9-deoxy-delta-9-prostaglandin-d2 and Pancreatic-Neoplasms

Peroxisome proliferator-activated receptor-gamma (PPARgamma) ligands have been shown to possess anti-inflammatory properties that include the inhibition of transcription factor activation and the expression of inflammatory genes. Using pancreatic beta-cells, we have shown that PPARgamma ligands such as 15-deoxy-Delta(12,14)-prostaglandin J(2) (PGJ(2)) attenuate interferon-gamma-induced signal transducer and activator of transcription 1 activation and interleukin (IL)-1beta-induced nuclear factor-kappaB activation by a pathway that correlates with endoplasmic reticulum stress and the induction of the unfolded protein response (UPR). The UPR is a conserved cellular response activated by a number of cell stressors and is believed to alleviate the stress and promote cell survival. However, prolonged activation of the UPR results in cellular death by apoptosis. In this report, we have examined the effects of PGJ(2) on UPR activation and the consequences of this activation on cell survival. Consistent with induction of a cell death pathway, treatment of rat islets and RINm5F cells for 24 h with PGJ(2) results in caspase-3 activation and caspase-dependent beta-cell death. The actions of these ligands do not appear to be selective for beta-cells, because PGJ(2) stimulates macrophage apoptosis in a similar fashion. Associated with cell death is the enhanced phosphorylation of eukaryotic initiation factor 2alpha (eIF2alpha), and in cells expressing a mutant of eIF2alpha that cannot be phosphorylated, the stimulatory actions of PGJ(2) on caspase-3 activation are augmented. These findings suggest that, whereas PGJ(2)-induced UPR activation is associated with an inhibition of cytokine signaling, prolonged UPR activation results in cell death, and that eIF2alpha phosphorylation may function in a protective manner to attenuate cell death.

Topics: Animals; Apoptosis; Caspase 3; Cells, Cultured; Enzyme Activation; Eukaryotic Initiation Factor-2; Insulin-Secreting Cells; Insulinoma; Ligands; Macrophages; Male; Mice; Mutation; Pancreatic Neoplasms; Phosphorylation; PPAR gamma; Prostaglandin D2; Protein Folding; Rats; Rats, Sprague-Dawley; Time Factors

The PI3K pathway contributes to the invasive properties and apoptosis resistance that epitomize pancreatic cancers. PPARgamma is a ligand-activated transcription factor with anti-inflammatory and anti-tumor effects; the mechanisms of tumor suppression are unknown. The purpose of this study was to examine whether activation of PPARgamma can increase the expression of the tumor suppressor PTEN and inhibit PI3K activity. AsPC-1 human pancreatic cancer cells, transfected with a PPRE-luciferase construct, demonstrated increased luminescence following treatment with PPARgamma ligands, indicating the presence of functional PPARgamma protein. The selective PPARgamma ligand rosiglitazone increased PTEN expression in AsPC-1 cells; concurrent treatment with GW9662, which inhibits PPARgamma activation, prevented the increase in PTEN protein levels. Levels of phosphorylated Akt decreased as PTEN levels increased, indicating inhibition of PI3K activity. Taken together, our results suggest that activation of PPARgamma may represent a novel approach for the treatment of pancreatic cancer by increasing PTEN levels and inhibiting PI3K activity.

Topics: DNA-Binding Proteins; Genes, Reporter; Humans; Ligands; Nuclear Proteins; Pancreatic Neoplasms; Phosphatidylinositol 3-Kinases; Phosphoric Monoester Hydrolases; Prostaglandin D2; Protein Serine-Threonine Kinases; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-akt; PTEN Phosphohydrolase; Receptors, Cytoplasmic and Nuclear; Recombinant Fusion Proteins; Repressor Proteins; Thiazoles; Thiazolidinediones; Transcription Factors; Tumor Cells, Cultured; Tumor Suppressor Proteins