The A2A Adenosine Receptor Is a Dual Coding Gene A NOVEL MECHANISM OF GENE USAGE AND SIGNAL TRANSDUCTION

Background:Adora2a encodes A(2A) adenosine receptor (A(2A)R) and a new protein (uORF5) translated from an out-of-frame AUG. Results: uORF5 exists in tissues where the Adora2a transcript is detected and is up-regulated by A(2A)R activation. uORF5 suppresses AP1-mediated transcription. Conclusion:Adora2a encodes two distinct proteins (A(2A)R and uORF5) in an A(2A)R-dependent manner. Significance: uORF5 may participate in the functions of A(2A)R during pathophysiological conditions. The A(2A) adenosine receptor (A(2A)R) is a G protein-coupled receptor and a major target of caffeine. The A(2A)R gene encodes alternative transcripts that are initiated from at least two independent promoters. The different transcripts of the A(2A)R gene contain the same coding region and 3-untranslated region and different 5-untranslated regions that are highly conserved among species. We report here that in addition to the production of the A(2A)R protein, translation from an upstream, out-of-frame AUG of the rat A(2A)R gene produces a 134-amino acid protein (designated uORF5). An anti-uORF5 antibody recognized a protein of the predicted size of uORF5 in PC12 cells and rat brains. Up-regulation of A(2A)R transcripts by hypoxia led to increased levels of both the A(2A)R and uORF5 proteins. Moreover, stimulation of A(2A)R increased the level of the uORF5 protein via post-transcriptional regulation. Expression of the uORF5 protein suppressed the AP1-mediated transcription promoted by nerve growth factor and modulated the expression of several proteins that were implicated in the MAPK pathway. Taken together, our results show that the rat A(2A)R gene encodes two distinct proteins (A(2A)R and uORF5) in an A(2A)R-dependent manner. Our study reveals a new example of the complexity of the mammalian genome and provides novel insights into the function of A(2A)R.