Submitted on September 7, 2007
Accepted on December 10, 2007
Cortisol stimulates the zinc signalling pathway and expression of metallothioneins and ZnT1 in rainbow trout gill epithelial cells
Nic R Bury1, Mi-Ja Chung2, Armin Sturm3, Paul A. Walker4, and Christer Hogstrand5*
1 Kings College, London, United States
2 Division of Food Sciences and Technology, Korea University, Seoul, Korea, Republic of
3 Aquacutlure, Striling University, Stirling, United Kingdom
4 Cells to Tissues, Manchester University, Manchester, United Kingdom
5 Department of Life Sciences, King's College London, London, United Kingdom
* To whom correspondence should be addressed. E-mail: christer.hogstrand{at}kcl.ac.uk.
Intracellular zinc signalling 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 crosstalk between the glucocorticoid and zinc signalling pathways in cultured rainbow trout gill epithelial cells. Rainbow trout metallothionein-A (MTA) gene possesses a putative glucocorticoid response element (GRE) and multiple metal response elements (MRE) 1042 base pair upstream of the start codon, whereas metallothionein-B (MTB) and zinc transporter-1 (ZnT1) have multiple MREs but no GREs in this region. Cortisol increased MTA, MTB and ZnT1 gene expression and this stimulation was enhanced if cells were treated with cortisol and together with zinc. Cells treated with zinc showed increased zinc accumulation, transepithelial zinc influx (apical to basolateral), and intracellular labile Zn2+ concentrations. These responses were also significantly enhanced during in cells pre-treatmented with cortisol and zinc. The cortisol-mediated effects were blocked by the glucocorticoid receptor (GR) antaagonist RU486, indicating mediation via a GR. In reporter-gene assays, zinc stimulated MTA promoter activity while cortisol did not. Furthermore, cortisol significantly reduced zinc-stimulated MTA promoter activity in cells expressing exogenous rainbow trout GR. These results demonstrate cortisol enhances cellular zinc uptake, which in turn stimulates expression of MTA, MTB and ZnT1 genes.
