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PMID:15840570

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Citation

Vatamaniuk, OK, Bucher, EA, Sundaram, MV and Rea, PA (2005) CeHMT-1, a putative phytochelatin transporter, is required for cadmium tolerance in Caenorhabditis elegans. J. Biol. Chem. 280:23684-90

Abstract

Phytochelatins (PCs), (gamma-Glu-Cys)n Gly polymers that were formerly considered to be restricted to plants and some fungal systems, are now known to play a critical role in heavy metal (notably Cd2+) detoxification in Caenorhabditis elegans. In view of the functional equivalence of the gene encoding C. elegans PC synthase 1, ce-pcs-1, to its homologs from plant and fungal sources, we have gone on to explore processes downstream of PC fabrication in this organism. Here we describe the identification of a half-molecule ATP-binding cassette transporter, CeHMT-1, from C. elegans with an equivalent topology to that of the putative PC transporter SpHMT-1 from Schizosaccharomyces pombe. At one level, CeHMT-1 satisfies the requirements of a Cd2+ tolerance factor involved in the sequestration and/or elimination of Cd x PC complexes. Heterologous expression of cehmt-1 in S. pombe alleviates the Cd2+-hypersensitivity of hmt- mutants concomitant with the localization of CeHMT-1 to the vacuolar membrane. Suppression of the expression of ce-hmt-1 in intact worms by RNA interference (RNAi) confers a Cd2+-hypersensitive phenotype similar to but more pronounced than that exhibited by ce-pcs-1 RNAi worms. At another level, it is evident from comparisons of the cell morphology of ce-hmt-1 and cepcs-1 single and double RNAi mutants that CeHMT-1 also contributes to Cd2+ tolerance in other ways. Whereas the intestinal epithelial cells of ce-pcs-1 RNAi worms undergo necrosis upon exposure to toxic levels of Cd2+, the corresponding cells of ce-hmt-1 RNAi worms instead elaborate punctate refractive inclusions within the vicinity of the nucleus. Moreover, a deficiency in CeHMT-1 does not interfere with the phenotype associated with CePCS-1 deficiency and vice versa. Double ce-hmt-1; ce-pcs-1 RNAi mutants exhibit both cell morphologies when exposed to Cd2+. These results and those from our previous investigations of the requirement for PC synthase for heavy metal tolerance in C. elegans demonstrate PC-dependent, HMT-1-mediated heavy metal detoxification not only in S. pombe but also in some invertebrates while at the same time indicating that the action of CeHMT-1 does not depend exclusively on PC synthesis.

Links

PubMed Online version:10.1074/jbc.M503362200

Keywords

ATP-Binding Cassette Transporters/chemistry; ATP-Binding Cassette Transporters/genetics; ATP-Binding Cassette Transporters/physiology; Adaptation, Physiological/physiology; Amino Acid Sequence; Animals; Base Sequence; Cadmium/pharmacology; Caenorhabditis elegans/physiology; Caenorhabditis elegans Proteins/chemistry; Caenorhabditis elegans Proteins/genetics; Caenorhabditis elegans Proteins/physiology; Cloning, Molecular; Glutathione; Metalloproteins/metabolism; Molecular Sequence Data; Phytochelatins; Reverse Transcriptase Polymerase Chain Reaction; Schizosaccharomyces/genetics

Significance

Annotations

Gene product Qualifier GO Term Evidence Code with/from Aspect Extension Notes Status

CAEEL:HMT1

located_in

GO:0005774: vacuolar membrane

ECO:0000314: direct assay evidence used in manual assertion

C

Seeded From UniProt

complete

CAEEL:HMT1

enables

GO:0015086: cadmium ion transmembrane transporter activity

ECO:0000314: direct assay evidence used in manual assertion

F

Seeded From UniProt

complete

CAEEL:HMT1

involved_in

GO:0070574: cadmium ion transmembrane transport

ECO:0000314: direct assay evidence used in manual assertion

P

Seeded From UniProt

complete

CAEEL:HMT1

involved_in

GO:0046686: response to cadmium ion

ECO:0000315: mutant phenotype evidence used in manual assertion

P

Seeded From UniProt

complete


See also

References

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