15-Lipoxygenase-2 gene regulation by its product 15-(S)-hydroxyeicosatetraenoic acid through a negative feedback mechanism that involves peroxisome proliferator-activated receptor gamma.

An inverse relationship exists between the expression of 15-lipoxygenase-2 (15-LOX-2) and peroxisome proliferator-activated receptor gamma (PPARgamma) in normal prostate epithelial cells (PrECs) compared with their expression in prostate carcinoma cells (PC-3). The reason for this difference, however, is unknown. We hypothesized that this inverse expression partly involves the 15-LOX-2 promoter and 15-S-hydroxyeicosatetraenoic acid (15-(S)-HETE), a product of 15-LOX-2 that binds to PPARgamma. We identified an active steroid nuclear receptor half-site present in the 15-LOX-2 promoter fragment F-5 (-618/+177) that can interact with PPARgamma. After forced expression of wild-type PPARgamma, 15-(S)-HETE (1 microM) decreased F-5 reporter activity in PrECs whereas forced expression of 15-LOX-2 resulted in 15-(S)-HETE production which enhanced F-5 activity in PC-3. In contrast, the expression of dominant-negative PPARgamma reversed the transcriptional activation of F-5 by enhancing it 202-fold in PrEC or suppressing it in PC-3; the effect in PC-3 was positively increased 150-fold in the presence of 15-(S)-HETE (1 microM). Peroxisome proliferator-activated receptor gamma interacted with 15-LOX-2 promoter sequences in pulldown experiments using biotinylated 15-LOX-2 (-560/-596 bp) oligonucleotides. In gelshift analyses PPARgamma and orphan receptor RORalpha were shown to interact with the F-5 fragment in PC-3 cells. These data suggest that crosstalk mechanisms exist between the 15-LOX-2 gene and PPARgamma to counterbalance expression and help explain the inverse relationship of these genes in normal versus cancer cells.

Differential expression of cyclooxygenase-2 and its regulation by tumor necrosis factor-alpha in normal and malignant prostate cells.

Cyclooxygenase (COX)-2 expression is elevated in some malignancies; however, information is scarce regarding COX-2 contributions to the development of prostate cancer and its regulation by inflammatory cytokines. The present study compared and contrasted the expression levels and subcellular distribution patterns of COX-1 and COX-2 in normal prostate [prostate epithelial cell (PrEC), prostate smooth muscle (PrSM), and prostate stromal (PrSt)] primary cell cultures and prostatic carcinoma cell lines (PC-3, LNCaP, and DU145). The basal COX-2 mRNA and protein levels were high in normal PrEC and low in tumor cells, unlike many other normal cells and tumor cells. Because COX-2 levels were low in prostate smooth muscle cells, prostate stromal cells, and tumor cells, we also examined whether COX-1 and COX-2 gene expression was elevated in response to tumor necrosis factor-alpha (TNF-alpha), a strong inducer of COX-2 expression. Northern blot analysis and reverse transcription-PCR demonstrated different patterns and kinetics of expression for COX-1 and COX-2 among normal cells and tumor cells in response to TNF-alpha. In particular, COX-2 protein levels increased, and the subcellular distribution formed a distinct perinuclear ring in the normal cells at 4 h after TNF-alpha exposure. The COX-2 protein levels also increased in cancer cells, but the subcellular distribution was less organized; COX-2 protein appeared diffuse in some cells and accumulated as focal deposits in the cytoplasm of other cells. TNF-alpha induction of COX-2 and prostaglandin E2 correlated inversely with induction of apoptosis. We conclude that COX-2 expression may be important to PrEC cell function. Although it is low in stromal and tumor cells, COX-2 expression is induced by TNF-alpha in these cells, and this responsiveness may play an important role in prostate cancer progression.

Interferon-beta prevents the upregulation of interleukin-8 expression in human melanoma cells.

The constitutive expression of interleukin-8 (IL-8) by human melanoma cells correlates with their metastatic potential. The exposure of human melanoma cells to the inflammatory cytokines IL-1 beta or tumor necrosis factor-alpha (TNF-alpha) upregulated IL-8 expression in a time-dependent and concentration-dependent manner. This enhanced expression of IL-8 was inhibited by cycloheximide or actinomycin-D. Treatment of melanoma cells with interferon (IFN) alpha, beta, or gamma did not affect the constitutive expression of IL-8, but IFN-alpha and IFN-beta blocked the upregulation of IL-8 expression in cells treated with IL-1 beta or TNF-alpha subsequent to or simultaneously with the IFN. These data suggest that the expression of IL-8 in human melanoma cells can be upregulated by inflammatory cytokines and that IFN-alpha and IFN-beta can counterregulate this stimulation.

Cell density-dependent regulation of basic fibroblast growth factor expression in human renal cell carcinoma cells.

We investigated some of the mechanisms that regulate the expression of basic fibroblast growth factor (bFGF) in human renal cell carcinoma (HRCC). HRCC SN12PM6 cells were cultured as adherent monolayers. The expression of steady-state bFGF mRNA (measured by in situ hybridization and Northern blot) and protein (measured by immunohistochemistry and ELISA) correlated inversely with the culture density. Tumor cells harvested from dense cultures (low bFGF expression) and plated under sparse conditions expressed high levels of bFGF mRNA and protein prior to cell division, suggesting that bFGF may be a competence factor. Similar data were obtained with human vascular endothelial cells. The expression of bFGF was not regulated by spent culture medium, cell cycle, or rate of cell division but was down-regulated by contract inhibition. These data show that the expression of bFGF in HRCC is cell density dependent.

Cell density-dependent modulation of basic fibroblast growth factor expression by human interferon-beta.

The production of basic fibroblast growth factor (bFGF) by human renal cell carcinoma (HRCC) is associated with induction of angiogenesis. Incubation of HRCC cells with human interferon alpha (IFN-alpha) or interferon beta (IFN-beta) downregulates the expression of bFGF and, hence, angiogenesis. The purpose of this study was to analyze the downregulation of the expression of bFGF in HRCC cells by IFN-alpha and IFN-beta. Human HRCC SN12PM6 cells cultured under sparse conditions expressed 3-7-fold higher levels of steady-state bFGF-specific mRNA transcripts and cellular bFGF protein than did confluent cultures. IFN-alpha or IFN-beta inhibited the steady-state expression of bFGF mRNA transcripts and cellular bFGF protein in a concentration-dependent manner in sparse but not confluent cultures. Moreover, IFN-beta downregulated the transcription rate of bFGF genes and inhibited the de novo synthesis of bFGF protein only in sparse cultures. The results demonstrate that the inhibitory effects of IFN- and -beta on bFGF expression are cell-density dependent.

Activation of inducible nitric oxide synthase gene in murine macrophages requires protein phosphatases 1 and 2A activities.

The purpose of these studies was to identify phosphatase activities required for the production of nitric oxide in murine macrophages exposed to lipopolysaccharide (LPS), synthetic lipopeptide (LPP), and mouse interferon-gamma (IFN-gamma). The in vitro treatment of macrophages with IFN-gamma and LPS or IFN-gamma and LPP resulted in production of NO, which was inhibited by addition of the specific phosphatase 1 and 2A (PP1/2A) inhibitors okadaic acid (OA), calyculin A, and cantharidin (but not the nonactive analogues okadaic acid tetraacetate and 1,4-dimethylendothall). OA suppressed the accumulation of steady-state inducible NO synthase (iNOS) mRNA and iNOS protein (without alteration of their stability). The cytosol and nuclei of control macrophages contained large amounts of PP1/2A activities that were inhibited by OA in a dose-dependent manner. Taken together, these data indicate that PP1/2A activities are involved in the regulation of iNOS gene expression in murine macrophages.

Interferons alpha and beta down-regulate the expression of basic fibroblast growth factor in human carcinomas.

We investigated the influence of interferons alpha, beta, and gamma (IFN-alpha, -beta, and -gamma) on the production of basic fibroblast growth factor (bFGF) by human renal carcinoma cells. The human renal carcinoma cell metastatic line SN12PM6 was established in culture from a lung metastasis and SN12PM6-resistant cells were selected in vitro for resistance to the antiproliferative effects of IFN-alpha or IFN-beta. IFN-alpha and IFN-beta, but not IFN-gamma, down-regulated the expression of bFGF at the mRNA and protein levels by a mechanism independent of their antiproliferative effects. Down-regulation of bFGF required a long exposure (> 4 days) of cells to low concentrations (> 10 units/ml) of IFN-alpha or IFN-beta. The withdrawal of IFN-alpha or IFN-beta from the medium permitted SN12PM6-resistant cells to resume production of bFGF. The incubation of human bladder, prostate, colon, and breast carcinoma cells with noncytostatic concentrations of IFN-alpha or IFN-beta also produced down-regulation of bFGF production.

Natural and recombinant human interleukin 1-beta is cytotoxic for human melanoma cells.

Human peripheral blood monocytes stimulated with LPS were found to release an activity that was cytotoxic for the A375 melanoma. Biochemical and immunological characterization of the activity indicated that IL 1-beta was the cytotoxic agent. Human recombinant IL 1-beta, purified to homogeneity, was directly cytotoxic for A375. Tumor necrosis factor, also released by activated monocytes, was not cytotoxic for the A375 melanoma.

Visualization of primate high density lipoproteins isolated by density gradient ultracentrifugation.

High density lipoproteins (HDL) isolated by density gradient ultracentrifugation from the plasma of monkeys ingesting semipurified diets are barely visible. This creates difficulty in separating HDL from other lower density lipoproteins following centrifugation and necessitates collecting lared quantities of background density solution to insure complete recovery of the HDL fraction. A simple procedure is described involving the addition of beta-carotene to nonhuman primate plasma prior to centrifugation which results in the delineation of HDL as a discrete yellow-orange band without affecting certain physical properties of HDL or interfering with standard lipid and protein assays.