Related Experiment Videos
D(4) dopamine receptor differentially regulates Akt/nuclear factor-kappa b and extracellular signal-regulated kinase
1Laboratory of Molecular Pharmacology, Department of Pharmacology and Physiology, MCP Hahnemann School of Medicine, Philadelphia, Pennsylvania, USA.
Abstract:
The present study was designed to investigate the role of D(4) dopamine receptors in regulating the Akt/nuclear factor-kappa B (NF-kappa B) and extracellular signal-regulated kinase (ERK) signaling pathways. The D(4) dopamine receptor agonist PD168077 induced time- and dose-dependent activation of Akt and ERK in D(4)MN9D cells that stably express D(4) dopamine receptors. Maximal Akt and ERK stimulation was achieved at 1 microM PD168077. The agonist-mediated stimulations of Akt and ERK were abolished when cells were preincubated with 50 ng/ml PTX or with 1 microM L745,870, a D(4) dopamine receptor antagonist, indicating that activation of the Akt or ERK pathways is mediated by D(4) dopamine receptors and require a pertussis toxin-sensitive G protein. We also detected a time- and dose-dependent activation of NF-kappa B. Activation of NF-kappa B by 1 microM PD168077 was attenuated in D(4)MN9D cells that were transfected with a kinase-deficient Akt but not in cells transfected with a dominant negative Ras (N17Ras), suggesting that NF-kappa B activation requires Akt but is independent of Ras. In contrast, the transfection of N17Ras into D(4)MN9D cells blunted D(4) dopamine receptor-mediated ERK activation, indicating a Ras-dependent mechanism. Moreover, PP2 (20 nM), an inhibitor of Src, blocked D(4) receptor-mediated SHC phosphorylation and ERK activation. In contrast, transfection of a kinase-dead Akt did not alter D(4) receptor-stimulated ERK. However, PP2 and the mitogen activated protein kinase kinase inhibitor PD98059 did not change D(4) receptor-mediated Akt/NF-kappa B activation. All these indicate that distinct mechanisms mediate ERK and Akt/NF-kappa B activation by D(4) dopamine receptor stimulation. We also demonstrated that D(4) receptor-stimulated cell proliferation is mediated by the Src/SHC/Ras/ERK pathway.
Insights
Dopamine D4 receptors activate Akt and ERK pathways through distinct mechanisms. D4 receptor stimulation also drives cell proliferation via the Src/SHC/Ras/ERK pathway, highlighting key signaling roles.
Area of Science:
- Neuropharmacology
- Molecular Biology
- Cell Signaling
Background:
- Dopamine receptors, particularly the D4 subtype, are implicated in various neurological functions.
- Understanding the downstream signaling pathways regulated by D4 dopamine receptors is crucial for elucidating their physiological roles.
- The Akt and extracellular signal-regulated kinase (ERK) pathways are critical for cell survival, proliferation, and differentiation.
Purpose of the Study:
- To investigate the role of D4 dopamine receptors in regulating the Akt/nuclear factor-kappa B (NF-kappa B) and ERK signaling pathways.
- To delineate the specific molecular mechanisms underlying D4 receptor-mediated activation of these signaling cascades.
- To determine the involvement of D4 receptor signaling in cell proliferation.
Main Methods:
- Utilized D4MN9D cells stably expressing D4 dopamine receptors.
- Administered D4 dopamine receptor agonist PD168077 and antagonist L745,870.
- Employed pertussis toxin (PTX) treatment, transfection with kinase-deficient Akt and dominant-negative Ras (N17Ras), and inhibitors like PP2 and PD98059.
- Assessed activation of Akt, ERK, NF-kappa B, and SHC phosphorylation.
Main Results:
- D4 dopamine receptor agonist PD168077 dose- and time-dependently activated Akt and ERK pathways.
- Activation of Akt and ERK was mediated by D4 receptors and required a pertussis toxin-sensitive G protein.
- NF-kappa B activation was dependent on Akt but independent of Ras, while ERK activation was Ras-dependent.
- Src kinase activity was essential for D4 receptor-mediated SHC phosphorylation and ERK activation.
- Distinct signaling mechanisms mediate Akt/NF-kappa B and ERK activation by D4 receptors.
- D4 receptor-stimulated cell proliferation is driven by the Src/SHC/Ras/ERK pathway.
Conclusions:
- D4 dopamine receptor stimulation differentially regulates Akt/NF-kappa B and ERK signaling pathways through distinct mechanisms.
- The Src/SHC/Ras/ERK pathway is critical for D4 receptor-mediated cell proliferation.
- These findings provide novel insights into the complex signaling networks governed by D4 dopamine receptors.