The ubiquitin-conjugating enzymes, Ubc4 and Cdc34, mediate cadmium resistance in budding yeast through different mechanisms.
The expression of the genes encoding the ubiquitin-conjugating enzymes, Ubc4, Ubc5, and Ubc7, has been reported to be induced by cadmium in budding yeast. In contrast, we have reported that the overexpression of Cdc34, another ubiquitin-conjugating enzyme, confers resistance to cadmium. In the present study, we examined the effects of overexpression of Ubc4, Ubc5, or Ubc7 on the sensitivity of budding yeast to cadmium. We found that yeast cells that overexpressed Ubc4, but not Ubc5 or Ubc7, showed similar cadmium resistance as yeast cells that overexpressed Cdc34. The ubiquitination levels of cellular proteins were significantly increased by overexpression of Ubc4 as well as by Cdc34. As previously reported, yeast cells overexpressing Cdc34 were resistant to cadmium even in the presence of the proteasome inhibitor MG132. However, the acquired resistance to cadmium by overexpression of Ubc4 was not observed in the presence of MG132. Cdc34 overexpression has been shown to inactivate the transcriptional activity of Met4 by accelerating its ubiquitination and to reduce expression of the MET25 gene, a target gene of Met4. Unlike Cdc34, overexpression of Ubc4 did not affect the expression of the MET25 gene. These findings suggest that the mechanism of acquired resistance to cadmium by overexpression of Ubc4 is different from that of Cdc34 and that Ubc4 confers resistance to cadmium by ubiquitination of proteins other than Met4 and accelerates the degradation of these proteins in the proteasomes.
Hwang
Gi-Wook
GW
Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan.
Furuchi
Takemitsu
T
Naganuma
Akira
A
D064173:Anaphase-Promoting Complex-Cyclosome; D019256:Cadmium Chloride / Q000633:toxicity*; D003001:Cloning, Molecular; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D025141:Drug Resistance, Fungal / Q000235:genetics; D004785:Environmental Pollutants / Q000633:toxicity*; D007976:Leupeptins / Q000494:pharmacology; D010957:Plasmids; D012441:Saccharomyces cerevisiae / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000096:biosynthesis*; D044763:Ubiquitin-Conjugating Enzymes / Q000096:biosynthesis*; D043743:Ubiquitin-Protein Ligase Complexes / Q000096:biosynthesis*; D001616:beta-Galactosidase / Q000378:metabolism
D015853:Cysteine Proteinase Inhibitors; D004785:Environmental Pollutants; D007976:Leupeptins; D029701:Saccharomyces cerevisiae Proteins; C577449:CDC34 protein, S cerevisiae; C501306:Ubc4 protein, S cerevisiae; D044763:Ubiquitin-Conjugating Enzymes; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D001616:beta-Galactosidase; D019256:Cadmium Chloride; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde