Serotonin 2C Receptor (5-HT2CR) mRNA Editing–Induced Down-Regulation of 5-HT2CR Function in Xenopus Oocytes: the Significance of Site C Editing

Abstract

Abstract. Serotonin 2C receptor (5-HT2CR) mRNA receives editing at 5 nucleotide positions (sites A -E) located in the sequence encoding the second intracellular loop of 5-HT2CR. 5-HT2CR mRNA without editing and with editing at sites AB, ABD, ABC, ABCD, and C are translated to 6 isoforms of 5-HT2CR: INI(non-edited), VNI(AB), VNV(ABD), VSI(ABC), VSV(ABCD), and ISI(C), respectively. In this study, we investigated electrophysiologically the ability of these isoforms to couple with the G protein / phospholipase C (PLC) system using Xenopus oocytes injected with edited 5-HT2CR RNAs and muscarinic M 1 receptor (M1R) RNA. The efficacy with which 5-HT stimulated each isoform was calculated by comparing 5-HT-induced current with 100 μ M acetylcholine-induced M1R current. Stimulation with 5-HT of INI(non-edited), VNI(AB), VNV(ABD), VSI(ABC), VSV(ABCD), and ISI(C) expressed in Xenopus oocytes showed concentration-dependent responses with EC 50 values of 8.6, 17.2, 76,5, 22.0, 91.2, and 20.3 nM, respectively. No significant difference in the ability of 5-HT to induce currents among the oocytes expressing these isoforms was detected, but in the oocytes expressing VSI(ABC) or VSV(ABCD), 5-HT had a significantly reduced ability to induce currents. These results suggest that editing at site C together with sites A and B and/or D markedly reduces 5-HT2CR function by generating isoforms with reduced ability to activate PLC.

Serotonin 2c receptor RNA editing in major depression and suicide

“…Similarly, editing efficiency at sites A, B, E, C, and D (analyzed as repeated measures) was lower in MDD NoSuic compared with two other groups. In contrast, the frequencies of the nonedited ( NONE ) variant and the AD variant that encode high-functioning receptor isoforms (Niswender et al 1999; Wang et al 2000b; Tohda et al 2010) were higher in MDD NoSuic than in NC or MDD Suic (Figure 3). There were no significant differences between NC and MDD Suic .…”

“…Specifically, the sum of frequencies of all transcripts edited at the E or C sites, and the frequency of the most abundant mRNA variant, ABCD (Figure 3), which collectively represent a population of the low-functioning receptor isoforms (Niswender et al 1999; Wang et al 2000b; Tohda et al 2010), were lower in MDD NoSuic compared with NC and MDD Suic . Similarly, editing efficiency at sites A, B, E, C, and D (analyzed as repeated measures) was lower in MDD NoSuic compared with two other groups.…”

“…On average, 561,291 ± 55,851 (Mean ± SE) reads were obtained for each subject, thus providing reliable (with 99% probability) detection of even the rarest editing variants, with abundance of < 0.001% (Morabito et al 2010). The mean values of frequencies of the mRNA variants and efficiencies of editing at each of the five editing sites within each of the study groups (NC, MDD Suic , MDD NoSuic ) are shown in Table II and in Supplementary Table 2, respectively In addition, because previous studies suggested that editing at the E or C sites by themselves or in combination with other sites is sufficient to markedly reduce 5-HT 2C R function (Niswender et al 1999; Wang et al 2000b; Tohda et al 2010), we computed and analyzed frequencies of editing at the E or C sites. As in our earlier studies of human DLPFC (Dracheva et al 2008), only six of the variants, which contained editing combinations ABCD, ABD, NONE, A, AD , and ACD , were observed at ∼5% or greater frequency in all three study groups (Table II).…”

Changes in the expression of BNIP-3 and other neuronal factors during the cultivation period of primary cultured rat cerebral cortical neurons and an assessment of each factor's functions

“…Based on these observations, it may be hypothesized that some of the factors produced by the 5-HT2CR mRNA at day 15 serve physiological roles at the moment of synaptogenesis. Many reports have mentioned the various phenomena of 5-HT2CR mRNA, including the short variant of RNA [7,17], the generation of the 95-nt fragment from the 5-HT2CR mRNA [17], the existence of the binding site for MBII-52 (a type of small RNA) [18], and the functional regulation of 5-HT2CR activity via RNA editing [19]. The 5-HT2CR mRNA product may serve an important function during the synaptic joining.…”

Serotonin 2C Receptor as a Superhero: Diversities and Talents in the RNA Universe for Editing, Variant, Small RNA and Other Expected Functional RNAs

“…Among 5 editing sites, the editing frequencies at the A and B sites are kept low in the rat brain during fetal development, but these are approximately completely edited from just after birth (29). Under full editing of the A/B site, namely, in the brain after birth, it is suggested that editing of the C site decides the strength of the 5-HT2C signal (30).…”