Lysophosphatidic acid attenuates the cytotoxic effects and degree of peroxisome proliferator-activated receptor gamma activation induced by 15-deoxy Delta(12), (14)-prostaglandin J(2) in neuroblastoma cells

摘要

PPARgamma (peroxisome proliferator-activated receptor gamma) is a ligand-activated transcription factor that responds to 15dPGJ(2) (15-deoxyA Delta(12.14)-prostglandin J(2)). 15dPGJ(2), in vitro, halts neuroblastoma cell growth, but reported mechanisms vary. Here we evaluated the modulatory effects of endogenous serum lipid mitogens upon the extent of 15dPGJ(2)-induced growth inhibition and on the precise cellular responses of neuroblastoma cells to PPARgamma activation. We show that 15dPGJ2 specifically inhibited cell growth in both complete and delipidated media. 15dPGJ2-induced growth inhibition was accompanied by decreased cell viability, although the effect was far more marked in delipidated medium than in complete medium. Incubation with 15dPGJ(2) in complete medium resulted in cytoplasmic changes characteristic of type II programmed cell death (autophagy), while prior serum lipid removal resulted in cell death via an apoptotic mechanism. These distinct, serum lipid-dependent cellular responses to 15dPGJ(2) were accompanied by increases in the expression of a reporter gene construct containing a PPAR response element of 2.3-fold in complete medium, but of 4.8-fold in delipidated medium. Restoration of the serum lysolipid LPA (lysophosphaticlic acid) to cells in delipidated medium reduced 15dPGJ(2)-mediated PPARgamma activation, growth inhibition and cell death; following addition of S1P (sphingosine 1-phosphate), decreases were apparent but more marginal. Further, while the effects of LPA in del ipiclated medium were mediated through a G(i)/phosphomositide 3-kinase/MAPK (mitogen-activated protein kinase) pathway, those of S1P did not involve the MAPK component. These data suggest that the serum lysolipid LPA modulates the degree of PPARgamma activation and the precise cellular response to 15dPGJ(2) via activation of a G(i)/phosphoinositide 3-kinase/MAPK pathway.