Wendy Van Poyer

Characterization of a Receptor for Insect Tachykinin‐Like Peptide Agonists by Functional Expression in a Stable Drosophila Schneider 2 Cell Line

Abstract: STKR is an insect G protein‐coupled receptor, cloned from the stable fly Stomoxys calcitrans. It displays sequence similarity to vertebrate tachykinin [or neurokinin (NK)] receptors. Functional expression of the cloned STKR cDNA 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 stably transfected S2‐STKR cells. Vertebrate tachykinins (or neurokinins) did not evoke any effect at concentrations up to 10‐5M, but an antagonist of mammalian neurokinin receptors, spantide II, inhibited the Lom‐TK III‐induced calcium response. Further analysis showed that the agonist‐induced intracellular release of calcium ions was not affected by pretreatment of the cells 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 neurokinin‐dependent signaling processes.

Tachykinin-like Peptides and Their Receptors: A Review

Abstract: Tachykinin‐like peptides have been identified in many vertebrate and invertebrate species. On the basis of the data reviewed in this paper, these peptides can be classified into two distinct subfamilies, which are recognized by their respective sequence characteristics. All known vertebrate tachykinins and a few invertebrate ones share a common C‐terminal sequence motif, ‐FXGLMa. The insect tachykinins, which have a common ‐GFX1GX2Ra C‐terminus, display about 30% of sequence homology with the first group.

Phenolamine-dependent adenylyl cyclase activation in Drosophila Schneider 2 cells

Drosophila Schneider 2 (S2) cells are often employed as host cells for non-lytic, stable expression and functional characterization of mammalian and insect G-protein-coupled receptors (GPCRs), such as biogenic amine receptors. In order to avoid cross-reactions, it is extremely important to know which endogenous receptors are already present in the non-transfected S2 cells. Therefore, we analyzed cellular levels of cyclic AMP and Ca2+, important second messengers for intracellular signal transduction via GPCRs, in response to a variety of naturally occurring biogenic amines, such as octopamine, tyramine, serotonin, histamine, dopamine and melatonin. None of these amines (up to 0.1 mM) was able to reduce forskolin-stimulated cyclic AMP production in S2 cells. Furthermore, no agonist-induced calcium responses were observed. Nevertheless, the phenolamines octopamine (OA) and tyramine (TA) induced a dose-dependent increase of cyclic adenosine monophosphate (AMP) production in S2 cells, while serotonin, histamine, dopamine and melatonin (up to 0.1 mM) did not. The pharmacology of this response was similar to that of the octopamine-2 (OA2) receptor type. In addition, this paper provides evidence for the presence of an endogenous mRNA encoding an octopamine receptor type in these cells, which is identical or very similar to OAMB. This receptor was previously shown to be positively coupled to adenylyl cyclase.