PT  - JOURNAL ARTICLE
AU  - Emilie Ceraudo
AU  - Mizuho Horioka
AU  - Jordan M. Mattheisen
AU  - Tyler D. Hitchman
AU  - Amanda R. Moore
AU  - Manija A. Kazmi
AU  - Ping Chi
AU  - Yu Chen
AU  - Thomas P. Sakmar
AU  - Thomas Huber
TI  - Uveal Melanoma Oncogene <em>CYSLTR2</em> Encodes a Constitutively Active GPCR Highly Biased Toward Gq Signaling
AID  - 10.1101/663153
DP  - 2019 Jan 01
TA  - bioRxiv
PG  - 663153
4099  - http://biorxiv.org/content/early/2019/06/06/663153.short
4100  - http://biorxiv.org/content/early/2019/06/06/663153.full
AB  - The G protein-coupled receptor (GPCR) cysteinyl-leukotriene receptor 2 (CysLTR2) with a single amino acid mutation at position 3.43 (Leu replaced with Gln at position 129 in transmembrane helix 3) causes uveal melanoma in humans. The ability of CysLTR2-L129Q to cause malignant transformation has been hypothesized to result from constitutive activity. We show that CysLTR2-L129Q is a constitutively active mutant (CAM) that strongly drives Gq/11 signaling pathways in melan-a melanocytes and in HEK293T cells in culture. However, the mutant receptor only very weakly recruits beta-arrestins 1 and 2. The mutant receptor displays profound signaling bias while avoiding arrestin-mediated downregulation. The mechanism of the signaling bias results from the creation of a hydrogen-bond network that stabilizes the active G protein signaling state through novel interactions with the highly-conserved NPxxY motif on helix 7. Furthermore, the mutation destabilizes a putative allosteric sodium-binding site that usually stabilizes the inactive state of GPCRs. Thus, the mutation has a dual role of promoting the active state while destabilizing inactivating allosteric networks. The high degree of constitutive activity renders existing orthosteric antagonist ligands of CysLTR2 ineffective as inverse agonists of the mutant. CysLTR2 is the first example of a GPCR oncogene that encodes a GPCR with constitutive highly biased signaling that can escape cellular downregulation mechanisms.