Characterization of a receptor for insect tachykinin-like peptide agonistsby functional expression in a stable Drosophila Schneider 2 cell line

STKR is an insect G protein-coupled receptor, cloned from the stable fly St omoxys calcitrans. It displays sequence similarity to vertebrate tachykinin [or neurokinin (NK]) receptors. Functional expression of the cloned STKR c DNA was obtained in cultured Drosophila melanogaster Schneider 2 (S2) cells . Insect tachykinin-like peptides or "insectatachykinins," such as Locusta tachykinin (Lom-TK) III, produced dose-dependent calcium responses in stabl y transfected S2-STKR cells. Vertebrate tachykinins (or neurokinins) did no t evoke any effect at concentrations up to 10(-5) M, but an antagonist of m ammalian neurokinin receptors, spantide II, inhibited the Lom-TK III-induce d calcium response. Further analysis showed that the agonist-induced intrac ellular release of calcium ions was not affected by pretreatment of the cel ls with pertussis toxin. The calcium rise was blocked by the phospholipase C inhibitor U73122. in addition, Lom-TK III was shown to have a stimulatory effect on the accumulation of both inositol 1,4,5-trisphosphate and cyclic AMP. These are the same second messengers that are induced in mammalian ne urokinin-dependent signaling processes.