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Báo cáo khoa học: An antimicrobial peptide tachyplesin acts as a secondary secretagogue and amplifies lipopolysaccharide-induced hemocyte exocytosis

In the horseshoe crab, bacterial lipopolysaccharide (LPS) induces exocyto-sis by granular hemocytes, resulting in the secretion of various defense molecules, such as lectins and antimicrobial peptides, via a G protein-mediating signaling pathway. This response is a key component of the horseshoe crab innate immune response against infectious microorganisms. Here, we report an endogenous amplification mechanism for LPS-induced hemocytes exocytosis. | ềFEBS Journal An antimicrobial peptide tachyplesin acts as a secondary secretagogue and amplifies lipopolysaccharide-induced hemocyte exocytosis Aya Ozaki1 Shigeru Ariki1 and Shun-ichiro Kawabata Department of Biology Faculty of Sciences Kyushu University Fukuoka Japan Keywords exocytosis horseshoe crab innate immunity secretagogue tachyplesin Correspondence S. Kawabata Department of Biology Faculty of Sciences Kyushu University Fukuoka 812-8581 Japan Tel Fax 81 92 642 2632 E-mail skawascb@mbox.nc.kyushu-u.ac.jp 1Note A. Ozaki and S. Ariki contributed equally to this work Received 30 March 2005 revised 25 May 2005 accepted 31 May 2005 doi 10.1111 j.1742-4658.2005.04800.x In the horseshoe crab bacterial lipopolysaccharide LPS induces exocyto-sis by granular hemocytes resulting in the secretion of various defense molecules such as lectins and antimicrobial peptides via a G proteinmediating signaling pathway. This response is a key component of the horseshoe crab innate immune response against infectious microorganisms. Here we report an endogenous amplification mechanism for LPS-induced hemocytes exocytosis. The concentration of LPS required for maximal secretion decreased in proportion to the density of hemocytes suggesting the presence of a positive feedback mechanism for secretion via a mediator secreted from hemocytes. The exocytosed fluid of hemocytes was found able to induce hemocyte exocytosis in the absence of LPS. Furthermore tachyplesin a major antimicrobial peptide of hemocytes was able to trigger exocytosis in an LPS-independent manner which was inhibited by a phospholipase C inhibitor U-73122 and a G protein inhibitor pertussis toxin. Surface plasmon resonance analysis showed that tachyplesin directly interacts with bovine G protein. These findings suggest that the tachyple-sin-induced hemocyte exocytosis also occurs via a G protein-mediating signaling pathway. We concluded that tachyplesin functions not only as an antimicrobial substance but also as a .