Induction of a metallothionein-like protein in human lymphocytes

Trace elements and rheumatoid arthritis (RA)--pathogenetic and therapeutic aspects

Rheumatoid arthritis is characterized by increased activity of macrophages which produce toxic forms of oxygen. Such oxygen has been suggested as mediator also of rheumatoid inflammation. Gold accumulates in lysosomes of the macrophages and stabilizes lysosomal and other cell membranes leading to reduced liberation of toxic oxygen. Intracellular production of metallothionein can be induced. Zinc in high doses parenterally can immobilize macrophages and also induce metallothionein-like proteins. Copper and zinc are components of SOD which detoxifies oxygen, and copper-thiolate complexes are reported to be anti-inflammatory. The therapeutic effect of penicillamine and other thiols like aurothiomalate may also be related to an anti-oxidative action. Therapeutic induction of increased intracellular levels of glutathione or administration of selenium in such a form that it incorporates into glutathione-peroxidase and increases the efficacy of the enzyme may lead to accelerated metabolism of toxic oxygen.

Metallothionein in human thrombocyte precursors, CD61+ megakaryocytes

The in vitro biosynthesis of metallothionein (MT) was investigated in thrombocyte precursors (megakaryocytes) isolated from human cord blood. Biosynthesis and induction of MT in magnetic cell sorting-separated CD61(+) megakaryocytes was confirmed by immunohistochemical staining using monoclonal mouse anti-MT. The presence of MT was detected both in the nuclear and in the cytoplasmic area. Using RT-PCR, in vitro upregulation/induction of total MT transcripts was observed in CD61(+) cells at 48 h post-treatment with 100 micromol/L of zinc supplement. Seven isoform-specific mRNAs namely, MT-1A, MT-1B, MT-1E, MT-1G, MT-1H, MT-1X, and MT-2A were detected in the similar cell populations left untreated with zinc.

Metallothionein isogene transcription in red blood cell precursors from human cord blood

The in vitro transcription patterns for 10 functional metallothionein (MT) isogenes have been investigated in red blood cell (RBC) precursors from human cord blood. Active transcription status of the isogenes, MT-0, MT-1A, MT-1B, MT-1E, MT-1G, MT-1X, and MT-2A, was detected in both ex vivo expanded RBC precursors (burst-forming unit-erythroid) and glycophorin A(+) and CD71(+) cells separated by magnetic cell sorting. Transcription patterns of these isogenes were analyzed at different times of incubation with the addition of Zn supplement. In neither the ex vivo expanded precursors nor glycophorin A(+) and CD71(+) cells could MT-1F and MT-3 be detected. Transcripts of MT-4 were detected in glycophorin A(+) and CD71(+) cells. Erythropoietin-responsive constitutive transcription of MT-1X and possible interleukin-3-responsive downregulation of MT-2A in ex vivo expanded precursors reveal their effect on MT biosynthesis. Biosynthesis and induction of MT at the protein level in the RBC precursors was also demonstrated by immunoblotting.

Metallothionein: a potential marker for differentiating benign and neoplastic gastrointestinal lymphoid infiltrates

Metallothioneins (MT) are low molecular weight, metal-binding proteins. The induction of MT synthesis by cytokines, hormones and other cytotoxic agents indicates its role in cellular proliferation and differentiation as well as in cellular defense mechanisms. Previous studies have detected expression of MT in various human tumors by immunohistochemical staining. In certain cases the presence of MT in a tumor may be associated with its resistance against radiation and chemotherapeutic agents. Immunohistochemical staining of MT using a rabbit polyclonal anti-rat liver MT antibody was carried out in eight gastric, two small bowel and one large bowel lymphomas, and in ten control gastrointestinal (gastric, colonic and small bowel) biopsies or excised bowel segments with benign lymphoid infiltrates. The primary antibody against rat liver MT readily cross-reacts with human MT. The neoplastic cells in nine of 11 malignant lymphomas showed weak to intense staining for MT, mostly in cytoplasm. In these cells a few nuclei (less than 5% of all tumor cells) were stained positively for MT. The benign lymphocytes in the gastrointestinal excised specimens and biopsies were mostly negative; four cases showed few positive cells. The giant cells were also positive for MT in a Crohn's disease case. We conclude that the presence or absence of MT in lymphocytes, detected by immunohistochemistry, may indicate the growth patterns of these cells. The distinct pattern of MT staining in malignant lymphoma in our study is suggestive of a potential use of MT staining as a discriminator between benign and malignant lymphoid tissues.

Interest of zinc determination in leucocyte fractions for the assessment of marginal zinc status

In order to test the sensitivity of leucocyte zinc determination in the assessment of zinc status, an isolation procedure of mononuclear (MNC) and polymorphonuclear (PMNC) cell fractions was developed. Zinc concentrations in cells from healthy subjects were (mean +/- SD, in mumol/10(10) cells): 0.81 +/- 0.24 in MNC and 0.55 +/- 0.06 in PMNC. In patients suffering from several diseases known to be associated with a marginal impairment in zinc status (cirrhosis, cancer, obesity, endocrine and rheumatic diseases), these concentrations did not differ from those in controls except in rheumatic patients in whom MNC zinc was increased (1.05 +/- 0.42 mumol/10(10) cells) and correlated with erythrocyte sedimentation rate (r = 0.41, P less than 0.01). This relation was also significant in the whole study population (r = 0.39, P less than 0.01). Leucocyte zinc therefore appears to have a limited value in the assessment of marginally impaired zinc status, except in inflammatory states.

Mitogenicity and metallothionein induction: two separate effects of zinc ions on human mononuclear blood cells

The mitogenic effect of elevated concentrations of zinc ions on human lymphocytes was found to be inhibited by the glucocorticoid hormone dexamethasone. The effect decreased progressively from complete block to partial inhibition when the culture period before the addition of dexamethasone was prolonged. In contrast, dexamethasone did not inhibit an induced formation of metallothionein in mononuclear cells. Furthermore, dexamethasone itself was found to induce small amounts of metallothionein. Apparently, the mitogenic effect and the induction of metallothionein by zinc ions in mononuclear cells occur by mutually independent mechanisms.

Metallothionein-like proteins and cell resistance to cis-dichlorodiammineplatinum(II) in L1210 cells

Our studies on the mechanism of resistance of the murine leukemia L1210-PDD line to cis-dichlorodiammineplatinum(II) (cis-DDP) have not shown why it is 10-fold more resistant to the drug than the L1210 line. For this reason we investigated metallothionein-like proteins ('MTs') in these cells. Soluble protein extracts from cultures treated for 24 h with cis-DDP, zinc sulphate or saline were anaerobically eluted from columns of chemically reduced Sephadex G-75, and the profiles of zinc, copper and platinum were determined along with those for incorporated radioactive cyst(e)ine and tyrosine. Both saline-treated cell lines contained similar levels of 'MTs', which were induced by exposure to a minimally toxic level of zinc (100 microM). Zinc induction of 'MTs' was nearly 4-fold greater in L1210 than in L1210-PDD cells. The levels of mRNA for metallothionein I (MTI) and II (MTII) in uninduced cells were measured by dot-blotting with a cDNA probe. The L1210-PDD cells contained 80% of the MTI and 41% of the MTII compared with L1210 cells, confirming the similar levels in uninduced cells. L1210-PDD cells were 2-fold more sensitive than L1210 cells to cadmium and equally sensitive to zinc. Thus, the resistance of L1210-PDD cells to cis-DDP was not associated with cross-resistance to group IIb metals, whereas their sensitivity to cadmium did reflect the relative inability of the cells to synthesize 'MTs'. The L1210 cells produced 'MTs' when treated with 0.5 and 5.0 microM cis-DDP, but the L1210-PDD cells did not when treated with 5.0-40 microM cis-DDP. Small amounts of platinum (less than 21% of the total eluted) were bound to 'MTs' in both cell lines, but platinum provided a minor portion of the 'MT'-bound metals, with zinc and copper contributing the bulk. The basis for the resistance of L1210-PDD cell to cis-DDP is neither an increased level of 'MTs' in the resistant cells nor an enhanced ability to increase the synthesis of 'MTs' after drug exposure.

Induction of metallothionein production by zinc in human mononuclear cells

1. Low mol. wt proteins with high Cd-binding capacity were found to be induced by Zn in cultured monocytes and lymphocytes. 2. In T cell cultures one protein was found to be induced by 125 microM Zn for 6 days, while in monocytes and B enriched cells under these conditions two proteins were found, of which the one with higher mol. wt had similar electrophoretic mobility to the T cell protein on polyacrylamide gels. 3. Mol. wt criteria and crossreactivity towards anti-metallothionein (Mt) antibody identified these proteins to be Mts of about 23 and 27 kDa mol. wt. 4. Metal binding studies indicated that monocyte and lymphocyte Mts had a higher affinity to Zn compared to Cd than rat liver Mt and Mts from Cd-resistant substrains of a human epithelial and a murine fibroblast cell line. 5. The presence of the T cell mitogen phytohemagglutinin (PHA) was found not to be necessary for this Mt induction by Zn.

Cadmium-induced synthesis of metallothioneins in human lymphocytes and monocytes

Cd2+-binding proteins of peripheral blood lymphocytes and monocytes have not well been characterized so far, although they are expected to be a clue for understanding Cd2+ toxicity in those immune competent cells. We separated a family of Cd2+-binding proteins from Cd2+-exposed human peripheral blood lymphocytes by gel filtration chromatography, and characterized them by SDS-gel electrophoresis. The proteins showed electrophoretic behaviours closely similar to metallothioneins (MTs) of HeLa cells derived from human cervical carcinoma. The proteins were also found in Cd2+-exposed monocytes, and were inducible by Cd2+ in both lymphocytes and monocytes. Anti-MT serum specifically precipitated these proteins, which were thus identified as MTs. These results suggest that the two classes of the cells involved in the immune system possess a protective mechanism against Cd2+ through MTs. A variety of human lymphoid cell lines derived from both T and B cells were also found to have capacity to synthesize MTs in response to Cd2+.

The origin of metallothionein in red blood cells

The origin of metallothionein (MT) in red blood cells (RBCs) from a mouse given cadmium was studied in connection with RBC kinetics. Plasma Cd concentration rapidly decreased 3 hr following 109CdCl2 (2 mg/kg, sc) administration, whereas RBC Cd increased from 2 to 4 days, followed by a gradual decrease. RBC Cd was found to be distributed more in the high-molecular-weight fraction than in the MT fraction 12 hr after administration. But, thereafter, Cd increased rapidly in the MT fraction to show changes with time similar to Cd level in RBCs. Hepatic damage induced in a mouse given 21 injections of Cd, with resultant marked elevation of plasma MT concentrations, did not cause any change in RBC Cd concentration. MT was hardly transferred to RBC when a mouse RBC suspension was incubated with mouse hepatic MT. To examine the relationship of Cd-MT and erythropoietic function, mice in the normal group, the phenylhydrazine-induced anemia group (PH), the transfusion-induced plethora group (TR), and the erythropoietin administered plethora group (TR + EP) were given 109CdCl2. Three days after administration, Cd concentration in its RBCs and its MT fraction remarkably increased in the PH group, and was greatly decreased in the TR group. A significant increase was noted in the TR + EP group as compared with the TR group. These results indicate that MT in the RBCs is formed in erythroblasts.

In vitro modulation of murine natural killer cytotoxicity by zinc

The in vitro effects of zinc on natural killer (NK) activity of murine spleen cells were studied. The pretreatment of splenocytes with non-toxic concentrations of ZnSO4 induced a decrease of lytic activity against YAC-1 and RDM4 targets. The lytic function of non-activated and poly(I) X poly(C)-activated NK cells was similarly inhibited. When the interaction of effector cells with zinc was studied for 5 min, a significant inhibition of NK lysis was noted, which was maximal after 30 min. Zinc was undoubtedly responsible for the observed effects, since the concurrent addition of both zinc and suitable concentrations of o-phenanthroline, a Zn++ chelating agent, made it possible to maintain a normal level of lysis. Moreover, the pretreatment of spleen cells with increased concentrations of o-phenanthroline also inhibited NK lysis, suggesting that a physiological intracellular zinc content is required to maintain an optimal lytic function of NK cells. Although the lysis was completely suppressed after the addition of 10(-4) M ZnSO4, the frequency of target-binding cells (TBC), which was assumed to represent the first stage of NK-mediated cytolysis, was only partly inhibited. The results are discussed in view of a possible action of zinc on cell membrane functions, enzyme systems, and release of lymphokines.