Cortisol stimulates the zinc signaling pathway and expression of metallothioneins and ZnT1 in rainbow trout gill epithelial cells

Abstract

Bury NR, Chung MJ, Sturm A, Walker PA, Hogstrand C. Cortisol stimulates the zinc signaling pathway and expression of metallothioneins and ZnT1 in rainbow trout gill epithelial cells. Am J Physiol Regul Integr Comp Physiol 294: R623-R629, 2008. First published December 12, 2007 doi:10.1152/ajpregu.00646.2007.-Intracellular zinc signaling is important in the control of a number of cellular processes. Hormonal factors that regulate cellular zinc influx and initiate zinc signals are poorly understood. The present study investigates the possibility for cross talk between the glucocorticoid and zinc signaling pathways in cultured rainbow trout gill epithelial cells. The rainbow trout metallothionein A (MTA) gene possesses a putative glucocorticoid response element and multiple metal response elements 1042 base pairs upstream of the start codon, whereas metallothionein B (MTB) and zinc transporter-1 (ZnT1) have multiple metal response elements but no glucocorticoid response elements in this region. Cortisol increased MTA, MTB, and ZnT1 gene expression, and this stimulation was enhanced if cells were treated with cortisol together with zinc. Cells treated with zinc showed increased zinc accumulation, transepithelial zinc influx (apical to basolateral), and intracellular labile zinc concentrations. These responses were also significantly enhanced in cells pretreated with cortisol and zinc. The cortisol-mediated effects were blocked by the glucocorticoid receptor (GR) antagonist RU-486, indicating mediation via a GR. In reporter gene assays, zinc stimulated MTA promoter activity, whereas cortisol did not. Furthermore, cortisol significantly reduced zinc-stimulated MTA promoter activity in cells expressing exogenous rainbow trout GR. These results demonstrate that cortisol enhances cellular zinc uptake, which in turn stimulates expression of MTA, MTB, and ZnT1 genes. glucocorticoid receptor; metal-regulatory transcription factor-1; fish; metals; glucocorticoid response element METALLOTHIONEINS (MT) are small cysteine-rich metal-binding proteins that in mammals exist as four major isoforms: MT-I, -II, -III, and -IV (53). MT-I and MT-II constitute metalinducible intracellular proteins that are expressed in most cells. In contrast, MT-III and MT-IV are not metal inducible and are expressed specifically in the central nervous system and squamous epithelia, respectively (40, 51). The biological functions of MT-I and MT-II include buffering of intracellular zinc, protection against metal toxicity (38, 43), and defense against oxidative stress (6, 12). The MTs found in different fish species are homologous to the mammalian MT and are functionally equivalent to the MT-I and MT-II isoforms (31).The induction of MT expression by zinc is coordinated by metal-regulatory transcription factor-1 (MTF1; Ref. 17). MTF1 is evolutionary conserved, and orthologues are present in Drosophila melanogaster, fish, mice, and humans (3,8,15,56). Zinc causes MTF1 to translocate to the nucleus (47, 48) and enhances MTF1 binding to metal response ele...

Mitochondrial Bioenergetics

“…Similar to my findings, hypoxia increased MT mRNA levels in gills of the European glass eel, Anguilla anguilla (Pierron et al 2007) and in mammalian tissues (Raleigh et al 1998;Murphy et al 1999Murphy et al , 2008. To increase MT transcript levels, hypoxia possibly acted via general stress response wherein increased levels of cortisol would activate the glucocorticoid response element (GRE) in the MT-A promoter (Bury et al 2008) to regulate MT-A gene expression but not MT-B because the latter lacks a GRE.…”

The redox biology of redox-inert zinc ions

“…Glucocorticoid receptors also belong to the nuclear hormone receptors with two tetrathiolate zinc fingers sensitive to oxidative stress. In epithelial cells of fish gill cells, cortisol increases the uptake of zinc, the increase of "free" zinc ion concentrations and the MTF-1-dependent expression of ZnT-1 and two MTs [158]. Glucocorticoids also affect cognitive functions.…”

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