Larvae of the small white butterfly, Pieris rapae, express a novel serotonin receptor

Abstract

The biogenic amine serotonin (5-hydroxytryptamine, 5-HT) is a neurotransmitter in vertebrates and invertebrates. It acts in regulation and modulation of many physiological and behavioral processes through G-protein-coupled receptors. Five 5-HT receptor subtypes have been reported in Drosophila that share high similarity with mammalian 5-HT1A, 5-HT1B, 5-HT2A, 5-HT2B, and 5-HT7 receptors. We isolated a cDNA (Pr5-HT8 ) from larval Pieris rapae, which shares relatively low similarity to the known 5-HT receptor classes. After heterologous expression in HEK293 cells, Pr5-HT8 mediated increased [Ca(2+)]i in response to low concentrations (< 10 nM) of 5-HT. The receptor did not affect [cAMP]i even at high concentrations (> 10 μM) of 5-HT. Dopamine, octopamine, and tyramine did not influence receptor signaling. Pr5-HT8 was also activated by various 5-HT receptor agonists including 5-methoxytryptamine, (±)-8-Hydroxy-2-(dipropylamino) tetralin, and 5-carboxamidotryptamine. Methiothepin, a non-selective 5-HT receptor antagonist, activated Pr5-HT8 . WAY 10635, a 5-HT1A antagonist, but not SB-269970, SB-216641, or RS-127445, inhibited 5-HT-induced [Ca(2+)]i increases. We infer that Pr5-HT8 represents the first recognized member of a novel 5-HT receptor class with a unique pharmacological profile. We found orthologs of Pr5-HT8 in some insect pests and vectors such as beetles and mosquitoes, but not in the genomes of honeybee or parasitoid wasps. This is likely to be an invertebrate-specific receptor because there were no similar receptors in mammals. We isolated a cDNA (Pr5-HT8) from larval Pieris rapae, which shares relatively low similarity to the known GPCRs. After heterologous expression in HEK293 cells, Pr5-HT8 mediated increased [Ca(2+)]i in response to low concentrations (< 10 nM) of 5-HT and various 5-HT receptor agonists. We found orthologs of Pr5-HT8 in some insect pests and vectors such as beetles and mosquitoes, but not in the genomes of honeybee, parasitoid wasps, or mammals.

Keywords: 5-hydroxytryptamine; GPCR; insecticide; neurotransmitter; pharmacology; serotonin.