PGE ₂ upregulates gene expression of dual oxidase in a lepidopteran insect midgut via cAMP signalling pathway

Abstract

In insect midgut, prostaglandins (PGs) play a crucial role in defending bacterial and malarial pathogens. However, little is known about the PG signalling pathway in the midgut. A dual oxidase ( Se-Duox ) with presumed function of catalysing reactive oxygen species (ROS) production in the midgut was identified in beet armyworm, Spodoptera exigua . Se-Duox was expressed in all developmental stages, exhibiting relatively high expression levels in the midgut of late larval instars. Se-Duox expression was upregulated upon bacterial challenge. RNA interference (RNAi) of Se-Duox expression significantly suppressed ROS levels in the midgut lumen. The suppression of ROS levels increased insecticidal activity of Serratia marcescens after oral infection. Interestingly, treatment with a PLA 2 inhibitor prevented the induction of Se-Duox expression in response to bacterial challenge. On the other hand, addition of its catalytic product rescued the induction of Se-Duox expression. Especially, PG synthesis inhibitor significantly suppressed Se-Duox expression, while the addition of PGE 2 or PGD 2 rescued the inhibition. Subsequent PG signals involved cAMP and downstream components because specific inhibitors of cAMP signal components such as adenylate cyclase (AC) and protein kinase A (PKA) significantly inhibited Se-Duox expression. Indeed, addition of a cAMP analogue stimulated Se-Duox expression in the midgut. Furthermore, individual RNAi specific to PGE 2 receptor (a trimeric G-protein subunit), AC, PKA or cAMP-responsive element-binding protein resulted in suppression of Se-Duox expression. These results suggest that PGs can activate midgut immunity via cAMP signalling pathway by inducing Se-Duox expression along with increased ROS levels.

HMG-Like DSP1 Mediates Immune Responses of the Western Flower Thrips (Frankliniella occidentalis) Against Beauveria bassiana, a Fungal Pathogen

“…PGE 2 induces Ca 2+ signals through its specific receptor on the membrane via cAMP ( 42 ). Especially, the promoter of Duox gene in S. exigua has a cAMP response element (CRE) that can bind to CRE-binding protein, which is activated by cAMP in response to PGE 2 ( 46 ). Immune responses of F. occidentalis in response to TSWV infection have been analyzed.…”

Eicosanoid Signaling in Insect Immunology: New Genes and Unresolved Issues

“…Dual oxidase (Duox) is a main immune executor for gut immunity in insects by producing reactive oxygen species (ROS) [ 71 ]. In S. exigua, a Duox gene ( Se-Duox ) is expressed in the midgut of late larval instars and is upregulated by a bacterial challenge [ 72 ]. In this study, RNAi of Se-Duox expression significantly suppressed ROS amounts in the midgut lumen.…”

Dorsal switch protein 1 as a damage signal in insect gut immunity to activate dual oxidase via an eicosanoid, PGE2

“…Inhibition of eicosanoid biosynthesis prevents ROS production of the midgut upon pathogen infection ( 14 ). In the midgut of another lepidopteran Plutella xylostella , Duox gene expression and subsequent ROS production are essential for defending against bacterial pathogens ( 15 ). These results suggest that eicosanoids can mediate ROS production by activating Duox in the lepidopteran insects.…”

“…Eicosanoid production is initiated by the release of free C20 PUFA from phospholipids by the catalytic activity of phospholipase A 2 (PLA 2 ) ( 17 ). Among eicosanoids, prostaglandins (PGs) play a crucial role in mediating various immune responses in the midguts of lepidopteran and dipteran insects ( 15 , 18 ). In particular, several PGs along with the PGE 2 receptor and its downstream signal components have been found in S. exigua and mediate the induction of intracellular Ca 2+ levels ( 19 ).…”