Alternative splicing of the ADAR1 transcript in a region that functions either as a 5′-UTR or an ORF

Abstract

The ADAR enzymes mediate the hydrolytic deamination of adenosines in specific RNA substrates and thereby diversify both the transcriptome and the proteome in metazoan species. Three promoters drive the transcription from the ADAR1 gene yielding the ADAR1-A, -B, and -C transcripts, which, in turn, lead to the production of two protein isoforms, namely, iADAR1 and cADAR1. In this study, we establish the presence of a previously unidentified alternative intron within the 59-end of the common second exon of mRNAs encoding ADAR1 in primate species-a region that can function either as a 59-UTR or an ORF. In addition, it is shown that the relative expression of the three promoter-specific ADAR1 transcripts is tissue specific and that the novel intron is excised from all transcripts, but at different relative levels indicating a specific regulation of the alternative splicing. Finally, possible functional consequences of the splicing are investigated. From these studies, we conclude that the alternatively spliced ADAR1-A transcript is immune to nonsense-mediated decay although it is a potential substrate. Moreover, this transcript is associated with translating ribosomes, which suggests that a truncated version of iADAR1 is expressed.

PTBP1 induces ADAR1 p110 isoform expression through IRES-like dependent translation control and influences cell proliferation in gliomas

“…A 136-nt alternative intron was identified within the ADAR1 p150 transcripts between AUG1 and AUG2 in a previous study [26] that could generate other isoforms (approximately, 144 kDa). Splice variants of a large number of genes could exhibit abnormal expression in GBM cells, such as GLI1 [27].…”

“…It has been reported that three different promoters control the transcriptional levels of the human ADAR1 gene [23][24][25][26] (Fig. 1a).…”

Activity Regulation of Adenosine Deaminases Acting on RNA (ADARs)

“…2) [63,64]. Two of these promoters (1B and 1C) are constitutive promoters that drive the expression of transcripts that encode a short version (931 aa) of the ADAR1 protein (ADAR1S, cADAR1 or p110), while the third (1A) is an interferon-induced promoter that drives the expression of transcripts that encode an N-terminally extended form (1226 aa) of ADAR1 (ADAR1L, iADAR1 or p150) [48,61,63,65]. Only the interferon-inducible ADAR1 transcript contains a translation initiation codon in exon 1, [63], while the two constitutively expressed forms of ADAR1 start at the downstream AUG296 codon that is present in exon 2 [48,61].…”

“…Only the interferon-inducible ADAR1 transcript contains a translation initiation codon in exon 1, [63], while the two constitutively expressed forms of ADAR1 start at the downstream AUG296 codon that is present in exon 2 [48,61]. The relative expression of the three promoter-specific ADAR1 transcripts is tissue specific [65]. In the human brain, a constitutively high expression of ADAR1 is driven by promoter 1B, and a negligible expression results from promoter 1C.…”

ADARs: allies or enemies? The importance of A‐to‐I RNA editing in human disease: from cancer to HIV‐1

“…In addition to its complex transcriptional control with multiple promoters, ADAR1 expression is further complicated by the presence of several splicing events; in fact, in addition to the alternatively spliced exon 1A‐C discussed above, ADAR1 pre‐mRNA undergoes numerous splicing events, some of which either include or delete amino acids that are important for enzymatic activity (George, Wagner & Samuel, 2005; Liu et al , 1997; Lykke‐Andersen, Pinol‐Roma & Kjems, 2007; Patterson & Samuel, 1995). Recently, a new alternative intron has been found within the coding exon 2 (exon position 243–378nt) (Cenci et al , 2008; Lykke‐Andersen et al , 2007). Interestingly, this new splicing event partly overlaps the promoter activity previously identified in this exon (position 216–333nt) (Kawakubo & Samuel, 2000).…”