Paraoxonase 2 is down-regulated by the Pseudomonas aeruginosa quorumsensing signal N-(3-oxododecanoyl)-L-homoserine lactone and attenuates oxidative stress induced by pyocyanin

Biochem J. 2010 Jan 27;426(1):73-83. doi: 10.1042/BJ20091414.


Two virulence factors produced by Pseudomonas aeruginosa are pyocyanin and N-(3-oxododecanoyl)-L-homoserine lactone (3OC12). Pyocyanin damages host cells by generating ROS (reactive oxygen species). 3OC12 is a quorum-sensing signalling molecule which regulates bacterial gene expression and modulates host immune responses. PON2 (paraoxonase-2) is an esterase that inactivates 3OC12 and potentially attenuates Ps. aeruginosa virulence. Because increased intracellular Ca2+ initiates the degradation of PON2 mRNA and protein and 3OC12 causes increases in cytosolic Ca2+, we hypothesized that 3OC12 would also down-regulate PON2. 3OC12 and the Ca2+ ionophore A23187 caused a rapid cytosolic Ca2+ influx and down-regulated PON2 mRNA, protein and hydrolytic activity in A549 and EA.hy 926 cells. The decrease in PON2 hydrolytic activity was much more extensive and rapid than decreases in protein, suggesting a rapid post-translational mechanism which blocks PON2's hydrolytic activity. The Ca2+ chelator BAPTA/AM [1,2-bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis(acetoxymethyl ester)] diminished the ability of 3OC12 to decrease PON2, demonstrating that the effects are mediated by Ca2+. PON2 also has antioxidative properties and we show that it protects cells from pyocyanin-induced oxidative stress. Knockdown of PON2 by transfecting cells with siRNA (small interfering RNA) rendered them more sensitive to, whereas overexpression of PON2 protected cells from, pyocyanin-induced ROS formation. Additionally, 3OC12 potentiated pyocyanin-induced ROS formation, presumably by inactivating PON2. These findings support a key role for PON2 in the defence against Ps. aeruginosa virulence, but also reveal a mechanism by which the bacterium may subvert the protection afforded by PON2.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 4-Butyrolactone / analogs & derivatives*
  • 4-Butyrolactone / metabolism
  • 4-Butyrolactone / pharmacology
  • Aryldialkylphosphatase / genetics
  • Aryldialkylphosphatase / metabolism*
  • Biological Transport / drug effects
  • Blotting, Western
  • Calcimycin / pharmacology
  • Calcium / metabolism
  • Calcium / physiology
  • Cell Line
  • Cell Survival / genetics
  • Cell Survival / physiology
  • Down-Regulation / drug effects*
  • Enzyme Activation
  • Homoserine / analogs & derivatives*
  • Homoserine / metabolism
  • Homoserine / pharmacology
  • Humans
  • Oxidative Stress / drug effects*
  • Pseudomonas aeruginosa / metabolism*
  • Pyocyanine / pharmacology*
  • Quorum Sensing / drug effects
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / physiology
  • Virulence / genetics


  • N-(3-oxododecanoyl)homoserine lactone
  • RNA, Small Interfering
  • Calcimycin
  • Homoserine
  • Pyocyanine
  • Aryldialkylphosphatase
  • 4-Butyrolactone
  • Calcium