Showing papers by "Michael Karin published in 1980"

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

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.

Glucocorticoid hormone receptor mediated induction of metallothionein synthesis in HeLa cells.

Abstract: HeLa cells grown in chemically defined medium lacking glucocorticoids synthesize metallothioneins, low molecular-weight heavy-metal binding proteins. Dexamethasone and hydrocortisone increase the rate of metallothionein synthesis five- to ten-fold. Maximal induction is achieved with 10(-8)M dexamethasone and 10 (-7)M hydrocortisone. Half-maximal induction is achieved at 5 X 10(-9)M dexamethasone and 5 X 10(-8)M hydrocortisone. Although carried for many generations in the absence of any glucocorticoids, HeLa cells (clone S) contain 25,000 specific 3H-dexamethasone receptors that translocate into the nucleus after one hour of incubation. 3H-dexamethasone binds to a single class of receptors with an apparent Kd = 18.8 nM. A variety of steroids can be classified into three classes, based on their effect on metallothionein synthesis: (a) full agonists (optimal inducers), (b) intermediate effectors which have either partial agonist or antagonist activities, and (c) inactive steroids. There is a correlation between the effects on metallothionein synthesis of different steroids and their ability to compete with 3H-dexamethasone binding. We conclude that metallothionein is induced in HeLa cells by a glucocorticoid receptor mediated mechanism.