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Calcium-dependent phosphorylation processes control brain aromatase in quail.
J Balthazart1, M Baillien, T D Charlier
1Center for Cellular and Molecular Neurobiology, Research Group in Behavioural Neuroendocrinology, University of Liège, 17 place Delcour (Bat. L1), B-4020 Liège, Belgium. jbalthazart@ulg.ac.be
The European Journal of Neuroscience
|May 20, 2003
Summary
Rapid brain aromatase activity is down-regulated by protein kinase C (PKC) and other kinases through direct phosphorylation of the aromatase enzyme. This rapid regulation mechanism involves specific serine, threonine, and tyrosine residues on the enzyme.
Area of Science:
- Neuroendocrinology
- Molecular Endocrinology
- Enzyme Regulation
Background:
- Oestrogen synthase (aromatase) activity in the brain is primarily regulated by slow gene transcription via sex steroid receptors.
- Recent findings suggest rapid, minutes-scale regulation of aromatase activity by Ca2+-dependent protein phosphorylation in quail brain homogenates.
Purpose of the Study:
- To investigate the rapid, direct mechanisms by which protein kinases down-regulate aromatase activity in quail brain homogenates.
- To identify specific phosphorylation sites on the aromatase enzyme affected by kinase activity.
Main Methods:
- Biochemical assays on quail brain homogenates to assess aromatase activity under phosphorylating conditions.
- Western blotting of immunoprecipitated aromatase to detect changes in protein phosphorylation (serine, threonine, tyrosine).
- Cloning, sequencing, and bioinformatic analysis of quail aromatase to identify potential phosphorylation sites.
Main Results:
- Ca2+-dependent protein phosphorylation, involving protein kinase C (PKC), and potentially PKA and CAMK, rapidly down-regulates aromatase activity.
- Phosphorylation directly modifies the aromatase molecule, increasing levels of phosphorylated serine, threonine, and tyrosine residues.
- Quail aromatase sequence analysis revealed 15 predicted phosphorylation sites, with Thr455 and Thr486 matching consensus sequences for kinases affecting activity.
Conclusions:
- Multiple protein kinases, including PKC, rapidly modulate aromatase activity in the brain through direct phosphorylation of the enzyme.
- Phosphorylation of specific residues, likely Thr455 and/or Thr486, underlies the rapid down-regulation of aromatase activity.
- This provides a novel, rapid regulatory pathway for aromatase activity in the brain distinct from slower transcriptional control.