Zinc-, copper- and cadmium-binding protein in Ehrlich ascites tumour cells

Abstract

The properties of Ehrlich ascites tumour cells exposed in vivo to cadmium were investigated as a function of the zinc status of the host animals. Tumour-cell growth was inhibited by cadmium in both zinc-sufficient and zinc-deficient animals. However, cells in zinc-sufficient tumours accumulate much less cadmium than those in deficient tumours. The subcellular distributions of cadmium and zinc do not depend on zinc status. Cadmium and zinc are bound to a low-molecular-weight protein with properties similar to metallothionein. Without exposure to cadmium, a zinc-and copper-binding protein is still present that behaves like a metallothionein. This protein can rapidly bind cadmium added to Ehrlich cells in vitro. It is shown that the zinc-and copper-binding protein contains free thiol groups. Ehrlich cells isolated from cadmium-treated animals are viable and show normal incorporation of uridine into RNA, but the cellular uptake of thymidine and its incorporation into DNA are inhibited.

On the sensitivity of metallothioneins to oxidation during isolation

“…More recently a metal-binding protein having a number of properties associated with metallothioneins has been isolated from Ehrlich ascitestumour cells (Petering et al. 1978: Koch et al, 1980. It binds nearly equal amounts of zinc and copper.…”

Metal-dependent protein folding: Metallation of metallothionein

“…However, presence of metal-free protein in vivo was first reported in the early 1980s when several studies showed that a number of tumor cell lines contained elevated levels of MT-like protein or their mRNA [16][17][18]. Following these initial reports, several tumor cell lines were, in fact, found to contain MT with unsaturated metal-binding sites as well as a relatively large pool of apo-MT [18][19][20].…”

Ligand substitution reactions of metallothioneins with EDTA and apo-carbonic anhydrase.

“…The study of metallothionein function has been stimulated recently by the demonstration that Zn-thionein is a normal constituent of cells under various physiological conditions including cancer (3)(4)(5)(6)(7)(8). The question of its role in metabolism arises.…”

“…Chemical studies of metallothionein reactions have not progressed far beyond the first report after its identification in cells (2). Hence, although metallothionein binds cadmium after exposure of the host to this toxic metal and recently has been shown to bind zinc and copper under various physiological conditions, no bioinorganic studies have provided a foundation for reasonable hypotheses as to the meaning of these results (3)(4)(5)(6)(7)(8). Such studies are difficult because there are seven sites that may be occupied by a combination of Zn and Cd ions.…”