Toll family members bind multiple Spätzle proteins and activate antimicrobial peptide gene expression in Drosophila

J Biol Chem. 2019 Jun 28;294(26):10172-10181. doi: 10.1074/jbc.RA118.006804. Epub 2019 May 14.

Abstract

The Toll signaling pathway in Drosophila melanogaster regulates several immune-related functions, including the expression of antimicrobial peptide (AMP) genes. The canonical Toll receptor (Toll-1) is activated by the cytokine Spätzle (Spz-1), but Drosophila encodes eight other Toll genes and five other Spz genes whose interactions with one another and associated functions are less well-understood. Here, we conducted in vitro assays in the Drosophila S2 cell line with the Toll/interleukin-1 receptor (TIR) homology domains of each Toll family member to determine whether they can activate a known target of Toll-1, the promoter of the antifungal peptide gene drosomycin. All TIR family members activated the drosomycin promoter, with Toll-1 and Toll-7 TIRs producing the highest activation. We found that the Toll-1 and Toll-7 ectodomains bind Spz-1, -2, and -5, and also vesicular stomatitis virus (VSV) virions, and that Spz-1, -2, -5, and VSV all activated the promoters of drosomycin and several other AMP genes in S2 cells expressing full-length Toll-1 or Toll-7. In vivo experiments indicated that Toll-1 and Toll-7 mutants could be systemically infected with two bacterial species (Enterococcus faecalis and Pseudomonas aeruginosa), the opportunistic fungal pathogen Candida albicans, and VSV with different survival times in adult females and males compared with WT fly survival. Our results suggest that all Toll family members can activate several AMP genes. Our results further indicate that Toll-1 and Toll-7 bind multiple Spz proteins and also VSV, but they differentially affect adult survival after systemic infection, potentially because of sex-specific differences in Toll-1 and Toll-7 expression.

Keywords: Spätzle; antimicrobial peptide (AMP); cytokine response; gene regulation; insect immunity; sex-specific difference; signal transduction; toll receptor.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antimicrobial Cationic Peptides / genetics
  • Antimicrobial Cationic Peptides / metabolism*
  • Bacteria / isolation & purification
  • Bacterial Infections / genetics
  • Bacterial Infections / metabolism
  • Bacterial Infections / microbiology*
  • Drosophila Proteins / genetics
  • Drosophila Proteins / metabolism*
  • Drosophila melanogaster / growth & development*
  • Drosophila melanogaster / metabolism*
  • Drosophila melanogaster / microbiology
  • Female
  • Gene Expression Regulation*
  • Male
  • Promoter Regions, Genetic
  • Signal Transduction
  • Toll-Like Receptors / genetics
  • Toll-Like Receptors / metabolism*

Substances

  • Antimicrobial Cationic Peptides
  • Drosophila Proteins
  • Toll-Like Receptors
  • spz protein, Drosophila
  • DRS protein, Drosophila