title: Insect cytokine growth-blocking peptide triggers a termination system of cellular immunity by inducing its binding protein.
abstract: Growth-blocking peptide (GBP) is a 25-amino acid cytokine found in lepidopteran insects that possesses diverse biological activities such as stimulation of immune cells (plasmatocytes), cell proliferation, and larval growth regulation. We found another novel function of GBP that induces a hemolysis of another class of blood cells (oenocytoids). In the lysate of oenocytoids we identified a GBP-binding protein that shows a specific affinity for GBP. The characterization of purified GBP-binding protein and its cDNA demonstrated it as a 49.5-kDa novel protein with a C-terminal region displaying limited homology to several insect lipoproteins. Results of Northern and Western blotting indicated that the GBP-binding protein should be synthesized only in blood cells. Immunoelectron microscopic analyses confirmed that indirect immunoreactive signals were mostly localized in oenocytoids. Kinetic and biological analyses of interaction between GBP and the binding protein showed their strong binding was followed by clearance of GBP from hemolymph, thus indicating that this protein might function as an inhibitory factor against GBP. Based on these results, we propose that insect cytokine GBP shows multifunctions even in cellular immunity: it serves to stimulate immune cells and afterward silences its own action by inducing the binding protein through specific hemolysis.
authors.affiliation: Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan.
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Yasunori
authors.initials: Y
authors.lastname: Oda
authors.forename: Masahide
authors.initials: M
authors.lastname: Uryu
authors.forename: Yoichi
authors.initials: Y
authors.lastname: Hayakawa
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D001681:Biological Assay; D015152:Blotting, Northern; D015153:Blotting, Western; D016207:Cytokines / Q000737:chemistry* / Q000378:metabolism / Q000502:physiology*; D018076:DNA, Complementary / Q000378:metabolism; D006434:Hemocytes / Q000378:metabolism; D006458:Hemolymph; D006461:Hemolysis; D019476:Insect Proteins / Q000737:chemistry* / Q000502:physiology*; D007700:Kinetics; D007915:Lepidoptera; D016253:Microscopy, Immunoelectron; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013997:Time Factors
chemical_list: D016207:Cytokines; D018076:DNA, Complementary; D019476:Insect Proteins; D010455:Peptides; C068690:growth blocking peptide, Apanteles kariyai