Induction and subcellular localization of metallothionein in regenerating rat liver

A highly specific antiserum against rat liver metallothionein (MT) was raised in a Japanese white rabbit. Using this anti-MT antiserum, we found that MT was localized in the nuclei as well as in the cytoplasm of hepatocytes in newborn rats. Since it is known that these cells are growing actively, we suspected that there was a relationship between the localization of MT in cell nuclei and the cell proliferation. Therefore, the induction and subcellular localization of MT were examined in rat liver remaining after 70% removal. MT was induced in the remnant liver rapidly after the hepatectomy, its concentration being about 80-fold higher than that of the intact liver. Flow cytometric analysis revealed that MT was translocated into the nuclei from the cytoplasm of hepatocytes during liver regeneration after partial hepatectomy. The highest MT level in the nuclei was observed 24 h after hepatectomy. MT-stained positive nuclei were in S to G2M phases of the cell cycle of regenerating hepatocytes, and the nuclei in G1 phase were not stained with anti-MT antiserum. The increase in hepatic MT levels did not directly cause MT translocation into the nuclei. These results suggested that MT was a cell cycle-dependent, nuclear protein.

Localization of metallothionein in aged human brain

The localization of metallothionein (MT), a small molecular weight heavy metal binding protein in aged human brain, was investigated by immunohistochemical techniques. The amount of MT and heavy metals (Zn, Cu) were also assayed by radioimmunoassay and atomic absorption spectrophotometry, respectively. Immunohistochemically, MT was found in the pia mater, ependymal cells, protoplasmic astrocytes nand glial processes neuropil of the gray matter and fibrous astrocytes of the white matter of the telencephalon, whereas oligodendroglia and microglia did not show any positive immunostaining for MT. Cytoplasm, glial processes and some nuclei of protoplasmic and fibrous astrocytes showed strong MT immunostaining. Vascular feet and adventitia were also positive for MT immunostaining. Moreover, the pia mater, astrocytes and ependyma in the diencephalon, mesencephalon, pons, medulla oblongata and spinal cord showed the same positive immunostaining for MT as the telencephalon. In the cerebellum, Bergmann's glia, protoplasmic astrocytes of the granular layer and fibrous astrocytes of the white matter showed strongly positive immunostaining for MT. According to the radioimmunoassay, the amount of MT in the brain was relatively high at about 39.3 +/- 9.5 micrograms/g wet weight; of the heavy metals in the brain, zinc and copper were detected.

Copper-metallothionein distribution in the liver of Long-Evans cinnamon rats: studies on immunohistochemical staining, metal determination, gel filtration and electron spin resonance spectroscopy

Distribution of metallothionein (MT) and copper ion (Cu) in the liver of LEC (Long-Evans Cinnamon) rats was investigated to examine the relationship between Cu-MT induction and the development of hepatitis followed by hepatocellular carcinomas. Immunohistochemical studies on MT in the liver of LEC rats indicated that MT is accumulated in nuclei and cytosols. Both MT and Cu, estimated by radioimmunoassay and flameless atomic absorption spectrometry, respectively, in subcellular fractions of the liver were found to be concentrated highest in cytosols, followed by nuclei, mitochondria and microsomal fractions. Gel-filtration (Sephadex G-75) studies demonstrated that MT is induced as the Cu-MT form. Furthermore, the Cu-MT fragment purified by the gel-filtration contains the Cu(I)-MT form, as demonstrated by ESR (electron spin resonance) measurements at 77K. These results will be important for understanding the development of hepatitis in LEC rats.

Analysis of mammalian metallothionein isoforms by high-resolution SDS-gel electrophoresis

Metallothioneins (MTs) are cysteine-rich heavy metal-binding proteins, whose possible functions are thought to be the protection against toxic metals as well as the regulation of essential metals. It is known that there are several MT isoforms, but the biological roles of the individual isoforms have not been elucidated. To facilitate the functional analysis of these isoforms, we improved an analytical method of MTs developed previously, which is based on a denaturing gel electrophoresis of chemically modified MTs. The established technique makes it possible not only to separate MT isoforms with a high resolution, but to estimate the levels of the individual isoforms by analyzing directly crude cell extracts. By this method, six MT isoforms were identified in the extracts of Cd-exposed human cells. It was also revealed that there is an apparent heterogeneity of the rat liver MT; five isoforms were identified in the liver extracts of Cd-injected rats. The present method will be useful in the functional analysis of the MT isoforms, as well as in a variety of aspects of the MT studies.

Induction of metallothionein by CdCl2 administration in rat prostate

Metallothionein (MT) induction in the rat prostate gland was investigated by means of cadmium chloride administration. Ten-week-old male Wistar rats housed with cadmium free food were divided into three groups of six rats each and castrated. After seven days, 1 mg of testosterone propionate per rat was injected subcutaneously once a day until the end of the experiment. After three weeks, rats were injected daily for six days with a physiological saline, 0.3 mg/kg CdCl2, and 0.9 mg/kg CdCl2. MT concentration of the ventral and dorsal lobes was significantly increased in the three groups in proportion to the dose of CdCl2. MT content of the lateral lobe in three groups was also increased, but was not significantly different. Immunohistochemically, MT was induced mainly in the ventral lobe in the basal cells, and in the lateral and dorsal lobes in the epithelial cells. The weights of the prostatic lobes were similar in the three groups, and no histological change was identified. These results suggested that MT in the prostate was induced by cadmium administration, and that it may prevent cellular damage from harmful metals.

Copper-metallothionein induction in the liver of LEC rats

Recently, copper (Cu) was found to be unusually accumulated, suggesting the induction of metallothionein (MT) in the liver of LEC rats (Long-Evans rats with a cinnamon-like coat color), which develop spontaneous jaundice with hereditary hepatitis. Thus, the direct relationship between the unusual Cu accumulation and the induction of Cu-MT was investigated by giving LEC rats Cu-overloaded or Cu-deficient diets. Results based on the determinations of Cu and MT levels in several organs, as well as the gel-filtration profiles of the cytosols of liver homogenates, showed that dietary Cu induced Cu-MT and development of hepatic injury associated with jaundice.

Immunohistochemical study of metallothionein in human seminal vesicles

Metallothionein (MT) in human seminal vesicles was examined by use of the avidin-biotin-peroxidase complex method. Tissues were obtained from six patients with prostate cancer who underwent luteinizing hormone-releasing hormone agonist or estrogen therapy before radical prostatectomy (group 1) and from 18 patients without hormone therapy (three with prostate cancer, three with urinary bladder cancer, and twelve free of urogenital diseases at autopsy) (group 2). MT was localized in the cytoplasm and nuclei of epithelial cells and also in secretory products in the lumen. The epithelial cells lacked uniformity in immunoreaction; for instance, some stained strongly while others stained weakly. Smooth muscle cells were found to have positive immunoreaction, but other connective tissues had no immunoreaction. The number of strongly positive cells in group 1 was fewer than that in group 2 (not significant), and the secretory products in group 1 had no immunoreaction. These results suggest that MT is synthesized in the epithelial cells of the seminal vesicles and secreted into the fluids, and that the synthesis of MT is suppressed by the hormone therapy.

Unusual accumulation of copper related to induction of metallothionein in the liver of LEC rats

Copper (Cu), iron (Fe), zinc (Zn) and manganese (Mn) levels in organs of LEC rats (Long-Evans rats with a cinnamon-like coat color), which develop spontaneous jaundice with hereditary hepatitis, were determined by instrumental neutron activation analysis method. Unusual accumulations of Cu in the liver of LEC rats were found, depending on the age of the animals, the metal concentration being more than approximately 20-40 times those of normal LEA rats (Long-Evans rats with an agouti coat color). Fe and Zn were also accumulated, in addition to Cu, significantly in the LEC rats. The unusual Cu accumulations in the liver of LEC rats were associated with the induction of metallothionein, estimated by radioimmunoassay method, in the liver of LEC rats, rather than that of superoxide dismutase, estimated by electron spin resonance -spin trapping method. These findings suggest that the unusual Cu accumulation in LEC rats is involved in the development of jaundice, hepatic injury and hepatocellular carcinoma.

Metallothionein of prostatic tissues and fluids in rats and humans

We analyzed metallothionein (MT) in rat prostates by gel filtration and radioimmunoassay. The concentration of MT in the prostate, kidney and liver of cadmium-induced rats was measured. The concentration of MT was also measured in normal prostate, benign prostatic hyperplasia, prostate cancer and the prostatic fluids from various prostatic diseases in humans. MT was detected in rat prostates by gel filtration and radioimmunoassay. The concentration of MT (micrograms/g wet tissue) was 0.3 +/- 0.1 (S.D.) in the ventral lobe, 30.4 +/- 24.0 in the lateral lobe, 5.2 +/- 0.9 in the dorsal lobe, 25.0 +/- 6.4 in the kidney and 2.0 +/- 1.5 in the liver of the rat control group. Change in MT content in CdCl2-induced organs increased quantitatively with the dose administered. The concentration of MT (micrograms/g wet tissue) in human prostate was 99.3 +/- 121.8 in the peripheral zone (PZ), 12.0 +/- 8.5 in the preprostatic region (PR), 7.3 +/- 3.1 in the central zone (CZ), 17.5 +/- 15.0 in benign hyperplastic nodules (A) and 4.2 +/- 0.5 in cancer tissue (CA). MT concentration in PZ was very high and that of CA, low (p less than 0.05). MT concentration in prostatic fluids (ng/mg protein) was 11.5 +/- 5.7 in normal patients, 3.8 +/- 2.3 in acute prostatitis, 6.5 +/- 3.7 in chronic prostatitis with pyuria, 39.6 +/- 3.9 in chronic prostatitis without pyuria and 16.9 +/- 3.0 in benign prostatic hyperplasia. We concluded that MT in the prostate is induced by heavy metals and secreted into prostatic fluid. Possibly, it is a marker of secretory function in the prostate.

Localization of metallothionein in nuclei of growing primary cultured adult rat hepatocytes

In primary cultured adult rat hepatocytes stimulated by epidermal growth factor and insulin, dramatic changes in the subcellular distribution of metallothionein were clarified by indirect immunofluorescence using antisera specific for this protein. Metallothionein was detected only in the cytoplasm of cultured hepatocytes in the G0 and G1 phases, but was concentrated in the cell nuclei in the early S phase. The strongest staining pattern in the nuclei was observed 12 h after stimulation. Subsequently, the intensity of metallothionein staining in the nuclei decreased. These results suggest that primary cultured hepatocytes are suitable for examining the relation between subcellular localization of metallothionein and cell growth.

Cd2+-induced synthesis of metallothionein in HeLa cells

HeLa cells synthesize metallothioneins in response to Cd2+. The kinetics of thionein (apoprotein of metallothionein) synthesis was studied by pulse-labelling the cells with [35S]cysteine and measuring relative amounts of the labelled thioneins separated by electrophoresis. Thionein synthesis rapidly increases in the first 6-8 h after exposure to 0.5 micrograms of Cd2+/ml, and begins to decrease in a few hours after reaching the maximum. However, the rate of synthesis never returns to the basal value at least in 30 h after Cd2+ exposure; instead, the second increase in thionein synthesis occurs at 16-18 h. A possible regulatory mechanism of thionein synthesis is discussed from these results, together with the data on intracellular accumulation and subcellular distribution of 109Cd2+. The initial increase of thionein synthesis is accompanied by an increase of mRNA coding for thioneins (MT-mRNA). The induction of MT-mRNA is sensitive to Actinomycin D, but not to cycloheximide, suggesting transcriptional regulation without any mediating protein synthesis. Two thionein isomers are coded for by mRNA molecules of almost the same size, which is similar to that of hepatic MT-mRNA of mouse and rat.

Evidence for more than two metallothionein isoforms in primates

Two isoforms of metallothionein (MT) have in general been identified in mammalian cells. We have analyzed Cd2+-induced MTs of primate origin and demonstrated the presence of more than two isoforms. Four low molecular weight Cd2+-binding proteins were separated from Cd2+-exposed HeLa cells by gel filtration and ion-exchange chromatography and identified as MTs by amino acid analysis. These were carboxymethylated and analyzed by electrophoresis under denaturing conditions. Three of these proteins were found to be distinct molecules. We also analyzed hepatic MTs from Cd2+-exposed rhesus monkeys, which have previously been partially separated. In this case, five distinct isomers were detected.

Bone and kidney lesions in experimental cadmium intoxication

Young male rats were fed a diet containing cadmium (0, 10, 30, 100, and 300 ppm) so as to morphologically investigate the relationship between bone and kidney lesions caused by experimental cadmium intoxication. In the early stage of the experiment, before the occurrence of kidney lesions, ingeted cadmium caused osteoporotic changes in bone. In later stages, slight pathologic changes in the kdidney occurred in association with urinary excretion of cadmium. However, there was no evidence of osteomalacic change in bone during the 12-week experimental period. These findings suggest that cadmium may act primarily on bone, rather than secondarily through disturbances of the kidneys, which have some protective ability against cadmium intoxication in the early stage of ingestion of the metal.

Tyrosinase as glycoprotein

Purified tyrosinase T1 was incubated with neuraminidase. The catalytic activity of tyrosinase was essentially retained, after this treatment. The tyrosinase band (Dopa stained) was transformed into a new less anodic form, similar to tyrosinase T2, on disc electrophoresis. The band of protein was also converted to the same position as the Dopa stained. The other hand, the only one PAS stained band of native tyrosinase T1 was splitted into the three slower-moving bands. One was consistent with Dopa and protein stained bands. The other two were much more slower than the former band and completely free of peptide and enzymic activity. The PAS-densitometric value of native tyrosinase T1 was almost equal to those of three separated bands in total. These results suggest that mammalian tyrosinase is a kind of glycoprotein.