The metallothioneins (MTs) are a group of small, ubiquitous, cysteine- rich proteins that avidly bind heavy metal ions. Because MT binds to and is induced by heavy metal ions, it is generally believed that MT evolved to protect living organisms against the toxicity of heavy metals. However, investigators have argued persuasively that it is unlikely that the primary function of MT is to protect cells against heavy metals. Thus the exact function of MT remains an enigma. Gene transfer studies with mammalian cell lines demonstrate that the over-expression of MT results in the cells becoming resistant to the toxicity of heavy metals and alkylating agents. The latter observation is of interest because alkylating agents are known to be carcinogenic in mammals. Although some correlative data suggests that increased levels of MT also protect tissues in vivo against the toxicity of heavy metals, this association is not always observed. At the present time, there is not information about the potential role MT might play in protecting tissues against the toxic and carcinogenic action of alkylating agents. The objective of this project is to produce transgenic mice that over- express MT and to use these mice to test the following hypothesis: Increased expression of MT will protect an organism from the cytotoxic and carcinogenic action of heavy metals and alkylating agents.
The specific aims of this project are as follows: 1. To produce and characterize transgenic mice that carry the human- transferrin promoter fused to the human MT-II(Alpha) gene (phTF/hMT- II(alpha). These transgenic mice will over-express the MT-II(Alpha) gene in liver and brain. 2. To determine if the over-expression of MT protects an organism from the toxicity of heavy metals. The hepatotoxicity of Cd will be compared in phTF/hMT-II(Alpha) transgenic mice and mice without the transgene, and the mechanism responsible for the reduced hepatotoxicity will be studied. 3. To determine if the over-expression of MT protects an organism from carcinogenesis induced by alkylating agents. The ability of N-nitroso-N- methylurea(NMU) to induce liver tumors in phTF/hMT-II(Alpha) transgenic mice and mice without the transgene will be compared, and the mechanism responsible for the reduced hepatocarcinogenesis will be studied.
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