Pharmacological Characterization of STKR,an Insect G Protein-Coupled Receptor for Tachykinin-Like Peptides

摘要

STKR is a G protein-coupled receptor that was cloned from the stable fly, Stomoxys calcitrans. Multiple sequence compari-sons show that the amino acid sequence of this insect receptor displays several features that are typical for tachykinin (or neu-rokinin, NK) receptors. Insect tachykinin-related peptides, also referred to as "insectatachykinins," produce dose-dependent calcium responses in Drosophila melanogaster Schneider 2 cells, which are stably transfected with this receptor (S2-STKR). These responses do not depend on the presence of extracellular Ca~(2+)-ions. A rapid agonist-induced increase of inositol 1,4,5-tris- phosphate (IP_3) is observed. This indicates that the agonist-in-duced cytosolic Ca~(2+)-rise is caused by a release of Ca~(2+)ions from intracellular calcium stores. The pharmacology of STKR is ana- lyzed by studying the effects of the most important antago-nists for mammalian NK-receptors on STKR-expressing insect cells. The results show that spantide II, a potent substance P antagonist, is a real antagonist of insectatachykinins on STKR. We have also tested the activity of a variety of natural insect-atachykinin analogs by microscopic image analysis of calcium responses in S2-STKR cells. At a concentration of 1 #mu#M, almost all natural analogs produce a significant calcium rise in stable S2-STKR cells. Interestingly, Stc-TK, an insectatachykinin that was recently discovered in the stable fly (S. calcitrans), also proved to be an STKR-agonist. Stc-TK, a potential physiologi- calligand for STKR, contains an Ala-residue (or A) instead of a highly conserved Gly-residue (or G). Arch. Insect Biochem.