Regulation of serotonin-2C receptor G-protein coupling by RNA editing

Abstract

The neurotransmitter serotonin (5-hydroxytryptamine, 5-HT) elicits a wide array of physiological effects by binding to several receptor subtypes. The 5-HT2 family of receptors belongs to a large group of seven-transmembrane-spanning G-protein-coupled receptors and includes three receptor subtypes (5-HT2A, 5-HT(2B) and 5-HT(2C)) which are linked to phospholipase C, promoting the hydrolysis of membrane phospholipids and a subsequent increase in the intracellular levels of inositol phosphates and diacylglycerol. Here we show that transcripts encoding the 2C subtype of serotonin receptor (5-HT(2C)R) undergo RNA editing events in which genomically encoded adenosine residues are converted to inosines by the action of double-stranded RNA adenosine deaminase(s). Sequence analysis of complementary DNA isolates from dissected brain regions have indicated the tissue-specific expression of seven major 5-HT(2C) receptor isoforms encoded by eleven distinct RNA species. Editing of 5-HT(2C)R messenger RNAs alters the amino-acid coding potential of the predicted second intracellular loop of the receptor and can lead to a 10-15-fold reduction in the efficacy of the interaction between receptors and their G proteins. These observations indicate that RNA editing is a new mechanism for regulating serotonergic signal transduction and suggest that this post-transcriptional modification may be critical for modulating the different cellular functions that are mediated by other members of the G-protein-coupled receptor superfamily.

Editor meets silencer: crosstalk between RNA editing and RNA interference

“…3a). Emeson and colleagues discovered a total of five A→I RNA editing sites located in the second intracellular loop or G-protein-coupling domain of 5-HT 2C R 55 . Combinatorial editing of the five sites results in changes in three codons, Ile, Asn and Ile, to possibly six different amino-acid residues, resulting in the expression of up to 24 receptor isoforms with altered G-protein-coupling functions.…”

“…Q/R-site editing also regulates the tetramerization and intracellular trafficking of the receptor protein 111 . b | Serotonin receptors have important roles in physiological and behavioural processes such as circadian rhythms, emotional control and feeding behaviour 55,64 . G-protein-coupling functions of serotonin (5-HT) receptor-2C (5-HT 2C R) are dramatically reduced by A→I RNA editing that occurs at five sites (A, B, C, D and E sites).…”

“…G-protein-coupling functions of serotonin (5-HT) receptor-2C (5-HT 2C R) are dramatically reduced by A→I RNA editing that occurs at five sites (A, B, C, D and E sites). For example, the potency of the agonist-stimulated G-proteincoupling activity of the fully edited receptor isoform (Val-Gly-Val) is reduced by 20-fold compared with the unedited receptor isoform (Ile-Asn-Ile) 50,55 . The fold-back double-stranded (ds)RNA structure, which consists of short dsRNA regions, bulges and loops, is formed because of partial complementarity of the exon and intronic editing-site complementary sequence (ECS; which is essential for editing).…”

Increased serotonin 2C receptor mRNA editing: a possible risk factor for suicide

“…16,17 A limited number of gene transcripts (B30), mostly those that encode channels and neurotransmitter receptors (for example, mammalian glutamate receptors, 5-HT 2C R, potassium channel Kv1.1, and Drosophila melanogaster sodium channel), have been identified to date. [18][19][20][21] When editing occurs within a coding region, it has the potential to alter codon specificity because the ribosome reads inosine as guanosine (G) resulting in altered amino-acid sequence and potentially protein function. In most cases, edited and unedited versions of a given receptor/channel coexist expanding the functional range of the receptor population.…”

“…ADAR3 is expressed exclusively in the brain; however, its catalytic substrate has not been identified. 23 5-HT 2C R mRNA is edited at five closely spaced adenosine residues (termed A, B, E, C and D editing sites), allowing for the generation of 32 different mRNA variants and 24 different protein isoforms of the receptor, ranging from the unedited Ile156-Asn158-Ile160 (INI) isoform to the fully edited Val156-Gly158-Val160 (VGV) isoform 18 (Figure 1). Pharmacological studies have shown that the unedited isoform, INI, possesses considerable constitutive activity-an ability to spontaneously activate intracellular signaling pathways in the absence of agonist stimulation.…”