Long-term low level glucocorticoid exposure induces persistent repression in chromatin

Area of Science:

• Endocrinology
• Epigenetics
• Molecular Biology

Background:

• Environmental hormones can induce lasting epigenetic changes.
• Glucocorticoids are key stress hormones with known cellular effects.
• Chromatin structure plays a critical role in gene regulation.

Purpose of the Study:

• To investigate the epigenetic consequences of long-term, low-concentration glucocorticoid exposure.
• To examine the impact on glucocorticoid-responsive genes within different chromatin structures.
• To understand the mechanism of persistent gene repression.

Main Methods:

• Cell culture models were used to study gene expression.
• The Mouse Mammary Tumor Virus (MMTV) promoter was analyzed under various exposure conditions.
• Endogenous glucocorticoid-responsive genes were assessed following prolonged hormone treatment.

Main Results:

• Short-term glucocorticoid exposure induced the MMTV promoter in both integrated and transient forms.
• Longer exposure led to transient repression of the integrated promoter.
• Persistent repression of integrated MMTV and endogenous genes occurred after prolonged low-dose exposure, preventing glucocorticoid receptor binding.

Conclusions:

• Long-term, low-concentration glucocorticoid exposure induces persistent epigenetic repression of target genes.
• This repression is mediated by a chromatin-dependent mechanism.
• The mechanism disrupts the binding of both GR-dependent and GR-independent transcription complexes, affecting gene induction by various stimuli.