title: Manduca sexta serpin-5 regulates prophenoloxidase activation and the Toll signaling pathway by inhibiting hemolymph proteinase HP6.
abstract: Insect immune responses include prophenoloxidase (proPO) activation and Toll pathway initiation, which are mediated by serine proteinase cascades and regulated by serpins. Manduca sexta hemolymph proteinase-6 (HP6) is a component of both pathways. It cleaves and activates proPO activating proteinase 1 (PAP1) and hemolymph proteinase-8 (HP8), which activates proSpätzle. Inhibitors of HP6 could have the capability of regulating both of these innate immune proteinase cascade pathways. Covalent complexes of HP6 with serpin-4 and serpin-5 were previously isolated from M. sexta plasma using immunoaffinity chromatography with serpin antibodies. We investigated the inhibition of purified, recombinant HP6 by serpin-4 and serpin-5. Both serpin-4 and serpin-5 formed SDS-stable complexes with HP6 in vitro, and they inhibited the activation of proHP8 and proPAP1. Serpin-5 inhibited HP6 more efficiently than did serpin-4. Injection of serpin-5 into larvae resulted in decreased bacteria-induced antimicrobial activity in hemolymph and reduced the bacteria-induced expression of attacin, cecropin and hemolin genes in fat body. Injection of serpin-4 had a weaker effect on antimicrobial peptide expression. These results indicate that serpin-5 may regulate the activity of HP6 to modulate proPO activation and antimicrobial peptide production during immune responses of M. sexta.
authors.affiliation: Department of Biochemistry, Kansas State University, Manhattan, KS 66506, USA.
authors.forename: Chunju
authors.initials: C
authors.lastname: An
authors.forename: Michael R
authors.initials: MR
authors.lastname: Kanost
mesh_terms: D000818:Animals; D004156:Catechol Oxidase / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004792:Enzyme Precursors / Q000378:metabolism*; D006458:Hemolymph / Q000201:enzymology*; D019476:Insect Proteins / Q000378:metabolism* / Q000502:physiology; D007814:Larva / Q000187:drug effects / Q000201:enzymology; D018402:Manduca / Q000201:enzymology* / Q000276:immunology / Q000378:metabolism; D000073718:Pancreatitis-Associated Proteins; D010447:Peptide Hydrolases / Q000378:metabolism*; D011480:Protease Inhibitors / Q000302:isolation & purification / Q000494:pharmacology*; D015843:Serpins / Q000302:isolation & purification / Q000494:pharmacology* / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects; D051193:Toll-Like Receptors / Q000378:metabolism
chemical_list: D004792:Enzyme Precursors; D019476:Insect Proteins; D000073718:Pancreatitis-Associated Proteins; D011480:Protease Inhibitors; C000612141:REG3A protein, human; D015843:Serpins; D051193:Toll-Like Receptors; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D010447:Peptide Hydrolases