Zinc and the Msc2 zinc transporter protein are required for endoplasmic reticulum function

Abstract

In this report, we show that zinc is required for endoplasmic reticulum function in Saccharomyces cerevisiae. Zinc deficiency in this yeast induces the unfolded protein response (UPR), a system normally activated by unfolded ER proteins. Msc2, a member of the cation diffusion facilitator (CDF) family of metal ion transporters, was previously implicated in zinc homeostasis. Our results indicate that Msc2 is one route of zinc entry into the ER. Msc2 localizes to the ER when expressed at normal levels. UPR induction in low zinc is exacerbated in an msc2 mutant. Genetic and biochemical evidence indicates that this UPR induction is due to genuine ER dysfunction. Notably, we found that ER-associated protein degradation is defective in zinc-limited msc2 mutants. We also show that the vacuolar CDF proteins Zrc1 and Cot1 are other pathways of ER zinc acquisition. Finally, zinc deficiency up-regulates the mammalian ER stress response indicating a conserved requirement for zinc in ER function among eukaryotes.

Evolution of Differences in Transport Function in Slc11a Family Members

“…We therefore predicted that cytosolic Zn 2ϩ levels would be lower in Slc11a1 expressing cells compared with non-transformed cells and cells expressing Slc11a2. A method to indicate levels of intracellular labile Zn 2ϩ by measuring ␤-galactosidase activity was implemented, using a ZRE-lacZ reporter construct, previously developed to monitor Zn 2ϩ levels in yeast cells (39). The Zap1 transcription factor is activated in zinc-limited cells, whereas it is repressed under zinc-replete conditions.…”

Demonstration and Characterization of the Heterodimerization of ZnT5 and ZnT6 in the Early Secretory Pathway

“…This is because numerous zinc-binding proteins that are secreted out of the cells or are resident within the intracellular organelles capture zinc as they are transported in the early secretory pathway, although a recent study suggests the existence of an alternative mechanism (14). ZnT5, ZnT6, ZnT7, and their orthologues have been shown to play key roles in the performance of this task (15)(16)(17)(18)(19). Most CDF/ZnT proteins form homo-oligomers (dimers) to perform their functions (12, 13, 16, 20 -22).…”

OmZnT1 and OmFET, two metal transporters from the metal-tolerant strain Zn of the ericoid mycorrhizal fungus Oidiodendron maius, confer zinc tolerance in yeast

“…2). In S. cerevisiae, two other CDF family members, Msc2p (gi|285811222) and Zrg17p (gi|285814687), form a heteromeric zinc transport complex in the ER membranes, and they have been implicated in the homeostatic maintenance of ER function ( Ellis et al, 2004 andGaither andEide, 2001). However, Msc2p and Zrg17p are not orthologs of OmZnT1 ( Fig.…”

“…The CDF transporters Zrc1p and Cot1p are the major determinants of zinc tolerance in yeast (Gaither and Eide, 2001), and they are responsible for the vacuolar delivery and sequestration of zinc ( MacDiarmid et al, 2000 andMacDiarmid et al, 2002). Two other CDF members, Msc2p and Zrg17p, form a heteromeric zinc transport complex in the ER membranes, and have been implicated in the homeostatic maintenance of ER function (Ellis et al, 2004 andEllis et al, 2005). The yeast transcription factor Zap1p regulates zinc homeostasis at the transcriptional level, by controlling the expression of both ZIP (e.g.…”