AP-1 DNA binding activity induced by hyperosmolality in the rat hypothalamic supraoptic and paraventricular nuclei

Area of Science:

• Neuroscience
• Molecular Biology
• Endocrinology

Background:

• Immediate early gene products, including c-fos and c-jun, function as transcription factors.
• These factors bind to the AP-1 site, regulating target gene expression in response to stimuli.
• c-fos induction is known in hypothalamic nuclei (PVN, SON) after hyperosmotic stimulation.

Purpose of the Study:

• To investigate AP-1 DNA binding activity in rat hypothalamic nuclei (PVN, SON) and striatum following hyperosmotic stimulation.
• To determine if the observed binding activity involves c-Fos/Fra and c-Jun proteins.

Main Methods:

• Electrophoretic mobility shift assay (EMSA) was used to measure AP-1 DNA binding activity.
• Nuclear extracts were prepared from PVN, SON, and striatum of rats 2 hours after hypertonic saline injection.
• Supershift assays with c-Fos/Fra and c-Jun antibodies were employed to identify the binding proteins.

Main Results:

• Hyperosmolality significantly increased AP-1 DNA binding activity in the SON and PVN, but not in the striatum.
• The binding was specific to the AP-1 consensus sequence, as shown by competitive displacement assays.
• Supershift and blocking assays confirmed the presence of c-Fos/Fra and c-Jun in the DNA-protein complex.

Conclusions:

• Hyperosmotic stimulation selectively and specifically enhances AP-1 DNA binding activity in the hypothalamic PVN and SON.
• This increased activity, involving c-Fos/Fra and c-Jun, likely plays a crucial role in regulating downstream gene expression in response to osmotic challenges.