-induced apoptosis does not require PPAR in breast cancer cells

Naturally occurring derivatives of arachidonic acid are potent agonists for the nuclear hormone receptor peroxisome proliferator-activated receptor gamma (PPAR ) and block cancer cell proliferation through the induction of apoptosis. We have previously reported that induction of apoptosis using cyclopentenone prostaglandins of the J series, including 15deoxy 12,14 PGJ 2 (15dPGJ 2 ), is associated with a high degree of PPAR-response element (PPRE) activity and requires early de novo gene expression in breast cancer cells. In the current study, we used pharmacologic and genetic approaches to test the hypothesis that PPAR is required for 15dPGJ 2 -induced apoptosis. The PPAR agonists 15dPGJ 2 , trogliltazone (TGZ), and GW7845, a synthetic and highly selective tyrosine-based PPAR agonist, all increased transcriptional activity of PPAR , and expression of CD36, a PPAR -dependent gene. Transcriptional activity and CD36 expression was reduced by GW9662, a selective and irreversible PPAR antagonist, but GW9662 did not block apoptosis induced by 15dPGJ 2 . Moreover, dominant negative expression of PPAR blocked PPRE transcriptional activity, but did not block 15dPGJ 2 -induced apoptosis. These studies show that while 15dPGJ 2 activates PPRE-mediated transcription, PPAR is not required for 15dPGJ 2 -induced apoptosis in breast cancer cells. Other likely mechanisms through which cyclopentenone prostaglandins induce apoptosis of cancer cells are discussed. — Clay, C. E., A. Monjazeb, J. Thorburn, F. H. Chilton, and K. P. High. 15-Deoxy12,14 -prostaglandin J 2 -induced apoptosis does not require PPAR in breast cancer cells. J. Lipid Res. 2002. 43: 1818–1828. Supplementary key words cyclopentenone prostaglandins • arachidonic acid metabolism • peroxisome proliferator-activated receptor Peroxisome proliferator-activated receptor gamma (PPAR ) is a ligand activated transcription factor that induces expression of PPAR-response element (PPRE) containing genes critical to diabetes, obesity, inflammation, and cancer (1). PPAR is activated by a diverse array of synthetic compounds including thiazolidinediones (TZDs), triterpenoids and tyrosine-based compounds, and naturally occurring lipid compounds including derivatives of fatty acid metabolism and oxidized fractions of LDL. The tyrosine based PPAR agonists (GW7845 and GW1929) induce neuroblastoma differentiation (2), inhibit mammary carcinogenesis (3), reverse the diabetic phenotype in mouse models (4), and block atherosclerosis (5) in part by inhibiting vascular smooth muscle cell proliferation and neointima formation (6). The synthetic triterpinoid 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid (CDDO) induces differentiation and apoptosis in human osteosarcoma and myeloid leukemia cells (7, 8). The TZDs, troglitazone (TGZ, Rezulin ® ), rosiglitazone (Rosi, BRL49653, Avandia ® ), and pioglitazone (Pio, Actos ® ) are effective anti-diabetes drugs and reduce the growth of several cancer cell types (9). However, their clinical application as chemotherapeutic drugs has been discouraging to date, due to unpredictable clinical performance and lack of efficacy in human trials (10–12). However, very recent data suggest that some properties of these drugs may not be related to their capacity to activate PPAR (13), suggesting there may be opportunities to enhance the anti-cancer activity of these compounds by better understanding their mechanism of action while maintaining their relative safety versus conventional chemotherapeutic agents. Of the naturally occurring PPAR agonists, the cyclopentenone prostaglandin, 15deoxy 12,14 PGJ 2 (15dPGJ 2 ), is among the most potent for both transactivating PPAR Abbreviations: CDDO, 2-cyano-3,12-dioxoolean-1,9-dien-28-oic acid; DN, dominant negative PPAR ; 15dPGJ 2 , 15deoxy 12,14 PGJ 2 ; PPAR , peroxisome proliferator-activated receptor gamma; PPRE, PPAR-response element; ROS, reactive oxygen species; TGZ, troglitazone; TZD, thiazolidinedione; WT, wild type PPAR . 1 To whom correspondence should be addressed. e-mail: khigh@wfubmc.edu Manuscript received 8 June 2002 and in revised form 24 July 2002. Published, JLR Papers in Press, August 16, 2002. DOI 10.1194/jlr.M200224-JLR200 by gest, on July 9, 2018 w w w .j.org D ow nladed fom