Phosphatidylinositol-(3,4,5)-Trisphosphate Induces Phagocytosis of NonmotilePseudomonas aeruginosa
ABSTRACTPathogenic bacteria that establish chronic infections in immunocompromised patients frequently undergo adaptation or selection for traits that are advantageous for their growth and survival. Clinical isolates ofPseudomonas aeruginosa, a Gram-negative, opportunistic bacterial pathogen, exhibit a temporal transition from a motile to a nonmotile phenotype through loss of flagellar motility during the course of chronic infection. This progressive loss of motility is associated with increased resistance to both antibiotic and immune clearance. We have previously shown that loss of bacterial motility enablesP. aeruginosato evade phagocytic clearance bothin vitroandin vivoand fails to activate the phosphatidylinositol 3-kinase (PI3K)/Akt-dependent phagocytic pathway. Therefore, we tested the hypothesis that clearance of phagocytosis-resistant bacteria could be induced by exogenously pretreating innate immune cells with the Akt-activating molecule phosphatidylinositol-(3,4,5)-trisphosphate (PIP3). Here, we demonstrate that PIP3induces the uptake of nonmotileP. aeruginosaby primary human neutrophils >25-fold, and this effect is phenocopied with the use of murine phagocytes. However, surprisingly, mechanistic studies revealed that the induction of phagocytosis by PIP3occurs because polyphosphoinositides promote bacterial binding by the phagocytes rather than bypassing the requirement for PI3K. Moreover, this induction was selective since the uptake of other nonmotile Gram-negative, but not Gram-positive, bacteria can also be induced by PIP3. Since there is currently no treatment that effectively eradicates chronicP. aeruginosainfections, these findings provide novel insights into a potential methodology by which to induce clearance of nonmotile pathogenic bacteria and into the endogenous determinants of phagocytic recognition ofP. aeruginosa.