Orphan G protein-coupled receptor, GPR41, induces apoptosis via a p53/bax pathway during ischemic hypoxia and reoxygenation

Orphan receptors that couple to G protein without known ligands are conside red to relate directly to drug discovery, Here, we examine the expression o f various orphan receptors in H9c2 cells during ischemic hypoxia and reoxyg enation. Among orphan receptors examined, the level of G protein-coupled re ceptor 41 (GPR41) mRNA increases significantly, with a peak at 2 h after re oxygenation, and recovers to the control level by 3 h after reoxygenation. The level of glyceraldehyde-3-phosphate dehydrogenase mRNA used as an inter nal control remains almost constant. The levels of c-fos and c-jun mRNA inc rease significantly with ischemic hypoxia and reoxygenation. The transfecti on of GPR41 into H9c2 cells results in a significant decrease in cell numbe r, with DNA fragmentation observed by in vitro and in situ assay. The amoun t of p53 protein increases significantly in the nuclei of cells expressing GPR41, accompanying an increase in the transcriptional activity of p53. Con sistent with the activation of p53, the level of bat mRNA is significantly increased, which leads to an increase in Bar protein. Furthermore, the expr ession of a deletion mutant of a GPR41, which lacks the G protein binding s ite and shows an attenuation of intracellular phosphorylation signals to H9 c2 cells, inhibits cell death and the increase in p53 protein within 24 h a fter reoxygenation, These observations demonstrate that GPR41 is a novel re ceptor that activates p53 leading to apoptosis during reoxygenation after i schemic hypoxia in H9c2 cells. We have designated GPR41 as the hypoxia-indu ced apoptosis receptor, HIA-R.