Trends in Molecular Medicine
The role of pyocyanin in Pseudomonas aeruginosa infection
Section snippets
Regulation of PCN biosynthesis
PCN is synthesized from chorismate through a series of complex steps mediated by gene products encoded by two phzABCDEFG operons, and by the phzH, phzM and phzS genes, which modify precursors into the tricyclic compound (Figure 1) 14, 15. PCN synthesis is regulated by quorum sensing (QS), a process involving a cell-density-dependent accumulation of low molecular weight signal molecules that enable bacteria to modulate the expression of virulence genes [16]. These molecules,
PCN-induced injury revealed by in vitro systems
Because P. aeruginosa infection is multifactorial, involving numerous virulence factors, it has been difficult to discern the role of PCN during lung infection. To overcome this obstacle, most studies examining the toxicity of PCN have used in vitro cell culture systems with purified PCN. These in vitro studies reveal that PCN causes a wide spectrum of cellular damage and might contribute to the persistence of P. aeruginosa in the lungs of patients with CF. In particular, early studies showed
PCN is an evolutionarily conserved virulence factor of P. aeruginosa in hosts of multiple phyla
P. aeruginosa can infect hosts of multiple phylogenetic backgrounds, including plants, nematodes and insects 3, 4, 9, 10, 11. Surprisingly, many studies reveal extensive conservation in the virulence mechanisms used by P. aeruginosa to infect evolutionarily divergent hosts 3, 4. One of these conserved virulence factors is PCN. For example, PCN participates in the fast killing of the nematode Caenorhabditis elegans by producing reactive oxygen intermediates (Table 1) [10]. PCN-deficient strains
PCN is crucial for lung infection in mice
The requirement for PCN in lung infection was recently demonstrated in mice [12]. In an acute pneumonia model, adult CD-1 mice were unable to clear the wild-type P. aeruginosa strains PA01 and PA14, with bacterial titers increasing greater than tenfold. By contrast, CD-1 mice could clear infection by the PCN-deficient mutant strains mvfR, phzB1, phzM and phzS. The bacterial loads were 1000–10 000 lower than their respective wild-type strains within 16 h (Table 1) [12]. The in vivo fitness of
Exploiting yeast genomics to identify evolutionarily conserved targets of PCN
Despite numerous documentations of the PCN-mediated cellular injuries, few targets in human cells are known. A lack of molecular targets might have lead to an underestimation of the mechanisms by which PCN causes toxicity. Based on the finding that PCN is capable of killing fungi [30], Ran et al. [13] hypothesized that the eukaryotic cellular pathways that are interrupted by PCN were evolutionarily conserved. They devised a Saccharomyces cerevisiae deletion library screen and recovered 50 yeast
Can PCN help P. aeruginosa compete with other opportunistic pathogens in the CF airways
One unique biochemical feature of PCN is that it can be reduced nonenzymatically by either NADH or NADPH. By contrast, other redox-cycling drugs, such as paraquat (methyl viologen), require paraquat:NAD(P)H-dependent oxidoreductases that are plentiful in bacteria [45]. The seminal paper by Hassan and Fridovich [46] revealed that the antimicrobial activity of PCN was oxygen dependent. Recent evidence from two independent research groups suggests that the airway mucus of patients with CF,
Potential therapeutic strategies for PCN-associated pathogenesis
Apart from being a Cl− channel, CFTR also downregulates the expression of important alternative channels, such as ENaC (epithelial sodium channel) and CaCCs (Ca2+-dependent Cl− channels), while upregulating the function of ORCCs (outwardly rectifying Cl− channels) and VRACs (volume-regulated anion channels) [52]. The reduction of properly localized and inactive ΔF508-CFTR, as a result of V-ATPase inactivation and ATP depletion by PCN, might further destabilize the regulation of these ion
Concluding remarks
Recently acquired information about the virulence roles of PCN in vivo and the evolutionarily conserved molecular targets of PCN should provide strong support that the full virulence of P. aeruginosa during airway infections requires PCN biosynthesis, and strengthens the credibility of previous in vitro observations about PCN-mediated injury and killing of lung epithelial cells. Future efforts to correlate PCN secretion and toxicity to the inactivation of various PCN targets in localized and
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