A labile hyperphosphorylated c-Fos protein is induced in mouse fibroblast cells treated with a combination of phorbol ester and anti-tumor promoter curcumin

Opposing effects of curcuminoids on serum stimulated and unstimulated angiogenic response

Curcumin is known to be a potent wound healer. Despite this, studies on curcumin using certain model systems have shown it to be anti-angiogenic. Results of the present investigations suggest that curcumin causes opposing effects on angiogenesis in serum stimulated and unstimulated conditions. The evidence in support of this are: (a) in serum free conditions, curcumin promoted sprouting in rat aortic ring, increased vascular density in CAM and induced morphological changes indicative of angiogenic phenotype in HUVECs and rat aortic endothelial cells in culture, (b) increased the expression of biochemical markers of angiogenesis such as CD 31, E-selectin, VEGF and VEGFR-2 in HUVECs on treatment with curcumin, and (c) supplementation of curcumin along with serum caused decrease in CD 31 and E-selectin levels, downregulation of VEGF, angiopoietin-1 and VEGFR-2 and delayed formation of capillary network-like structure. Proangiogenic effect of the individual components of the natural curcumin differed and the presence of the three components in the natural mixture has a synergistic effect. Effect of curcuminoids in the absence of serum appears to depend on VEGF as (a) anti-VEGF antibody blocked the effect of curcuminoids (b) curcuminoids caused decrease in PAR modification of VEGF increasing its biological activity. Treatment with curcuminoids in serum-free conditions resulted in activation of PI3K-Akt pathway; but in serum-supplemented condition, curcuminoids caused inhibition of the MAPK pathways thereby inhibiting the expression of angiogenic phenotype. These results suggest that PI3K-Akt and MAPK pathways involved in the expression of angiogenic phenotype respond differently to the extracellular microenvironment.

Curcumin enhances cystic fibrosis transmembrane regulator expression by down-regulating calreticulin

Curcumin has been reported to correct cystic fibrosis caused by the DeltaF508 mutation of the cystic fibrosis transmembrane regulator (CFTR) but its mechanistic action remains unclear. We have recently demonstrated that the ER chaperone calreticulin (CRT) negatively regulates the CFTR cell surface expression and activity. Thus, we aimed at determining whether CRT mediates the effect of curcumin on CFTR. We show here that the treatment with curcumin of Chinese hamster ovary cells suppressed CRT expression and increased wild-type CFTR but did not affect DeltaF508 CFTR expression. However, we determined that although curcumin did not augment DeltaF508 CFTR expression, it enhanced the functional competence of DeltaF508 CFTR induced by 26 degrees C incubation. Knock down of CRT by siRNA at low-temperature had a similar effect. Our findings suggest that the positive effect of curcumin on CFTR expression is mediated through the down-regulation of CRT, a negative regulator of CFTR.

Multiple biological activities of curcumin: a short review

Turmeric (Curcuma longa rhizomes), commonly used as a spice is well documented for its medicinal properties in Indian and Chinese systems of medicine. It has been widely used for the treatment of several diseases. Epidemiological observations, though inconclusive, are suggestive that turmeric consumption may reduce the risk of some form of cancers and render other protective biological effects in humans. These biological effects of turmeric have been attributed to its constituent curcumin that has been widely studied for its anti-inflammatory, anti-angiogenic, anti-oxidant, wound healing and anti-cancer effects. As a result of extensive epidemiological, clinical, and animal studies several molecular mechanisms are emerging that elucidate multiple biological effects of curcumin. This review summarizes the most interesting in vitro and in vivo studies on the biological effects of curcumin.

Curcumin suppresses interleukin 1beta-mediated microsomal prostaglandin E synthase 1 by altering early growth response gene 1 and other signaling pathways

Curcumin (diferuloylmethane) is one of the phytophenolic compounds found in the turmeric plant with anti-inflammatory and anticarcinogenic activities. One possible mechanism for these activities is the inhibition of prostaglandin (PG) E(2) formation. In this study and other reports, curcumin suppresses interleukin-1beta-induced formation of prostaglandin E(2) in a concentration-dependent manner. Interleukin-1beta-induced microsomal prostaglandin E synthase 1 (mPGES-1) and cyclooxygenase-2 were attenuated by curcumin at the protein and mRNA levels, but a more dramatic inhibition of mPGES-1 expression was observed at lower concentrations of curcumin in A549 human lung epithelial cells. The inhibition of mPGES-1 expression by curcumin shifted the arachidonic acid profile from PGE(2) to PGF(2alpha) and 6-keto-PGF(1alpha) as major metabolites. The expression of early growth response gene 1 (EGR-1), a key transcription factor of cytokine-induced mPGES-1, was inhibited by curcumin. Incubation with siRNA for EGR-1 inhibited interleukin (IL)-1beta-induced mPGES-1, and the controlled expression of EGR-1 increased the mPGES-1 expression. Several proinflammatory signaling molecules, such as nuclear factor kappaB (NF-kappaB) and mitogen-activated protein kinases, are also known to affect curcumin-regulated gene expression. Curcumin inhibited IkappaBalpha phosphorylation and degradation and thus reduced the expression of mPGES-1. Curcumin suppressed cytokine-induced mPGES-1 by inhibiting phosphorylation of Jun N-terminal kinase (JNK)1/2. However, EGR-1 expression was suppressed by lower concentrations of curcumin, as compared with JNK1/2 and IkappaBalpha. These results indicate that curcumin inhibits IL-1beta-induced PGE(2) formation by inhibiting the expression of mPGES-1 that is mediated by suppression of EGR-1 expression as well as NF-kappaB and JNK1/2.

Human wee1 kinase is directly transactivated by and increased in association with c-Fos/AP-1: rheumatoid synovial cells overexpressing these genes go into aberrant mitosis

Wee1 kinase downregulates the M-phase promoting factor, a complex of cdc2 and cyclin B kinase, that controls mitotic cell division. We isolated human wee1 kinase gene promoter and found that it contained one AP-1-binding motif in its promoter region (5'-CGAGTCA-3'; -823/-817), through which wee1 kinase gene was directly transactivated by c-Fos/AP-1. In rheumatoid synovial cells, wee1 kinase was increased in conjunction with the increase of c-Fos/AP-1 and the substrate of wee1, cdc2, was phosphorylated. The amount of wee1 and c-Fos and the phosphorylation of cdc2 were decreased after treatment of the cells with an inhibitor of AP-1, curcumin. A significant proportion of cultured synovial cells of the patients with rheumatoid arthritis, but not those of osteoarthritis, shifted to a tetraploid (4C) state upon long-term culture. Thus, human wee1 kinase gene is directly transactivated by and increased in association with c-Fos/AP-1, and rheumatoid synovial cells overexpressing these genes go into aberrant mitosis.

The structural determinants responsible for c-Fos protein proteasomal degradation differ according to the conditions of expression

c-fos gene is expressed constitutively in a number of tissues as well as in certain tumor cells and is inducible, in general rapidly and transiently, in virtually all other cell types by a variety of stimuli. Its protein product, c-Fos, is a short-lived transcription factor that heterodimerizes with various protein partners within the AP-1 transcription complex via leucine zipper/leucine zipper interactions for binding to specific DNA sequences. It is mostly, if not exclusively, degraded by the proteasome. To localize the determinant(s) responsible for its instability, we have conducted a genetic analysis in which the half-lives of c-Fos mutants and chimeras made with the stable EGFP reporter protein were compared under two experimental conditions taken as example of continous and inducible expression. Those were constitutive expression in asynchronously growing Balb/C 3T3 mouse embryo fibroblasts and transient induction in the same cells undergoing the G0/G1 phase transition upon stimulation by serum. Our work shows that c-Fos is degraded faster in synchronous- than in asynchronous cells. This difference in turnover is primarily accounted for by several mechanisms. First, in asynchronous cells, a unique C-terminal destabilizer is active whereas, in serum-stimulated cells two destabilizers located at both extremities of the protein are functional. Second, heterodimerization and/or binding to DNA accelerates protein degradation only during the G0/G1 phase transition. Adding another level of complexity to turnover control, phosphorylation at serines 362 and 374, which are c-Fos phosphorylation sites largely modified during the G0/G1 phase transition, stabilizes c-Fos much more efficiently in asynchronous than in serum-stimulated cells. In both cases, the reduced degradation rate is due to inhibition of the activity of the C-terminal destabilizer. However, in serum-stimulated cells, this effect is partially masked by the activation of the N-terminal destabilizer and basic domain/leucine zipper-dependent mechanisms. Taken together, our data show that multiple degradation mechanisms, differing according to the conditions of expression, may operate on c-Fos to ensure a proper level and/or timing of expression. Moreover, they also indicate that the half-life of c-Fos during the G0/G1 phase transition is determined by a delicate balance between opposing stabilizing and destabilizing mechanisms operating at the same time.

Differential regulation of cytokines and transcription factors in liver by curcumin following hemorrhage/resuscitation

Inflammatory cytokines interleukin 1 (IL-1), IL-2, IL-6, and tumor necrosis factor-alpha (TNF-alpha) have been recognized as important mediators of pathophysiological and immunological events associated with shock. These inflammatory events after hemorrhage and resuscitation are characterized by the activation of transcription regulators such as nuclear factor-kappaB (NF-kappaB) and activator protein-1 (AP-1). Curcumin, an anti-inflammatory remedy used in Indian medicine, is known to suppress NF-kappaB and AP-1 activation and also to reduce ischemia-reperfusion injuries in animal models. Therefore, the aim of this study was to determine whether administration of curcumin before hemorrhagic shock has any salutary effects on cytokines and the redox-sensitive transcription factors NF-kappaB and AP-1. mRNA levels of IL-1alpha, IL-1beta, IL-2, IL-6, IL-10, and TNF-alpha were determined by reverse transcriptase-polymerase chain reaction in rat livers collected at 2 and 24 h after hemorrhage/resuscitation. The effect of curcumin on the activation of NF-kappaB and AP-1 was determined by electrophoretic mobility shift assays. Significant increases in the levels of liver cytokines IL-1alpha, IL-1beta, IL-2, IL-6, and IL-10 were observed in the 2-h posthemorrhage/resuscitation group compared with sham animals. In contrast, oral administration of curcumin for 7 days followed by hemorrhage/resuscitation regimen resulted in significant restoration of these cytokines to depleted levels, and, in fact, IL-1beta levels were lower than sham levels. Also, the 24-h postresuscitation group showed similar patterns with some exceptions. NF-kappaB and AP-1 were differentially activated at 2 and 24 h posthemorrhage and were inhibited by curcumin pretreatment. Serum aspartate transaminase estimates indicate decreased liver injury in curcumin-pretreated hemorrhage animals. These results suggest that protection against hemorrhage/resuscitation injury by curcumin pretreatment may result from the inactivation of transcription factors involved and regulation of cytokines to beneficial levels.

Picroliv modulates antioxidant status and down-regulates AP1 transcription factor after hemorrhage and resuscitation

Resuscitation from hemorrhagic shock initiates profound changes in the liver that are likely to contribute to end organ damage and resultant dysfunction after shock. Extensive research in this area has indicated the potential of free radical scavenging strategy for better management of the pathophysiology following hemorrhage-resuscitation (H/R) injury. We studied the effect of a novel pharmacological agent, picroliv, on hepatocellular injury and redox status, as well as its possible mechanism of action in a H/R model in adult rats. Anesthetized rats were subjected to hemorrhagic shock by bleeding 30 mL/kg body weight. After 60 min of shock, rats were resuscitated with twice the shed blood volume of lactated Ringer's solution and were sacrificed 2 h after resuscitation. We observed that picroliv (12 mg/kg) pretreatment, given orally for 7 days, resulted in a significant decrease in serum aspartate transaminase and gamma-glutamyl transpeptidase levels. Picroliv also inhibited the lipid peroxidation and nitric oxide release that occurred after H/R and altered the activity of glutathione reductase in a favorable manner, thereby suggesting better antioxidant status. Picroliv significantly down-regulated the stress-sensitive transcription factor AP1 and decreased the level of c-fos mRNA as well as c-jun and c-fos proteins in liver tissue, indicating that its actions could be mediated through AP1 and associated signal transduction pathways. These findings suggest that picroliv has the potential to be developed as a protective agent against H/R injury.

Antagonism of glucocorticoid receptor transactivity and cell growth inhibition by transforming growth factor-beta through AP-1-mediated transcriptional repression

We have examined the interaction of the glucocorticoid receptor (GR) and transforming growth factor-beta (TGF-beta) signal pathways because of their mutual involvement in the regulation of cell growth, development and differentiation. Most studies of this cross-talk event have focused on the effects of glucocorticoids (GCs) on TGF-beta responses. In this work, we show that TGF-beta can antagonize dexamethasone (Dex)-mediated growth suppression in mouse fibrosarcoma L929 cells. TGF-beta also repressed GR-mediated reporter (pMMTV-CAT) gene expression in a concentration-dependent manner, with an IC(50) of 5 ng/ml of TGF-beta. Maximal inhibition (76%) was observed at 10 ng/ml of TGF-beta. Conversely, Dex inhibited TGF-beta-mediated promoter (p3TP-Lux) activity in these same cells. As TGF-beta inhibition of GR-mediated gene expression occurred after Dex-mediated nuclear translocation of GR, we conclude that TGF-beta inhibition of GR signaling occurs at the level of GR-mediated transcription activity. However, TGF-beta did not repress GR-mediated gene expression using the pGRE(2)E1B-CAT minimal promoter construct, suggesting that TGF-beta did not inhibit intrinsic GR activity but, rather, required DNA-binding factor(s) distinct from GR. As the MMTV promoter contains several putative AP-1 binding sites, we hypothesized that AP-1, a transcription factor composed of c-jun and c-fos proteins, might be involved in the TGF-beta inhibition of GR functions. Curcumin, a potent inhibitor of AP-1 expression, completely abolished the inhibitory effect of TGF-beta on GR-mediated gene expression without affecting GR activity in the absence of TGF-beta, and this drug blocked TGF-beta-induced binding of AP-1 to a response element derived from the MMTV sequence. Furthermore, curcumin abolished TGF-beta inhibition of Dex-induced growth suppression. Taken as a whole, our data suggest that TGF-beta can antagonize the growth inhibitory properties of GR by blocking GR transactivity at complex promoters through a mechanism involving transcriptional repression by DNA-bound AP-1.

Molecular mechanisms underlying chemopreventive activities of anti-inflammatory phytochemicals: down-regulation of COX-2 and iNOS through suppression of NF-kappa B activation

A wide array of phenolic substances, particularly those present in edible and medicinal plants, have been reported to possess substantial anticarcinogenic and antimutagenic activities. The majority of naturally occurring phenolics retain antioxidative and anti-inflammatory properties which appear to contribute to their chemopreventive or chemoprotective activity. Cyclooxygenase-2 (COX-2) inducible and nitric oxide synthase (iNOS) are important enzymes that mediate inflammatory processes. Improper up-regulation of COX-2 and/or iNOS has been associated with pathophysiology of certain types of human cancers as well as inflammatory disorders. Since inflammation is closely linked to tumor promotion, substances with potent anti-inflammatory activities are anticipated to exert chemopreventive effects on carcinogenesis, particularly in the promotion stage. Examples are curcumin, a yellow pigment of turmeric (Curcuma longa L., Zingiberaceae), the green tea polyphenol epigallocatechin gallate (EGCG), and resveratrol from grapes (Vitis vinifera, Vitaceae) that strongly suppress tumor promotion. Recent studies have demonstrated that eukaryotic transcription factor nuclear factor-kappa B (NF-kappa B) is involved in regulation of COX-2 and iNOS expression. Several chemopreventive phytochemicals have been shown to inhibit COX-2 and iNOS expression by blocking improper NF-kappa B activation. Multiple lines of compelling evidence indicate that extracellular-regulated protein kinase and p38 mitogen-activated protein kinase are key elements of the intracellular signaling cascades responsible for NF-kappa B activation in response to a wide array of external stimuli. Curcumin, EGCG and resveratrol have been shown to suppress activation of NF-kappa B. One of the plausible mechanisms underlying inhibition of NF-kappa B activation by aforementioned phytochemicals involves repression of degradation of the inhibitory unit I kappa B alpha, which hampers subsequent nuclear translocation of the functionally active subunit of NF-kappa B.

Curcuminoids inhibit the angiogenic response stimulated by fibroblast growth factor-2, including expression of matrix metalloproteinase gelatinase B

We have studied mechanisms controlling activation of the gelatinase B gene (matrix metalloproteinase-9) by fibroblast growth factor-2 (FGF-2) during angiogenesis, and the effects of the natural product curcuminoids on this process. Using a transgenic mouse (line 3445) harboring a gelatinase B promoter/lacZ fusion gene, we demonstrate FGF-2 stimulation of reporter gene expression in endothelial cells of invading neocapillaries in the corneal micropocket assay. Using cultured corneal cells, we show that FGF-2 stimulates DNA binding activity of transcription factor AP-1 but not NF-kappaB and that AP-1 stimulation is inhibited by curcuminoids. We further show that induction of gelatinase B transcriptional promoter activity in response to FGF-2 is dependent on AP-1 but not NF-kappaB response elements and that promoter activity is also inhibited by curcuminoids. In rabbit corneas, the angiogenic response induced by implantation of an FGF-2 pellet is inhibited by the co-implantation of a curcuminoid pellet, and this correlates with inhibition of endogenous gelatinase B expression induced by FGF-2. Angiostatic efficacy in the cornea is also observed when curcuminoids are provided to mice in the diet. Our findings provide evidence that curcuminoids target the FGF-2 angiogenic signaling pathway and inhibit expression of gelatinase B in the angiogenic process.

Estradiol suppresses type I collagen synthesis in mesangial cells via activation of activator protein-1

BACKGROUND

Estradiol suppresses the synthesis of type I collagen by murine mesangial cells. However, neither the alpha 1(I) nor the alpha 2(I) collagen gene contains an estrogen-response element. Because estradiol modulates the transcription of several genes that lack an estrogen-response element but contain a regulatory activator protein-1 (AP-1) binding motif, we hypothesized that AP-1 may mediate estradiol-induced suppression of type I collagen synthesis.

METHODS

We measured type I collagen synthesis in murine mesangial cells exposed to estradiol, phorbol 12-myristate 13-acetate (an activator of AP-1), or curcumin (an inhibitor of AP-1). We also assessed the effects of estradiol on the steady-state level of c-fos and c-jun mRNA and on the binding of mesangial cell nuclear extracts to an AP-1 consensus binding site oligonucleotide.

RESULTS

Estradiol (10(-10) M to 10(-7) M) suppressed type I collagen synthesis by murine mesangial cells in a dose-dependent manner (10(-7) M, 43.7 +/- 8.2% of control values, P < 0.001). Phorbol 12-myristate 13-acetate (10 microM, four-hr exposure) also decreased type I collagen in the media. In contrast, curcumin (1 microM) increased type I collagen. Estradiol increased the steady-state level of c-fos mRNA twofold at 30 minutes, with a return to basal levels at one hour. This was associated with a greater than threefold increase in the binding of nuclear extracts from estradiol-treated mesangial cells to an AP-1 consensus binding site oligonucleotide. Estradiol-enhanced binding of nuclear extracts to the AP-1 oligonucleotide was reversed by cycloheximide.

CONCLUSIONS

These data suggest that estradiol suppresses collagen I synthesis by murine mesangial cells via enhanced AP-1 activity.

Role of activating protein-1 in the regulation of the vascular cell adhesion molecule-1 gene expression by tumor necrosis factor-alpha

Endothelial cell surface expression of VCAM-1 is one of the initial steps in the pathogenesis of atherosclerosis. The inflammatory response transcription factor nuclear factor (NF)-kappaB plays an important role in the regulation of VCAM-1 expression by various stimuli including tumor necrosis factor (TNF)-alpha. Other transcription factors may modulate this response through interaction with NF-kappaB factors. Since c-Fos/c-Jun (activating protein-1 (AP-1)) are expressed in vascular endothelium during proinflammatory conditions, we investigated the role of AP-1 proteins in the expression of VCAM-1 by TNF-alpha in SV40 immortalized human microvascular endothelial cells (HMEC). TNF-alpha induced expression of both early protooncogenes, c-fos and c-jun. The ability of TNF-alpha to activate the kappaB-motif (kappaL-kappaR)-dependent VCAM-1 promoter-chloramphenicol acetyltransferase (CAT) reporter gene lacking a consensus AP-1 element was markedly inhibited by co-transfection of the expression vector encoding c-fos ribozyme, which decreases the level of c-fos by degrading c-fos mRNA, or c-fos or c-jun oligonucleotides. Conversely, co-transfection of c-Fos and c-Jun encoding expression vectors potentiated the p65/NF-kappaB-mediated transactivation of the VCAM-1 promoter-CAT reporter gene. Furthermore the c-Fos encoding expression vector potentiated by 2-fold the transactivation activity of a chimeric transcriptional factor Gal/p65 (containing the transactivation domain of p65 and the DNA binding domain of the yeast transcriptional factor Gal-4). Consistent with the promoter studies, curcumin and NDGA, inhibitors of AP-1 activation, markedly inhibited the ability of TNF-alpha to activate the expression of VCAM-1 mRNA levels at concentrations that did not inhibit the activation of NF-kappaB. In gel mobility supershift assays, the antibodies to c-Fos or c-Jun inhibited the binding of TNF-alpha-activated nuclear NF-kappaB to the kappaL-kappaR, suggesting that both c-Fos and c-Jun interacted with NF-kappaB. These results suggest that AP-1 proteins may mediate the effect of TNF-alpha in the regulation of VCAM-1 expression through interaction with NF-kappaB factors in endothelial cells.

Inhibition of tissue factor gene activation in cultured endothelial cells by curcumin. Suppression of activation of transcription factors Egr-1, AP-1, and NF-kappa B

Binding of plasma factor VII(a) to tissue factor (TF) initiates the coagulation cascade. In health, TF is not expressed in endothelial cells. However, endothelial cells express TF in response to lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF alpha), and other biological stimuli. TF expression by endothelial cells is implicated in thrombotic disorders in patients with a variety of clinical disorders. In the present study, we demonstrate that curcumin (diferulolylmethane), a known anticarcinogenic and anti-inflammatory agent, inhibited phorbol 12-myristate 13-acetate (PMA), LPS, TNF alpha, and thrombin-induced TF activity and TF gene transcription in human endothelial cells. The present data show that curcumin prevented the activation of c-Rel/p65, which is essential for TF gene activation in endothelial cells, by impairing the proteolytic degradation inhibitor protein, I kappa B alpha. The data also show that curcumin downregulated AP-1 binding activity. The present studies are the first to demonstrate that PMA, but not LPS, TNF alpha, and thrombin, induced Egr-1 binding to the second serum-responsive region (SRR-2) of TF promoter and that curcumin inhibited the PMA-induced Egr-1 binding to SRR-2. Overall, the data suggest that the anticarcinogenic and anti-inflammatory properties of curcumin may be related to its ability to inhibit cellular gene expression regulated by transcription factors NF-kappa B, AP-1, and Egr-1.