Destruxins are a class of insecticidal, anti-viral, and phytotoxic
cyclic depsipeptides that are also studied for their toxicity to
cancer cells. They are produced by various fungi, and a direct relationship has been established between Destruxin production and the virulence of the entomopathogen Metarhizium anisopliae. Aside from opening
calcium channels, their in vivo mode of action during pathogenesis remains largely uncharacterized. To better understand the effects of a Destruxin, we looked at changes in gene expression following injection of
Destruxin A into the fruit fly Drosophila melanogaster. Microarray results revealed reduced expression of various
antimicrobial peptides that play a major role in the humoral immune response of the fly. Flies co-injected with a non-lethal dose of
Destruxin A and the normally innocuous Gram-negative bacteria Escherichia coli, showed increased mortality and an accompanying increase in bacterial titers. Mortality due to
sepsis was rescued through ectopic activation of components in the IMD pathway, one of two signal transduction pathways that are responsible for
antimicrobial peptide induction. These results demonstrate a novel role for
Destruxin A in specific suppression of the humoral immune response in insects.