Expression of the Yeast Cation Diffusion Facilitators Mmt1 and Mmt2 Affects Mitochondrial and Cellular Iron Homeostasis: EVIDENCE FOR MITOCHONDRIAL IRON EXPORT

Liangtao Li,Ren Miao,Xuan Jia,Diane M Ward,Jerry Kaplan

doi:10.1074/jbc.m114.574723

Abstract

Mmt1 and Mmt2 are highly homologous yeast members of the cation diffusion facilitator transporter family localized to mitochondria. Overexpression of MMT1/2 led to changes in cellular metal homeostasis (increased iron sensitivity, decreased cobalt sensitivity, increased sensitivity to copper), oxidant generation, and increased sensitivity to H2O2. The phenotypes due to overexpression of MMT1&2 were similar to that seen in cells with deletions in MRS3 and MRS4, genes that encode the mitochondrial iron importers. Overexpression of MMT1&2 resulted in induction of the low iron transcriptional response, similar to that seen in Δmrs3Δmr4 cells. This low iron transcriptional response was suppressed by deletion of CCC1, the gene that encodes the vacuolar iron importer. Measurement of the activity of the iron-dependent gentisate 1,2-dioxygenase from Pseudaminobacter salicylatoxidans expressed in yeast cytosol, showed that changes in Mmt1/2 levels affected cytosol iron concentration even in the absence of Ccc1. Overexpression of MMT1 resulted in increased cytosolic iron whereas deletion of MMT1/MMT2 led to decreased cytosolic iron. These results support the hypothesis that Mmt1/2 function as mitochondrial iron exporters.

Highlights

Mmt1 and Mmt2 are homologous mitochondrial proteins that belong to the family of cation diffusion facilitators
We show that the effects of overexpression of MMT1 and MMT2 (MMT1&2) are suppressed by deletion CCC1, similar to that seen when CCC1 is deleted in ⌬mrs3⌬mrs4 cells
These results support the view that mitochondria can act as an iron reservoir and that in the absence of either mitochondria or vacuolar iron sequestration, iron toxicity is exacerbated by increased cytosolic iron

Summary

Background

Mmt and Mmt are homologous mitochondrial proteins that belong to the family of cation diffusion facilitators. Overexpression of MMT1&2 resulted in induction of the low iron transcriptional response, similar to that seen in ⌬mrs3⌬mr cells This low iron transcriptional response was suppressed by deletion of CCC1, the gene that encodes the vacuolar iron importer. Studies have suggested that Mmt and Mmt, which are homologous members of the cation diffusion facilitator family (CDF), might function as mitochondrial iron exporters [18]. These proteins are found in fungi and plants, but there is no defined vertebrate homologue. We show that independent of CCC1, Mmt and Mmt are mitochondrial iron exporters

EXPERIMENTAL PROCEDURES

RESULTS

DISCUSSION