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

C/EBPzeta (CHOP/Gadd153) is a negative regulator of LPS-induced IL-6 expression in B cells

C/EBPzeta was originally identified as a gene induced upon DNA damage and growth arrest. It has been shown to be involved in the cellular response to endoplasmic reticulum stress. Because of sequence divergence from other C/EBP family members in its DNA-binding domain and its consequent inability to bind the C/EBP consensus-binding motif, C/EBPzeta can act as a dominant negative inhibitor of other C/EBPs. C/EBP transactivators are essential to the expression of many proinflammatory cytokines and acute phase proteins, but a role for C/EBPzeta in regulating their expression has not been described. We found that expression of C/EBPzeta is induced in response to LPS treatment of B cells at both the mRNA and protein levels. Correlating with the highest levels of C/EBPzeta expression at 48 h after LPS treatment, there is an increased association of C/EBPzeta with C/EBPbeta, and both the abundance of C/EBP DNA-binding species and IL-6 expression are downregulated. Furthermore, ectopic expression of C/EBPzeta inhibited C/EBPbeta-dependent IL-6 expression from both the endogenous IL-6 gene and an IL-6 promoter-reporter. These results suggest that C/EBPzeta functions as negative regulator of IL-6 expression in B cells and that it contributes to the transitory expression of IL-6 that is observed after LPS treatment.

15-Deoxy-Delta(12,14)-prostaglandin J2 induces apoptosis through activation of the CHOP gene in HeLa cells

Cyclopentenone prostaglandins (PGs) of the J series, which are produced by dehydration of PGD(2), have been reported to induce apoptosis in various cell lines. One of these cyclopentenone PGs, 15-deoxy-Delta(12,14)-prostaglandin J(2) (15-d-PGJ(2)), is the most potent inducer of apoptosis in the series, but the signaling pathways by which it induces apoptosis are poorly understood. We recently reported that cyclopentenone PGs accumulate in the endoplasmic reticulum (ER) and it has been shown that the transcription factor CHOP is induced by ER-stresses and elicits apoptosis. In the present study we demonstrated that 15-d-PGJ(2) induces CHOP mRNA/protein in HeLa cells via activation of the conserved regions in the CHOP promoter. Using several mutants of the CHOP promoter fragments, we found that two regions, CCAAT/enhancer-binding protein (C/EBP) site at -313 and ER-stress element (ERSE) at -93, are involved in activation of the CHOP gene by 15-d-PGJ(2). These results suggest that 15-d-PGJ(2) activates the CHOP promoter in two distinct pathways that could induce apoptosis of HeLa cells.

GADD153-mediated anticancer effects of N-(4-hydroxyphenyl)retinamide on human hepatoma cells

The anticancer effects of N-(4-hydroxyphenyl)retinamide (4HPR), a potential chemopreventive or chemotherapeutic retinamide, are thought to be derived from its ability to induce apoptosis. However, the mechanism of apoptosis induced by 4HPR remains unclear. Thus, this study was designed to identify the gene(s) responsible for induction of apoptosis by 4HPR. Apoptosis was effectively induced by 4HPR in human hepatoma cells. Using the differential display-PCR method, a gene involved in the response to 4HPR was identified, and cells in which the expression of that gene was modulated were analyzed for survival, induction of apoptosis, and cell cycle. GADD153, a gene involved in growth arrest and apoptosis, was preferentially expressed in human hepatoma cells as well as in other cancer cells during 4HPR-induced apoptosis. 4HPR regulates GADD153 expression at the post-transcriptional level in Hep 3B cells and at the transcriptional and post-transcriptional levels in SK-HEP-1 cells, when assayed by in vitro transfection and mRNA stability experiments. To determine the role of the GADD153 protein overexpression that is induced by 4HPR, Hep 3B cells with ectopic overexpression of GADD153 were found to be growth-arrested (at G(1)) and readily underwent apoptosis following treatment with 4HPR or even when they reached confluence. N-Acetyl-l-cysteine or GADD153 antisense significantly protected the cells from 4HPR-induced apoptosis, accompanying by the inhibition of GADD153 overexpression. Parthenolide-mediated overexpression of GADD153 resulted in enhanced 4HPR-induced apoptosis. These results suggest that GADD153 overexpression induced by 4HPR may contribute to the anticancer effects (induction of apoptosis and growth arrest) of 4HPR on cancer cells.

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.

CHOP/GADD153 gene expression response to cellular stresses inhibited by prior exposure to ultraviolet light wavelength band C (UVC). Inhibitory sequence mediating the UVC response localized to exon 1

CHOP/GADD153 is both an activating and repressing transcription factor that is markedly induced in response to a variety of cellular stresses. The CHOP/GADD153 gene was originally cloned because of its inducibility by ultraviolet light wavelength band C (UVC) and has since been found to be activated in response to many different cellular stresses. Some of the recent studies have questioned the UVC responsiveness of the CHOP gene. Contradiction in our own data led us to reexamine the UVC effects on CHOP expression. UVC is capable of strongly activating the mouse CHOP promoter in stably transfected NIH 3T3 cells but has only a modest and transient effect on the level of the CHOP messenger RNA. In addition to its positive effect on CHOP promoter activity, we show that UVC negatively affects CHOP mRNA and protein expression. Pretreatment of NIH 3T3 cells with UVC markedly attenuates the subsequent induction of CHOP mRNA by the cellular stress activators methylmethane sulfate, tunicamycin, glucose deprivation, and methionine deprivation for as long as at least 16 h. This inhibitory effect of UVC on CHOP expression in response to stress is independent of the presence or absence of p53 and does not involve mRNA degradation as opposed to the UVC effect that inhibits p21 expression seen only in the absence of p53. The target of the inhibitory effect of UVC on CHOP expression is located in the first exon of the gene, a 5'-untranslated region that is unusually conserved between different species. These findings suggest that an unknown function encoded by the 5'-untranslated region somehow modifies the response of CHOP gene transcription to UVC.

15-Deoxy-Delta(12,14)-prostaglandin J(2) facilitates thyroglobulin production by cultured human thyrocytes

A cyclopentenone-type prostaglandin, 15-deoxy-Delta(12, 14)-prostaglandin J(2) (15-d-PGJ(2)), has been shown to induce the cellular stress response and to be a ligand for the peroxisome proliferator-activated receptor (PPAR)-gamma. We studied its effect on the basal and thyrotropin (TSH)-induced production of thyroglobulin (TG) by human thyrocytes cultured in the presence of 10% FBS. In 15-d-PGJ(2)-treated cells in which the agent itself did not stimulate cAMP production, both the basal production of TG and the response to TSH were facilitated, including the production of TG and cAMP, whereas such production was decreased in untreated cells according to duration of culture. PGD(2) and PGJ(2), which are precursors to 15-d-PGJ(2), exhibited an effect similar to 15-d-PGJ(2). However, the antidiabetic thiazolidinediones known to be specific ligands for PPAR-gamma, and WY-14643, a specific PPAR-alpha ligand, lacked this effect. 15-d-PGJ(2) and its precursors, but not the thiazolidinediones, induced gene expression for heme oxygenase-1 (HO-1), a stress-related protein, and strongly inhibited interleukin-1 (IL-1)-induced nitric oxide (NO) production. Cyclopentenone-type PGs have been recently shown to inhibit nuclear factor-kappaB (NF-kappaB) activation via a direct and PPAR-independent inhibition of inhibitor-kappaB kinase, suggesting that, in human thyrocytes, such PGs may inhibit IL-1-induced NO production, possibly via an inhibition of NF-kappaB activation. On the other hand, sodium arsenite, a known activator of the stress response pathway, induced HO-1 mRNA expression but lacked a promoting effect on TG production. Thus 15-d-PGJ(2) and its precursors appear to facilitate TG production via a PPAR-independent mechanism and through a different pathway from the cellular stress response that is available to cyclopentenone-type PGs. Our findings reveal a novel role of these PGs associated with thyrocyte differentiation.

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.

Cyclopentenone prostaglandins as potential inducers of phase II detoxification enzymes. 15-deoxy-delta(12,14)-prostaglandin j2-induced expression of glutathione S-transferases

Exposure of cells to a wide variety of chemoprotective compounds confers resistance to a broad set of carcinogens. For a subset of the chemoprotective compounds, protection is generated by an increase in the abundance of protective enzymes, such as glutathione S-transferases (GSTs). In the present study, we developed a cell culture system that potently responds to phenolic antioxidants and found that antitumor prostaglandins (PGs) are potential inducers of GSTs. We screened primary hepatocytes and multiple cell lines for inducing GST activity upon incubation with the phenolic antioxidant (tert-butylhydroquinone) and found that rat liver epithelial RL34 cells most potently responded. Based on an extensive screening of diverse chemical agents on the induction of GST activity in RL34 cells, the J2 series of PGs, 15-deoxy-Delta(12,14)-prostaglandin J2 (15-deoxy-Delta(12,14)-PGJ2) in particular, were found to be potential inducers of GST. Enhanced gene expression of Class pi GST isozyme (GSTP1) by 15-deoxy-Delta(12,14)-PGJ2 was evident as a drastic elevation of the mRNA level. Hence, we examined the molecular mechanism underlying the 15-deoxy-Delta(12, 14)-PGJ2-induced GSTP1 gene expression. From functional analysis of various deletion mutant genes, we found that the 15-deoxy-Delta(12, 14)-PGJ2 reponse element was localized in a region containing a GSTP1 enhancer I (GPEI) that consists of two imperfect phorbol 12-O-tetradecanoylphorbol-13-acetate response elements. When the GPEI was combined with the minimum GSTP1 promoter, the element indeed showed an enhancer activity in response to 15-deoxy-Delta(12, 14)-PGJ2. Point mutations of either of the two imperfect 12-O-tetradecanoylphorbol-13-acetate response elements in GPEI completely abolished the enhancer activity. Gel mobility shift assays demonstrated that 15-deoxy-Delta(12,14)-PGJ2 specifically stimulated the binding of nuclear proteins including the transcription factor c-Jun, but not Nrf2, to GPEI. These results suggest that 15-deoxy-Delta(12,14)-PGJ2 induces the expression of the rat GSTP1 gene through binding of proteins, including c-Jun, to a specific GPEI.

Identification of cDNAs for Sox-4, an HMG-Box protein, and a novel human homolog of yeast splicing factor SSF-1 differentially regulated during apoptosis induced by prostaglandin A2/delta12-PGJ2 in Hep3B cells

We have examined specific genes whose expression is altered during apoptosis induced by prostaglandin (PG)A2 and Delta12-PGJ2 in human hepatocellular carcinoma Hep3B cells. Using mRNA differential display, we have identified two genes: one is specifically up-regulated and encodes for human Sox-4 (Sry-HMG box gene) and the other is significantly down-regulated and is the human homolog of yeast Ssf-1, a novel splicing factor. Northern blot analysis confirmed their differential expressions. Interestingly, Sox-4 was highly expressed in subcutaneous tumors grown in nude mice as a xenograft from Hep3B cells. These results suggest that the expression of Sox-4 may be related to the apoptosis pathway leading to cell death as well as to tumorigenesis, and that Ssf-1 gene may serve as a negative regulator of PGA2/Delta12-PGJ2-mediated Hep3B cell apoptosis.

Antiproliferative Effect of IL-1 Is Mediated by p38 Mitogen-Activated Protein Kinase in Human Melanoma Cell A375

The role of p38 mitogen-activated protein kinase (MAPK) in IL-1-induced growth inhibition was investigated using IL-1-sensitive human melanoma A375-C2-1 cells and IL-1-resistant A375-R8 cells. In both cells, p38 MAPK was activated by IL-1. A selective inhibitor for p38 MAPK, SB203580, almost completely recovered the IL-1-induced growth inhibition in A375-C2-1 cells. IL-1-induced IL-6 production was also suppressed by SB203580. However, the reversal effect of SB203580 was not due to the suppression of IL-6 production because the SB203580 effect was still observed in the presence of exogenous IL-6. Down-regulation of ornithine decarboxylase (ODC) activity as well as its protein level has been shown to be essential for IL-1-induced growth inhibition. SB203580 also reversed the IL-1-induced down-regulation of ODC activity and intracellular polyamine levels without affecting ODC mRNA levels in A375-C2-1 cells. In IL-1-resistant R8 cells, however, IL-1 only slightly suppressed ODC activity. In A375-C2-1 cells, the mRNA expression level of antizyme (AZ), a regulatory factor of ODC activity, has been shown to be up-regulated by IL-1. IL-1-induced up-regulation of AZ mRNA level was not affected by SB203580. These findings demonstrate that p38 MAPK plays an important role in IL-1-induced growth inhibition in A375 cells through down-regulating ODC activity without affecting the level of ODC mRNA and AZ mRNA. In IL-1-resistant A375-R8 cells, IL-1 signaling pathway is deficient between p38 MAPK activation and down-regulation of ODC activity.

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.

p53-Independent activation of the gadd45 promoter by Delta12-prostaglandin J2

A p53-inducible gene, the growth arrest and DNA damage-inducible gene 45 (gadd45), is associated with cell growth inhibition, DNA damage response and DNA repair. Here we report that Delta12-prostaglandin J2 (Delta12-PGJ2), an in vivo metabolite of arachidonic acid, which inhibits cell proliferation, induces gadd45 mRNA in HeLa cells. Because the p53 protein in HeLa cells is inactivated by papilloma virus E6, this type of gadd45 induction appears to be p53-independent. The induction was dose-dependent, and the maximum induction was observed at a concentration of 7.5 microgram/ml. In a time course study, gadd45 mRNA was induced 3 h after the addition of 7.5 microgram/ml Delta12-PGJ2. To investigate the transcriptional mechanism of gadd45 mRNA induction, we cloned a human genomic DNA fragment containing the gadd45 promoter region, and investigated the effect of Delta12-PGJ2 on the gadd45 promoter activity. In HeLa cells, 7.5 microgram/ml Delta12-PGJ2 markedly stimulated the gadd45 gene promoter about 20-fold or more. On the other hand, Delta12-PGJ2 did not stimulate the promoter activity of a reporter plasmid containing only p53 binding sites in HeLa cells, indicating that the gadd45 promoter activation by Delta12-PGJ2 was not mediated by p53. These results suggest that one of the mechanisms of cell growth arrest by Delta12-PGJ2 is mediated through a p53-independent induction of gadd45.

The pharmacology and toxicology of polyphenolic-glutathione conjugates

Polyphenolic-glutathione (GSH) conjugates and their metabolites retain the electrophilic and redox properties of the parent polyphenol. Indeed, the reactivity of the thioether metabolites frequently exceeds that of the parent polyphenol. Although the active transport of polyphenolic-GSH conjugates out of the cell in which they are formed will limit their potential toxicity to those cells, once within the circulation they can be transported to tissues that are capable of accumulating these metabolites. There are interesting physiological similarities between the organs that are known to be susceptible to polyphenolic-GSH conjugate-mediated toxicity. In addition, the frequent localization of gamma-glutamyl transpeptidase to cells separating the circulation from a second fluid-filled compartment coincides with tissues that are susceptible either to polyphenolic-GSH conjugate-induced toxicity or to quinone and reactive oxygen species-induced toxicity. Polyphenolic-GSH conjugates therefore contribute to the nephrotoxicity, nephrocarcinogenicity, and neurotoxicity of a variety of polyphenols.

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.

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.

Protective role of p21(Waf1/Cip1) against prostaglandin A2-mediated apoptosis of human colorectal carcinoma cells

Prostaglandin A2 (PGA2) suppresses tumor growth in vivo, is potently antiproliferative in vitro, and is a model drug for the study of the mammalian stress response. Our previous studies using breast carcinoma MCF-7 cells suggested that p21(Waf1/Cip1) induction enabled cells to survive PGA2 exposure. Indeed, the marked sensitivity of human colorectal carcinoma RKO cells to the cytotoxicity of PGA2 is known to be associated with a lack of a PGA2-mediated increase in p21(Waf1/Cip1) expression, inhibition of cyclin-dependent kinase activity, and growth arrest. To determine if cell death following exposure to PGA2 could be prevented by forcing the expression of p21(Waf1/Cip1) in RKO cells, we utilized an adenoviral vector-based expression system. We demonstrate that ectopic expression of p21(Waf1/Cip1) largely rescued RKO cells from PGA2-induced apoptotic cell death, directly implicating p21(Waf1/Cip1) as a determinant of the cellular outcome (survival versus death) following exposure to PGA2. To discern whether p21(Waf1/Cip1)-mediated protection operates through the implementation of cellular growth arrest, other growth-inhibitory treatments were studied for the ability to attenuate PGA2-induced cell death. Neither serum depletion nor suramin (a growth factor receptor antagonist) protected RKO cells against PGA2 cytotoxicity, and neither induced p21(Waf1/Cip1) expression. Mimosine, however, enhanced p21(Waf1/Cip1) expression, completely inhibited RKO cell proliferation, and exerted marked protection against a subsequent PGA2 challenge. Taken together, our results directly demonstrate a protective role for p21(Waf1/Cip1) during PGA2 cellular stress and provide strong evidence that the implementation of cellular growth arrest contributes to this protective influence.

Prostaglandin A2 blocks the activation of G1 phase cyclin-dependent kinase without altering mitogen-activated protein kinase stimulation

Prostaglandin A2 (PGA2) reversibly blocked the cell cycle progression of NIH 3T3 cells at G1 and G2/M phase. When it was applied to cells synchronized in G0 or S phase, cells were blocked at G1 and G2/M, respectively. The G2/M blockage was transient. Microinjected oncogenic leucine 61 Ras protein could not override the PGA2 induced G1 blockage, nor could previous transformation with the v-raf oncogene. The serum-induced activation of mitogen-activated protein kinase was not inhibited by PGA2 treatment. These data suggest that PGA2 blocks cell cycle progression without interfering with the cytosolic proliferative signaling pathway. Combined microinjection of E2F-1 and DP-1 proteins or microinjected adenovirus E1A protein, however, could induce S phase in cells arrested in G1 by PGA2, indicating that PGA2 does not directly inhibit the process of DNA synthesis. In quiescent cells, PGA2 blocked the normal hyperphosphorylation of the retinoblastoma susceptible gene product and the activation of cyclin-dependent kinase (CDK) 2 and CDK4, in response to serum stimulation. PGA2 treatment elevated the p21Waf1/Cip1/Sdi1 protein expression level. These data indicate that PGA2 may arrest the cell cycle in G1 by interfering with the activation of G1 phase CDKs.

Prostaglandin A2 protein interactions and inhibition of cellular proliferation

Some prostaglandins inhibit cellular proliferation in a wide variety of cell types, but the mechanism of inhibition is not known. The most potent inhibitors of proliferation appear to be prostaglandins of the A and J series. These prostaglandins have been reported to form covalent bonds to cellular proteins (Narumiya, S., Ohno, K., Fukushima, M., Fujiwara, M. (1987) J. Pharm. Exp. Ther., 242, 306-311). However, the proteins have not been identified or shown to be involved in the inhibition of proliferation. Prostaglandin A2-biotin provided a sensitive method to demonstrate binding of prostaglandin A2 (PGA2) to cellular proteins of 43, 50, and 56 kilodaltons in K562 erythroleukemia cells. Similar PGA2-binding proteins were also present in mouse fibroblasts and porcine aortic endothelial cells. The PGA2-binding proteins preexist in K562 cells and were not induced by exposure to the prostaglandin. Furthermore, binding of PGA2 to these proteins correlated to the inhibition of proliferation. Therefore, one or more of the PGA2-binding proteins may be involved in the inhibition of cellular proliferation by PGA2.

Differential activation of peroxisome proliferator-activated receptors by eicosanoids

Peroxisome proliferator-activated receptors (PPARs) are nuclear hormone receptors that regulate gene transcription in response to peroxisome proliferators and fatty acids. PPARs also play an important role in the regulation of adipocyte differentiation. It is unclear, however, what naturally occurring compounds activate each of the PPAR subtypes. To address this issue, a screening assay was established using heterologous fusions of the bacterial tetracycline repressor to several members of the peroxisome proliferator-activated receptor (PPAR) family. This assay was employed to compare the activation of PPAR family members by known PPAR activators including peroxisome proliferators and fatty acids. Interestingly, the activation of PPARs by fatty acids was partially inhibited by the cyclooxygenase inhibitor indomethacin, which prevents prostaglandin synthesis. Indeed, prostaglandins PGA1 and 2, PGD1 and 2, and PGJ2-activated PPARs, while a number of other prostaglandins had no effect. We also screened a variety of hydroxyeicosatetraenoic acids (HETEs) for the ability to activate PPARs. 8(S)-HETE, but not other (S)-HETEs, was a strong activator of PPAR alpha. Remarkably, PPAR activation by 8(S)-HETE was stereoselective. In addition, 8(S)-HETE was able to induce differentiation of 3T3-L1 preadipocytes. These results indicate that PPARs are differentially activated by naturally occurring eicosanoids and related molecules.

Involvement of protein kinase in delta 12-prostaglandin J2-induced expression of rat heme oxygenase-1 gene

We recently identified the cis-regulatory element and its specific nuclear binding factors for delta 12-prostaglandin (PG) J2-induced expression of the rat heme oxygenase, HO-1 [Koizumi, T., Odani, N., Okuyama, T., Ichikawa, A. and Negishi, M. (1995) J. Biol. Chem. 270, in press]. Here we further examined the molecular mechanism underlying the delta 12-PGJ2-induced HO-1 gene expression. Protein kinase inhibitors, 2-aminopurine and staurosporine, suppressed the delta 12-PGJ2-induced HO-1 mRNA and the nuclear protein binding to the delta 12-PGJ2-responsive cis-regulatory element in rat basophilic leukemia cells. Furthermore, the nuclear protein binding to the element was suppressed by in vitro phosphatase treatment of the nuclear proteins from delta 12-PGJ2-treated cells. These findings suggest that delta 12-PGJ2 induces the expression of the HO-1 gene through phosphorylation of the nuclear proteins which bind to the delta 12-PGJ2-responsive element.

Identification of a cis-regulatory element for delta 12-prostaglandin J2-induced expression of the rat heme oxygenase gene

We recently reported that delta 12-prostaglandin (PG) J2 caused various cells to synthesize heme oxygenase, HO-1 (Koizumi, T., Negishi, M., and Ichikawa, A. (1992) Prostaglandins 43, 121-131). Here we examined the molecular mechanism underlying the delta 12-PGJ2-induced HO-1 synthesis. delta 12-PGJ2 markedly stimulated the promoter activity of the 5'-flanking region of the rat HO-1 gene from -810 to +101 in rat basophilic leukemia cells. From functional analysis of various deletion mutant genes we found that the delta 12-PGJ2-responsive element was localized in a region from -690 to -660, containing an E-box motif, which was essential for the delta 12-PGJ2-stimulated promoter activity. When the region containing the delta 12-PGJ2-responsive element was combined with a heterologous promoter, SV40 promoter, in the sense and antisense direction, the element showed an enhancer activity in response to delta 12-PGJ2. Gel mobility shift assays demonstrated that delta 12-PGJ2 specifically stimulated the binding of two nuclear proteins to the E-box motif of this region. These results indicate that delta 12-PGJ2 induces the expression of the rat HO-1 gene through nuclear protein binding to a specific element having an E-box motif.

Prostaglandin biosynthesis by fat body from the tobacco hornworm, Manduca sexta

We describe prostaglandin (PG) biosynthesis by microsomal-enriched preparations of fat body from larvae of the tobacco hornworm Manduca sexta. Four major PGs were synthesized under most experimental conditions, PGA2, PGE2, PGD2 and PGF2 alpha. PGA2, was the predominant product under most conditions. Unlike mammals, in which PGA2, is generally thought to arise from non-enzymatic rearrangements of PGE2, the fat body preparations did not convert exogenous PGE2 into PGA2. These findings suggest that PGA2 is an important fat body product that is synthesized by a route that does not involve PGE2. The PG synthase activity and the overall profile of PG synthesis were sensitive to experimental conditions, including incubation time, temperature, and protein concentration. Optimal PG biosynthesis was observed with 1 mg of microsomal-rich protein, incubated at 30 degrees C for 1-2 min. The fat body preparations is sensitive to two non-steroidal anti-inflammatory drugs, indomethacin and naproxen, both of which inhibited PG synthesis at low dosages.

The gadd and MyD genes define a novel set of mammalian genes encoding acidic proteins that synergistically suppress cell growth

A remarkable overlap was observed between the gadd genes, a group of often coordinately expressed genes that are induced by genotoxic stress and certain other growth arrest signals, and the MyD genes, a set of myeloid differentiation primary response genes. The MyD116 gene was found to be the murine homolog of the hamster gadd34 gene, whereas MyD118 and gadd45 were found to represent two separate but closely related genes. Furthermore, gadd34/MyD116, gadd45, MyD118, and gadd153 encode acidic proteins with very similar and unusual charge characteristics; both this property and a similar pattern of induction are shared with mdm2, whic, like gadd45, has been shown previously to be regulated by the tumor suppressor p53. Expression analysis revealed that they are distinguished from other growth arrest genes in that they are DNA damage inducible and suggest a role for these genes in growth arrest and apoptosis either coupled with or uncoupled from terminal differentiation. Evidence is also presented for coordinate induction in vivo by stress. The use of a short-term transfection assay, in which expression vectors for one or a combination of these gadd/MyD genes were transfected with a selectable marker into several different human tumor cell lines, provided direct evidence for the growth-inhibitory functions of the products of these genes and their ability to synergistically suppress growth. Taken together, these observations indicate that these genes define a novel class of mammalian genes encoding acidic proteins involved in the control of cellular growth.

The gadd and MyD genes define a novel set of mammalian genes encoding acidic proteins that synergistically suppress cell growth

A remarkable overlap was observed between the gadd genes, a group of often coordinately expressed genes that are induced by genotoxic stress and certain other growth arrest signals, and the MyD genes, a set of myeloid differentiation primary response genes. The MyD116 gene was found to be the murine homolog of the hamster gadd34 gene, whereas MyD118 and gadd45 were found to represent two separate but closely related genes. Furthermore, gadd34/MyD116, gadd45, MyD118, and gadd153 encode acidic proteins with very similar and unusual charge characteristics; both this property and a similar pattern of induction are shared with mdm2, whic, like gadd45, has been shown previously to be regulated by the tumor suppressor p53. Expression analysis revealed that they are distinguished from other growth arrest genes in that they are DNA damage inducible and suggest a role for these genes in growth arrest and apoptosis either coupled with or uncoupled from terminal differentiation. Evidence is also presented for coordinate induction in vivo by stress. The use of a short-term transfection assay, in which expression vectors for one or a combination of these gadd/MyD genes were transfected with a selectable marker into several different human tumor cell lines, provided direct evidence for the growth-inhibitory functions of the products of these genes and their ability to synergistically suppress growth. Taken together, these observations indicate that these genes define a novel class of mammalian genes encoding acidic proteins involved in the control of cellular growth.

Cell cycle arrest by prostaglandin A1 at the G1/S phase interface with up-regulation of oncogenes in S-49 cyc- cells

Our previous studies have implied that prostaglandins inhibit cell growth independent of cAMP. Recent reports, however, have suggested that prostaglandin arrest of the cell cycle may be mediated through protein kinase A. In this report, in order to eliminate the role of c-AMP in prostaglandin mediated cell cycle arrest, we use the -49 lymphoma variant (cyc-) cells that lack adenylate cyclase activity. We demonstrate that dimethyl prostaglandin A1 (dmPGA1) inhibits DNA synthesis and cell growth in cyc- cells. DNA synthesis is inhibited 42% by dmPGA1 (50 microM) despite the fact that this cell line lacks cellular components needed for cAMP generation. The ability to decrease DNA synthesis depends upon the specific prostaglandin structure with the most effective form possessing the alpha, beta unsaturated ketone ring. Dimethyl PGA1 is most effective in inhibiting DNA synthesis in cyc- cells, with prostaglandins PGE1 and PGB1 being less potent inhibitors of DNA synthesis. DmPGE2 caused a significant stimulation of DNA synthesis. S-49 cyc- variant cells exposed to (30-50 microns) dmPGA1, arrested in the G1 phase of the cell cycle within 24 h. This growth arrest was reversed when the prostaglandin was removed from the cultured cells; growth resumed within hours showing that this treatment is not toxic. The S-49 cyc- cells were chosen not only for their lack of adenylate cyclase activity, but also because their cell cycle has been extensively studied and time requirements for G1, S, G2, and M phases are known. Within hours after prostaglandin removal the cells resume active DNA synthesis, and cell number doubles within 15 h suggesting rapid entry into S-phase DNA synthesis from the G1 cell cycle block.(ABSTRACT TRUNCATED AT 250 WORDS)

Purification and characterization of a fatty acid binding protein from human prostatic tissue

Epidemiological studies suggest the existence of a strong relationship between the incidence of prostatic cancer and the intake of dietary lipids in humans. However, very little information is available on intracellular fatty acid metabolism in human prostatic tissue. The objective of this study was to identify and subsequently characterize a fatty acid binding protein of human prostatic tissue. A fatty acid binding protein (FABP) was purified and characterized from human prostatic tissue. The purified FABP had an apparent molecular mass of 15.0 +/- 1.0 kDa as averaged from three different methods, sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE), gel filtration and amino acid analysis. The pI value of the protein was determined to be 6.8. Scatchard analysis of fatty acid binding to the purified FABP from malignant prostatic tissue showed a Kd value of 0.53 +/- 0.02 microM for arachidonic acid (n = 5). The Kd values of FABP purified from benign prostatic tissue were 0.57 +/- 0.02 microM for oleic acid and 0.51 +/- 0.04 microM for arachidonic acid (n = 5). Fatty acid analysis revealed that the level of endogenously bound arachidonic acid was about 2.5-fold higher in FABP from malignant than from benign tissue. In addition, both malignant and benign tissues contained the same concentration of FABP. The concentrations of FABP in malignant and benign tissues were 19.2 +/- 1.8 and 21.4 +/- 2.1 micrograms per mg of total cytosolic protein, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)