Thyroid hormone action is disrupted by bisphenol A as an antagonist

Area of Science:

• Endocrinology
• Molecular Toxicology
• Environmental Health

Background:

• Bisphenol A (BPA) is a known estrogen receptor agonist.
• Potential endocrine-disrupting effects of chemicals on thyroid function are under investigation.
• The impact of BPA on thyroid hormone receptors (TRs) remains largely unknown.

Purpose of the Study:

• To investigate the effects of Bisphenol A (BPA) on thyroid hormone receptor (TR) mediated transcription.
• To determine if BPA acts as an antagonist or agonist for TRs.
• To elucidate the molecular mechanisms underlying BPA's interaction with TRs.

Main Methods:

• Transient gene expression assays to assess TR-mediated transcriptional activity.
• Dose-response experiments using physiological concentrations of thyroid hormone (T3).
• Analysis of T3 binding inhibition and cofactor recruitment using mammalian two-hybrid assays.

Main Results:

• BPA demonstrated dose-dependent suppression of T3-stimulated transcription, acting as a TR antagonist.
• BPA activated transcription from a negatively regulated TSHalpha promoter suppressed by T3.
• BPA inhibited T3 binding to rat hepatic nuclear TRs with a K(i) of 200 micro M.
• BPA recruited nuclear corepressors to the TR in a mammalian two-hybrid assay.

Conclusions:

• BPA antagonizes T3 action at the transcriptional level by displacing T3 and recruiting transcriptional repressors.
• This is the first report demonstrating BPA's antagonistic effect on T3 action.
• BPA has the potential to disrupt nuclear hormone receptor function and interfere with hormonal homeostasis.