Human Monocytic Leukemia U937 Cells Research Articles

Chidamide inhibits t(8;21) AML cell proliferation and AMK1/ETO and C-KIT expression by inhibiting ERK1/2 signaling pathway.

Backgroundt(8;21) acute myeloid leukemia (AML) is a highly heterogenous hematological malignancy. Histone deacetylases inhibitors (HDACi) are a group of small-molecule compounds with extensive anti-tumor activity. Chidamide (CS055) is a selective HDACi independently developed by China. We aimed to investigate its anti-tumor activity and mechanism in t(8;21) AML cells.MethodsHuman AML SKNO-1 cells were transfected with AML1/ETO-siRNA to obtain SKNO-1-si-A/E cells. Human acute monocytic leukemia U937 cells were transfected with AML1/ETO fusion gene to obtain U937-A/E cells. AML1/ETO-positive (Kasumi-1, U937-A/E and SKNO-1) and AML1/ETO-negative AML cells (HL-60, U937, SKNO-1-siA/E) were treated with chidamide (0.125, 0.25 and 0.5 µM). Cell proliferation was evaluated by CCK-8 assay. Cell apoptosis and cell cycle was detected by flow cytometry. Microarray profiling of SKNO-1 cells was performed. The level of histone 3 acetylation and ERK1/2 phosphorylation was determined by Western blot. AML1/ETO and C-KIT mRNA expression was detected by real time quantitative PCR (RT-qPCR). Kasumi-1 and SKNO-1 cells were treated with U0126, a special inhibitor of ERK1/2, and cell proliferation and ERK1/2 phosphorylation level was examined.ResultsChidamide inhibited the proliferation, induced cell cycle arrest, and stimulated cell apoptosis of AML1/ETO-positive AML cells. Microarray profiling showed that 13 differentially expressed genes were involved both in the “ERK1/2” pathway and “apoptosis” functions. Chidamide inhibited histone 3 acetylation and ERK1/2 phosphorylation in AML1/ETO-positive AML cells. U0126 inhibited the proliferation of AML1/ETO-positive AML cells via regulating the ERK1/2 pathway.ConclusionsOur results suggested that chidamide inhibits t(8;21) AML cell proliferation and AMK1/ETO and C-KIT expression by inhibiting ERK1/2 signaling pathway.

Low-density lipoprotein as an opsonin promoting the phagocytosis of Pseudomonas aeruginosa by U937 cells.

Low-density lipoprotein (LDL) was recently reported to be an opsonin, enhancing the phagocytosis of group A Streptococcus (GAS) by human monocytic leukemia U937 cells due to the binding of LDL to some GAS strains. We postulated that LDL might also promote the opsonophagocytosis of Pseudomonas aeruginosa by U937 cells since this bacterium interacts with LDL. In this study, P. aeruginosa (CMCC10104), U937 cells, and human LDL were used in phagocytosis assays to test our hypothesis. Escherichia coli strain BL21, which does not interact with LDL, was used as a negative control. Colony counting and fluorescence microscopy were used to determine the bacterial quantity in the opsonophagocytosis assays. After incubation of U937 cells and P. aeruginosa with LDL (100 µg/ml) for 15 and 30 min, phagocytosis was observed to be increased by 22.71% and 32.90%, respectively, compared to that seen in the LDL-free group. However, LDL did not increase the phagocytosis of E. coli by U937 cells. In addition, we identified CD36 as a major opsonin receptor on U937 cells, since an anti-CD36 monoclonal antibody, but not an anti-CD4 monoclonal antibody, almost completely abolished the opsonophagocytosis of P. aeruginosa by U937 cells.

Resveratrol strongly enhances the retinoic acid-induced superoxide generating activity via up-regulation of gp91-phox gene expression in U937 cells

The membrane bound cytochrome b558 composed of gp91-phox and p22-phox proteins, and cytosolic proteins p40-, p47-and p67-phox are important components of superoxide (O2−)-generating system in phagocytes. Here, we describe that resveratrol, a pleiotropic phytochemical belonging to the stilbenoids, dramatically activates the O2−-generating system during retinoic acid (RA)-induced differentiation of human monoblastic leukemia U937 cells to macrophage-like cells. When U937 cells were cultured in the presence of RA and resveratrol, the O2−-generating activity increased more than 5-fold compared with that in the absence of the latter. Semiquantitative RT-PCR showed that co-treatment with RA and resveratrol strongly enhanced transcription of the gp91-phox compared with those of the RA-treatment only. On the other hand, immunoblot analysis revealed that co-treatment with RA and resveratrol caused remarkable accumulation of protein levels of gp91-phox (to 4-fold), p22-phox (to 5-fold) and p47-phox (to 4-fold) compared with those of the RA-treatment alone. In addition, ChIP assay suggested that resveratrol participates in enhancing the gene expression of gp91-phox via promoting acetylation of Lys-9 residues and Lys-14 residues of histone H3 within chromatin around the promoter regions of the gene. These results suggested that resveratrol strongly enhances the RA-induced O2−-generating activity via up-regulation of gp91-phox gene expression in U937 cells.

Antioxidation and antiproliferation of ethanol extracts from edible mushrooms against U937 human monocytic leukemia cells

Antioxidation and antiproliferation of ethanol extracts from edible mushrooms against U937 human monocytic leukemia cells

Momilactone B induces apoptosis and G1 arrest of the cell cycle in human monocytic leukemia U937 cells through downregulation of pRB phosphorylation and induction of the cyclin-dependent kinase inhibitor p21Waf1/Cip1

Momilactone B, a terpenoid phytoalexin present in rice bran, has been shown to exhibit several biological activities. The present study was conducted using cultured human leukemia U937 cells to elucidate the possible mechanisms by which momilactone B exerts its anticancer activity, which to date has remained poorly understood. Momilactone B treatment of U937 cells resulted in a dose-dependent inhibition of cell growth and induced apoptotic cell death as detected by chromatin condensation, DNA fragmentation, the cleavage of poly(ADP-ribose) polymerase and Annexin V-FITC staining. Flow cytometric analysis revealed that momilactone B resulted in G1 arrest in cell cycle progression, which was associated with the dephosphorylation of retinoblastoma protein (pRB) and enhanced binding of pRB with the E2F transcription factor family proteins. Treatment with momilactone B also increased the expression of cyclin-dependent kinase (Cdk) inhibitor p21Waf1/Cip1 in a p53-independent manner, without any noticeable changes in G1 cyclins and cyclin-dependent kinases (Cdks), except a slight decrease in cyclin E. Moreover, in vitro kinase assay indicated that momilactone B significantly decreased Cdk4- and Cdk6-associated kinase activities through a notably increased binding of p21 to Cdk4 and Cdk6. Our results demonstrated that momilactone B caused G1 cell cycle arrest and apoptosis in U937 cells through the induction of p21 expression, inhibition of Cdk/cyclin-associated kinase activities, and reduced phosphorylation of pRB, which may be related to anticancer activity.

Cytotoxicity and Apoptosis-Inducing Effect of Soybean Broth Cultured with Microorganisms Used in the Production of Fermented Soybean Foods on Human Monoblastic Leukemia U937 Cells

Cytotoxicity and Apoptosis-Inducing Effect of Soybean Broth Cultured with Microorganisms Used in the Production of Fermented Soybean Foods on Human Monoblastic Leukemia U937 Cells

Effects of RNA interference targeting HOXA9 on the proliferation and apoptosis of human acute monocytic leukemia U937 cells

Objective To investigate the effects of small interference RNA (siRNA) targeting HOXA9 on the proliferation and apoptosis of human acute monocytic leukemia U937 cell line.Methods Effective and specific siRNA oligo targeting HOXA9 was designed and compounded.It was transfected transiently into U937 cells by cationic liposome.The cells was divided into three groups:experimental group(siRNA targeting HOXA9 was transfected by liposome),negative control group (negative siRNA was transfected by liposome) and cell control group (add equal cells and medium).The expression of HOXA9 mRNA and protein were detected by reverse transcription PCR and Western blot.The cell proliferation was assessed by MTT.The apoptosis of each group were measured by Annexin V-FITC.Results Aftcr transfected by siRNA targeting HOXA9,the relative mRNA expression levels of HOXA9 in the experimental group,negative control group and cell control group were (22.980±0.548) ％,(82.371±1.517) ％ and (84.637±2.252) ％,respectively (P ＜ 0.05),and the relative protein expression levels were (50.377±2.773).％,(105.500±3.900) ％ and (111.392±3.905) ％,respectively (P ＜ 0.05).The inhibitory rates of cell proliferation and the apoptosis rates of the experimental group were significantly increased.The inhibitory rates of cell proliferation of 24 h,48 h and 72 h were (41.909±4.333) ％,(54.470±3.756) ％ and (65.835±1.024) ％,respectively,and the apoatosis rate was (26.800±2.081) ％.Compared with 2 controls,the experimental group differences had statistically significance (P ＜ 0.05).Conclusion siRNA targeting HOXA9 can effectively silence HOXA9 gene expression in U937 cell,suppress cell proliferation and induce cell apoptosis obviously,which providing experimental basis for clinical lenkemia therapy by targeting HOXA9 gene. Key words: Genes, Homeobox A9; Leukemia; RNA interference; U937 cells

7,8-dihydroxyflavone induces G1 arrest of the cell cycle in U937 human monocytic leukemia cells via induction of the Cdk inhibitor p27 and downregulation of pRB phosphorylation

We investigated the mechanisms of the anti-proliferative action of 7,8-dihydroxyflavone (7,8-DHF), a member of the flavonoid family, in U937 human monocytic leukemia cells. We found that 7,8-DHF time-dependently inhibited the growth of U937 cells, arresting them in the G1 phase of their cell cycle and inducing apoptosis. 7,8-DHF-induced G1 arrest was correlated with downregulation of cyclin E, with a concomitant upregulation of cyclin-dependent kinase (Cdk) inhibitors including p27, and association of p27 with Cdk2 was markedly induced in 7,8-DHF-treated cells. We also observed that downregulation of the phosphorylation of retinoblastoma protein (pRB) by this flavonoid was associated with enhanced binding of pRB and the transcription factor E2F-1. Overall, our results demonstrate a combined mechanism for the anticancer effects of 7,8-DHF that involves the inhibition of pRB phosphorylation and induction of p27 as targets for 7,8-DHF.

Mechanism of Hericium erinaceus (Yamabushitake) mushroom-induced apoptosis of U937 human monocytic leukemia cells

Phytochemicals in some foods are a potential source of bioactive safe compounds for cancer chemoprevention and suppression of tumor initiation, promotion, and metastasis. In the present study, we evaluated hot water (HWE), microwaved 50% ethanol (MWE), acidic (ACE), and alkaline (AKE) extracts of the fruitbody (sporocarp) of Hericium erinaceus (Yamabushitake, Lion's Mane) mushrooms for their ability to induce apoptosis (programmed cell death) in U937 human monocytic leukemia cells. Cell culture, cell viability, cytotoxicity, flow cytometry, chromosomal DNA integrity, mitochondrial membrane potential, expression of pro- and anti-apoptotic proteins, and activation and inhibition of caspase assays were carried out to help define the mechanism of observed apoptosis. The aqueous and aqueous/ethanolic extracts were active in all assays, whereas the acidic and alkaline extracts with the similar proximate compositions were both inactive. The results of the bioassays with the active extracts are consistent with an apoptosis mechanism governing suppression of the cell proliferation pathway that involves activation of mitochondria-mediated caspase-3 and caspase-9 but not caspase-8. Proximate analysis of the freeze-dried mushroom powder showed that it contains high amounts of proteins, carbohydrates, and minerals. The results indicate that H. erinaceus mushrooms may have therapeutic potential against human leukemia.

Liver Fibrosis In Myeloid Leukemia of Down Syndrome

AbstractAbstract 874 Background.Fibrosis is a common complication of leukemia with a megakaryoblastic blast phenotype. Children with Down syndrome (DS) have an increased risk for two hematological disorders with a predominantly megakaryoblastic phenotype. First, approximately 10% of newborns with DS develop Transient Leukemia (TL; also termed Transient Myeloproliferative disorder, TMD), which is self-resolving in the majority but associated with life-threatening complications in approximately 15% of cases. Liver fibrosis and failure are predominant causes of fatal outcomes in these infants. Second, children with DS develop acute myeloid leukemia, predominantly with a megakaryoblastic phenotype, approximately 150-times more often than the general pediatric population during the first 4 years of life. Somatic mutations of GATA1 are specific for TL/TMD and myeloid leukemia of DS. We found significant liver fibrosis in NOD/SCID recipients of human DS myeloid cells. We are using this model to define the mechanisms that control the development of this potentially life-threatening complication. Methods.Recipients were engrafted with primary human DS myeloid leukemia cells and cells of the human DS myeloid leukemia cell line GRW (established at our institution). U937 human monocytic leukemia cells, which lack trisomy 21, were used in control experiments. Cells were injected into the right femur of 8-week-old irradiated NOD/SCID mice, which had also been injected with anti-NK (anti-CD122) antibody. Phenotypic analysis at 4 to 6 weeks after transplantation used standard cytological, histological and flowcytometric methods (CD45, CD61 and CD34 antibodies were obtained from B&D). Affymetrix human Gene ST1.0 expression arrays were used to compare GRW and U937 cells. Specific gene expression was quantified by TaqMan real time RT-PCR relative to b-actin (Applied Biosystems). Results.Organ fibrosis in recipients of DS myeloid leukemia cells. Primary cells from patients with DS myeloid leukemia engrafted murine recipients and caused moderate bone marrow fibrosis. Transplantation of GRW human DS myeloid cells resulted in significant infiltration of recipient liver and bone marrow (33±10% of mononuclear cells, n=6). The frequency of the leukemia-initiating cells was 1/87,448 by limiting dilution. Marked fibrosis of the liver developed within 6 weeks of transplantation. Fibrosis-associated gene expression in DS myeloid leukemia cells. DS myeloid leukemia cells (GRW) expressed significantly more PDGFD and FGF17 transcripts than non-DS myeloid leukemia control cells (U937). PDGFD transcripts were 4.3-fold more abundant in GRW cells than U937 cells (p=2.67 × 10-7; n=4). FGF17 expression levels were moderately increased (1.24, p=0.07). Quantitative real time RT-PCR analysis confirmed expression of PDGFD in DS myeloid leukemia cells (GRW) (5.55 × 10-4PDFGD/b-actin transcripts; n=4) and did not detect measurable expression in control (U937) cells. FGF17 transcripts were approximately 100-fold more abundant in DS myeloid leukemia cells (GRW) cells compared to U937 controls (4.85 × 10-4 and 4.91 × 10-6 for FGF17/b-actin transcripts, n=4). Analysis of fibrosis-associated gene expression in recipient (murine) liver cells in response to transplanted DS myeloid leukemia cells (GRW) and functional analysis of the role of PDGFD and FGF17 expression in DS myeloid leukemia cells is underway. Conclusion.Organ fibrosis is a significant cause of mortality of children with DS and megakaryoblastic disorders, particularly during the newborn period. Chemotherapy frequently is unable to achieve a timely reversal of this process. Better understanding of the mechanisms controlling the development of organ fibrosis is required to develop better anti-fibrotic intervention. The observed phenotype of marked liver fibrosis in murine recipients of the human DS myeloid leukemia cell line GRW provides an experimental tool to determine the components of the fibrogenic process both in infiltrating leukemia cells and recipient liver tissue. PDGFD and FGF17 expression by DS myeloid leukemia cells has been identified as possible inducer of organ fibrosis. The model can now be used to define tissue responses to infiltrating human DS myeloid leukemia cells in liver tissue of recipients and to determine the functional role of candidate genes in DS myeloid leukemia cells by altering expression levels prior to transplantation. Disclosures:No relevant conflicts of interest to declare.

Curcumin dramatically enhances retinoic acid-induced superoxide generating activity via accumulation of p47-phox and p67-phox proteins in U937 cells

The membrane bound cytochrome b558 composed of large gp91-phox and small p22-phox subunits, and cytosolic proteins p40-, p47- and p67-phox are important components of superoxide ( O 2 - )-generating system in phagocytes and B lymphocytes. A lack of this system in phagocytes is known to cause serious life-threatening infections. Here, we describe that curcumin, a polyphenol responsible for the yellow color of curry spice turmeric, dramatically activates the O 2 - -generating system during retinoic acid (RA)-induced differentiation of human monoblastic leukemia U937 cells to macrophage-like cells. When U937 cells were cultured in the presence of RA and curcumin, the O 2 - -generating activity increased more than 4-fold compared with that in the absence of the latter. Semiquantitative RT-PCR showed that co-treatment with RA and curcumin slightly enhanced gene expressions of the five components compared with those of the RA-treatment only. On the other hand, immunoblot analysis revealed that co-treatment with RA and curcumin caused remarkable accumulation of protein levels of p47-phox (to 7-fold) and p67-phox (to 4-fold) compared with those of the RA-treatment alone. These results suggested that curcumin dramatically enhances RA-induced O 2 - -generating activity via accumulation of cytosolic p47-phox and p67-phox proteins in U937 cells. Therefore, it should have the potential as an effective modifier in therapy of leukemia and/or as an immunopotentiator.

Carbon monoxide stimulates global protein methylation via its inhibitory action on cystathionine β-synthase

Although carbon monoxide derived from heme oxygenase has been reported to exert diverse biological actions in mammals, macromolecules responsible for its direct reception and functional outcomes of the gas binding remain largely unknown. Based on our previous results in vivo suggesting carbon monoxide serves as an inhibitor of cystathionine β-synthase that rate-limits transsulfuration pathway for generation of hydrogen sulfide, we have herein hypothesized that the gas might serve as a regulator of protein methylation through accelerating turnover of remethylation cycle residing at the upstream of the enzyme. Metabolomic analysis in human monoblastic leukemia U937 cells in culture revealed that application of carbon monoxide-releasing molecules caused increases in methionine and S-adenosylmethionine and a decrease in cystathionine in the cells, suggesting the cystathionine β-synthase inhibition by carbon monoxide. Under these circumstances, the cells exhibited global protein arginine methylation: this event was also reproduced by the cell treatment with hemin, a heme oxygenase-1 inducer. The protein arginine methylation elicited by carbon monoxide was attenuated by knocking down cystathionine β-synthase with its small interfering RNA or by blocking S-adenosylhomocysteine hydrolase with adenosine dialdehyde, suggesting remethylation cycling is necessary to trigger the methylation processing. Furthermore, proteins undergoing the carbon monoxide-induced arginine methylation involved histone H3 proteins, suggesting chromatin modification by the gas. Collectively with our studies in vivo showing its inhibitory action on endogenous hydrogen sulfide production, the current results suggest that not only inhibition of transsulfuration pathway for H2S generation but also activation of protein methylation accounts for notable biological actions of carbon monoxide via the cystathionine β-synthase inhibition.

Cdk inhibitors의 발현 증가 및 pRB 인산화 저해에 의한 HDAC inhibitor인 sodium butyrate에 의한 인체백혈병세포의 G1 arrest유발

We investigated the effects of sodium butyrate, a histone deacetylase inhibitor, on the cell cycle progression in human monocytic leukemia U937 cells. Exposure of U937 cells to sodium butyrate resulted in growth inhibition, G1 arrest of the cell cycle and induction of apoptosis in a dose-dependent manner as measured by MTT assay and flow cytometry analysis. The increase in G1 arrest was associated with the down-regulation in cyclin D1, E, A, cyclin-dependent kinase (Cdk) 4 and 6 expression, and up-regulation of Cdk inhibitors such as p21 and p27. Sodium butyrate treatment also inhibited the phosphorylation of retinoblastoma protein (pRB) and p130, however, the levels of transcription factors E2F-1 and E2F-4 were not markedly modulated. Furthermore, the down-regulation of phosphorylation of pRB and p130 by this compound was associated with enhanced binding of pRB and E2F-1, as well as p130 and E2F-4, respectively. Overall, the present results demonstrate a combined mechanism involving the inhibition of pRB/p130 phosphorylation and induction of Cdk inhibitors as targets for sodium butyrate that may explain some of its anti-cancer effects in U937 cells.

Apoptosis inducement of bigelovin from Inula helianthus‐aquatica on human Leukemia U937 cells

Inula helianthus-aquatica C. Y. Wu is a traditional medicinal plant used to treat some cancers in folk herbal medicine of Yunnan, China. Bigelovin, a sesquiterpene lactone isolated from this herb, potently inhibits the growth of a panel of eight cancer cell lines, especially in human monoblastic leukemia U937 cells with an IC(50) value of 0.47 microM. Characteristic morphological features of apoptosis were observed in U937 cells treated with bigelovin. Annexin V and nuclear DNA content distribution assays showed that the percentage of Annexin V positive cells increased to 8.86% (24 h) with 1 microM bigelovin treatment, and cells treated with bigelovin at this concentration apparently arrested at G(0)/G(1) phase compared with the control. These data suggested that cytotoxic effect of bigelovin on U937 cells involves induction of apoptosis, and the cell cycle is arrested at G(0)/G(1) phase.

Selective activation of NF‐κB and E2F by low concentration of arsenite in U937 human monocytic leukemia cells

Arsenite has been reported to exert dose-dependent dual effects: triggering apoptosis at relatively high concentrations, whereas inducing partial differentiation at low concentrations in leukemia cells. However, the relevant molecular mechanisms of its action at low and nonapoptotic concentrations remain to be elucidated. We examined the effect of arsenite on activation of key transcription factors in cultured U937 human monocytes/macrophages. Electrophoretic mobility shift assay (EMSA), protein/DNA array and luciferase reporter assay were used to analyze the effect of arsenite on the functional activities of transcription factors. Protein/DNA array analysis showed that activation of E2F was seen after 6-h exposure to 1 and 10 microM arsenite. In contrast, activation of NF-kappaB took place only at 1 microM arsenite, whereas 10 microM arsenite showed no recognizable effect on this nuclear transcription factor in the protein/DNA array analysis. EMSA using a NF-kappaB consensus probe indicates the functional activation of RelB/p50 in the presence of 1 microM arsenite, confirming the above results. Luciferase reporter assay for NF-kappaB showed activation of NF-kappaB in the presence of 1 microM arsenite. Interleukin (IL)-8 and B-cell-activating factor of the tumor necrosis factor family (BAFF) mRNA expression, which have been shown to be regulated through NF-kappaB, were activated in the presence of 1 microM arsenite. These results support the hypothesis that the primary action of nonapoptotic concentrations of arsenite in this cell line is activation of NF-kappaB, signaling as a decision maker for end results such as inflammation disease or cancer. This finding offers the possibility of providing a logical explanation for the observations made by many scientists that chronic exposure of human populations to low doses of arsenic is significantly correlated to clinical signs of inflammation in many tissues.

Involvement of extracellular signal-related kinase signaling in esculetin induced G1 arrest of human leukemia U937 cells

This study was conducted to further elucidate the possible mechanisms by which esculetin, a coumarin compound, exerts its anti-proliferative action on cultured human monocytic leukemia U937 cells. The inhibitory effects of esculetin on cell viability were found to be associated with a G1 arrest in cell cycle progression that was concomitant with an inhibition of cyclin E and an induction of cyclin-dependent kinase (Cdk) inhibitor p21/WAF1/CIP1 in a p53-independent manner. Cells that were treated with esculetin showed increased binding of p21 with Cdk2 and Cdk4 that was paralleled by a marked decrease in the Cdk2 and Cdk4 kinase activities with no change in their expression. We also observed that down-regulation of the phosphorylation of retinoblastoma protein (pRB) by this compound was associated with enhanced binding of pRB and the transcription factor E2F-1. Further investigation showed that inhibition of the extracellular-regulated kinase (ERK) signaling pathway reduced the induction of p21 and the inhibition of pRB phosphorylation and cyclin E expression by esculetin, which in turn overcame the G1 arrest and growth inhibition that was induced by esculetin. These data demonstrate that the ERK pathway participates in p21 induction and subsequently leads to a decrease in the kinase activity of Cdks and inhibition of pRB phosphorylation in esculetin-mediated G1 arrest of U937 cells.

Isolation of Tryptophol as an Apoptosis-Inducing Component of Vinegar Produced from Boiled Extract of Black Soybean in Human Monoblastic Leukemia U937 Cells

We isolated a novel apoptosis-inducing component, tryptophol, from vinegar produced from boiled extract of black soybean (black soybean vinegar). Compound-6 purified from an ethyl acetate extract of black soybean vinegar using high performance liquid chromatography (HPLC) induced fragmentation of DNA and the development of apoptotic bodies (characteristic physiological features of apoptosis) in U937 cells. By analysis of chemical structure, this active compound was identified as tryptophol. Tryptophol induced apoptosis involving caspase-8 and -3 activation, followed by cleavage of poly (ADP-ribose) polymerase (PARP), as shown by measurement of enzyme activity and immunoblot analysis. The cell viability of normal lymphocytes separated from human blood was less affected by tryptophol, and fragmentation of DNA was not induced in normal lymphocytes. These results indicate that tryptophol isolated from black soybean vinegar inhibited the proliferation of U937 cells by inducing apoptosis via a pathway involving caspase-8 followed by caspase-3, without affecting normal lymphocytes.

Suppression of U937 human monocytic leukemia cell growth by dideoxypetrosynol A, a polyacetylene from the sponge Petrosia sp., via induction of Cdk inhibitor p16 and down-regulation of pRB phosphorylation

Dideoxypetrosynol A, a polyacetylene from the marine sponge Petrosia sp., is known to exhibit significant selective cytotoxic activity against a small panel of human tumor cell lines, the mechanisms of which however, are poorly understood. The aim of the present study was to further elucidate the possible mechanisms by which dideoxypetrosynol A exerts its anti-proliferative action in cultured human monocytic leukemia U937 cells. We observed that the proliferation-inhibitory effect of dideoxypetrosynol A was due to the induction of G1 arrest in the cell cycle, the effects of which were associated with up-regulation of cyclin D1 and down-regulation of cyclin E, in a concentration-dependent manner without any change in cyclin-dependent-kinases (Cdks) expression. Dideoxypetrosynol A markedly induced the levels of Cdk inhibitor p16/INK4a expression. Furthermore, down-regulation of phosphorylation of retinoblastoma protein (pRB) by this compound was associated with enhanced binding of pRB and transcription factor E2F-1. Overall, our results demonstrate a combined mechanism involving the inhibition of pRB phosphorylation and induction of p16 as targets for dideoxypetrosynol A, may explain some of its anti-cancer effects.

C-Abl acetylation by histone acetyltransferases regulates its nuclear-cytoplasmic localization.

c-Abl function is strictly dependent on its subcellular localization. Using an in vitro approach, we identify c-Abl as a new substrate for p300, CBP (CREB-binding protein) and PCAF (p300/CBP-associated factor) histone acetyltransferases. Remarkably, acetylation markedly alters its subcellular localization. Point mutagenesis indicated that Lys 730, located in the second nuclear localization signal, is the main target of p300 activity. It has previously been reported that c-Abl accumulates in the cytoplasm during myogenic differentiation. Here, we show that c-Abl protein is acetylated at early stages of myogenic differentiation. Indeed, acetylation on Lys 730 drives c-Abl accumulation in the cytoplasm and promotes differentiation. Thus, Lys 730 acetylation is a novel post-translational modification of c-Abl and a novel mechanism for modulating its subcellular localization that contributes to myogenic differentiation.

Inhibition of telomerase activity in U937 human monocytic leukemia cells by Compound K, a ginseng saponin metabolite

Telomerase activation is detected in most cancerous cells; hence, telomerase is a highly selective target for cancer therapy, which plays an important role in the apoptotic process. We have previously reported that the ginseng saponin metabolite, Compound K (20-O-D-glucopyranosyl-20(S)-protopanaxadiol, IH901), inhibits cell proliferation by inducing apoptosis and cell cycle arrest at the G1 phase. The present study investigated the regulation of telomerase activity in Compound K treated U937 cells. Compound K treatment caused a reduction in telomerase activity and down-regulated the human telomerase reverse transcriptase (hTERT) gene, resulting in the decreased expressions of its protein, and of the c-Myc and Sp1 proteins (transcription factors of hTERT). These results indicate that the anticancer activity of Compound K could be mediated by inhibition of the telomerase activity.