Cytotoxicities and induction of metallothionein (MT) and metal regulatory element (MRE)-binding transcription factor-1 (MTF-1) messenger RNA levels in the zebrafish (Danio rerio) ZFL and SJD cell lines after exposure to various metal ions.

Using zebrafish liver (ZFL) and caudal fin (SJD) cell-line models, the induction of metallothionein (MT) and metal regulatory element-binding transcription factor-1 (MTF-1) mRNA levels by various metal ions (Zn(2+)(,) Cd(2+), Cu(2+), Hg(+), As(3+), As(5+), Cr(3+) and Cr(6+)) were studied using the real-time PCR. The LC(50)-24h values of the metal ions were determined for the two cell lines prior to their exposure to different concentrations (10%, 25%, 50%, 75% and 100% LC(50) values) of the heavy metal ions for RNA assay. The two cell lines were sensitive to As(3+), Cd(2+) and Hg(+). Zn(2+)and Cu(2+) were moderately toxic, and As(5+) and Cr(3+) were less toxic to both cell lines. Each of the metal ions tested was found to cause significant induction of the mRNA levels in the SJD cells. Only Zn(2+), Cd(2+), Cu(2+), Hg(2+) and As(3+) caused significant induction of MT mRNA levels in ZFL cells. Zn(2+)and Cd(2+) were efficient MT inducers in the two cell lines, but As(3+) and As(5+) are strong inducers only in the SJD cell line. In both cell lines, Cu(2+) and Hg(2+) are moderate inducers, and Cr(3+) and Cr(6+) were weak inducers of MT mRNA. MTF-1 induction is believed to be insufficient to cause MT gene induction, but As(3+) and Cd(2+) induced MTF-1 in ZFL cell line. Cd(2+) was the most efficient inducer of MT in the cell lines, and also induced MTF-1 levels with clear dose-responsiveness in SJD cell line. These results indicated that MT induction can occur without MTF-1 induction for many metal ions such as Zn(2+) and Cu(2+).