Zinc homeostasis governed by Golgi-resident ZnT family members regulates ERp44-mediated proteostasis at the ER-Golgi interface
Yuta Amagai, Momo Yamada, Toshiyuki Kowada, Tomomi Watanabe, Yuyin Du, Rong Liu, Satoshi Naramoto, Satoshi Watanabe, Junko Kyozuka, Tiziana Anelli, Tiziana Tempio, Roberto Sitia, Shin Mizukami, Kenji Inaba
Abstract
Abstract Many secretory enzymes acquire essential zinc ions (Zn 2+ ) in the Golgi complex. ERp44, a chaperone operating in the early secretory pathway, also binds Zn 2+ to regulate its client binding and release for the control of protein traffic and homeostasis. Notably, three membrane transporter complexes, ZnT4, ZnT5/ZnT6 and ZnT7, import Zn 2+ into the Golgi lumen in exchange with protons. To identify their specific roles, we here perform quantitative Zn 2+ imaging using super-resolution microscopy and Zn 2+ -probes targeted in specific Golgi subregions. Systematic ZnT-knockdowns reveal that ZnT4, ZnT5/ZnT6 and ZnT7 regulate labile Zn 2+ concentration at the distal, medial, and proximal Golgi, respectively, consistent with their localization. Time-course imaging of cells undergoing synchronized secretory protein traffic and functional assays demonstrates that ZnT-mediated Zn 2+ fluxes tune the localization, trafficking, and client-retrieval activity of ERp44. Altogether, this study provides deep mechanistic insights into how ZnTs control Zn 2+ homeostasis and ERp44-mediated proteostasis along the early secretory pathway.