Immune role of Drosophila melanogaster Kazal-type serine protease inhibitor CG14933
Authors: Alexandra Hrdina 1; Shu Kondo 2,3; Igor Iatsenko 1
Affiliations: 1) Max Planck Institute for Infection Biology, Berlin, Germany ; 2) Department of Biological Science and Technology, Faculty of Advanced Engineering, Tokyo University of Science, Tokyo, Japan; 3) Invertebrate Genetics Lab, National Insitute of Genetics, Mishima, Japan
Keywords: c. innate immunity; k. host/pathogen interactions
Serine protease inhibitors (serpins) exhibit major regulatory functions in the proteolytic cascades of both arthropods and mammals. In Drosophila melanogaster, two of the major immune responses, the Toll pathway and the melanization cascade, are tightly regulated by serpins. Despite their known function in immunity, only a few of the 30 genes predicted to encode for serpins have been characterized, and knowledge about their exact mechanism in which they control the immune response to prevent excessive activation is still scarce. In this study, we investigate the immune role of the previously uncharacterized Drosophila putative serpin CG14933 containing a Kazal domain. By using CG14933SK1 flies, a mutant devoid of any CG14933 expression, as well as RNAi knockdown and deficiency models, we show that flies lacking the gene show an increased susceptibility to Pseudomonas entomophila infection but not to any other infections that we tested. This clearly indicates an involvement of CG14933 in Drosophila immunity, although CG14933 itself is not induced by infection. We demonstrate that CG14933 has no role in the regulation of major immune pathways and does not act as a neutralizer of bacterial proteases. Additionally, we found that in adult CG14933SK1 flies, active phenoloxidase levels are significantly increased compared to wild type flies. We were able to rescue the sensitivity phenotype to P. entomophila infection by employing a double mutant devoid of both CG14933 and PPO1, the prophenoloxidase activated in early stages of infection. Moreover, by using tissue-specific RNAi-mediated silencing of CG14933 we reveal a significant role of the gene in the fat body of Drosophila. Altogether, we propose that CG14933 plays a role in negatively regulating the melanization response in Drosophila. Furthermore, we provide evidence of a possible link between excessive melanization and increased susceptibility to P. entomophila infection.