COX-1 is coupled with mPGES-1 and ABCC4 in human cervix cancer cells

Upregulation of Prostaglandin E2 by Inducible Microsomal Prostaglandin E Synthase-1 in Colon Cancer

Purpose

Prostaglandin E₂ (PGE₂) is known to promote carcinogenesis and cancer progression in colon cancer. Enzymes involved in the metabolism of PGE₂ include cyclooxygenase (COX)-2, microsomal prostaglandin E synthase-1 (mPGES-1), and 15-prostaglandin dehydrogenase (15-PGDH). The current study aims to determine how PGE₂ is expressed by examining patients with colorectal cancer and evaluating colon cancer cells to gain insight into changes in relevant enzymes upon induction of PGE₂.

Methods

The concentration of PGE₂ was measured in tumor tissues and adjacent normal mucosal tissues of 26 patients with colon cancer. The expression of COX-1, COX-2, mPGES-1, and 15-PGDH proteins was measured. The concentration of PGE₂ in FET colon cancer cells was measured both in the initial status and after stimulation by tumor necrosis factor (TNF)-α. The expression levels of PGE₂-related enzymes were measured as well.

Results

There was no significant difference in the average concentration of PGE₂, which was measured at 453.1 pg/mL in cancer tissues and 401.2 pg/mL in normal mucosa. Among PGE₂-related enzymes, 15-PGDH was expressed at a lower level in tumor cells than in normal mucosa. In colon cancer cells, PGE₂ was found to be upregulated upon stimulation by TNF-α, which led to strong induction of mPGES-1 without any change in the expression of COX-2 among the PGE₂-related enzymes.

Conclusion

These results demonstrated that PGE₂ can be induced by stimuli such as TNF-α, and suggest that activation of mPGES-1 is more closely related than that of COX-2 in the induction of PGE₂ on colon cancer.

COX-2-PGE2-EPs in gynecological cancers

PURPOSE

Nonsteroidal anti-inflammatory drugs (NSAIDs) and selective COX-2 inhibitors (COXibs) inhibit the progression of endometrial cancer, ovarian cancer and cervical cancer. However, concerning the adverse effects of NSAIDs and COXibs, it is still urgent and necessary to explore novel and specific anti-inflammation targets for potential chemoprevention. The signaling of cyclooxygenase 2-prostaglandin E₂-prostaglandin E₂ receptors (COX-2-PGE₂-EPs) is the central inflammatory pathway involved in the gynecological carcinogenesis.

METHODS

Literature searches were performed to the function of COX-2-PGE₂-EPs in gynecological malignancies.

RESULTS

This review provides an overview of the current knowledge of COX-2-PGE₂-EPs signaling in endometrial cancer, ovarian cancer and cervical cancer. Many studies demonstrated the upregulated expression of the whole signaling pathway in gynecological malignancies and some focused on the function of COX-2 and cAMP-linked EP2/EP4 and EP3 signaling pathway in gynecological cancer. By contrast, roles of EP1 and the exact pathological mechanisms have not been completely clarified. The studies concerning EP receptors in gynecological cancers highlight the potential advantage of combining COX enzyme inhibitors with EP receptor antagonists as therapeutic agents in gynecological cancers.

CONCLUSION

EPs represent promising anti-inflammation biomarkers for gynecological cancer and may be novel treatment targets in the near future.

Cyclooxygenase-1 (COX-1) and COX-1 Inhibitors in Cancer: A Review of Oncology and Medicinal Chemistry Literature

Prostaglandins and thromboxane are lipid signaling molecules deriving from arachidonic acid by the action of the cyclooxygenase isoenzymes COX-1 and COX-2. The role of cyclooxygenases (particularly COX-2) and prostaglandins (particularly PGE₂) in cancer-related inflammation has been extensively investigated. In contrast, COX-1 has received less attention, although its expression increases in several human cancers and a pathogenetic role emerges from experimental models. COX-1 and COX-2 isoforms seem to operate in a coordinate manner in cancer pathophysiology, especially in the tumorigenesis process. However, in some cases, exemplified by the serous ovarian carcinoma, COX-1 plays a pivotal role, suggesting that other histopathological and molecular subtypes of cancer disease could share this feature. Importantly, the analysis of functional implications of COX-1-signaling, as well as of pharmacological action of COX-1-selective inhibitors, should not be restricted to the COX pathway and to the effects of prostaglandins already known for their ability of affecting the tumor phenotype. A knowledge-based choice of the most appropriate tumor cell models, and a major effort in investigating the COX-1 issue in the more general context of arachidonic acid metabolic network by using the systems biology approaches, should be strongly encouraged.

Equilibrative Nucleoside Transporter 1 (ENT1, SLC29A1) Facilitates Transfer of the Antiretroviral Drug Abacavir across the Placenta

Abacavir is a preferred antiretroviral drug for preventing mother-to-child human immunodeficiency virus transmission; however, mechanisms of its placental transfer have not been satisfactorily described to date. Because abacavir is a nucleoside-derived drug, we hypothesized that the nucleoside transporters, equilibrative nucleoside transporters (ENTs, SLC29A) and/or Na⁺-dependent concentrative nucleoside transporters (CNTs, SLC28A), may play a role in its passage across the placenta. To test this hypothesis, we performed uptake experiments using the choriocarcinoma-derived BeWo cell line, human fresh villous fragments, and microvillous plasma membrane (MVM) vesicles. Using endogenous substrates of nucleoside transporters, [³H]-adenosine (ENTs, CNT2, and CNT3) and [³H]-thymidine (ENTs, CNT1, and CNT3), we showed significant activity of ENT1 and CNT2 in BeWo cells, whereas experiments in the villous fragments and MVM vesicles, representing a model of the apical membrane of a syncytiotrophoblast, revealed only ENT1 activity. When testing [³H]-abacavir uptakes, we showed that of the nucleoside transporters, ENT1 plays the dominant role in abacavir uptake into placental tissues, whereas contribution of Na⁺-dependent transport, most likely mediated by CNTs, was observed only in BeWo cells. Subsequent experiments with dually perfused rat term placentas showed that Ent1 contributes significantly to overall [³H]-abacavir placental transport. Finally, we quantified the expression of SLC29A in first- and third-trimester placentas, revealing that SLC29A1 is the dominant isoform. Neither SLC29A1 nor SLC29A2 expression changed over the course of placental development, but there was considerable interindividual variability in their expression. Therefore, drug-drug interactions and the effect of interindividual variability in placental ENT1 expression on abacavir disposition into fetal circulation should be further investigated to guarantee safe and effective abacavir-based combination therapies in pregnancy.

Expression of Concentrative Nucleoside Transporters ( SLC28A) in the Human Placenta: Effects of Gestation Age and Prototype Differentiation-Affecting Agents

Equilibrative ( SLC29A) and concentrative ( SLC28A) nucleoside transporters contribute to proper placental development and mediate uptake of nucleosides/nucleoside-derived drugs. We analyzed placental expression of SLC28A mRNA during gestation. Moreover, we studied in choriocarcinoma-derived BeWo cells whether SLC29A and SLC28A mRNA levels can be modulated by activity of adenylyl cyclase, retinoic acid receptor activation, CpG islands methylation, or histone acetylation, using forskolin, all- trans-retinoic acid, 5-azacytidine, and sodium butyrate/sodium valproate, respectively. We found that expression of SLC28A1, SLC28A2, and SLC28A3 increases during gestation and reveals considerable interindividual variability. SLC28A2 was shown to be a dominant subtype in the first-trimester and term human placenta, while SLC28A1 exhibited negligible expression in the term placenta only. In BeWo cells, we detected mRNA of SLC28A2 and SLC28A3. Levels of the latter were affected by 5-azacytidine and all- trans-retinoic acid, while the former was modulated by sodium valproate (but not sodium butyrate), all- trans-retinoic acid, 5-azacytidine, and forskolin that caused 25-fold increase in SLC28A2 mRNA; we documented by analysis of syncytin-1 that the observed changes in SLC28A expression do not correlate with the morphological differentiation state of BeWo cells. Upregulated SLC28A2 mRNA was reflected in elevated uptake of [³H]-adenosine, high-affinity substrate of concentrative nucleoside transporter 2. Using KT-5720 and inhibitors of phosphodiesterases, we subsequently confirmed importance of cAMP/protein kinase A pathway in SLC28A2 regulation. On the other hand, SLC29A genes exhibited constitutive expression and none of the tested compounds increased SLC28A1 expression to detectable levels. In conclusion, we provide the first evidence that methylation status and activation of retinoic acid receptor affect placental SLC28A2 and SLC28A3 transcription and substrates of concentrative nucleoside transporter 2 might be taken up in higher extent in placentas with overactivated cAMP/protein kinase A pathway and likely in the term placenta.

Amino acid concentrations and protein metabolism of two types of rat skeletal muscle in postprandial state and after brief starvation

We have investigated amino acid concentrations and protein metabolism in musculus extensor digitorum longus (EDL, fast-twitch, white muscle) and musculus soleus (SOL, slow-twitch, red muscle) of rats sacrificed in the fed state or after one day of starvation. Fractional protein synthesis rates (FRPS) were measured using the flooding dose method (L-[3,4,5-3H]phenylalanine). Activities of two major proteolytic systems in muscle (the ubiquitin-proteasome and lysosomal) were examined by measurement of chymotrypsin like activity of proteasome (CTLA), expression of ubiquitin ligases atrogin-1 and muscle-ring-finger-1 (MuRF-1), and cathepsin B and L activities. Intramuscular concentrations of the most of non-essential amino acids, FRPS, CTLA and cathepsin B and L activities were in postprandial state higher in SOL when compared with EDL. The differences in atrogin-1 and MuRF-1 expression were insignificant. Starvation decreased concentrations of a number of amino acids and increased concentrations of valine, leucine, and isoleucine in blood plasma. Starvation also decreased intramuscular concentrations of a number of amino acids differently in EDL and SOL, decreased protein synthesis (by 31 % in SOL and 47 % in EDL), and increased expression of atrogin-1 and MuRF-1 in EDL. The effect of starvation on CTLA and cathepsin B and L activities was insignificant. It is concluded that slow-twitch (red) muscles have higher rates of protein turnover and may adapt better to brief starvation when compared to fast-twitch (white) muscles. This phenomenon may play a role in more pronounced atrophy of white muscles in aging and muscle wasting disorders.

Long-term administration of tenofovir or emtricitabine to pregnant rats; effect on Abcb1a, Abcb1b and Abcg2 expression in the placenta and in maternal and fetal organs

OBJECTIVES

Tenofovir and emtricitabine are very effective and well-tolerated antiretrovirals representing current backbone of the antiretroviral combination regimens for the prevention of perinatal HIV transmission. The aim of our study was to determine whether tenofovir or emtricitabine administered in long-term fashion affect expression of two widely described pharmacokinetic determinants, P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2), in maternal or fetal biological tissues.

METHODS

For this purpose, pregnant Wistar rats were administered tenofovir (2.25 mg/kg/day), emtricitabine (3.5 mg/kg/day) or saline i.m. for 10 days (from the 12th to 21st gestation day). On the 22nd day, the placenta and maternal/fetal intestine, brain, kidneys and liver were sampled and analysed for Abcb1a, Abcb1b and Abcg2 expression; placental and newborns' weights were also monitored.

KEY FINDINGS

We found that long-term application of tenofovir or emtricitabine did not significantly affect expression of Abcb1a, Abcb1b and Abcg2 in either maternal or fetal organs. However, tenofovir administration significantly increased placenta-to-birthweight ratio, a strong indicator of various diseases occurring later in life.

CONCLUSIONS

Our data broaden current knowledge on safety profile of tenofovir and emtricitabine use in pregnancy. Nevertheless, further research in other mammal species, including humans, is important to fully elucidate this issue.

Upregulation of COX-2 in the lung cancer promotes overexpression of multidrug resistance protein 4 (MRP4) via PGE2-dependent pathway

It is apparent that lung cancer is associated with inflammation, with accompanying hallmark elevations of cyclooxygenase 2 (COX-2) and prostaglandin E2 (PGE2) levels. However, the effects of these changes on MRP efflux transporters have not been thoroughly investigated before. Here, we report that upregulation of COX-2 can induce overexpression of MRP4 in both A549 non-small-cell lung cancer cell lines and mouse lung cancer models. In A549 cells, phorbol 12-myristate 13-acetate (PMA) treatment induced upregulation of COX-2 and MRP4 together, but not other MRP transporters. Transient overexpression of human COX-2 cDNA also specifically increased COX-2 and MRP4. Moreover, COX inhibitor treatment and COX-2-specific siRNA significantly inhibited the upregulation of MRP4. Additionally, PMA-treatment increased extracellular PGE2 levels, likely due to increased MRP4 function. Likewise, COX-2-specific siRNA reduced extracellular PGE2 levels. Furthermore, COX-2 upregulation resulted in an increase in mPGES-1, an enzyme responsible for PGE2 production. Finally, metastasized lung cancer model mice exhibited increased expression levels of COX-2 and MRP4, as well as mPGES-1. In conclusion, the present study suggests that overexpression of MRP4 in lung cancer may be attributable to COX-2 upregulation via a PGE2-dependent pathway.

Organic cation transporter 3 (OCT3/SLC22A3) and multidrug and toxin extrusion 1 (MATE1/SLC47A1) transporter in the placenta and fetal tissues: expression profile and fetus protective role at different stages of gestation

In our previous study, we described synchronized activity of organic cation transporter 3 (OCT3/SLC22A3) and multidrug and toxin extrusion 1 (MATE1/SLC47A1) transporter in the passage of organic cations across the rat placenta and the role of these transporters in fetal defense; in this study, we hypothesized that changes in placental levels of OCT3 and MATE1 throughout gestation might affect the fetal protection and detoxification. Using quantitative RT-PCR, Western blot analysis, and immunohistochemistry, we were able to detect Oct3/OCT3 and Mate1/MATE1 expression in the rat placenta as early as on Gestation Day (gd) 12 with increasing tendency toward the end of pregnancy. Comparing first versus third trimester human placenta, we observed stable expression of OCT1 and decreasing expression of OCT2 and OCT3 isoforms. Contrary to the current literature, we were able to detect also MATE1/MATE2 isoforms in the human placenta, however, with considerable inter- and intraindividual variability. Using infusion of 1-methyl-4-phenylpyridinium (MPP(+)), a substrate of OCT and MATE transporters, into pregnant dams, we investigated the protective function of the placenta against organic cations at different gds. The highest amount of MPP(+) reached the fetus on gd 12 while from gd 15 onward, maternal-to-fetal transport of MPP(+) decreased significantly. We conclude that increased expression of placental OCT3 and MATE1 along with general maturation of the placental tissues results in significantly lower transport of MPP(+) from mother to fetus. In contrast, decreasing expression of OCT3 and MATE1 in human placenta indicates these transporters may play a role in fetal protection preferentially at earlier stages of gestation.

Cyclooxygenase-2, not microsomal prostaglandin E synthase-1, is the mechanism for interleukin-1β-induced prostaglandin E2 production and inhibition of insulin secretion in pancreatic islets

Arachidonic acid is converted to prostaglandin E(2) (PGE(2)) by a sequential enzymatic reaction performed by two isoenzyme groups, cyclooxygenases (COX-1 and COX-2) and terminal prostaglandin E synthases (cPGES, mPGES-1, and mPGES-2). mPGES-1 is widely considered to be the final enzyme regulating COX-2-dependent PGE(2) synthesis. These generalizations have been based in most part on experiments utilizing gene expression analyses of cell lines and tumor tissue. To assess the relevance of these generalizations to a native mammalian tissue, we used isolated human and rodent pancreatic islets to examine interleukin (IL)-1β-induced PGE(2) production, because PGE(2) has been shown to mediate IL-1β inhibition of islet function. Rat islets constitutively expressed mRNAs of COX-1, COX-2, cPGES, and mPGES-1. As expected, IL-1β increased mRNA levels for COX-2 and mPGES-1, but not for COX-1 or cPGES. Basal protein levels of COX-1, cPGES, and mPGES-2 were readily detected in whole cell extracts but were not regulated by IL-1β. IL-1β increased protein levels of COX-2, but unexpectedly mPGES-1 protein levels were low and unaffected. In microsomal extracts, mPGES-1 protein was barely detectable in rat islets but clearly present in human islets; however, in neither case did IL-1β increase mPGES-1 protein levels. To further assess the importance of mPGES-1 to IL-1β regulation of an islet physiologic response, glucose-stimulated insulin secretion was examined in isolated islets of WT and mPGES-1-deficient mice. IL-1β inhibited glucose-stimulated insulin secretion equally in both WT and mPGES-1(-/-) islets, indicating that COX-2, not mPGES-1, mediates IL-1β-induced PGE(2) production and subsequent inhibition of insulin secretion.

Aspirin extrusion from human platelets through multidrug resistance protein-4-mediated transport: evidence of a reduced drug action in patients after coronary artery bypass grafting

OBJECTIVES

In this study we investigate: 1) the role of multidrug resistance protein-4 (MRP4), an organic anion unidirectional transporter, in modulating aspirin action on human platelet cyclooxygenase (COX)-1; and 2) whether the impairment of aspirin-COX-1 interaction, found in coronary artery bypass grafting (CABG) patients, could be dependent on MRP4-mediated transport.

BACKGROUND

Platelets of CABG patients present a reduced sensitivity to aspirin despite in vivo and in vitro drug treatment. Aspirin is an organic anion and could be a substrate for MRP4.

METHODS

Intracellular aspirin concentration and drug COX-1 activity, measured by thrombin-induced thromboxane B2 (TxB2) production, were evaluated in platelets obtained from healthy volunteers (HV) and hematopoietic-progenitor cell cultures reducing or not reducing MRP4-mediated transport. Platelet MRP4 expression was evaluated, in platelets from HV and CABG patients, by dot-blot or by immunogold-electromicrographs or immunofluorescence-microscopy analysis.

RESULTS

Inhibition of MRP4-mediated transport by dipyridamole or Mk-571 increases aspirin entrapment and its in vitro effect on COX-1 activity (142.7 ± 34.6 pg/10(8) cells vs. 343.7 ± 169.3 pg/10⁸ cells TxB2-production). Platelets derived from megakaryocytes transfected with MRP4 small interfering ribonucleic acid have a higher aspirin entrapment and drug COX-1 activity. Platelets from CABG patients showed a high expression of MRP4 whose in vitro inhibition enhanced aspirin effect on COX-1 (349 ± 141 pg/10⁸ cells vs. 1,670 ± 646 pg/10⁸ cells TxB2-production).

CONCLUSIONS

Aspirin is a substrate for MRP4 and can be extruded from platelet through its transportation. Aspirin effect on COX-1 is little-related to MRP4-mediated aspirin transport in HV, but in CABG patients with MRP4 over-expression, its pharmacological inhibition enhances aspirin action in an efficient way.

Microsomal prostaglandin E synthase-1 and 5-lipoxygenase: potential drug targets in cancer

There is strong evidence for a role of prostaglandin (PG)E(2) in cancer cell proliferation and tumour development. In PGE(2) biosynthesis, cyclooxygenases (COX-1/2) convert arachidonic acid to PGH(2), which can be isomerized to PGE(2) by PGE synthases, including microsomal PGE synthase-1 (MPGES-1). Data describing genetic deletions of MPGES-1 are reviewed. The results suggest that MPGES-1 is an alternative therapeutic target for cancer cells and tumours that express this enzyme. Several compounds that target COX-2 or MPGES-1 also inhibit 5-lipoxygenase. This may be advantageous for treatment of some forms of cancer.

Microsomal prostaglandin E synthase 1 determines tumor growth in vivo of prostate and lung cancer cells

There is strong evidence for a role of prostaglandin E(2) (PGE(2)) in cancer cell proliferation and tumor development. In PGE(2) biosynthesis, cyclooxygenases (COX-1/COX-2) convert arachidonic acid to PGH(2), which can be isomerized to PGE(2) by microsomal PGE-synthase-1 (MPGES-1). The human prostate cancer cell line DU145 expressed high amounts of MPGES-1 in a constitutive manner. MPGES-1 expression also was detectable in human prostate cancer tissues, where it appeared more abundant compared with benign hyperplasia. By using shRNA, we established stable and practically complete knockdown of MPGES-1, both in DU145 cells with high constitutive expression and in the non-small cell lung cancer cell line A549, where MPGES-1 is inducible. For microsomes prepared from knockdown clones, conversion of PGH(2) to PGE(2) was reduced by 85-90%. This resulted in clear phenotypic changes: MPGES-1 knockdown conferred decreased clonogenic capacity and slower growth of xenograft tumors (with disintegrated tissue structure) in nude mice. For DU145 cells, MPGES-1 knockdown gave increased apoptosis in response to genotoxic stress (adriamycin), which could be rescued by exogenous PGE(2). The results suggest that MPGES-1 is an alternative therapeutic target in cancer cells expressing this enzyme.