Inhibition of activator protein 1 activity and neoplastic transformation by aspirin

Cyclooxygenase-independent inhibition of dendritic cell maturation by aspirin

When immature human myeloid dendritic cells were differentiated in vitro in the presence of aspirin, they were unable to stimulate T-cell proliferation. Aspirin and its major metabolite salicylate changed the surface marker phenotype of dendritic cells. The drugs particularly suppressed the levels of CD83 and the secreted p40 unit of interleukin-12 (IL-12), both markers of mature dendritic cells; 50% inhibitory concentration (IC50) values were 2.5 mM, a concentration more than 100 times greater than the concentration at mid-point inhibition (ID50) value for inhibition of prostaglandin synthesis. Concomitantly, the levels of CD14, a marker of monocytes/macrophages, increased above the levels found in immature dendritic cells. Cyclooxygenase inhibitors ketoprofen, indomethacin and NS-398 had no effect at concentrations more than a thousand-fold higher than their IC50 values. The effects were independent of the presence of prostaglandin E2 in the medium. Salicylates suppressed activation of the nuclear transcription factor kappaB, which regulates dendritic cell differentiation, but their effects on mature dendritic cells were negligible. Hence, aspirin inhibits dendritic cell function by inhibiting their terminal differentiation at concentrations achieved in the blood of patients chronically treated with high-dose aspirin.

Role of p38 mitogen-activated protein kinases in ultraviolet-B irradiation-induced activator protein 1 activation in human keratinocytes

The effects of p38 mitogen-activated protein kinases on ultraviolet (UV) B irradiation-induced activator protein 1 (AP-1) activation were studied in a human keratinocyte cell line, HaCaT. The HaCaT cells were stably transfected with a plasmid containing a promoter fragment of human collagenase 1 driving a luciferase reporter gene. There is an AP-1-binding site within this fragment, without any other known transcription factor-binding sites. As we reported previously, UVB significantly induces activation of AP-1 and p38 in HaCaT cells. SB202190, a p38-specific inhibitor, inhibits UVB-induced p38 activation and c-fos gene expression. In the present study, we further examined the role of p38 in UVB-induced AP-1 activation. We observed that SB202190 strongly inhibited UVB-induced AP-1 transactivation at different time points and UVB doses in transfected HaCaT cells. Furthermore, SB202190 markedly inhibited UVB-induced AP-1 DNA binding as determined by mobility shift analyses. These results suggested, for the first time, that activation of p38 is required for UVB-induced AP-1 activation in human keratinocytes. In addition, a potential mechanism of UVB-induced AP-1 activation through p38 is to enhance AP-1 complex binding to its target DNA. Because c-fos gene expression plays a critical role in UVB-induced AP-1 activation and p38 is required for UVB-induced c-fos gene expression in HaCaT cells, as reported previously, a potential UVB signaling cascade for AP-1 activation in human keratinocytes has been determined. This cascade involves UVB, p38 activation, c-fos gene expression, and AP-1 activation.

Tumor cell-derived prostaglandin E2 inhibits monocyte function by interfering with CCR5 and Mac-1

The cyclooxygenases (COX)-1 and COX-2 are key enzymes in the conversion of arachidonic acid to prostaglandins and other eicosanoids. Whereas COX-1 is expressed ubiquitously, COX-2 is an immediate-early gene often associated with malignant transformation, and a role for the COX enzymes in tumor initiation and promotion is discussed. Nonsteroidal anti-inflammatory drugs (NSAIDs) like aspirin and indomethacin that block COX-1 and -2 have been shown to have beneficial effects for tumor patients. Therefore, these compounds have gained interest also among oncologists. However, the molecular mechanism by which NSAIDs inhibit carcinogenesis is not clearly understood. The prostaglandin-dependent and -independent effect may both account for their antineoplastic action. We show here that tumor cells derived from different tumors regularly produce prostaglandin E(2) (PGE(2)) interfering with the function of monocytes. In particular, PGE(2) inhibits the potential of monocytes to migrate in the direction of a chemotactic stimulus and to adhere to endothelial cell. This inhibition is most probably due to a modulation of the chemokine receptor CCR5 and the beta2-integrin Mac-1. Both down-regulation of CCR5 and reduced expression of Mac-1 may diminish the potential of peripheral blood monocytes to leave blood vessels and invade target tissues. Since both dysfunctions can be restored with NSAIDs, our findings help to explain the molecular chemopreventive action of NSAIDs on tumor formation and progression.

Inhibition of transcription factors by anti-inflammatory and anti-rheumatic drugs: can variability in response be overcome?

1. The drugs used in the treatment of rheumatoid arthritis (RA) form a diverse group with unpredictable adverse effects, mostly weak efficacy and variable responses. Despite their differences, a common feature of many anti-inflammatory and disease-modifying anti-rheumatic drugs (DMARD) is inhibition of pro-inflammatory transcription factors, particularly nuclear factor (NF)-kappaB and activator protein (AP)-1. 2. The present brief review identifies those drugs capable of inhibiting transcription factors, particularly steroids, gold salts, D-penicillamine, cyclosporine A and possibly salicylates. 3. The newer biological inhibitors of tumour necrosis factor (TNF)-alpha and interleukin (IL)-1beta are capable of indirect inhibition of NF-kappaB activation, although even with these potent agents the problem of variability in response has not disappeared. 4. The development of selective inhibitors of the transcription factor NF-kappaB should have the benefit of the anti-inflammatory drugs and DMARD, both new and old. 5. It is hypothesized that this strategy will overcome much of the variability in the therapeutic response and adverse effects that limit the usefulness of the existing drugs in the treatment of RA.

Activation of p38 MAP kinase and ERK are required for ultraviolet-B induced c-fos gene expression in human keratinocytes

The effects of p38 MAP kinase and ERK on UVB induced c-fos gene expression were studied in a human keratinocyte cell line, FL30. UVB significantly increased c-fos gene expression at both the transcriptional and protein levels. p38 and ERK were also significantly activated after UVB irradiation. Treating the cells with p38 inhibitor SB202190 inhibited p38 activation, but not ERK; treating the cells with MEK-1 inhibitor PD98059 inhibited ERK activation without suppressing p38 activation. The kinase activation was determined by Western blots using phospho-p38 or ERK antibodies, or an in vivo p38 activity assay. Further studies demonstrated that blocking p38 almost completely abrogated UVB induced c-fos gene transcription and c-Fos protein synthesis. Inhibiting ERK partially abrogated UVB induced c-fos transcriptional and protein levels. Suppression of both p38 and ERK not only completely blocked UVB induced c-fos expression, but also decreased c-fos gene basal expression. Our data indicated that p38 may play a more important role than ERK in UVB induced c-fos expression in human keratinocytes. Since c-fos expression may play an important role in UVB induced AP-1 activation, and AP-1 activation is known to play a role in tumor promotion, both p38 and ERK could be potential targets for chemoprevention of skin cancer.

Antioxidant properties of aspirin: characterization of the ability of aspirin to inhibit silica-induced lipid peroxidation, DNA damage, NF-kappaB activation, and TNF-alpha production

Electron spin resonance (ESR) was used to investigate the reaction of aspirin toward reactive oxygen species, such as hydroxyl radicals (*OH), superoxide radicals (O2-) and H2O2. The Fenton reaction (Fe(II) + H2O2 ---> FE(III) + *OH + OR) was used as a source of *OH radicals. The results show that aspirin is an efficient *OH radical scavenger with a reaction rate constant of k = 3.6 x 10(10) M(-1) sec(-1), which is faster than several well established antioxidants, such as ascorbate, glutathione and cysteine. However, aspirin is not a good scavenger for O2- or H2O2. Through its antioxidant property, aspirin exhibited a protective effect against silica-induced lipid peroxidation and DNA strand breakage. Aspirin also inhibited the activation of nuclear transcription factor-kappaB induced by silica, lipopolysaccharide or the transition metal, Fe(II), as demonstrated by electrophoretic mobility shift assay. The results show that aspirin functions as an antioxidant via its ability to scavenge *OH radicals. This antioxidant property may explain some of its various physiological and pharmacological actions.

Aspirin reduces apolipoprotein(a) (apo(a)) production in human hepatocytes by suppression of apo(a) gene transcription

High serum lipoprotein(a) (Lp(a)) is a risk factor for vascular disorders. Our preliminary observations suggest that, in some patients with coronary heart disease with high serum Lp(a) levels, administration of aspirin reduced Lp(a) levels. Therefore, we aimed to analyze the effects of aspirin on the production of apo(a), the expression of apolipoprotein(a) (apo(a)) mRNA and the transcriptional activity of apo(a) gene promoter. Aspirin (5 mM) reduced the apo(a) levels in culture medium of human hepatocytes and suppressed apo(a) mRNA expression to 73% and 85% of the controls, respectively. Aspirin also reduced the transcriptional activity of apo(a) gene transfected into HepG2 hepatoma cells in a dose-dependent manner, with a maximal effect at 5 mM (44.3 +/- 1.5% of the control). Sodium salicylate (5 mM) also reduced apo(a) gene transcription, whereas indomethacin (10 microM) had no effect. Deletion analysis of apo(a) gene promoter showed that promoter region extending from -30 to +138 is critical for the effect of aspirin. Furthermore, enhanced production, mRNA expression, and gene transcription of apo(a) by interleukin-6 were also inhibited by aspirin. These results demonstrate that aspirin reduces apo(a) production from hepatocytes via reduction of the transcriptional activity of apo(a) gene with suppression of apo(a) mRNA expression. The suppression of apo(a) production by aspirin may at least in part play a role in the anti-atherogenic effect of aspirin in vascular disorders.

The aryl hydrocarbon receptor (AHR)/AHR nuclear translocator (ARNT) heterodimer interacts with naturally occurring estrogen response elements

To determine the molecular mechanisms underlying the "cross talk" between the activity of 2,3,7,8-tetra-chlorodibenzo-p-dioxin (TCDD), which binds to arylhydrocarbon receptor (AHR) and estradiol (E2)-liganded estrogen receptor (ER), we first examined the initial step of estrogen action, ligand binding to ER. None of the AHR ligands tested, i.e. TCDD, benzo[a]pyrene, 3,3',4,4',5-pentachlorobiphenyl, beta-naphthoflavone, or alpha-naphthoflavone, bound to ER alpha. We report the first examination of TCDD interaction with ER beta: TCDD did not displace E2 from ER beta. We then examined a second possible mechanism, i.e. direct inhibition of ER alpha binding to estrogen response elements (EREs) by the AHR/AHR nuclear translocator (ARNT) complex. The AHR/ARNT heterodimer did not bind either a full or half-site ERE. However, AHR/ARNT bound specifically to oligomers containing naturally occurring EREs derived from the human c-fos, pS2, and progesterone receptor (PR) gene promoters that include xenobiotic response element (XRE)-like sequences. In contrast, neither purified E2-liganded-ER from calf uterus or recombinant human ER alpha bound a consensus XRE. TCDD inhibited E2-activated reporter gene activity from a consensus ERE and from EREs in the pS2, PR, and Fos genes in transiently transfected MCF-7 human breast cancer cells. However, this inhibition was not reciprocal since E2 did not inhibit TCDD-stimulated luciferase activity from the CYP1A1 promoter in transiently transfected MCF-7 or human endometrial carcinoma HEC-1A cells. We propose that at least part of the mechanism by which the AHR/ARNT complex inhibits estrogen action is by competitively inhibiting ER alpha binding to imperfect ERE sites, adjacent to or overlapping XREs.

Inhibitory effects of deferoxamine on UVB-induced AP-1 transactivation

Production of reactive oxygen species (ROS) by iron can contribute directly to DNA and protein damage and may contribute to cell signaling and proliferation. We have examined the effects of the iron(III) chelator deferroxamine (DFO) and iron (FeCl(3)) on UVB (290-320 nm)-induced activator protein 1 (AP-1) signaling. The ability of DFO to inhibit UVB-induced AP-1 transactivation was tested in a human keratinocyte cell line stably transfected with a luciferase reporter driven by a single AP-1 element. DFO treatment 24 h prior to UVB irradiation reduced UVB-induced AP-1 transactivation by approximately 80%, with the effect of DFO diminishing as pre-treatment time was shortened. Treatment with FeCl(3) a minimum of 6 h prior to UVB potentiated the UVB induction of AP-1 transactivation by 2-3-fold. DFO was able to ablate both the UVB induction of AP-1 transactivation as well as the potentiation by FeCl(3). The antioxidants Trolox and N-acetyl cysteine were both able to inhibit UVB-induced AP-1 transactivation and Trolox was able to inhibit the potentiation of UVB-induced AP-1 by FeCl(3). These results indicate that UVB-induced AP-1 activation may be in part due to oxidant effects of UVB and intercellular iron.

Freshly fractured crystalline silica induces activator protein-1 activation through ERKs and p38 MAPK

The transcription factor activator protein-1 (AP-1) reportedly plays an important role in the induction of neoplastic transformation and multiple genes involved in cell proliferation, differentiation, and inflammation. To investigate the mechanisms of silica-induced carcinogenesis, AP-1-luciferase reporter transgenic mice were used as an in vivo model, whereas the JB6 mouse epidermal cell line and a rat lung epithelial cell line were employed as in vitro models to study the effects of silica at the molecular level. Freshly fractured silica caused an 8-fold increase in AP-1 activity in JB6 cells and a 2.5-fold increase in rat lung epithelial cells. The induction of AP-1 activity in cultured cell lines was time- and dose-dependent. Intratracheal administration of silica was also able to induce AP-1 transactivation in transgenic mice. AP-1 activation was first observed at 2 days after silica administration and reached its maximum at 3 days post-exposure of the mice to silica. The signal transduction pathways for AP-1 activation were also investigated using these cell lines. The results demonstrate that freshly fractured silica stimulates mitogen-activated protein kinase (MAPK) family members, as determined by the phosphorylation of p38 MAPK and extracellular signal-regulated protein kinases (ERKs). Inhibition of ERKs with PD98059 or of p38 with SB203580 significantly inhibited silica-induced AP-1 activation. These findings demonstrate for the first time that freshly fractured silica induces AP-1 activation, which may be mediated through p38 MAPK and ERK pathways. Unraveling the complex mechanisms associated with these events may provide insights into the initiation and progression of silica-induced carcinogenesis.

Antioxidant properties of aspirin: characterization of the ability of aspirin to inhibit silica-induced lipid peroxidation, DNA damage, NF-kappaB activation, and TNF-alpha production

Electron spin resonance (ESR) was used to investigate the reaction of aspirin toward reactive oxygen species, such as hydroxyl radicals (*OH), superoxide radicals (O2-) and H2O2. The Fenton reaction (Fe(II) + H2O2 ---> FE(III) + *OH + OR) was used as a source of *OH radicals. The results show that aspirin is an efficient *OH radical scavenger with a reaction rate constant of k = 3.6 x 10(10) M(-1) sec(-1), which is faster than several well established antioxidants, such as ascorbate, glutathione and cysteine. However, aspirin is not a good scavenger for O2- or H2O2. Through its antioxidant property, aspirin exhibited a protective effect against silica-induced lipid peroxidation and DNA strand breakage. Aspirin also inhibited the activation of nuclear transcription factor-kappaB induced by silica, lipopolysaccharide or the transition metal, Fe(II), as demonstrated by electrophoretic mobility shift assay. The results show that aspirin functions as an antioxidant via its ability to scavenge *OH radicals. This antioxidant property may explain some of its various physiological and pharmacological actions.

Inhibition of p38 MAP kinase increases okadaic acid mediated AP-1 expression and DNA binding but has no effect on TRE dependent transcription

By performing in vitro kinase assays we found in papilloma producing 308 mouse keratinocytes that okadaic acid elevated activities of extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinases (JNKs) and p38 mitogen-activated protein kinases (MAPKs). This okadaic acid mediated activation of MAP kinases correlated with increased AP-1 binding to a consensus TPA responsive element (TRE) and elevated TRE dependent transcription. To determine the role of p38 MAP kinases in these processes we employed the specific p38 MAP kinase inhibitor SB 203580. Using orthophosphate labeling we showed a decrease in phosphorylation of MAPK activated protein kinase-2 (MAPKAP-K2) indicating reduced activity of p38 MAPKs utilizing this kinase as substrate. In contrast, we found that SB 203580 raised activities of ERK-1/2 and JNKs. Electrophoretic mobility shift assays revealed an increase in TRE binding activity in response to SB 203580 most likely resulting from increased expression of the major TRE binding components JunD and FosB as indicated by Western blot analyses. Increased TRE DNA binding failed to lead to increased transactivation correlating with the inability of SB 203580 to increase phosphorylation of these AP-1 proteins. These data indicate that SB 203580 sensitive p38 MAP kinases are not involved in okadaic acid mediated increases in TRE DNA binding and transactivation.

Translocation of protein kinase Cepsilon and protein kinase Cdelta to membrane is required for ultraviolet B-induced activation of mitogen-activated protein kinases and apoptosis

UV-induced signal transduction may be involved in tumor promotion and induction of apoptosis. The role of protein kinase C (PKC) in UVB-induced signal transduction is not well understood. This study showed that UVB markedly induced translocation of membrane-associated PKCepsilon and PKCdelta, but not PKCalpha, from cytosol to membrane. Dominant negative mutant (DNM) PKCepsilon or PKCdelta inhibited UVB-induced translocation of PKCepsilon and PKCdelta, respectively. UVB-induced activation of extracellular signal-regulated protein kinases (Erks) and c-Jun NH2-terminal kinases (JNKs) was strongly inhibited by DNM PKCepsilon and PKCdelta, whereas the DNM of PKCalpha was less effective on the UVB-induced phosphorylation of Erks and JNKs. Among the PKC inhibitors used only rottlerin, a selective inhibitor of PKCdelta, markedly inhibited the UVB-induced activation of Erks and JNKs, but not p38 kinases. Safingol, a selective inhibitor for PKCalpha, did not show any inhibitory effect on UVB-induced mitogen-activated protein kinase activation. GF109203X is a stronger inhibitor of classical PKC than novel PKC. Lower concentrations of GF109203X (<10 microM) had no effect on UVB-induced activation of Erks or JNKs. However, at higher concentrations (over 20 microM), GF109203X inhibited UVB-induced activation of JNKs, Erks, and even p38 kinases. Meanwhile, rottlerin and GF109203X markedly inhibited UVB-induced apoptosis of JB6 cells, whereas safingol had little inhibitory effect. DNM-Erk2 cells and PD98059, a selective inhibitor for mitogen-activated protein kinase/extracellular signal-regulated kinase 1 that directly activates Erks, inhibited UVB-induced apoptosis. DNM-JNK1 cells also blocked UVB-induced apoptosis, whereas SB202190, a specific inhibitor for p38 kinases, did not produce the inhibitory effect. These data demonstrate that PKCdelta and PKCepsilon, but not PKCalpha, mediate UVB-induced signal transduction and apoptosis in JB6 cells through activation of Erks and JNKs.

Metabolic targets of cancer chemoprevention: interruption of tumor development by inhibitors of arachidonic acid metabolism

Tumor promotion is understood as a process that favors the clonal outgrowth of single mutated (initiated) cells to premalignant lesions through co-mitogenic and anti-apoptotic effects. This process can be evoked by repeated induction of a regenerative tissue response as achieved either by irritation and wounding or by agents (tumor promoters) that interact with the corresponding pathways of cellular signaling. Metabolic processes regulated by such pathways and essential for tumor development are potential targets of cancer chemoprevention. Examples are provided by the expression of ornithine decarboxylase and the activation of eicosanoid formation from arachidonic acid. Arachidonic acid metabolism is a particularly attractive and important target of chemopreventive measures. Its induction is a characteristic response to tissue damage and irritation and an apparently critical event in epithelial tumor promotion. Inhibitors of eicosanoid formation, such as nonsteroidal anti-inflammatory drugs, rank among the most powerful chemopreventive agents in animal models and have been shown to halve the incidence of colorectal cancer in man. Recently, the role of cyclooxygenase-2 (COX-2)-catalyzed prostaglandin synthesis has been the subject of much attention. COX-2 is a typical 'emergency enzyme', since in most tissues it is transiently induced only in the course of repair and defense reactions. In epithelial neoplasia, i.e. in skin and colorectal tumors, the enzyme is constitutively overexpressed along different molecular pathways, and it seems to be critically involved in tumor promotion. Consequently, specific COX-2 inhibitors have been shown to exhibit considerable cancer chemopreventive potential. The putative role of other pathways of arachidonic acid metabolism in tumor promotion and malignant progression is presently under investigation.

Requirement of Erk, but not JNK, for arsenite-induced cell transformation

Trivalent arsenic (arsenite, As3+) is a human carcinogen, which is associated with cancers of skin, lung, liver, and bladder. However, the mechanism by which arsenite causes cancer is not well understood. In this study, we found that exposure of Cl 41 cells, a well characterized mouse epidermal cell model for tumor promotion, to a low concentration of arsenite (<25 microM) induces cell transformation. Interestingly, arsenite induces Erk phosphorylation and increased Erk activity at doses ranging from 0.8 to 200 microM, while higher doses (more than 50 microM) are required for activation of JNK. Arsenite-induced Erk activation was markedly inhibited by introduction of dominant negative Erk2 into cells, while expression of dominant negative Erk2 did not show inhibition of JNK and MEK1/2. Furthermore, arsenite-induced cell transformation was blocked in cells expressing the dominant negative Erk2. In contrast, overexpression of dominant negative JNK1 was shown to increase cell transformation even though it inhibits arsenite-induced JNK activation. Our results not only show that arsenite induces Erk activation, but also for the first time demonstrates that activation of Erk, but not JNK, by arsenite is required for its effects on cell transformation.

Suppression of inducible cyclooxygenase 2 gene transcription by aspirin and sodium salicylate

The pharmacological action of salicylate cannot be explained by its inhibition of cyclooxygenase (COX) activity. In this report, the effects of aspirin and sodium salicylate on COX-2 expressions in human umbilical vein endothelial cells and foreskin fibroblasts were evaluated. Aspirin and sodium salicylate at therapeutic concentrations equipotently blocked COX-2 mRNA and protein levels induced by interleukin-1beta and phorbol 12-myristate 13-acetate. The suppressing effect was more pronounced in cultured cells deprived of fetal bovine serum for 24 h, suggesting that it may be cell cycle related. Salicylate inhibited nascent COX-2 transcript synthesis but had no effect on COX-2 mRNA stability. It inhibited COX-2 promoter activity in a concentration-dependent manner. In mice pretreated with aspirin (10 and 30 mg/kg), followed by challenge with lipopolysaccharide, COX-2 mRNA expression in peritoneal macrophages was markedly suppressed. These findings suggest that salicylate exerts its antiinflammatory action in part by suppressing COX-2 induction, thereby reducing the synthesis of proinflammatory prostaglandins.

Vanadate-induced activation of activator protein-1: role of reactive oxygen species

The present study was undertaken to test the hypothesis that the toxicity and carcinogenicity of vanadium might arise from elevation of reactive oxygen species leading to activation of the transcription factor activator protein-1 (AP-1). The AP-1 transactivation response has been implicated as causal in transformation responses to phorbol esters and growth factors. To investigate the possible activity of vanadium in the activation of AP-1, we treated mouse epidermal JB6 P+ cells stably transfected with an AP-1 luciferase reporter plasmid with various concentrations of vanadate. This resulted in concentration-dependent transactivation of AP-1. Superoxide dismutase (SOD) and catalase inhibited AP-1 activation induced by vanadate, indicating the involvement of superoxide anion radical (O2-*), hydroxyl radical (*OH) and/or H2O2 in the mechanism of vanadate-induced AP-1 activation. However, sodium formate, a specific *OH scavenger, did not alter vanadate-induced AP-1 activation, suggesting a minimal role for the *OH radical. NADPH enhanced AP-1 activation by increasing vanadate-mediated generation of O2-*. N-acetylcysteine, a thiol-containing antioxidant, decreased activation, further showing that vanadate-induced AP-1 activation involved redox reactions. Calphostin C, a specific inhibitor of protein kinase C (PKC), inhibited activation of AP-1, demonstrating that PKC is involved in the cell signal cascades leading to vanadate-induced AP-1 activation. Electron spin resonance (ESR) measurements show that JB6 P+ cells are able to reduce vanadate to generate vanadium(IV) in the presence of NADPH. Molecular oxygen was consumed during the vanadate reduction process to generate O2-* as measured by ESR spin trapping using 5,5-dimethyl-L-pyrroline N-oxide as the spin trapping agent. SOD inhibited the ESR spin adduct signal, further demonstrating the generation of O2-* in the cellular reduction of vanadate. These results provide support for a model in which vanadium, like other classes of tumor promoters, transactivates AP-1-dependent gene expression. In the case of vanadium, AP-1 transactivation is dependent on the generation of O2-* and H2O2, but not *OH.

Sodium Salicylate Activates Caspases and Induces Apoptosis of Myeloid Leukemia Cell Lines

Nonsteroidal antiinflammatory agents (NSAIA) have been shown to exert potent chemopreventive activity against colon, lung, and breast cancers. In this study, we show that at pharmacological concentrations (1 to 3 mmol/L) sodium salicylate (Na-Sal) can potently induce programmed cell death in several human myeloid leukemia cell lines, including TF-1, U937, CMK-1, HL-60, and Mo7e. TF-1 cells undergo rapid apoptosis on treatment with Na-Sal, as indicated by increased annexin V binding capacity, cpp-32 (caspase-3) activation, and cleavage of poly (ADP-ribose) polymerase (PARP) and gelsolin. In addition, the expression of MCL-1, an antiapoptotic member of the BCL-2 family, is downregulated during Na-Sal–induced cell death, whereas the expression of BCL-2, BAX, and BCL-XL is unchanged. Z-VAD, a potent caspase inhibitor, prevents the cleavage of PARP and gelsolin and rescues cells from Na-Sal–induced apoptosis. In addition, we show that Na-Sal accelerates growth factor withdrawal-induced apoptosis and synergizes with daunorubicin to induce apoptosis in TF-1 cells. Thus, our data provide a potential mechanism for the chemopreventive activity of NSAIA and suggest that salicylates may have therapeutic potential for the treatment of human leukemia.

Sodium Salicylate Activates Caspases and Induces Apoptosis of Myeloid Leukemia Cell Lines

Nonsteroidal antiinflammatory agents (NSAIA) have been shown to exert potent chemopreventive activity against colon, lung, and breast cancers. In this study, we show that at pharmacological concentrations (1 to 3 mmol/L) sodium salicylate (Na-Sal) can potently induce programmed cell death in several human myeloid leukemia cell lines, including TF-1, U937, CMK-1, HL-60, and Mo7e. TF-1 cells undergo rapid apoptosis on treatment with Na-Sal, as indicated by increased annexin V binding capacity, cpp-32 (caspase-3) activation, and cleavage of poly (ADP-ribose) polymerase (PARP) and gelsolin. In addition, the expression of MCL-1, an antiapoptotic member of the BCL-2 family, is downregulated during Na-Sal–induced cell death, whereas the expression of BCL-2, BAX, and BCL-XL is unchanged. Z-VAD, a potent caspase inhibitor, prevents the cleavage of PARP and gelsolin and rescues cells from Na-Sal–induced apoptosis. In addition, we show that Na-Sal accelerates growth factor withdrawal-induced apoptosis and synergizes with daunorubicin to induce apoptosis in TF-1 cells. Thus, our data provide a potential mechanism for the chemopreventive activity of NSAIA and suggest that salicylates may have therapeutic potential for the treatment of human leukemia.

Inhibition of ultraviolet B--induced c-fos gene expression and p38 mitogen-activated protein kinase activation by (-)-epigallocatechin gallate in a human keratinocyte cell line

(-)-Epigallocatechin gallate (EGCG), the major polyphenol isolated from green tea, is an active chemoprevention agent against cancer. However, the molecular mechanisms that underlie the inhibitory effects of EGCG are not well understood. In this study, we tested the effects of EGCG on ultraviolet (UV) B radiation-induced c-fos gene expression in a human keratinocyte cell line, HaCaT. EGCG inhibited UVB-induced steady-state message and transcriptional activation of the c-fos gene in a dose-dependent manner. Western analyses further indicated that EGCG had an inhibitory effect on UVB-induced accumulation of the c-fos protein within the same dose range. To further examine the mechanism by which EGCG inhibits UVB-induced c-fos expression, we tested the effect of EGCG on upstream activators of the c-fos gene. We found that EGCG significantly inhibited activation of p38 mitogen-activated protein kinase but not c-jun NH2-terminal kinase or extracellular signal-regulated protein kinase activation. Our previous studies have indicated that UVB-induced c-fos expression may play a key role in UVB-induced activation of the activator protein-1 transcription factor and EGCG-inhibited, UVB-induced activation of AP-1 in HaCaT cells. Because AP-1 is important for tumor promotion and c-fos is a major component of AP-1, the inhibitory effects of EGCG on c-fos expression may further explain the anti-tumor-promoting effects of EGCG.

Extracellular signal-regulated kinase 1/2-mediated phosphorylation of JunD and FosB is required for okadaic acid-induced activator protein 1 activation

Previously, we reported that in papilloma-producing 308 mouse keratinocytes, the tumor promoter okadaic acid, a serine-threonine phosphatase inhibitor, increased binding of activator protein 1 (AP-1) to a consensus 12-O-tetradecanoylphorbol-13-acetate-responsive element (Rosenberger, S. F., and Bowden, G. T. (1996) Oncogene 12, 2301-2308). In this study, we investigated the correlation between AP-1 DNA binding and transactivation and examined molecular mechanisms involved in this process. Using a luciferase reporter driven by region -74 to +63 of the human collagenase gene, we demonstrated induction of AP-1-mediated transcription following okadaic acid treatment. By performing in vitro kinase assays, we found elevated activities of extracellular signal-regulated kinase (ERK) 1/2, c-Jun N-terminal kinase, and p38 mitogen-activated protein kinase. The ERK-1/2-specific inhibitor PD 98059 completely abrogated okadaic acid-induced AP-1 transactivation without altering AP-1 expression, DNA binding, or complex composition. Phosphorylation analyses indicated that inhibition of ERK-1/2 decreased okadaic acid-elevated phosphorylation of JunD and FosB. To further examine the role of JunD and FosB in okadaic acid-induced AP-1 transactivation, we generated fusion proteins of the DNA-binding domain of the yeast transcription factor Gal4 and the transactivation domain of either JunD or FosB. Cotransfection experiments of these constructs with a Gal4-luciferase reporter demonstrated that both JunD and FosB are required for okadaic acid-induced transcription. Treatment with PD 98059 reduced JunD/FosB-dependent transactivation, suggesting that ERK-1/2-mediated phosphorylation is a critical component in this process.

Aspirin and some other nonsteroidal anti-inflammatory drugs inhibit cystic fibrosis transmembrane conductance regulator protein gene expression in T-84 cells

Cystic fibrosis (CF) is caused by mutations in the CF gene, which encodes CF transmembrane conductance regulator protein (CFTR), a transmembrane protein that acts as a cAMP-regulated chloride channel The disease is characterized by inflammation but the relationship between inflammation, abnormal transepithelial ion transport, and the clinical manifestations of CF are uncertain. The present study was undertaken to determine whether three nonsteroidal anti-inflammatory drugs (NSAIDs) (aspirin, ibuprofen, and indomethacin) modulate CFTR gene expression in T-84 cells. Treatment with NSAIDs reduced CFTR transcripts, and decreased cAMP-stimulated anion fluxes, an index of CFTR function. However, the two phenomena occurred at different concentrations of both drugs. The results indicate that NSAIDs can regulate both CFTR gene expression and the function of CFTR-related chloride transport, and suggest that NSAIDs act via multiple transduction pathways.

Inhibition of heat-shock protein 70 induction in intestinal cells overexpressing cyclooxygenase 2

BACKGROUND & AIMS

The cyclooxygenase (COX) enzymes catalyze the initial step of prostaglandin formation; the inducible form, COX-2, plays a role in inflammation. Heat-shock protein 70 (hsp70) is a stress-responsive gene important for cell survival; induction of hsp70 appears to be mediated, in part, by the prostaglandin pathway. We determined the effect of COX-2 overexpression on hsp70 induction in rat intestinal epithelial (RIE) cells.

METHODS

RIE cells transfected with COX-2 complementary DNA oriented in the sense (RIE-S) or antisense (RIE-AS) direction were subjected to a heat shock; RNA and protein were harvested and analyzed by Northern and Western blots, respectively. Gel shift assays were performed to assess DNA binding.

RESULTS

Both hsp70 messenger RNA and HSP70 protein levels were increased in the RIE-AS cells, whereas induction was markedly inhibited in the RIE-S cells after heat shock. Inhibition of heat-shock factor binding was noted in RIE-S cells, suggesting that heat-shock transcription factor regulation may explain the inhibition of hsp70. The COX-2 selective inhibitor, NS-398, reversed the effects of COX-2 overexpression.

CONCLUSIONS

The results support a functional role for the prostaglandin/COX pathway in the induction of hsp70. The findings underscore a potential regulatory mechanism involving an inverse relationship between COX-2 expression and hsp70 induction.

Modes of action of aspirin-like drugs: salicylates inhibit erk activation and integrin-dependent neutrophil adhesion

The anti-inflammatory effects of high-dose salicylates are well recognized, incompletely understood and unlikely due entirely to cyclooxygenase (COX) inhibition. We have previously reported a role for activation of the kinase Erk in CD11b/CD18 integrin-dependent adhesiveness of human neutrophils, a critical step in inflammation. We now report the effects of salicylates on neutrophil Erk and adhesion. Exposure of neutrophils to aspirin or sodium salicylate (poor COX inhibitor) inhibited Erk activity and adhesiveness of formylmethionyl-leucyl-phenylalanine- and arachidonic acid-stimulated neutrophils, consistent with anti-inflammation but not COX inhibition (IC50s = 1-8 mM). In contrast, indomethacin blocked neither Erk nor adhesion. Inhibition of Mek (proximal activator of Erk) also blocked stimulation of Erk and adhesion by formylmethionyl-leucyl-phenylalanineand arachidonic acid. Salicylate inhibition of Erk was independent of protein kinase A activation and generation of extracellular adenosine. These data are consistent with a role for Erk in stimulated neutrophil adhesion, and suggest that anti-inflammatory effects of salicylates may be mediated via inhibition of Erk signaling required for integrin-mediated responses.

Aspirin and Salicylate Induce Apoptosis and Activation of Caspases in B-Cell Chronic Lymphocytic Leukemia Cells

We analyzed the effect of aspirin, salicylate, and other nonsteroidal antiinflammatory drugs (NSAIDs) on the viability of B-chronic lymphocytic leukemia (B-CLL) cells. Aspirin induced a decrease in cell viability in a dose- and time-dependent manner. The mean IC50 for cells from 5 patients was 5.9 ± 1.13 mmol/L (range, 4.4 to 7.3 mmol/L). In some cases, 2.5 mmol/L aspirin produced an important cytotoxic effect after 4 days of incubation. No effect was observed with other NSAIDs, at concentrations that inhibit cyclooxygenase, such as ketorolac (10 μmol/mL), NS-398 (100 μmol/mL), or indomethacin (20 μmol/mL), thus suggesting the involvement of cyclooxygenase-independent mechanisms in aspirin-induced cytotoxicity. Salicylate also produced dose-dependent cytotoxic effects on B-CLL cells and the mean IC50 for cells from 5 patients was 6.96 ± 1.13 mmol/L (range, 5 to 7.8 mmol/L). Both aspirin and salicylate induced DNA fragmentation and the proteolytic cleavage of poly(ADP(adenosine 5′-diphosphate)-ribose) polymerase (PARP), demonstrating that both compounds induce apoptosis of B-CLL cells. Finally, inhibition of caspases by Z-VAD.fmk blocked proteolytic cleavage of PARP, DNA fragmentation, and cytotoxicity induced by aspirin. Mononuclear cells from normal donors showed a lower sensitivity than cells from B-CLL patients to aspirin as determined by analysis of cell viability. B and T lymphocytes from normal donors and T lymphocytes from CLL patients are more resistant to aspirin-induced apoptosis, as determined by analysis of phosphatidylserine exposure. These results indicate that aspirin and salicylate induce apoptosis of B-CLL cells by activation of caspases and that this activation involves cyclooxygenase-independent mechanisms.

© 1998 by The American Society of Hematology.

Aspirin and Salicylate Induce Apoptosis and Activation of Caspases in B-Cell Chronic Lymphocytic Leukemia Cells

We analyzed the effect of aspirin, salicylate, and other nonsteroidal antiinflammatory drugs (NSAIDs) on the viability of B-chronic lymphocytic leukemia (B-CLL) cells. Aspirin induced a decrease in cell viability in a dose- and time-dependent manner. The mean IC50 for cells from 5 patients was 5.9 ± 1.13 mmol/L (range, 4.4 to 7.3 mmol/L). In some cases, 2.5 mmol/L aspirin produced an important cytotoxic effect after 4 days of incubation. No effect was observed with other NSAIDs, at concentrations that inhibit cyclooxygenase, such as ketorolac (10 μmol/mL), NS-398 (100 μmol/mL), or indomethacin (20 μmol/mL), thus suggesting the involvement of cyclooxygenase-independent mechanisms in aspirin-induced cytotoxicity. Salicylate also produced dose-dependent cytotoxic effects on B-CLL cells and the mean IC50 for cells from 5 patients was 6.96 ± 1.13 mmol/L (range, 5 to 7.8 mmol/L). Both aspirin and salicylate induced DNA fragmentation and the proteolytic cleavage of poly(ADP(adenosine 5′-diphosphate)-ribose) polymerase (PARP), demonstrating that both compounds induce apoptosis of B-CLL cells. Finally, inhibition of caspases by Z-VAD.fmk blocked proteolytic cleavage of PARP, DNA fragmentation, and cytotoxicity induced by aspirin. Mononuclear cells from normal donors showed a lower sensitivity than cells from B-CLL patients to aspirin as determined by analysis of cell viability. B and T lymphocytes from normal donors and T lymphocytes from CLL patients are more resistant to aspirin-induced apoptosis, as determined by analysis of phosphatidylserine exposure. These results indicate that aspirin and salicylate induce apoptosis of B-CLL cells by activation of caspases and that this activation involves cyclooxygenase-independent mechanisms.

© 1998 by The American Society of Hematology.

Biochemical pharmacology of nonsteroidal anti-inflammatory drugs

Aspirin and conventional nonsteroidal anti-inflammatory drugs are nonselective inhibitors of cyclooxygenase-1 (COX-1) and COX-2 enzymes. Two classes of selective COX-2 inhibitors: (1) sulfonamides, such as L-745,337, and (2) tricyclic methyl sulfone derivatives, such as SC58125, have been developed. X-ray crystal structures of COX-1 and COX-2 have provided valuable information regarding the structural basis for their COX-2 selectivity. These compounds have less gastrointestinal complications in animal experiments. Their clinical efficacy and side-effects are being evaluated. Salicylate has very weak activity against either COX isoform and yet possesses anti-inflammatory actions. Recent studies indicate that it suppresses the expression of genes involved in inflammation. These activities may provide a plausible explanation for the pharmacological dilemma and, furthermore, may represent novel mechanisms for controlling inflammation.

Shortage of mitogen-activated protein kinase is responsible for resistance to AP-1 transactivation and transformation in mouse JB6 cells

The JB6 mouse epidermal cell system, which includes tumor promotion-sensitive (P+) and tumor promotion-resistant (P-) cells, is a well-established and extensively used cell culture model for studying the mechanism of late-stage tumor promotion. Tumor promoters, such as 12-O-tetradecanoylphorbol 13-acetate (TPA) or epidermal growth factor (EGF), induce high levels of activator protein 1 (AP-1) activity and large, tumorigenic, anchorage-independent colonies in soft agar at a high frequency in JB6 P+ cells, but not in JB6 P- cells. We report here a molecular explanation for the defect in the AP-1 activation and promotion-resistant phenotype of P- cells. We demonstrate that the lack of AP-1 activation and cell transformation responses to TPA and EGF in P- cells appears attributable to the low level of mitogen-activated protein kinase (MAPK) (extracellular signal-regulated protein kinase, Erk) in these cells. TPA and EGF induce transactivation of AP-1 activity in P+ cells but not in P- cells. Nonphosphorylated forms and TPA- or EGF-induced phosphorylated forms of Erks (Erk1 and Erk2) in P- cells were much lower than those in P+ cells. Stable transfection of wild-type MAPK (Erk2) into P- cells restored its response to TPA and EGF for both AP-1 activation and cell transformation. These results suggest that the shortage of MAPK (Erk1 and Erk2) appears to be an important contributor to the tumor promotion-resistant phenotype in JB6 cells.

Proteinase inhibitors I and II from potatoes specifically block UV-induced activator protein-1 activation through a pathway that is independent of extracellular signal-regulated kinases, c-Jun N-terminal kinases, and P38 kinase

Solar UV irradiation is the causal factor for the increasing incidence of human skin carcinomas. The activation of the transcription factor activator protein-1 (AP-1) has been shown to be responsible for the tumor promoter action of UV light in mammalian cells. We demonstrate that proteinase inhibitor I (Inh I) and II (Inh II) from potato tubers, when applied to mouse epidermal JB6 cells, block UV-induced AP-1 activation. The inhibition appears to be specific for UV-induced signal transduction for AP-1 activation, because these inhibitors did not block UV-induced p53 activation nor did they exhibit any significant influence on epidermal growth factor-induced AP-1 transactivation. Furthermore, the inhibition of UV-induced AP-1 activity occurs through a pathway that is independent of extracellular signal-regulated kinases and c-Jun N-terminal kinases as well as P38 kinases. Considering the important role of AP-1 in tumor promotion, it is possible that blocking UV-induced AP-1 activity by Inh I or Inh II may be functionally linked to irradiation-induced cell transformation.

Inhibition of ultraviolet B-induced activator protein-1 (AP-1) activity by aspirin in AP-1-luciferase transgenic mice

Aspirin is under consideration as a promising chemopreventative agent for human cancers. To study the usefulness of aspirin as a chemopreventative agent for UV-induced human skin cancer, we investigated the effect of aspirin on UVB-induced activator protein-1 (AP-1) activity. In the JB6 cell culture system, aspirin or sodium salicylate (SA) inhibited UVB-induced AP-1 activity in a dose-dependent manner; this inhibitory effect occurred only in cells pretreated with aspirin or SA before UVB irradiation but not cells treated with aspirin or SA after UVB irradiation. Furthermore, these inhibitory effects on UVB-induced AP-1 activity appeared to be mediated through blocking of activation of MAP kinase family members, including extracellular signal-regulated protein kinases, c-Jun N-terminal kinases, and p38. It was not due to absorption of UVB light by aspirin. In the skin of AP-1-luciferase transgenic mice, UVB irradiation induced a rapid increase in AP-1 activity, which reached the peak at 48 h post-UVB irradiation. The topical pretreatment of mouse skin with aspirin markedly blocked the UVB-induced AP-1 transactivation in vivo. These data provide the first evidence that aspirin and SA are inhibitors of UV-induced signal transduction and thus could be used as a chemopreventative agent for skin cancer.