Regulation of metallothionein in teleosts: Induction of MTmRNA and protein by cadmium in hepatic and extrahepatic tissues of a marine flatfish, the turbot (Scophthalmus maximus)

Synthesis of the heavy metal-binding protein metallothionein (MT) was determined in the major organs of accumulation of Cd (liver, kidney and gills) of a marine flatfish, the turbot, after intraperitoneal (i.p.) administration of varying doses of Cd. Synthesis of MTmRNA and MT were linearly related to dose only at low Cd dosages (up to ca. 100 mu gCd/kg). Induction of MTmRNA was rapid, peaking 1-2 days after Cd administration in gills and kidneys, at 4 days in liver. In all three tissues, at low doses of Cd, MTmRNA levels declined with an apparent half life of 5-7 days and for a given dose of Cd, similar MTmRNA concentrations were attained. Induction of MT levels temporally followed that of MTmRNA. Steady state levels of MT were attained more quickly at a low dose of Cd. At acute Cd doses of >200 mu gCd/kg, MT gene transcription and protein translation appeared to be progressively reduced, inferring that the rate of MT synthesis was limiting due to cytotoxicity of the high acute Cd dosage. In contrast to MTmRNA levels which were induced to similar levels in the three tissues, MT levels decreased in the order liver > kidneys > gills implying differences in translational processes.