Paraoxonase 2 Serves a Proapopotic Function in Mouse and Human Cells in Response to the Pseudomonas aeruginosa Quorum-sensing Molecule N-(3-Oxododecanoyl)-homoserine Lactone

Abstract

Pseudomonas aeruginosa use quorum-sensing molecules, including N-(3-oxododecanoyl)-homoserine lactone (C12), for intercellular communication. C12 activated apoptosis in mouse embryo fibroblasts (MEF) from both wild type (WT) and Bax/Bak double knock-out mice (WT MEF and DKO MEF that were responsive to C12, DKO(R) MEF): nuclei fragmented; mitochondrial membrane potential (Δψ(mito)) depolarized; Ca(2+) was released from the endoplasmic reticulum (ER), increasing cytosolic [Ca(2+)] (Ca(cyto)); and caspase 3/7 was activated. DKO(R) MEF had been isolated from a nonclonal pool of DKO MEF that were non-responsive to C12 (DKO(NR) MEF). RNAseq analysis, quantitative PCR, and Western blots showed that WT and DKO(R) MEF both expressed genes associated with cancer, including paraoxonase 2 (PON2), whereas DKO(NR) MEF expressed little PON2. Adenovirus-mediated expression of human PON2 in DKO(NR) MEF rendered them responsive to C12: Δψ(mito) depolarized, Ca(cyto) increased, and caspase 3/7 activated. Human embryonic kidney 293T (HEK293T) cells expressed low levels of endogenous PON2, and these cells were also less responsive to C12. Overexpression of PON2, but not PON2-H114Q (no lactonase activity) in HEK293T cells caused them to become sensitive to C12. Because [C12] may reach high levels in biofilms in lungs of cystic fibrosis (CF) patients, PON2 lactonase activity may control Δψ(mito), Ca(2+) release from the ER, and apoptosis in CF airway epithelia. Coupled with previous data, these results also indicate that PON2 uses its lactonase activity to prevent Bax- and Bak-dependent apoptosis in response to common proapoptotic drugs like doxorubicin and staurosporine, but activates Bax- and Bak-independent apoptosis in response to C12