Cadmium Inhibition of Met30p Ubiquitin Ligase Disrupts Phospholipid Traffic Between the Endoplasmic Reticulum and Mitochondria.

Abstract

Mitochondrial membrane biogenesis requires the interorganelle transport of lipids. Phosphatidylserine (PtdSer) synthesized in the ER and related membranes (mitochondria-associated membrane (MAM)) is transported to the mitochondria and decarboxylated to form phosphatidylethanolamine (PtdEtn). Previously, PtdSer transport from ER and MAM to mitochondria has been shown to be defective in the yeast mutant strain (pstA1-1). The pstA1-1 strain harbors a mutation in the MET30 gene. The Met30p is a subunit of the SCF ubiquitin ligase complex. The transcription factor, Met4p, is an ubiquitination target of SCFMET30 ubiquitin ligase. Recent studies show that heavy metal, cadium (Cd), disrupts the interaction between the components of SCFMET30 ubiquitin ligase, resulting in accumulation of non-ubiquitinated and active forms of Met4p. Here, we tested if Cd exposure affects PtdSer transport from ER to mitochondria. In vivo phospholipid transport measurements demonstrate that Cd inhibits PtdSer transport in a dose dependent manner. When treated with 1 mM Cd, the formation of PtdEtn, an indicator of PtdSer transport, was decreased 65%. In vitro PtdSer transport measurements also show that Cd inhibits the lipid transport from MAM to mitochondria. The pstA1-1 strain was hypersensitive to growth inhibition by Cd, but could be rescued by supplementation with ethanolamine, which partially bypasses defects in lipid transport. The data indicate that inhibition of PtdSer transport to mitochondria is one of the downstream effects exerted by the toxic compound, Cd. Supported by NIH 5R37 GM32453