Metallothioneins in Human Kidneys and Associated Tumors

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Abstract

Human kidneys and their associated tumors (nonneoplastic kidney tissues from patients with a transitional cell carcinoma or an adenocarcinoma and the adenocarcinomas themselves) were evaluated for their Zn, Cd, and Cu contents as well as for their metallothionein (MT) level. The total Cd content was correlated with the MT content, and both values were significantly decreased in the adenocarcinomas in comparison with the other tissues. After extraction and separation by anion-exchange chromatography, MT-0 was identified in the nonneoplastic tissues from both the adenocarcinomas as well as the transitional cell carcinomas. Since until now MT-0 protein was only found in human fetal liver and in Zn-stimulated human monocytes, a possible role for this isoform as an oncofetal marker is hypothesized. Separation of the isoforms of MT by reversed-phase high-performance liquid chromatography and sequence analysis showed besides MT-1e and MT-1l the isoform-MT-1g, which is not expressed in the healthy kidney, and MT-1k, an isoform which is not yet demonstrated in renal tissues. We conclude that the expression profile of the MT isoforms in the kidney changes due to the presence of a tumor.

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Single-step method of RNA isolation by acid guanidinium thiocyanate-phenol-chloroform extraction.

P. Chomczynski, N Sacchi (1987)

A new method of total RNA isolation by a single extraction with an acid guanidinium thiocyanate-phenol-chloroform mixture is described. The method provides a pure preparation of undegraded RNA in high yield and can be completed within 4 h. It is particularly useful for processing large numbers of samples and for isolation of RNA from minute quantities of cells or tissue samples.

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Basal metallothionein in tumors: widespread presence of apoprotein.

Asima Pattanaik, C.Frank Shaw, David Petering … (1994)

A survey has been conducted of solid and ascites tumors from mice and solid tumors in rats for the presence of metallothionein or metallothionein-like protein. In most tumors, a positive identification was made on the basis of Sephadex G-75 and HPLC-DEAE chromatography followed by competitive radioimmunoassay for metallothionein. Apometallothionein was revealed in a number of tumors for the first time by comparing the Sephadex G-75 chromatographic profiles of Zn in native cytosol and Cd in cytosol incubated briefly with CdCl2 to saturate free binding sites on the protein before Sephadex G-75 chromatography. In two cases unsaturation of metallothionein was correlated with a lack of zinc in the ascites fluid which supplies the tumor with zinc.

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Discrepancy between the nephrotoxic potencies of cadmium-metallothionein and cadmium chloride and the renal concentration of cadmium in the proximal convoluted tubules.

C Dorian, V Gattone, C D Klaassen (1995)

Acute exposure to inorganic cadmium produces hepatotoxicity, but no renal injury. In contrast, chronic exposure to Cd produces nephrotoxic effects. However, a single injection of cadmium bound to metallothionein (CdMT) can produce nephrotoxicity similar to that seen with chronic exposure to Cd. It is generally thought that CdMT is nephrotoxic because more CdMT than CdCl2 distributes to the kidney. To test this hypothesis, the toxic effects and distribution of Cd were compared after iv injection of CdMT and CdCl2 to mice. CdMT increased urinary excretion of glucose, and protein indicating renal injury. This dysfunction occurred with dosages as low as 0.2 mg Cd/kg. In contrast, renal function was unaltered by CdCl2 administration, even at dosages as high as 3 mg Cd/kg. CdMT distributed almost exclusively to the kidney, whereas CdCl2 preferentially distributed to the liver. However, a high concentration of Cd was also found in the kidneys after CdCl2 administration. In fact, the renal Cd concentration after administration of a high but nonnephrotoxic dose of CdCl2 was equal to or higher than that obtained after injection of nephrotoxic doses of CdMT. Light microscopic autoradiography studies, using 0.3 mg Cd/kg as CdMT and 3 mg Cd/kg as CdCl2, indicated that Cd from CdMT preferentially distributed to the convoluted segments (S1 and S2) of the proximal tubules, whereas Cd from CdCl2 distributed equally to the various segments (convoluted and straight) of the proximal tubules. However, the concentration of Cd at the site of nephrotoxicity, the proximal convoluted tubules, was higher after CdCl2 than after CdMT administration. A higher Cd concentration in both apical and basal parts of the proximal cells was found after CdCl2 than after CdMT administration. Therefore, the reason why CdMT is nephrotoxic and CdCl2 is not nephrotoxic is not due to a higher concentration of Cd in the target cells after CdMT than after CdCl2 administration.