Serotonin-2C receptor pre-mRNA editing in rat brain and in vitro by splice site variants of the interferon-inducible double-stranded RNA-specific adenosine deaminase ADAR1.

The interferon-inducible RNA-specific adenosine deaminase (ADAR1) is an RNA editing enzyme implicated in the site-selective deamination of adenosine to inosine in cellular pre-mRNAs. The pre-mRNA for the rat serotonin-2C receptor (5-HT2CR) possesses four editing sites (A, B, C, and D), which undergo A-to-I nucleotide conversions that alter the signaling function of the encoded G-protein-coupled receptor. Measurements of 5-HT2CR pre-mRNA editing in vitro revealed site-specific deamination catalyzed by ADAR1. Three splice site variants, ADAR1-a, -b, and -c, all efficiently edited the A site of 5-HT2CR pre-mRNA, but the D site did not serve as an efficient substrate for any of the ADAR1 variants. Mutational analysis of the three double-stranded (ds) RNA binding motifs present in ADAR1 revealed a different relative importance of the individual dsRNA binding motifs for deamination of the A site of 5-HT2CR and synthetic dsRNA substrates. Quantitative reverse transcription-polymerase chain reaction analyses demonstrated that the 5-HT2CR pre-mRNA was most highly expressed in the choroid plexus of rat brain. However, ADAR1 and the related deaminase ADAR2 showed significant expression in all regions of the brain examined, including cortex, hippocampus, olfactory bulb, and striatum, where the 5-HT2CR pre-mRNA was extensively edited.