Synergistic upregulation of erythropoietin receptor (EPO-R) expression by sense and antisense EPO-R transcripts in the canine lung.

We previously found increased erythropoietin receptor (EPO-R) protein levels in vigorously growing canine lungs after pneumonectomy (PNX), suggesting a role for paracrine EPO signaling in lung growth and remodeling. Now we find that sense and antisense EPO-R transcripts (sEPO-R and asEPO-R, respectively) are concordantly up-regulated in the post-PNX remaining lung, leading to the hypothesis that sEPO-R and asEPO-R interactions enhance EPO signaling during lung growth. We cloned a canine asEPO-R cDNA, which is fully complementary to the sense strand of the EPO-R gene from 2.5kb 3' to the sense stop codon, and extends into the 5' UTR of the sEPO-R transcript. Both asEPO-R and sEPO-R transcripts colocalize with EPO-R protein in the same lung cells. In cultured human embryonic kidney (HEK293) cells, transfection with sEPO-R (+FLAG tag) cDNA alone increased EPO-R protein expression (anti-EPO-R and anti-FLAG). At constant sEPO-R cDNA levels, cotransfection with escalating asEPO-R cDNA further increased recombinant EPO-R protein expression. The asEPO-R transcript harbors two putative opening reading frames (ORFs). Separate transfection of each asEPO-R ORF cDNA resulted in differential stimulatory effects on EPO-R protein expression. We conclude that both sEPO-R and asEPO-R transcripts contribute to in vivo up-regulation of EPO-R protein expression in the post-PNX remaining lung. This demonstrates synergism between sense-antisense EPO-R transcripts in response to physiological stimulation in a robust model of induced lung growth.