Modulation of the rat angiotensin type 1a receptor by an upstream short open reading frame.

The rat angiotensin type 1a receptor (ATR) is a peptide hormone G protein-coupled receptor (GPCR) that plays a key role in electrolyte homeostasis and blood pressure control. There is a highly conserved short open reading frame (sORF) in exon 2 (E2) that is downstream from exon 1 (E1) and upstream of the ATR coding region located in exon 3 (E3). To determine the role of this E2 sORF in ATR signaling, human embryonic kidney-293 (HEK293) cells were transfected with plasmids containing ATR cDNA with either an intact or disrupted E2 sORF. The intact sORF attenuated the efficacy of angiotensin (Ang) II (p < 0.001) and sarcosine,Ile,Ile-Ang II (SII), (p < 0.01) to activate ATR signaling through extracellular signal-related kinases 1/2 (ERK1/2). A time-course showed agonist-induced ATR-mediated ERK1/2 activation was slower in the presence of the intact compared to the disrupted sORF [Ang II: p < 0.01 and SII: p < 0.05]. Ang II-induced ERK1/2 activation was completely inhibited by the protein kinase C (PKC) inhibitor Ro 31-8220 regardless of whether the sORF was intact or disrupted. Flow cytometric analyses suggested the intact sORF improved cell survival; the percentage of live cells increased (p < 0.05) while the percentage of early apoptotic cells decreased (p < 0.01) in cells transfected with the ATR plasmid containing the intact sORF. These findings have implications for the regulation of ATRs in physiological and pathological conditions and warrant investigation of sORFs in the 5' leader sequence (5'LS) of other GPCRs.