn of ZnT10 mRNA levels in cultured intestinal and neuroblastoma cell lines and demonstrate reduced transcription from the ZnT10 promoter at an elevated extracellular Zn concentration. These features of ZnT10 localisation, regulation and function, together with the discovery that ZnT10 is expressed a high levels in brain tissue, indicate that ZnT10 has a role in regulating Zn homeostasis in the brain so may have relevance to the development of neurodegenerative disease.