PT - JOURNAL ARTICLE AU - Arnauld Belmer AU - Stephane Doly AU - Vincent Setola AU - Sophie M. Banas AU - Imane Moutkine AU - Katia Boutourlinsky AU - Terry Kenakin AU - Luc Maroteaux TI - Role of the N-terminal Region in G-Protein Coupled Receptor Functions: Negative Modulation Revealed by 5-HT2B Receptor Polymorphisms AID - 10.1124/mol.113.089086 DP - 2013 Jan 01 TA - Molecular Pharmacology PG - mol.113.089086 4099 - http://molpharm.aspetjournals.org/content/early/2013/10/30/mol.113.089086.short 4100 - http://molpharm.aspetjournals.org/content/early/2013/10/30/mol.113.089086.full AB - Putative role of the N-terminal region of rhodopsin-like seven transmembrane biogenic amine receptors in agonist-induced signaling has not yet been clarified despite recent advances in seven transmembrane receptor structural biology. Given the existence of N-terminal non-synonymous polymorphisms (R6G;E42G) within the HTR2B gene in a drug-abusing population, we assessed whether these polymorphisms affect 5-HT2B receptor in vitro pharmacological and coupling properties in transfected COS-7 cells. Modification of the 5-HT2B receptor N-terminus by the R6G;E42G polymorphisms, increases such agonist signaling pathways as inositol phosphate accumulation as assessed by either classical or operational models. The N-terminal R6G;E42G mutations of the 5-HT2B receptor also increase cell proliferation and slow its desensitization kinetics compared to the wild type receptor, further supporting a role for the N-terminus in transduction efficacy. Furthermore, by co-expressing a tethered wild type 5-HT2B receptor N-terminus with a 5-HT2B receptor bearing a N-terminal deletion, we were able to restore original coupling. This reversion to normal activity of a truncated 5-HT2B receptor by co-expression of the membrane-tethered wild type 5-HT2B receptor N-terminus was not observed using a membrane-tethered 5-HT2B receptor R6G;E42G N-terminus. These data suggest that the N-terminus exerts a negative control over basal as well as agonist-stimulated receptor activity that is lost in the R6G;E42G mutant. Our findings reveal a new and unanticipated role of the 5-HT2B receptor N-terminus as a negative modulator, affecting both constitutive and agonist-stimulated activity. Moreover, our data caution against excluding the N-terminus and extracellular loops in structural studies of this seven transmembrane receptor family.