dRYBP Contributes to the Negative Regulation of the Drosophila Imd Pathway

Abstract

The Drosophila humoral innate immune response fights infection by producing antimicrobial peptides (AMPs) through the microbe-specific activation of the Toll or the Imd signaling pathway. Upon systemic infection, the production of AMPs is both positively and negatively regulated to reach a balanced immune response required for survival. Here, we report the function of the dRYBP (drosophila Ring and YY1 Binding Protein) protein, which contains a ubiquitin-binding domain, in the Imd pathway. We have found that dRYBP contributes to the negative regulation of AMP production: upon systemic infection with Gram-negative bacteria, Diptericin expression is up-regulated in the absence of dRYBP and down-regulated in the presence of high levels of dRYBP. Epistatic analyses using gain and loss of function alleles of imd, Relish, or skpA and dRYBP suggest that dRYBP functions upstream or together with SKPA, a member of the SCF-E3-ubiquitin ligase complex, to repress the Imd signaling cascade. We propose that the role of dRYBP in the regulation of the Imd signaling pathway is to function as a ubiquitin adaptor protein together with SKPA to promote SCF-dependent proteasomal degradation of Relish. Beyond the identification of dRYBP as a novel component of Imd pathway regulation, our results also suggest that the evolutionarily conserved RYBP protein may be involved in the human innate immune response.

Transglutaminase-catalyzed incorporation of polyamines masks the DNA-binding region of the transcription factor Relish

“…Many factors are involved in regulating the IMD pathway in Drosophila (36, 37): peptidoglycan-recognition protein (PGRP)-LB and PGRP-SC (amidases against peptidoglycans) digest peptidoglycans to non-stimulatory fragments (38 -40), Casper represses the expression of IMD pathway-controlled antimicrobial peptide genes (41), PIMS/Rudra/Pirk interacts with the complex of PGRP-LC (a membrane-bound receptor for peptidoglycans) and the IMD protein to reduce IMD pathway immune signaling (42)(43)(44), the Pvr receptor tyrosine kinase attenuates the JNK and NF-B arms of the IMD pathway (45), PGRP-LF forms a non-signaling complex with PGRP-LC (46), Drosophila Ring and YY1-binding protein promotes the proteasomal degradation of Relish (47), and defense repressor 1 regulates the activation of the IMD pathway in the brain (48,49). Chronic activation of the IMD pathway leads to inflamma- tory gut diseases and reduces lifespan (50, 51), clearly indicating that distinct proteins and enzymes have evolved into essential regulatory factors to evade uncontrollable conditions for the IMD pathway.…”

Thorax Injury Lowers Resistance to Infection in Drosophila melanogaster

“…Drosophila immunity studies are somewhat divided between the two inoculation sites. In some studies pathogens are injected into the abdomen (24,26,(36)(37)(38)(39), and in others they are injected into the thorax (16,(40)(41)(42)(43), while many published papers do not report the site of infection at all. This procedural variance illustrates the general belief that site of inoculation is relatively unimportant to output phenotypes-a belief that is strongly contradicted by our current data.…”

The Drosophila Imd Signaling Pathway

“…Drosophila CYLD interacts with the IKK protein Kenny and also negatively regulates Imd signaling (75,76). Activated Relish is targeted for ubiquitination and proteasomal degradation by the SCF complex (77), possibly promoted by the ubiquitin-binding protein dRYBP (78). Dredd is inhibited by the RING-domain containing protein Dnr1 (79,80), whereas Caspar, a homolog of the mammalian FAF1, inhibits the Dredd-mediated cleavage of Relish (81).…”