title: Induction and degradation of Zn-, Cu- and Cd-thionein in Chang liver cells.
abstract: Human liver cells (Chang liver) were exposed to 5 micrograms Zn, 2.5 micrograms Cu or 1 microgram Cd/ml in cultured medium. These exogeneous heavy metals were accumulated by the cells and induced de novo synthesis of metallothionein after a 3-h incubation period. The production of Zn-, Cu- or Cd-thionein started in the cells with accumulation of 1 nmol Zn, 0.3 nmol Cu and 0.1 nmol Cd/mg cytosol protein and subsequently the amounts of metal-binding thioneins increased in agreement with the relative amount of metal accumulated in the cytosol over a 24-h period. When cells containing Zn- or Cu-thionein were placed in metal free medium, 70% or 25% of the zinc or copper bound to each original metallothionein was released after 3 h; bound metals decreased to 85% and 65% respectively after 24 h. The disappearance of metal from metallothionein correlated with increases of metal in the medium. On the other hand, 35S-counts incorporated into Zn- and Cu-thionein decreased only to 40% and 15% of the levels in the original metallothionein after 3 h; 35S-counts decreased to 65% and 45%, respectively, after 24 h, indicating that metals bound to metallothionein decreased more quickly than 35S-counts. These results suggest that metals were released from metallothionein and were excreted into the medium. However, 35S- and 109Cd-counts in Cd-thionein changed very little, if at all, in the cells even after a 24-h incubation period. Our data strongly suggest that Zn- and Cu-thionein are degraded in the cells, but that Cd-thionein remains longer than either Zn- or Cu-thionein. When cells containing Zn-thionein were incubated in metal-free medium, Zn-thionein was digested in the cells and peptide fragments ranging about 200-400 daltons were excreted from the cells.
mesh_terms: D000818:Animals; D001711:Biotransformation; D002104:Cadmium / Q000378:metabolism / Q000494:pharmacology; D002460:Cell Line; D002478:Cells, Cultured; D002852:Chromatography, Ion Exchange; D003300:Copper / Q000378:metabolism / Q000494:pharmacology; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008668:Metallothionein / Q000096:biosynthesis* / Q000378:metabolism*; D011868:Radioisotopes; D051381:Rats; D011919:Rats, Inbred Strains; D013462:Sulfur Radioisotopes; D013936:Thymidine / Q000378:metabolism; D014316:Tritium; D015032:Zinc / Q000378:metabolism / Q000494:pharmacology
chemical_list: D011868:Radioisotopes; D013462:Sulfur Radioisotopes; C004203:cadmium-binding protein; C007121:copper thionein; C021267:zinc thionein; D002104:Cadmium; D014316:Tritium; D003300:Copper; D008668:Metallothionein; D015032:Zinc; D013936:Thymidine