Therapeutic potential of GW501516 and the role of Peroxisome proliferator-activated receptor ß/δ and B-cell lymphoma 6 in inflammatory signaling in human pancreatic cancer cells.

Peroxisome proliferator-activated receptor ß/δ (PPARß/δ) is a member of the nuclear receptor superfamily and a ligand-activated transcription factor that is involved in the regulation of the inflammatory response via activation of anti-inflammatory target genes and ligand-induced disassociation with the transcriptional repressor B-cell lymphoma 6 (BCL6). Chronic pancreatitis is considered to be a significant etiological factor for pancreatic cancer development, and a better understanding of the underlying mechanisms of the transition between inflammation and carcinogenesis would help further elucidate chemopreventative options. The aim of this study was to determine the role of PPARß/δ and BCL6 in human pancreatic cancer of ductal origin, as well as the therapeutic potential of PPARß/δ agonist, GW501516. Over-expression of PPARß/δ inhibited basal and TNFα-induced Nfkb luciferase activity. GW501516-activated PPARß/δ suppressed TNFα-induced Nfkb reporter activity. RNAi knockdown of Pparb attenuated the GW501516 effect on Nfkb luciferase, while knockdown of Bcl6 enhanced TNFα-induced Nfkb activity. PPARß/δ activation induced expression of several anti-inflammatory genes in a dose-dependent manner, and GW501516 inhibited Mcp1 promoter-driven luciferase in a BCL6-dependent manner. Several pro-inflammatory genes were suppressed in a BCL6-dependent manner. Conditioned media from GW501516-treated pancreatic cancer cells suppressed pro-inflammatory expression in THP-1 macrophages as well as reduced invasiveness across a basement membrane. These results demonstrate that PPARß/δ and BCL6 regulate anti-inflammatory signaling in human pancreatic cancer cells by inhibiting NFκB and pro-inflammatory gene expression, and via induction of anti-inflammatory target genes. Activation of PPARß/δ may be a useful target in pancreatic cancer therapeutics.

Role of Peroxisome Proliferator-Activated Receptor ß/δ and B-Cell Lymphoma-6 in Regulation of Genes Involved in Metastasis and Migration in Pancreatic Cancer Cells.

PPARß/δ is a ligand-activated transcription factor that regulates various cellular functions via induction of target genes directly or in concert with its associated transcriptional repressor, BCL-6. Matrix remodeling proteinases are frequently over-expressed in pancreatic cancer and are involved with metastasis. The present study tested the hypothesis that PPARß/δ is expressed in human pancreatic cancer cells and that its activation could regulate MMP-9, decreasing cancer cells ability to transverse the basement membrane. In human pancreatic cancer tissue there was significantly higher expression of MMP-9 and PPARß/δ, and lower levels of BCL-6 mRNA. PPARß/δ activation reduced the TNF α -induced expression of various genes implicated in metastasis and reduced the invasion through a basement membrane in cell culture models. Through the use of short hairpin RNA inhibitors of PPARß/δ, BCL-6, and MMP-9, it was evident that PPARß/δ was responsible for the ligand-dependent effects whereas BCL-6 dissociation upon GW501516 treatment was ultimately responsible for decreasing MMP-9 expression and hence invasion activity. These results suggest that PPARß/δ plays a role in regulating pancreatic cancer cell invasion through regulation of genes via ligand-dependent release of BCL-6 and that activation of the receptor may provide an alternative therapeutic method for controlling migration and metastasis.

The oxidative stress mediator 4-hydroxynonenal is an intracellular agonist of the nuclear receptor peroxisome proliferator-activated receptor-beta/delta (PPARbeta/delta).

Liver insufficiency and damage are major causes of death and disease worldwide and may result from exposure to environmental toxicants, specific combinations or dosages of pharmaceuticals, and microbial metabolites. The generation of reactive intermediates, in particular 4-hydroxynonenal (4-HNE), is a common event in liver damage caused by a variety of hepatotoxic drugs and solvents. The peroxisome proliferator-activated receptors (PPARs) are nuclear receptors that are involved in the transcriptional regulation of lipid metabolism as well as other biological functions. Importantly, we have observed that the PPARbeta/delta-/- mouse is more susceptible to chemically induced hepatotoxicity than its wild-type counterpart, and our objective in this study was to elucidate the mechanism(s) by which PPARbeta/delta confers protection to hepatocytes. We hypothesized that PPARbeta/delta plays a protective role by responding to toxic lipids and altering gene expression accordingly. In support, oxidized-VLDL and constituents including 13-S-hydroxyoctadecadienoic acid (13-S-HODE) and 4-HNE are PPARbeta/delta ligands. A structure-activity relationship was established where 4-HNE and 4-hydroperoxynonenal (4-HpNE) enhanced the activity of the PPARbeta/delta subtype while 4-hyroxyhexenal (4-HHE), 4-oxo-2-Nonenal (4-ONE), and trans-4,5-epoxy-2(E)-decenal did not activate this receptor. Increasing PPARbeta/delta activity with a synthetic agonist decreased sensitivity of hepatocytes to 4-HNE and other toxic agents, whereas inhibition of this receptor had the opposite result. Gene expression microarray analysis identified several important PPARbeta/delta-regulated detoxification enzymes involved in 4-HNE metabolism that are regulated at the transcript level. This research established 4-HNE as an endogenous modulator of PPARbeta/delta activity and raises the possibility that agonists of this nuclear receptor may be utilized to prevent or treat liver disease associated with oxidative damage.