Production of Metallothionein and Heat-Shock Proteins in Response to Metals

Abstract

Production of Metallothionein and Heat-Shock Proteins in Response to Metals. Bauman, J. W., Liu, J., and Klaassen, C. D. (1993). Fundam. Appl. Toxicol. 21, 15-22.Acute stress, such as heat, and some metals, such as arsenite, will induce a specific group of stress proteins referred to as heat-shock proteins. The heat-shock proteins contribute to the survival of cells following a variety of stresses. Similarly, metals such as cadmium and zinc, will increase the levels of metallothionein (MT). The metal-binding protein, MT, has also been found to have a protective role in the cellular response to acute stresses like heavy metals. The purpose of the present study was to examine the production of these proteins in response to metals. Rat hepatocytes were maintained in monolayer culture for 22 hr, and subsequently treated with various concentrations of metals for 4 hr, or incubated at 43.5°C for 15-60 min. Following two washes with fresh media, the cells were labeled with [35S]methionine (25 μCi/ml) in methionine-free media for 4 hr for determination of heat-shock protein production, or reincubated in fresh media for 20 hr for MT determination. Heat-shock protein production was determined by SDS-polyacrylamide gel electrophoresis followed by autoradiography. The autoradiograms were quantified by densitometric scanning. MT was determined by the Cd/hemoglobin affinity assay. Three metals (arsenite, cadmium, and zinc) strongly increased the heat-shock proteins. Whereas arsenite was a much less effective inducer of MT than was cadmium or zinc, arsenite was as effective as the other metals in inducing heat-shock proteins. Nickel was a good inducer of MT; however, it resulted in only a slight increase in the levels of heat-shock proteins. Heat-shock treatment was found to cause a major elevation in heat-shock proteins levels while actually decreasing the levels of MT. In conclusion, while similarities exist between induction of heat-shock protein and MT, there is not always a good correlation between the various stresses that induce heat-shock proteins and those that induce MT.