Dibutyltin disrupts glucocorticoid receptor function and impairs glucocorticoid-induced suppression of cytokine production.
BACKGROUND
Organotins are highly toxic and widely distributed environmental chemicals. Dibutyltin (DBT) is used as stabilizer in the production of polyvinyl chloride plastics, and it is also the major metabolite formed from tributyltin (TBT) in vivo. DBT is immunotoxic, however, the responsible targets remain to be defined. Due to the importance of glucocorticoids in immune-modulation, we investigated whether DBT could interfere with glucocorticoid receptor (GR) function.


METHODS
We used HEK-293 cells transiently transfected with human GR as well as rat H4IIE hepatoma cells and native human macrophages and human THP-1 macrophages expressing endogenous receptor to study organotin effects on GR function. Docking of organotins was used to investigate the binding mechanism.


RESULTS
We found that nanomolar concentrations of DBT, but not other organotins tested, inhibit ligand binding to GR and its transcriptional activity. Docking analysis indicated that DBT inhibits GR activation allosterically by inserting into a site close to the steroid-binding pocket, which disrupts a key interaction between the A-ring of the glucocorticoid and the GR. DBT inhibited glucocorticoid-induced expression of phosphoenolpyruvate carboxykinase (PEPCK) and tyrosine-aminotransferase (TAT) and abolished the glucocorticoid-mediated transrepression of TNF-alpha-induced NF-kappaB activity. Moreover, DBT abrogated the glucocorticoid-mediated suppression of interleukin-6 (IL-6) and TNF-alpha production in lipopolysaccharide (LPS)-stimulated native human macrophages and human THP-1 macrophages.


CONCLUSIONS
DBT inhibits ligand binding to GR and subsequent activation of the receptor. By blocking GR activation, DBT may disturb metabolic functions and modulation of the immune system, providing an explanation for some of the toxic effects of this organotin.
Gumy
Christel
C
Division of Molecular and Systems Toxicology, Department of Pharmaceutical Sciences, University of Basel, Basel, Switzerland.
Chandsawangbhuwana
Charlie
C
Dzyakanchuk
Anna A
AA
Kratschmar
Denise V
DV
Baker
Michael E
ME
Odermatt
Alex
A
D000818:Animals; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D003907:Dexamethasone / Q000378:metabolism; D015536:Down-Regulation / Q000187:drug effects; D004353:Drug Evaluation, Preclinical; D052244:Endocrine Disruptors / Q000494:pharmacology; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D009947:Organotin Compounds / Q000494:pharmacology*; D011485:Protein Binding / Q000187:drug effects; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation / Q000187:drug effects; D014162:Transfection
D016207:Cytokines; D052244:Endocrine Disruptors; D016328:NF-kappa B; D009947:Organotin Compounds; D011965:Receptors, Glucocorticoid; C056189:di-n-butyltin; D003907:Dexamethasone