Related Experiment Videos
Ras involvement in signal transduction by the serotonin 5-HT2B receptor
J M Launay1, G Birraux, D Bondoux
1Institut de Génétique et de Biologie Moléculaire et Cellulaire, Université L. Pasteur de Strasbourg, CNRS, INSERM, BP 163-67404 Illkirch Cedex, France.
Abstract:
The family of serotonin 5-HT2 receptors stimulates the phospholipase C second messenger pathway via the alpha subunit of the Gq GTP-binding protein. Here, we show that agonist stimulation of the 5-HT2B receptor subtype stably expressed in the mouse fibroblast LMTK- cell line causes a rapid and transient activation of the proto-oncogene product p21ras as measured by an increase in GTP-bound Ras in response to serotonin. Furthermore, 5-HT2B receptor stimulation activates p42mapk/p44mapk (ERK2/ERK1) mitogen-activated protein kinases as assayed by phosphorylation of myelin basic protein. Antibodies against p21ras, Galphaq, -beta, or -gamma2 subunits of the GTP-binding protein inhibit MAP kinase-dependent phosphorylation. The MAP kinase activation is correlated with a stimulation of cell division by serotonin. In addition to this mitogenic action, transforming activity of serotonin is mediated by the 5-HT2B receptor since its expression in LMTK- cells is absolutely required for foci formation and for these foci to form tumors in nude mice. Finally, we detected expression of the 5-HT2B receptor in spontaneous human and Mastomys natalensis carcinoid tumors and, similar to the 5-HT2B receptor transfected cells, the Mastomys tumor cells are also responsive to serotonin with similar coupling to p21ras activation.
Insights
Serotonin 5-HT2B receptor activation stimulates cell division and tumor formation by engaging the Ras/MAPK pathway. This pathway is implicated in carcinoid tumors, suggesting a role for serotonin signaling in cancer development.
Area of Science:
- Molecular Biology
- Cell Signaling
- Oncology
Background:
- Serotonin 5-HT2 receptors activate the Gq GTP-binding protein and phospholipase C.
- The 5-HT2B receptor subtype's role in cell signaling and oncogenesis is not fully understood.
Purpose of the Study:
- To investigate the signaling pathways downstream of the 5-HT2B receptor.
- To determine the role of 5-HT2B receptor in serotonin-induced cell proliferation and transformation.
- To examine 5-HT2B receptor expression in human and Mastomys natalensis carcinoid tumors.
Main Methods:
- Stable expression of 5-HT2B receptor in mouse fibroblast LMTK- cells.
- Measurement of GTP-bound Ras and MAPK phosphorylation.
- Inhibition studies using antibodies against G-protein subunits.
- Assessment of cell division, foci formation, and tumor growth in nude mice.
- Detection of 5-HT2B receptor expression in tumor tissues.
Main Results:
- Serotonin stimulation of 5-HT2B receptor rapidly activates p21ras and p42mapk/p44mapk (ERK1/2).
- MAP kinase activation is dependent on p21ras and Gq/Gbeta/Ggamma subunits.
- 5-HT2B receptor is required for serotonin-induced cell division, foci formation, and tumor growth.
- 5-HT2B receptor is expressed in carcinoid tumors, and tumor cells show serotonin-responsive p21ras activation.
Conclusions:
- The 5-HT2B receptor mediates serotonin's mitogenic and transforming activities through the Ras/MAPK pathway.
- 5-HT2B receptor signaling is relevant to carcinoid tumor biology and may represent a therapeutic target.