The 5' Untranslated Regions of the Rat A_2A Adenosine Receptor Gene Function as Negative Translational Regulators

Abstract

Abstract:The rat A 2A adenosine receptor (A 2A -R) gene contains two promoters, P1 and P2, which produce transcript 1 and transcript 2, respectively. These transcripts differ in the lengths of their 5Ј untranslated regions (5ЈUTR1: 514 bp, initiated from P1; 5ЈUTR2: 221 bp, initiated from P2) but encode the same protein. In the present study, we demonstrate that transcript 2 is present in various tissues at different levels, whereas transcript 1 is found only in the striatum. In the striatum, the level of transcript 2 is ϳ300-fold higher than that of transcript 1. The 5ЈUTR of both transcripts suppresses the expression of A 2A -R and a firefly luciferase reporter gene at the translational level; this suppression is not observed after mutational inactivation of an "out-offrame" upstream AUG codon. Translational suppression by the 5ЈUTR was also confirmed in cells using a bicistronic strategy. Collectively, these data suggest that P2 is the major promoter of the rat A 2A -R gene. The 5ЈUTR of the rat A 2A -R gene exerts an inhibitory effect on translation by an upstream open reading frame. Because the 5ЈUTR of the A 2A -R gene possesses strong interspecies homology, translational suppression may be a general mechanism by which the expression of the A 2A -R gene is regulated.