9-deoxy-delta-9-prostaglandin-d2 and Carcinoma--Hepatocellular

Peroxisome proliferator-activated receptors (PPARs) mediate the effects of various ligands, known as peroxisome proliferators, a heterogeneous class of compounds including industrial chemicals, pharmaceuticals, and biomolecules such as fatty acids and eicosanoids. Among peroxisome proliferators, fibrate derivatives are considered specific ligands for PPARα, whereas eicosanoids, such as PGJ2, for PPARγ. The study aimed to clarify the relation between PPARs and apoptosis or proliferation on the same type of cells, using clofibrate as specific ligand of PPARα and PGJ2 as specific ligand of PPARγ. The cells used were human hepatocarcinoma HepG2 cells. The results showed that PPARα protein content increased in HepG2 cells treated with clofibrate, causing apoptosis in a time- and concentration-dependent way, as evidenced by the citofluorimetric assay and determination of BAD, myc and protein phosphatase 2A protein content. It also emerged that PPARγ increased in the same cells when treated with a specific ligand of this PPAR; in this case the increase of PPARγ did not cause an increase of apoptosis, but a time- and concentration-dependent inhibition of cell proliferation, evidenced by decreased cell numbers and increased number of cells in the G0/G1 phase of the cycle. It may be concluded that PPARα is chiefly related to apoptosis and PPARγ to cell proliferation.

Topics: Apoptosis; bcl-Associated Death Protein; Carcinoma, Hepatocellular; Cell Cycle; Cell Proliferation; Clofibrate; Hep G2 Cells; Humans; Ligands; Liver Neoplasms; Osmolar Concentration; PPAR alpha; PPAR gamma; Prostaglandin D2; Protein Phosphatase 2; Proto-Oncogene Proteins c-myc; Signal Transduction; Time Factors

We examined a possible role for heat shock factor-1 (HSF-1) in the negative regulation of HO-1 gene expression in human Hep3B hepatoma cells responding to stimulation with 15-deoxy-Delta12,14-prostaglandin J2 (15d-PGJ2) and arsenite. Overexpression of HSF-1 and heat-shock experiments indicated that HSF-1 repressed the 15d-PGJ2-and arsenite-induced HO-1 gene expression through directly binding to the consensus heat shock element (HSE) of the HO-1 gene promoter. In addition, point mutations at specific HSE sequences of the HO-1 promoter-driven luciferase plasmid (pGL2/hHO3.2-Luc) abolished the heat shock- and HSF-1-mediated repression of reporter activity. Overall, it is possible that HSF-1 negatively regulates HO-1 gene expression, and that the HSE present in the -389 to -362 region mediates HSF-1-induced repression of human HO-1 gene expression.

Topics: Antineoplastic Agents; Arsenites; Blotting, Western; Carcinoma, Hepatocellular; Cell Line, Tumor; DNA-Binding Proteins; Electrophoretic Mobility Shift Assay; Enzyme Induction; Gene Expression Regulation, Enzymologic; Genes, Reporter; Heat Shock Transcription Factors; Heme Oxygenase (Decyclizing); Heme Oxygenase-1; Humans; Luciferases; Membrane Proteins; Mutagenesis, Site-Directed; Plasmids; Point Mutation; Promoter Regions, Genetic; Prostaglandin D2; Reverse Transcriptase Polymerase Chain Reaction; Time Factors; Trans-Activators; Transcription Factors; Transcriptional Activation

Human hepatocarcinoma cells (SK-HEP-1) were induced to die through apoptosis by treatment with delta 12-prostaglandin (PG)J2, as characterized by the appearance of a typical DNA ladder. The induction of apoptosis by delta 12-PGJ2 was specifically blocked by cycloheximide (CHX). Western analysis using anti-p53 or anti-WAF1 monoclonal antibodies demonstrated that these two protein levels were increased 3 h after delta 12-PGJ2 treatment, and accumulated for up to 12 h. The induction of p53 protein seemed to be dependent on the increase of p53 mRNA level, which was inhibited by CHX treatment. However, delayed addition of CHX after delta 12-PGJ2 treatment failed to affect both p53 mRNA levels and DNA fragmentation following delta 12-PGJ2 treatment, indicating that the inhibition of p53 synthesis may contribute to the protective effect of CHX against delta 12-PGJ2-mediated cytotoxicity. Therefore, our results suggest that the initial events caused by delta 12-PGJ2, leading ultimately to SK-HEP-1 cell death, involve a certain process required for p53 induction. However, the finding that delta 12-PGJ2 is also active against Hep 3B cells which are devoid of a functional p53 indicates that p53 may not be the critical requirement for inducing apoptosis by delta 12-PGJ2.

Topics: Apoptosis; Carcinoma, Hepatocellular; Cell Survival; Cyclin-Dependent Kinase Inhibitor p21; Cyclins; Cycloheximide; DNA, Neoplasm; Humans; Prostaglandin D2; Prostaglandins, Synthetic; RNA, Messenger; Tumor Cells, Cultured; Tumor Suppressor Protein p53

9-deoxy-delta 9,delta 12-13,14-dihydro-prostaglandin D2 (delta 12-PGJ2) is a potent inhibitor of proliferation of tumor cells. In the present study, the effect of delta 12-PGJ2 on the alpha-fetoprotein(AFP) and the albumin gene expression was analyzed in HuH-7 human hepatoma cells. delta 12-PGJ2 inhibited the cell growth and reduced the medium AFP concentrations dose-dependently. To determine whether this decline of AFP depends only on the relative decrease in cell numbers by delta 12-PGJ2, or is in part, due to the decrease in the cellular AFP synthesis by delta 12-PGJ2, Northern blot analysis was performed in this study. By Northern blotting, it was shown that delta 12-PGJ2 caused a marked reduction in the levels of the AFP mRNA and the albumin mRNA. In contrast, the level of the beta-actin mRNA was not changed by delta 12-PGJ2. In the transient chloramphnicol acetyltransferase plasmid transfection experiments, delta 12-PGJ2 did not suppress the AFP enhancer activity, which possibly regulates both the AFP and the albumin gene expression in HuH-7 hepatoma cells, but resulted in the selective repression of the AFP and the albumin promoter activity. These results suggest that delta 12-PGJ2 suppresses not only cell growth but also expression of the AFP gene and the albumin gene at the transcriptional level in human hepatoma cells.

Topics: Albumins; alpha-Fetoproteins; Blotting, Northern; Carcinoma, Hepatocellular; Cell Division; Chloramphenicol O-Acetyltransferase; Enzyme-Linked Immunosorbent Assay; Gene Expression; Humans; Liver Neoplasms; Promoter Regions, Genetic; Prostaglandin D2; RNA, Messenger; Transfection; Tumor Cells, Cultured