Comparative studies of zinc metabolism in cultured chinese hamster cells with differing metallothionein-induction capacities

Abstract

Previous work in our laboratory led to the isolation of a cadmium (Cd)-resistant variant (Cd(r)2C10) of the line CHO Chinese Hamster cell having a 10-fold greater resistance to the cytotoxic action of Cd(2+) compared with the CHO cell. This resistance was attributed to an increased capacity of the Cd(2+)-resistant Cd(r)2C10 subline to induce synthesis of the Cd(2+)- and Zn(2+)-binding protein(s), metallothionein(s) (MT). Evidence that Cd(2+) behaves as an analog of the essential trace metal, Zn(2+), especially as an inducer of MT synthesis, suggested that the Cd(r) and CHO cell types could be employed to investigate cellular Zn(2+) metabolism. In the present study, measurements were made to compare CHO and Cd(r) cell types for (a) growth as a function of the level of ZnCl2 added to the culture medium, (b) uptake and subcellular distribution of Zn(2+), and (c) capacity to induce MT synthesis. The results of these measurements indicated that (a) both CHO and Cd(r) cell types grew normally (T d≊16-18 h) during exposures to Zn(2+) at levels up to 100 μM added to the growth medium, but displayed abrupt growth inhibition at higher Zn(2+) levels, (b) Cd(r) cells incorporate fourfold more Zn(2+) during a 24-h exposure to the maximal subtoxic level of Zn(2+) and (c) the CHO cell lacks the capacity to induce MT synethesis while the Cd(r) cell is proficient in this response during exposure to the maximal subtoxic Zn(2+) level. These findings suggest that (a) the CHO and Cd(r) cell systems will be useful in further studies of cellular Zn(2+) metabolism, especially in comparisons of Zn(2+) metabolism in the presence and absence of induction of the Zn(2+)-sequestering MT and (b) a relationship exists between cellular capacity to induce MT synthesis and capacity for cellular Zn(2+) uptake.