Cecropins as a marker of Spodoptera frugiperda immunosuppression during entomopathogenic bacterial challenge

Abstract

An antimicrobial peptide (AMP) of the cecropin family was isolated by HPLC from plasma of the insect pest, Spodoptera frugiperda. Its molecular mass is 3910.9 Da as determined by mass spectrometry. Thanks to the EST database Spodobase, we were able to describe 13 cDNAs encoding six different cecropins which belong to the sub-families CecA, CecB, CecC and CecD. The purified peptide identified as CecB1 was chemically synthesized (syCecB1). It was shown to be active against Gram-positive and Gram-negative bacteria as well as fungi. Two closely related entomopathogenic bacteria, Xenorhabdus nematophila F1 and Xenorhabdus mauleonii VC01 T showed different susceptibility to syCecB1. Indeed, X. nematophila was sensitive to syCecB1 whereas X. mauleonii had a minimal inhibitory concentration (MIC) eight times higher. Interestingly, injection of live X. nematophila into insects did not induce the expression of AMPs in hemolymph. This effect was not observed when this bacterium was heat-killed before injection. On the opposite, both live and heat-killed X. mauleonii induced the expression of AMPs in the hemolymph of S. frugiperda. The same phenomenon was observed for another immune-related protein lacking antimicrobial activity. Altogether, our data suggest that Xenorhabdus strains have developed different strategies to supplant the humoral defense mechanisms of S. frugiperda, either by increasing their resistance to AMPs or by preventing their expression during such host-pathogen interaction.

Comprehensive Analysis of Gene Expression Profiles of the Beet Armyworm Spodoptera exigua Larvae Challenged with Bacillus thuringiensis Vip3Aa Toxin

“…Up-regulation of AMPs induced by bacterial infection, bacterial feeding (including Bacillus sp), or by Cry toxins, has been previously reported in S. exigua [26-28] and in other lepidopteran [16,30,32,48,49,66-68]. In general, the regulated AMPs exhibited an increase in transcription with time following the same pattern previously described for S. exigua attacin [28].…”

Effects of <i>Musca domestica</i> Cecropin on the Adhesion and Migration of Human Hepatocellular Carcinoma BEL-7402 Cells

“…1,2) They are able to form specific amphipathic alpha-helices, which allow them to target nonpolar lipid cell membranes, and have strong antibiotic activity against both Gram-positive and Gram-negative bacteria at low micromolar concentrations. 3,4) More recent studies have also indicated the antitumor activity of cecropins against various cancer cell lines of leukemia, lymphoma, colon carcinoma, small cell lung cancer and gastric cancer, but without damage to human normal cells which would make it a good candidate for the development of anti-tumor agents. 5,6) The Musca domestica gene cecropin (GenBank accession number: EF175878) was cloned in our laboratory from the larva.…”

Partner-specific induction ofSpodoptera frugiperdaimmune genes in response to the entomopathogenic nematobacterial complexSteinernema carpocapsae-Xenorhabdus nematophila

“…Varied activity spectra have also been found for several insects’ lysozymes and LLPs (53–57). Interestingly, all of the categories and subcategories cited above were represented in the two tissues, indicating that their antimicrobial responses are diversified and that the factors responsible for their disappearance in the hemolymph (24, 41) probably act at a post-transcriptional level. About a half of the genes presented similar and significant induction profiles in the hemocytes and in the fat body.…”

“…Studies in diverse insect models have also shown that both partners produce factors impairing melanization (28–31), hemocyte’s viability (32–36) and the production of cellular immune responses by several ways (27–29, 31, 37, 38). Finally, both X. nematophila and S. carpocapsae secrete proteolytic factors degrading cecropin AMPs (39, 40) and the bacterium has also been shown to reduce more globally the hemolymph antimicrobial activity, as well as AMP transcription in lepidopteran models (24, 39, 41, 42).…”