Lysophosphatidic acid attenuates the cytotoxic effects and degree of peroxisome proliferator-activated receptor γ activation induced by 15-deoxyΔ12,14-prostaglandin J2 in neuroblastoma cells

摘要

pPPARγ (peroxisome proliferator-activated receptor γ) is a ligand-activated transcription factor that responds to 15dPGJsub2/sub (15-deoxy-Δsup12,14/sup-prostglandin Jsub2/sub). 15dPGJsub2/sub, iin vitro/i, halts neuroblastoma cell growth, but reported mechanisms vary. Here we evaluated the modulatory effects of endogenous serum lipid mitogens upon the extent of 15dPGJsub2/sub-induced growth inhibition and on the precise cellular responses of neuroblastoma cells to PPARγ activation. We show that 15dPGJsub2/sub specifically inhibited cell growth in both complete and delipidated media. 15dPGJsub2/sub-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 15dPGJsub2/sub 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 15dPGJsub2/sub 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 (lysophosphatidic acid) to cells in delipidated medium reduced 15dPGJsub2/sub-mediated PPARγ 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 delipidated medium were mediated through a Gsubi/sub/phosphoinositide 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 PPARγ activation and the precise cellular response to 15dPGJsub2/sub via activation of a Gsubi/sub/phosphoinositide 3-kinase/MAPK pathway./p