RNA-editing of the 5-HT(2C) receptor alters agonist-receptor-effector coupling specificity.
1. The serotonin(2C) (5-HT(2C)) receptor couples to both phospholipase C (PLC)-inositol phosphate (IP) and phospholipase A(2) (PLA(2))-arachidonic acid (AA) signalling cascades. Agonists can differentially activate these effectors (i.e. agonist-directed trafficking of receptor stimulus) perhaps due to agonist-specific receptor conformations which differentially couple to/activate transducer molecules (e.g. G proteins). Since editing of RNA transcripts of the human 5-HT(2C) receptor leads to substitution of amino acids at positions 156, 158 and 160 of the putative second intracellular loop, a region important for G protein coupling, we examined the capacity of agonists to activate both the PLC-IP and PLA(2)-AA pathways in CHO cells stably expressing two major, fully RNA-edited isoforms (5-HT(2C-VSV), 5-HT(2C-VGV)) of the h5-HT(2C) receptor. 2. 5-HT increased AA release and IP accumulation in both 5-HT(2C-VSV) and 5-HT(2C-VGV) expressing cells. As expected, the potency of 5-HT for both RNA-edited isoforms for both responses was 10 fold lower relative to that of the non-edited receptor (5-HT(2C-INI)) when receptors were expressed at similar levels. 3. Consistent with our previous report, the efficacy order of two 5-HT receptor agonists (TFMPP and bufotenin) was reversed for AA release and IP accumulation at the non-edited receptor thus demonstrating agonist trafficking of receptor stimulus. However, with the RNA-edited receptor isoforms there was no difference in the relative efficacies of TFMPP or bufotenin for AA release and IP accumulation suggesting that the capacity for 5-HT(2C) agonists to traffic receptor stimulus is lost as a result of RNA editing. 4. These results suggest an important role for the second intracellular loop in transmitting agonist-specific information to signalling molecules.
Berg
K A
KA
Department of Pharmacology, Mail Code 7764, University of Texas Health Science Center, San Antonio, Texas, TX 78229-3900, USA. berg@uthscsa.edu
Cropper
J D
JD
Niswender
C M
CM
Sanders-Bush
E
E
Emeson
R B
RB
Clarke
W P
WP
D000662:Amphetamines / Q000494:pharmacology; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D001667:Binding, Competitive / Q000187:drug effects; D002027:Bufotenin / Q000494:pharmacology; D016466:CHO Cells; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D004873:Ergolines / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D008238:Lysergic Acid Diethylamide / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011814:Quipazine / Q000494:pharmacology; D017393:RNA Editing; D011869:Radioligand Assay; D044405:Receptor, Serotonin, 5-HT2C; D011985:Receptors, Serotonin / Q000235:genetics / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000378:metabolism* / Q000494:pharmacology; D014316:Tritium
D000662:Amphetamines; D004873:Ergolines; D007295:Inositol Phosphates; D010879:Piperazines; D020033:Protein Isoforms; D044405:Receptor, Serotonin, 5-HT2C; D011985:Receptors, Serotonin; D017366:Serotonin Receptor Agonists; D002027:Bufotenin; D014316:Tritium; C018406:1-(3-trifluoromethylphenyl)piperazine; D016718:Arachidonic Acid; D012701:Serotonin; D011814:Quipazine; D008238:Lysergic Acid Diethylamide; C015952:4-iodo-2,5-dimethoxyphenylisopropylamine; C031649:mesulergine