Insulin signaling inhibits the 5-HT2C receptor in choroid plexus via MAP kinase.
BACKGROUND
G protein-coupled receptors (GPCRs) interact with heterotrimeric GTP-binding proteins (G proteins) to modulate acute changes in intracellular messenger levels and ion channel activity. In contrast, long-term changes in cellular growth, proliferation and differentiation are often mediated by tyrosine kinase receptors and certain GPCRs by activation of mitogen-activated protein (MAP) kinases. Complex interactions occur between these signaling pathways, but the specific mechanisms of such regulatory events are not well-understood. In particular it is not clear whether GPCRs are modulated by tyrosine kinase receptor-MAP kinase pathways.


RESULTS
Here we describe tyrosine kinase receptor regulation of a GPCR via MAP kinase. Insulin reduced the activity of the 5-HT2C receptor in choroid plexus cells which was blocked by the MAP kinase kinase (MEK) inhibitor, PD 098059. We demonstrate that the inhibitory effect of insulin and insulin-like growth factor type 1 (IGF-1) on the 5-HT2C receptor is dependent on tyrosine kinase, RAS and MAP kinase. The effect may be receptor-specific: insulin had no effect on another GPCR that shares the same G protein signaling pathway as the 5-HT2C receptor. This effect is also direct: activated MAP kinase mimicked the effect of insulin, and removing a putative MAP kinase site from the 5-HT2C receptor abolished the effect of insulin.


CONCLUSIONS
These results show that insulin signaling can inhibit 5-HT2C receptor activity and suggest that MAP kinase may play a direct role in regulating the function of a specific GPCR.
Hurley
Joyce H
JH
Department of Biochemistry and Molecular Biology, Indiana University School of Medicine, Indianapolis, Indiana, USA. johurley@iupui.edu
Zhang
Shengwen
S
Bye
Leighan S
LS
Marshall
Mark S
MS
DePaoli-Roach
Anna A
AA
Guan
Kunliang
K
Fox
Aaron P
AP
Yu
Lei
L
D000818:Animals; D002478:Cells, Cultured; D002831:Choroid Plexus / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I; D008297:Male; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D018408:Patch-Clamp Techniques; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D044405:Receptor, Serotonin, 5-HT2C / Q000235:genetics / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000037:antagonists & inhibitors / Q000378:metabolism; D058830:Serotonin 5-HT2 Receptor Antagonists; D015398:Signal Transduction / Q000502:physiology*; D014981:Xenopus; D018631:ras Proteins / Q000378:metabolism
D004791:Enzyme Inhibitors; D005419:Flavonoids; D007328:Insulin; D044405:Receptor, Serotonin, 5-HT2C; D043562:Receptors, G-Protein-Coupled; D058830:Serotonin 5-HT2 Receptor Antagonists; D007334:Insulin-Like Growth Factor I; D011505:Protein-Tyrosine Kinases; D020928:Mitogen-Activated Protein Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D018631:ras Proteins; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one