Sangtaek Oh

Interferon regulatory factor-1 is prerequisite to the constitutive expression and IFN-γ-induced upregulation of B7-H1 (CD274)

Majority of cancer cells upregulate co‐inhibitory molecule B7‐H1 which confers resistance to anti‐tumor immunity, allowing cancers to escape from host immune surveillance. We addressed the molecular mechanism underlying the regulation of cancer‐associated B7‐H1 expression in response to interferon‐γ (IFN‐γ). Using promoter constructs in luciferase assay, the region between 202 and 320 bp from the translational start site is responsible for B7‐H1 expression. Electrophoretic mobility shift assay, site‐directed mutagenesis and knockdown experiment using siRNA revealed that interferon regulatory factor‐1 (IRF‐1) is primarily responsible for the constitutive B7‐H1 expression as well as for the IFN‐γ‐mediated B7‐H1 upregulation in a human lung cancer cell line A549. Additionally, AG490, a Janus activated kinase/signal transducer and activator of transcription inhibitor, greatly abolished the responsiveness of A549 cells to IFN‐γ by reducing the IRF‐1 transcription. Our findings support a critical role of IRF‐1 in the regulation of constitutive and IFN‐γ‐induced expression of B7‐H1 in cancer cells.

Direct Inhibition of GSK3β by the Phosphorylated Cytoplasmic Domain of LRP6 in Wnt/β-Catenin Signaling

Wnt/β-catenin signaling plays a central role in development and is also involved in a diverse array of diseases. Binding of Wnts to the coreceptors Frizzled and LRP6/5 leads to phosphorylation of PPPSPxS motifs in the LRP6/5 intracellular region and the inhibition of GSK3β bound to the scaffold protein Axin. However, it remains unknown how GSK3β is specifically inhibited upon Wnt stimulation. Here, we show that overexpression of the intracellular region of LRP6 containing a Ser/Thr rich cluster and a PPPSPxS motif impairs the activity of GSK3β in cells. Synthetic peptides containing the PPPSPxS motif strongly inhibit GSK3β in vitro only when they are phosphorylated. Microinjection of these peptides into Xenopus embryos confirms that the phosphorylated PPPSPxS motif potentiates Wnt-induced second body axis formation. In addition, we show that the Ser/Thr rich cluster of LRP6 plays an important role in LRP6 binding to GSK3β. These observations demonstrate that phosphorylated LRP6/5 both recruits and directly inhibits GSK3β using two distinct portions of its cytoplasmic sequence, and suggest a novel mechanism of activation in this signaling pathway.

Natural derivatives of curcumin attenuate the Wnt/β-catenin pathway through down-regulation of the transcriptional coactivator p300

Curcumin, a component of turmeric (Curcuma longa), has been reported to suppress beta-catenin response transcription (CRT), which is aberrantly activated in colorectal cancer. However, the effects of its natural analogs (demethoxycurcumin [DMC] and bisdemethoxycurcumin [BDMC]) and metabolite (tetrahydrocurcumin [THC]) on the Wnt/beta-catenin pathway have not been investigated. Here, we show that DMC and BDMC suppressed CRT that was activated by Wnt3a conditioned-medium (Wnt3a-CM) without altering the level of intracellular beta-catenin, and inhibited the growth of various colon cancer cells, with comparable potency to curcumin. Additionally, DMC and BDMC down-regulated p300, which is a positive regulator of the Wnt/beta-catenin pathway. Notably, THC also inhibited CRT and cell proliferation, but to a much lesser degree than curcumin, DMC, or BDMC, indicating that the conjugated bonds in the central seven-carbon chain of curcuminoids are essential for the inhibition of Wnt/beta-catenin pathway and the anti-proliferative activity of curcuminoids. Thus, our findings suggest that curcumin derivatives inhibit the Wnt/beta-catenin pathway by decreasing the amount of the transcriptional coactivator p300.

Anti-asthmatic effect of marine red alga (Laurencia undulata) polyphenolic extracts in a murine model of asthma.

The aim of the present work is focused on protective effects of an edible red alga, Laurencia undulata ethanolic (EtOH) extracts (LU) containing a large amount of polyphenols against OVA-induced murine allergic airway reactions using in vivo histological and cytokine assay. Mice sensitized and challenged with ovalbumin (OVA) showed typical asthmatic reactions as follows: an increase in the number of eosinophil in bronchoalveolar lavage fluid; a marked influx of inflammatory cells into the lung around blood vessels and airways, and airway luminal narrowing; the development of airway hyperresponsiveness; the detection of TNF-alpha and Th2 cytokines, such as IL-4 and IL-5 in the bronchoalveolar lavage (BAL) fluid; and detection of allergen-specific IgE in the serum. The successive intraperitoneal administration of LU before the last airway OVA-challenge resulted in a significant inhibition of all asthmatic reactions. These results suggest that L. undulata polyphenolic extracts possess therapeutic potential for combating bronchial asthma associated with allergic diseases.

Diclofenac attenuates Wnt/β-catenin signaling in colon cancer cells by activation of NF-κB

The dysregulation of Wnt/β‐catenin signaling and subsequent upregulation of β‐catenin response transcription (CRT) occur frequently in colon cancer cells. Non‐steroidal anti‐inflammatory drugs (NSAIDs) can repress CRT in colorectal cancer, but little is known about the mechanism of action. We show that the NSAID diclofenac inhibits Wnt/β‐catenin signaling without altering the level of β‐catenin protein and reduces the expression of β‐catenin/TCF‐dependent genes. Diclofenac induced the degradation of IκBα, which increased free nuclear factor κB (NF‐κB) in cells. Also, the ectopic expression of p65, which is a component of NF‐κB, suppressed CRT. Our findings suggest that diclofenac inhibits Wnt/β‐catenin signaling via the activation of NF‐κB in colon cancer cells.

Decursin suppresses human androgen-independent PC3 prostate cancer cell proliferation by promoting the degradation of beta-catenin.

Alterations in the Wnt/β-catenin pathway are associated with the development and progression of human prostate cancer. Decursin, a pyranocoumarin isolated from the Korean Angelica gigas root, inhibits the growth of androgen-independent human prostate cancer cells, but little is known about its mechanism of action. Using a cell-based screen, we found that decursin attenuates the Wnt/β-catenin pathway. Decursin antagonized β-catenin response transcription (CRT), which was induced with Wnt3a-conditioned medium and LiCl, by promoting the degradation of β-catenin. Furthermore, decursin suppressed the expression of cyclin D1 and c-myc, which are downstream target genes of β-catenin and thus inhibited the growth of PC3 prostate cancer cells. In contrast, decursinol, in which the (CH3)2–C=CH–COO–side chain of decursin is replaced with–OH, had no effect on CRT, the level of intracellular β-catenin, or PC3 cell proliferation. Our findings suggest that decursin exerts its anticancer activity in prostate cancer cells via inhibition of the Wnt/β-catenin pathway.

Stimulation of protein kinase C-α suppresses colon cancer cell proliferation by down-regulation of β-catenin

We reported previously that protein kinase C‐α (PKC‐α) negatively regulates Wnt/β‐catenin signalling pathway. The current study explores the role of PKC‐α in the regulation of proliferation of colon cancer cells, which contain aberrant up‐regulation of intracellular β‐catenin. In colon tissue and cells, an inverse correlation was observed between the expression levels of PKC‐α and intracellular β‐catenin. Activation of PKC‐α inhibited β‐catenin response transcription by down‐regulation of intracellular β‐catenin and induced phosphorylation of the N‐terminal serine and threonine residues (Ser33/Ser37/Thr41) of β‐catenin, marking it for proteasomal degradation, in colon cancer cells. Pharmacological inhibition or depletion of PKC‐α‐abrogated PKC‐α‐mediated β‐catenin down‐regulation and phosphorylation in colon cancer cells. Notably, the Ser45 residue of β‐catenin was essential for PKC‐α‐induced β‐catenin down‐regulation in colon cancer cells. Moreover, PKC‐α activation repressed the expression of cyclin D1 and c‐myc, which are known β‐catenin target genes, and thus inhibited the growth of colon cancer cells. These findings suggest that PKC‐α negatively regulates colon cancer cell proliferation viaβ‐catenin phosphorylation/down‐regulation and may facilitate the development of new strategies to treatment of colon cancer.

Murrayafoline A attenuates the Wnt/β-catenin pathway by promoting the degradation of intracellular β-catenin proteins

Molecular lesions in Wnt/beta-catenin signaling and subsequent up-regulation of beta-catenin response transcription (CRT) occur frequently during the development of colon cancer. To identify small molecules that suppress CRT, we screened natural compounds in a cell-based assay for detection of TOPFalsh reporter activity. Murrayafoline A, a carbazole alkaloid isolated from Glycosmis stenocarpa, antagonized CRT that was stimulated by Wnt3a-conditioned medium (Wnt3a-CM) or LiCl, an inhibitor of glycogen synthase kinase-3beta (GSK-3beta), and promoted the degradation of intracellular beta-catenin without altering its N-terminal phosphorylation at the Ser33/37 residues, marking it for proteasomal degradation, or the expression of Siah-1, an E3 ubiquitin ligase. Murrayafoline A repressed the expression of cyclin D1 and c-myc, which is known beta-catenin/T cell factor (TCF)-dependent genes and thus inhibited the proliferation of various colon cancer cells. These findings indicate that murrayafoline A may be a potential chemotherapeutic agent for use in the treatment of colon cancer.

The 15-Deoxy-Δ12,14-prostaglandin J2 inhibits LPS-stimulated AKT and NF-κB activation and suppresses interleukin-6 in osteoblast-like cells MC3T3E-1

AIMS Periodontitis is a chronic inflammatory disease that results in gingival inflammation and periodontal tissue destruction and is accompanied by alveolar bone resorption and eventual tooth loss. We examined the effect of 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)) on periodontitis by inhibiting the production of interleukin-6 (IL-6). MAIN METHODS Osteoblast-like cells MC3T3E-1 were pretreated with 15d-PGJ(2) before being incubated with lipopolysaccharide (LPS), the effect of 15d-PGJ(2) on IL-6 production, expression and its regulatory mechanisms were studied by reverse transcription-polymerase chain reaction (RT-PCR), Western blot, electrophoretic mobility shift assay (EMSA), and confocal laser scanning microscopy study. KEY FINDINGS 15d-PGJ(2) inhibits LPS-stimulated IL-6 production in a concentration-dependent manner in osteoblast-like cells MC3T3E-1, without appreciable cytotoxicity. To further examine the mechanism responsible for the inhibition of IL-6 production by 15d-PGJ(2), we examined the effect of 15d-PGJ(2) on nuclear factor-kappaB (NF-kappaB) activation and the phosphorylation of protein kinase B (Akt). 15d-PGJ(2) treatment clearly reduced the DNA binding activity of NF-kappaB in LPS-stimulated osteoblast-like cells MC3T3E-1, an effect that was mediated by inhibiting the degradation of inhibitor kappaB (IkappaB) and nuclear translocation of NF-kappaB p65 subunit. In addition, 15d-PGJ(2) attenuated the LPS-mediated Akt pathway. These effects of 15d-PGJ(2) were not abrogated by the PPARgamma antagonist, GW9662, indicating that they are PPARgamma-independent actions. SIGNIFICANCE These results suggest that 15d-PGJ(2) possess a potent suppressive effect on inflammatory responses of osteoblast-like cells MC3T3E-1 via the Akt and NF-kappaB pathways independent of PPARgamma and suggest that this compound may offer some insight into the development of a new therapeutic approach to the prevention and treatment of periodontal diseases.

Expression of glucocorticoid receptor mRNAs in glucocorticoid-resistant nasal polyps

Glucocorticoids (GCs) are the most effective group of medications available to treat inflammation. Although most patients with inflammation respond to GC, a small group of patients exhibit persistent GC-resistance with prolonged inflammation. Previously, it was proposed that the GC-resistance is caused by low amount of human GC receptor (hGRα) and/or excessive presence of a GC receptor isoform, hGRβ that was generated from alternative splicing of the hGR message. We have tested this hypothesis by investigating correlation between the expression pattern of hGR mRNAs in patients with inflammatory nasal polyps and the effectiveness of GC treatment. We have performed reverse transcription PCR analysis of mRNAs coding each hGRα and hGRβ in nasal tissues. hGRα mRNA was more expressed in patients with nasal polyps than in normal subjects. However, the elevated hGRα mRNA expression was decreased after GC treatment. Compared with hGRα mRNA expression, level of hGRβ mRNA expression was very low in all groups. In patients, hGRβ mRNA was expressed at a similar level regardless of GC efficacy, indicating that there is no correlation between the GC sensitivity and the expression level of hGRβ mRNA. Thus, persistent GC-resistance is not associated with low expression of hGRa or over- expression of hGRβ.