title: Involvement of DNA hypermethylation in down-regulation of the zinc transporter ZIP8 in cadmium-resistant metallothionein-null cells.
abstract: The Zrt/Irt-related protein 8 (ZIP8) encoded by slc39a8 is now emerging as an important zinc transporter involved in cellular cadmium incorporation. We have previously shown that mRNA and protein levels of ZIP8 were decreased in cadmium-resistant metallothionein-null (A7) cells, leading to a decrease in cadmium accumulation. However, the mechanism by which ZIP8 expression is suppressed in these cells remains to be elucidated. In the present study, we investigated the possibility that epigenetic silencing of the slc39a8 gene by DNA hypermethylation is involved in the down-regulation of ZIP8 expression. A7 cells showed a higher mRNA level of DNA methyltransferase 3b than parental cells. Hypermethylation of the CpG island of the slc39a8 gene was detected in A7 cells. Treatment of A7 cells with 5-aza-deoxycytidine, an inhibitor of DNA methyltransferase, caused demethylation of the CpG island of the slc39a8 gene and enhancement of mRNA and protein levels of ZIP8. In response to the recovery of ZIP8 expression, A7 cells treated with 5-aza-deoxycytidine showed an increase in cadmium accumulation and consequently an increase in sensitivity to cadmium. These results suggest that epigenetic silencing of the slc39a8 gene by DNA hypermethylation plays an important role in the down-regulation of ZIP8 in cadmium-resistant metallothionein-null cells.
authors.affiliation: Laboratory of Molecular Nutrition and Toxicology, Faculty of Pharmaceutical Sciences, Tokushima Bunri University, Yamashiro-cho, Tokushima 770-8514, Japan.
authors.forename: Hitomi
authors.initials: H
authors.lastname: Fujishiro
authors.forename: Satomi
authors.initials: S
authors.lastname: Okugaki
authors.forename: Saori
authors.initials: S
authors.lastname: Yasumitsu
authors.forename: Shuichi
authors.initials: S
authors.lastname: Enomoto
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Himeno
mesh_terms: D000818:Animals; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D002104:Cadmium / Q000378:metabolism* / Q000494:pharmacology; D027682:Cation Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D002478:Cells, Cultured; D018899:CpG Islands; D019175:DNA Methylation; D015254:DNA Modification Methylases / Q000037:antagonists & inhibitors; D000077209:Decitabine; D044127:Epigenesis, Genetic; D020868:Gene Silencing; D008668:Metallothionein / Q000235:genetics*; D051379:Mice; D018345:Mice, Knockout; D012333:RNA, Messenger / Q000096:biosynthesis; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: D027682:Cation Transport Proteins; D012333:RNA, Messenger; C530151:SLC39A8 protein, human; D002104:Cadmium; D000077209:Decitabine; D008668:Metallothionein; D015254:DNA Modification Methylases; D001374:Azacitidine