Caspase-1-like regulation of the proPO-system and role of ppA and caspase-1-like cleaved peptides from proPO in innate immunity.
Invertebrates rely on innate immunity to respond to the entry of foreign microorganisms. One of the important innate immune responses in arthropods is the activation of prophenoloxidase (proPO) by a proteolytic cascade finalized by the proPO-activating enzyme (ppA), which leads to melanization and the elimination of pathogens. Proteolytic cascades play a crucial role in innate immune reactions because they can be triggered more quickly than immune responses that require altered gene expression. Caspases are intracellular proteases involved in tightly regulated limited proteolysis of downstream processes and are also involved in inflammatory responses to infections for example by activation of interleukin 1ß. Here we show for the first time a link between caspase cleavage of proPO and release of this protein and the biological function of these fragments in response to bacterial infection in crayfish. Different fragments from the cleavage of proPO were studied to determine their roles in bacterial clearance and antimicrobial activity. These fragments include proPO-ppA, the N-terminal part of proPO cleaved by ppA, and proPO-casp1 and proPO-casp2, the fragments from the N-terminus after cleavage by caspase-1. The recombinant proteins corresponding to all three of these peptide fragments exhibited bacterial clearance activity in vivo, and proPO-ppA had antimicrobial activity, as evidenced by a drastic decrease in the number of Escherichia coli in vitro. The bacteria incubated with the proPO-ppA fragment were agglutinated and their cell morphology was altered. Our findings show an evolutionary conserved role for caspase cleavage in inflammation, and for the first time show a link between caspase induced inflammation and melanization. Further we give a more detailed understanding of how the proPO system is regulated in time and place and a role for the peptide generated by activation of proPO as well as for the peptides resulting from Caspase 1 proteolysis.
Department of Comparative Physiology, Uppsala University, Uppsala, Sweden.
Miti
M
Jearaphunt
Department of Comparative Physiology, Uppsala University, Uppsala, Sweden.
Chadanat
C
Noonin
Department of Comparative Physiology, Uppsala University, Uppsala, Sweden; Aquatic Molecular Genetics and Biotechnology Laboratory, National Center for Genetic Engineering and Biotechnology (BIOTEC), National Science and Technology Development Agency, Pathumthani, Bangkok, Thailand.
Pikul
P
Jiravanichpaisal
Department of Comparative Physiology, Uppsala University, Uppsala, Sweden.
Seiko
S
Nakamura
Center of Excellence for Molecular Biology and Genomics of Shrimp, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok, Thailand.
Anchalee
A
Tassanakajon
Department of Comparative Physiology, Uppsala University, Uppsala, Sweden.
Irene
I
Söderhäll
Department of Comparative Physiology, Uppsala University, Uppsala, Sweden; Science for Life Laboratory, Department of Comparative Physiology, Uppsala University, Uppsala, Sweden.
Kenneth
K
Söderhäll
D000818:Animals; D060829:Arthropod Proteins / Q000276:immunology* / Q000378:metabolism; D003400:Astacoidea / Q000201:enzymology / Q000276:immunology*; D020170:Caspase 1 / Q000276:immunology* / Q000378:metabolism; D004156:Catechol Oxidase / Q000276:immunology* / Q000378:metabolism; D004792:Enzyme Precursors / Q000276:immunology* / Q000378:metabolism; D007113:Immunity, Innate / Q000502:physiology*; D010455:Peptides / Q000276:immunology* / Q000378:metabolism; D059748:Proteolysis
D060829:Arthropod Proteins; D004792:Enzyme Precursors; D010455:Peptides; C038451:pro-phenoloxidase; D004156:Catechol Oxidase; D020170:Caspase 1