Post-translational mechanisms of the ZIP family of zinc channels

• Main Author: Nimmanon, Thirayost
• Published: Cardiff University 2016
• Subjects: 572
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.694946

Zinc is an essential trace metal involved in diverse cellular processes. Cellular zinc levels are controlled by three families of proteins, including ZIP channels, which facilitate zinc influx into the cytosol. Aberrant function of many ZIP channels has been associated with human diseases. However, their cellular mechanisms are relatively unclear. Importantly, our group have reported that ZIP7 function is triggered by CK2−mediated phosphorylation on residues S275 and S276, and have created a pZIP7 antibody that recognises this phosphorylated form of ZIP7. This project therefore aimed to decipher post−translational mechanisms of three ZIP channels: ZIP7, ZIP6, and ZIP10. Computational analysis of ZIP sequences revealed salient characteristics of ZIP channels, especially those belonging to the LIV−1 subfamily, and detected multiple potential phosphorylation sites in the cytosolic loop between TM3 and TM4 of ZIP3, ZIP4, ZIP6, ZIP7 and ZIP10. Characterisation of the pZIP7 antibody revealed that it specifically recognised ZIP7 when phosphorylated on S275 and S276 and accurately indicated increased or impaired function of the protein. Employing different antibody arrays, phosphorylation of multiple kinases by ZIP7 overexpression or zinc was demonstrated, introducing multiple signalling pathways as downstream cascades of ZIP7−mediated zinc release from intracellular stores. An investigation on ZIP6 detected that it was phosphorylated by CK2, CK1, GSK−3, and PLK1 exclusively in mitotic cells. This led to a deeper discovery of the cellular mechanism of ZIP6 in mitosis involving its heteromer formation with ZIP10 and its binding to pS727 STAT3, which also bound to pStathmin, a protein required for microtubule reorganisation. Importantly, ZIP6 and ZIP10 antibody treatment successfully inhibited mitosis in multiple breast cancer cell lines, either nocodazole−induced or endogenous. Collectively, this project has provided a deeper insight into ZIP7, ZIP6 and ZIP10 cellular mechanisms, introduced pZIP7 antibody as a potential biomarker, and proposed ZIP6 and ZIP10 antibodies as promising mitosis−blocking agents.