The Pleiotropic GPCR Ligand Rotigotine Acts as a beta-arrestin Biased Ligand on Orphan Receptor GPR52

Despite large progress made on understanding G protein‐coupled receptors (GPCRs) roles, there is still a large group in this family which has no identified endogenous ligand and thus are defined as ‘orphan’ GPCRs. One such orphan GPCR is GPR52, which has little homology to other members of this family, the highest identity being with another orphan GPCR, GPR21 (71%). GPR52 is a Gs‐coupled receptor which constitutively increases cellular cAMP levels and it has been proposed to play a role in locomotor activity through modulation of dopamine receptors. On the other hand, rotigotine, a non‐ergoline dopamine agonist, is a FDA approved drug for treatment of Parkinson's disease (PD) and restless leg syndrome. However, rotigotine binds to high affinity to other GPCRs, including α2‐adrenergic and HTR1A receptors, but the clinical relevance of these effects remains unknown. To find new ligands for GPCRs we examined the effects of multiple pleiotropic ligands, like rotigotine, against 45 orphan GPCRs. We found that rotigotine induced β‐arrestin mobilization by GPR52 (232 ± 28 %, n=8) but not by any other tested orphan GPR. Surprisingly, rotigotine did not change cAMP levels in GPR52‐transfected HEK293 cells (98.5 ± 23.38%, n=4). In contrast, FTBMT, a previously reported GPR52 agonist, strongly increased cAMP levels (290.85 ± 25.65%, n=4), but it failed to change β‐arrestin mobilization (86.88 ± 16%, n=4). Our data indicate that rotigotine and FTBMT act as biased ligands on GPR52 preferentially activating specific signaling pathways. This conclusion is supported by the effects on other signaling pathways: both rotigotine and FTBMT stimulated GPR52 mediated MAPK phosphorylation, but only FTBMT enhanced AKT phosphorylation. Although the overall sequence similarity between GPR52 and DRD2 dopamine receptor is less than 15%, the alignment of these two receptors in the transmembrane domains resembles 28% homology. Based on the crystal structure of risperidone binding to its receptor DRD2, the binding of rotigotine to DRD2 was modelled and the computational model was extended to rotigotine interaction with GPR52. Using this method, two key amino acids in the 3 rd transmembrane domain of GPR52, I 121 and K 125 , were identified as crucial sites for binding for both rotigotine and FTBMT. In conclusion, rotigotine and FTBMT are biased agonists of orphan GPR52, which can be used for further exploring its patho‐physiological functions. Support or Funding Information Supported by HUMAA Endowed Founder's Chair in Basic Science Award and Office of Naval Research (N00014‐17‐1‐2105 and N00014‐18‐1‐2145) to YF. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .