SILENCING OF Bc1-2 GENE BY SMALL HAIRPIN RNA INHIBITS GROWTH OF NB4 CELLS

Objective： To investigate the effects of small hairpin RNA（shRNA） targeting Bcl-2 on the growth of NB4 cell line. Methods： Two of pairs oligonucleotides for short hairpin expression targeting the coding region of Bcl-2 mRNA were designed and chemically synthesized. Annealed oligonucleotides were inserted into Pgenesil-1 vector downstream of U6 promoter to construct RNAi plasmid. Oligonucleotide with a scrambled sequence was used as a negative control. Recombinant expression vector was identified by enzyme cutting and sequencing. Bcl-2 shRNAs were transfected into NB4 cell with Lipofectamine 2000. Western-Blot of Bcl-2 protein expression in NB4 cells was performed after transfection. The inhibition of cell growth was assessed by a MTT assay. Results： Enzyme cutting and sequencing showed that the insertion sequence was correct. Western-Blot assay showed that the expression level of Bcl-2 protein in NB4 cells decreased after Bcl-2 shRNAs treatment. There was no difference in Bcl-2 protein levels between control shRNA and untreated cells. Viable cells at 72 and 96 h after treatment with Bcl-2 shRNAs were less than that after treatment with control shRNAs and untreated NB4 cells, respectively （P〈0.05）. Control shRNA had no significant effect on the growth of the cells. Conclusion： Bcl-2 shRNA could effectively inhibit the growth of NB4 cells. Bcl-2 shRNA might be an effective anti-leukemia candidate.

Construction and Significance of Directional Expression cDNA Library from Human NB4 Cells

Human acute premyeloid leukemia cell cDNA expression library was constructed to screen acute premyeloid leukemia tumor antigen. Total RNA and purified mRNA were extracted from human premyeloid cell line NB4. First and second strands of cDNA were synthesized by reverse transcription. After blunting, the cDNA fragments were ligated with EcoR Ⅰ adapters. Then the cDNAs were digested with Xho Ⅰ, and less than 400 bp cDNA fragment was removed by Sephacryl S400 spin column, the remaining were ligated with λZAP vector. The recombinants were packaged in vitro , and a small portion of packaged phage was used to infect E. coli XL1 Blue MRF' for titration. The recombinants were examined by color selection. In order to evaluate the size of cDNA inserts and the diversity of library, the pBK CMV phagemid was excised from the ZAP express vector by using ExAssist helper phage with XLOLR strain, and then the pBK CMV phagemid was digested by Xho Ⅰ and EcoR Ⅰ. The results showed that the NB4 cell line cDNA library consisting of 1.65×10 6 recombinant bacteriophages was constructed with the recombinant ratio of 99.6 %. The average length of the recombinant exogenous inserts was about 1.7 kb. It was concluded that the constructed cDNA library are deserved to screen target clones.

Effect of realgar on telomerase activity and hTERT-mRNA expression in NB4 cells

Objective: To evaluate whether realgar could down-regulate human telomerase reverse transcriptase (hTERT) gene expression and telomerase activity in acute promyelocytic leukemia cell line-NB4 cells. Methods: The expression of hTERT-mRNA was analyzed by semi-quantitative reverse transcriptase polymerase chain reaction (RT-PCR). Telomerase activity was determined by polymerase chain reaction enzyme-linked immunoassay (PCR-ELISA). Flow cytometry using PI staining was applied to analyze the cell cycle and apoptosis. Results: Treatment of NB4 cells with 155, 300, 600 μg/L realgar reduced telomerase activity significantly accompanying with decrease of hTERT-mRNA and increasing cell apoptosis. G2/M phase arrest appeared when treated with realgar in 300, 600 μg/L. Conclusion: It is suggested that telomerase activity of NB4 cells can be specifically inhibited by realgar through the down-regulation of hTERT gene expression. G2/M phase arrest and apoptosis by realgar in NB4 cells might be related to the reduction of telomerase activity and hTERT-mRNA expression.

EFFECTS OF CURCUMIN ON PROLIFERATION OF NB4 CELLS AND ACETYLATION OF HISTONE H3 AND P53

Objective: To investigate the effects of curcumin on the proliferation of NB4 cells and the acetylation of histone H3 and no-histone p53. Methods: NB4 cells were cultured and treated with or without curcumin at different concentration (50 μ mol/L, 25μ mol/L, 12.5μ mol/L, 6.25μ mol/L, 3.125μ mol/L) at various time points (oh, 4h, 8h, 12h, 24h). Western blot analysis was performed to determine the level of acetylated histone H3, p53 and acetylated p53, MTT assay was performed to examine the proliferation of NB4 cells. Results: the proliferation of NB4 cells was inhibited by curcumin in a time- and dose-dependent manner, the IC50 at 24h and 36h were 40μ mol/L and 25μ mol/L respectively. The levels of acetylated histone H3 and acetylated p53 were increased obviously. Conclusion: curcumin possessed the founction of deacetylases inhibitor, increased the level of acetylated histone H3 and the expression of tumor suppressor p53, enhanced later’s activity, and inhibited the proliferation of NB4 cell.

Stimulation of staphylococcal enterotoxin A combined with PML-RARα peptide on the specifical T-cells against NB4 cell line

Objective： To investigate the effects of staphyococcal enterotoxin A （SEA） on the cytotoxicity of T cells stimulated by PML-RARa peptide in vitro. Methods： Peripheral blood mononuclear cells （MNC） from healthy donor were obtained by density gradient centrifugation on Ficoll-Hypaque, MNC were cultured with PML-RARa peptide and SEA for 20 days. After induction, the cytotoxicity of T cells induced against NB4 and K562 cell lines were examined by Cell Counting Kit-8 （CCK-8）. The CD4 and CD8 surface markers on the harvested CD3^＋ T cells were detected by flow cytometry （FCM）. Results： The cytotoxicity of T cells induced by PML-RARa peptide with SEA was higher than that of T cells induced only by PML-RARa peptide against NB4 cells. The FCM assay showed that the ratio of CD4^＋/CD8^＋ T cells were gradually decreased in both groups of PML-RARα peptide whether with SEA or not at the intervals of day 5,10 and 20 day after induction, but the most significantly decreased by PML-RARe peptide with SEA. Conclusion： The specific cytotoxicity of T cells induced by PML-RARa peptide against NB4 cells could be enhanced with superantigen SEA.

EFFECTS OF PML AND PML/RMRα ANTISENCE OLIGO-NUCLEOTIDE ON PROMYELOCYTIC LEUKEMIA CELL NB4

Objective: To investigate the effects of anti-PML (promyelocytic leukemia) or anti-PML/RAR( (promyelocytic leukemia/retionic acid receptor() antisense oligonucleotides on cell growth, expression of PML-RAR( mRNA and PML-RAR(/PML protein location of NB4 cell lines. Methods: RT-PCR was used for detecting PML-RAR( mRNA expression, trypan blue exclusion for cell count, methylcellose assay for leukemic colony forming unit detection, immuno- fluorescence for PML-RAR(/PML protein location. Results: Both anti-PML start codon region antisence (STAS) and anti-PML-RAR( fusion region antisence (FUAS) could inhibit cell growth and the formation of acute myelocytic colony forming unit of cells(AML-CFU). Cells become partial differentiated at days 5, being more obvious in FUAS-treated cells than in STAS ones. Down regulation of PML-RAR( mRNA expression occurred at 24 hours in STAS and FUAS-treated cells and maintained for up to 72 hours. Immuno-fluorescence analysis with anti-PML monoclonal antibody showed a remarkable decrease even complete disappearance of microgranules. The residual granules became enlarged as discrete dots (<10 per cell), similar to normal POD structure in some STAS-treated cells at 24 hours. At 72 hours, nearly all the granules disappeared. Similar changes were observed in FUAS-treated cells. Conclusion: Both PML and PML-RAR( antisence oligonucleotides can specially block the expression of PML-RAR( at mRNA and protein levels. PML protein is implicated in the regulations of cell differentiation.

Synthesis and anti-tumor activity of all-trans retinoic acid derivatives

A series of retinoate and retinamide derivatives were designed, synthesized, and their anti-tumor activities were investigated in NB4 by MTT and flow cytometry assays （FCM）. All compounds showed cytotoxicity, especially compounds la and ld exhibited a higher cytotoxicity than other derivatives and all-trans rethaoic acid （ATRA）. Furthermore, compound 1d could induce NB4 cell lines differentiation efficiently. O 2009 Fei Hu Chert. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.

Effects of red orpiment on cell morphology and expression of PML mRNA and protein in NB4 and HL-60 cells

Objective To investigate the effects of red orpiment on cell morphology, expression of promyelocytic leukemia (PML) mRNA and its protein localization in NB4 and HL-60 cell lines.Methods Cell morphology was assayed by Wright's staining and fluorescence staining, while PML mRNA expression was determined by RT-PCR. PML protein localization by evaluated by immunofluorescence staining. Results The typical apoptosis was found in NB4 and HL-60 cells after treatment with red orpiment. The fusion protein was no longer observed in NB4 cells, PML protein was relocated, and then degraded. In HL-60 cells, PML protein underwent a similar progress. The expression of promyelocytic leukemia (PML) mRNA was not changed in the treated cells.Conclusion Red orpiment inhibits the proliferation of leukemia cells by inducing them to undergo apoptosis.

STUDY ON EFFECTS OF QUERCETIN ON PML GENE AND PROTEIN IN LEUKEMIA CELL LINES

Objective To investigate the effect of quercetin on PML gene and protein expression andlocalization in leukemia cell lines. Methods Cell morphology was assayed by Wright's stain and fluorescence stain, and PML mRNA expression by RT-PCR , PML protein localization by immuno-fluorescence. Results NB4 and HL-60 cells differentiated morphologically after treatment with all-trans-retinoic acid (ATRA) while K562 cells did not differentiate. Typical apoptosis was found in each cell line after treatment with quercetin. Immuno-fluorescence analysis showed , after treatment with ATRA , the fusion protein disappeared in NB4 cells and PML protein relocated , while HL-60 and K562 cells had no difference from control cells. After treatment with quercetin, the fusion protein disappeared in NB4 cells, PML protein relocated, then degraded. In HL-60 cells and K562 cells, PML protein also located and then degraded . The expression of PML mRNA was not changed in all three cell lines after treatment with ATRA or quercetin. Conclusion PML plays the role of differentiation and apoptosis inducer in leukemia cells at the translational level. PML in POD plays the role of apoptosis inducer and the growth control of leukemia cells.

STUDY ON EFFECTS OF RED ORPIMENT AND ATRA ON PML GENE AND PROTEIN IN LEUKEMIA CELL LINES

Objective :To investigate PML. gene and protein expression and localization in leukemia cell lines. Methods Cell morphology was assayed by Wright’s stain and fluorescence stain, and PML mRNA expression by RT-PCR, PML protein localization by immuno-fluorescence. Results NB4 and HL-60 cells differentiated morphologically after treatment with anti-retinoic acid (ATRA ) while K562 cells did not differentiate. Typical apoptosis was found in each cell line after treatment with red orpiment. Immuno-fluorescence analysis showed, after treatment with ATRA, the fusion protein disappeared in NB4 cells and the PML protein relocated, while HL-60 and K562 cells had no difference from control cells. After treatment with red orpiment, the fusion protein disappeared in NB4 cells, then degraded, which was also seen in HL-60 cells and K562 cells. The expression of PML mRNA was not changed in all three cell lines after treatment with ATRA or red orpiment. Conclusion PML plays the role of differentiation and apoptosis inducer in leukemia cells at the translational level. PML in POD plays the role of apoptosis inducer and the growth control of leukemia cells.

Berbamine selectively induces apoptosis of human acute promyelocytic leukemia cells via survivin-mediated pathway

Background Currently, resistance and relapse are still major problems in acute promyelocytic leukemia （APL） cases. Thus, new agents that override the resistance are crucial to the development of curative therapies for APL. In this study, we investigated the effects of berbamine on the proliferation of APL cell line NB4 and its possible mechanisms. Methods NB4 cells were treated with berbamine at different concentrations （0-64 μg/ml） for 72 hours. MTT assay was used to determine proliferation inhibition of NB4 cells. Cell apoptosis was evaluated by both flow cytometry （FCM） and morphological examination. PML/RAR-α and survivin mRNAs were measured by nested-RT-PCR and RT-PCR, respectively. Activated-caspase 3 was determined by FCM. Results Berbamine greatly inhibited the proliferation of NB4 cells in dose- and time-dependent manners, and its IC50 value was 3.86 μg/ml at 48 hours. Both morphological observations and FCM results showed that berbamine induced apoptosis of NB4 cells with concomitant increase of activated caspase-3 and decrease of survivin mRNA. After treatment with berbamine at 8 μg/ml for 48 hours, the percentage of apoptotic cells increased from 2.83% to 58.44% （P〈0.01）, and the percentage of cells with activated-caspase 3 elevated from 2.06% to 70.89% （P〈0.01）, whereas, level of survivin mRNA was reduced to 38.24% of control （P〈0.01）. However, no significant change was observed in PML/RAR-α mRNA.Conclusions Berbamine induces caspase-3-dependent apoptosis of leukemia NB4 cells via survivin-mediated pathway, suggesting that berbamine may be a novel potential agent against APL with a mechanism distinct from that of all-trans retinoic acid （ATRA） and arsenic trioxide （ATO）.