MOLECULAR-CLONING AND EXPRESSION OF A 5-HYDROXYTRYPTAMINE7 SEROTONIN RECEPTOR SUBTYPE

We have utilized the polymerase chain reaction technique to selectivel y amplify a G protein-coupled receptor cDNA from rat kidney proximal c onvoluted tubule mRNA, which exhibits high homology with previously cl oned serotonin receptors. Sequencing of a full-length clone isolated f rom a rat hippocampal cDNA library revealed an open reading frame of 1 ,212 base pairs encoding a 404-residue protein with seven hydrophobic regions predicted to represent transmembrane-spanning domains. Within the transmembrane regions, this receptor was found to be 44-50% identi cal with various members of the 5-HT1, 5-HT5, and 5-HT6 subfamilies wi th lower (37-40%) homology to the 5-HT2-like receptors. Northern blots revealed a approximately 3.6-kilobase transcript localized in various brain regions with the following rank order of abundance: hypothalamu s > hippocampus = mesencephalon > cerebral cortex = olfactory bulb > o lfactory tubercle. Expression of this clone in COS-7 cells resulted in the appearance of high affinity, saturable binding of [H-3]lysergic a cid diethylamide ([H-3]LSD; K(D)= 5 nM) and [H-3]serotonin ([H-3]5-HT; K(D) = 1 nM). Among endogenous biogenic amines, only 5-HT completely inhibited radioligand binding. The inhibition of radioligand binding b y other serotonergic agents revealed a pharmacological profile that do es not correlate with any previously described serotonin receptor subt ype. In addition, this receptor exhibits high affinity for a number of tricyclic antipsychotic and antidepressant drugs including clozapine, loxapine, and amitriptyline. In HEK-293 cells stably transfected with this receptor, serotonin elicits a potent stimulation of adenylylcycl ase activity. The distinct structural and pharmacological properties o f this receptor suggests that it represents a completely novel seroton in receptor subtype, which we propose to designate 5-HT7. Based on its pharmacology and its localization to limbic and cortical regions of t he brain, it is likely that this receptor may play a role in several n europsychiatric disorders that involve serotonergic systems.