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Published on: July 16, 2013
Reduction of dopamine beta-hydroxylase gene expression by calcium in bovine chromaffin cells
1Department of Biochemistry, University of Ulsan College of Medicine, Seoul, Korea.
Abstract:
We determined the effect of Ca++ influx on dopamine beta-hydroxylase (DBH) gene expression in primary cultured bovine chromaffin cells. The Ca++ ionophore A23187 (100nM) specifically reduced DBH mRNA to 15 +/- 10% of the untreated control while tyrosine hydroxylase was induced (142 +/- 15%) and phenylethanolamine N-methyltransferase was unchanged (107 +/- 11%). This effect on DBH was also observed with ionomycin, reversed by EGTA and unaffected by cycloheximide. Depolarization by potassium also resulted in DBH reduction which was reversed by the voltage dependent Ca++ channel blockers nifedipine and verapamil. DBH mRNA level reduced by A23187 could be re-induced by forskolin and DBH induced by forskolin could be reduced by the ionophore, suggesting that the cAMP and Ca++ pathways might act independently in regulating DBH gene expression.
Insights
Calcium influx significantly reduces dopamine beta-hydroxylase (DBH) gene expression in bovine chromaffin cells. This effect is independent of protein synthesis and suggests distinct cAMP and calcium signaling pathways regulate DBH.
Area of Science:
- Neuroscience
- Molecular Biology
- Cell Biology
Background:
- Dopamine beta-hydroxylase (DBH) is crucial for catecholamine biosynthesis.
- Regulation of DBH gene expression is vital for neuronal function.
- Calcium (Ca++) influx is a key signaling mechanism in chromaffin cells.
Purpose of the Study:
- To investigate the impact of Ca++ influx on DBH gene expression.
- To elucidate the signaling pathways involved in DBH regulation.
Main Methods:
- Primary cultured bovine chromaffin cells were used.
- Cells were treated with Ca++ ionophores (A23187, ionomycin), potassium depolarization, and channel blockers (nifedipine, verapamil).
- Messenger RNA (mRNA) levels of DBH, tyrosine hydroxylase, and phenylethanolamine N-methyltransferase were quantified.
Main Results:
- A23187 significantly reduced DBH mRNA levels to 15% of control.
- Tyrosine hydroxylase was induced (142%), while phenylethanolamine N-methyltransferase remained unchanged (107%).
- Potassium-induced depolarization also reduced DBH, an effect blocked by nifedipine and verapamil.
- Forskolin could re-induce DBH mRNA, and A23187 reduced forskolin-induced DBH, indicating independent cAMP and Ca++ pathways.
Conclusions:
- Ca++ influx, via voltage-dependent channels, actively suppresses DBH gene expression.
- The cAMP and Ca++ signaling pathways appear to regulate DBH expression independently.
- These findings offer insights into the complex molecular mechanisms controlling catecholamine synthesis.
