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Multiple phospholipase activation by OX(1) orexin/hypocretin receptors
L Johansson1, M E Ekholm, J P Kukkonen
1Department of Neuroscience, Unit of Physiology, Uppsala University, Uppsala, Sweden.
Cellular and Molecular Life Sciences : CMLS
|May 20, 2008
Summary
Orexin-1 receptors activate multiple phospholipases, generating diacylglycerol via Phospholipase D and C pathways. Different concentrations reveal distinct phospholipase C activities, influencing downstream signaling.
Area of Science:
- Cellular signaling and receptor pharmacology
- Biochemistry of lipid metabolism
Background:
- Orexin receptors (OX1) are G protein-coupled receptors involved in various physiological processes.
- Phospholipase activation is a key mechanism in cellular signal transduction pathways.
Purpose of the Study:
- To investigate the coupling of OX1 receptors to phospholipase activation.
- To characterize diacylglycerol generation pathways downstream of OX1 receptor stimulation.
- To elucidate the specific phospholipase activities involved at varying orexin-A concentrations.
Main Methods:
- Biochemical assays to measure enzyme activity.
- Real-time fluorescence methods for dynamic cellular response monitoring.
- Experiments conducted in Chinese hamster ovary (CHO) cells.
Main Results:
- Low orexin-A concentrations activate Phospholipase D, producing diacylglycerol.
- Higher orexin-A concentrations activate Phospholipase C, hydrolyzing phosphatidylinositol (PI) or phosphatidylinositol monophosphate (PIP).
- Further increased orexin-A concentrations activate Phospholipase C to hydrolyze phosphatidylinositol bisphosphate (PIP(2)), releasing diacylglycerol and inositol-1,4,5-trisphosphate.
Conclusions:
- OX1 receptors couple to multiple phospholipase activities, including Phospholipase D and at least two distinct Phospholipase C activities.
- Diacylglycerol and phosphatidic acid are preferred products at low agonist concentrations.
- Activated Phospholipase C primarily increases diacylglycerol rather than inositol-1,4,5-trisphosphate at lower concentrations.
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