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Ras-dependent activation of fibroblast mitogen-activated protein kinase by 5-HT1A receptor via a G protein beta
M N Garnovskaya1, T van Biesen, B Hawe
1Department of Medicine (Nephrology and Cardiology), Duke University Medical Center, Durham, North Carolina, USA.
Abstract:
Serotonin (5-HT) is a potent mitogen in many cells types, an action which is frequently mediated through pertussis toxin-sensitive G proteins. In the current study, we used pharmacological inhibitors and dominant negative signaling constructs to delineate elements which participate in the activation of MAPK, a growth-associated mitogen-activated protein kinase, by human G protein-coupled 5-HT1A receptor transfected into CHO-K1 cells in a stable manner. The activation pathway does not directly involve phorbol ester-sensitive protein kinase C types, but does require (i) pertussis toxin-sensitive G protein beta gamma-subunits, (ii) a staurosporine- and genistein-sensitive protein kinase, (iii) phosphoinositide-3'-kinase activity, (iv) activation of Sos in a multimolecular complex that contains p46Shc, and p52Shc, and Grb2, (v) the GTPase p21Ras, and (vi) the protein kinase p74Raf-1. These data demonstrate that the 5-HT1A receptor mediates MAPK activity by convergence upon a common activation pathway that is shared with receptor tyrosine kinases.
Insights
Serotonin (5-HT) activates the mitogen-activated protein kinase (MAPK) pathway via the 5-HT1A receptor. This process involves specific G protein subunits and kinases, converging with receptor tyrosine kinase pathways.
Area of Science:
- Cellular signaling pathways
- Molecular biology
- Receptor pharmacology
Background:
- Serotonin (5-HT) acts as a mitogen in various cell types, often mediated by pertussis toxin-sensitive G proteins.
- Understanding the specific signaling cascades initiated by G protein-coupled receptors (GPCRs) like the 5-HT1A receptor is crucial for elucidating cellular growth regulation.
Purpose of the Study:
- To delineate the specific molecular components involved in the activation of mitogen-activated protein kinase (MAPK) by the human G protein-coupled 5-HT1A receptor.
- To investigate the signaling pathway downstream of the 5-HT1A receptor in a stably transfected CHO-K1 cell line.
Main Methods:
- Utilized pharmacological inhibitors and dominant-negative signaling constructs to probe the MAPK activation pathway.
- Employed stable transfection of CHO-K1 cells with the human 5-HT1A receptor for experimental analysis.
Main Results:
- MAPK activation by the 5-HT1A receptor does not directly involve protein kinase C (PKC) but requires pertussis toxin-sensitive G protein beta gamma-subunits.
- The pathway necessitates a staurosporine- and genistein-sensitive protein kinase, phosphoinositide-3'-kinase (PI3K) activity, and the activation of Sos within a complex containing Shc proteins and Grb2.
- p21Ras and p74Raf-1 are essential components, indicating a convergence of the 5-HT1A receptor pathway with receptor tyrosine kinase signaling.
Conclusions:
- The 5-HT1A receptor mediates MAPK activation through a defined pathway involving G protein subunits, PI3K, Ras/Raf signaling cascade.
- This pathway converges with signaling cascades typically activated by receptor tyrosine kinases, highlighting a shared mechanism for growth factor signaling.