Cancer Stem Cell Phenotype Is Supported by Secretory Phospholipase A2 in Human Lung Cancer Cells.

Background Lung cancer stem cells (CSCs) are a subpopulation of cells that drive growth, invasiveness, and resistance to therapy. Inflammatory eicosanoids are critical to maintain this malignant subpopulation. Secretory phospholipase A₂ group IIa (sPLA₂) is an important mediator of the growth and invasive potential of human lung cancer cells and regulates eicosanoid production. We hypothesized that sPLA₂ plays a role in the maintenance of lung CSCs. Methods Cancer stem cells from lung adenocarcinoma cell lines H125 and A549 were isolated using aldehyde dehydrogenase activity and flow cytometry. Protein and mRNA levels for sPLA₂ were compared between sorted cells using Western blotting and quantitative reverse transcriptase-polymerase chain reaction techniques. Chemical inhibition of sPLA₂ and short-hairpin RNA knockdown of sPLA₂ were used to evaluate effects on tumorsphere formation. Results Lung CSCs were isolated in 8.9% ± 4.1% (mean ± SD) and 4.1% ± 1.6% of H125 and A549 cells respectively. Both sPLA₂ protein and mRNA expression were significantly elevated in the CSC subpopulation of H125 (p = 0.002) and A549 (p = 0.005; n = 4). Knockdown of sPLA₂ significantly reduced tumorsphere formation in H125 (p = 0.026) and A549 (p = 0.001; n = 3). Chemical inhibition of sPLA₂ resulted in dose-dependent reduction in tumorsphere formation in H125 (p = 0.003) and A549 (p = 0.076; n = 3). Conclusions Lung CSCs express higher levels of sPLA₂ than the non-stem cell population. Our findings that viral knockdown and chemical inhibition of sPLA₂ reduce tumorsphere formation in lung cancer cells demonstrate for the first time that sPLA₂ plays an important role in CSCs. These findings suggest that sPLA₂ may be an important therapeutic target for human lung cancer. [ABSTRACT FROM AUTHOR]