Metallothionein mRNA induction in HeLa cells in response to zinc or dexamethasone is a primary induction response

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Abstract
Metallothioneins (MTs) are low molecular weight, heavy metal binding proteins unique in their high cysteine content and high affinity for Zn2+, Cd2+, Hg2+, Ag2+ and Cu2+ (refs 1–3). The synthesis of MTs is induced by zinc or cadmium in the liver and kidney4–8 and in cultured cells9–12. More recently MT induction by the steroid hormone dexamethasone (Dex) has been demonstrated in HeLa cells13 and adrenalectomized rats14. Because glucocorticoid hormones lead to an intracellular accumulation of zinc15–17, the question arises of whether the induction of MT gene expression by steroids is a ‘primary induction response’ (ref. 18), or due to elevated intracellular Zn2+. The glucocorticoid-induced transport of Zn2+ is dependent on concurrent protein synthesis10,19. We now show that, in contrast to glucocorticoid-stimulated Zn2+ transport, the Zn2+ and Dex induction of translatable MT-mRNA is independent of concomitant protein synthesis but not RNA synthesis; that is, MT induction by either agent is a primary induction response18.

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