Cell cycle regulation of glucocorticoid receptor function.

Area of Science:

• Cell Biology
• Molecular Endocrinology
• Signal Transduction

Background:

• The glucocorticoid receptor (GR) plays a crucial role in regulating gene expression in response to glucocorticoid hormones.
• Cell cycle progression can influence various cellular processes, including signal transduction pathways.

Purpose of the Study:

• To investigate the cell cycle-dependent regulation of glucocorticoid receptor (GR) nuclear translocation, transactivation, and phosphorylation.
• To understand how G2 phase synchronization affects GR function and signaling.

Main Methods:

• Synchronization of mouse L cell fibroblasts at different cell cycle phases (G0, S, G2).
• Assay of glucocorticoid-dependent transactivation of the mouse mammary tumor virus promoter.
• Analysis of glucocorticoid and heavy metal induction of the Metallothionein-1 gene.
• Monitoring of GR nuclear translocation, retention, and phosphorylation status using dexamethasone and RU486.

Main Results:

• Glucocorticoid-dependent transactivation was impaired in G2-synchronized cells, affecting both GR target genes and the Metallothionein-1 gene.
• GRs translocated to the nucleus in G2 cells but were inefficiently retained, redistributing to the cytoplasm.
• GRs bound to the antagonist RU486 showed efficient nuclear retention in G2 cells.
• Altered GR phosphorylation patterns were observed in G2-synchronized cells.

Conclusions:

• Glucocorticoid receptor (GR) function, including nuclear retention and transactivation, is specifically regulated during the G2 phase of the cell cycle.
• Cell cycle-dependent regulation of protein kinases and phosphatases likely influences GR nuclear retention, recycling, and activity.