Characterization of Gene Expression Profiles of Metallothionein-Null Cadmium-Resistant Cells

Abstract

To understand metallothionein (MT)-independent mechanisms for cadmium (Cd) resistance in mammalian cells, we previously established MT-null Cd-resistant cells from embryonic fibroblast cells of MT-I and -II knockout mice. The Cd resistance of these cells was conferred primarily by a marked reduction of Cd accumulation. To identify genes responsible for Cd resistance as well as Cd transport, we carried out several DNA microarray analyses using cDNAs obtained from two clones of Cd-resistant cells and parental cells. A competitive hybridization of Cy3- and Cy5-probed cDNAs on a DNA chip was carried out with dye-swapping. After a careful examination of the reproducibility and reliability of the data obtained using five different chips, it was found that the expression of 78 genes was enhanced and that of 48 genes was reduced in Cd-resistant cells compared with those in parental cells. These genes include those involved in signal transduction, ubiquitin pathway, and cell-to-cell interactions. Several genes for transporters including solute carrier family transporters and ATP-binding cassette transporters were up- or down-regulated. The examination of mRNA levels using quantitative real-time PCR revealed that the expression of Slc39a14 encoding ZIP14, a member of the zinc transporter ZIP (ZRT-, IRT-like protein) family, was markedly down-regulated in both clones of Cd-resistant cells. Although it is not yet clear whether ZIP14 has the ability to transport Cd, these results suggest that the lowered expression of ZIP14 may be involved in Cd resistance in MT-null cells.