Diffuse large B-cell lymphoma and red cell autoimmunity: clinical role and pathogenesis.

Diffuse large B-cell lymphoma (DLBCL) is the most common form of B-cell non-Hodgkin lymphoma (B-NHL) with significant morbidity and mortality despite advancements in treatment. Lymphoma and autoimmune disease both result from breakdowns in normal cell regulatory pathways, and epidemiological studies have confirmed both that B-NHL is more likely to develop in the setting of autoimmune diseases and vice versa. Red cell immunity, as evidenced by direct antiglobulin test (DAT) positivity, has been linked to DLBCL and more recently the pathogenic causes of this association have begun to be better understood using molecular techniques. This project aimed to explore the relationship between red cell autoimmunity and DLBCL. DAT positivity was more common in DLBCL as compared to healthy controls (20.4% vs 3.7%, p=0.0005). Univariate analysis found a non-significant trend towards poorer overall survival in the DAT positive (DAT+) compared to the DAT negative (DAT-) groups (p=0.087). High throughput sequencing was used to compare mutations in DLBCL from DAT+ and DAT- patients. The most frequently mutated genes in 15 patient samples were KMT2D (n=13), MYOM2 (n=9), EP300 (n=8), SPEN (n=7), and ADAMTSL3 (n=7), which were mutated in both DAT+ and DAT- groups. BIRC3 (n=3), FOXO1 (n=3) and CARD11 (n=2) were found to be mutated only in samples from the DAT+ group. These gene mutations may be involved in disease development and progression, and potentially represent targets for future therapy. The immunoglobulin genotype IGHV4-34 is seen more frequently in DLBCL clones than in normal B cells and has intrinsic autoreactivity to self-antigens on red cells, which is largely mediated by two motifs within the first framework region (FR1); Q6W7 and A24V25Y.26 These motifs form a hydrophobic patch which determines red cell antigen binding and are frequently mutated away from self-reactivity in normal B cells. If this does not occur this may provide constant B cell receptor signalling which encourages lymphoma development, a theory known as antigen driven lymphomagenesis. As with previous studies, IGHV4-34 was over-represented (15.6%) in our DLBCL cohort. Furthermore, of 6 IGHV4-34-expressing DLBCL samples five had unmutated hydrophobic patch mutations providing further evidence for antigen-driven lymphomagenesis. Mutation analysis of these five samples demonstrated high frequency of mutations in several genes, including CREBBP and NCOR2. Further research could explore if mutations in CREBBP and NCOR2 work in conjunction with the preserved QW and AVY motifs to promote lymphomagenesis in IGHV4-34-expressing B cells, and if so, could guide future targeted therapy.

Plasma cells arise from differentiation of clonal lymphocytes and secrete IgM in Waldenström macroglobulinemia.

Waldenström macroglobulinemia (WM) is characterized by bone marrow infiltration with malignant lymphoplasmacytic cells (LPCs), a smaller population of plasma cells (PCs), and hypersecretion of IgM monoclonal protein. Here, we show that CD45low, CD38+, and CD138+ PCs and CD45high, CD38-, CD138-, CD19+, and CD20+ LPCs carry a heterozygous L265P mutation in the Toll-like receptor signaling adaptor MYD88. Both PCs and LPCs express the same auto-reactive IgHV sequences, suggesting a similar clonal origin and role for auto-antigens in WM cell survival. PCs are primarily responsible for IgM production even without substantial cell proliferation. When cultured in isolation, LPCs give rise to more differentiated PCs and secrete less IgM. Our analyses suggest that malignant PCs arise from the clonal LPC population, and are primarily responsible for IgM secretion in WM. Targeting malignant PCs may have therapeutic benefits in the treatment of WM and improve the duration of response and potentially, survival.

Pyrrolidine dithiocarbamate reverses Bcl-xL-mediated apoptotic resistance to doxorubicin by inducing paraptosis.

Elevated Bcl-xL expression in cancer cells contributes to doxorubicin (DOX) resistance, leading to failure in chemotherapy. In addition, the clinical use of high-dose doxorubicin (DOX) in cancer therapy has been limited by issues with cardiotoxicity and hepatotoxicity. Here, we show that co-treatment with pyrrolidine dithiocarbamate (PDTC) attenuates DOX-induced apoptosis in Chang-L liver cells and human hepatocytes, but overcomes DOX resistance in Bcl-xL-overexpressing Chang-L cells and several hepatocellular carcinoma (HCC) cell lines with high Bcl-xL expression. Additionally, combined treatment with DOX and PDTC markedly retarded tumor growth in a Huh-7 HCC cell xenograft tumor model, compared to either mono-treatment. These results suggest that DOX/PDTC co-treatment may provide a safe and effective therapeutic strategy against malignant hepatoma cells with Bcl-xL-mediated apoptotic defects. We also found that induction of paraptosis, a cell death mode that is accompanied by dilation of the endoplasmic reticulum and mitochondria, is involved in this anti-cancer effect of DOX/PDTC. The intracellular glutathione levels were reduced in Bcl-xL-overexpressing Chang-L cells treated with DOX/PDTC, and DOX/PDTC-induced paraptosis was effectively blocked by pretreatment with thiol-antioxidants, but not by non-thiol antioxidants. Collectively, our results suggest that disruption of thiol homeostasis may critically contribute to DOX/PDTC-induced paraptosis in Bcl-xL-overexpressing cells.

α-Actinin 4 potentiates nuclear factor κ-light-chain-enhancer of activated B-cell (NF-κB) activity in podocytes independent of its cytoplasmic actin binding function.

Glomerular podocytes are highly specialized terminally differentiated cells that act as a filtration barrier in the kidney. Mutations in the actin-binding protein, α-actinin 4 (ACTN4), are linked to focal segmental glomerulosclerosis (FSGS), a chronic kidney disease characterized by proteinuria. Aberrant activation of NF-κB pathway in podocytes is implicated in glomerular diseases including proteinuria. We demonstrate here that stable knockdown of ACTN4 in podocytes significantly reduces TNFα-mediated induction of NF-κB target genes, including IL-1ß and NPHS1, and activation of an NF-κB-driven reporter without interfering with p65 nuclear translocation. Overexpression of ACTN4 and an actin binding-defective variant increases the reporter activity. In contrast, an FSGS-linked ACTN4 mutant, K255E, which has increased actin binding activity and is predominantly cytoplasmic, fails to potentiate NF-κB activity. Mechanistically, IκBα blocks the association of ACTN4 and p65 in the cytosol. In response to TNFα, both NF-κB subunits p65 and p50 translocate to the nucleus, where they bind and recruit ACTN4 to their targeted promoters, IL-1ß and IL-8. Taken together, our data identify ACTN4 as a novel coactivator for NF-κB transcription factors in podocytes. Importantly, this nuclear function of ACTN4 is independent of its actin binding activity in the cytoplasm.

Control of antioxidative response by the tumor suppressor protein PML through regulating Nrf2 activity.

Oxidative stress is a consequence of an imbalance between reactive oxygen species (ROS) production and the ability of the cytoprotective system to detoxify the reactive intermediates. The tumor suppressor promyelocytic leukemia protein (PML) functions as a stress sensor. Loss of PML results in impaired mitochondrial complex II activity, increased ROS, and subsequent activation of nuclear factor erythroid 2-related factor 2 (Nrf2) antioxidative pathway. We also demonstrate that sulforaphane (SFN), an antioxidant, regulates Nrf2 activity by controlling abundance and subcellular distribution of PML and that PML is essential for SFN-mediated ROS increase, Nrf2 activation, antiproliferation, antimigration, and antiangiogenesis. Taking the results together, we have uncovered a novel antioxidative mechanism by which PML regulates cellular oxidant homeostasis by controlling complex II integrity and Nrf2 activity and identified PML as an indispensable mediator of SFN activity.

Monensin, a polyether ionophore antibiotic, overcomes TRAIL resistance in glioma cells via endoplasmic reticulum stress, DR5 upregulation and c-FLIP downregulation.

Tumor necrosis factor-related apoptosis-induced ligand (TRAIL) is preferentially cytotoxic to cancer cells over normal cells. However, many cancer cells, including malignant glioma cells, tend to be resistant to TRAIL. Monensin (a polyether ionophore antibiotic that is widely used in veterinary medicine) and salinomycin (a compound that is structurally related to monensin and shows cancer stem cell-inhibiting activity) are currently recognized as anticancer drug candidates. In this study, we show that monensin effectively sensitizes various glioma cells, but not normal astrocytes, to TRAIL-mediated apoptosis; this occurs at least partly via monensin-induced endoplasmic reticulum (ER) stress, CHOP-mediated DR5 upregulation and proteasome-mediated downregulation of c-FLIP. Interestingly, other polyether antibiotics, such as salinomycin, nigericin, narasin and lasalocid A, also stimulated TRAIL-mediated apoptosis in glioma cells via ER stress, CHOP-mediated DR5 upregulation and c-FLIP downregulation. Taken together, these results suggest that combined treatment of glioma cells with TRAIL and polyether ionophore antibiotics may offer an effective therapeutic strategy.

Rottlerin induces apoptosis of HT29 colon carcinoma cells through NAG-1 upregulation via an ERK and p38 MAPK-dependent and PKC δ-independent mechanism.

Rottlerin, a selective inhibitor of novel isoforms of protein kinase C δ (PKC δ), has been shown to exert multiple effects on cancer cells, including inhibition of cell proliferation and migration. However, the molecular mechanisms responsible for these effects are not fully understood. We found that rottlerin dramatically induced non-steroidal anti-inflammatory drug activated gene-1 (NAG-1) expression in both p53 wild-type and p53-null cancer cell lines, suggesting that NAG-1 upregulation is a common response to rottlerin that occurs independently of p53 in multiple cell lines. Although rottlerin is known to inhibit PKC δ, PKC δ siRNA and overexpression of dominant-negative (DN)-PKC δ did not affect rottlerin-mediated induction of NAG-1. These results suggest that rottlerin induces NAG-1 upregulation via a PKC δ-independent pathway. We also observed that CHOP protein levels were significantly increased by rottlerin, but CHOP siRNA did not affect rottlerin-induced NAG-1 expression. In addition, we demonstrated the involvement of the mitogen-activated protein kinase (MAP kinase) signal transduction pathway in rottlerin-induced NAG-1 expression. Inhibitors of MEK (PD98059) and p38 MAP kinase (SB203580) prevented rottlerin-induced NAG-1 expression. Furthermore, we found that down-regulation of NAG-1 attenuated rottlerin-induced apoptosis. Collectively, the results of this study demonstrate, for the first time, that upregulation of NAG-1 contributes to rottlerin-induced apoptosis in cancer cells.

Mitogen-activated protein kinase extracellular signal-regulated kinase 2 phosphorylates and promotes Pin1 protein-dependent promyelocytic leukemia protein turnover.

The promyelocytic leukemia (PML) protein is a tumor suppressor that has an important role in several cellular processes, including apoptosis, viral infection, DNA damage repair, cell cycle regulation, and senescence. PML is an essential component of sub-nuclear structures called PML nuclear bodies (NBs). Our laboratory has previously demonstrated that the peptidyl-prolyl cis-trans isomerase, Pin1, binds and targets PML for degradation in a phosphorylation-dependent manner. To further elucidate the mechanisms underlying Pin1-mediated PML degradation, we aimed to identify one or more factors that promote PML phosphorylation. Here we show that treatment with U0126, an inhibitor of the ERK2 upstream kinases MEK1/2, leads to an increase in PML protein accumulation and an inhibition of the interaction between Pin1 and PML in MDA-MB-231 breast cancer cells. Consistent with this observation, phosphorylated ERK2 partially co-localized with PML NBs. Although U0126 up-regulated exogenous wild-type PML levels, it did not have an effect on the steady-state level of a mutant form of PML that is defective in binding Pin1. In addition, exogenous wild-type, but not Pin1 binding-defective PML protein expression levels were decreased by overexpression of ERK2. In contrast, knockdown of ERK2 by siRNA resulted in an increase in PML protein levels and an increase in the formation of PML NBs. Using phospho-specific antibodies, we identified Ser-403 and Ser-505 as the ERK2 targets that promote Pin1-mediated PML degradation. Finally, we demonstrated that EGF induced activation of ERK and interaction between PML and phosphorylated ERK resulting in a decrease in PML protein levels. Taken together, our results support a model in which Pin1 promotes PML degradation in an ERK2-dependent manner.

Curcumin inhibits phorbol myristate acetate (PMA)-induced MCP-1 expression by inhibiting ERK and NF-kappaB transcriptional activity.

Monocyte chemoattractant protein-1 (MCP-1) is a potent mediator of macrophage migration and therefore, plays an essential role in early events of inflammation. In the present study, we show the protein kinase C activator, phorbol myristate acetate (PMA), potently induced mRNA expression and secretion of the C-C chemokine MCP-1 in U937 cells. We found that curcumin, a natural biologically active compound extracted from rhizomes of Curcuma species, significantly inhibited the PMA-induced increase in MCP-1 expression and secretion. These effects of curcumin are dose dependent and correlate with the suppression of MCP-1 mRNA expression levels. Curcumin inhibited PMA-mediated activation of extracellular signal-regulated kinase (ERK) and NF-kappaB transcriptional activity. Therefore, one possible anti-inflammatory mechanism of curcumin may be to inhibit the secretions of inflammatory MCP-1 chemokine.

Rottlerin induces heme oxygenase-1 (HO-1) up-regulation through reactive oxygen species (ROS) dependent and PKC delta-independent pathway in human colon cancer HT29 cells.

Heme oxygenase-1 (HO-1) is a cytoprotective enzyme activated by its substrate heme and diverse stimuli. The induction of HO-1 gene expression is one of the important events in cellular response to pro-oxidative and pro-inflammatory insults. In this study, the effect of rottlerin, a putative PKC delta inhibitor, on HO-1 expression in HT29 human colon cancer cells was investigated. Rottlerin-induced HO-1 at both protein and mRNA levels in a dose- and time-dependent manner. Rottlerin-mediated HO-1 induction was abrogated in the presence of N-acetylcysteine (NAC) or glutathione (GSH). Rottlerin induced nuclear translocation of NF-E2-related factor 2 (Nrf2) and increased antioxidant response element (ARE)-driven transcriptional activity. Additionally, rottlerin activated p38 mitogen-activated protein kinase (MAPK) and ERK. The pharmacological inhibition of ERK and p38 MAPK inhibited rottlerin-induced HO-1 up-regulation. However, suppression of protein kinase C delta (PKC delta) expression by siRNA or overexpression of WT-PKC delta did not abrogate the rottlerin-mediated induction of HO-1. These results suggest that rottlerin induces up-regulation of HO-1 via PKC delta-independent pathway. Taken together, the present study identified rottlerin as a novel inducer of HO-1 expression and identified the mechanisms involved in this process.

Superoxide anion and proteasomal dysfunction contribute to curcumin-induced paraptosis of malignant breast cancer cells.

Curcumin is considered a pharmacologically safe agent that may be useful in cancer chemoprevention and therapy. Here, we show for the first time that curcumin effectively induces paraptosis in malignant breast cancer cell lines, including MDA-MB-435S, MDA-MB-231, and Hs578T cells, by promoting vacuolation that results from swelling and fusion of mitochondria and/or the endoplasmic reticulum (ER). Inhibition of protein synthesis by cycloheximide blocked curcumin-induced vacuolation and subsequent cell death, indicating that protein synthesis is required for this process. The levels of AIP-1/Alix protein, a known inhibitor protein of paraptosis, were progressively downregulated in curcumin-treated malignant breast cancer cells, and AIP-1/Alix overexpression attenuated curcumin-induced death in these cells. ERK2 and JNK activation were positively associated with curcumin-induced cell death. Mitochondrial superoxide was shown to act as a critical early signal in curcumin-induced paraptosis, whereas proteasomal dysfunction was mainly responsible for the paraptotic changes associated with ER dilation. Notably, curcumin-induced paraptotic events were not observed in normal breast cells, including mammary epithelial cells and MCF-10A cells. Taken together, our findings on curcumin-induced paraptosis may provide novel insights into the mechanisms underlying the selective anti-cancer effects of curcumin against malignant cancer cells.

Interleukin-1beta promotes the expression of monocyte chemoattractant protein-1 in human aorta smooth muscle cells via multiple signaling pathways.

Monocyte chemoattractant protein-1 (MCP1) plays a key role in monocyte/macrophage infiltration to the sub-endothelial space of the blood vessel wall, which is a critical initial step in atherosclerosis. In this study, we examined the intracellular signaling pathway of IL-1beta-induced MCP1 expression using various chemical inhibitors. The pretreatment of a phosphatidylcholine (PC)-specific PLC (PC-PLC) inhibitor (D609), PKC inhibitors, or an NF-kapaB inhibitor completely suppressed the IL-1beta-induced MCP1 expression through blocking NF-gammaB translocation to the nucleus. Pretreatment with inhibitors of tyrosine kinase or PLD partially suppressed MCP1 expression and failed to block nuclear NF-kappaB translocation. These results suggest that IL-1beta induces MCP1 expression through activation of NF-kappaB via the PC-PLC/PKC signaling pathway.

Rottlerin induces apoptosis via death receptor 5 (DR5) upregulation through CHOP-dependent and PKC delta-independent mechanism in human malignant tumor cells.

Rottlerin has been shown to induce antiproliferation and apoptosis of human cancer cell lines. In this study, we demonstrate a novel mechanism of rottlerin-induced apoptosis via death receptor (DR) 5 upregulation. We found that treatment with rottlerin significantly induces DR5 expression both at its messenger RNA and protein levels. Downregulation of DR5 expression with small-interfering RNA (siRNA) efficiently attenuated rottlerin-induced apoptosis, showing that the critical role of DR5 in this cell death. Rottlerin-induced DR5 upregulation was accompanied by CCAAT/enhancer-binding protein-homologous protein (CHOP) protein expression and rottlerin-induced increase of DR5 promoter activity was diminished by mutation of a CHOP-binding site of DR5 promoter. Although rottlerin is known to be as an inhibitor of novel isoforms of protein kinase C (PKC), specifically PKC delta, not only suppression of PKC delta expression by siRNA but also overexpression of wild-type-PKC delta or dominant-negative-PKC delta did not affect the rottlerin-mediated induction of DR5 in our study. These results suggest that rottlerin induces upregulation of DR5 via PKC delta-independent pathway. Furthermore, subtoxic dose of rottlerin sensitizes human cancer cells, but not normal cells, to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis. Thus, DR5-mediated apoptosis, which is induced by rottlerin alone or by the combined treatment with rottlerin and TRAIL, may offer a new therapeutic strategy against cancer.

Quercetin sensitizes human hepatoma cells to TRAIL-induced apoptosis via Sp1-mediated DR5 up-regulation and proteasome-mediated c-FLIPS down-regulation.

This study demonstrates that combined treatment with subtoxic doses of quercetin (3',3',4',5,7-pentahydroxyflavone), a flavonoid found in many fruits and vegetables, plus tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) induces rapid apoptosis in TRAIL-resistant hepatocellular carcinoma (HCC) cells. Effective induction of apoptosis by the combined treatment with quercetin and TRAIL was not blocked by overexpression of Bcl-xL, which is known to confer resistance to various chemotherapeutic agents. These results suggest that this combined treatment may provide an attractive strategy for treating resistant HCCs. While the proteolytic processing of procaspase-3 by TRAIL was partially blocked in various HCC cells treated with TRAIL alone, co-treatment with quercetin efficiently recovered TRAIL-induced caspase activation. We found that quercetin treatment of HCC cells significantly up-regulated the mRNA and protein levels of DR5, a death receptor of TRAIL, in a transcription factor Sp1-dependent manner. Furthermore, treatment with quercetin significantly decreased the protein levels of c-FLIP, an inhibitor of caspase-8, through proteasome-mediated degradation. Finally, administration of small interfering RNA against DR5 or overexpression of c-FLIPS, but not c-FLIPL, significantly attenuated quercetin-stimulated TRAIL-induced apoptosis. Collectively, these findings show that quercetin recovers TRAIL sensitivity in various HCC cells via up-regulation of DR5 and down-regulation of c-FLIPS.

Rottlerin induces pro-apoptotic endoplasmic reticulum stress through the protein kinase C-delta-independent pathway in human colon cancer cells.

Rottlerin, a compound reported to be a PKC delta-selective inhibitor, has been shown to induce growth arrest or apoptosis of human cancer cell lines. In our study, rottlerin dose-dependently induced apoptotic cell death in colon carcinoma cells. Treatment of HT29 human colon carcinoma cells with rottlerin was found to induce a number of signature ER stress markers; phosphorylation of eukaryotic initiation factor-2alpha (eIF-2alpha), ER stress-specific XBP1 splicing, and up-regulation of glucose-regulated protein (GRP)-78 and CCAAT/enhancer-binding protein-homologous protein (CHOP). However, suppression of PKC delta expression by siRNA or overexpression of WT-PKC delta and DN-PKC delta did not abrogate the rottlerin-mediated induction of CHOP. These results suggest that rottlerin induces up-regulation of CHOP via PKC delta-independent pathway. Furthermore, down-regulation of CHOP expression using CHOP siRNA attenuated rottlerin-induced apoptosis. Taken together, the present study thus provides strong evidence to support an important role of ER stress response in mediating the rottlerin-induced apoptosis.

Resveratrol induces pro-apoptotic endoplasmic reticulum stress in human colon cancer cells.

Resveratrol (3,4',5 tri-hydroxystilbene), a naturally occurring polyphenolic compound highly enriched in grapes and red wine, has been shown to induce anti-proliferation and apoptosis of human cancer cell lines. Resveratrol-induced dose-dependent apoptotic cell death in colon carcinoma cells, was measured by FACS analysis. Treatment of HT29 human colon carcinoma cells with resveratrol was found to induce a number of signature ER stress markers; phosphorylation of eukaryotic initiation factor-2alpha (eIF-2alpha), ER stress-specific XBP1 splicing and CCAAT/enhancer-binding protein-homologous protein (CHOP). In addition, resveratrol induced up-regulation of glucose-regulated protein (GRP)-78, suggesting the induction of ER stress. Furthermore, the inhibition of caspase-4 activity by z-LEVD-fmk significantly reduced resveratrol-induced apoptosis. Taken together, the present study therefore provides strong evidence to support an important role of ER stress response in mediating the resveratrol-induced apoptosis.

Expression of cyclin D3 through Sp1 sites by histone deacetylase inhibitors is mediated with protein kinase C-delta (PKC-delta) signal pathway.

The histone deacetylase (HDAC) inhibitors are an exciting new class of drugs that are targeted as anti-cancer agents. These compounds can induce growth arrest, apoptosis, and/or terminal differentiation in a variety of cancers. The inhibition of HDACs shifts toward hyper-acetylation, thereby driving transcriptional activation. In present study, HDAC inhibitor apicidin was used to elucidate the effect on expression of cell cycle related proteins and the molecular mechanism for transcriptional regulation of cyclin D3 in response to HDAC inhibitors in human colon cancer cells. We found that apicidin increases the transcriptional activity of cyclin D3 gene, which results in accumulation of cyclin D3 mRNA and protein. Apicidin-induced cyclin D3 expression is mediated by Sp1 sites within the cyclin D3 promoter. Apicidin-mediated cyclin D3 expression is attenuated by rottlerin, a specific protein kinase C-delta (PKC-delta) inhibitor, but not mitogen-activated protein kinases (MAPKs) inhibitors. Furthermore, suppression of PKC-delta expression by transfection with its siRNA prominently attenuated apicidin-induced cyclin D3 expression. These results indicate that the cyclin D3 induction caused by apicidin was associated with PKC-delta signaling pathway not MAPKs signaling pathways. Taken together, these results suggest that the activation of cyclin D3 transcription by HDAC inhibitor apicidin was mediated through Sp1 sites and pointed to the possible participation of PKC-delta.

ESE-3 transcription factor is involved in the expression of death receptor (DR)-5 through putative Ets sites.

The death receptor 5 (DR-5), a receptor for tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), is critical for TRAIL-mediated apoptosis in various tumor cells. The ESE-3, a member of Ets transcription factors, regulates the expression of a variety of cellular genes by binding to purine-rich GGAA/T core sequence in cooperation with other transcription factors and co-factors. In this study, we demonstrate for the first time that ESE-3 regulates DR-5 expression through Ets binding sequences on the DR-5 promoter. Using a combination of the electrophoretic mobility shift assay and the luciferase reporter assay, we identified putative Ets sites responsible for ESE-3 transcriptional activity on the DR-5 promoter. In addition, we show the possible involvement of co-factors CBP and p300 in ESE-3-mediated DR-5 up-regulation.

Differential inhibitory effects of baicalein and baicalin on LPS-induced cyclooxygenase-2 expression through inhibition of C/EBPbeta DNA-binding activity.

To evaluate the possible mechanisms responsible for the anti-inflammatory effects of baicalein or baicalin, lipopolysaccharide (LPS)-induced inflammatory responses in cultured Raw 264.7 cells were studied. In the present study, baicalein and baicalin, a flavonoid present in the root of Scutellaria baicalensis Georgi, were examined for their effects on LPS-induced cyclooxygenase-2 (COX-2) gene expression in Raw 264.7 macrophages. Baicalein, but not baicalin, inhibited COX-2 gene expression in LPS-induced Raw 264.7 cells. However, both polyphenolic compounds inhibited LPS-induced inducible nitric oxide synthase (iNOS) protein expression, iNOS mRNA expression, and NO production in a dose-dependent manner. To investigate the mechanism by which baicalein inhibits COX-2 gene expression, we examined activation of mitogen-activated protein kinases (MAPKs) in Raw 264.7 cells. We did not observe any significant change in the phosphorylation of MAPKs between baicalein- and baicalin-treated cells. Baicalein and baicalin had no effect on LPS-induced nuclear factor-kappaB (NF-kappaB) and cAMP response element binding protein (CREB) DNA binding activity. Baicalein, but not baicalin, significantly inhibited the DNA binding activity of CCAAT/enhancer binding protein beta (C/EBPbeta) These results indicated that differential effects of baicalein and baicalin on COX-2 gene expression in LPS-induced Raw 264.7 cells were mediated through inhibition of C/EBPbeta DNA binding activity. Taken together, these results suggest that baicalein acts to inhibit inflammation through inhibition of COX-2 gene expression through blockade of C/EBPbeta DNA binding activity.