The "activated" hepatic glucocorticoid-receptor complex. Its generation and properties

Area of Science:

• Biochemistry
• Molecular Biology
• Endocrinology

Background:

• The glucocorticoid receptor (GR) regulates gene expression by binding to DNA.
• Activation of the GR-glucocorticoid complex is necessary for nuclear translocation and DNA binding.
• Understanding GR activation conditions is key to deciphering its regulatory role.

Purpose of the Study:

• To investigate the conditions required for the activation of the hepatic cytosol glucocorticoid receptor-glucocorticoid complex.
• To determine the influence of temperature, ionic strength, and specific ions on GR activation.
• To characterize the biochemical changes associated with GR activation.

Main Methods:

• DNA-cellulose binding assays to assess receptor activation.
• Isofocusing to analyze changes in receptor charge.
• Sucrose density gradient centrifugation to evaluate alterations in receptor size/complex formation.

Main Results:

• GR activation is slow at 0°C but rapid at 25°C, with completion in 1 hour.
• Calcium (10 mM CaCl2) and high salt (150 mM NaCl) accelerate activation at 0°C.
• Activation involves a shift in isoelectric point from 7.1 to 6.1, without changing sedimentation coefficient.
• Manganese ions (MnCl2) precipitate the unactivated complex more effectively than the activated form.

Conclusions:

• GR activation is a temperature-dependent process influenced by ionic strength and specific cations like Ca2+.
• Activation involves a conformational change, indicated by isoelectric point shift, enabling DNA binding.
• These findings provide insights into the molecular mechanisms regulating glucocorticoid hormone action.