CeHMT-1, a putative phytochelatin transporter, is required for cadmium tolerance in Caenorhabditis elegans.
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.
Vatamaniuk
Olena K
OK
Plant Science Institute, Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Bucher
Elizabeth A
EA
Sundaram
Meera V
MV
Rea
Philip A
PA
D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D000222:Adaptation, Physiological / Q000502:physiology*; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002104:Cadmium / Q000494:pharmacology*; D017173:Caenorhabditis elegans / Q000502:physiology*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D003001:Cloning, Molecular; D005978:Glutathione; D008667:Metalloproteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D054811:Phytochelatins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012568:Schizosaccharomyces / Q000235:genetics
D018528:ATP-Binding Cassette Transporters; D029742:Caenorhabditis elegans Proteins; C504067:HMT-1 protein, C elegans; D008667:Metalloproteins; D002104:Cadmium; D054811:Phytochelatins; D005978:Glutathione