Inhibition of Ca²⁺-Independent Phospholipase A₂ Decreases Prostate Cancer Cell Growth by p53-Dependent and Independent Mechanisms

Abstract

The mechanisms by which Ca 2ϩ -independent phospholipase A 2 (iPLA 2 ) mediates cell growth in p53-positive LNCaP and p53-negative PC-3 prostate cancer cell lines were studied. Exposure of cells to the iPLA 2 selective inhibitor bromoenol lactone (BEL; 0 -20 M) induced concentration-and time-dependent decreases in cell growth based on 3-(4, dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide staining and cell number. Decreased cell growth was not caused by cell death as BEL exposure did not alter nuclear morphology or increase annexin V (apoptotic cell marker) or propidium iodide (necrotic cell marker) staining after 48 h. Decreased growth correlated to a G 1 /G 0 arrest in LNCaP cells and a G 2 /M arrest in PC-3 cells. In LNCaP cells, G 1 arrest was preceded by time-(0 -48 h) and concentration-dependent (0 -10 M) increases in the expression of the tumor suppresser protein p53 and the cyclin-dependent kinase inhibitor p21. Increases in p53 expression preceded increases in p21 expression by 8 h. In LNCaP cells, BEL treatment decreased the expression of the p53 antagonist Mdm2, while increasing Akt phosphorylation. BEL treatment also increased Akt phosphorylation in PC-3 cells, but Mdm2 was not detected. The ability of BEL to increase Akt phosphorylation was inhibited by the phosphoinositide 3-kinase inhibitor LY294002 [2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one]. BEL treatment also decreased agonist-induced activation of the epidermal growth factor receptor. These data suggest that inhibition of iPLA 2 decreases prostate cancer cell growth by p53-dependent and independent mechanisms. Furthermore, alterations in Mdm2 and epidermal growth factor receptor activation following BEL exposure suggest novel roles for iPLA 2 in prostate cancer cell signaling.

Pharmacological Targeting of the Integrated Protein Kinase B, Phosphatase and Tensin Homolog Deleted on Chromosome 10, and Transforming Growth Factor-β Pathways in Prostate Cancer

“…This was associated with G o /G 1 stage cell cycle arrest proceeded by increased p53 and p21 and decreased expression of the p53 antagonist MDM2 (Sun et al, 2008). Bromoenol lactone also inhibited proliferation of the PC-3 (mutant p53) cell type, indicating that both p53-dependent and -independent pathways can be influenced by cPLA2.…”

Enhanced antitumor activity of low-dose continuous administration schedules of topotecan in prostate cancer

“…Our previous studies in LNCaP and PC-3 cells using other lactone derivatives demonstrated that G 2 /M arrest correlated with activation of p21, and that p21 could be activated in the absence of p53. 28,29 Thus, we assessed the hypothesis that changes in cell cycle induced by metronomic dosing regimens were mediated by p21 using immunoblot analysis. We also assessed p53 expression in LNCaP cells as these underwent a slight, but significant sub G 1 arrest after 72 h, which can be mediated by p53.…”

Regulation and Pathological Role of p53 in Cisplatin Nephrotoxicity

“…ER-iPLA 2 , an ER-associated protein, may regulate p53 signaling at different levels. In cancer cell lines, inhibition of ER-iPLA 2 induced growth arrest and probably apoptosis via p53-dependent and -independent mechanisms Sun et al, 2008); however, in renal tubular cells, ER-iPLA 2 was demonstrated to participate in cisplatin-induced apoptosis downstream of p53 and upstream of caspase 3 (Cummings et al, 2004). Thus, p53 may simultaneously induce cell death and survival signals during cisplatin nephrotoxicity through transactivation of different sets of genes.…”