Pirk Is a Negative Regulator of the Drosophila Imd Pathway

Abstract

NF-κB transcription factors are involved in evolutionarily conserved signaling pathways controlling multiple cellular processes including apoptosis and immune and inflammatory responses. Immune response of the fruit fly Drosophila melanogaster to Gram-negative bacteria is primarily mediated via the Imd (immune deficiency) pathway, which closely resembles the mammalian TNFR signaling pathway. Instead of cytokines, the main outcome of Imd signaling is the production of antimicrobial peptides. The pathway activity is delicately regulated. Although many of the Imd pathway components are known, the mechanisms of negative regulation are more elusive. In this study we report that a previously uncharacterized gene, pirk, is highly induced upon Gram-negative bacterial infection in Drosophila in vitro and in vivo. pirk encodes a cytoplasmic protein that coimmunoprecipitates with Imd and the cytoplasmic tail of peptidoglycan recognition protein LC (PGRP-LC). RNA interference-mediated down-regulation of Pirk caused Imd pathway hyperactivation upon infection with Gram-negative bacteria, while overexpression of pirk reduced the Imd pathway response both in vitro and in vivo. Furthermore, pirk-overexpressing flies were more susceptible to Gram-negative bacterial infection than wild-type flies. We conclude that Pirk is a negative regulator of the Imd pathway.

Antimicrobial peptides and cell processes tracking endosymbiont dynamics

“…As mentioned above, elicitation of immune pathways can be reduced by secreted PGRPs with amidase activity, which degrade immunogenic peptidoglycans [51][52][53]. Signal transduction can also be decreased by intracellular regulators such as Pirk, which binds to the IMD pathway membrane receptor and causes its internalization [54,55], or by the products of genes such as caudal, which represses the NF-kB-dependent AMP gene expression in the gut, therefore allowing the tolerance of gut microbiota in Drosophila [56]. However, no orthologues of known negative immune regulators have been shown to be highly expressed in the S. oryzae bacteriome.…”

Genome-Wide RNA Interference inDrosophilaCells Identifies G Protein-Coupled Receptor Kinase 2 as a Conserved Regulator of NF-κB Signaling

“…I. Kleino (University of Helsinki, Helsinki, Finland). S2 cells were transfected with the Gprk2-GFP fusion construct essentially as described previously (30). Overexpression of Gprk2-GFP fusion protein in S2 cells was induced with 350 mM CuSO 4 for 36 h. For HeLa cell transfection, cells were seeded onto coverslips on six-well plates, and 24 h later, the cells were transfected with 0.1 mg GRK5-GFP construct.…”

“…S2 cells were transfected with Gprk2-V5 full-length or deletion constructs and Cactus-myc constructs in pMT/V5/HisA vector (Invitrogen/Life Technologies) and coimmunoprecipitated, separated, transferred on the membrane, and detected essentially as described (30).…”

The dual oxidase gene BdDuox regulates the intestinal bacterial community homeostasis of Bactrocera dorsalis

“…With routine microbial burdens, such as those found in the absence of infection, the presence of a commensal-derived peptidoglycan constitutively activates the Imd pathway at a low level of activation. The basal activity of this pathway is maintained at a low level by various negative regulators, including peptidoglycanrecognition protein (PGRP)-LF (Maillet et al, 2008), Pirk (Kleino et al, 2008) and amidase PGRPs (notably PGRP-LB and PGRP-SC1a) (Bischoff et al, 2006;Zaidman-Rémy et al, 2006. However, acute infection with pathogenic bacteria results in the release of large quantities of peptidoglycan fragments during drastic bacterial division (Buchon et al, 2013) that transiently increases the Imd pathway activity to trigger AMP production.…”