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 (Zn2+, Cd2+, Cu2+, Hg+, As3+, As5+, Cr3+ and Cr6+) were studied using the real-time PCR. The LC50-24 h 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% LC50 values) of the heavy metal ions for RNA assay. The two cell lines were sensitive to As3+, Cd2+ and Hg+. Zn2+and Cu2+ were moderately toxic, and As5+ and Cr3+ 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 Zn2+, Cd2+, Cu2+, Hg2+ and As3+ caused significant induction of MT mRNA levels in ZFL cells. Zn2+and Cd2+ were efficient MT inducers in the two cell lines, but As3+ and As5+ are strong inducers only in the SJD cell line. In both cell lines, Cu2+ and Hg2+ are moderate inducers, and Cr3+ and Cr6+ were weak inducers of MT mRNA. MTF-1 induction is believed to be insufficient to cause MT gene induction, but As3+ and Cd2+ induced MTF-1 in ZFL cell line. Cd2+ 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 Zn2+ and Cu2+.