title: Reduction of glucocorticoid receptor ligand binding by the 11-beta hydroxysteroid dehydrogenase type 2 inhibitor, Thiram.
abstract: Endogenous and synthetic glucocorticoids (GCs), such as cortisol and dexamethasone (Dex), modulate airway inflammation, regulate the production of surfactant by lung epithelial cells, and influence fetal lung maturation. The 11-beta hydroxysteroid dehydrogenase type 2 (HSD2) enzyme catalyzes the oxidation of bioactive cortisol and Dex to their 11-keto metabolites. Thiram (tetramethylthiuram disulfide) specifically inhibits HSD2 activity by oxidizing cysteine residues located in the cofactor binding domain of the enzyme. During studies performed to define a potential role for HSD2 in modulating GC action in human lung epithelial cells, we observed that exposure of intact human lung epithelial cells (NCI-H441) to 50 microM Thiram significantly attenuated the down-stream effects of Dex (100 nM) on the expression of two GC-sensitive genes, pulmonary surfactant proteins A and B. This observation appeared to be inconsistent with simple inhibition of HSD2 activity. Although Thiram inhibited HSD2 oxidase activity in a dose-dependent manner without affecting HSD2 protein expression, Thiram also reduced specific binding of [3H]-Dex to the glucocorticoid receptor (GR). Pre-treatment of cells with 1 mM dithiothreitol (DTT), a thiol-reducing agent, completely blocked the inhibitory effect of Thiram on ligand binding. These results are suggestive that Thiram may alter the ligand-binding domain of the GR by oxidizing critical thiol-containing amino acid residues. Taken collectively, these data demonstrate that attenuated down-stream GC signaling, via decreased binding of ligand to the GR, is a novel cellular effect of Thiram exposure in human lung epithelial cells.
authors.affiliation: Department of Anatomy and Cell Biology, Roy J. and Lucille A. Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA.
authors.forename: Mark R
authors.initials: MR
authors.lastname: Garbrecht
authors.forename: Zygmunt S
authors.initials: ZS
authors.lastname: Krozowski
authors.forename: Jeanne M
authors.initials: JM
authors.lastname: Snyder
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Schmidt
mesh_terms: D043209:11-beta-Hydroxysteroid Dehydrogenase Type 2 / Q000037:antagonists & inhibitors*; D015152:Blotting, Northern; D002460:Cell Line; D003907:Dexamethasone / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008024:Ligands; D011485:Protein Binding; D011965:Receptors, Glucocorticoid / Q000378:metabolism*; D013893:Thiram / Q000494:pharmacology*
chemical_list: D004791:Enzyme Inhibitors; D008024:Ligands; D011965:Receptors, Glucocorticoid; D013893:Thiram; D003907:Dexamethasone; D043209:11-beta-Hydroxysteroid Dehydrogenase Type 2