Expressional Control of a Cadmium-transporting P1B-type ATPase by a Metal Sensing Degradation Signal

David J Adle,Jaekwon Lee

doi:10.1074/jbc.m806054200

Abstract

Cadmium is a highly toxic environmental contaminant implicated in various diseases. Our previous data demonstrated that Pca1, a P1B-type ATPase, plays a critical role in cadmium resistance in yeast S. cerevisiae by extruding intracellular cadmium. This illustrates the first cadmium-specific efflux pump in eukaryotes. In response to cadmium, yeast cells rapidly enhance expression of Pca1 by a post-transcriptional mechanism. To gain mechanistic insights into the cadmium-dependent control of Pca1 expression, we have characterized the pathway for Pca1 turnover and the mechanism of cadmium sensing that leads to up-regulation of Pca1. Pca1 is a short-lived protein (t1/2 < 5 min) and is subject to ubiquitination when cells are growing in media lacking cadmium. Distinct from many plasma membrane transporters targeted to the vacuole for degradation via endocytosis, cells defective in this pathway did not stabilize Pca1. Rather, Pca1 turnover was dependent on the proteasome. These data suggest that, in the absence of cadmium, Pca1 is targeted for degradation before reaching the plasma membrane. Mapping of the N terminus of Pca1 identified a metal-responding degradation signal encompassing amino acids 250-350. Fusion of this domain to a stable protein demonstrated that it functions autonomously in a metal-responsive manner. Cadmium sensing by cysteine residues within this domain circumvents ubiquitination and degradation of Pca1. These data reveal a new mechanism for substrate-mediated control of P1B-type ATPase expression. Cells have likely evolved this mode of regulation for a rapid and specific cellular response to cadmium.

Highlights

Tivation of proteins and oxidative stress [4, 9, 10]
Direct cadmium sensing by the degradation signal prevents turnover, which leads to enhanced expression of Pca1
Pca1 constructs were functional in conferring cadmium resistance (Fig. 1B)

Summary

Introduction

Tivation of proteins and oxidative stress [4, 9, 10]. Cadmium markedly increases mutation rates by inhibiting the DNA mismatch repair system [11]. Metal Sensing Degradation Signal in a P1B-type ATPase transcript levels [30], which suggests a new mode of substratemediated regulation for this family of proteins. Rsp5 is an E3 ubiquitin- Pca1(1–392)-CaCRP fusion was fully functional in conferring protein ligase that is known to be involved in regulation of sev- copper tolerance to yeast cells indicating correct folding and eral plasma membrane proteins, such as metal-dependent trafficking (Fig. 4A).

Results

Conclusion