Simultaneous induction of Pb-metallothionein-like protein and Zn-thionein in the liver of rats given lead acetate

Abstract

Administration of a sublethal dose of lead acetate to rats induced the simultaneous synthesis of a Pb-metallothionein (Pb-MT)-like protein (Pb-BP) and Zn-thionein (Zn-BP) in the liver. The Pb-BP had an apparent molecule mass of 6900 Da and seemed to bind preferentially to lead in the liver cytosol. The Zn-BP was identified by comparison of the Mr, elution profiles from Sephadex G-75 and DEAE-Sephadex A-25 columns, and polyacrylamide-gel-electrophoretic mobility, with those of rat liver Zn-MT-II. The Pb-BP accumulated in the liver to a maximum 6 h after the intraperitoneal injection of lead acetate and accounted for about 60% of the lead in the liver cytosol at this stage. However, after that, it gradually decreased in the liver, until it was close to the basal amount 24 h after the induction. In contrast, the amount of Zn-MT increased gradually, reached a maximum 12 h after the administration of lead acetate and maintained a constant value until at least 24 h after the induction. Amino acid analysis of the Pb-BP indicated that it contained about 280% half-cysteine. These results strongly suggest that lead acetate induces the synthesis of Pb-MT as well as Zn-MT in rat liver.

Exposure of Human Proximal Tubule Cells to Cd 2+ ,Zn 2+ , and Cu 2+ Induces Metallothionein Protein Accumulation but not Metallothionein Isoform 2 mRNA

“…A lack of induction of MT protein was also noted when the HPT cells were exposed to Ag2+ at both lethal and sublethal concentrations. Even though silver is classified as having minor toxicity, these findings are of interest because the intentional use of silver in medical and dental products increases potential exposure (40 Pb2+ has been reported to induce hepatic but not renal MT in animals (34,(43)(44)(45)(46)(47) (49). In this study, the pattern of gene expression was determined for the MT-2A, MT-lA, B, E, F, and G genes in three pairs of cell lines in which one member of each pair was resistant to cisplatin.…”

The Metallothionein-Null Phenotype Is Associated with Heightened Sensitivity to Lead Toxicity and an Inability to Form Inclusion Bodies

“…16 However, the role of MT in lead toxicity has been only poorly defined. Lead can stimulate MT production in vitro and in vivo in some cases 18,19,23 but not in others. 25 Our results indicate that in vitro lead exposure induces MT in the WT cells used in the present study.…”

“…17 However, any mitigating role for MT in lead toxicity is still only poorly defined. In this regard, lead has been shown to induce the synthesis of MT in several instances, 19,[22][23][24] which implicates, but does not definitively establish, a role in lead metabolism. On the other hand, this induction seems rather modest compared to many other metals and occurs only in the liver, 18 perhaps indicating stress-mediated induction.…”

Cloning, characterization, and gene expression analysis of a novel cadmium metallothionein gene in Tetrahymena pigmentosa

“…In the black scabbard fish, there are some relationships between MT and Hg concentrations, although this relationship is tissue dependent (Bebianno et al, 2007). MT or MT-like proteins were reported to be induced by Pb in rats, human, and fish (Ikebuchi et al, 1986;Church et al, 1993;Cheung et al, 2005). The MTT5 gene in T. thermophila showed stronger induction to Pb than Cd (Diaz et al, 2007).…”