Transglutaminase-Catalyzed Protein-Protein Cross-Linking Suppresses the Activity of the NF-κB–Like Transcription Factor Relish

Abstract

Cross-linking of proteins by mammalian transglutaminases (TGs) plays important roles in physiological phenomena such as blood coagulation and skin formation. We show that Drosophila TG suppressed innate immune signaling in the gut. RNA interference (RNAi) directed against TG reduced the life span of flies reared under conventional nonsterile conditions but not of those raised under germ-free conditions. In conventionally reared flies, TG RNAi enhanced the expression of genes encoding antimicrobial peptides in the immune deficiency (IMD) pathway. Wild-type flies that ingested gut lysates prepared from conventionally reared TG RNAi-treated flies had shorter life spans. In conventionally reared flies, TG RNAi triggered apoptosis in the gut and induced the nuclear translocation of Relish, the NF-κB (nuclear factor κB)-like transcription factor of the IMD pathway. Wild-type flies that ingested synthetic amine donors, which inhibit the TG-catalyzed protein-protein cross-linking reaction, showed nuclear translocation of Relish and enhanced expression of genes encoding IMD-controlled antimicrobial peptide genes in the gut. We conclude that TG-catalyzed Relish cross-linking suppressed the IMD signaling pathway to enable immune tolerance against commensal microbes.

RNA Interference Directed against the Transglutaminase Gene Triggers Dysbiosis of Gut Microbiota in Drosophila

“…1, which confirmed that RNAi directed against the TG gene reduces the lifespan of flies under conventional non-sterile conditions (23). To investigate the effects of TG-RNAi on the gut microbiota, gut microbes of 0.5-day-old and 10-day-old non-TG-RNAi or TG-RNAi flies were analyzed using next-generation sequencing of 16S rRNA gene (rDNA) clones.…”

“…RNAi of the TG gene enhances the expression of IMD-AMPs, including Cecropin A1 and Diptericin, which decreases the lifespan concomitant with apoptosis of the midgut cells, compared with non-TG-RNAi flies (23). Interestingly, TG-RNAi does not decrease the lifespan of germ-free flies, whereas non-TG-RNAi flies that ingest gut lysates prepared from conventionally reared TG-RNAi flies have a short lifespan (23). We hypothesized that TG-RNAi causes dysbiosis of the gut microbiota, leading to a short lifespan.…”

“…In invertebrates, such as horseshoe crabs, crayfish, and Drosophila, TG-mediated crosslinking of specific proteins is involved in hemolymph coagulation and cuticle formation (19 -22). Drosophila carries a single TG gene, which cross-links the nuclear factor-B-like transcription factor Relish in the IMD pathway in midgut cells to suppress the expression of antimicrobial peptides (23). RNAi of the TG gene enhances the expression of IMD-AMPs, including Cecropin A1 and Diptericin, which decreases the lifespan concomitant with apoptosis of the midgut cells, compared with non-TG-RNAi flies (23).…”

“…Drosophila carries a single TG gene, which cross-links the nuclear factor-B-like transcription factor Relish in the IMD pathway in midgut cells to suppress the expression of antimicrobial peptides (23). RNAi of the TG gene enhances the expression of IMD-AMPs, including Cecropin A1 and Diptericin, which decreases the lifespan concomitant with apoptosis of the midgut cells, compared with non-TG-RNAi flies (23). Interestingly, TG-RNAi does not decrease the lifespan of germ-free flies, whereas non-TG-RNAi flies that ingest gut lysates prepared from conventionally reared TG-RNAi flies have a short lifespan (23).…”

The Role of the Phylogenetically Conserved Cochaperone Protein Droj2/DNAJA3 in NF-κB Signaling

“…Nuclear translocation of Relish in Drosophila is regulated by transglutaminase, which catalyzes the protein-protein crosslinking of Relish (67). Therefore, further studies are needed to evaluate the hypothesis that Droj2 functions with transglutaminase to regulate cross-linking reactions.…”