Manduca sexta serpin-5 regulates prophenoloxidase activation and the Toll signaling pathway by inhibiting hemolymph proteinase HP6 |
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| Authors: | Chunju An Michael R. Kanost |
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| Affiliation: | 1. Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506 USA;2. Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078 USA;1. Center of Excellence for Molecular Biology and Genomics of Shrimp, Department of Biochemistry, Faculty of Science, Chulalongkorn University, 254 Phayathai Road, Bangkok 10330, Thailand;2. National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency (NSTDA), 113 Paholyothin Road, Klong1, Klong Luang, Pathumthani 12120, Thailand;1. Division of Biology, Kansas State University, Manhattan, KS 66506, USA;2. Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA;1. Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, KS 66506, USA;2. Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078, USA;1. Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078, USA;2. Boyce Thompson Institute, Cornell University, Ithaca, NY 14853, USA;3. Division of Biology, Kansas State University, Manhattan, KS 66506, USA;4. Department of Biology, University of Massachusetts, Amherst, MA 01003, USA |
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| 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. |
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