Prostaglandin E2 increases proenkephalin mRNA level in rat astrocyte-enriched culture

Regulation of interleukin-12 gene expression and its anti-tumor activities by prostaglandin E2 derived from mammary carcinomas

Interleukin-12 (IL-12)-mediated immune responses are critical for the control of malignant development. Tumors can actively resist detrimental immunity of the host via many routes. Prostaglandin E2 (PGE2) is one of the major immune-suppressive factors derived from many types of tumors. Here, we show that systemic administration of recombinant IL-12 could therapeutically control the growth of aggressive TS/A and 4T1 mouse mammary carcinomas. However, PGE2 produced by tumors potently inhibits the production of endogenous IL-12 at the level of protein secretion, mRNA synthesis, and transcription of the constituent p40 and p35 genes. The inhibition can be reversed by NS-398, a selective inhibitor of the enzymatic activity of cyclooxygenase 2 in PGE2 synthesis. Moreover, PGE2-mediated inhibition of IL-12 production requires the functional cooperation of AP-1 and AP-1 strongly suppresses IL-12 p40 transcription. Blocking PGE2 production in vivo results in a marked reduction in lung metastasis of 4T1 tumors, accompanied by enhanced ability of peritoneal macrophages to produce IL-12 and spleen lymphocytes to produce interferon-gamma. This study contributes to the elucidation of the molecular mechanisms underlying the interaction between a progressive malignancy and the immune defense apparatus.

Cyclooxygenase-2 inhibitor (SC-236) suppresses activator protein-1 through c-Jun NH2-terminal kinase

BACKGROUND AND AIMS

Aspirin exerts antitumor effect partly through blocking tumor promoter-induced activator protein-1 (AP-1) activation. The aim of this study is to determine how specific COX-2 inhibitor SC-236 mediates antitumor effect by modulation of AP-1-signaling pathway.

METHODS

AP-1 transcriptional activity and DNA-binding activity were detected by luciferase reporter assay and gel shift assay, separately. Mitogen-activated protein kinase (MAPK) activation was determined by Western blot and in vitro kinase assay. Antisense oligonucleotide against c-Jun-N-terminal kinase (JNK) was used to suppress JNK expression.

RESULTS

We showed that SC-236 inhibited 12-O-tetradecanoylphorbol-13-acetate (PMA)-induced cell transformation in a dose-dependent manner in JB6 cells. At a dose range (12.5-50 micromol/L) that inhibited cell transformation, SC-236 also inhibited anchorage-independent cell growth and AP-1-activation in 3 gastric cancer cells, independent of COX-prostaglandin synthesis. SC-236 down-regulated c-Jun-NH2-terminal kinase phosphorylation and activity. Suppression of JNK activity reversed the inhibitory effect on AP-1 activity by SC-236 and suppressed gastric cancer cell growth, indicating that the inhibitory effect of SC-236 on AP-1 activation and cell growth was through interaction with JNK.

CONCLUSIONS

The inhibitory effect on JNK-c-Jun/AP-1 activation contributes to the antitumor effect of COX-2-specific inhibitor, and inhibition of JNK activation may have a therapeutic benefit against gastric cancer.

NS-398 and piroxicam suppress UVB-induced activator protein 1 activity by mechanisms independent of cyclooxygenase-2

Cyclooxygenases (COX) are rate-limiting enzymes that catalyze the conversion of arachidonic acid to prostaglandins, which are involved in many physiological and pathophysiological responses. COX-2, one of two isoforms of COX, was recently found to play an important role in carcinogenesis in many cell and tissue types. COX-2 inhibitors, which belong to the family of nonsteroidal anti-inflammatory drugs, are believed to be effective in many biological activities such as tumor chemoprevention because of their inhibition of COX-2. However, in the present study we found that both piroxicam, a general COX inhibitor, and NS-398, a COX-2 selective inhibitor, effectively suppressed the activation of transcription factor activator protein 1 (AP-1) induced by ultraviolet B (UVB) or 12-O-tetradecanoylphorbol-13-acetate in mouse epidermal JB6 cells. These COX-2 inhibitors could also inhibit 12-O-tetradecanoylphorbol-13-acetate-induced cell transformation. UVB significantly increased AP-1 activity in Cox-2(-/-) fibroblasts transfected with an AP-1 luciferase reporter gene, and this increase was blocked by NS-389 or piroxicam. In JB6, Cox-2(-/-), or wild-type Cox-2(+/+) cells, both NS-398 and piroxicam inhibited UVB-induced phosphorylation of c-Jun NH(2)-terminal kinases, the kinases that activate the AP-1/c-Jun complex. Based on our results, we propose that the inhibition of AP-1 activity by COX-2 inhibitors NS-398 or piroxicam may occur by a mechanism that is independent of COX-2.

Novel target for induction of apoptosis by cyclo-oxygenase-2 inhibitor SC-236 through a protein kinase C-beta(1)-dependent pathway

Nonsteroidal anti-inflammatory drugs (NSAIDs) reduce the risk of gastrointestinal cancers. Recently, a similar protective effect has been demonstrated by the specific cyclo-oxygenase-2 (COX-2) inhibitors. However, the exact mechanism that accounts for the anti-proliferative effect of specific COX-2 inhibitors is still not fully understood, and it is still controversial whether these protective effects are predominantly mediated through the inhibition of COX-2 activity and prostaglandin synthesis. Identification of molecular targets regulated by COX-2 inhibitors could lead to a better understanding of their pro-apoptotic and anti-neoplastic activities. In the present study, we investigated the effect and the possible molecular target of a COX-2-specific inhibitor SC-236 on gastric cancer. We showed that SC-236 induced apoptosis in gastric cancer cells. However, this effect was not dependent on COX-2 inhibition. SC-236 down-regulated the protein expression and kinase activity of PKC-beta(1), increased the expression of PKCdelta and PKCeta, but did not alter the expression of other PKC isoforms in AGS cells. Moreover, exogenous prostaglandins or PGE(2) receptor antagonists could not reverse the inhibition effect on PKCbeta(1) by SC-236, which suggested that this effect occurred through a mechanism independent of cyclo-oxygenase activity and prostaglandin synthesis. Overexpression of PKCbeta(1) attenuated the apoptotic response of AGS cells to SC-236 and was associated with overexpression of p21(waf1/cip1). Inhibition of PKCbeta(1)-mediated overexpression of p21(waf1/cip1) partially reduced the anti-apoptotic effect of PKCbeta(1). The down-regulation of PKCbeta(1) provides an explanation for COX-independent apoptotic effects of specific COX-2 inhibitor in cultured gastric cancer cells. We also suggest that PKCbeta(1) act as survival mediator in gastric cancer, and its down-regulation by COX-2 inhibitor SC-236 may provide new target for future treatment of gastric cancer.

Mechanisms of prostaglandin E2-induced interleukin-6 release in astrocytes: possible involvement of EP4-like receptors, p38 mitogen-activated protein kinase and protein kinase C

The expression of cyclooxygenase-2 (COX-2) and the synthesis of prostaglandin E2 (PGE2) as well as of cytokines such as interleukin-6 (IL-6) have all been suggested to propagate neuropathology in different brain disorders such as HIV-dementia, prion diseases, stroke and Alzheimer's disease. In this report, we show that PGE2-stimulated IL-6 release in U373 MG human astroglioma cells and primary rat astrocytes. PGE2-induced intracellular cAMP formation was mediated via prostaglandin E receptor 2 (EP2), but inhibition of cAMP formation and protein kinase A or blockade of EP1/EP2 receptors did not affect PGE2-induced IL-6 synthesis. This indicates that the cAMP pathway is not part of PGE2-induced signal transduction cascade leading to IL-6 release. The EP3/EP1-receptor agonist sulprostone failed to induce IL-6 release, suggesting an involvement of EP4-like receptors. PGE2-activated p38 mitogen-activated kinase (p38 MAPK) and protein kinase C (PKC). PGE2-induced IL-6 synthesis was inhibited by specific inhibitors of p38 MAPK (SB202190) and PKC (GF203190X). Although, up to now, EP receptors have only rarely been linked to p38 MAPK or PKC activation, these results suggest that PGE2 induces IL-6 via an EP4-like receptor by the activation of PKC and p38 MAPK via an EP4-like receptor independently of cAMP.

Prostaglandin E2 signalling pathway in human T lymphocytes from healthy and conjunctiva basal cell carcinoma-bearing subjects

Prostaglandin E-induced signal transduction pathways in human T cells from healthy and uveal melanoma-bearing subjects were studied. Transfection experiments showed that PGE2 was able to phosphorylate and activate the fusion trans-activator of the cAMP responsive element-binding protein (CREB). Phosphorylation was at least partially mediated by protein kinase A, as evidenced by the effects of specific kinase inhibitors. Western blotting experiments, which were performed to identify the CREB/ATF2 family members involved in the response to PGE2, revealed a modulation of proteins CREB1, CREB2 and ATF2 and phosphorylation of the 43 kDa form of CREB. Experiments of immunoprecipitation with CREB-binding protein (CBP) demonstrated that, after PGE2 treatment, all of the CREB/ATF isoforms studied, as well as the phosphorylated form of CREB (p-CREB), interacted with CBP. In basal conditions, T cells from patients with conjunctiva basal cell carcinoma showed the presence of p-CREB, which coimmunoprecipitated with CBP. CREB phosphorylation did not modify after PGE2 treatment whereas the p-CREB fraction bound to CBP increased in a delayed manner compared to normal subjects.

Omega 3 but not omega 6 fatty acids inhibit AP-1 activity and cell transformation in JB6 cells

Epidemiological and animal-based investigations have indicated that the development of skin cancer is in part associated with poor dietary practices. Lipid content and subsequently the derived fatty acid composition of the diet are believed to play a major role in the development of tumorigenesis. Omega 3 (omega3) fatty acids, including docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA), can effectively reduce the risk of skin cancer whereas omega 6 (omega6) fatty acids such as arachidonic acid (AA) reportedly promote risk. To investigate the effects of fatty acids on tumorigenesis, we performed experiments to examine the effects of the omega3 fatty acids EPA and DHA and of the omega6 fatty acid AA on phorbol 12-tetradecanoate 13-acetate (TPA)-induced or epidermal growth factor (EGF)-induced transcription activator protein 1 (AP-1) transactivation and on the subsequent cellular transformation in a mouse epidermal JB6 cell model. DHA treatment resulted in marked inhibition of TPA- and EGF-induced cell transformation by inhibiting AP-1 transactivation. EPA treatment also inhibited TPA-induced AP-1 transactivation and cell transformation but had no effect on EGF-induced transformation. AA treatment had no effect on either TPA- or EGF-induced AP-1 transactivation or transformation, but did abrogate the inhibitory effects of DHA on TPA- or EGF-induced AP-1 transactivation and cell transformation in a dose-dependent manner. The results of this study demonstrate that the inhibitory effects of omega3 fatty acids on tumorigenesis are more significant for DHA than for EPA and are related to an inhibition of AP-1. Similarly, because AA abrogates the beneficial effects of DHA, the dietary ratio of omega6 to omega3 fatty acids may be a significant factor in mediating tumor development.

Endometrial and myometrial corticotropin-releasing hormone (CRH): its regulation and possible roles

In human endometrium, both epithelial and stroma cells produce corticotropin-releasing hormone (CRH). Both types of cells also possess specific CRH-binding sites indicating a local effect of endometrial CRH. The transcription of the CRH gene in human endometrium is under the control of steroid hormones and locally produced prostanoids and interleukins. Endometrial CRH interacts with locally produced prostaglandins and interleukins. Based on these observations it can be hypothesized that CRH, prostaglandins and interleukins form a network responsible for the communication between epithelial and stromal cells, at the level of the endometrium, and between endometrial and myometrial cells at the level of uterus. The net product of these interaction is the micro-regulation of the decidualizing process and the preparation of endometrium for the implantation/nidation of the conceptus. Indeed, this network may represent the core of the intrauterine neuroendocrine-immune interactions involved in the decidualization of stroma and implantation of blastocyst. In addition, this network appears to be essential for the fine-tuning of myometrial tone.

Regulation of c-fos gene expression by lipopolysaccharide and cycloheximide in C6 rat glioma cells

The effect of lipopolysaccharide (LPS) on the expression of immediate early genes, such as c-fos and c-jun, was examined in C6 rat glioma cells. LPS (1 microg/ml) alone did not affect c-fos mRNA level. LPS, however, transiently increased c-jun mRNA level. Cycloheximide (CHX, 20 microM), a protein synthesis inhibitor, alone caused increases of c-fos and c-jun mRNA levels. LPS showed a potentiating effect in the regulation of c-fos mRNA level, whereas LPS showed an additive action for the regulation of CHX-induced c-jun mRNA expression. To determine if CREB and mitogen-activated protein kinases (MAPKs) are involved in the regulation of c-fos mRNA expression by LPS and CHX, Western blot was carried out using the phosphorylated form of antibodies against ERK, JNK, p38, and CREB. LPS transiently increased the phosphorylation of p38-MAPK and CREB. In addition, LPS alone elevated phosphorylation of ERK (p44/p42) MAPK in a time-dependent manner. Furthermore, LPS plus CHX enhanced phosphorylation of ERK, p38, and CREB in a synergistic manner. Our results suggest that the phosphorylation of ERK, p38, and CREB may be involved in the regulation of synergistic c-fos mRNA expression induced by LPS plus CHX in C6 rat glioma cells.

Prostaglandin E2 stimulates AP-1-mediated CD14 expression in mouse macrophages via cyclic AMP-dependent protein kinase A

PGs play a functional role in the early stage of Gram-negative bacterial infections, because this prostanoid is produced rapidly by epithelial cells after a bacterial infection. CD14, one of the LPS receptors, is a key molecule in triggering the response to bacterial LPS in association with a Toll-like molecule. Therefore, in this study, we investigated the effect of PG on CD14 expression in mouse macrophages. PGE1, PGE2, and PGA1 among the PGs tested strongly stimulated the expression of the CD14 gene in the cells. The stimulatory action also was observed by Western blot analysis. cAMP-elevating agents stimulated expression of CD14 gene as well. Protein kinase A inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide (H-89), but not protein kinase C inhibitor 3-(1-[3-(dimethylamino)propyl]-1H-indol-3-yl)-4-(1H-indol-3-yl)-1H-py rrole-2,5-dione (GF109203X), abolished the stimulated expression of CD14. A run-on assay showed that PGE2 stimulated the CD14 gene expression at the transcriptional level via protein kinase A. PGE2 also stimulated activation of AP-1, a heterodimer of c-Jun and c-Fos, because the prostanoid increased specific binding of nuclear proteins to the AP-1 consensus sequence and stimulated AP-1-promoted luciferase activity. PGE2-stimulated expression of CD14 was inhibited by antisense c-fos and c-jun oligonucleotides, but not by their sense oligonucleotides. Finally, PGE2 pretreatment synergistically stimulated LPS-induced expression of IL-1beta and IL-6 genes in mouse macrophages. Therefore, the present study demonstrates that PGE2 has the ability to stimulate AP-1-mediated expression of CD14 in mouse macrophages via cAMP-dependent protein kinase A.