Protease IV, a quorum sensing‐dependent protease of Pseudomonas aeruginosa modulates insect innate immunity

Abstract

SummaryIn Pseudomonas aeruginosa, quorum sensing (QS) plays an essential role in pathogenesis and the QS response controls many virulence factors. Using a mealworm, Tenebrio molitor as a host model, we found that Protease IV, a QS-regulated exoprotease of P. aeruginosa functions as a key virulence effector causing the melanization and death of T. molitor larvae. Protease IV was able to degrade zymogens of spätzle processing enzyme (SPE) and SPE-activating enzyme (SAE) without the activation of the antimicrobial peptide (AMP) production. Since SPE and SAE function to activate spätzle, a ligand of Toll receptor in the innate immune system of T. molitor, we suggest that Protease IV may interfere with the activation of the Toll signaling. Independently of the Toll pathway, the melanization response, another innate immunity was still generated, since Protease IV directly converted Tenebrio prophenoloxidase into active phenoloxidase. Protease IV also worked as an important factor in the virulence to brine shrimp and nematode. These results suggest that Protease IV provides P. aeruginosa with a sophisticated way to escape the immune attack of host by interfering with the production of AMPs.

Quorum sensing and policing of Pseudomonas aeruginosa social cheaters

“…LasI catalyzes the synthesis of a diffusible quorum-sensing signal, N-3-oxo-dodecanoyl homoserine lactone (3OC12-HSL), which binds to the transcription factor LasR (3). LasR activates many genes including those encoding extracellular proteases such as elastase (4,5) and the rhlI and rhlR genes in response to 3OC12-HSL binding. RhlI catalyzes production of the freely diffusible butyryl-HSL (C4-HSL) and, in response to C4-HSL, the transcription factor RhlR activates a set of genes, which overlap those activated by LasR (1, 6, 7).…”

Post-secretional activation of Protease IV by quorum sensing in Pseudomonas aeruginosa

“…aeruginosa produces many extracellular proteases, such as elastase (LasB, pseudolysin), LasA (staphylolysin), LasD (staphylolysin), alkaline protease (AprA, aeruginolysin), small protease (PASP), large extracellular protease (LepA), and protease IV (PIV) 2, 9–14 . Many of them, such as LasB, LasA, AprA, and PIV are under the transcriptional control of QS 7, 11 . Thus the QS mutant that is incapable of producing acyl-HSLs is much less virulent with tiny production of extracellular proteases 11 .…”

“…Many of them, such as LasB, LasA, AprA, and PIV are under the transcriptional control of QS 7, 11 . Thus the QS mutant that is incapable of producing acyl-HSLs is much less virulent with tiny production of extracellular proteases 11 .…”

“…aeruginosa and a major virulence factor for the Pseudomonas corneal and lung infections 2, 15, 16 . It also works as a virulence factor to various invertebrates, such as Tenebrio molitor (insect), Caenorhabaditis elegans (nematode), and Artemia salina (aquatic crustacean) 11 . Since a mutation on piv gene causes P .…”

“…Since a mutation on piv gene causes P . aeruginosa to be much less virulent to these invertebrates as QS mutations and parenteral inject of purified PIV effectively kills insects without other factors 7, 11 , it was expected that the artificial expression of PIV by non-QS promoter (eg, arabinose-inducible promoter) should restore the virulence of the QS mutant to insect. However, we found that QS mutant overexpressing PIV by arabinose-inducible promoter was not able to kill insect, even though it produced high levels of normal PIV.…”