title: Prostaglandin mediates down-regulation of phenoloxidase activation of Spodoptera exigua via plasmatocyte-spreading peptide-binding protein.
abstract: Insect immunity is innate and highly efficient to defend against various pathogens. However, uncontrolled excessive immune responses would be highly detrimental and energy-consuming processes. An insect cytokine, plasmatocyte-spreading peptide (SePSP), induces hemocyte-spreading behavior as well as activates phenoloxidase (PO) in the beet armyworm, Spodoptera exigua. A hemocyte transcriptome of S. exigua contains a partial sequence of a putative PSP-binding protein (SePSP-BP1). SePSP-BP1 was expressed in most larval stages except in the last instar. However, a bacterial challenge induced SePSP-BP1 expression in the last instar especially in hemocytes and fat body. Injecting a double-stranded RNA specific to SePSP-BP1 (dsPSP-BP1) suppressed the induction of SePSP-BP1 expression in response to bacterial challenge. The larvae treated with dsPSP-BP1 suffered high mortality to infection of nonpathogenic bacteria due to uncontrolled high PO activity. SePSP significantly induced PO activity. The eicosanoid synthesis inhibitor, dexamethasone (DEX), inhibited SePSP-mediated PO activation. However, treatment with prostaglandin E2 (PGE2) induced a transient increase of PO activity under DEX treatment. Treatment of dsPSP decreased the duration of PO activation induced by PGE2, while treatment of dsPSP-BP1 increased the induced period. These results suggest that prostaglandin mediates PSP signals in both upregulation of PO activity and its subsequent downregulation via SePSP-BP1.
authors.affiliation: Department of Bioresource Sciences, Andong National University, Andong, Republic of Korea.
authors.forename: Jiyeong
authors.initials: J
authors.lastname: Park
authors.forename: Yonggyun
authors.initials: Y
authors.lastname: Kim
mesh_terms: D000818:Animals; D001483:Base Sequence; D016207:Cytokines / Q000378:metabolism; D015536:Down-Regulation; D004926:Escherichia coli; D005216:Fat Body; D006434:Hemocytes; D007814:Larva / Q000201:enzymology / Q000276:immunology* / Q000382:microbiology; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000378:metabolism; D011453:Prostaglandins / Q000378:metabolism*; D011485:Protein Binding; D018411:Spodoptera / Q000201:enzymology / Q000276:immunology* / Q000382:microbiology
chemical_list: D016207:Cytokines; D011453:Prostaglandins; D014442:Monophenol Monooxygenase
keywords: Spodoptera exigua; eicosanoid; immune; phenoloxidase; prostaglandin