RNA editing of the human serotonin 5-hydroxytryptamine 2C receptor silences constitutive activity.
RNA transcripts encoding the serotonin 5-hydroxytryptamine 2C (5-HT2C) receptor (5-HT2CR) undergo adenosine-to-inosine RNA editing events at up to five specific sites. Compared with rat brain, human brain samples expressed higher levels of RNA transcripts encoding the amino acids valine-serine-valine (5-HT2C-VSV) and valine-glycine-valine (5-HT2C-VGV) at positions 156, 158, and 160, respectively. Agonist stimulation of the nonedited human receptor (5-HT2C-INI) and the edited 5-HT2C-VSV and 5-HT2C-VGV receptor variants stably expressed in NIH-3T3 fibroblasts demonstrated that serotonergic agonists were less potent at the edited receptors. Competition binding experiments revealed a guanine nucleotide-sensitive serotonin high affinity state only for the 5-HT2C-INI receptor; the loss of high affinity agonist binding to the edited receptor demonstrates that RNA editing generates unique 5-HT2CRs that couple less efficiently to G proteins. This reduced G protein coupling for the edited isoforms is primarily due to silencing of the constitutive activity of the nonedited 5-HT2CR. The distinctions in agonist potency and constitutive activity suggest that different edited 5-HT2CRs exhibit distinct responses to serotonergic ligands and further imply that RNA editing represents a novel mechanism for controlling physiological signaling at serotonergic synapses.
Niswender
C M
CM
Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232-6600, USA.
Copeland
S C
SC
Herrick-Davis
K
K
Emeson
R B
RB
Sanders-Bush
E
E
D016475:3T3 Cells; D000241:Adenosine / Q000378:metabolism; D000818:Animals; D001667:Binding, Competitive; D001923:Brain Chemistry; D006801:Humans; D007288:Inosine / Q000378:metabolism; D007536:Isomerism; D051379:Mice; D017393:RNA Editing; D051381:Rats; D044405:Receptor, Serotonin, 5-HT2C; D011985:Receptors, Serotonin / Q000378:metabolism*
D044405:Receptor, Serotonin, 5-HT2C; D011985:Receptors, Serotonin; D007288:Inosine; D000241:Adenosine