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

Abstract

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 50-24 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% 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+.