N-myc suppression and cell cycle arrest at G1 phase by prostaglandins

Combined COX-2/PPARγ Expression as Independent Negative Prognosticator for Vulvar Cancer Patients

Vulvar cancer incidence numbers have been rising steadily over the past decades. Especially the number of young patients with vulvar cancer increased recently. Therefore, the need to identify new prognostic factors for vulvar carcinoma is more apparent. Cyclooxygenase-2 (COX-2) has long been an object of scientific interest in the context of carcinogenesis. This enzyme is involved in prostaglandin synthesis and the latter binds to nuclear receptors like PPARγ. Therefore, the aim of this study was to investigate COX-2- and PPARγ- expression in tissues of vulvar carcinomas and to analyze their relevance as prognostic factors. The cytoplasmatic expression of COX-2 as well as PPARγ is associated with a significantly reduced survival, whereas nuclear expression of PPARγ results in a better survival. Especially the combined expression of both COX-2 and PPARγ in the cytoplasm is an independent negative prognosticator for vulvar cancer patients.

The Role of PPAR Ligands in Controlling Growth-Related Gene Expression and their Interaction with Lipoperoxidation Products

Peroxisome proliferators-activated receptors (PPARs) are ligand-activated transcription factors that belong to the nuclear hormone receptor superfamily. The three PPAR isoforms (α, γ and β/δ) have been found to play a pleiotropic role in cell fat metabolism. Furthermore, in recent years, evidence has been found regarding the antiproliferative, proapoptotic, and differentiation-promoting activities displayed by PPAR ligands, particularly by PPARγ ligands. PPAR ligands affect the expression of different growth-related genes through both PPAR-dependent and PPAR-independent mechanisms. Moreover, an interaction between PPAR ligands and other molecules which strengthen the effects of PPAR ligands has been described. Here we review the action of PPAR on the control of gene expression with particular regard to the effect of PPAR ligands on the expression of genes involved in the regulation of cell-cycle, differentiation, and apoptosis. Moreover, the interaction between PPAR ligands and 4-hydroxynonenal (HNE), the major product of the lipid peroxidation, has been reviewed.

Investigation of anticancer mechanism of clavulone II, a coral cyclopentenone prostaglandin analog, in human acute promyelocytic leukemia

The marine prostanoid clavulones were shown to exert cytotoxicity against several cancer cells. In the present study, we illustrate the pathways utilized by clavulone II to trigger apoptotic signaling in human acute promyelocytic leukemia HL-60 cells. Exposure of cells to clavulone II resulted in early induction of phosphatidylserine externalization, mitochondrial dysfunction, and alteration of the cell cycle. Down-regulated expression of cyclin D1 explained the effect of clavulone II on G1 phase arrest of the cell cycle. Clavulone II induced the disruption of mitochondrial membrane potential and activation of caspase-8, -9 and -3 in a time- and concentration-dependent manner. Furthermore, the effect of 3 microM clavulone II was accompanied by the up-regulation of Bax, down-regulation of Mcl-1, and cleavage of Bid. Taken together, it is suggested that low concentrations of clavulone II induce the antiproliferative effect through the down-regulation of cyclin D1 expression and G1 arrest of the cell cycle, while that of high concentration induce the apoptotic cell death via the modulation of members of caspases and Bcl-2 family proteins in HL-60 cells.

Peroxisome proliferator-activated receptor ligands affect growth-related gene expression in human leukemic cells

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated nuclear receptors. Three subtypes of PPARs (alpha, beta, and gamma) have been identified in different tissues. PPAR alpha and PPAR gamma ligands inhibit cell proliferation and induce differentiation in several human cell models. We demonstrated that both PPAR alpha (clofibrate and ciprofibrate) and PPAR gamma ligands (troglitazone and 15 deoxy-prostaglandin J2, 15d-PGJ2) inhibited growth, induced the onset of monocytic-like differentiation, and increased the proportion of G0/G1 cells in the HL-60 leukemic cell line. Moreover, 3 days after the treatment with 2.5 microM 15d-PGJ2, an increase in sub-G0/G1 population occurred, compatible with an induction of programmed cell death. To clarify the mechanisms involved in HL-60 growth inhibition due to the effects of PPAR ligands, we investigated their action on the expression of some genes involved in the control of cell proliferation, differentiation, and cell cycle progression such as c-myc, c-myb, and cyclin D1 and D2. Clofibrate (50 microM), ciprofibrate (50 microM), and 15d-PGJ2 (2.5 microM) inhibited c-myb and cyclin D2 expression, whereas they did not affect c-myc and cyclin D1 expression. Only troglitazone (5 microM) decreased c-myc mRNA and protein levels, besides decreasing c-myb and cyclin D2. The down-regulations of c-myb and cyclin D2 expression represent the first evidence of the inhibitory effect exerted by PPAR ligands on these genes. Moreover, the inhibition of c-myc expression by troglitazone may depend on a PPAR-independent mechanism.

Induction of apoptosis dependent on caspase activities and growth arrest in HL-60 cells by PGA2

Prostaglandin (PG) A2 has been reported to inhibit the growth or induce apoptosis of various tumor cells. In the present study, PGA2 inhibited the growth of HL-60 cells and concomitantly-induced nuclear condensation and DNA fragmentation, characteristics of apoptosis. Down-regulation of c-myc mRNA, and activation of caspase-3 were observed in the PGA2 -treated cells. PGA2-induced DNA fragmentation was completely abolished in the presence of zVAD-Fmk or zDEVD-Fmk. But, relative cell survival was not improved up to that of untreated cells by pretreatment of caspase inhibitors, and c-myc down-regulation was not recovered by caspase inhibitors, either. Moreover, cytochrome c release and activation of caspase-9 was also observed in apoptotic cells and a specific inhibitor of caspase-9 (zLEHD-Fmk) prevented both DNA fragmentation and activation of caspase-3, but not relative cell survival, implying the upstream mitochondrial event of caspase-3 activation. In addition, antagonistic Fas antibody (ZB4) exerted no effect on the apoptosis. Taken together, these results suggest that PGA2 may induce the apoptosis as well as growth inhibition in HL-60 cells, and cytochrome c release and caspase activation seem to play a critical role in this apoptosis which might be independent or downstream of growth inhibition associated with c-myc down-regulation.

Cyclopentenone prostaglandins: new insights on biological activities and cellular targets

The cyclopentenone prostaglandins PGA2, PGA1, and PGJ2 are formed by dehydration within the cyclopentane ring of PGE2, PGE1, and PGD2. PGJ2 is metabolized further to yield Delta(12)-PGJ(2) and 15-deoxy-Delta(12,14)-PGJ(2) (15d-PGJ(2)). Various compounds within the cyclopentenone prostaglandin family possess potent anti-inflammatory, anti-neoplastic, and anti-viral activity. Most actions of the cyclopentenone prostaglandins do not appear to be mediated by binding to G-protein coupled prostanoid receptors. Rather, the bioactivity of these compounds results from their interaction with other cellular target proteins. 15-deoxy-Delta(12,14)-PGJ(2) is a high affinity ligand for the nuclear receptor PPARgamma and modulates gene transcription by binding to this receptor. Other activities of the cyclopentenone prostaglandins are mediated by the reactive alpha,beta-unsaturated carbonyl group located in the cyclopentenone ring. The transcription factor NF-kappaB and its activating kinase are key targets for the anti-inflammatory activity of 15d-PGJ2, which inhibits NF-kappaB-mediated transcriptional activation by PPARgamma-dependent and independent molecular mechanisms. Other cyclopentenone prostaglandins, such as Delta(7)-PGA1 and Delta(12)-PGJ2, have strong anti-tumor activity. These compounds induce cell cycle arrest or apoptosis of tumor cells depending on the cell type and treatment conditions. We review here recent progress in understanding the mechanisms of action of the cyclopentenone prostaglandins and their possible use as therapeutic agents.

Preparation and evaluation of o/w type emulsions containing antitumor prostaglandin

Antitumor prostaglandins(PGs) such as Delta12-PGJ2 and Delta7-PGA1 possess a cyclopentenone or cross-conjugated dienone structures. Antitumor PGs are actively incorporated through cell membrane and control gene expression. Very recent studies clarified that P53 independent expression of p21 and gadd 45, activation of PPARgamma are involved in antitumor mechanism of these PGs. At the low concentration, these PGs exhibit physiological or pathological activity such as osteoblast calcification, promotion of colon cancer cell proliferation. COMPARE PROGRAM using human 38 tumor cell lines suggested that antitumor mechanism of Delta7-PGA1 and 13, 14-dihydro-15-deoxy-Delta7-PGA1 methyl ester (TEI-9826) are quite different from other anticancer agents which are clinically used. Lipid microspheres and Lipiodol formulation were examined as dosage form of the PGs and lipid microspheres were selected for further study. At first lipid microspheres integrated TEI-9038 (Lipo TEI-9038) was chosen as a candidate for clinical trial. However Lipo TEI-9038 failed to exhibit substantial antitumor effect because of its enzymatic instability and toxicity in vivo. Lipo TEI-9826 was then selected as promising candidate for clinical trial because of its stability in serum. Lipo TEI-9826 exhibited marked antitumor effect in several animal models including CDDP resistant nude mice model. Pharmacokinetic and toxicological studies using rats suggested that continuous infusion is the most suitable administration method for Lipo TEI-9826. New type emulsifier, Controlled High Pressure Process Homogenizer (De-BEE 2000 and mini De-BEE) was developed during the preclinical studies on manufacturing process of Lipo TEI-9826. These results warrant the clinical trial for Lipo TEI-9826 in CDDP resistant cancer.

Effect of the novel prostaglandin A1 derivative TEI-6363 on ROS17/2.8 cell differentiation in vitro

The effect of TEI-6363 (5-[E-4-N,N-dimethylaminophenylmethylene]-4-hydroxy-2-[1-methyl imidazole-2-ilthio]-4-[4-phenylbutyl]-2-cyclopentenone), a chemically synthesized prostaglandin A1 derivative, on cell proliferation and osteoblastic differentiation was investigated concurrently. ROS17/2.8 cells (a rat osteosarcoma-derived cell line) were treated with TEI-6363 at two concentrations, 10(-7) and 10(-6) M, and viable cells were counted to assess cytotoxic effects and determine the growth curve. After 96 h of treatment, there was no evidence of any effect of TEI-6363 on cell viability at either concentration. However, a clear inhibitory effect on cell proliferation was observed after treatment with 10(-6) M TEI-6363 for 24 h or longer. A pulse-treatment experiment showed that TEI-6363 induced the inhibition of proliferating ROS17/2.8 cells 24 h after addition. The inhibition of proliferation was associated with G1-arrest demonstrated by flow cytometric analysis, and incorporation of [3H]thymidine by ROS17/2.8 cells was decreased. Osteoblastic differentiation (assessed on the basis of increased alkaline phosphatase activity and collagen synthesis) was induced by TEI-6363 treatment at 10(-6) M following G1-arrest and inhibition of cell proliferation. These results suggest that TEI-6363 arrested the cell cycle of ROS17/2.8 cells at the G1 phase and induced osteoblastic differentiation. These results did not appear to be dependent on a marked cytotoxic effect.

The role of c-Myc and heat shock protein 70 in human hepatocarcinoma Hep3B cells during apoptosis induced by prostaglandin A2/Delta12-prostaglandin J2

Prostaglandin (PG) A2 (PGA2) and Delta12-PGJ2 have potent antiproliferative activity on various tumor cell growths in vitro. In this study, we investigated the mechanism of PGA2/Delta12-PGJ2-mediated apoptosis, including intracellular apoptosis-related genes in human hepatocarcinoma Hep3B cells. Hep3B cells treated with PGA2/Delta12-PGJ2 showed that a time-dependent DNA fragmentation characterized by marked apoptosis and the elevation of c-myc mRNA expression. In proportion to the increased c-myc gene transcription, heat shock protein 70 (hsp70) mRNA was induced from 1 to 24 h after PGA2/Delta12-PGJ2 treatment. The transfection of c-myc antisense oligomers in Hep3B cells significantly delayed the induction of HSP70 expression and blocked formation of DNA fragmentation by PGA2/Delta12-PGJ2. Moreover, overexpressed HSP70 showed an increased resistance to apoptosis by PGA2/Delta12-PGJ2 treatment. These results demonstrated that the decreased survival in response to PGA2/Delta12-PGJ2 was causally related to the amount of c-myc and the induction of c-myc regulated the elevation of HSP70 which have been known to correlate with a resistance to apoptosis.

Cell cycle-dependent modulation of promoter activities of RB and WAF1/Cip1 genes

A universal inhibitor of cyclin-dependent kinases, WAF1/Cip1 can dephosphorylate the RB gene product to arrest the cell cycle at the G1 phase. Here we show that the mRNA level and the promoter activities of the RB and WAF1/Cip1 genes exhibit cell cycle-dependent change when cells are released from either serum-starvation or the confluent cell state with serum. RB expression and promoter activity are elevated at middle to late G1. In contrast, the mRNA and promoter activity of the WAF1/Cip1 gene increase at early G1. These results suggest that the RB and WAF1/Cip1 expression and promoter activities depend not only on serum, but also on the cell cycle progression itself. Moreover, we identified the responsive region for serum-released cell cycle progression in the RB promoter and mapped it to the region between -4 and -182 relative to the initiating codon of the RB gene. The region in the WAF1/Cip1 promoter responsible for the serum-released cell cycle progression mapped not to the p53 binding site, but to the 374 base-pair region between -1770 and -1396 from the transcription start site.

Effects of cyclopentenone prostaglandins and related compounds on insulin-like growth factor-I and Waf1 gene expression

The molecular pathways by which the cyclopentenone prostaglandins (PGA and PGJ series) inhibit cell growth and tumorigenicity are poorly understood. These cellular responses may be caused by specific regulation of growth-related and stress-induced genes. A variety of prostaglandins were tested for their ability to regulate insulin-like growth factor-I (IGF-I) and Waf1 gene expression in C6 rat glioma cells. The prostaglandins (in order of potency) PGJ2 > PGA1 > PGA2, approximately PGD2 >> PGE2 all significantly repressed IGF-I gene expression. With the exception of PGE2, the same prostaglandins that repressed IGF-I also induced Waf1 gene expression. However, the order of potency for Waf1 induction was different than for IGF-I repression: PGA2 > PGA1 approximately PGJ2 > PGD2. The different order of potency of the prostaglandins in regulating IGF-I and Waf1 gene expression suggests that different intracellular signals may be involved in regulating the two genes. Augmentation of glutathione levels by pretreatment of cells with N-acetyl-L-cysteine attenuated the effect of PGA2 on IGF-I and Waf1 gene expression. conversely, depletion of the intracellular glutathione pool by pretreatment with buthionine sulfoximine potentiated the effect of PGA2 on the expression of both genes. These results suggest that conjugation with glutathione prevents the regulation of gene expression by PGA2. We also tested the effect of several simpler compounds that contain a five-membered ring system on IGF-I and Waf1 gene expression. 2-Cyclopenten-1-one, but not cyclopentene or cyclopentene, repressed IGF-I and induced Waf1 gene expression, demonstrating the requirement for an alpha, beta-unsaturated carbonyl for regulation of the two genes. The dione compound 4-cyclopentene-1,3-dione, which has two potentially reactive carbons rather than one, was considerably more potent than 2-cyclopentene-1-one in repressing IGF-I gene expression (IC50 = 30 microM for 4-cyclopentene-1,3-dione as compared with 167 microM for 2-cyclopentene-1-one). Additional results indicated that diethyl maleate, which has two alpha,beta-unsaturated carbonyls in a non-cyclic configuration, also repressed IGF-I gene expression (IC50 = 214 microM) and induced Waf1 gene expression, indicating that the cyclic structure is not required for either effect.

Induction of apoptosis, p53 and heme oxygenase-1 by cytotoxic prostaglandin delta12-PGJ2 in transformed endothelial cells

Delta12-prostaglandin (PG)J2, which has been reported to have potent growth inhibitory activity in various tumor cells, induced apoptosis at 5 microg/ml culture medium in transformed mouse endothelial (F2) cells. Immunoblot analysis using anti-p53 or anti-WAF1 antibodies demonstrated that these two proteins had increased following delta12-PGJ2 treatment in F2 cells. Western blotting analysis using anti-heme oxygenase-1 (heat shock protein (HSP)32) antibody also revealed that delta12-PGJ2 induced HSP32 formation in F2 cells. HSP32 was also induced by heat shock treatment at 43 degrees C for 90 min. In contrast, HSP72 was not induced by heat shock or by delta12-PGJ2 treatment. In agreement with these findings, HSP32 immunofluorescence in the cytoplasm of F2 cells was intensified by delta12-PGJ2 treatment. More intense HSP32 immunoreactivity was similarly observed after heat shock treatment. These results suggest that delta12-PGJ2 caused the apoptotic cell death of F2 cells, which involved a certain process required for p53 or HSP32 induction.

Prostaglandin A2 specifically represses insulin-like growth factor-I gene expression in C6 rat glioma cells

The cyclopentenone PGs (PGA and PGJ series) inhibit tumor cell proliferation in vitro and tumorigenesis in vivo via mechanisms that are at present poorly understood. The C6 rat glioma cell line synthesizes and secretes insulin-like growth factor-I (IGF-I), which is believed to act as an autocrine factor for these cells. PGA2 inhibits the proliferation of the C6 cells and causes an increase in the fraction of cells in the G1 phase of the cell cycle. The inhibition of cell proliferation by PGA2 is accompanied by a decrease in the abundance of IGF-I messenger RNA (mRNA). This regulation of IGF-I gene expression is specific, as the abundance of hypoxanthine-guanine phosphoribosyl transferase (HPRT) and ubiquitin mRNA is not significantly affected by PGA2. The repression of IGF-I gene expression is observed at PGA2 concentrations as low as 10 microM and is evident within 4 h after treatment of the C6 cells with PGA2. In addition to specifically regulating the expression of the IGF-I gene, PGA2 also decreases the abundance of cyclin D1 mRNA and increases the abundance of Waf1 mRNA. The inhibition of cell proliferation by PGA2 is partially reversed by coaddition of IGF-I, indicating partial dominance of IGF-I action over PGA2 action. To investigate the molecular basis for the regulation of IGF-I gene expression by PGA2, we developed a sensitive RT-PCR assay for IGF-I nuclear transcripts. A similar assay was developed for quantifying HPRT transcripts, which were used as a control. Treatment of the C6 cells with 20 microM PGA2 resulted in approximately a 6-fold decrease in IGF-I mRNA and IGF-I nuclear transcripts. In contrast, HPRT mRNA and nuclear transcript levels were not significantly affected by PGA2. These results indicate that the decrease in IGF-I mRNA abundance that occurs in response to PGA2 is caused largely by a decrease in IGF-I nuclear transcript levels. To identify the cis-acting element that mediates the effect of PGA2 on IGF-I transcription, C6 cells were transiently transfected with IGF-I/luciferase expression constructs in which luciferase transcription is driven by IGF-I P1 promoter fragments extending from -1711 to -328 or from -1114 to +328 relative to the beginning of exon 1. Treatment of cells with PGA2 in these transient transfection assays did not decrease luciferase activity. These results suggest that the cis-acting regulatory element required for the response to PGA2 is located outside the -1711 to +328 promoter interval.

Induction of c-fos protooncogene transcription and apoptosis by delta 12-prostaglandin J2 in human Pl-21 myeloid leukemia and RC-K8 pre-B lymphoma cells

delta 12-prostaglandin J2 (PGJ2) is a dehydration product of PGD2 and thought to be the most potent antitumor agent among prostaglandin compounds. We examine the cytotoxic effects of PGJ2 on the cell growth of leukemia/lymphoma cells. PGJ2 inhibited the growth of both human PL-21 myeloid leukemia and RC-K8 pre-B lymphoma cells in culture in a dose-dependent manner with fragmentation of nucleus and formation of apoptotic body. Agarose gel electrophoresis revealed DNA ladder formation in the cells treated with PGJ2. Furthermore, PGJ2 induced a rapid and transient expression of apoptosis-related protooncogene, c-fos, in both cells. The gene transcriptional rate was remarkably increased approximately 3.3-fold in PGJ2 treated cells, but the stability of c-fos mRNA was not significantly changed. Inhibition of de novo protein synthesis with cycloheximide increased c-fos mRNA stability but not abrogated PGJ2-induced c-fos transcription. These data suggest that PGJ2 can induce apoptosis of human leukemia/lymphoma cells and the rapid activation of c-fos protooncogene transcription in which de novo protein synthesis is not required.

Inhibition of G1 cyclin-dependent kinase activity during growth arrest of human breast carcinoma cells by prostaglandin A2

Prostaglandin A2 (PGA2) potently inhibits cell proliferation and suppresses tumor growth in vivo, but little is known regarding the molecular mechanisms mediating these effects. Here we demonstrate that treatment of breast carcinoma MCF-7 cells with PGA2 leads to G1 arrest associated with a dramatic decrease in the levels of cyclin D1 and cyclin-dependent kinase 4 (cdk4) and accompanied by an increase in the expression of p21. We further show that these effects occur independent of cellular p53 status. The decline in cyclin D and cdk4 protein levels is correlated with loss in cdk4 kinase activity, cdk2 activity is also significantly inhibited in PGA2-treated cells, an effect closely associated with the upregulation of p21. Immunoprecipitation experiments verified that p21 was indeed complexed with cdk2 in PGA2-treated cells. Additional experiments with synchronized MCF-7 cultures stimulated with serum revealed that treatment with PGA2 prevents the progression of cells from G1 to S. Accordingly, the kinase activity associated with cdk4, cyclin E, and cdk2 immunocomplexes, which normally increases following serum addition, was unchanged in PGA2-treated cells. Furthermore, the retinoblastoma protein (Rb), a substrate of cdk4 and cdk2 whose phosphorylation is necessary for cell cycle progression, remains underphosphorylated in PGA2-treated serum-stimulated cells. These findings indicate that PGA2 exerts its growth-inhibitory effects through modulation of the expression and/or activity of several key G1 regulatory proteins. Our results highlight the chemotherapeutic potential of PGA2, particularly for suppressing growth of tumors lacking p53 function.

Effect of cytotoxic prostaglandin, delta 12-prostaglandin J2 on E-cadherin expression in transformed epidermal cells in culture

The cyclopentenone prostaglandins (PGs), such as delta 12-PGJ2 and PGA1, are potent inhibitors of growth in a variety of cultured cells, including human epidermal cells. To clarify the mechanism of the cytotoxicity of these PGs, we examined the effects of delta 12-PGJ2 on the function and expression of E-cadherin, which plays a major role in the maintenance of intercellular adhesion, in transformed human epidermal cells in culture (HSC-1). A 12-h incubation with 5 micrograms/ml of delta 12-PGJ2 did not affect the cell-binding activity of E-cadherin expressed in HSC-1 cells. Immunoblot analysis using a monoclonal antibody specific to human E-cadherin revealed that a 12-h incubation with 5 micrograms/ml of delta 12-PGJ2 induced E-cadherin expression in HSC-1 cells. Immunofluorescence using a monoclonal antibody against human E-cadherin demonstrated that E-cadherin was localized to the cell-cell contact regions in HSC-1 cells. Following a 12-h incubation with 5 micrograms/ml of delta 12-PGJ2, E-cadherin was also detected in a uniform pattern along cell junctions, although cell morphology was changed by the presence of cytotoxic PGs. These results suggest that the cytotoxicity of cyclopentenone PGs is related, at least in part, to E-cadherin expression in transformed human epidermal cells.

Preclinical studies of antitumor prostaglandins by using human ovarian cancer cells

Pleiotropic actions of antitumor prostaglandins (PGs) on tumor cells are reviewed including our preclinical results focused on human ovarian cancer. Regarding inhibition of cell proliferation, antitumor PGs exerts its action as a G1 blocking agent. The cyclopentenone PGs inhibit myc oncogene expression while inhibiting the cell cycle progression and results in apoptotic cell death and growth inhibition. Cyclopentenone PGs inhibit growth of various tumors transplanted to mice or nude mice and show adjuvant effects to cis-diamminedichloroplatinum(II) (CDDP). In order to elucidate a role of antitumor PGs in immune systems, relevance of effects on tumor growth with those on the immune systems are also discussed with our results.

Differential changes of adrenoceptor- and muscarinic receptor-linked prostacyclin synthesis by the aorta and urinary bladder of the diabetic rat

1. The effect of experimental diabetes mellitus (DM; hyperglycaemic, non-ketototic; 2 months duration) in the rat on receptor-linked prostacyclin (PGI2) synthesis (measured as 6-oxo-PGF1 alpha by radioimmunoassay) was studied in the aorta and urinary bladder using adrenaline, angiotensin II (AII) and acetylcholine (ACh). Signal transduction systems were studied via stimulation of PGI2 synthesis with phorbol ester dibutyrate (PDBU; a protein kinase C activator [PKC]), Ca2+ ionophore A23187 (A23187) and thapsigargin (both elevate intracellular Ca2+, activating phospholipase A2 [PLA2]) and arachidonate (AA; substrate for PGI2 synthesis). 2. In response to adrenaline, AII and phorbol ester, aortic PGI2 release was markedly reduced (all > 75%) in diabetic rats compared to controls. EC50s of the dose-response curves for adrenaline, AII and PDBU were also markedly increased in aortae from DM rats compared to controls. Although there was decreased output of PGI2 in response to A23187 by aortae from diabetic rats compared to controls, there was no difference in the EC50s (mean +/- s.e. mean: diabetic, 2.7 +/- 0.2 x 10(-6) M; controls 2 +/- 0.18 x 10(-6) M). There were no differences in PGI2 release (or in the EC50s) in response to thapsigargin or AA between aortae from diabetic and control rats. 3. In the urinary bladder, there was a marked increase in PGI2 output in response to ACh and a marked decrease in EC50s for the ACh-PGI2 dose-response curves in diabetic rats (EC50 = 5.8 +/- 0.32 x 10(-7) M) compared to controls (EC50 = 2.2 +/- 0.15 x 10(-6) M). Although there was an increase in PGI2 output in the urinary bladders from diabetic rats in response to A23187, there were no differences in the EC50s (control, 1.8 +/- 0.2 x 10-6 M; diabetic, 1.1 +/- 0.15 X 10-6 M). In the urinary bladders, there were no differences in PGI2 output (or the EC50s) in response to PDBU, thapsigargin or AA between diabetic or control rats.4. These data indicate that: (i) reduced PGI2 synthesis coupled to adrenoceptors and AII receptors in the aortae of diabetic rats may be due to diminished PKC activity and not to changes in receptor density and/or affinity, Ca2+ stores, PLA2, cyclo-oxygenase or PGI2 synthase; (ii) the diametrically opposite effect of DM on ACh-stimulated PGI2 synthesis is not due to an increase in PKC activity, but possibly to an increase in muscarine receptor number and/or affinity; (iii) changes in receptor-linked PGI2 synthesis are not ubiquitous in experimental DM and may be organ-specific.

Induction of 72-kD heat shock protein and cytoskeleton damage by cytotoxic prostaglandin delta 12-PGJ2 in transformed human epidermal cells in culture

Cyclopentenone prostaglandins (PG) such as delta 12-PGJ2 and PGA are potent inhibitors of growth in a variety of cultured cells, including human epidermal cells. To clarify the mechanism of PG cytotoxicity in human epidermal cells, we examined the effects of delta 12-PGJ2 on the induction of a heat shock protein (HSP), and on the organization of cytoskeletons in the HSC-I-transformed human epidermal cell line. Immunoblot analysis using a monoclonal antibody specific for the 72-kD heat shock protein (HSP72) revealed that a 12-h incubation with 5 micrograms/ml of delta 12-PGJ2 induced HSP72 formation in HSC-I cells. HSP72 was also induced by heat shock treatment at 43 degrees C for 90 min. The quantity of HSP72 produced was markedly decreased by co-treatment with 1 microgram/ml of cycloheximide in delta 12-PGJ2-treated cells, and similarly reduced in HSC-I cells following heat treatment. Immunofluorescence using a monoclonal antibody to HSP72 demonstrated that HSP72 was localized mainly in the cytoplasm of HSC-I cells. Following treatment with 5 micrograms/ml of delta 12-PGJ2, however, HSP72 was found in the nucleolus as well as in the cytoplasm. The accumulation of HSP in the nucleolus was similarly prominent in HSC-I cells after treatment at 43 degrees C for 90 min. Addition of delta 12-PGJ2 to confluent HSC-1 cells resulted in the disappearance of actin filaments and the disarrangement of keratin filaments, as visualized with fluorescent-labeled phallacidine or immunofluorescence. These results suggest that the cytotoxicity of cyclopentenone PG is related to the induction of HSP72, and to cytoskeleton damage in transformed human epidermal cells in culture.

Prostaglandins A and J arrest the cell cycle of cultured vascular smooth muscle cells without suppression of c-myc expression

The effects of prostaglandins (PGs) A and J, which are anti-tumor eicosanoids, on the proliferation of cultured vascular smooth muscle cells were investigated. Serum-stimulated DNA synthesis was potently inhibited by PGA1, PGA2, PGJ2, and delta 12-PGJ2 in similar dose-dependent fashions. The effects of PGA1 and PGA2 were reversible when they were removed from the culture media, whereas recoveries were only partial in the cells treated with PGJ2 and delta 12-PGJ2. PGs were effective even if they were added immediately before entry into S phase. Inhibition of DNA synthesis was sustained when hydroxyurea, which blocks cell cycle at the G1/S border, was added after the removal of PGA2, and vice versa; PGs blocked DNA synthesis when they were added after the removal of hydroxyurea. Levels of c-myc mRNA formed two peaks during the G1 phase, at 1-2 h and at 8-12 h. The PGs did not affect the first elevation, but enhanced the second and sustained it up to 18-24 h, whereas in controls, c-myc mRNA decreased quickly after entry into S phase. The rate of degradation of c-myc mRNA was much smaller in PG-treated cells than in nontreated cells. We conclude, therefore, that PGA and PGJ inhibit a crucial event(s) in the cell cycle occurring at the G1/S border, but that this inhibition is not accompanied by the reduction in c-myc gene expression in contrast with some types of tumor cells treated with PGs.

Induction of HSP70 gene expression by the antiproliferative prostaglandin PGA2: a growth-dependent response mediated by activation of heat shock transcription factor

Prostaglandins (PG) of the A series are potent inhibitors of cell proliferation. Recently, it was shown that PGA2-induced growth arrest was associated with the increased synthesis of stress proteins encoded by the HSP70 gene family. In this study, we have examined the molecular basis for this increases HSP70 expression. Northern (RNA) blot analysis and nuclear run-on assays demonstrated that induction of high levels of HSP70 mRNA results from an increase in the rate of transcription. High-level induction is specific to the HSP70 family of heat shock proteins and is rapid, reversible, dose dependent, and specific for PGs capable of growth-arresting HeLa cells. In addition, the response was found to be highly dependent on the growth state of the cells, as induction occurs in growing but not in confluent nongrowing cell populations. Induction is dependent on the activation of heat shock factor. Cycloheximide pretreatment, which inhibits the antiproliferative effects of PGA2, prevents activation of the heat shock factor and induction of HSP70 mRNA by PGA2. These results support a role for HSP70 in mediating the antiproliferative effects of PGA2.

Induction of HSP70 gene expression by the antiproliferative prostaglandin PGA2: a growth-dependent response mediated by activation of heat shock transcription factor

Prostaglandins (PG) of the A series are potent inhibitors of cell proliferation. Recently, it was shown that PGA2-induced growth arrest was associated with the increased synthesis of stress proteins encoded by the HSP70 gene family. In this study, we have examined the molecular basis for this increases HSP70 expression. Northern (RNA) blot analysis and nuclear run-on assays demonstrated that induction of high levels of HSP70 mRNA results from an increase in the rate of transcription. High-level induction is specific to the HSP70 family of heat shock proteins and is rapid, reversible, dose dependent, and specific for PGs capable of growth-arresting HeLa cells. In addition, the response was found to be highly dependent on the growth state of the cells, as induction occurs in growing but not in confluent nongrowing cell populations. Induction is dependent on the activation of heat shock factor. Cycloheximide pretreatment, which inhibits the antiproliferative effects of PGA2, prevents activation of the heat shock factor and induction of HSP70 mRNA by PGA2. These results support a role for HSP70 in mediating the antiproliferative effects of PGA2.

Regulation of C-myc protooncogene expression in osteoblastic cells by arachidonic acid metabolites: relationship to proliferation

Prostaglandin E2 and leukotriene B4 are metabolites of arachidonic acid with well-characterized effects on osteoblastic cells. Prostaglandin E2 has been shown to be a potent bone-resorbing agent and to stimulate as well as inhibit osteoblastic cell proliferation. Leukotriene B4 has also been demonstrated to stimulate or inhibit osteoblastic cell proliferation, depending on the cell type tested. In the present study, the potential relationship of the effects of prostaglandin E2 and leukotriene B4 on osteoblastic cell proliferation to c-myc protooncogene expression was investigated. Prostaglandin E2 has been shown previously to inhibit normal rat osteoblastic cell proliferation. The present studies show that prostaglandin E2 at 10(-6) M decreased c-myc expression in these cells. In the human osteoblastic osteosarcoma cell line, G292, prostaglandin E2 increased c-myc expression and inhibited proliferation. In contrast, epidermal growth factor increased DNA synthesis as well as c-myc expression. Prostaglandin E2 also inhibited proliferation of another human osteoblastic osteosarcoma cell line, Saos-2, but it did not produce any changes in c-myc expression. In these cells, epidermal growth factor did not affect either DNA synthesis or c-myc expression. Leukotriene B4 did not show any effects on c-myc expression in any of the osteoblastic cells tested.

Cell growth inhibition by prostaglandin A2 results in elevated expression of gadd153 mRNA

Treatment of Hela cells with prostaglandin A2 (PGA2) resulted in a marked inhibition of cell proliferation which was associated with a significant induction of gadd153 mRNA, a member of a novel class of genes associated with growth arrest and DNA damage. Induction of gadd153 mRNA was specific to prostaglandins capable of arresting cell growth and was dose-dependent with the maximum effect seen at 36 microM PGA2. Induction was rapid, occurring within 2-4 h and reaching a maximum by 8 h. These effects were reversible as removal of PGA2 resulted in a rapid decline in gadd153 mRNA levels coincident with resumption of cell growth. PGA2 induction of gadd153 mRNA was completely prevented by the presence of actinomycin D at a concentration sufficient to block transcription and was partially inhibited (50%) by the protein synthesis inhibitor cycloheximide. The presence of the protein kinase inhibitor 2-aminopurine decreased the PGA2 induction of gadd153 mRNA by greater than 90%, suggesting that cellular kinases play a role in the induction of gadd153 by PGA2. Thus PGA2-mediated growth arrest provides a useful model to further define the role of gadd153 in the negative control of cell growth.

Delta 12-prostaglandin J2 mimics heat shock in inducing cell cycle arrest at G1 phase

Using a human neuroblastoma cell line GOTO, the effects of delta 12-prostaglandin (PG) J2 on the modulation of cell cycle progression and protein synthesis were examined in comparison with those caused by heat shock (HS). delta 12-PGJ2 induced G1 arrest, the peak of which was obtained at 24 h and continued for 72 h. HS was found to induce G1 arrest earlier than delta 12-PGJ2. Furthermore, sequential HS could maintain G1 arrest. delta 12-PGJ2 induced the synthesis of several heat shock proteins (HSPs) in a manner similar to HS. Using immunoblot analysis, HSP72 was detected prior to inducing G1 arrest and accumulated during the subsequent 72h. The content of HSP72 induced by HS also correlated well with the induction, release, and maintenance of G1 arrest. In addition, both delta 12-PGJ2 and HS induced HSP72 mRNA and simultaneously suppressed N-myc mRNA expression. These results suggest that delta 12-PGJ2 and HS regulate cell cycle progression of GOTO cells via similar mechanisms.