| Summary: | 碩士 === 國立清華大學 === 生命科學系 === 88 === Metallothionein (MT) gene expression is regulated by metals and several non-metallic compounds. In this work, we found that serum factors can effectively induced MT gene expression in human HepaG2 cells. MT gene was activated when the culture medium was replaced by a fresh one. Analysis of the culture medium components that may be associated with the MT gene activation revealed that only directly addition of serum resulted in a stimulation of MT gene. The stimulatory effect was down-regulated by both inhibitors of protein kinase A and C. The inactivation of MT gene expression by both protein kinase inhibitors was correlated to the reduction of metal response element-binding transcription factor-1 (MTF-1) binding activity as analyzed by electrophoretic mobility shift assay (EMSA). Calcium might also be involved in the MT activation pathway, since addition of the intracellular calcium chelator BAPTA-AM could partially inhibit serum-induced MT gene expression. However, calcium ionophore A23187 has no effect in serum-induced MT gene expression. In addition to calcium chelator, intracellular zinc chelator, TPEN, can also abolish the induction of MT by serum. Further analysis of the serum-induced MT gene expression showed that thiol redox potential is involved in the regulatory mechanism. When serum was given with the presence of 10 mM glutathione (GSH), MT gene expression was inactivated. However, MT gene was turned on when GSH was replaced by glutathione disulfide (GSSG). Other thiol/dithiol group compounds also examined, such as dithiothreitol, N-aceytlcysteine, cysteine, 5,5'-dithiobis-(2-nitrobenzoic acid) and 2,2'-dithiodipyridine, the results were the same with GSH/GSSG treatment. Results from our study indicate that protein kinase activities in the cells and thiol redox potential of the medium are associated with the regulation of serum-induced MT gene expression.
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